Symposium NM05 : Colloidal Nanoparticles---From Synthesis to Applications

The few lateral flow assays (LFAs) established for detecting the endocrine disrupting chemical (EDC) bisphenol A (BPA) have employed citrate-stabilized gold nanoparticles (GNPs), which have inevitable limitations and instability issues. To address these limitations, we developed more stable sensitive lateral flow assay by designing strategies for modifying the surfaces of gold nanostructures with polyethylene glycol and then testing their effectiveness and sensitivity toward BPA in an LFA.
To further enhance detection, the work was extended to the incorporation of gold nannostructures into the design of a surface-enhanced Raman scattering lateral flow assay (SERS-LFA). The assay includes high-SERS-performance gold nanoparticles, i.e., 40 nm gold nanostars (GNSs), and 4-aminothiolphenol (4-ATP) as a Raman reporter. To demonstrate the performance of this SERS-LFA kit toward BPA detection, we tested BPA stock solutions with concentrations ranging from 0 to 32 ppb. Without the application of any enhancement strategy, this modified BPA LFA can achieve a naked-eye limit of detection (LOD) of 0.8 ng/mL, which is 12.5 times better than the LOD of other reported BPA LFAs, and a quantitative LOD of 0.472 ng/mL. The limit of detection for the SERS signals was 0.074, which was 202 and 8 times more sensitive than those of visual intensity and color intensity quantification, respectively. The range of quantification of the SERS signals doubled compared to that of color intensity quantification.

This talk will provide an overview of our recent developments in the design of nanomaterials for ultrasensitive biosensing. Bio-responsive nanomaterials are of growing importance with potential applications including drug delivery, diagnostics and tissue engineering (1). Using enzyme-mediated signal readouts we have developed a suite of nanoparticle based ultrasensitive biosensing approaches as well as a cell/tissue-interfacing nanoneedle platform (2). We are applying these biosensing approaches both in high throughput drug screening and to diagnose diseases ranging from cancer to global health applications.
[1] Stevens MM, George JH, Exploring and engineering the cell surface interface., Science, 2005, Vol:310, Pages:1135-1138.
[2] Howes PD, Chandrawati R, Stevens MM, 2014, Colloidal nanoparticles as advanced biological sensors, Science, 2013, Vol:346, DOI: 10.1126/science.1247390.

Platinum-nickel (Pt-Ni) octahedral based nanomaterials represent an emerging class of highly active electrochemical catalysts, but can not meet the increasing activity demand for broad application and suffer from stability issue. We introduced Cu into octahedral Pt-Ni with controlled morphology. The octahedral Pt-Ni-Cu shows significantly enhanced activity and stability compared to octahedral Pt-Ni catalysts for cathode oxygen reduction reaction (ORR) , which is demonstrated to be a potential electrochemical catalyst. Computational simulation confirmed that the presence of Cu can improve the transition metal (Ni and Cu) retention thus improve both activity and stability.

Ni nanoparticles (NPs) catalyze many chemical reactions, in which they can become contaminated or agglomerate, resulting in poorer performance. We report deposition of silica (SiO₂) onto Ni NPs from tetraethyl orthysilicate (TEOS) through a reverse microemulsion approach, which is accompanied by an unexpected etching process. Ni NPs with an initial average diameter of 27 nm were embedded in composite SiO₂-overcoated Ni NPs (SiO₂-Ni NPs) with an average diameter of 30 nm. Each SiO₂-Ni NP contained a ~7-nm oxidized Ni core and numerous smaller oxidized Ni NPs with diameters of ~2 nm distributed throughout the SiO₂ shell. Etching of the Ni NPs is attributed to use of ammonium hydroxide as a catalyst for deposition of SiO₂. Aliquots acquired during the deposition and etching process reveal agglomeration of SiO₂ and Ni NPs, followed by dissociation into highly uniform SiO₂-Ni NPs. This etching and embedding process may also be extended to other core materials. The stability of SiO₂-Ni NPs was also investigated under high-temperature oxidizing and reducing environments. The structure of the SiO₂-Ni NPs remained significantly unchanged after both oxidation and reduction, which suggests structural durability when used for catalysis.

Hafnium oxide (HfO₂) with a k-edge of 50 keV is being explored as a clinical X-ray contrast agent. HfO₂ NPs are also in clinical trials as radiosensitizers that induce immune action against tumor sites. However, the unpredictable stability of commercially available HfO₂ makes it hard to predict their pharmacokinetics and their size range of ₍(50-100 nm) results in zero clearance from an in vivo system. Therefore, in this study we have executed a modular approach for the design and scalable synthesis of novel, non-sintered, 4-8 nm metal oxide nanoparticles (e.g. Hafnium oxide, Gadolinium oxide) with 40-60 fold higher X-ray attenuation cross-sections than the NPs diameter. Contrast-enhanced computed tomography (CT) and spectral (color) X-ray CT with the aid of these new class of probes have the potential to enable targeted image guided therapeutics with CT as a lower cost and higher resolution alternative to PET and MRI.
Amorphous HfO₂ seed NPs, ~1.5 nm in size, embedded in a polycationic mesh and immobilized inside a silica template, were prepared by the simultaneous reduction and stabilization of tetrakis dimethyl amido hafnium by oleylamine at >250°C in a polyol solvent. Seed NPs were subsequently subjected to high-temperature calcination (>650°C), followed by alkaline digestion of the silica template, to prepare crystalline HfO₂ NPs. As-prepared HfO₂ NPs were surface functionalized with a monolayer of fluorescent silane to enable fluorescence imaging. The hydrodynamic diameter and zeta potential were measured using dynamic light scattering. In vitro cytocompatibility was characterized using established methods which included Live/Dead assay and confocal laser scanning microscopy after incubating NPs with HeLa cancer cells and THP-1 macrophage cells at 25-200 mg NPs/100,000 cells
We achieved >95% efficient conversion of the amorphous seed NPs to crystalline orthorhombic-HfO₂ NPs. HfO₂ NPs were ~4-5 nm in diameter and formed non-sintered flocculants, 220-290 nm in diameter. As-prepared CY5 tagged-HfO₂ NPs exhibited simultaneous X-ray contrast and fluorescence in multispectral imaging. Both HfO₂ and CY5 tagged-HfO₂ NPs remained well-dispersed over 24 h. The measured zeta potential was -13 to -16 mV. Encapsulating the HfO₂ NPs in a SiO₂ shell reduced the hydrodynamic diameter to ~30 nm and inhibited the formation of flocculants. MTT and Live/Dead assays confirmed that the HfO₂ NPs were neither cytotoxic nor pro-inflammatory. Confocal microscopy confirmed highly efficient uptake of Cy5-HfO₂ NPs by HeLa cells and THP-1 cells.
HfO₂ NPs were prepared using a novel templated synthesis resulting in crystalline NPs, ~4-5 nm in diameter, which flocculate into 220-290 nm clusters. Therefore, these NPs provide both long blood circulation and eventual renal clearance through phagocytic breakdown after delivery as radiographic imaging probe or radiosensitizer.

The future of semiconductor quantum dots (QDs) in biomedical imaging lies not with well-established CdSe-based materials that raise issues of toxicity and limited tissue penetration depths, but rather with heavy metal-free compositions that emit in the near infrared (NIR) and short wave infrared (SWIR) in addition to visible wavelength ranges. With this motivation, we have developed semiconductor quantum shells (QSs) comprising non-toxic constituents. These ZnSe/InP/ZnS core/shell/shell structures are dubbed QSs because their Inverted-Type I bandgap structure yields quantum confinement-based emission from the InP shell. The excitonic emission from the QSs is tunable from the visible through the NIR with shell thickness, yielding emission peaks ranging from 515 – 850 nm. This tunablility range is wider than that seen for Type I InP QDs, particularly expanding emission deeper in the first optical tissue window, which spans from 650 – 950 nm. In this talk, I will detail the synthetic control of these heterostructured nanomaterials. In depth photophysical characterization has elucidated the structure/function relationship, enabling the concerted design of these emitters. Of particular note is our ability to match the brightness of emitters of various colors by tuning both the core size and shell thickness. The presentation will include early nanotoxicity and animal imaging results.

In this talk, I will summarize the recent research on the crystal phase-engineering of novel nanomaterials in my group. It includes the first-time synthesis of hexagonal-close packed (hcp) Au nanosheets (AuSSs) on graphene oxide, surface-induced phase transformation of AuSSs from hcp to face-centered cubic (fcc) structures, the first-time synthesis of 4H hexagonal phase Au nanoribbons (NRBs) and their phase transformation to fcc Au RNBs, and the epitaxial growth of 4H Ag, Pt, Pd, PtAg, PdAg, PtPdAg, Rh, Ir, Ru, Os and Cu on 4H Au NRBs. Importantly, the concept of crystal-phase heterostructure is proposed.

Traditional approaches to nanoparticle size control generally attempt to control size by controlling the nucleation step and varying the number of nuclei formed. I will present several approaches to nanoparticle size control and systematic variation that seeks to control and systematically vary nanoparticle size using identical nucleation events, but varying the nanoparticle growth. The approaches have in common the constant addition of nanoparticle precursor that leads to a steady state reaction. This method, referred to as the Extended LaMer mechanism, leads to a linear increase in nanoparticle volume with time. The reaction can be extended for as long as the nanoparticles remain colloidally stable, allowing for systematic variation of nanoparticle sized through a wide range. The approach is general and can be applied to a range of synthetic systems to produce nanoparticles with exceptional reproducibility in size. One can also take advantage of the loss in colloidal stability to design a reaction that precipitates at a desired size. Since this loss of solubility is essentially a phase transition, the nanoparticle size is controlled by thermodynamics and not kinetics. This improve the ease of reproducibility of nanoparticle size with or without careful control of the reaction kinetics. A continuous reaction using this precipitation approach in magnetic nanoparticles will be discussed as will scale up and applications of these nanoparticles. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Well-defined, organically-modified ZnO nanoparticles were prepared via an efficient hydrolysis route, without the need for surfactant co-ligands, washing or size-selection steps. The products have a narrow size distribution and are soluble in organic solvents. The synthesis involves reacting a mixture of alkylzinc carboxylate complex and excess diethylzinc with water to yield carboxylate-capped ZnO nanoparticles. Varying the ratio of the different organometallic species enables control of either size or degree of surface modification.
The bottom-up synthesis of ligand-stabilized functional nanoparticles from molecular precursors is widely applied but is difficult to study mechanistically. In this organometallic system, which avoids excess ligand, ³¹P NMR spectroscopy can be used to follow the trajectory of phosphinate ligands during the synthesis. Initially, we established the structures of a range of ligated zinc oxo clusters, containing 4, 6 and 11 zinc atoms, showing that the clusters interconvert rapidly and self-assemble in solution based on thermodynamic equilibria rather than nucleation kinetics. Subsequently, we identified these clusters in situ during the synthesis of phosphinate-capped zinc oxide nanoparticles. Unexpectedly, the ligand is sequestered to a stable Zn₁₁ cluster during the majority of the synthesis and only becomes coordinated to the nanoparticle surface, in the final step. In addition to a versatile and accessible route to (optionally doped) zinc clusters, the findings provide an understanding of the role of well-defined molecular precursors during the synthesis of small (2–4 nm) nanoparticles.
These stabilised ZnO nanoparticles can be combined with copper nanoparticles to form colloidal catalysts. In a slurry phase reactor, these systems have proven to be highly active in methanol synthesis compared to the analogue heterogeneous Cu/ZnO/Al₂O₃. The increased catalytic activity appears to correlate with a higher exposed surface area and with the selection of the capping ligand, which plays a role in supporting re-structuring and stability.

Colloidal-based solution syntheses offer a scalable and cost-efficient means of producing nanoscale semiconductors in high yield. While much progress has been made towards the controlled and tailorable synthesis of semiconductor nanocrystals in solution, it remains a substantial challenge to fully characterize the products’ inherent carrier transport properties. This is often due to their irregular morphology or small dimensions, which usually demand the formation of colloidal assemblies or films as a prerequisite to performing electrical measurements. Here, we report a novel means for obtaining a comprehensive analyses of the electronic transport properties of individual colloidal semiconductor nanocrystals. First, we present the development of a novel solution chemistry-based synthetic approach to produce nearly monodisperse µm-scale 2D tin(II) sulfide (SnS) nanoribbons and square nanosheets using a one-pot, one-step, easily-scalable synthetic route. These syntheses represent a rare example in this size regime of essentially uniform, single-crystalline, 2D nanocrystals produced using colloidal chemistry. Next, we detail the structural characterization of these SnS materials, and describe how they are processed from solution to fabricate back-gated, top-contact solid-state devices from individual colloidal crystals. Finally, we interrogate their electronic transport properties by a combination of multi-point contact probe electrical transport measurements and time-resolved terahertz spectroscopy. These studies allow for the determination of carrier concentration, carrier mobility, conductivity, and the majority carrier type within an individual 2D colloidal nanocrystal. Our findings illustrate that minor manipulation of solution chemistries may afford products with substantively disparate charge carrier parameters, which are challenging to extract using common experimental practices, and underpins that this metrological strategy represents a significant and valuable advancement in the characterization of colloidally-synthesized semiconductors.

Carbon dots, as a rising fluorescent materials have attracted continuously attention for potential applications in LED, solar cells, sensor, bioimaging and photocatalyst. However, its photo luminescent quantum yield (PL QY) is still quite low, especially emission in long wavelength region like red light. Herein, we proposed increasing the PL QY by doped carbon dots with N or S, N. The PL QY of carbon dots dramatically rises up after doping with N. It can reach over 90%. The carbon dots prepared via bottom-up route show excitation independent emission. In order to extend the absorption in the visible light region, S element is further introduced into the carbon dots to form S, N co-doped carbon dots. Due to the introduction of S and N, there is another S state was introduced into the band gap. That results in the new emission at red light region. Blue, green and red light emissions were obtained from carbon dots. Due to the excellent biocompatibility and low cytotoxicity, we further conjugated the cisplatin with carbon dots to obtain the theranostic agent. We explored to adding more function onto the carbon dots, like self-targeting and therapeutic function to construct the nanomedicine integrating with targeting, bio-imaing and therapy function together.

Platonic particles are promising materials with nanoscale light-matter interactions in plasmonics and biosensing, due to their unique structure caused by vertices, edges and facets. The position and orientation of Platonic particles play a crucial role in determining the resultant assembled structures at a liquid/liquid interface. Therefore, it is desirable to develop a reliable theory that can predict the interfacial configuration of an isolated Platonic nanoparticle from nanoparticle-solvent interactions and solvent-solvent interactions. Here, we numerically explored all possible orientations of a Platonic nanoparticle, including three specific orientations: vertex up, edge up, and facet up orientations. We found that a specific orientation is more preferred than random orientations. We also demonstrated that the free energy change theory could quantitatively predict the position and orientation of an isolated Platonic nanoparticles at a liquid/liquid interface, where the surface wettability of the nanoparticle determined the most stable position and the preferred orientation. Molecular dynamics simulations were used to test our theory where the surface wettability of a Platonic solid was adjusted from extremely hydrophobic to extremely hydrophilic by changing the charge amount on the Ag surface. The molecular dynamics simulation results were in excellent agreement with our theoretical prediction for an isolated Ag Platonic nanoparticle at a hexane/water interface. Our proposed theory bridges molecular-level simulations and assembly structure of Platonic nanoparticles in experiments, in which the insights from nanoparticle wettability in solvents can be used to predict macroscopic superlattice structure in experiments. This work advances our ability to precisely predict the final structures of the Platonic nanoparticle assemblies at a liquid/liquid interface.

Significance of the surface passivation of II-VI colloidal quantum dots (QDs) on their photophysical properties is discussed. Optically forbidden nature of surface-associated states makes their direct measurements challenging. Our DFT-based simulations of CdSe QDs ligated by anionic ligands, such as carboxylates, thiolates, and hydrides, provide insights into the role the acidic ligands play during synthesis and ligand exchange, as well as in manipulating QD’s optical response. Thus, our calculations reveal much more complicated exchange mechanism of the native surface ligands of CdSe QDs with phenyl-dithiocarbamates (PTCs) as it was thought before. PTCs decompose during exchange with native ligands, while only a small portion of deprotonated PTCs covalently bounds to the Cd-enriched surface. Our calculations also reveal that attachment of the hydride to Se sites results in strong distortions of Cd-Se bounds leading to ‘cleaning’ out of extra Se ions from the QD surface (in a form of SeH₂ gas) and eliminating Se-associated trap states. On the other hand, adsorption of H^- on Cd, when the surface is enriched by metal ions, results in blue-shifted lower-energy transitions with very high oscillator strength, which likely responsible for experimentally observed emission enhancement of CdSe QDs treated by hydrides. The calculated results allow for explanations of experimental trends and observables sensitive to surface defects and ligand passivation and offering guidance for controlling the optical response of II-VI nanostructures by means of surface ligand engineering.

Complex nanoparticles, which contain multiple elements, crystal structures, and architectures, are useful for elucidating principles of fundamental thermodynamics and can be applied in fields spanning catalysis to plasmonics. However, the combinations of elements that have been explored thus far in these systems are limited by a lack of combinatorial methods for preparing multiplexed nanoparticle systems. In this presentation, we will discuss how correlative electron microscopy can be used to study the structures and dynamics of complex nanoparticles generated in scanning probe-deposited polymer nanoreactors. Metal, oxide, and hybrid metal-oxide nanoparticles of a variety of compositions and structures can be rapidly generated on electron-transparent substrates with exquisite site-specificity. These particles can then be easily relocated multiple times, enabling repeated, correlated characterization at the individual nanoparticle level. Moreover, polymer nanoreactors provide a viable platform for studying coarsening and solvent-particle interactions at the nanoscale and can be analyzed using in situ electron microscopy. This work demonstrates how polymer nanoreactors, when combined with advanced electron microscopy techniques, can be used as a versatile methodology for understanding the structure–function relationships as well as the formation mechanisms of complex nanoparticles, especially during their synthesis and processing.

The precise control of hetero-interface and doping induced band gap engineering, in colloidal semiconductor based hetero-nanocrystals (metal/semiconductor) and doped nanocrystals, is very important for the efficient energy or charge transfer through hetero-interface and then their novel optoelectronic properties exploration and their new energy, new optoelectronic devices applications. Growth of monocrystalline semiconductor based metal/semiconductor hybrid nanocrystals (core/shell and heterodimer) with modulated composition, morphology and interface strain are the prerequisite for exploring their plasmon-exciton coupling, efficient electron/hole separation, and enhanced photoctalysis properties. We realized nanoscale monocrystalline growth of the semiconductor shell on metal nanocrystals, the precise relative positions and hetero-interface between original building blocks to precisely synthesize metal/semiconductor hetero-nanostructures and hetero-valent doped semiconductor nanostructures, in particular the hetero-valent dopant engineering. These controls enable the fine tuning of doped level, plasmon-exciton coupling, Plasmon enhanced photocatalytic performance and enhanced photovoltaic, electrical properties applications.
References:
1.J. Zhang, Y. Tang, K. Lee, M. Ouyang, Nature 2010, 466, 91.
2.J. Zhang, Y. Tang, K. Lee, M. Ouyang, Science 2010, 327, 1634.
3.Q. Zhao, J. Zhang*, etc., Adv. Mater. 2014, 26, 1387.
4.H.Qian, J. Zhang*, etc., NPG Asian Mater. (2015) 7, e152; doi:10.1038/am.2014.120.
5.J. Gui, J. Zhang*, etc., Angew. Chem. Int. Ed. 2015, 54，3683-3687.
6.J. Liu, Q. Zhao, J. Zhang*, etc., Adv. Mater. 2015, 27，2753-2761.
7.M. Ji, M. Xu, J. Zhang*, etc. Adv. Mater. 2016, 28, 3094–3101.
8.J. Zhang*, Q. Di, etc. J. Phys. Chem. Lett.2017, 8, 4943-4953. (Invited perspective)

Selectively permeable membranes with high flux and high selectivity have important implications in many areas, such as water desalination, CO2 capture, H2 removal or purification, O2 separation, as well as selective ion transport for fuel cells and lithium batteries. Reduced membrane thickness and precisely constructed pore size/chemistry are the two keys for achieving combined high flux and high selectivity. In natural biological system, membranes can be as thin as 4 nm, and the pores/chemistries are elaborately constructed via molecular assembly, resulting in unbeatable performance compared to synthetic membranes. A manufacturing approach that ensures the structural and compositional precision is critical for high performance membranes. ALD is a layer-by-layer deposition method that builds up a thin layer with atomic precisions, and colloidal self-assembly is a method of building up materials in nm-level precisions. The combination of the two provides a new approach for membrane fabrication. Using this approach, hierarchically structured sub-50nm thick ultra-thin membranes with precisely defined pore size and pore surface chemistry have been successfully fabricated. Excellent performances in CO2 and oxygen separation have been achieved. The authors would like to acknowledge the support from DOE SBIR award number DE-SC0017178.

Colloidal photonic crystals are photonic crystals made by bottom-up physical chemistry strategies from monodisperse spherical colloidal particles. The self-assembly process is leading to inherently three-dimensional structures with optical properties determined by the periodicity, induced by this ordering process, in the dielectric properties of the material. Apart from the optical properties, the nanoscopic periodicity, exemplified by SANS, can be transferred if the crystal is used as a template for depositing or removing material as e.g. vortex pinning in Nb thin films deposited on such a crystal.

The use of hollow spheres as building blocks has brought about a whole realm of unique possibilities. One, again derived from the periodicity, is the fabrication of three-dimensional hierarchical structures at the nanoscale. It is also possible to convert the hollow nanospheres to open nanorings, which can be used as templates for the unique core-shell nanoring topology. This topology leads to tunable plasmon resonances.

The best-known optical effect, though, is the photonic band gap, the range of energies, or wavelengths, that is forbidden for photons to exist in the structure. This photonic band gap is analogous to the electronic band gap of electronic semiconductor crystals. We have previously shown how with the proper photonic band gap engineering, we can insert allowed pass band defect modes and use the suppressing band gap in combination with the transmitting pass band to induce spectral narrowing of emission and improved energy transfer. We show now how with a high-quality narrow pass band in a broad stop band, it is possible to achieve photonic crystal lasing in self-assembled colloidal photonic crystals with a planar defect. In addition, with proper surface treatment in combination with patterning, we prepare for addressable integrated photonics. Finally, by incorporating a water in- and outlet, we can create optomicrofluidic structures on a photonic crystal allowing the optical probing of microreactors or micro-stopped-flow in the lab-on-an-optical-chip.

Plasmonic harvesting of solar energy to drive off-grid fuel generation is hindered by reaction selectivity, short (~100 fs) hot electron lifetimes, and catalyst stability. Au nanorods allow reaction specificity under solar irradiation via their tunable localized surface plasmon resonance (LSPR) and can be synthesized in gram-level quantities. This work exploits the longitudinal LSPR of Au nanorods to photodeposit Pt at targeted locations as a co-catalyst to expand hot electron lifetimes and promote reactant desorption. Time-resolved reaction kinetics between (i) the Pt(IV) precursor and (ii) plasmonic hot electrons at the Au nanorod surfaces were monitored by transmission UV-vis spectroscopy. The method is amenable to other metallic precursors. Discrete dipole computation of the Pt-decorated Au nanorods allow a priori design of photocatalysts with optimal energetics. These efforts provide a foundation towards economical manufacturing of plasmon-sensitized, bimetallic photoanodes that can spatially target specific photochemical reactions, such as C-C bond cleavage during ethanol oxidation.

For many years the semiconductor industry has been driven by decreasing the structural dimensions thus increasing the device density and boosting compute and memory performance. Today, true nanoscale dimensions are reached with, e.g., transistor fin-width of smaller than 10 nm in the current technology node. The semiconductor industry research agenda is no longer driven by exclusively scaling dimensions but by integrating new materials and devices offering additional functionality like sensing and transmission for IoT applications. In this regard, the integration of nanoscale, high quality crystalline materials with precise control of dimension and location on the silicon platform is crucial. We have developed the Template-Assisted Selective Epitaxy (TASE) approach to monolithically integrate a broad range of III-V compounds on Si for the applications in nanoelectronics and nanophotonics. In TASE the III-V semiconductor is grown within the confined space of an oxide template and results in an III-V-on-insulator structure which can be used for fabricating devices. High mobility semiconductors like InAs, GaAs and GaSb were grown by TASE and the structural and electronic properties were investigated in detail. TASE-grown III-V nanostructures seem to have superior properties compared with conventional grown nanowires. This is indicated by photoluminescence spectroscopy and also by low-temperature transport measurements. In a recent experiment we demonstrated ballistic 1D quantum transport in single InAs nanowires and cross-junctions. Characteristic 1D conductance plateaus are resolved in field-effect measurements across up to four nanowire junctions in series. Furthermore, the effect of size and symmetry of the nanowire cross section on the quantum confinement is investigated. In general, our investigations of the TASE materials as well as the fabricated nanoscale electronic and optical devices demonstrate the attractiveness of TASE to integrate nanoscale materials on silicon.

Silver nanoparticles (AgNPs) are among the most extensively used engineered nanomaterials in consumer products and biomedical applications. This is due to their ability to slowly release antibacterial Ag+ ions. Rising demand for AgNPs, especially in healthcare, is projected to drive the global AgNP market to approach USD 2.5 billion over the next 5 years. However, with increased use of AgNPs, their release into the environment raises both health and environmental concerns. Several studies have sought to evaluate the potential environmental outcomes of released AgNPs. Investigations of AgNP sulfidation have drawn particular attention due to the prevalence of sulfidation in aquatic environments,¹ and also due to interest in selective sulfidation for optical sensing and photonics applications. However, mechanistic details of the reaction pathway transforming AgNPs to silver sulfide (Ag₂S) remain controversial topics with conflicting results reported,^1,2 and knowledge regarding sulfidation kinetics is limited. Our in situ studies have sought to elucidate the fundamental mechanisms associated with AgNP aggregation behavior, sulfidation and crystallization kinetics by combining high-resolution synchrotron ultra-small-angle X-ray scattering (USAXS), small angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS)/X-ray diffraction (XRD) measurements focused on a well-controlled sulfidation process for polyvinylpyrrolidone (PVP)-coated monodisperse AgNP suspensions in the presence of fulvic acid. The combined methods simultaneously monitor a length-scale range from sub-Å to several micrometers,³ hence allowing quantitative characterization of the evolution in both atomic structure and nanoparticle suspension morphology (i.e., microstructure). Our in situ measurements have been complemented by ex situ high-resolution scanning transmission electron microscopy (STEM) of AgNPs previously subjected to the same sulfidation history. Under the real-time experimental conditions used, we find aggregation of the nanocrystalline AgNPs to be minimal with the AgNPs remaining spherical, or at least globular with facets, throughout the sulfidation process. Incorporation of sulfur ions into the AgNPs causes a monotonic increase in mean nanoparticle diameter, and the nanoparticles exhibit well-defined growth kinetics. We find that the degree of sulfidation is directly related to the availability of sulfur ions in solution, and the crystallization kinetics of Ag₂S correlate well with the nanoparticle growth kinetics. We also find that Ag+ ions do not leach into the solution during the sulfidation process.⁴

[1] B. Thalmann, A. Voegelin, E. Morgenroth & R. Kaegi; Environ. Sci.: Nano, 3, 203-212 (2016).
[2] J.M. Pettibone & J. Liu; Environ. Sci. Technol., 50, 11145-11153 (2016).
[3] N.M. Martin, A.J. Allen, R.I. MacCuspie & V.A. Hackley; Langmuir, 30, 11442-11452 (2014).
[4] F Zhang, A.J. Allen, A.C. Johnston-Peck, J. Liu & J.M. Pettibone; ACS Nano, submitted (2018).

Thin gold nanowires (NWs) represent ideal objects for fundamental studies as well as potential applications in sensing, catalysis, and electronic contacts for molecular devices. Various methods have been developed to grow and characterize thin Au NWs. Though exciting, the reported methods did not univocally address the questions of the nucleation and growth mechanism, which is of prime interest to tune the size of the NWs and thus their physicochemical properties. Furthermore, the atomic-scale structure of thin Au NWs is still under debate. We will present results of in situ high-energy XRD and atomic PDF studies on the nucleation, growth and 3D structure of Au NWs in solution. XRD data were taken in an interval of 5 min for up to 30 hours at room temperature. Gold clusters (size < 1 nm) are seen to nucleate fast and then continuously grow forming NWs with a diameter of < 2 nm and length of many tens of micrometers. A priori, one could anticipate that Au NWs of such a size would exhibit a weak tendency to depart from the bulk fcc structure, if at all. We find though that, due to competition between achieving optimal surface energy and atomic packing, the resulting Au NWs do not necessarily possess an fcc-type structure at atomic level. We elucidate how the unusual 3D structure of Au NWs evolves, including the unusually short Au-Au bonding distances, and show that the degree of its departure from the bulk fcc structure can be controlled through adjusting particular details in the synthesis protocol.

Copper nanoparticles (CuNPs) are attractive as a low-cost alternative to their silver and gold analogues for numerous applications, including emerging electronic devices based on organic and perovskite semiconductors, plasmonic hot-electron devices and nano-electrodes for molecular electronics. However, their potential has hardly been explored due to their higher susceptibility to oxidation in air. Here we present the unexpected findings of an investigation into the correlation between the stability of CuNPs in air and the structure of the thiolate capping ligand. The experiment design is based on monitoring (in real time) the oxidation of largely isolated CuNPs tethered to a solid substrate via the evolution of the localised surface plasmon resonance band - a direct approach which simplifies the interpretation of the data. Remarkably, of the 8 different ligands screened those with the shortest alkyl chain, -(CH₂)₂- , and a hydrophilic carboxylic acid end group are found to be the most effective at retarding oxidation in air. We also show that CuNPs are not etched by thiol solutions as previously reported, and address the important fundamental question of how the work function of small supported metal particles scales with particle size. Taken together these findings set the stage for greater utility of CuNPs for emerging electronic applications.

Solution-processing of semiconductor materials is an emerging strategy that can potentially reduce the cost of thin-film photovoltaic devices. The fundamental challenge accompanying this effort lies in processing of nanoparticles inks into high-performance solids that show high crystallinity and low defect density. This task becomes exceedingly difficult with a decreasing nanoparticle size. Here, we develop the ionic intercalation strategy by which nanostructured films are being forced to undergo an inter-particle ion exchange towards reducing the inter-surface tension (improves crystallinity) and achieving overall charge neutrality at boundaries (reduces defects). Such non-thermal interparticle fusion has been enabled by raising the ion solubility in deposited nanoparticles through establishing the lattice-solvent equilibrium regime. The degree of inter-particle intercalation has been varied towards achieving either a complete sintering of the film or a partial fusion that preserves the quantum confinement of individual dots. Thus, the ionic intercalation approach improves electrical characteristics of nanoparticle solids and provides a reliable starting platform for developing photovoltaic and other photoconducting solids.

The noble atom catalysts have attracted rapidly increasing attention due to their unique catalytic properties and maximized utilization for low-cost. However, the noble metal catalysts, downsized to clusters or single-metal atoms, are structurally unstable due to the natural tendency for metal atoms to diffuse and agglomerate, resulting in the formation of larger particles. In practical applications, it require that the single atom not only have higher activity, but also have satisfying stability. Moreover, the high density of single atom catalysts also was required to meet the practical applications such as fuel cells¹. We used atomic layer deposition technique (ALD) to produce high density of isolated single Pt atom catalysts with high stability on different supports. Those single Pt atom catalysts have been investigated for the different reactions such as methanol oxidation reaction (MOR)² and hydrogen evolution reaction (HER)³, where they exhibit significantly enhanced catalytic activity and high stability in comparison to their nanoparticle counterparts. We also studied the mechanism for design of high stable single atom catalysts by ALD^3-5 and revealed the mechanisms of the unexpectedly high electrocatalytic activity of the single atom², which can deliver atomic-level understanding of catalytic active sites and provide insights into the design of high performance of novel catalytic systems. We will used area-selected ALD to prepare Pt-based high stable catalysts for fuel cells⁶.


References:
N. Cheng, Y. Shao, J. Liu and X. Sun, Electrocatalysts by Atomic Layer Deposition for Fuel Cell Applications. Nano Energy (2016) In press doi:10.1016/j.nanoen.2016.01.016 (review paper)
S. H. Sun, G. X. Zhang, N. Gauquelin, N. Chen, J. G. Zhou, S. L. Yang, W. F. Chen, X. B. Meng, D. S. Geng, M. N. Banis, R. Y. Li, S. Y. Ye, S. Knights, G. A. Botton, T. K. Sham and X. L. Sun, Sci Rep-Uk, 2013, 3, 1775.
Niancai Cheng , Samantha Stambula, Da Wang , Mohammad Norouzi Banis , Jian Liu , Adam Riese , Biwei Xiao , Ruying Li , Tsun-Kong Sham, Li-Min Liu, Gianluigi A. Botton and a. X. Sun, Nat. Commun., 7 (2016) 13638.
N. C. Cheng, M. N. Banis, J. Liu, A. Riese, S. C. Mu, R. Y. Li, T. K. Sham and X. L. Sun, Energ Environ Sci, 2015, 8, 1450-1455.
S. Stambula, N. Gauquelin, M. Bugnet, S. Gorantla, S. Turner, S. H. Sun, J. Liu, G. X. Zhang, X. L. Sun and G. A. Botton, J Phys Chem C, 2014, 118, 3890-3900.
N. Cheng, M. Banis, J. Liu, A. Riese, X. Li, R. Li S. Ye, S. Knights and X. Sun, Extremely stable platinum nanoparticles encapsulated in zirconia nanocages by area-selective atomic layer deposition for oxygen reduction reaction. Adv. Mater., 27 2 (2015) 277

Colloidal semiconductor nanomaterials offer unique opportunities for electronic and photonic applications. However, many of these materials contain elements that are toxic, exhibit poor stability, or are chemically incompatible with a target application. A potential alternative to conventional quantum dots that could overcome these challenges are colloidal group IV semiconductors with nanoscale dimensions. Quantum-confined Group IV nanomaterials exhibit optical properties that can be tuned from the visible with potential for mid-infrared properties by modifying composition. Here, I will present our recent results related to the synthesis of Group IV alloy nanocrystals as well as atomically-thin sheets of Group IV materials (e.g., silicane) with unique optical properties. I will address synthetic challenges that are specific to Group IV nanomaterials, surface functionalization strategies, and our progress in characterizing the optical properties of these materials.

Quantum Dots (QDs) are semiconductor nanocrystals with a wide range of potential applications including displays, photovoltaics, and biological labeling and tracking. Understanding the charge carrier dynamics of emerging quantum dot materials and correlating them to their structure, composition, and surface chemistry allows for QDs to be developed for different applications. One such system is InP QDs, which are being developed as a cadmium-free alternative to traditional CdSe QDs. InP offers size-tunable emission across the visible and near infrared spectral range. Shelling an InP core with a wide band gap material such as ZnSe increases the quantum yield from 2-3% up to ~50%, improves the QD’s photostability, and suppresses blinking. Many additional properties of InP QDs are yet to be fully studied and understood. Ultrafast fluorescence upconversion spectroscopy is a powerful technique used to characterize QDs by providing valuable information about their ensemble charge carrier and trapping dynamics. Femtosecond decay constants and their relative amplitudes provide insight into how these QDs’ trapping dynamics differ from those of traditional cadmium-based core-shell QDs. Traditionally, shelling a QD core leads to confinement of the electron and hole leading to improved photoluminescent properties by reducing the number of defects observed on the QD’s surface. Initial ultrafast measurements on a thick-shell InP-ZnSe QD sample show a fast initial 6.2 ± 1.7 picoseconds decay, traditionally associated with hole trapping. A second longer lived component represents radiative recombination.

References
1. Underwood, D. F.; Kippeny, T.; Rosenthal, S. J., Ultrafast Carrier Dynamics in CdSe Nanocrystals Determined by Femtosecond Fluorescence Upconversion Spectroscopy. J. Phys. Chem. B 2001, 105 (2), 436-443.
2. Keene, J. D.; McBride, J. R.; Orfield, N. J.; Rosenthal, S. J., Elimination of Hole–Surface Overlap in Graded CdS_xSe_1–x Nanocrystals Revealed by Ultrafast Fluorescence Upconversion Spectroscopy. ACS Nano 2014, 8 (10), 10665-10673.

Colloidal CdSe nanoplatelets (NPLs) are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self-assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face-to-face self-assembly of CdSe nanoplatelets into micron-long polymer-like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re-dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1-dimensional structures are flexible and feature a “living polymer” character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends. [1] We also show that these ribbons of stacked board-shaped NPL twist upon the addition of oleic acid ligand, leading to chiral ribbons that reach several micrometers in length and display a well-defined pitch of ~400 nm. We demonstrate that the chirality originates from surface strain caused by the ligand because isolated NPLs in dilute solution undergo a transition from a flat to a twisted shape as the ligand coverage increases. When the platelets are closely stacked within ribbons, the individual twist propagates over the whole ribbon length. These results show that a ligand-induced mechanical stress can strongly distort thin NPLs and that this stress can be expressed at a larger scale, paving the way to stress engineering in assemblies of nanocrystals. Such a structural change resulting from a simple external stimulus could have broad implications for the design of sensors and other responsive materials. [2]

[1] S. Jana, P. Davidson, B. Abécassis, Angew. Chem. Int. Ed. , 55, 9371, (2016)
[2] S. Jana, M. de Frutos, P. Davidson, B. Abécassis, Ligand-induced twisting of nanoplatelets and their self-assembly into chiral ribbons. Sci. Adv. 3, e1701483 (2017).

Now a day, advanced optical spectroscopy studies at the level of individual nanocrystals can be perform routinely. In parallel, advances in Hi-Res transmission electron microscopy allow imaging not only the size and shape of the nanocrystals but also their internal composition. However, for most of the times, these two powerful characterization experiments were applied on two different sets of a nanocrystal ensemble. As a result, establishing direct optical-structural property correlation becomes impossible. Here in this talk we will review our recent experiments, in which single nanocrystal, time tagged, time correlated photon counting experiments and z contrast scanning TEM experiments were performed on the same set of individual core/thick-shell nanocrystals quantum dots (i.e. giant QD or g-QDs). Direct correlation of individual g-QDs’ emission characteristics (i.e. lifetimes and photon emission statistics etc.) with their size, shape and composition allows us to identify photo-charging of the g-QDs, not the existence of dark g-QD subpopulation, as the physical origin of the imperfect QY of the core/thick-shell nanocrystals. Furthermore, by extending the experiment to high temperature and high light flux regime, we investigated PL bleaching issue of the nanocrystals that is hindering the application of nanocrystals in solid-state lighting. The experiment allows us to eliminate heat and light induced changes in shell-thickness and composition of the g-QD as a mechanism responsible for the PL bleaching. The experiment further shows that while the charging of g-QDs is partly responsible, the creation of hot carrier traps that intercept the excitons before they relax to the ground state is mainly responsible for permanent PL bleaching. More interestingly, we also observed that the g-QDs that are prone to charging are more resistant to the creation of hot carrier traps and hence permanent PL bleaching. These fundamental understandings on structure-function relationships open path toward nano-engineering fine internal structure of g-QDs for higher emission efficiency and thermal stability.

The device performance of PbS heterojunction quantum dot (QD) solar cells is hindered by defects at the pn-junction interface, which forms trap states and leads to interface recombination. We design an advanced architecture for the device by introducing a CdSe QD buffer layer at junction between the PbS QDs and ZnO nanoparticles (NPs). We passivate the CdSe QD layer by CdI₂ to achieve n-type doping shown by current-voltage and capacitance-voltage measurement. We optimize the band alignment by exploiting the size-dependent band structure of CdSe QDs to facilitate carrier transport across the junction studied under different illumination conditions. We also show that the CdSe QD buffer layer not only reduces interface recombination but also provides additional photo-generated carriers through external quantum efficiency (EQE) and time-resolved microwave conductivity (TRMC) measurements, which is consistent with the calculated device parameters. Therefore, we fabricate the ZnO NP/CdSe QD/PbS QD solar cell that has significantly higher open circuit voltage and short circuit current density resulting in a 25% enhancement in power conversion efficiency compared to the reference device without the CdSe QD layer.

Quantum dots (QDs) sensitized solar cells (QDSCs)^[1] are achieving considerable attention, due to versatile optoelectronic properties of QDs such as size-tunable band gap, high absorption coefficient, large dipole moment, solution processability and the possibility of multiple exciton generation^[2-4]. However, the record photoconversion efficiency (PCE) of QDSCs reaches to only 12.07%, still lower than the commercial silicon solar cells (typical in the range of 20-40%) and new emerging star perovskite solar cells ^[5]. The possible reasons for this relatively low PCE of QDSCs are mainly associated with narrow light harvesting range of QDs and carrier recombination at the interfaces or within the QDs. This demands the further development of highly efficient QDs to be applied as light harvester to boost the PCE of QDSCs, as the QDs have the immense potential and easy to control their optoelectronic properties. The surface passivation of QD core with shell layer of different materials/thickness has been shown to be an effective approach, which offers a significantly enhanced quantum yield (QY), prolonged PL lifetime and improved chemical, thermal and photochemical/physical stability compared to bare QDs due to the reduced density of surface trap states/defects and optimized electronic band alignment between core and shell ^[6-8]. Herein, we explore a nano-engineering approach to highlight the influence of CdSe_xS_1-x interfacial alloyed layers between the core and shell on the optoelectronic properties of CdSe/(CdS)₆ “giant” core/shell QDs. We will discuss the benefits of interface engineering of core/shell QDs in terms to improve the optoelectronic properties as well as the PCE of liquid junction QDSCs. Resulting newly engineered alloyed core/shell QDs based QDSCs, yielding a maximum PCE of 7.12%, which is mainly attributed to broadening of the absorption spectrum and higher electron-hole transfer rate in favorable stepwise electronic band alignment with respect to reference core/shell QDs, offers a new path to improve PCE of liquid junction QDSCs will be also presented and discussed.
References
[1] S. Rühle, M. Shalom, A. Zaban, Chem. Phys. Chem, 2010, 11, 2290.
[2] S. V. Kershaw, A. S. Susha, A. L. Rogach, Chem. Soc. Rev., 2013, 42, 3033.
[3] I. J. Kramer, E. H. Sargent, Chem. Rev., 2014, 114, 863.
[4] A. J. Nozik, M. C. Beard, J. M. Luther, M. Law, R. J. Ellingson, J. C. Johnson, Chem. Rev., 2010, 110, 6873.
[5] S. Jiao, J. Du, Z. Du, D. Long, W. Jiang, Z. Pan, Y. Li, X. Zhong, J. Phys. Chem. Lett. 2017, 8, 559.
[6] H. Zhao, D. Wang, T. Zhang, M.Chaker, D. Ma, Chem. Commun., 2010, 46, 5301.
[7] P. Reiss, M. Protiere, L. Li, Small, 2009, 5, 154.
[8] Y. Chen, J. Vela, H. Htoon, J. L. Casson, D. J. Werder, D. A. Bussian, V. I. Klimov, J. A. Hollingsworth, J. Am. Chem. Soc., 2008, 130, 5026.

Porphyrin and its derivatives with macrocyclic aromatic conjugation system were excellent organic semiconductor materials and ideal building blocks based on the unique planar, rigid molecular geometry. Molecular self-assembly is a powerful method to the synthesis of nanostructured materials with fine-tuning of the morphology and size. Through designing molecules and supramolecular entities, desired structure and function can be achieved. Here, we report a general microemulsion-based approach to the synthesis of a wide variety of porphyrin nanocrystals with controlled size and morphologies by using different porphyrin as building blocks. This method is based on a designed oil-in-water (O/W) normal microemulsion system. The porphyrin molecules are gathered, assembled, and fixed together spontaneously by the hydrophobic Vander Waals and π-π interaction during controlled evaporation of low boiling point oil solvent in the restricted, micrometer 3-D space provided by microemulsion droplets. The size, shape, component and surface charge of the porphyrin nanocrystals can be controlled by designed experiment parameters. This bottom-up assembly approach opens the way to constructing different monodispersed porphyrin nanocrystals by using oil-soluble porphyrin as building blocks, which may serve as larger building blocks for constructing integrated macroscopic architectures or devices for the fundamental study and practical applications of nanoscience and nanotechnology.

Producing hollow nanoparticles of different size and shape is a challenging job. Galvanic replacement reaction (GRR) is considered as one of the reliable and reproducible synthesis technique to produce hollow nanoparticles. The number of available template materials for GRR is limited. In this work, As(0) nanoparticles are used as template materials which are capable of producing almost similar sized hollow gold nanoparticles (HGNPs). Here two different size ranges (viz., 50±7 and 70±10 nm) As(0) nanoparticles are synthesized by sodium borohydride reduction of arsenite under controlled pH (7-9), and controlled temperature (10° C and 40° C). Further, the reducing property of these As(0) nanoparticles are exploited to form two different sized HGNPs with average diameter 55±7 and 72±7 nm. These HGNPs are designated as AuNP1 and AuNP2. The controlled medium pH restricts the reduction of arsenite to As(0) and not to AsH₃. The catalytic reduction of 4-nitrophenol (4-NP), which is although a toxic compound but used in many industries, to 4-aminophenol (4-AP), an industrially important compound, is a well studied model reaction. The size-dependent catalytic activities of AuNP1 and AuNP2 have been examined on the reduction of 4-NP to 4-AP in the presence of sodium borohydride. While both the nanoparticles exhibit excellent catalytic activity, the smaller particles (AuNP1) are observed to be more effective. The turn over frequency (TOF) of AuNP1 shows much higher value of 300 h^-1 in terms of molar ratio of Au:4-NP:NaBH₄ (1:50:50000) as compared to other gold catalysts used for 4-NP reduction. The reaction is carried out with various catalyst doses and various initial 4-NP concentrations. In all cases the reaction follows first order kinetics. The TOF for the catalytic reaction using AuNP1 and AuNP2 suggests that AuNP1 bears ~6 times higher catalytic activity compared to that of AuNP2. Both the nanocatalysts can be reused up to fourth cycle with good efficiency. In addition, it is also possible to control the size of As(0) by varying the reaction time which ultimately can lead to the formation of different sized HGNPs.

Naturally occurring responsive systems such as folding and unfolding in self-assembled DNA bundles prove natural designs are hierarchical, with structures and property on multiple scales through interactions of subunits or building blocks. Mimicking these designs in fabrication of active materials requires a clear picture of energy landscaping that governs local interactions such as hydrogen bonding, van der Waals interactions, dipole-dipole interaction, capillary forces, etc, which will provide correct thermodynamic end points as well as facile kinetics for precise control of hierarchical structure for responsive functions. To date, fabrications of active and responsive nanostructures have been conducted at ambient pressure and largely relied on these specific chemical or physical interactions. Using our recently developed stress-induced assembly (SIA) as an artificial actuator, we can emulate natural folding and unfolding processes to explore energy landscaping that govern local interactions. Through SIA, we can design new classes of active materials with controlled structure and function and investigate new properties resulting from the folding and unfolding processes. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink and swell during compression and release of pressure, allowing precise tuning of interparticle symmetry and spacing, ideal for controlled investigation of distance-dependent energy couplings and collective chemical and physical property such as surface plasmon resonance. Moreover, beyond a threshold pressure, nanoparticles are forced to contact and sinter, forming new classes of chemically and mechanically stable 1-3D nanostructures that cannot be manufactured by current top-down or bottom-up methods. Depending on the orientation of the initial nanoparticle arrays, 1-3D ordered nanostructures (Au, Ag, etc.) including nanorods, nanowires, nanosheets, and nanoporous networks can be fabricated. The SIA method mimics embossing and imprinting manufacturing processes and opens exciting new avenues for the study of responsive behaviors of active materials during compression (folding) and pressure release (unfolding). Exerting stress-dependent control over the structure of nanoparticle or building block arrays provides a unique and robust system to understand collective chemical and physical characteristics of nanocrystal superlattices.

When nanofibers and nanoparticles combined at the nanoscale, they create new features in the material and therefore new areas of use. In this study, dense medium plasma technique is used for nanoparticles synthesis which is novel, cost-efficient, and fast technology when is compared with other common nanoparticles synthesis techniques. It allows initiation and sustainment of discharges in a co-existing liquid/vapor medium at atmospheric pressure and offers a significantly higher efficiency for the processing of liquid-phase materials in comparison to other existing plasma technologies. Carbon-based nanoparticles are synthesized from an arc sustained in benzene (purity, 99.5%) between iron electrodes by the lab-made-dense medium plasma system. Processing parameters are summarized as volume of benzene;30 ml, distance between plasma electrodes: 0.5 cm, discharge time: 10 second. Then, separated carbon nanoparticles are integrated with the polyvinylpyrrolidone (PVP) nanofibers produced by the electrospinning method. Nanocomposite fiber processing parameters are optimized (polymer concentration, 7.8-8.0 %w/v; ratio of polymer solution /nanoparticle; distance of electrode, 10-25 cm; processing time 5-30 min) and than they are characterized by contact angle measurements, scanning electron microscopy and transmission electron microscopy. At the same time, electrical conductivity of nanocomposite mats are also tested for foreseeing usage in biomedical application. Results showed that diameter of carbon nanoparticles are 46±8nm. New material, carbon nanoparticle containing PVP nanofiber mats are presented in transmission electron microscopy. It is a super hydrophilic mat material (static contact angle is lower than 10 °). According to the optimization of processing parameters, the diameter of nanocomposite fibers are able to reach 150 ±75nm. Electrochemical impedance spectroscopy is used to determine the nanofiber mat resistance. After accurate calibration and fitting of the impedance spectra to the equivalent circuit, nanocomposite mat resistance is found to be dramatically higher than that for the bare PVP nanofiber mat resistance. According to these results, a potential biomedical application of new material is discussed. In this study, carbon nanoparticles containing PVP nanofibers have been fabricated via electrospinning technique for the first time and a new class of mat membranes based on dense medium plasma based nanocomposites have been prepared and evaluated for medical devices. .It has a great potential to use as biocompatible, light, insulator new material.

Nanotechnology based devices are widely explored in the field of electronics, communication, bio-medical, sensing etc. In addition to these, the potential of nanotechnology baseddevices is very large in the field of agriculture with respect to addressing global challenges of various levels of pollutions, environmental monitoring, food quality analysis, enviornmental decontimantion, climate change, water purification, plant protection, pesticide detection etc. This has accelerated a lot of research in the development of variety of nanomaterials and nanotechnology-derived devices owing to ease of portability, better stability, and sensitivity.Nanocrystalline Gold in the form of quantum dots, nanocapsules, thin films and nanoparticles are already in use for the detection of pesticides, the enhancement of nutrients absorption by plants, the delivery of active ingredients to specific sites and water treatment processes. In current Study Gold Nanoparticles (GNPs) prepared by chemical route of ~8 nm in diameter were used for the detection of organochlorine endosulfan pesticide (ESP) as Colormetric Sensor and the design of GNPS based chemical sensor for its quantitative estimation has also been proposed. The Original wine red color of GNPs changes in to various shades of blue after addition of different concentrations of ESP solutions. This change in solution colour is attributed to the decrease in inter-particle distances to less than approximately the average particle diameter due to re-organization of GNPs into aggregates in the form of patterned and non-patterned structures. These results are also confirmed by UV-VIS spectroscopy, in which surface plasmon resonance and its second order peaks are observed in their visible spectra. GNPs based sensing electrode has been used for designing of ESP detection chemical sensor at ambient temperature. The response and sensitivity of ESP sensor parameters are obtained from their recovery curves between the change in resistance vs. time. The result shows minor variation in resistance with ESP concentration with good repeatability. The results will be discussed in detail at the time of presentation.

Photodynamic therapy (PDT), which involves a generation of cytotoxic reactive oxygen species (ROS) by light activation of photosensitizers, has emerged as a promising minimally invasive therapeutic strategy for various types of cancer. However, because it inherently employs oxygen to generate ROS, hypoxia inevitably occurs during PDT. Cancer hypoxia is known to prevent effective cancer treatment, leading to cancer progression by promoting tumor metastasis, initiation of angiogenesis, and receptor upregulation. Herein, we design and synthesize biocompatible manganese ferrite nanoparticle-anchored mesoporous silica nanoparticles (MFMSNs) to overcome hypoxia, and consequently enhancing the therapeutic efficiency of PDT. By exploiting the continuously oxygen-generating property of manganese ferrite nanoparticles through Fenton reaction, MFMSNs successfully relieve hypoxia using a relatively small amount of nanoparticles and improve etherapeutic outcomes of PDT for tumors in vivo. In addition, it exhibits excellent T2 contrast effect in magnetic resonance imaging, allowing in vivo tracking of nanoparticles. These findings suggest a great potential of MFMSNs for effective theranostic agents in cancer therapy. (J. Kim et al. J. Am. Chem. Soc. 2017, 139, 10992-10995)

Hollow silica NPs (HSNPs) have been studied widely as a promising material for various field of applications such as catalysis, drug delivery, cell-labeling, and optical coatings, due to its attractive features like biocompatibility, controllable surface areas and large void volumes, as well as suitable chemical and thermal stability. The template method is a facile and straightforward approach to synthesize HSNPs. Hard templates such as inorganic nanoparticles, polystyrene nanoparticles, and hydroxyapatite nanoparticles, were employed to produce the uniform HSNPs with uniform and tunable void space and shell thickness. High temperature (around 500 °C) post-processing is normally required to remove the hard templates. In contrast, soft templates such as emulsion micelles7, and vesicles could be simply washed away by using a selective solvent at room temperature. However, the preparation of soft templates with a uniform size under 100 nm typically required at least two surfactants and relatively tedious stabilization procedures. Herein, we introduced a microreactor-assisted system with a hydrodynamic focusing micromixer (HFM) to control the conformations of the HSNPs with poly(acrylic acid) (PAA) as soft template. The PAA can self-assemble into globular when meets with the “unfavorable” solvent such as ethanol. Following this self-assembled conformation which is called thermodynamic-locked (TML) conformation, like the other single surfactant/polyelectrolyte, PAA TML in solution has a strong tendency towards aggregation before the growth of silica shells. In the batch reaction, due to the uneven mixing between free PAA chains and “unfavorable” solvent, PAA chains were under the different transition or aggregation stages which finally led to a broad size distribution of the PAA templates. In our system, with the assistance of the HFM in which the transition and aggregation of PAA chains are controlled by varying the mixing time through flow rates, flow rate ratio and PAA concentration, we can obtain the HSNPs only in ~30 nm. By modifying the PAA concentration, the necklace conformation of PAA TML were successfully preserved by the silica shells. COMSOL Multiphysics was performed to investigate the fluidic profile in the microreactor system. The quality of these HSNPs was demonstrated by fabricating anti-reflective coatings on the top of monocrystalline PV cells. Our HSNPs thin film exhibited much higher enhancement of the power conversion efficiency (PCE) than their batch counterparts.

Due to its excellent optical properties, gold nanomaterials with anisotropic morphology are playing an important role in biomedical applications, specifically in the use of Surface Enhanced Raman Spectroscopy (SERS) technique for biological assays. In this work, we verified the behavior of the star shape nanoparticle peaks obtained by chemical synthesis (precursor reactant: HAuCl4, cationic surfactant: CTAB) and whose peaks were formed from the different concentrations of gold seeds (55, 65, 75 and 85 ul) which were added to the total solution (5.275 ml). The shape and size of the nanoparticles was verified with a Hitachi S-5500 microscope with a BF & DF SEM / STEM detector, and for the diameter distribution (hydrodynamic) was carried out by the dynamic light distribution technique with a Malvern DLS system Zetasizer Nano ZS. Particle sizes (peak-to-peak considering) were obtained with variations from 107 to 166 nm. The results suggest adding 75 ul of gold seeds to obtain uniform nanostars with well-defined peaks. These gold nano-stars could be applied for identification of specific membrane markers for the study of different types of cancer by the SERS technique

Colloidal 4-ethynylstyryl and octyl cocapping silicon quantum dot (4-Es/Oct Si QD) and its spin-coated film were synthesized and fabricated at three different curing temperatures, 150, 250, and 350 °C under argon for 4 h. Thermal cross-linking of 4-ethynylstyryl terminated 4-Es/Oct Si QD during the curing process was confirmed by differential scanning calorimetry for the 4-Es/Oct Si QD powder and by Fourier transforms infrared spectroscopy for the Si QD thin films. The effect of thermal cross-linking of 4-ethynylstyryl capping groups on the electronic coupling between Si QDs in Si QD solids of thin film states was investigated by monitoring optical and electrical properties of the Si QD thin films at different curing temperatures. The optical bandgap values estimated from the extinction-coefficient graphs of 4-Es/Oct Si QD thin films are 2.83 eV, 2.7 eV, to 2.45 eV at the curing temperature of 150, 250, and 350 °C, respectively. Moreover, ultraviolet–visible absorbance and photoluminescence spectroscopy of the Si QD thin films showed a distinct extension into the longer wavelength. In addition, their current–voltage measurements showed an increase leakage current with increasing curing temperatures. The thermal cross-linking of 4-ethynylstyryl capping groups at curing temperatures of 250 and 350 °C and thermal decomposition of octyl capping groups at 350 °C decrease width and height of the energy barrier between the two QD neighbors, allow the expansion of the wavefunctions of individual Si QDs, and overlap with the neighboring QDs, thus strengthening electronic coupling between the Si QDs in QD solids, inducing significant changes in the valence band-edge, optical, and electrical properties.

Silicon has been investigated as a high-capacity anode material for Lithium ion batteries while the cycle life desired to improve further for practical application. In this study, we adopt artificial solid electrolyte interphase (SEI) layers to improve cycle life by employing surface modification of silicon nanocrystals (Si NCs). silica nanoparticles (SiO₂ NPs) were reduced by magnesiothermic reaction to generate oxide coated silicon nanocrystals (Si NCs@SiO_x). The hydride terminated Si NCs (H-Si NCs) were produced from Si NCs@SiO_x through wet etching process using hydrofluoric acid (HF). Dimethylethoxyvinyl silane-capped Si NCs (DMEVS-Si NCs) were synthesized by using the H-Si NCs via thermal hydrosilylation reaction. The siloxane polymer-encapsulated Si NCs (polymer-Si NCs) were synthesized form DMEVS-Si NCs and methyltrimethoxysilane (MTMS) via hydrolysis-condensation reaction. Silicon anodes were fabricated by mixing the active material (Si NCs@SiO_x, H-Si NCs, DMEVS-Si NCs or polymer-Si NCs), polyacrylic acid (PAA), and Super P Li carbon black. The coin-type (2032R) half-cell with the silicon anodes were cycled at a rate of 0.2C between 0.01 and 2.5 V. The case of polymer-NCs showed significantly improved cyclic properties compared to the others due to the siloxane based polymer acting as an artificial SEI layer.

Noninvasive near infrared light responsive cancer treatment is a promising modality, however some inherent drawbacks of conventional phototherapy heavily restrict their application in clinic. Rather than producing heat or reactive oxygen species, here we developed a multifunctional yolk-shell nanoplatforms could generate plenty of microbubbles upon laser irradiation. The bubbles are able to kill cancer cells due to mechanical effect and the damage is efficiently amplified by small interference RNA (siRNA) which is absorbed on the surface of nanoparticles. In vitro experiments demonstrate this nanoplatform exhibits almost the same transfer efficiency of siRNA comparing with commercial transfection agents and possesses excellent bubble-production ability. The results of cellular toxicity test verify the siRNA improve the damage to cancer cells caused by gasification process upon NIR laser exposure. After surface modification, the yolk-shell nanoparticles could target cancer cells selectively. Guided by photoacoustic and ultrasonic imaging, these results are confirmed in a humaized orthotropic lung cancer model. The yolk-shell nanoplatforms demonstrate outstanding tumor regression with few side effect under a relatively low laser power density. Therefore, the multifunctional nanoparticles that combining bubble-induced mechanical effect with RNA interference are expected to be an effective NIR light responsive oncotherapy.

Inorganic perovskite semiconductor quantum dots have proven to be useful material for electronic devices, such as light emitting devices (LEDs), solar cells, and radiation detectors due to their tuneable optical properties, thin linewidth emission spectra, wide bandgap, and high absorption coefficient.^1-4 Recently, organic-metal halide perovskite materials have attracted extensive research due to their unique optical properties and solution-based processing techniques.^5-6 In this work, for the first time, we synthesize high band gap monodispersed novel perovskite halide nanocrystals and nanowires with tuneable optical properties by colloidal route method via mixed metal alloying with Group 13 metals in the ABX₃ perovskite and A₃BX₅ crystal structures. The size (15-30 nm) of these nanocrystals can be tuned by the reaction condition. Halide composition can also be varied to achieve the desired optical properties. Finally, we successfully controlled the shape of these nanocrystals and synthesize nanowires with some phase change in the crystal structure. We present the advantage of wide bandgap perovskite semiconductors, showed its photoconductivity and time response which proves the potential application in photodetectors, piezoelectric applications and X-ray detection.

References:
1. Yang, Yixing, et al. "High-efficiency light-emitting devices based on quantum dots with tailored nanostructures." Nature Photonics 9.4 (2015): 259-266.
2. Anikeeva, Polina O., et al. "Quantum dot light-emitting devices with electroluminescence tunable over the entire visible spectrum." Nano letters 9.7 (2009): 2532-2536.
3. Chuang, Chia-Hao M., et al. "Improved performance and stability in quantum dot solar cells through band alignment engineering." Nature materials 13.8 (2014): 796-801.
4. Farzaneh, Azadeh, and Mohammad Reza Abdi. "CsI nanocrystal doped with Eu 2+ ions for radiation detection." Journal of Luminescence(2017).
5. Deschler, Felix, et al. "High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors." (2014).
6. Yakunin, Sergii, et al. "Detection of X-ray photons by solution-processed lead halide perovskites." Nature photonics 9.7 (2015): 444-449.

While there has been remarkable success in generating silver (Ag) nanoplates, and they have considerable potential applications, their degradation behavior in certain environments remains poorly understood. In the current work, we investigated the chemical stability of triangular Ag nanoplates. A one-step water-based synthesis regulated by the coordination of ligands to Ag cations was successfully employed to produce triangular Ag nanoplates with a high yield. The Ag nanoplates were irreversibly degraded when they were aged with poly(styrene-4-sulfonate) (PSS) at room temperature, and the corresponding localized surface plasmon resonances (LSPR) of the Ag nanoplates changed as well. In contrast, when the Ag nanoplates were aged with potassium persulfate (KPS), the shape evolution of Ag nanoplates was found to depend on the external temperature, and the Ag nanoplate solutions showed different final colors when different external temperatures were applied. These results exhibit important implications for the behavior of triangular Ag nanoplates in a wide variety of plasmonic applications and can be applied to the colorimetric sensing of the temperature history.

The design and preparation of hollow non-spherical microparticles are of great significance for their potential applications, but the development of a facile synthetic method based on the one-step production remains a great challenge. In this study, a new template-free method based on the dispersion polymerization was successfully developed to produce hollow polystyrene (PS) microparticles with anisotropic nanostructures in a single step. In the synthesis, ammonium persulfate (APS) which served as an initiator and as a co-stabilizer in dispersion polymerization played a critical role for formation and growth of the highly uniform and stable hollow PS microparticles. The experimental conditions such as the concentration of an initiator and a stabilizer could be adjusted to permit the shape-controlled synthesis of PS microparticles, that is, with control over the particle size and the degree of concavity. Based on our results and observations, a plausible mechanism for the formation of the hollow PS microparticles with novel morphology was proposed.

Hollow nanostructures such as nanocages and nanoframes can serve as advanced catalysts with their enlarged active surface areas, and hence they have been of widespread interest. Despite the recent progress in the synthesis of this class of nanomaterials, hollow nanostructures with tunable compositions and controlled morphologies have rarely been reported. Here, we report a facile synthetic route to a series of mixed cobalt/nickel sulfide octahedral nanocages. The sulfidation of CoO octahedral nanoparticles generates CoO@Co_xS_y core–shell octahedra, and the in situ etching of CoO core and annealing yield Co₉S₈ (pentlandite) octahedral nanocages (ONC). The addition of Ni precursor during the etching/annealing process of CoO@Co_xS_y core-shell octahedra progressively yields hollow ONC structures of Co_9-xNi_xS₈, Ni₉S₈, Ni₉S₈/β-NiS, and Ni₃S₂/β-NiS via cation exchange reactions. Mixed cobalt/nickel sulfide, Co_9-xNi_xS₈ ONC shows superior oxygen evolution reaction activity to monometallic sulfide ONC structures, demonstrating the synergy between cobalt and nickel.

Peritoneal carcinomatosis (PC) is a fatal condition arising in gastrointestinal tract characterized by poor prognosis and poor understanding of the disease. PC patients administered drugs locally in the tumor region such as intraperitoneal chemotherapy, often suffer from low drug retention time and tumor penetration. Herein, we synthesized Lithocholic acid (LCA)-conjugated disulfide-linked polyethyleneimine (ssPEI) micelle nanoconstruct by covalently conjugating ssPEI and LCA, thereby forming nano-micellar structures which loaded with paclitaxel (LAPMi-PTX) drug for IPCh. Incorporation of positive surface charge aided in prolonged peritoneal retention presumably by ascites fluid-induced protein corona formation and the subsequent size expansion caused resistance against crossing the lymphatic openings for the undesired clearance. Furthermore, preferential tumor penetration by LAPMi-PTX is attributable to the permeation enhancing properties of LCA, and subsequent tumor activatable drug release was induced by the presence of the disulfide linkages. By integrating these properties, LAPMi exhibited prolonged peritoneal residence time, enhanced tumor permeation and chemotherapeutic effect clearly evidenced by in vitro tumor spheroid and in vivo studies. Importantly, our strategy enabled significant PC inhibition and the overall survival rate of tumor-bearing mice. In conclusion, we provided a new paradigm of intractable PC treatment by enabling the prolonged residence time of nanoconstruct and thereby enhancing tumor penetration and anti-tumor therapy.

Acknowledgements
This work was financially supported by Basic Science Research Program (No. 2016R1A2B4011184 & 2016K2A9A1A06921661) and the Pioneer Research Center Program (2014M3C1A3053035) through the National Research Foundation of Korea (NRF) funded by the Korean government, MSIP.

Nanostructured metal chalcogenides have received a great attention in a variety of applications, which includes fuel cells, solar cells, supercapacitors, thermoelectric devices and sensors. Especially, mixed metal chalcogenides show a great promise due to their energy tunability and catalytic robustness under harsh operating condition. The template-mediated growth of nanoparticles is a very efficient method to synthesize well-defined colloidal nanocrystals because the template can be used as a platform where other materials are deposited by reduction or template components are released out by dissolution of template itself. In this research, we report a facile synthesis of mixed metal chalcogenides with well-defined structure prepared by template-mediated method toward hydrogen evolution reaction.

Bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is mandatory for clean and sustainable alternative energy sources. To improve the efficiency of the overall water splitting, highly efficient and stable bifunctional electrocatalysts in acidic media is vital for polymer electrolyte membrane (PEM) electrolyzers. Herein, we synthesized cactus like Cu_2-xS@IrS_y@IrRu (CIS@IrRu) alloy nanoparticles via template mediated method, which show highly efficient HER and OER electrocatalytic activity. Due to the dendritic structure and stable IrS_y shell, the cactus like CIS@IrRu nanoparticles exhibit highly efficient HER and OER catalytic activity in acidic media. The CIS@IrRu nanoparticles show the Ir/Ru composition dependent electrocatalytic activity with best bifunctional performace at the Ir ratio to Ru is 1.00 to 1.07. More significantly, in the overall water splitting, CIS@Ir_0.48Ru_0.52 reach 10 mA cm^-2 at the voltage of 1.56 V in 0.1 M HClO₄ electrolyte and maintain high electrocatalytic activity after durability test without structural deformation.

Development of electrocatalysts with reduced noble metal content with enhanced catalytic performance has been of importance in cost-effective design of renewable energy conversion devices. The design of core-shell nanoparticles as electrocatalysts represents a promising approach for preparing not only limiting the use of expensive precious metals also developing catalytic activity. Herein, simple one-pot synthetic route to fabricate anisotropic hexagonal-shaped core-shell nanosandwich structures with binary and ternary composition will be reported. Also, the core composition of hexagonal nanosandwich structures is easily controllable by modulating the amount of precursor. The hexagonal core-shell nanosandwich possesses enhanced electrocatalytic activity toward oxygen evolution reaction (OER), with their OER activity being dependent on their core compositions.

Ceria nanoparticles are used in chemical mechanical planarization (CMP) slurry for their selective removal of oxides over nitrides. This is the result of a reversible redox reaction at the surface of the particles allowing these particles to participate in both the chemical and mechanical aspects of planarization. A key property that determines the ability of ceria to undergo this reaction is the ratio of Ce³⁺/Ce⁴⁺ on the surface of the particles. As this ratio increases, so does the interaction with the oxide surface, resulting in an increased removal rate. Most studies to date focus on how synthesis and particle size effect these ratios but ignore the changes that could arise when introducing the particles to a slurry environment.

In this study, X-ray photoelectron spectroscopy (XPS) was used to measure the ratio of Ce³⁺/Ce⁴⁺ as a function of several slurry properties such as pH, oxidizing agent and surfactant. The effects of these properties were examined in virgin and aged slurries, and as a function of concentration and type.

It appears that slurry age and pH have little effect on the particles, but much depends on the peak fitting method, which is not yet a settled question in the XPS community. We discuss these findings and their implications for the specific design of future slurries.

A prerequisite to build advanced plasmonic architectures is the ability to precisely control the organization of metal nanoparticles in space. To this end, DNA origami represents an ideal construction platform owing to its unique sequence specificity and structural versatility. In this talk, we demonstrate novel dynamic systems which exhibit interesting optical properties. We also discuss about the inevitable evolution from static to dynamic systems along with the fast development of this inter-disciplinary field.

Colloidal syntheses have unequivocally demonstrated seed design as a decisive factor in determining the growth pathway along which an emerging nanostructure follows. With the seed size, shape, composition, and internal defect structure all proving crucial, there has been a concerted effort to manipulate the seed formation process. Seed preparation techniques reliant on oxidative etching, capping agents, centrifugation, and kinetically and thermodynamically controlled regimes are now routinely used. Our group has devised a synthetic strategy in which seed-mediated colloidal syntheses are practiced on nanostructures that are immobilized on the substrate surface. While numerous seed-mediated colloidal growth modes have been adapted to the substrate platform, much of the prior art pertaining to seed formation proves unadaptable or is drastically altered by the substrate surface. Instead, seeds are formed in periodic arrays using a vapor-phase directed assembly technique that is most closely related to solid-state dewetting. Within the scope of this strategy lies numerous opportunities to place new controls on the seed formation process that are reliant on such factors as substrate-imposed epitaxy and the engineering of defects through substrate-imposed strain. Moreover, these seeds can then be used to form unique templates suitable for heterogeneous depositions or galvanic replacement reactions. Here, we will describe the techniques used to generate seeds, demonstrate their utility in forming substrate-based noble metal nanostructures, and provide an understanding of the opportunities and challenges that lie ahead.

In this talk we describe the use of electric fields to drive nanocrystals assembly into superlattices. First we demonstrate that field driven assembly can deposit well-ordered superlattices with diffraction peaks out to (2,2,8) over large (cm²) areas. The process is amenable to wafer-level deposition, reversible and several orders of magnitude faster than conventional solvent evaporation or co-solvent techniques. The electric field controls the nanocrystal flux making the deposition process akin to vapor deposition. Beyond simply depositing films, this flux control allows us to systematically change the nucleation density and growth rates. In this work we use in situ quartz crystal microbalance to measure growth rates and ex situ imaging to measure nucleation density. We use nickel and silver nanocrystals to show that films can grow either via a layer-by-layer or by an island formation mechanism. We show that the ligand plays a central role in determining whether nanocrystals assemble into thin films or colloidal crystals. This level of control allows us to tune the correlation length, which we expect to have advantages for fundamental studies and to benefit device performance.

Work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Nanocrystals (NCs) act as building blocks and self-assemble into long-range periodic superlattice structures. Such assemblies not only maintain the size-dependent properties of individual nanocrystals, but also can give rise to enhanced or novel properties from near-field coupling. Control of this material-by-design approach requires a better understanding of nucleation and growth mechanism. One approach is to dry a pure solution and assemble supercrystals under equilibrium conditions. However, due to the weak interactions between NCs through ligands, it is often difficult to achieve large domain sizes, even in very slow processes, lasting from days to weeks.

Here, we use Fe₂O₃ spherical NCs as a model system to demonstrate an assembly approach based on the interdiffusion of NC solutions and anti-solvents. The anti-solvents are miscible to the solution but poor solvents for NCs (e. g., polar solvents for NCs coated with non-polar ligands). The diffusion at the interface creates a non-equilibrium condition to accelerate nucleation and allows growth control through the solvent/solution properties, such as polarity, miscibility, viscosity, solubility of solutes, etc. This approach not only accelerates the growth of superlattice into large grains, which could take weeks without anti-solvents, down to hours, but also facilitates exploration of new polymorphs. The solution processes are in situ characterized by SAXS/WAXS (Small and Wide Angle X-ray Scattering), to probe the periodic structures from atomic (NCs structure) to ~100nm (superlattice) length scales on the CMS beamline (11-BM) at NSLS II.

Ordered ensembles, also known as superlattices, have been formed with a large variety of nanocrystals. The structure of nanocrystal superlattices have been extensively studied and well documented; however, their assembly process is poorly understood. In this work, we demonstrate an in situ space-/time-resolved small angle X-ray scattering (SAXS) measurement and use it to probe the assembly of silver (Ag) nanocrystal superlattices driven by electric fields. By measuring the volume fraction of nanocrystal solution as a function of position and time, we show that the electric field causes Ag nanocrystals to migrate to the anode, leading to a rapid accumulation of nanocrystals that assemble into highly ordered superlattices in several minutes. We have quantitively determined the nanocrystal velocity and flux under various field strengths and found out that a stronger electric field drives nanocrystal to migrate at a faster velocity and higher flux, which in turn cause superlattice to nucleate at a higher density and grow at a faster rate. The quantitative information obtained in this study allows a better understanding of nanocrystal self-assembly and can be used to correlate theoretical models with experimental results.

When a metal precursor is reduced in the presence of nanocages (i.e., nanostructures with a hollow interior and porous walls), the resultant metal atoms can, in principle, be deposited on both the outer and inner surfaces, or just the outer surface. We recently demonstrated that these two different scenarios of metal deposition could be deterministically achieved by controlling the reduction kinetics of the precursor. Specifically, if the precursor was reduced at fast kinetics, the solution reduction pathway would be favored, leading to the deposition only on the outer surface for the generation of double-shelled nanocages. When switched to a precursor with slow reduction kinetics, the precursor could readily diffuse into the interior of the nanocages prior to its reduction. As such, both the outer and inner surfaces of the nanocages were coated with atoms for the generation of triple-shelled nanocages. This work not only offers a new synthetic approach to metal nanocages with diverse compositions and structures but also demonstrates the necessity of controlling the relative rates of reduction and bulk diffusion of a metal precursor when nanostructures with a hollow interior and porous walls are used for seed-mediated growth.

Material formation in nature is precisely controlled in all aspects from crystal nucleation, growth to assembly to deliver superior functions. Specific biomolecule-material interactions have been hypothesized to play important roles in these processes. Proteins, polymers and small molecules have been extensively explored to replicate the degree of control in material formation in vitro and for nonbiogenic materials. However the organic-inorganic interfacial interaction is still far from being understood which hinders the further advancement of biomimetic material formation. In this talk I will share our efforts on decoding the myth of biomolecular specificity to material surface and their roles in controlling crystal nucleation and growth. The selection of facet specific short peptides and their abilities in guiding predictable morphology control of Pt nanocrystals will be first demonstrated. Then detailed experimental and theoretical studies on binding mechanism will be discussed. Based on mechanistic understanding, we designed small molecules bearing molecular signature for facet specific adsorption to modulate the nucleation/growth of the Pt and Pt alloy nanocrystals to deliver the expected nanostructures and functions. At the end of talk I will share our recent research on improving catalytic functions of nanocrystals through synthetic design. These studies open up opportunities in understanding the molecular details of inorganic-organic interface interaction, which can one day lead to the development of a library of molecular functions for biomimetic materials design and engineering.

Semiconductor nanocrystals (QDs) are characterized by a discrete density of states that resembles that of atoms. When an atomic system condenses into a solid, the degeneracy of atomic levels is lifted in accordance to Pauli’s exclusion principle, resulting into the formation of bands. In analogy, when a QD dispersion condenses into a crystalline solid, a supercrystal, the formation of mini-bands may be expected [1]. To obtain a conductive supercrystal, polydispersity must be below 7% [2], self-assembly must be controlled, and the QDs surface must be passivated with short (conductive) ligands [3]. Perfecting the self-assembly of QDs into a supercrystal may enable the observation of mini-bands and consequently boost the performance of QD based devices such as light emitting diodes, transistors, and solar cells.
We evaporate an oil-in-water emulsion to produce three-dimensional QD supercrystals [4]. The crystallization of QDs within each emulsion droplet is followed in situ using synchrotron-based X-ray radiation; we find that under a wide range of conditions, large (ca. 300 nm) QD single crystals grow. We characterize the efficiency of light absorption and emission in these supercrystals as compared to that of dispersed QDs. Furthermore, after performing established ligand exchange protocols with short conductive ligands on supercrystals, we observe a substantial decrease in inter-dot distance and increase in volume fraction while retaining three-dimensional long range order. Finally, we measure the conductivity of a single supercrystal and study its dependence on the crystallinity. We believe these findings suggest new approaches towards QD supercrystal device fabrication exhibiting both conductivity and structural order to enhance performance.
[1] O.L. Lazarenkova and A.A. Balandin. "Miniband formation in a QD crystal." Journal of Applied Physics (2001).
[2] P.N. Pusey, “The effect of polydispersity on the crystallization of hard spherical colloids.” Journal de Physique (1987).
[3] M. Kovalenko et al., "Colloidal nanocrystals with molecular metal chalcogenide surface ligands." Science (2009).
[4] B. De Nijs et al., "Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement." Nature materials (2015).

An optical phenomena based on the incident light absorption and transduction to the detectable thermal signal by plasmonic bimetallic Ag and Au nanocages (Ag@AuNCs) has been researched on free standing films. The photothermal response in the visible range (532 nm) is distinguishable. Specifically increasing the laser power to 100 mW led to visual burning of the free standing film (temperature increased greater than >150 °C). the molar concentration of the plasmonic Ag@AuNCs in polymer films is a primary factor that affects the photothermal dynamic response along with Ag@AuNCs distribution. This is supposed to result from the Ag@AuNCs assembled in a layer that leads to electromagnetic field enhancement. The unusual observation in polymer films is that the UV-visible spectra (extinction efficiency) and photothermal response (T_max) do not rely on the content of the polymer and show a comparable (by value in magnitude) photothermal response at a different polymer composition at the same Ag@AuNCs concentration.
This work was supported in part by NSF ECCS-1006927, NSF CBET 1134222 and the University of Arkansas Foundation. UV-visible spectroscopy was supported by NSF EEC-1138248. The Arkansas Bio Nano Materials Characterization Facility is supported in part by the NSF. I thank Jeremy R. Dunklin, Samir V. Jenkins, Jingyi Chen and D. Keith Roper

Colloidal semiconductor nanocrystals (NCs) are prized for their size-dependent optical and electronic properties and for their solution-based processability that enables the integration of these materials in devices. However, the long, insulating ligands commonly employed in the synthesis of colloidal NCs inhibit strong interparticle coupling and charge transport once NCs are assembled to form NC solids. We employ a range of short, compact ligand chemistries to exchange the long, insulating ligands used in synthesis and to increase interparticle coupling.¹ These ligand exchange processes can have a dramatic influence on NC surface chemistry as well as the organization of NCs in solids, showing examples of short-range order.² Synergistically, we use 1) thermal evaporation and diffusion^3,4 and 2) wet-chemical methods⁵ to introduce extrinsic impurities and non-stoichiometry that serve to passivate surface traps and dope NC solids. We show strong electronic coupling in combination with doping allows us to control the carrier type and concentration and to design high mobility n- and p-type materials. We give examples where n- and p-type semiconductor NC solids are used to construct flexible, electronic transistors and integrated circuits and optoelectronic solar photovoltaics and photodetectors.^3,4,6,7 In combination with metal and insulating NCs, we demonstrate flexible, all-NC field-effect transistors.⁸

(1) Fafarman, A. T.; Koh, W.; Diroll, B. T.; Kim, D. K.; Ko, D.-K.; Oh, S. J.; Ye, X.; Doan-Nguyen, V.; Crump, M. R.; Reifsnyder, D. C.; Murray, C. B.; Kagan, C. R. J. Am. Chem. Soc. 2011, 133 (39), 15753–15761.
(2) Oh, S. J.; Wang, Z.; Berry, N. E.; Choi, J.-H.; Zhao, T.; Gaulding, E. A.; Paik, T.; Lai, Y.; Murray, C. B.; Kagan, C. R. Nano Lett. 2014, 14 (11), 6210–6216.
(3) Choi, J. H.; Fafarman, A. T.; Oh, S. J.; Ko, D. K.; Kim, D. K.; Diroll, B. T.; Muramoto, S.; Gillen, J. G.; Murray, C. B.; Kagan, C. R. Nano Lett. 2012, 12 (5), 2631–2638.
(4) Oh, S. J.; Berry, N. E.; Choi, J.-H.; Gaulding, E. A.; Paik, T.; Hong, S.-H.; Murray, C. B.; Kagan, C. R. ACS Nano 2013, 7 (3), 2413–2421.
(5) Oh, S. J.; Berry, N. E.; Choi, J.-H.; Gaulding, E. A.; Lin, H.; Paik, T.; Diroll, B. T.; Muramoto, S.; Murray, C. B.; Kagan, C. R. Nano Lett. 2014, 14 (3), 1559–1566.
(6) Stinner, F. S.; Lai, Y.; Straus, D. B.; Diroll, B. T.; Kim, D. K.; Murray, C. B.; Kagan, C. R. Nano Lett. 2015, 15 (10), 7155–7160.
(7) Oh, S. J.; Uswachoke, C.; Zhao, T.; Choi, J.-H.; Diroll, B. T.; Murray, C. B.; Kagan, C. R. ACS Nano 2015, 9 (7), 7536–7544.
(8) Choi, J.-H.; Wang, H.; Oh, S. J.; Paik, T.; Sung, P.; Sung, J.; Ye, X.; Zhao, T.; Diroll, B. T.; Murray, C. B.; Kagan, C. R. Science (80-. ). 2016, 352 (6282), 205–208.

Daniel Jostes, Tobias Jochum, Jan Niehaus, H. Weller
Physical Chemistry Department, University Hamburg.


Meanwhile the large scale synthesis of high quality Cadmium Selenide (CdSe) quantum dots (QD) with high quantum yield and small size distribution is established. This CdSe QD can be used in different technological applications for example biological imaging and display-devices. The use of cadmium in electronic devices is strongly restricted by the EU (RoHS), therefore it is necessary to replace Cadmium in variant fields. One of the most promising material to remove cadmium is Indium Phosphide (InP). InP is potentially less toxic, not restricted in electronic devices and has similar optical properties. Hereby we present a large scale synthesis of InP quantum dots with a continuous flow reactor. This synthesis is based on Wells dehalosilylation reaction, with indium(III)acetate and tris(trimethylsilyl)phosphine (TMSP). We succeeded producing InP QD with different sizes by variating the growth temperature and the flow rate. Moreover it is possible by adding selenium to improve the QY (>40%) including small full widths at half maxima (FWHM <50nm). Furthermore improvement of the QY (>70%) can be achieved by adding a shell on the alloyed core.

Nanolithography is the main method for manufacturing of integrated circuits and relies on the solubility changes of light-sensitive photoresists. Demand for smaller features has driven the industry from 193 nm (6.4 eV) deep UV (DUV) light to more energetic 13.5 nm (92 eV) extreme UV (EUV) light. This transition requests photoresists able to absorb light effectively at this wavelength and inducing the desired chemistry changes. Inorganic materials are stronger absorbers of EUV than conventional organic resists and a lot of effort has been put into developing metal oxide resist based on e.g. Zr, Hf and Sn. In this work we investigate a new photoresist based on quantum dots (QDs). These quantum dots are nanoparticles of strongly EUV-absorbing elements such as PbS and PbTe. QDs are easy to produce and can be tuned for optical and electrical properties based on size and surface chemistry. Here we present the behavior of these materials under EUV irradiation. We investigate the solubility changes, together with the changes of the surface ligation to elucidate the mechanism of the chemical changes.

The shape anisotropy of nanoparticle building blocks is of critical importance in determining their packing symmetry and assembly directionality. While there has been extensive research on the effect of their overall geometric shapes, the importance of nanometer morphology details is not well-recognized or understood. Here we draw on shape-anisotropic gold triangular nanoprism building blocks with either morphology details on their tips or their side facets as examples of demonstration. By fine-tuning the balance among internanoparticle interactions, we observed a series of unexpected polymorphic assemblies with unique plasmonic coupling properties. [1,2] Our study can guide future work in both nanoparticle synthesis and self-assembly; nanoscale geometrical features in anisotropic nanoparticles can be used as an important handle to control directional interactions for nonconventional ordered assemblies and to enrich diversity in self-assembly structure and function.
Ref (1): Nano Letters 17 (5), pp 3270–3275 (2017).
Ref (2): Nature Communications, 8, 761 (2017)

We develop and apply liquid cell transmission electron microscopy (TEM) for real time imaging of nanoparticle interaction and self-assembly. With PbSe nanoparticles as a model system, we study nanoparticle superlattice formation and structural transformation of the superlattice upon ligand exchange. The ligand mediated nanoparticle rotation, nanoparticle two dimensional movement, etc. dynamic information has been obtained by in situ observation. We apply automated image analysis method to estimate nanoparticle interaction forces as a function of inter-nanoparticle distance. Our in situ study provides critical insights on nanoparticle self assembly mediated by ligand interactions.

Chemists are often regarded as “architects”, who are capable of building up complex molecular structures in the ultrasmall world. However, compared with organic chemistry, nanochemistry dealing with nanoparticles in the size range from 1 to 100 nm is less precise in terms of synthesis, composition, and structure. Such an imprecise nature of nanochemistry has impeded rational control and in-depth understanding of structures and properties of nanomaterials.

Recently, thiolate-protected gold nanoclusters have emerged as a paradigm of atomically precise nanomaterials¹. In this poster, I will first discuss how to synthesize atomically precise gold nanoclusters containing ~10 to ~1000 gold atoms (i.e. 1 to 3 nm), as well as their total structure determination by single-crystal X-ray diffraction. Then, I will show that how the precise nature of these nanomaterials allows us to discover, decipher and understand many intriguing nanoscale phenomena, including the transformation chemistry at the nanoscale², periodicities in nanoclusters³, a supermolecular origin of “magic sizes”⁴, and the emergence of hierarchical structural complexity in the nanoparticle system⁵.

[1] R. Jin, C. Zeng, M. Zhou, Y. Chen, Chem. Rev.116, 10346-10413 (2016).
[2] C. Zeng, C. Liu, Y. Pei, R. Jin, ACS Nano 7, 6138-6145 (2013).
[3] C. Zeng, Y. Chen, K. Iida, K. Nobusada, K. Kirschbaum, K. J. Lambright, R. Jin, J. Am. Chem. Soc. 138, 3950-3953 (2016).
[4] C. Zeng, Y. Chen, C. Liu, K. Nobusada, N. L. Rosi, R. Jin, Sci. Adv. 1, e1500425 (2015).
[5] C. Zeng, Y. Chen, K. Kirschbaum, K. J. Lambright, R. Jin, Science 354, 1580-1584 (2016).

Nanocages have received considerable attention in recent years for catalytic applications owing to their high utilization efficiency of atoms and well-defined facets. Here we report, for the first time, the synthesis of Ru cubic nanocages with ultrathin walls, in which the atoms are crystallized in a face-centered cubic (fcc) rather than hexagonal close-packed (hcp) structure. The key to the success of this synthesis is to ensure layer-by-layer deposition of Ru atoms on the surface of Pd cubic seeds by controlling the reaction temperature and the injection rate of a Ru(III) precursor. By selectively etching away the Pd from the Pd@Ru core−shell nanocubes, we obtain Ru nanocages with an average wall thickness of 1.1 nm or about six atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal structure rather than the hcp structure observed in bulk Ru. The synthesis has been successfully applied to Pd cubic seeds with different edge lengths in the range of 6−18 nm, with smaller seeds more favorable for the formation of Ru shells with a flat, smooth surface due to a shorter distance for surface diffusion of the Ru adatoms. Self-consistent density functional theory calculations indicate that these unique fcc-structured Ru nanocages might possess promising catalytic properties for ammonia synthesis compared to hcp Ru(0001), on the basis of strengthened binding of atomic N and substantially reduced activation energies for N₂ dissociation, which is the rate-determining step for ammonia synthesis on hcp Ru catalysts.

Controlled synthesis of the metal nanoparticles (NPs) is an important topic due to distinct optical properties of its metal NPs depend on their size, shape and surface morphology. Especially, nanoshell structure have interesting properties for their tunable surface plasmon resonance bands easily just by varying the ratio of core size to metallic shell thickness or controlling surface morphology of metallic shell. In that sense, a controlling surface morphology of metal nanoshell is one of the key factors to change surface plasmon resonance and scattering properties of such NPs. In general, surface morphology control of nanoshell has been studied by changing surfactant such as cetyltrimethylammonium bromide (CTAB) and their halide derivatives or introducing seed-mediated synthesis for kinetically controlled reaction. However, they have several problems such as a using excessive amount of bulky surfactant and time-consuming multi-step processes.
In this poster, we presented one-step and a surfactant-free synthesis for controlling morphology and thickness of silver nanoshells using alkylamines as a reductant and capping agent. As alkylamines, the butylamine, octylamine, dodecylamine, hexadecylamine, ethanolamine, 3-amino-1-propanol and tributylamine were used for studying on effects of an alkyl chain length, an existence of hydroxyl group, and the degree of alkyl chain in silver shell formation, which result in a change on surface morphology and thickness of silver nanoshell. This change were attributed to several factors such as selective capping properties, steric effect, reducing power along the alkylamine.
Confirming the enhanced scattering properties of synthesized silver nanoshell with different surface morphologies, optical properties of each silver nanoshells were investigated by observing Surface Enhanced Raman Scattering (SERS) at the single particle levels. According to nanoshell surface morphology, intense and uniform SERS signal was detected for single particle and their SERS enhancement factor for each particle were calculated up to ~10⁷. This enhanced scattering properties of silver nanoshell showed a potential as ultra-high sensitive NIR SERS probe for in vivo or ex vivo targeting experiment.

For solution-processed optoelectronics such as Organics Light-emitting diodes (LEDs), Quantum dot LEDs, Perovskite LEDs, many researchers focus on ZnO nanoparticles (NP) as electron injection layer (EIL) which has appropriate properties; it has deep valence band (~7.8 eV), large bandgap (~3.4eV), high intrinsic electron mobility (~ 200 cm²V^-1S^-1). However, the ZnO NPs have many defects on the surface, it results in an exciton quenching, and then it has a bad effect on the device. Moreover, due to the large barrier between the workfunction of ZnO NPs and the lowest unoccupied molecular orbital (LUMO) of emissive layer, electron cannot inject efficiently. In recent years, to reduce workfunction of ZnO, Polyethylenimine (PEI) have studied as the interfacial bilayer onto the ZnO NP films (PEI/ZnO bilayer). However, surface defects of PEI/ZnO bilayer still remain.
Herein, we suggest introduction of hybridization between ZnO NPs and Polyethylenimine (PEI:ZnO hybrid layer), called organic/inorganic hybrid materials. PEI:ZnO hybrid layer passivates the surface defect of ZnO NPs and reduces the energy barrier through dipole effect. To study how much surface defect of PEI:ZnO hybrid layer is passivated, we utilized X-ray photoelectron spectroscopy (XPS). In case of PEI:ZnO hybrid layer, lattice oxygen peak (O_L, 530.2eV) is 92.7%, deficient oxygen sites peak (O_V, 531.4eV) is 7.2% and ratio of oxygen vacancy to lattice of oxygen (O_V / O_L) is only 0.078. On the other hand, For PEI/ZnO bilayer, O_L is 75.01%, O_V is 19.8%, and oxygen vacancy ratio (O_V / O_L) is 0.264. We found that PEI:ZnO hybrid layer more passivate the surface defect than PEI/ZnO bilayer. In addition, we fabricated electron only device which use linear PEI and branched PEI and we investigate the electron injection mechanism. Linear PEI contain all secondary amines, in contrast to branched PEI which contain primary, secondary and tertiary amino groups. We show that their amino group can affect the binding of PEI:ZnO hybrid, and electron injection mechanisms can be identified. In case of breached PEI has better electron injection ability than linear PEI. As a result, it is found that branched PEI:ZnO hybrid layer has good surface defect passivation and electron injection ability.

Rational synthesis and design of intermetallic nanoalloys (NAs) and nanocomposites (NCs) as efficient, low-cost oxygen reduction reaction (ORR) electrocatalysts require robust understanding of processing-structure-property relations to enable systematic tailoring of their architectures and compositions without using unwanted chemicals/surfactants/ligands. We address such challenges with our recently developed tandem LASiS-GRR^1,2 as a facile, green yet, efficient route for colloidal synthesis of: 1) binary (PtCo)/ternary (PtCuCo) NAs with reduced Pt contents,^3,4 and 2) Co₃O₄/nitrogen-doped graphene oxide (NGO) hybrid NCs (HNC)⁵ as efficient ORR electrocatalysts. Here, the transformative concept is that LASiS-GRR exploits the high-energy physico-chemical pathways emerging from liquid-confined, laser-induced plasma, and GRR mechanisms to produce NAs/NCs with varied sizes, compositions and alloying without using any detrimental chemicals/surfactants. Detailed structural and chemical analyses reveal uniformly alloyed cores with Pt-rich shells for the PtCo NAs and PtCu-rich shells with minor Cu contents for the PtCuCo ternary NAs. Our previous studies have established outstanding ORR activities for the PtCo NAs in acid electrolytes while enabling Pt content reductions.⁴ And now, the Pt₇₀Cu₂₁Co₉ ternary NAs indicate a c.a. 4 and 6-fold increase in mass and specific activities respectively as compared to commercial Pt/C catalysts, while allowing a 25-30% (at.) reduction in Pt.³ On the other hand, systematic spectroscopic studies on the HNC samples indicate both chemical and charge-driven interactions responsible for embedding Co₃O₄ nanoparticles onto the NGO films. ORR activities for the Co₃O₄/NGO HNCs are found to be comparable to commercial Pt catalysts without using any precious metals.⁵ Such enhanced activities are attributed to: 1) surfactant/ligand-free synthesis technique that prevents catalytic site degradations; 2) systematic alloying of ternary transition metals (Cu) to optimally position the Pt d-band center between that of Pt and PtCo NAs, thereby tuning their binding affinities for oxygen/oxygenated species; and 3) nitrogen doping in 2D HNCs promoting higher electron conductivity while hindering aggregation between 0D Co₃O₄ nanocubes. Our results indicate future potentials of tandem LASiS-GRR yet to be unleashed for rapid and reproducible manufacturing of diverse colloidal NAs/NCs with interfacial energetics/arrangements designed for superior electrocatalytic activities.
References:
(1) D. Mukherjee, S. Hu; Patent Appl. 15/132,916, USA, 2016.
(2) S. Hu, G. Goenaga, C. Melton, T. A. Zawodzinski, D. Mukherjee; Appl. Catal. B: Env., 2016, 182, 286.
(3) S. Hu, K. M. Cheng, E. L. Ribeiro, K. Park, B. Khomami, D. Mukherjee; Catal. Sci. Tech., 2017, 7, 2074.
(4) S. Hu, M. Tian, E. L. Ribeiro, G. Duscher, D. Mukherjee; J. Power Sour., 2016, 306, 413.
(5) S. Hu, E. L. Ribeiro, S. A. Davari, M. K. Tian, D. Mukherjee, B. Khomami; RSC Adv., 2017, 7, 33166.

Due to their low-cost and adaptable technology, colloidal quantum dots (CQD) have attracted extensive interest, especially for photovoltaic applications. In the last few years, the power conversion efficiency (PCE) of CQD based solar cells has increased from 0.01% to over 10%. Compared to other types of CQD solar cells, CuInS_xSe _2-x (CISSe) quantum dot based solar cells draw a lot of attention because of the heavy-metal free and non-toxic character of the material. The highest PCE reported so far in this material system is 11.7%, though this used a liquid electrolyte which is inconvenient for the mass deployment of of devices. Solid state CuInS₂ based CQD solar cells, despite significant effort, have a champion PCE of only around 1%. The main ways to improve on these nanoparticle cells are to enhance carrier mobilities, tune band offsets at heterojunctions, increase control of the surface passivation and build better device architectures. In this report, we have focused on improving the device structure and charge carrier extraction by employing tin dioxide as a window layer to improve the electrical mobility and passivate the surface of mesoporous-TiO₂ in order to decrease the surface defects. By this approach, a dramatic boost in the current was observed, which lead to the significant increase in the overall device performance.

Excited states generated in energy upconversion process in NaYF₄:Yb³⁺,Tm³⁺ nanoparticles may enable a range of biomedical and material applications. We describe preparative and post-preparative control of upconversion, with particular emphasis on ultraviolet upconversion. A series of hydrothermal syntheses were performed with ytterbium doping ratios ranging from 0 to 99.5%. Initially, UV luminescence intensity increases substantially with an increased presence of ytterbium as ytterbium participates in energy transfer upconversion to improve luminescent yield. However, as the doping ratio of ytterbium increases, substantial loss of luminescence occurs due to energy migration through ytterbium, likely through surface sites, non-radiatively dissipating energy from the system. We investigated NIR and UV luminescence from these UNPs under conditions of pulsed 980 nm excitation, with the pulse width varied from 10 to 2000 µs. The duty cycle was kept constant so the average power (energy/time) delivered by excitation was the same for any of the pulse widths tested. We observed that the UV and NIR emission intensities have vastly different responses to changes in excitation pulse width in this range. NIR emission intensity changes relatively little with the pulse width. In stark juxtaposition, UV luminescence shows three orders of magnitude reduction of intensity upon changing excitation regimen from a long pulse width to a short one. The highly nonlinear luminescence response to pulse width enables control of UV luminescence intensity in the manner resembling that of a binary switch. Through the use of preparative techniques and a novel excitation modulation scheme, we demonstrated control of upconversion pathways, so NIR to UV upconversion can be turned on and off while maintaining NIR to NIR upconversion, in support of applications combining photochemistry and imaging.

Ternary CuInX₂ (X= S, Se, Te) nanocrystals (NCs) have attracted increasing attention as promising alternatives for CdX or PbX NCs due to their low toxicity, large absorption cross-sections across a broad spectral range and wide photoluminescence (PL) tunability (~550 to ~1100 nm for X= S). To achieve properties that are inaccessible to single component CuInX₂ NCs (e.g., high PL quantum yields, stability, carrier localization regime), researchers have been synthesizing colloidal CuInX₂-based hetero-NCs (HNCs) (e.g., CuInS₂/ZnS concentric core/shell HNCs, CuInS₂/CdS tetrapods, CuInSe₂/CuInS₂ dot-in-rod HNCs). Anisotropic CuInX₂-based HNCs are particularly interesting, since they are expected to exhibit novel properties, such as polarized NIR PL and spatial charge separation, which are attractive for many applications (e.g., polarized LEDs, photocatalysts, luminescent solar concentrators, solar cells).
Nevertheless, reports on the synthesis of anisotropic CuInX₂-based HNCs are scarce. This is probably related to the difficulty in balancing the reactivities of multiple precursors and the high solid-state diffusion rates of all the cations involved in the CuInX₂ lattice. In this work, we report a two-step pathway that yields CuInS₂/ZnS dot core/ rod shell HNCs via a seeded growth approach. The wurtzite CuInS₂ NCs used as seeds are obtained by cation exchange in template Cu_2-xS NCs. The CuInS₂ NC seeds are injected together with the S precursor in a hot solution of Zn precursor and suitable coordinating ligands, which leading to heteroepitaxial growth of ZnS primarily on single polar facet of the seeds, as demonstrated by high-angle annular dark-field scanning transimission electron microscopy and electron tomography. These colloidal wurtzite CuInS₂/ZnS dot-in-rod HNCs have large molar extinction coefficients, PL in the NIR (~800 nm) with PL quantum yield ~20%, and are readily dispersible in a variety of solvents.

The M1 form of vanadium dioxide exhibits a reversible first-order metal insulator transition (MIT) at 67 ^οC and is therefore of significant interest for many nanoelectronics and nano-optics devices applications. Synthetically, however, formation of VO₂(M1) nanoparticles is challenging because of the complexity of the V-O phase diagram, which includes several structurally related VO₂ polymorphs and V_nO_2n-1 Magneli phases, as well as the tendency to instead form the metastable (B) phase of VO₂, which does not exhibit a MIT above room temperature, during solution growth. VO₂ nanoparticle domains have been incorporated into nanoscale heterostructures through solution phase epitaxial growth on the tips of rutile TiO₂ nanorods. Four distinct classes of VO₂–TiO₂–VO₂ nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO₂–TiO₂–VO₂ nanostructure has a different insulator-metal transition temperature that depends on the VO₂ domains sizes and the TiO₂–VO₂ interfacial strain characteristics. Incorporating the switchable M1 form of VO₂ into solution-synthesized nanoscale heterostructures would enable fundamental studies of the size-dependent MIT transition behavior in VO₂ and potentially allow the feature sizes of device architectures that could utilize the abrupt electrical and optical switching capabilities of VO₂ to be scaled down to significantly smaller dimensions.

Metal-Amino Acid Nanocrystals Synthesis and Applications

Amino acid is a naturally occurring organic molecule can be mass-synthesized and has been manufactured commercially. As a basic unit of proteins, amino acid is nontoxic and can be absorbed in vivo, which has led to its application in many fields. Therefore, if amino acid molecules can be used as building blocks to combine with specific metal ions, the novel functional nanomaterials should have great applications in many fields.

Terbium-aspartic acid (Tb-Asp) nanocrystals with chirality-dependent tunable fluorescent properties can be synthesized through a facile synthesis method through the coordination between Tb and Asp. Asp with different chirality (dextrorotation/D and levogyration/L) changes the stability of coordination center following fluorescent absorption/emission ability difference. Compared with L-Asp, D-Asp can coordinate Tb to form more stable center, following the higher quantum yield and longer fluorescence life. Fluorescent intensity of Tb-Asp linearly increases with increase ratio of D-Asp in the mixed chirality Tb-Asp system, and the fluorescent properties of Tb-Asp nanocrystals can be tuned by adjusting the chirality ratio. Tb-Asp nanocrystals possess many advantages, such as high bio-compatibility, without any color in visible light irradiation, mono-dispersion with very small size, long fluorescent life. Those characteristics will bring its great potential in many application fields, such as low-cost anti-fake markers and advertisements using ink-jet printer or mold molding when dispersed in PDMS. In addition, europium (Eu) can also been used to synthesize Eu-Asp nanoparticles. Importantly, the facile, low cost, high yield and mass-productive “green” synthesis approach opens a new door for synthesis and application of the new generation fluorescent nanocrystals, which will have great impact in nanomaterial technology. (Baojin Ma, et al. ACS nano 11.2 (2017): 1973-1981)

Further, other metal-amino acid nanocrystals are being synthesized and will be applied in many fields according their unique properties. Through structure design and property optimization, it can be believed that the novel metal-amino acid nanocrystals with multi-functions will have very important and wide applications.

Stable and concentrated silver nanocolloids (AgNCs) have attracted considerable attentions as “functional inks” to manufacture fine metal electrode patterns toward application of flexible electronics, using printing-based device production (or printed electronics) technologies. Recently, we developed a groundbreaking printing technique, called as “surface photo-reactive nanometal printing (SuPR-NaP)”, which allows easy manufacture of ultrafine conductive silver patterns with a high submicron resolution [1]. It was demonstrated that the technique relies on a unique effect of nanoparticle (NP) chemisorption on a patterned photo-activated surface, as is enabled by using specific AgNCs that are obtained by thermal decomposition of oxalate-bridging silver alkyl-amine complexes [2]. These AgNCs are composed of silver NPs (with diameter of about 13 nm) encapsulated by alkyl-amines and a slight amount of oleic acid and can be suspended at a high concentration of 40 wt% in a 4:1 mixed dispersant of n-octane and n-butanol. The peculiar nature of the AgNCs is that the high dispersion stability is maintained for a long period of time (more than a month), whereas the high surface reactivity for NP chemisorption is possible on the activated surface that is equipped with carboxylate groups in the SuPR-NaP technique [1,3].
In this presentation, we will discuss that the above-mentioned unique compatibility between the high dispersion stability and high NP chemisorption reactivity of the AgNCs are closely correlated with the choice of mixed dispersant as used for the AgNCs. We investigated the dependence of dispersion stability of AgNCs on the dispersant composition by using confocal dynamic light scattering (CDLS) technique that can probe the size distribution of colloidal particles in the concentrated AgNCs [3]. We found that the dispersion stability dramatically depends on the dispersant compositions. Especially, we here focused on a content of methanol which is inevitably included in the AgNCs during the synthetic processes. We prepared AgNCs that contain methanol less than a few %, 10%, 20% and 30% by changing the solvent composition by controlling the drying and adding methanol content during the preparation of the AgNCs. By measuring the suspended particle size of these AgNCs by the CDLS technique, it was observed that dispersion stability got worse and the ratio of large aggregates increased in the AgNCs that contain more methanol. It was also observed that the conductivity and the degree of sintering in the electrode patterns obtained by the SuPR-NaP technique increased by adding more methanol. We will discuss the effect of solvent composition on dispersion stability, phase separation, and self-sintering properties in the AgNCs.
[1] T. Yamada et al., Nat. Commun. 7, 11402 (2016). [2] M. Itoh et al., J. Nanosci. Nanotech. 9, 6655 (2009). [3] K. Aoshima et al., under review.

Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with broad application in optoelectronics and energy. Chemical functionalization has evolved into a powerful tool to tailor properties of these 2D TMDs; however, functionalization strategies have been largely limited to the metallic 1T-polytype. The work herein illustrates that 2H-semiconducting liquid-exfoliated tungsten disulfide (WS₂) undergoes a spontaneous redox reaction with gold (III) chloride (AuCl₃). Au nanoparticles (NPs) predominantly nucleate at nanosheet edges with tuneable NP size and density. AuCl₃ is preferentially reduced on multi-layer WS₂ and resulting large Au aggregates are easily separated from the colloidal dispersion by simple centrifugation. This process may be exploited to enrich the dispersions in laterally large, monolayer nanosheets. It is proposed that thiol groups at edges and defects sides reduce the AuCl₃ to Au0 and are in turn oxidized to disulfides. Optical emission, i.e. photoluminescence, of the monolayers remained pristine, while the electrocatalytic activity towards the hydrogen evolution reaction is significantly improved. Taken together, these improvements in functionalization, fabrication, and catalytic activity represent an important advance in the study of these emerging 2D nanostructures.

Quantifying RNA mutations at the single cell is critical for detection of viral mutations and ultimately for viral population control, especially in highly mutating viruses such as the influenza virus¹. To that end, creating a highly sensitive tool that can track viral mutations intracellularly will provide mechanistic insight into viral evolution. We are designing a nanoparticle platform consisting of gold nanostars with a switchable surface enhanced Raman spectroscopy (SERS) - fluorescent beacons that allows for accurate and high resolution single particle-based influenza A virus (IAV) population sequencing without the need of PCR amplification. The nanoparticle platform has been developed to accommodate multiplexed intracellular imaging and sensing of various IAV gene sequences to account for viral population diversity². The switchable SERS-fluorescent nanostar probes are designed to become active in the presence of their viral RNA targets with signal intensity varying with the number of mutations present on the target. Additionally, the nanostars are synthesized to provide optimal Raman scattering by enabling surface conjugation in proximity to hot spots³. Upon intracellular uptake, the particles are monitored via fluorescence in the absence of target (OFF state) and will provide quantitative detection of viral RNA by the use of SERS ratios and calibration curves (ON state). The switchable nanoparticle probe is a promising method for intracellular imaging and quantification of IAV genome that can potentially be expanded to other types of viruses as well.

1.Cella, L. N., Blackstock, D., Yates, M. A., Mulchandani, A. & Chen, W. Detection of RNA viruses: current technologies and future perspectives. Critical reviews in eukaryotic gene expression 23, 125-137 (2013).
2. Hutchinson, E. C., von Kirchbach, J. C., Gog, J. R. & Digard, P. Genome packaging in influenza A virus. The Journal of general virology 91, 313-328, doi:10.1099/vir.0.017608-0 (2010).
3. Indrasekara, A. S. et al. Gold nanostar substrates for SERS-based chemical sensing in the femtomolar regime. Nanoscale 6, 8891-8899, doi:10.1039/c4nr02513j (2014)

Although infective endocarditis (IE) is relatively rare, it represents a severe infectious disease. Timely diagnosis of this fatal disease is of high importance though remained elusive to date. The first line of diagnosis, echocardiography (EE), suffers from limitations e.g. low sensitivity for vegetation (60-70%). One promising method is multi-slice CT with improved sensitivity over EE. The most common pathogen involved in the IE, Staphylococcus aureus (S. aureus) is notoriously reported in 36% of cases. Failing of the current therapies due to antibacterial drug resistance, low penetration of antibiotic into the vegetation and non-specific interaction of serum protein with drug are compelling reasons to seek new therapies for IE treatment. A property of traceable therapeutics would make it a better choice and preferential regime. In this regard, contrast agents are used to improve the sensitivity and enhance the tissue visualization on X-ray/CT.
Herein, we introduce a novel NP for the early diagnosis, therapy and follow-up of IE utilizing raspberry shaped hollow Hafnium oxide nanoparticles coated with a layer of silver nanoparticles (HfOx-Ag-NP). The NPs were synthesized by a surfactant free template assisted synthesis. Resorcinol and formaldehyde (RF) formed the inner core initially. The hafnium oxide was subsequently grown alongside with the secondary RF polymer through a sol- gel chemistry in one pot. The template was removed in the next step via calcination at 550 °C to obtain hollow raspberry shaped HNPs (~100 nm). The Ag NPs were grown on the rough outermost layer utilizing the silver mirror reaction. TEM and SEM confirmed the proper dendritic formation of NPs. Besides, Ag NP deposition was verified by EDS where the co-localization of Hf and Ag was observed.
The X-ray attenuation of the NPs compared with calcium showed significant enhancement. The Hounsfield unit (HU) as a measure of x-ray attenuation was calculated to be ~10 for 180 mM of Ca whereas for HfOx-Ag-NPs, HU was ~1790. Furthermore, these NPs demonstrated a 30% increase in HU compared with the conventional iodine based contrast agent (iohexol).
It was found that HfOx-Ag-NP could enhance the adhesion to the bacterial membrane through hydrophobic interactions of hairy features of HfOx NPs. In addition, surface decorated Ag NPs could synergistically boost the bacterial killing efficiency due to added antibacterial effects of Ag. Anti-bacterial property of HfOx-Ag-NP were established by OD decrease, colony count and live-dead assays. Studies also showed the effect in blood samples to mimick the physiological conditions and found to effectively suppress the growth and kill S. aureus. Overall, this is the first report on the application of CT contrast agents for the detection of IE using intrinsic property of Hf-NPs alongside with their therapeutic efficiency for bacterial eradication.

The cadmium telluride (CdTe) photovoltaics is an efficient and cost-effective photovoltaic technology platform for harvesting solar energy. However, device efficiency remains limited in part by low-open circuit voltage (V_OC) and fill factor (FF) due to inefficient transport of photo-generated charge carriers. Given the deep valence band of CdTe, the use of Cu/Au as a back contact serves primarily to narrow the width of the inherent Schottky evident in CdTe solar cells. (in our laboratory, copper/gold (Cu/Au) has been used as a standard back contact). For efficient transport of carriers to and into the back contact, a hole transport layer (HTL) is desired with valence band edge comparable to that of CdTe (~ -5.7 eV). Here, we report the solution-processed nanocrystal (NC) based thin films as HTLs in CdTe solar cells. The materials we discuss include the earth abundant iron pyrite (FeS₂) NCs, nickel-alloyed iron pyrite (Ni_xFe_1-xS₂) NCs, zinc copper sulfide (Zn_xCu_1-xS) nanocomposites, and perovskite based films. The FeS₂ and Ni_xFe_1-xS₂ NCs are synthesized by using hot-injection route, and then thin films are fabricated by drop-casting, and spin-coating techniques using colloidal NCs. Zn_xCu_1-xS thin films are fabricated by chemical bath deposition. These NC-based thin films are applied and studied as the HTLs in CdTe devices. On using these materials, the device performance increases by up to 10% compared to the standard Cu/Au back contact. We will discuss the benefits, challenges, and opportunities for these back contact materials in CdTe photovoltaics.

Early detection of cancer has shown promise in the reduction of cancer-related mortality and improvement of therapeutic outcomes. A variety of cancer biomarkers such as proteins, nucleic acids, as well as tumor cells offer valuable insight on cancer progression. Among these biomarkers, epithelial cell adhesion molecule (EpCAM) is one of the most abundantly used markers for detecting a broad variety of cancers. Changes in the expression of EpCAM have been associated with the onset of metastasis. However, the detection of variations in EpCAM expression with high sensitivity and selectivity remains challenging. Surface enhanced Raman spectroscopy (SERS) based biosensors have been used increasingly over the past few years for cancer detection and diagnosis. SERS-based imaging offers excellent sensitivity and has advantages over other detection techniques like fluorescence. The highly specific recognition enabled by SERS tags is provided via the use of aptamers or antibodies. Aptamers, comprising of single stranded DNA or RNA are a new class of detecting molecules with advantages of low immunogenicity and high stability and have demonstrated potential as an identification tool for cancer cell detection.
In this work, we developed a novel substrate using gold nanostars with EpCAM aptamer to detect small concentrations of EpCAM protein in solution. We used two different lengths of EpCAM DNA aptamer and looked at the differences in their binding to its target protein. Detailed characterization of the substrates was done using SERS maps and atomic force microscopy. SERS measurements showed that SERS intensity increased linearly with increasing concentrations of protein. We observed that having a shorter aptamer sequence and hence, fewer possible secondary configurations at room temperature improved the sensitivity of detection. These substrate based diagnostic devices could be employed in future to detect multiple cancer biomarkers present in blood and other body fluids without the need to label target proteins.

Plasmonic nanostructures have been employed as sensitizers in photocatalysis to achieve higher catalytic efficiency. Although the most widely used materials are gold and silver, aluminum has attracted interest in recent years as a new plasmonic material due to its natural high abundance, low toxicity and relatively high free carrier density. Moreover, it exhibits plasmon resonances which can be tuned from the ultraviolet through the visible via adjustment of size, shape, composition and the surrounding dielectric environment. Hot carriers generated in a plasmonic material can be injected into a catalytic semiconductor in hundreds of femtoseconds and enhance the photocatalytic activity. Understanding hot carrier relaxation processes is therefore crucial for applications.
In this work, we synthesized large aluminum nanocrystals in the solution phase (~98±12 nm in diameter) and report the first photophysical characterization of energy dynamics in these types of particles. Our nanoparticles displayed dipolar and quadrupolar localized surface plasmon resonance peaks at 392 nm and 269 nm, respectively. High resolution transmission electron microscopy shows the formation of a 3.7 nm thick native aluminum oxide layer. We used ultrafast transient spectroscopy to study the electron relaxation dynamics of these particles. We showed that the particles exhibit a decrease in light transmission across the broad visible and near-infrared regions on a 2 ps timescale associated with electron-lattice relaxation processes. The spectral response was qualitatively different near the interband transition region with a persistent bleach signal that provides a window into electron-electron thermalization dynamics. We found that these large particles exhibited fast thermal energy transfer (~250 ps timescale) which is comparable to that predicted for much smaller particles with diameters of ~10 nm. Using an extended two interface model, we demonstrated that the thin native oxide layer on the particles plays an important role in mediating fast thermal energy transfer, with minimal dependence on the shell thickness. We propose that using controlled surface modification strategies is an effective approach for engineering heat transfer rates in large nanoparticles. This is a beneficial strategy for photocatalytic and sensing applications where heat management is critical.

Mercury chalcogenide nanocrystals are an interesting platform for the design of low cost infrared photodetectors.¹ However up to recently it was impossible to push their absorption spectrum above 5µm (≈250meV).² In HgTe and HgSe, the Bohr radius is pretty large (≈40nm), thus large nano-objects need to be synthetized to reduce confinement and obtain narrower energy transitions.

HgSe nanocrystals are self-doped nanocrystals which give access to intraband transition to address the infrared range of the electromagnetic spectrum.³ We will in particular discuss the origin of doping and how the surface chemistry can be used to tune the doping level.⁴ We then further investigate the electronic properties of these nanocrystals made from a semimetal as the size is increasing and the quantum confinement is vanishing. We demonstrate, using a combination of X-ray photoemission, IR spectroscopy and transport measurements, that as the confinement is disappearing the nanoparticles behavior switches from a confined semiconductor to a metal behavior.⁵
To finish, I will briefly discuss our last results where we have been able to push the absorption of colloidal nanocrystals to the THz range (and up to 200µm).
References
Recent Progresses in Mid Infrared Nanocrystal based Optoelectronics, E. Lhuillier et al IEEE J Selec Top Quantum Elec 23, 1 (2017)
Mid-infrared HgTe colloidal quantum dot photodetectors, S. Keuleyan et al, Nat Photon 5, 489-493. (2011).
Infrared photo-detection based on colloidal quantum-dot films with high mobility and optical absorption up to the THz, E. Lhuillier et al, Nano Lett 16, 1282 (2016)
Surface Control of Doping in self-doped Nanocrystals, A. Robin et al ACS Appl. Mat. Interface 8, 27122−27128 (2016).
HgSe self-doped nanocrystals as a platform to investigate the effects of vanishing confinement, B. Martinez, et alACS Appl. Mat. Inter. (2017).

Iron oxide nanoparticles (ION) have been used recently as a drug delivery system and as a contrast agent for MRI diagnosis. The ION's can work as vectors with specific surface modifications to amplify the bioactive compound effect, enhance the liberation of specific drugs or interact with certain surface as cell membranes and biomolecules [1]. This works aims to the development of ION's with surface modifications to increase the interactions with plasmid DNA (pVAX1-NH36). The objective is to synthesize ION's stabilized with hydrophobic compounds and modified with a natural flavonoid (baicalin) [2, 3], recognize as selective attractive molecule for the DNA. Probable applications are in its use for DNA mechanical purification and as an intracellular contrast agent for DNA.

[1] P. Kothamasu, H. Kanumur, N. Ravur, C. Maddu, R. Parasuramrajam, and S. Thangavel, “Nanocapsules: the weapons for novel drug delivery systems.,” Bioimpacts, vol. 2, no. 2, pp. 71–81, 2012.

[2] A. López-Millán , P. Zavala-Rivera, Reynaldo Esquivel, Roberto Carrillo, E. Alvarez-Ramos, R. Moreno-Corral , R. Guzmán-Zamudio and A. Lucero-Acuña, “Aqueous-Organic Phase Transfer of Gold and Silver Nanoparticles Using Thiol-Modified Oleic Acid”, Applied Sciences, pp. 2, 2017.

[3] Sameena Yousufa, Israel V.M.V. Enocha,b, Paulraj Mosae Selvalumara, Dhanaraj Premnathc , “Chromenone-Conjugated Magnetic Iron Oxide Nanoparticles. Toward Conveyable Dna Binders”, Colloids and Surfaces b: Biointerfaces 135, pp. 448-457, 2015.

Emerging interest in the application of nanomaterials in drug delivery, nanoelectronics, development of sensors, etc. in recent years has led to the search for efficient protocols for tailoring nanomaterial properties and function on a molecular level. In particular, we aim to develop methodologies for modifying material surfaces cleanly and quantitatively using easy-to-implement chemical reactions. To this end, bioorthogonal chemistry — characterized by fast, clean, and biocompatible reactivity — represents an effective tool for the surface engineering of nanomaterial platforms with greater practicality and utility. We seek to incorporate these reactive systems (and their photo-activated analogs to provide spatial and temporal control) onto nanomaterial interfaces and investigate their interfacial chemistry. The integration of interfacial strain-promoted alkyne-azide and alkyne-nitrone cycloadditions (i-SPAAC and i-SPANC, respectively) and interfacial Staudinger-Bertozzi ligation (i-SBL) on material interfaces — namely, gold nanoparticles (AuNPs) — will be discussed with respect to their syntheses, characterization, and execution of their interfacial chemical function to attach, release, and replace molecules on the nanoparticle surface. Our ability to quantitate surface functionalities and monitor the interfacial chemistry on materials will be highlighted. These bioorthogonally reactive materials represent a new class of highly versatile nanoparticle platforms that can be easily derivatized for applications in materials science, chemical biology, and has great potential in the emerging area of self-sorting materials.

FePd magnetic nanoparticles (NPs) were developed as artificial enzymes with high biocompatibility and reusability, named ‘magnetozymes’, in a one-pot aqueous synthesis method using glutathione (GSH) and cysteine (Cys) as surfactants. The prepared hydrophilic FePd magnetozymes can be successfully re-dispersed in water and have high zeta potentials of 21.8 and 29.5 mV for Cys- and GSH-stabilized magnetozymes, respectively. The saturation magnetizations of the Cys- and GSH-conjugated magnetozymes, measured by a superconducting quantum interference device, are 4.7 and 41.4 emu g⁻¹, with both magnetozymes exhibiting superparamagnetism at 300 K. The catalytic activities were tested by measuring the reduction of fluorescent dye and hydrogen peroxide by optical absorption measurements and electrochemical characterization. The Cys-FePd and GSH-FePd NCs exhibited significantly enhanced efficiency, with catalytic constants more than 2- and 7- fold higher than horseradish peroxidase (HRP), respectively. The computational simulation and electrochemical analysis explain its enhancement of the catalytic effect that is resulted by fct-structure of FePd NCs as well as molecules surrounding NC surface. Furthermore, in vitro experiments reveal that the FePd NPs clearly behave like peroxidase to reduce ROS levels in mammalian cells. The cytotoxicity was analyzed by exposing the FePd magnetozymes to different cell lines for seven days, and they showed >90% viability at concentrations up to 20 μg mL^–1. The FePd magnetozymes, having high saturation magnetizations and biocompatibility, enable a variety of possible catalytic and biological applications such as recyclable peroxidase-mimicking enzymes, antioxidant agents, and biosensors.

Ultrasmall nanoparticles have come to play a huge role in modern materials chemistry. This development has challenged the conventional techniques for material characterization, which break down for structures on the nanoscale. However, total scattering combined with Pair Distribution Function analysis allows us to look further into nanostructure and establish the structure-property relation for advanced functional materials.[1]
We have applied X-ray total scattering with Pair Distribution Function analysis to elucidate the existence of polymorphism in the 29kDa gold nanocluster, Au₁₄₄₍SR)₆₀.[2] We have shown that apart from the well-known icosahedral cluster type, another decahedral polymorph, closer in structure to a twinned fcc structure also exist. Our data showed that for some thiol ligands, the two structures can coexist, illustrating their closeness in energy. The existence of polymorphism on the nanoscale opens for a new aspect in nanostructure engineering. In order to understand the relation between synthesis and structure, it is important to get further insight into the nucleation processes dictating the outcome of a reaction. We have recently shown that X-ray total scattering can be applied for in situ studies of particle formation, giving atomic scale insight into nucleation processes.[3, 4] Since structural information can be extracted from X-ray total scattering even for structures without long range order, in situ studies of particles nucleation allow deducing structures from precursor clusters over pre-nucleation clusters to the final nanoparticles. Here, we will present new results regarding the formation of monodisperse metal and metal oxide colloidal nanoparticles, getting closer to an understanding of the atomic scale processes in particle nucleation. In studies of several different nanoparticle systems, including colloidal iron oxide nanoparticles, we see that the structure of the clusters seen immediately after nucleation can be directly connected to the structural motifs present in the final nanoparticles, explaining the formation of defects in nanostructured particles.


1. Billinge, S. J. L.; Levin, I. Science 2007, 316, (5824), 561-565.
2. Jensen, K. M. O.; Juhas, P.; Tofanelli, M. A.; Heinecke, C. L.; Vaughan, G.; Ackerson, C. J.; Billinge, S. J. L. Nat Commun 2016, 7.
3. Jensen, K. M. O.; Andersen, H. L.; Tyrsted, C.; Bojesen, E. D.; Dippel, A. C.; Lock, N.; Billinge, S. J. L.; Iversen, B. B.; Christensen, M. ACS Nano 2014, 8, (10), 10704-10714.
4. Jensen, K. M. Ø.; Tyrsted, C.; Bremholm, M.; Iversen, B. B. ChemSusChem 2014, 7, (6), 1594-1611.

Quantum dimensional gold clusters are at the forefront of research owing to their characteristic size dependent optical and electrochemical properties. Of recent interest is their use as sensing agents due to their UV, visible, and near-IR luminescence (the wavelength of emission is ligand dependent). In addition, their use as high frequency broad band semiconductor material creates interest in military technology development. Nanoparticles are studied for their observable ability to transfer electrons. Characteristically nanoparticles have sensing potential due to electronic variations in their emission spectra. Magic number icosahedron Au₂₅L₁₈, and Au₁₄₄L₆₀ clusters were synthesized using a one phase method with L = hexanethiol as a stabilizing ligand, and compared to the Au₂₅L₁₈ bi-icosahedron synthesized using an alternate one phase method. The electronic transition states of each particle were observed through optical and electrochemical analysis. The clusters were characterized through observation of documented HOMO/LUMO gap using both optical and electrochemical techniques. Au₁₄₄-clusters indicated quantized double layer charge upon electrochemical analysis. Observation of quenching when coumarin is bound to gold core is observed through fluorescence quantum yield. Near IR luminescence was detected with the various geometries and observed enhancement between ligand variations. Transmission electron microscopy was employed to determine particle size, purity, and dispersity. The MPCs (Monolayer Protected Clusters) with the hexanethiol stabilizing ligand were then labelled with a coumarin dye via directed ligand exchange. The products of the exchange reaction were then compared with the MPC made from the coumarin ligand. Characterization details and applications will be presented.

The ability to dynamically organize functional nanoparticles (NPs) via the use of environmental triggers (temperature, pH, light, or solvent polarity) opens up important perspectives for rapid and convenient construction of a rich variety of complex assemblies and materials with new structures and functionalities. Here we report an unconventional strategy for crafting stable hairy NPs with light-enabled reversible and reliable self-assembly and tunable optical properties. Central to our strategy is to judiciously design amphiphilic star-like diblock copolymers comprising inner hydrophilic blocks and outer hydrophobic photoresponsive blocks as nanoreactors to direct the synthesis of monodisperse plasmonic NPs intimately and permanently capped with photoresponsive polymers. The size and shape of hairy NPs can be precisely tailored by modulating the length of inner hydrophilic block of star-like diblock copolymers. The perpetual anchoring of photoresponsive polymers on the NP surface renders the attractive feature of self-assembly and disassembly of NPs on demand using light of different wavelengths, as revealed by tunable surface-plasmon resonance absorption of NPs and the reversible transformation of NPs between their dispersed and aggregated states. By extension, the star-like block copolymer strategy enables the crafting of a family of stable stimuli-responsive NPs (e.g., temperature- or pH-sensitive polymer-capped magnetic, ferroelectric, upconversion, or semiconducting NPs) and their assemblies for fundamental research in self-assembly and crystallization kinetics of NPs as well as potential applications in optics, optoelectronics, magnetic technologies, sensory materials and devices, catalysis, nanotechnology, and biotechnology.

Colloidal quantum dots (QDs) are attractive materials for lasers, displays and other light-emitting applications due to their narrow spectral emission bandwidth, size-tunable bandgap and high-photoluminescence quantum yield (PLQY). However, QDs undergo inevitable degradation of their unique optical properties over time due to their sensitive surface chemistry. To overcome these limitations, several approaches have been used, such as overcoating with an inorganic semiconductor shell of a wider band gap (core/shell hetrostructures), surface functionalization with organic and inorganic ligands, or polymer coating and composite formation. In particular, core/shell heterostructured QDs with thick shells [so called “giant” QDs (g-QDs)] have shown dramatically modified single-dot properties (non-blinking, non-photobleaching) and clear suppression of non-radiative recombination pathways (Auger recombination, photoexcited-carrier surface trapping). However, we have recently determined that the outstanding properties afforded by the g-QD’s thick shell are sensitive to both the shell-structure quality (crystal defects) and the properties of the interfacial layer (sharp or smooth core/shell interface). In particular, the useful “lifetime” of the g-QD under conditions of elevated temperature and exposed to air or water is strongly dependent on these structural and interface properties. Significantly, we have further revealed that these aspects of the internal nanoscale structure can be precisely tailored by choice of synthetic parameters. Here, we will present our recent results on understanding this critical synthesis-structure-function nexus.

Degenerately doped metal oxide nanocrystals demonstrate a tunable localized surface plasmon resonance (LSPR) that can be integrated into a diverse range of optoelectronic applications. The energy and intensity of LSPR absorption can shift dramatically with defect composition, geometry and induced charge, allowing for dynamic modulation and application-specific spectral profiles. Anatase TiO₂ has recently been explored as a plasmonic metal oxide, following observation of an infrared (IR) LSPR feature in niobium-doped anatase nanocrystals (de Trizio et al, Chem. Mater., 2013). The energy and intensity of this IR LSPR feature in TiO₂ can be modulated by changing the free electron concentration with electrochemical charging in thin films (Dahlman et al, J. Am. Chem. Soc., 2015). However, the low energy and broad peak profile of LSPR in Nb-doped TiO₂ nanocrystals contrasts with the material’s high electronic conductivity as a film, which is comparable to standard transparent conductive oxides such as tin-doped indium oxide. This talk will investigate the LSPR of charged and Nb-doped anatase TiO₂ nanocrystals by ex situ infrared spectroscopy, and extract free carrier properties from simulated optical spectra.

Electronic properties of metal oxide plasmonics can be difficult to investigate for materials with LSPR energies in the mid-IR, because a different set of detectors, solvents and substrates must be used for IR transmittance or reflectance measurements. The concentration and scattering rates of free carriers in unbiased nanocrystals in solution are extracted from fits of FTIR transmittance spectra using the Drude model of carrier transport and Mie approximation of LSPR. The optical conductivity of Nb-doped TiO₂ nanocrystals is found to be significantly lower than the electronic conductivity in similar Nb-doped thin films, suggesting that anisotropic carrier transport in TiO₂ diminishes its optical response. Electrochemically-induced free carrier properties are explored through FTIR transmittance spectra of ex situ charged thin films of TiO₂ nanocrystals. The optical transmittance of charged films is fitted to a layered optical model and compared for different charging potentials and capacities. Electrochemical reduction is found to induce greater variations in carrier concentration than synthetic doping alone, and demonstrates different scattering behavior. The role of interparticle coupling and effective medium effects in films are explored as explanations for the divergent behavior of charged and unbiased nanocrystals. These measurements reveal the different behavior of synthetic and charging-induced free carriers in plasmonic metal oxides, and provide a robust strategy for investigating electronic properties in semiconductor nanocrystals by IR optical measurements.

Colloidal nanoplatelets (NPLs) are quasi-two-dimensional nanocrystals with atomically precise thickness in one dimension. Due to their highly anisotropic shape, they offer favorable optical properties such as narrow emission linewidths and large absorption cross-sections.^1,2 However, as-synthesized, NPLs exhibit poor photo- and chemical stability. Thus, strategies have been sought to improve their properties by adding a shell on the NPLs. For spherical quantum dots, recently developed recipes for growing high-quality shells are performed at high temperatures. However, to date, this strategy has not been extended to NPLs because of their low thermal stability compared to quantum dots.³ Here, we present a method for obtaining CdSe/CdS core/shell NPLs in which the shell is added at high temperatures (~300 °C).⁴ This enables the growth of uniform and thick CdS shells, which is not possible with existing continuous-growth protocols. We obtain high-quality monodisperse CdSe/CdS core/shell NPLs with narrow emission linewidths, high QYs, and suppressed blinking. Such samples exhibit emission peaks at 660-670 nm that can result in improvements for a wide range of applications in optics and optoelectronics relying on efficient and narrow red emitters.

1) S. Ithurria et al., Nat. Mater., 10, 936 (2011)
2) A. Yeltik et al., J. Phys. Chem. C, 119, 26768 (2015)
3) A. Riedinger et al., Nat. Mater., 16, 743 (2017)
4) A. A. Rossinelli et al., Chem. Commun., 53, 9938 (2017)

Self-assembly of colloidal nanocrystals into ordered architectures has attracted significant interest enabling innovative routes to manipulate the physiochemical properties for targeted applications. This study reports the self-assembly of CsPbBr₃ perovskite nanocrystals (NCs) in one-dimensional (1D) superlattice chains mediated by ligand-solvent interactions. CsPbBr₃ NCs synthesized at ≥ 170 °C and purified in a nonpolar solvent, hexane, self-assembled into 1D chains whereas when purified in polar solvents including toluene and ethyl acetate they were disordered or showed short-range 2D assemblies. The NCs assembled into 1D chain show a redshift in both the absorbance and photoluminescence spectra relative to the disordered NCs purified in 50/50 hexane/ethylacetate mixture. Microscopy and X-ray diffraction results confirm the formation of polymeric nanostrands in hexane followed by organization of the NCs into 1D chains along the nanostrands. Our results suggest excess aliphatic ligands remaining after purification of the NCs complex with ionic Cs+ and Br- species via hydrophobic effect; further the alkyl chains of these ligands interlace with each other via van der Waals forces. Collectively these interactions give rise to the nanostrands and subsequent self-assembly of CsPbBr₃ into 1D chains. In polar solvents the minimization of repulsive forces between the solvent and the ligands drives proximal CsPbBr₃ NCs together into short-range 2D assemblies or disordered clusters. Our solvent-assisted self-assembly approach provides a general strategy to design 1D superlattice chains of nanocrystals of any geometry, dimension, and composition by simply tuning the ligand-solvent interactions [1].
[1] J. Phys. Chem. C, 2017, 121 (33), pp 18186–18194

The ligand shell of nanoparticles has been the focus of many characterization approaches. Starting from some spectroscopic methods (infrared spectroscopy, and nuclear magnetic resonance mainly), and some density determination (thermal gravimetric analysis), the field has moved towards scanning probe microscopy that has allowed the establishment of unique morphologies like Janus, stripe-like, and random. New techniques have been recently developed to address the ligand shell characterization challange (MALDI-TOF, EPR, small angle neutron scattering, to name a few). In this talk, I will review the state of the art and try to show how to combine a few of such techniques to rapidly and reliably characterize the ligand shell of many nanoparticles.

Nanocrystals (NCs) can self-assemble into ordered superlattices and accordingly enhance or manifest collective properties from NC coupling, but the controlling ability of NC assembly remains poorly understood towards a controlled fabrication of desired superlattice. In this talk, I will use PbS NC as an example in which various variables are controlled in experiments to systematically address how NCs interact with surface coating ligands and surrounding solvent molecules under various environments and thus assemble into various superlattices. Using synchrotron-based small angle and wide angle x-ray scattering (SAXS and WAXS) and collected datasets, I will first talk about the nucleation and growth pathway and underlying mechanism of NC superlattice, and discuss the temperature-induced superlattice transformations. Based on insights gained, I will slightly get into how experimental parameters can be regulated to fabricate desired superlattice polymorphs, which allow for additional processing of NC superlattice for real applications.

The development of biomedical imaging techniques, such as computed X-ray tomography (CT), Magnetic Resonance Imaging (MRI), optical imaging, ultrasound, single photon emission computed tomography (SPECT) and positron emission tomography (PET), has provided very useful tools for diagnosis and therapy. These modalities give highly complementary information. For example, PET is a powerful tool for whole body imaging with outstanding detection sensitivity (less than picomolar range), whereas MRI and CT provide high-resolution anatomic information. MRI also permits a spectroscopy (MRS) and functional MRI (fMRI). Thus, it is an ultimate goal to combine two or more imaging modalities providing complementary information, such as morphology and function. Although the combination of PET and CT has already been successfully realized in clinical and preclinical studies, the major limitation is that CT has limited soft-tissue contrast, and need extra dose of radiation. Furthermore, the imaging is performed sequentially rather than simultaneously. So the preferred choices could be combination of the MRI with PET, not only because of the absence of ionizing radiation in MRI but also for its excellent soft-tissue contrast, and its flexible scan protocols. The MRI/PET could create enormous possibilities and provides completely new opportunities to study pathology and biochemical processes in vivo.
To take advantage of high resolution of MRI and the high sensitivity of PET, current researches are focused on the dual modalities imaging contrast agent. However, current approach for labeling magnetic NPs with the radioactive copper ion is through a chelator. Because it is not a covalent bond, the stability of the conjugation is always a severe concern, especially in an in vivo system. In contrast to surface modification, incorporating radioisotope into core of the nanoparticles received highly attention. But resulted iron oxide nanoparticles are rather polydisperse and irregular in shape.
To develop successful MRI nanoparticles, two criteria factors need to be well designed. a) Well controlled size of nanoparticles. b) The surface coating and functionalization. So far, no approaching have been achieved for intrinsitic labeling of MNPs with tunable size and surface modification. To address this problem, we developed a stable dual modalities magnetic NPs by incorporating copper ion into the core of the magnetic NPs with tunable size and surface coating reagents. We will further demonstrate that the nanoparticle can be used for PET-MRI dual modality imaging after doped with radioactive copper.

Lead sulfide nanocrystal quantum dots (QDs) possess size-dependent tunable photoluminescence (PL) from the near-infrared to the mid-infrared owing to the strong quantum confinement effect. Despite great interest in PbS QDs for both fundamental research and practical applications, single nanocrystal spectroscopy of PbS QDs with emission in the telecom wavelength range still remains challenging. Here, we report PL spectral and polarization studies for single PbS/CdS core/shell QDs that emit in the telecom O-band window (1260 nm - 1360 nm, i.e., 0.99 eV - 0.91 eV). Room-temperature PL spectral data reveal that there is a broad distribution of emission peak energy of single QDs spanning from 0.95 eV to 1.2 eV. A correlated TEM-PL analysis reveals that the inhomogeneous energetic broadening is related to PbS core size variation. Single PbS/CdS QDs demonstrate broad homogeneous linewidths with a mean value of 87.8 meV at room-temperature and 27.0 meV at 6 K, indicative of a much faster dephasing time compared to conventional CdSe QDs. Spectral diffusion of 10-20 meV detected for single PbS/CdS QDs at 6 K constitutes a significant contribution to the homogeneous linewidth broadening. We also report emission polarization for single PbS/CdS QDs, which has been corroborated by a theoretical calculation involving a consideration of shape asymmetry.

All-inorganic, CsPbX₃ (X=Cl, Br, I) quantum dot nanocrystals have been shown to have great promise for optical and optoelectronic applications due to excellent stability, high fluorescent quantum yields, and optical tunability via a facile halide exchange reaction. This presentation will discuss our recent progress obtaining refined synthetic control over either cation exchange or, alternatively, metal deposition on CsPbX₃ nanoparticles. The oleylamine ligand shell commonly used to stabilize all-inorganic perovskite nanocrystals may be used to reduce metal salts allowing for metal cations to either exchange with Pb²⁺ in the perovskite crystal lattice or deposit as elemental metal on the surface of the nanocrystals. Our central insight is that the reaction kinetics for exchange or deposition are driven by the excess metal cation in solution. For example, when gold salt alone is added to CsPbBr₃ nanoparticles, cation exchange occurs, but if an excess of Pb²⁺ is added, Au metal only deposits on the perovskite surface with domain size determined by the gold solution concentration. The cation exchange reaction represents a new manner of post-synthetic tunability that may aid in the search for lead free all-inorganic perovskite, producing in this case, the near-IR emitting mixed valence semiconductor, CsAu₂Br₆, reported for the first time after our initial studies. We also note the high fluorescence quantum yield maintained in Au-CsPbBr₃ heterostructures with efficiencies up to 75%. This surprising result could provide new insights into the optoelectronic properties of the all-inorganic perovskite nanocrystals, as well as the interactions between metal and semiconductors on the nanoscale, important for a variety of optoelectronic applications. We will discuss our recent progress expanding the range of all-inorganic Perovskite nanostructures obtainable via metal exchange and deposition reactions.

Nanoparticles from colloidal solution – with controlled composition, size, and shape – serve as excellent building blocks for plasmonic devices and metasurfaces. However, understanding hierarchical driving forces affecting geometry of oligomers and interparticle gap spacings is still needed to fabricate high density architectures over large areas. Here, electrohydrodynamic (EHD) flow is used as a long-range driving force to enable carbodiimide crosslinking between nanospheres yielding control of gap spacing in oligomers with sub-nanometer precision over mm² areas. Atomistic simulations elucidate that the transient attractive force provided by EHD flow is needed to provide a sufficient residence time for anhydride crosslinking to overcome slow reaction kinetics. This synergistic analysis shows assembly involves an interplay between long range driving forces increasing nanoparticle-nanoparticle interactions and probability that ligands are in proximity to overcome activation energy barriers associated with short range chemical reactions. Anhydride linkers between nanospheres are probed spectroscopically using surface enhanced Raman scattering (SERS) and UV-Vis. The anhydride linkers are cleavable via nucleophilic substitution and enable selective placement of molecules in electromagnetic hotspots. Absorption spectroscopy and electromagnetic full-wave simulations show variations in nanogap spacing have greater influence on optical response than variations in close packed oligomer geometry. The EHD flow – anhydride crosslinking assembly method produces a high density of close-packed oligomers with uniform gap spacings that produce uniform SERS response at low integration times and laser power. This enables fabrication of in-line microfluidic devices for sensing of the formation of bacterial biofilms as early as three hours after culturing due to high signal enhancements provided by plasmonic nanogaps. These results demonstrate the efficacy of colloidal driving forces to selectively enable chemical reactions leading to future assembly platforms for large area nanodevices.

Developing highly efficient catalysts is crucial for building practical electrochemical devices for energy conversions and for fuel generation. Here we present a new strategy to control Pt-alloy nanoparticle (NP) catalytic efficiency in acid and to extend the concept to prepare non-Pt NP structures for highly efficient electrochemical reduction or oxidation reactions.

Using FePt as a model system, we have demonstrated that solid solution type A1-FePt NPs can be converted to chemically ordered tetragonal L1₀-FePt NPs. These L1₀-FePt NPs are not only magnetically hard but also chemically robust against Fe leaching in acid. The fully ordered L1₀-FePt/Pt NPs show much enhanced catalysis for not only oxygen reduction reaction (ORR) in 0.1 M HClO₄, but also hydrogen evolution reaction (HER) in 0.5 M H₂SO₄. The concept has been successfully extended to CoPt, FeMPt, CoMPt (M = Au, Ag, Ni) NPs. For example, in the L1₀-FePd/Pd structure, the tightly packed L1₀-FePd causes the Pd shell to “shrink”, stabilizing the core structure against acid corrosion and enhancing the Pd catalysis for ORR in 0.1 M HClO₄ with Pt-like activity and durability. The L1₀-CoPt/Pt NPs show even higher activity than the L1₀-FePt/Pt for ORR or for electrochemical oxidation reactions. Our further studies indicate that MPd/Pd (M = Cu, Ni, Co) NPs could be tuned to achieve selective electrochemical reduction of CO₂.

Ultra-small metal nanoclusters (< 2 nm), with distinct physical and chemical properties, have emerged as a new front in nanomaterial research. Integrating them with programmable biopolymers (e.g., nucleic acids and polypeptides) can impart new functionalities such as tunable luminescence and stimuli responsivity into this highly versatile system. Herein, I will discuss the synthesis and assembly of a monodispersed, thermal responsive gold nanocluster templated by a programmable polypeptide, i.e., elastin like polymer (ELP). ELP is composed of repeating units of a specific amino acids sequence, i.e. (VPGXG)_n, where X can be any amino acid besides proline and n is the number of repeating units. The direct synthesis and controlled assembly of the thermal responsive gold nanoclusters with tailor-made ELP will be discussed in detail. These gold nanoclusters are characterized by various analytical tools including optical spectroscopy, mass spectrometry, electron microscopy, and X-ray photoelectron spectroscopy. Their thermal responsive properties are measured by dynamic light scattering at different temperatures. Significantly, we find that the ELP-templated gold nanoclusters exhibit considerably lower transition temperature than the free ELP, which makes them a promising probe for biomedical applications.

Interfacial forces between crystals that depend on their mutual crystallographic alignment enable diverse multiscale phenomena such as crystal growth by oriented attachment, nanoparticle self-/directed-assembly, Schiller layer formation, and grain boundary structuring in polycrystals. While the attraction or repulsion of two crystallites is based on a set of forces that are generally well understood, aspects of these forces that are sensitive to lattice alignment have been more difficult to probe. Conceptually, the types of interfacial forces that can be sensitive to relative orientation include Coulombic (due to the structured arrangement of charges at specific interfaces), van der Waals (vdW) (for lattices with anisotropic polarizability), solvation (due to the response of solvent to specific surface structure), and ion correlation forces (dispersion-based attraction of ions within interacting surface-specific electrical double layers). The theoretical underpinnings of these anisotropic forces are well established, but techniques that can isolate and measure their magnitudes for a given pair of interacting oriented crystal faces have generally been limited to use of macroscopic yet atomically flat single crystals. We report measurement of the attraction between rutile TiO₂ nanocrystals, as a function of their mutual orientation and surface hydration extent, via using environmental transmission electron microscopy (ETEM)-atomic force microscopy (AFM) technique. Atomically flat rutile AFM tips and opposing rutile substrates were fabricated by focused ion beam milling to excise nanocrystals from the surface of a single monolith that was pre-oriented, cut, and polished to prepare the (001) face. At tens of nanometers of separation the attraction is weak and shows no dependence on azimuthal alignment nor surface hydration. At separations of approximately one hydration layer the attraction is strongly dependent on azimuthal alignment, and systematically decreases as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory, and show that dispersion forces are capable of generating a torque between particles interacting in solution and between grains in materials.

DNA has emerged as an exceptional molecular building block to engineer DNA nanostructures of increasing complexity. I will discuss our recent progress in using designer complex DNA nanoarchitectures to direct the assembly of metallic nanoparticles and quantum dots into designer patterns and use of DNA architecture to encode precise biomimeralization.

Halide perovskite semiconductors can merge the highly efficient operational principles of conventional inorganic semiconductors with the low temperature solution processability of emerging organic and hybrid materials, offering a promising route towards cheaply generating electricity as well as light. Perovskites not only show exceptional primary optoelectronic properties such as a direct bandgap, small exciton binding energy, low carrier recombination rates, ambipolar transport, and tunability of the bandgap covering a wavelength range from the near infrared to the ultraviolet, but they are also very attractive for their ease of processability for mass production (e.g. printing from solution) and for the large availability of their chemical components. Following a surge of interest in this class of materials, research on halide perovskite nanocrystals as well has gathered momentum in the last three years. In such a narrow time span, several properties/features of halide perovskite nanocrystals were investigated, among them electroluminescence, lasing, anion-exchange, as well as control of size and shape such that nanocrystals in the quantum confinement regime were recently reported. The present talk will highlight the research activities of our group on halide perovskite nanocrystals and films with emphasis on synthesis,¹,² as well as structural, chemical,³ and surface transformations,⁴ and their applications in various types of devices.⁵ Our key contributions in this area include: the discovery of fast anion exchange as a means of tuning the emission from perovskite nanocrystals and its application in down-converting LEDs; the fabrication of nanostructures in the quantum confined regime; the development of colloidal inks for nanocrystal-based solar cells; new methods for a sustainable synthesis of nanocrystals; the study of 0D perovskites, their conversion to 3D perovskites and back.⁶


References
1 Akkerman, Q. A.; Motti, S. G.; Srimath Kandada, A. R.; Mosconi, E.; D’Innocenzo, V.; Bertoni, G.; Marras, S.; Kamino, B. A.; Miranda, L.; De Angelis, F.; Petrozza, A.; Prato, M.; Manna, L., J. Am. Chem. Soc. 2016, 138, 1010.
2 Shamsi, J.; Abdelhady, A. L.; Accornero, S.; Arciniegas, M.; Goldoni, L.; Kandada, A. R. S.; Petrozza, A.; Manna, L., ACS Energy Lett. 2016, 1, 1042.
3 Akkerman, Q. A.; D’Innocenzo, V.; Accornero, S.; Scarpellini, A.; Petrozza, A.; Prato, M.; Manna, L., J. Am. Chem. Soc. 2015, 137, 10276.
4 Palazon, F.; Akkerman, Q. A.; Prato, M.; Manna, L., ACS Nano 2016, 10, 1224.
5 Akkerman, Q. A.; Gandini, M.; Di Stasio, F.; Rastogi, P.; Palazon, F.; Bertoni, G.; Ball, J. M.; Prato, M.; Petrozza, A.; Manna, L., Nat. Energy 2016, 2, 16194.
6 Akkerman, Q. A.; Park, S.; Radicchi, E.; Nunzi, F.; Mosconi, E.; De Angelis, F.; Brescia, R.; Rastogi, P.; Prato, M.; Manna, L. Nano Lett. 2017,17, 1924–1930.

Utilizing the decay-to-recovery emission characteristics of unstable quantum dots (QD) under light exposure, a non-physical photopatterning method is developed. Due to the intrinsic nature of the evolution, several patterns based on polymer-QD composites, including a unique negative-to-positive pattern transformation with high contrast are possible. Furthermore, the transformation can be programmed to yield bright/dark region switch with the help of well-controlled exposure. The fabrication of a large scale (mm²) QD-polymer photopattern is a fast parallel process, as the transformation occurs within seconds. In addition, the photoluminescence of faded photopatterns (after sitting in ambient for a period of time) can be partially restored by light exposure. This flexible patterning method may find its application in light sensors, anti-counterfeiting labels and patterns where contrast should be realized without physical patterning.

In this study, we developed a method to fabricate a patterned films by using a combination of microreactor-assisted nanoparticle deposition (MAND) process and microfluidic channels. The MAND process is capable of generating nanoscale building blocks with controlled sizes, ranging from molecule clusters to nanoparticles, which allows for a more controlled and precise growth of nanostructures. Those nanomaterials serve as building blocks that can be delivered to the substrate surface through the microfluidic channels for a patterned film growth. The microfluidic channels are made of cured polydimethylsiloxane (PDMS) by using a replication from a patterned SU-8 photoresist-coated wafer. By combining the two process together, ZnO nanorods were successfully deposited on glass substrate. The mass transfer and the deposition mechanisms and kinetics were also studied. The scaling up for the MAND was achieved by numbering-up the microchannel unit operations in parallel, allowing for the deposition of the films on various scales.

It remains a challenge to synthesize Ag nanocubes in an aqueous system, although the polyol process was successfully adopted more than one decade ago. Here, we report an aqueous method for the synthesis of Ag nanocubes with an average edge length of 35–95 nm. It involves the formation of AgCl octahedra by mixing CF₃COOAg with cetyltrimethylammonium chloride, followed by the nucleation and growth of Ag nanocrystals in the presence of ascorbic acid (AA) and FeCl₃. The Fe³⁺/Fe²⁺ redox pair is responsible for the removal of multiply twinned seeds through oxidative etching. The Cl^– ions play two critical roles in the nucleation and growth of Ag nanocubes with a single-crystal structure. First, the Cl^– ions react with Ag⁺ ions to generate nanometer-sized AgCl octahedra in the initial stage of a synthesis. In the presence of room light and a proper reducing agent such as AA, the AgCl can be reduced to generate Ag_n nuclei followed by their evolution into single-crystal seeds and then Ag nanocrystals. Second, the Cl^–ions can act as a specific capping agent toward the Ag(100) surface, enabling the formation of Ag nanocubes with sharp corners and edges. Based on the results from a set of time-lapse studies and control experiments, we formulate a plausible mechanism to account for the formation of Ag nanocubes that resembles the formation and development of latent image centers in silver halide grains in the photographic process. In addition to the demonstration of a greener and economically more favorable method than the polyol process, this work also offers insights into the design of aqueous protocols for the synthesis of silver nanocrystals with controlled shapes.

Design and engineering of metal oxide materials with controlled nanostructures present important applications in nanoelelctronics and catalysis. In this presentation, we report a simple atomic layer deposition (ALD) assisted process to fabricate metal oxide nanostructures using self-assembled block copolymer polystyrene-b-polyvinylpyridine (PS-PVP) as the structure-directing template. PS-PVP self-assembles through phase separation, forming varied mesostructures such as micelles, tubes, and vesicles. These mesostructures have hydrophilic external interface that can be used as templates for further functionalization by reacting with metal oxide precursors. ALD was carried out to the hydrophilic interface of these mesostructures to grow metal oxide layers. Different oxides including TiO₂ and SiO₂ have been demonstrated at varied processing conditions. Through controlled ALD conditions, thickness of the metal oxide layer can be fine tuned. The capability of exerting rational control over dimension and composition of nanostructured metal oxides through combined block copolymer self-assembly and ALD processes provides new opportunities in new nanostructured materials.

Zinc Oxide (ZnO) nanocolumns (NCs) are promising building blocks for many existing and emerging applications owing to their unique optical, electrical, and piezoelectric properties. Specifically, the ZnO NCs could be used as seed layer for the growth of other oxide materials. Nanocolumnar ZnO is generally grown in randomly distributed arrays, in which the entire substrate is covered and only through lithographic methods is selectivity of growth location achieved. We propose a method to be able to grow ZnO NCs in hexagonally closed packed structure for spatially ordered seeding applications. Langmuir-Blodgett was used to construct a self-assembled monolayer of Silica Nanospheres (SNSs), 3.5 μm, 1.18 μm, 850nm, 500nm and 250nm in diameter, on silicon substrates. Z-axis oriented ZnO NCs were grown on top of the spheres using the glancing angle pulsed laser deposition (GAPLD) technique. ZnO columnar arrays grown in smaller SNSs diameter were observed to be vertical and at smaller sphere sizes, the colmuns were observed to form a hcp structure on top of each sphere grew in an hcp structure on top of each sphere. Columnar aspect ratios were found to be dependent on underlying sphere size as was c-axis crystallinity, with columns grown on 250nm SNSs showing considerable preffered orientation towards the (002). Columnar density per unit of coverage area was found to also be depend on underlying sphere size.

Lead-free ferroelectric materials with functionalities similar to lead zirconium titanate oxide (PZT) are of great interest in multitudes of technologies. PZT is considered the standard material for ferroelectric, piezoelectric and piezotronics applications but due to lead toxicity, the development of lead free piezoelectric materials with earth abundant elements has gained considerable attention in the ferroelectric community. Ferroelectric hysteresis behavior with high remnant polarization has been reported from LiNbO3 -type (LN-type) Zinc Stannate (ZnSnO3) hybrid nanoparticle-nanowire (NP-NW) arrayed films. Our group has previously reported the growth of ZnSnO3 in nanowire form on conducting substrates. Optimization studies of growth for LiNbO3 -type (LN-type) Zinc Stannate (ZnSnO3) NWs were performed. These nanowires show considerable potential for ferroelectric and piezotronic applications yet, random nanowire growth causes problems for device miniaturization and nano-force measurements as these require the use of a very small number (or even an individual) of wires in substrates. To achieve this, a novel template based technique using spatially ordered Aluminium doped Zinc Oxide/250nm-Silica Nanospheres (Al:ZnO/250nm-SNS) template was used as initial seed layer. A self- assembled silica nano template is constructed using Langmuir-Blodgett dip coating technique and subsequently, z-axis oriented Al:ZnO NCs were grown on top of the monolayer template using the glancing angle pulsed laser deposition (GAPLD) technique. Previous work has explored the tunability of Al:ZnO NCs aspect ratios due to on underlying sphere size. These Al:ZnO NCs can serve as nucleation sites for ZnSnO3 NWs. After template construction, the ZnSnO3 NW’s were grown using a low temperature solvothermal process. A structural study of the ZnSnO3 NW’s arrays grown on the Al:ZnO/250nm-SNS template using X-ray diffraction spectrometry will be performed for different growth conditions to find a preferential growth orientation and crystallinity of NW arrays on the template. Preferential growth of (012) plane of standard LN-type ZnSnO3 is expected, as reported in literature. After structural studies and characterization of the ZnSnO3 NWs is completed, mechanical studies will be performed to determine the formation of depletion zones and the separation of charges due to mechanical stresses on the wires. Regions in between NWs will be filled with a conducting material and with the application of a constant voltage in a direction perpendicular to the wires, a mechanical stress on the wires will change the overall measured voltage on the device.

Charge transport in colloidal nanocrystal films is mainly governed by the electronic coupling between nanocrystals. Since the bulky organic ligands on as-synthesized nanocrystals hinder charge transport, a common practice is to promote charge transport by replacing these long insulating native ligands with shorter ligands. This leads to a reduction in interparticle spacing that improves the electronic wavefunction overlap between adjacent nanocrystals.

Our group recently synthesized a new soluble precursor for SnSe that can also be utilized as a nanocrystal ligand. We first report on our precursor synthesis, which is carried out by reacting tin with dimethyl diselenide. We then characterize the precursor structure and its thermal decomposition product. Mass spectroscopy and nuclear magnetic resonance spectroscopy demonstrate that the precursor structure is tin(IV) methylselenolate, Sn[Se(CH₃)]₄. Differential scanning calorimetry and x-ray diffraction reveal that the precursor thermally decomposes into crystalline SnSe at 170°C.

This precursor creates avenues to make nanocomposites consisting of PbSe nanocrystals in a SnSe matrix. To explore this possibility, we carry out a solid-state ligand exchange of oleate capped PbSe nanocrystals with tin(IV) methylselenolate. We confirm the successful removal of oleate in this process with infrared spectroscopy. Heating of the nanocrystal films to 170°C transforms the precursor into SnSe and yields a PbSe-SnSe nanocomposite. In addition to these structural characterizations, we also report on our ongoing efforts to characterize carrier mobility, electrical conductivity, and Seebeck coefficient. We conduct these measurements using field effect transistor, van der Pauw, and differential thermovoltage techniques.

Energy harvesting is a process of capturing small amounts of energy that would otherwise be lost as light, sound, vibration, movement, or heat. Ferroelectrics, which are inherently piezoelectric and pyroelectric, can be used for energy harvesting through creating an electric field by generating an electric field in the opposite direction, change in pressure, and change in temperature. An example of one of the many ways these materials can be used is in tires, through compression and decompression that occurs when the tire comes in contact with the road as well as through outside temperature change. The energy created can be used in electric cars in order to extend the amount of time it can run before recharging.
The use of ferroelectric nanoparticles could allow for energy harvesting devices to be created less expensively due to the presence of both piezoelectric and pyroelectric properties as well as the increased piezoelectricity and pyroelectricity in nanoscale ferroelectrics. Ferroelectric nanoparticles can also be easily deposited onto a substrate which is less expensive than chemical vapor deposition or other high temperature evaporative manufacturing. The control over many different nanoparticle shapes and sizes may also yield new applications for ferroelectric materials. Additionally, the use of ferroelectric nanoparticles rather than a bulk ferroelectric material may achieve ultrahigh piezoelectric responses once the nanoparticles reach the size at which they exist in a single-domain state.
The ferroelectric nanoparticle aggregates to be used in this work are formed through a simple room-temperature cation exchange in which a solution of a metal chloride salt is injected into a solution of CdSSe graded alloy quantum dots and shaken causing ferroelectric aggregate formation. We expect to enhance these particles through gaining a full understanding of the effects of the metal chloride salt used as well as its concentration on the cation exchange process.

Colloidal nanocrystal solids exhibit exceptional electronic and optical properties that make them attractive for electronic and optoelectronic devices.¹ However, thermal transport properties also play an important role in such devices. For example, high thermal conductivities are desirable because this minimizes temperature rise during device operation, which subsequently leads to improved device performance and lifetime. Prior work on thermal transport in colloidal nanocrystal solids focused on ligand exchange strategies to modify thermal conductivity^{2, 3}. In this work, we explore ligand cross-linking as a means to increase the thermal conductivity of nanocrystal solids.

Our investigation into modifying thermal transport with ligand cross-linking is inspired by recent work by Dreyer et al.⁴ They demonstrated that oleate ligands in iron oxide nanocrystal supercrystals can be cross-linked via thermal annealing, and that this cross-linking leads to large increases in Young’s modulus. Classical thermal transport theory indicates that increasing the Young’s modulus of a material should increase its speed of sound and consequently its thermal conductivity.

To investigate whether this classical design rule applies to nanocrystal solids, we report on our thermal conductivity studies of iron oxide nanocrystal films with cross-linked ligands. We utilize the 3ω method to measure thermal conductivity and our preliminary findings reveal that ligand cross-linking can increase the thermal conductivity by a factor of ~2. We also conduct effective medium approximation modeling to better understand the underlying origins of this thermal conductivity increase.

References:
Boles, Michael A., Michael Engel, and Dmitri V. Talapin. "Self-assembly of colloidal nanocrystals: From intricate structures to functional materials." Chemical reviews 116.18 (2016): 11220-11289.
Ong, Wee-Liat, et al. "Surface chemistry mediates thermal transport in three-dimensional nanocrystal arrays." Nature Materials 12.5 (2013): 410-415.
Liu, Minglu, Yuanyu Ma, and Robert Y. Wang. "Modifying thermal transport in colloidal nanocrystal solids with surface chemistry." ACS nano 9.12 (2015): 12079-12087.
Dreyer, Axel, et al. "Organically linked iron oxide nanoparticle supercrystals with exceptional isotropic mechanical properties." Nature materials 15.5 (2016): 522-528.

Engineering of the core-shell interface for QDs has been shown to be of significant importance, however a thorough investigation to better understand this interface has not been demonstrated. Here we analyze CdSe core, CdSe/ZnS core/shell, and CdSe/Cd_1–xZn_xSe_1–yS_y core/graded shell QDs to understand the effect of the interface on the resulting stability of the QD. Changes in the emission characteristics (spectral shift and intensity change) were observed, depending on the QD architecture and exposure conditions. Specifically, upon light exposure core QD show very low stability, core-shell QDs show decay to recovery behavior, occurring over seconds to minutes, and core-graded shell QDs exhibit enhanced stability in terms of photoluminescence. Studies suggest that the decay dynamics associated with the QDs are a result of the strong influence of the surrounding environment (i.e. oxygen, humidity, light, etc.). This work offers general guidelines to understanding and evaluating emission characteristics of stable and unstable QDs. Tunability of the photoluminescence behavior can have great application in situations where long device lifetimes are highly desirable (e.g., QD displays, LEDs, and lasers), or in the case of exploring dynamic properties for tunable emission patterning

The strategy of p-doping colloidal PbS Quantum Dots (QDs) has been less developed compared to the synthesis of n-type and intrinsic PbS QDs, but they are equally important to device design. The most widely reported p-type PbS QD solids are fabricated based on solid state treatments and/or the doping effect of oxygen and humidity in air. However, for 3-nm PbS QDs commonly used in solar cells, these approaches either are accompanied by so aggressive chemistries that cause QDs to fuse or disturb the QD layer underneath during device fabrication, which also make the control over the final doping concentration in QD films difficult.

Here, we develop a method of p-doping PbS QDs through surface modifications in solution. By using colloidal atomic layer deposition (cALD), we grow sulfur atoms on the surface of PbS QDs in a controllable manner. We monitor evolution of the exciton absorption peak as the amount of sulfur increases, through which we configure the structure of PbS QDs with different surface stoichiometries, consistent with the elemental composition measured by energy-dispersive X-ray spectroscopy. We study the carrier concentration change in the PbS QD films with additional sulfur by current-voltage and capacitance-voltage measurements on the field-effect transistor geometry. We also measure photoconductivity and time-resolved microwave conductivity to characterize the carrier mobility and lifetime of PbS QDs after the sulfur cALD process. As the amount of sulfur increases, from a partial shell to full shell of sulfur on the surface, the hole concentration in PbS QDs increases, and the field effect hole mobility and photoconductivity first increase then decrease. As our method is conducted in solution phase, it is well compatible with current layer-by-layer device fabrication. With the enhanced p-type PbS QD layer, we fabricate Schottky junction and heterojunction solar cells and observe superior device performance due to improved contacts between PbS QD films and anodes, and extended depletion region within the intrinsic active layer.

Lead-Chalcogenide quantum dots (QDs) have attracted attention due to their tunable electrical and optical properties. In the QD solids, bulk-like electronic bands with bandwidth of 100~200 meV are expected to form which yield much higher carrier mobility and diffusion length compared to weakly-coupled QDs. However, the electronic properties (the local density of states, electron delocalization) of highly ordered QD arrays are not fully understood. In this work, the local density of state of a highly ordered monolayer PdSe superlattice was studied by low temperature scanning tunneling microscopy (STM).
A monolayer of PbSe QDs was prepared using the Langmuir Schaefer deposition technique. First, oleate-capped PbSe QDs dispersed in hexane were drop casted onto diethylene glycol surface. After the hexane was evaporated, a (111) in-plane oriented polycrystalline FCC superlattice was formed on the diethylene glycol surface. NH₄SCN solution was applied onto the oleate-capped PbSe superlattice film. The injection of NH₄SCN initiates the ligand exchange and phase transformation from an FCC to a simple cubic structure superlattice. A HF cleaned (001) Si substrate was stamped on the PbSe-SCN layer for superlattice film transfer to observe the cross section of the QDs by TEM. 200 cycle of Al₂O₃ ALD was employed at 75C to yield complete infilling of the QD layers. For STM measurements, HOPG (highly ordered pyrolytic graphite) substrates were cleaned by mechanical exfoliation using an adhesive tape. A monolayer QD superlattice was prepared on a HOPG substrate using same technique. Afterward, the HOPG sample was loaded into a commercial UHV scanning tunneling microscopy chamber (Omicron Technology) with a base pressure of 1x10^-10 torr. The sample was annealed at 75C for 3hr to remove the hydrocarbon and ligands from the surface. The topography of the QDs was observed with a tungsten tip prepared by electrochemical etching of a tungsten wire. The STM images were acquired in constant current mode (I = 0.03 nA) with a tip bias of +2V.
STM imaging showed that the PbSe QD monolayer had 4 fold symmetry with an average inter QD spacing of 7nm. It is also found the height fluctuation of the QDs was 1nm indicating size variation of the QDs and imperfect crystal structure of the superlattice. Scanning tunneling spectroscopy (STS) was performed to investigate the electronic structure of the PdSe QDs using a constant z-mode with an external lock-in amplifier in the bias range of -2 to 2V. The single point STS showed the band gap measured by STS varied from 0.8 eV to 1.2 eV indicating dependence of the bandgap on the size of the QDs. The STS measurements also showed the local variation on the electronic structure of the QDs within a same QD which can be attributed to the defect site. This result provides important information in the design of extended array of QDs with controlled properties.

Silicon-based organic polymers, known as silicones, give way for interesting technologies such as wearable electronics, highly compatible biomedical devices, and stretchable solar cells to become realities. In some architectures of these devices, luminescent materials such as semiconductor nanocrystals are dispersed within the polymers for optical absorption and emission effects – but creating these composites has implications for the mechanical behavior of the nanocrystal/polymer systems. Focusing specifically on polydimethylsiloxane (PDMS), some groups have observed that composites of luminescent silicon nanocrystals (SiNCs) and PDMS exhibit altered elastomeric mechanical properties due to reduced cross-linking sites available during PDMS curing. Here, we present our work on modeling the mechanical properties of the SiNCs/PDMS composites based upon the length of functionalizing ligands attached to the SiNCs, as established via experimental measurements on these composites.

We synthesized hydrogen-terminated SiNCs via an all-gas phase, non-thermal plasma reactor with silane, argon, and hydrogen as reactants. We then surface-functionalized the SiNCs via thermal hydrosilylation within an air-free environment using a Schlenk line. We chose 1-dodecene and 1-octadecene as functionalizing ligands to probe the effects of alkyl chain length on the mechanical properties of the resulting PDMS/nanocrystal composites. These functionalized nanocrystals were suspended and dispersed within the PDMS pre-polymer solution, cured, and cooled. The optical properties of the composites were characterized using photoluminescence spectroscopy and scanning confocal fluorescence spectroscopy combined with histological techniques to understand the distribution of the SiNCs within the PDMS matrix. We then evaluated the mechanical behavior of the composites using uniaxial tensile testing to determine the elastic modulus of the composite systems. Next, we employed a homogenization model to understand how altering the surface of silicon nanocrystals impacts the mechanical properties of the composite. The results of this work have implications for predicting the behavior of polymer/NC systems, pointing towards creating novel stretchable and flexible devices and sensors.

In this project, hydrothermal methods have been employed to synthesize carbon dots with different chemical composition from citric acid and amino acid. Oxygen-modified carbon dots (O-CDs), oxygen and nitrogen-modified carbon dots (N-CDs), and oxygen, nitrogen and sulfur modified carbon dots (N,S-CDs) have been successfully achieved. These carbon dots achieve strong blue-green luminescence. transmission electron microscopy (TEM) and dynamic light scattering (DLS) are used to characterize the structure and size of these carbon dots, which shows similar structure and size. The chemical composition of these carbon dots are obtained via Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which depicts the oxygen, nitrogen, and sulfur are well modified into carbon dots. These carbon dots could be used as artificial peroxidase for the detection of H2O2. The comprehensive study is performed to investigate the relationship between peroxidase-like catalytic activity and chemical composition in carbon dots.

Understanding of thermodynamic and segregation mechanisms in bimetallic nanoparticles is of great significance for their use in catalysis and other applications. Molecular dynamics simulations, with the many-body-embeded atom model (EAM) potentials, were carried out in this work to study the thermodynamic properties and segregation mechanisms of core-shell and alloyed-(PtPd)₉₂₃ -(AgPd)₉₂₃ bimetallic nanoparticles during heating and freezing processes under the NVT assembly formalisms. In general, the results showed a trend of Pd and Ag atoms to segregate on the particle surfaces; for the PdPt systems Pt atoms are diffussed towards the inner of the particles while in the case of AgPd nanoparticles, Pd was the species that spread towards the interior. Similar results have been earlier reported and can be explained in terms of the surface energy of the involved species. The obtained results are corroborated both from the radial distribution functions, the statistical radius and temperature dependence of Pd, Ag and Pt number of atoms on the surface. Moreover, the corresponding temperature-dependent caloric curves, Lindemann index and heat capacity were plotted considering that they are three significant criteria for locating the melting and freezing points of nanoparticles. At the end of the cooling processes almost all nanoparticles showed a tendency to the formation of icosaedral nanostructures and it was corroborated from the calculation of the order parameter Q₆ for each nanostructure.

Over the past decade, heavily-doped semiconductor nanostructures have emerged as an exceptionally powerful class of plasmonic materials due to the fact that their localized surface plasmon resonance frequency can be tuned greatly through changes in the density of free charge carriers, which can be controlled by the degree of doping, unlike metallic nanostructures which have nearly fixed charge carrier densities. In particular, copper chalcogenide nanocrystals have been studied widely in recent years because they exhibit an intrinsic plasmon band in the near infrared (NIR) spectral range. In the copper chalcogenides, localized surface plasmon resonances occur through the resonant excitation of high concentrations of free hole carriers in the valence band generated by large concentrations of copper vacancies present in the material. Herein, we investigate compositional tuning of the localized surface plasmon resonance frequency via careful control of the chalcogen composition for a set of small, isotropic copper chalcogenide nanocrystals with identical size, and also quantitatively evaluate their photothermal transduction efficiency. Moreover, we investigate changes in the plasmon response via control of shape and polarizability, as well as through gradual incorporation of metallic impurities in isotropic colloidal copper chalcogenide nanocrystals.

Semiconductor nanocrystals (NCs) are promising materials for the fabrication of opto-electronic devices. The chalcopyrite NCs such as CuInS₂ has been well explored, however, the properties of CuFeS₂ NCs are not well studied. Here, we report a thiol-free colloidal synthesis, characterization, and application of earth-abundant chalcopyrite (CuFeS₂) nanocrystals (NCs). The CuFeS₂ NCs were synthesized using hot-injection colloidal method, and are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman and UV-Vis-NIR spectroscopy. The synthesized CuFeS₂ NCs have tetragonal crystal structure (a = b = 0.5289 nm, c = 0.1042 nm) in chalcopyrite phase. Based on SEM imaging, the average particle size is ~ 100 nm, higher than the crystallite size (26 nm) obtained from Debye-Scherrer analysis, for NCs with growth time 30 minutes. The EDS measurement indicates the ratio of Cu, Fe, and S close to 1:1:2. Raman spectroscopy, determined using HeNe laser (632.8 nm), indicates active modes of vibrations at 290 (A₁), 351 (B₁), 470 (E) cm^-1. A very strong absorption peak at ~ 465 nm was observed for CuFeS₂ NCs with growth time 30 minutes or less. We will also discuss about the intermediate band absorption of these materials due to the empty Fe 3d orbitals. Similarly, these NCs-based films are p-type determined by thermal-probe measurement, and the average sheet resistance of the films are 7.3(±3.7) x10⁴ Ω ■^-1. Additionally, we will also address hole transport properties of these CuFeS₂ materials in energy harvesting applications.

Recently the use of nanomaterials for the diagnosis and detection of malignant diseases has increased due to the versatility and properties of these nanostructures. For this work 60 nm commercial gold nanoparticles (TED PELLA inc.) and Nanostars manufactured by chemical synthesis (precursor reagent: HAuCl4, cationic surfactant: CTAB) of 117 nm were used for coating. Malachite green Isotyocianate (MGITC), mPEG-SH and ortho-pyridyldisulfide-polyethylene glycol-N-succinimidyl propionate (OPSS-PEG-NHS) was used. A SERS active nanoparticle complex was obtained by addition of a solution of MGITC to the gold nanoparticles colloidal solution in a 1:6 ratio. Later, an mPEG-SH solution was added to the mix. The nanoparticle-MGITC-mPEG-SH complex stability was revised using a UV-Vis spectrophotometer and a JEOFL JEM 1000 transmission electron microscope. The SERS spectra were registered with a Raman Thermoscientific DXR microscopy system. Amplified bands associated with OPSS-PEG-NHS were identified in 389, 622, 859, 929, 1080, 1283, 1360, 1443, 1490 and 1450 cm^-1. The results indicate that through this methodology it is possible to identify gold nanomaterials coated with polymer through the Raman technique. In addition, greater amplification is observed with the use of nanostars compared to gold spheres. Finally, these nanomaterials are available for the marking of specific membrane for the study of different types of cancer by the SERS technique.

The antimicrobial effects of ions or salts of silver (Ag) are well known; However, the effects of Ag nanoparticles on microorganisms and the antimicrobial mechanism has recently been validated for different microbiological strains, as well as their cytotoxic effect in in vitro cellular models. In this work we report the synthesis of Ag nanoparticles using the extract of Eichhornia crassipes as reducing agent, and evaluated its antimicrobial activity with Escherichia coli. The morphology, size, chemical composition and inhibition properties of the nanoparticles as a function of the reduction time in the chemical synthesis were analyzed. The characterization was carried out by UV-Vis spectrophotometry, transmission electron microscopy and X-ray photoelectron spectroscopy. Nanoparticles with average diameters of 40 nm ± 10 nm were obtained and their antimicrobial activity with higher inhibition in Escherichia coli was recorded with The nanoparticle samples obtained at 120 min of the chemical reaction. These results suggest that Ag nanoparticles can be used as effective growth inhibitors in various microorganisms, making them applicable to various medical devices and antimicrobial control systems by modifying their concentration.

The radiative transition probability is a fundamental property for an optical transition. Extensive study on theoretical and experimental research has been conducted to relate the photonic environment around the emitter with electric dipole (ED) transition probabilities [1]. Nanocrystals (NCs) doped with luminescent ions are ideal as probes to test theoretical models. Recent work has established that the NC-cavity model accurately describes the influence of the refractive index n of surrounding medium on ED transition rates [2].
For magnetic dipole (MD) transitions theory predicts a simple n³ dependence of the MD transition rates. However, experimental evidence is difficult to obtain [3]. In the current study, we use hydrophobic Eu³⁺-doped core-shell NCs suspended in apolar solvents with different refractive index n. The ratio between the ED and MD transition rates and the total transition rate is in excellent agreement with the NC-cavity model for ED transitions and the simple n³ dependence for MD transitions. Moreover, Gd³⁺-doped core-shell NCs, whose ⁶P_7/2-⁸S_7/2 emission is of exclusive MD transition, are employed to see more insight. Thus our study provides the experimental evidence for the theoretically predicted n³ dependence for MD transition rates.

References
[1] J. Fluoresc. 2003, 13, 201-219.
[2] ACS Nano 2015, 9, 1801-1808.
[3] Phys. Rev. Lett. 1995, 74, 880-883.

Spinel-type Co₃O₄ finds applications in a wide range of technological fields, including gas sensing and clean energy conversion, where nanostructured Co₃O₄ may provide a cost-efficient alternative to Pt- and Ir-based catalysts for electrocatalytic water-splitting. As a particular challenge, however, the oxygen-based redox process involves a complex four-electron transfer resulting in poor reaction kinetics. Hence, efficient and robust catalysts promoting the oxygen evolution reaction (OER) are in great demand.

We here explore a synthetic approach based on the decomposition of thermally unstable solution-grown oleate precursors, where a similar methodology was previously described by Ehlert et al. for the preparation of ZnO nanoparticles.[1] The reaction conditions are optimized by systematically varying reactant concentrations and solvent mixtures as well as the decomposition temperature. Furthermore, we investigate the stabilizing and structure-directing effects of various other fatty acid ligands, such as stearate, myristate, and caprate. The reaction products are routinely characterized by UV/Vis spectroscopy, transmission electron microscopy, and small-angle x-ray scattering. Most importantly, we investigate the processes of nanoparticle formation under different reaction regimes by in-situ small-angle x-ray scattering in a temperature-controlled reaction cell.

Our synthetic strategy leads to ligand-stabilized CoO_x nanoparticles, and thus offers the opportunity for a dedicated ligand exchange [2]. This enables an ordered assembly of the nanoparticles into superlattices via selective loading into specific microdomains of phase-separated blockcopolymer systems, where post-synthetic conversion into Co₃O₄ is possible. For the direct synthesis of Co₃O₄ , cobaltous hydroxide precursors are employed which offer superior possibilities regarding size- and morphology control.[3]

In order to study the effects of particle morphology and size on the functional properties, the nanoparticles are investigated as electrocatalysts for the oxygen evolution reaction (OER). For this purpose, the materials are isolated as powders and immobilized on a rotating disc electrode for analysis in cyclic voltammetry. The resulting overpotentials towards the OER associated with these very well-defined, but randomly oriented nanoparticles will be discussed in comparison to reference materials as well as micron-scale mesocrystalline particles comprising a substructure based on co-oriented Co₃O₄ nanoparticles interspersed by pores.

[1] S Ehlert, T Lunkenbein, J Breu and S Förster, Coll. Surf. A 444 (2014), 76.
[2] S Ehlert, S M Taheri, D Pirner, M Drechsler, H-W Schmidt and S Förster, ACS Nano 8 (2014), 9410.
[3] Xiao, X., Liu, X., Zhao, H., Chen, D., Liu, F., Xiang, J., Hu, Z., and Li, Y. (2012) Facile Shape Control of Co₃O₄ and the Effect of the Crystal Plane on Electrochemical Performance. Advanced Materials 24, 5762.

The activity of biological components depends both on the nature of the chemical signal and on its density and spatial organization.^[1] Engineering materials with functional domains (e.g. anisotropic particles, patchy or multi-compartment particles) is of great interest due to their ability to mimic number of analogues in nature.^[2] Here we describe a new method to create bi-functional patchy silica particles (SiNP).
Several alkoxysilane precursors were designed and synthesized bearing (i) a self-assembling group (e.g. anthracene) protecting (ii) a function of interest for bioconjugation (amine) and (iii) an alkoxysilane moiety for the transfer of the assemblies at the surface of the SiNP by sol-gel chemistry. Alkoxysilane self-assemblies were analyzed in different solvents by analytical and imaging techniques (DLS, Spectroscopy, (cryo)TEM). This method enabled us to create size-controlled patches at the surface of the particle. Upon deprotection of the self-assembling groups, amines are revealed for the grafting of bioactive ligands. The density of those ligands was tuned by modifying the size of the patches by influencing the alkoxysilane self-assemblies.
A second molecule of interest can be grafted between the patches, simultaneously or in a two-steps synthesis, in order to create bi-functional particles. In this work, the SiNP were used as a multifunctional platform allowing the co-grafting of biomolecules of interest for axonal out-growth, namely laminin-binding domains that are penta-peptide epitopes (IKVAV)^[3] and sulfonate groups (SO₃^- obtained from the grafting of commercial alkoxysilane) that have been shown to interact with positively charged collagen.^[4][5]
The underlying motivation for this multi-component approach is to control the collagen scaffold bioactivity by adjusting the laminin epitope concentration via its chemical confinement, while maintaining the favorable mechanical and cell adhesion properties of collagen.

[1] Banani, S. F., Lee, H. O., Hyman, A. A., Rosen, M. K., Nat Rev Mol Cell Biol. 2017, 18, 287.
[2] Du, J., O’Reilly, R. K., Chem. Soc. Rev, 2011, 40, 2402.
[3] Sur, S., Pashuck, E. T., Guler, M. O., Ito, M., Stupp, S. I., Launey, T. Biomaterials 2012, 33, 545.
[4] Aimé, C., Mosser, G., Pembouong, G., Bouteiller, L., Coradin, T. Nanoscale, 2012, 4, 7127.
[5] Bancelin, S., Decencière, E., Machairas, V., Albert, C., Coradin, T., Schanne-Klein, M.-C., Aimé, C. Soft Matter, 2014, 10, 6651.

Over the last several decades, scientists endeavoured to develop machines and robots at nanoscopic scale and envisioned that that tiny artificial machines could be used to cure diseases or fabricate novel materials.^{1, 2} Particularly, the nano/micro-motor with the comparable size of a single cell shows great potential in the biomedical application.^{3, 4} Here we describe a visible/infrared light-driven swimmer based on core/shell silicon nanowire solar cell which can be fabricated by VLS process and followed by thermal diffusion doping. The silicon nanowire solar cell harvests energy efficiently from incident photon and induces the electrochemical reaction on the silicon surface. With the asymmetric distribution of the generated ions, the nanowire propels itself autonomously in solution via self-electrophoresis mechanism. Significantly, the as-prepared swimmer can be readily propelled at ultralow-intensity (3 mW/cm²) visible/near-infrared light which is desired for the biological application. Furthermore, the morphology of fracture surface plays a crucial effect on the motion behavior determined by the spatially-confined ions around the surface. Both experimental study and theoretical simulation demonstrated the detailed structure around p/n junction can dramatically change the nanomotor migration trajectory. Furthermore, due to the well-known light trapping effect inside silicon nanowire, the spectral response of the nanowire shows typical optical resonance which opens up a new dimension for controlling the light-driven nanomotor. These results imply a promising prospect for of individually light-controlled nano/micromachines.

REFERENCES
1. G. A. Ozin, I. Manners, S. Fournier-Bidoz and A. Arsenault, Adv. Mater., 2005, 17, 3011-3018.
2. W. Wang, W. Duan, S. Ahmed, T. E. Mallouk and A. Sen, Nano Today, 2013, 8, 531-554.
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Carbon dot-metal/metal oxide nanocomposites (CMN) are gaining attention in designing efficient catalytic systems where the water soluble Carbon dots (CDs) show dual functionality of a stabilizing agent as well as a reducing agent for the generation of metal nanoparticles in situ. The CDs in the nanocomposites, not only help in modulating electronic band structures of metal/metal oxides by its unique electron transfer property but they are also expected to significantly influence on their morphology and surface properties. Herein, we report the synthesis of CDs – Gold (CDs-Au) nanocomposites through solution method and have explored their catalytic property in the reduction of Nitroaromatics (NAs). The CDs, synthesized through microwave pyrolysis of a mixture of Citric acid(CA) and thiourea, were dissolved in Millipore water and then added into aqueous solution of HAuCl₄ to obtain a solution of the CDs – Au nanocomposites. The synthesized CDs and colloidal solution of CDs - Au nanocomposites were characterized in detail using UV-Vis spectroscopy, FT IR, XRD, TEM, HRTEM, EDX and XPS analysis. The catalytic efficacy of the CDs – Au nanocomposites were premised on real time monitoring of the reduction of NAs such as 4-Nitrophenol (4-NP), 4-Nitroaniline (4-NA) and Nitrobenzene (NB) by NaBH₄ using UV–Visible absorption spectroscopy. The apparent rate constants (K_app) of reduction of the NAs in the presence of the nanocatalysts were found to follow the pseudo-first-order kinetics having value of 1.37 × 10^-1 , 8.9 × 10^-2 and 5.35 × 10^-2 s^-1 for 4-NP , 4-NA and NB repectively. The apparent rate constant (1.37 × 10^-1 s^-1) observed for the reduction of 4-NP by NaBH₄ using CDs – Au nanocomposites has been found to be one of the highest values reported in literature so far thereby establishing nanocomposites their excellent efficacy as an catalyst.

Current dyeing techniques face growing environmental and economic challenges due to high consumption of water, salts, auxiliaries and energy, and production of substantial amounts of industrial polluting waste waters. We show here that dye-impregnated magnetic nanoparticles could be prepared to dye cotton fabrics and were recycled after the dyeing process using a magnet. In our approach, a conventional dye, Disperse Red 1 (DR1) was functionalized with trialkoxysilane groups through the nucleophilic addition reaction of 3-isocyanatopropyl triethoxysilane with DR1. The trialkoxysilane functionalized DR1 was used to coat the magnetic F₃O₄ nanoparticle cores through the Stöber method, yielding red magnetic F₃O₄@SiO₂ core-shell nanoparticles. These red magnetic nanoparticles can be easily dispersed in water and their movement can be manipulated with a magnet. The resulting suspension was used to dye cotton fabrics without the presence of any salts and auxiliaries. Large surface area and high surface energy of the nanoparticles were believed to be responsible for their high affinity toward the fabrics which ensured high fastness. Moreover, after the dyeing process, un-bonded dye nanoparticles in the waste can be recycled with a magnet for future use, avoiding tedious wastewater treatment. Thus, this technique provides an environment friendly and cost-effective dyeing process that will greatly benefit the textile industry.

In this research, we attempt to fabricated carbon nanotube (CNT) electrode with nano meter scaled gap by using sequential application of an alternative current (AC) dielectrophoretic (DEP) force. The nano-gap in the middle of CNT is formed by electrical break down which is induced by Joule heating.
This fabrication method is conducted under atmospheric condition with low cost apparatus set up, and production yield can be also monitored in a real time by in-situ measurement of electrical signal. Therefore, we can fabricated about tens of nano meter scaled electrode gap through simple and low cost method as compared to conventional lithography techniques that needs to high vacuum environment and expensive instrument with complex fabrication process.
In addition, we could generate DEP force fully enough to manipulate quantum dot (QD) through the CNT electrode with nano-gap. In general, it is impossible to manipulate the QD by using DEP force. Because nano materials under 10 nm is dominated by thermal force associating with Brownian motion, rather than other external force. Therefore, to manipulate the QD by electric field, the large strength of electric field is need to overcome the thermal force.
Strength of electric field is inversely dependent upon both gap size of electrode and shape of electrode. So we used the CNT having large aspect ratio that can generate large electric field gradient, and we also fabricated nano-gap in the middle of CNT electrode to significantly increase the strength of electric field.
As a result, we could successfully fabricated the CNT electrode with nano-gap through the Joule heating followed by application of DEP force. The minimum size of nano-gap is 18.8 nm. We could also trap the PbS QDs between CNT electrode by DEP force, and the size of QD aggregates can be controlled by adjusting the magnitude of electric field.
Finally, we tested optoelectronic response of device comprising with CNT electrode and QD aggregates under infrared (IR) or ultra-violet (UV) illumination. This nano optoelectronic device showed that resistance value under zero bias well followed the input signal of UV or IR illumination. This experimental results indicated that this hybrid type optoelectronic device have potential to used in optical sensor applications, and might give some another way to improve the electronic performance of QD conducting film.

Zinc oxide nanoparticles (ZnO NPs) have attracted great attention due to their ability to induce the generation of reactive oxygen species (ROS) under light irradiation. In this study, light-triggered ROS generation by ZnO NPs is utilized as a new therapeutic approach for targeted cancer therapy. Poly(ethylene glycol) (PEG)-coated ZnO NPs were synthesized and further conjugated to anticancer drugs. The drug-loaded ZnO NPs were efficiently internalized by cancer cells, resulting in efficient intracellular drug delivery. The ZnO NPs also induced the formation of ROS in the cancer cells under light irradiation, leading to light-triggered cell death. Importantly, synergistic anticancer effects were achieved by combined chemotherapy and light-triggered photodynamic therapy. This study demonstrates that drug-loaded ZnO NPs are promising nanoplatforms for targeted and effective anticancer activity

Light-active nanomaterials, which convert photon energy efficiently into chemical, electronic, or thermal energy, have been used widely with many practical applications in fields ranging from energy to health. Among common light sources, near-infrared (NIR) light is particularly suitable for excitation of light-responsive nanomaterials in the human body because it can penetrate into deep biological tissues, the result of low absorption by water and blood as well as weak scattering from soft tissue in the NIR region. Recently, an increasing number of studies have been conducted on hollow Au-Ag nanoshells (GNSs) comprising a thin alloyed shell and a hollow interior. GNSs can transfer NIR photon energy efficiently to generate local heat causing hyperthermia and triggering drug release or to produce cytotoxic ROS to kill cancer cells in a form of photodynamic therapy. However, the residual silver may result in the GNSs displaying instability and toxicity, especially in biological media.
Herein, we reported the synthesis of NIR–absorbing gold nanoframes (GNFs) and a systematic study comparing their physiological stability and biocompatibility with those of GNSs, which have been used widely as photothermal agents in biomedical applications because of their localized surface plasmon resonance (LSPR) in the NIR region. The GNFs were synthesized in three steps: galvanic replacement, Au deposition, and Ag dealloying, using silver nanospheres (SNP) as the starting material. The morphology and optical properties of the GNFs were dependent on the thickness of the Au coating layer and the degree of Ag dealloying. The optimal GNF exhibited a robust spherical skeleton composed of a few thick rims, but preserved the distinctive LSPR absorbance in the NIR region—even when the Ag content within the skeleton was only 10 wt%, fourfold lower than that of the GNSs. These GNFs displayed an attractive photothermal conversion ability, great photothermal stability, and could efficiently kill 4T1 cancer cells through light-induced heating. Moreover, the GNFs preserved their morphology and optical properties after incubation in biological media (e.g., saline, serum), whereas the GNSs were unstable under the same conditions because of rapid dissolution of the considerable silver content with the shell. Furthermore, the GNFs had good biocompatibility with normal cells (e.g., NIH-3T3 and hepatocytes; cell viability for both cells: >90%), whereas the GNSs exhibited significant dose-dependent cytotoxicity (e.g., cell viability for hepatocytes at 1.14 nM: ca. 11%), accompanied by the induction of reactive oxygen species. Finally, the GNFs displayed good biocompatibility and biosafety in an in vivo mouse model; in contrast, the accumulation of GNSs caused liver injury and inflammation. Our results suggest that GNFs have great potential to serve as stable, biocompatible NIR-light absorbers for in vivo applications, including cancer detection and combination therapy.

Hepatocellular carcinoma is a public health problem; it is the fifth most occurring and the second most deadly cancer. Hepatocellular carcinoma is one of the few cancers where incidence continues to increase with 700,000 cases per year worldwide and a practically equal number of deaths. It is mostly diagnosed in advanced stage and has a very poor prognosis, with a survival of 1 to 2 months. Until now, no conventional treatment is totally effective for patients in this stage. Therefore effective therapy is urgently needed.
It has been reported that drug nano-vehicles directed to tumor sites can potentially be used as an anticancer therapy with great safety and efficacy. The nano-vehicles promote high concentrations of drug within the tumor site, generating greater efficacy and low toxicity to the organism. The receptor-mediated endocytosis is a tempting way to direct the drug nano-vehicles to any type of target cells. Therefore, the selection of an appropriate receptor is important. It is well documented that the Ashwell-Morell receptor, asialoglycoprotein receptor (ASGPR) is primarily expressed on hepatocytes and in hepatocellular carcinoma. Due to high affinity of this receptor for galactose, the matrix of lactosylated albumin could be used as potential nano-vehicle targeting hepatocellular carcinomas. Moreover, albumin is an endogenous non-immune protein. Therefore, the objective of this work was to synthesize and characterize nanoparticles of lactosylated albumin that selectively bind hepatocellular carcinoma in an in-vitro model.
Previously to the synthesis of the nanoparticles, lactosylated albumin was produced and characterized by electrophoresis SDS-PAGE, assay of biorecognition using Riccinus communis lectins (specific for galactose) and the conjugation of lactose to albumin was confirmed by Fourier-transform infrared spectroscopy.
Lactosylated albumin nanoparticles, with low and high cross-linking, had a size distribution of 560 ± 18 nm and 539 ± 9 nm by both dynamic light scattering and scanning electron microscopy and atomic force microscopy. The surface charge was of -26 ± 0.15 mV and -24 ± 0.45 mV, respectively. Biorecognition, inhibition and competence assays of the nanoparticles of lactosylated albumin with the cell line HEPG2 showed specific interaction. These results indicate that the two types of nanoparticles can be potentially used for drug delivery purposes with selective selection towards the HEPG2 cell line.

The preparation of two-dimensional (2D) ordered micro/nanoparticle arrays holds significant potential for advanced functional material applications ranging from optoelectronic to biomedical devices. Various approaches have been reported in the literature to form ordered 2D particle arrays, including the particle self-assembly at the liquid-vapor (L-V) interface due to attractive interaction, particle monolayer formation on a solid substrate in a thin liquid film via capillary interaction, and deposition of particles on an electrode surface by electrostatic (or electrophoretic) forces. In this study, we focus on the large-scale fabrication of highly ordered particle monolayers on the L-V interface of a water layer. Silica particles of two different sizes were chosen as candidates: 0.5 and 1 μm in diameter, and the particles were coated with a polydopamine (PDA) capping layer. To investigate the influence of the particle hydrophobicity on the monolayer formation process, 1-dodecanethiol molecules were grafted on the outer surface of the PDA layer. Microliter suspension drops (1-butanol as solvent) of the coated particles were continuously added on the water surface, and the dispensing rate was controlled via a high-precision syringe pump. 2D ordered particulate films are gradually formed driven by the strong Marangoni convection. The resulting particle monolayer was carefully transferred to a solid substrate for morphological investigation. 2D hexagonal close-packed (HCP) particle arrays with a length scale of centimeters were observed. The results suggest that an appropriate degree of surface hydrophobicity of the particles is critical for the formation of a highly ordered particulate film structure. Monolayers with HCP morphology are favored when the particles are weakly hydrophobic, whereas films with particle agglomerates are favored when particles are strongly hydrophobic.

Heavy metal ions contamination in wastewater has drawn much attention due to a great threat to human health. Metal ions such as copper, iron, lead, and chromium, have high toxic and nonbiodegradable properties. Generally, adsorption is regarded as an effective and economical method for the removal and recovery of heavy metal ions. The adsorption properties of adsorbents depend on the functional groups on their surfaces. Recently, the electrospinning technique has become a versatile approach for producing nanofibers with high surface area-to-volume and flexibility for chemical/physical functionalization. It has been found that an adsorbent containing nitrogen-based ligands is effective in forming complexation with metal ions. As a kind of commodity textile materials, polyacrylonitrile (PAN) electrospinning nanofibers could be modified to contain a chelating group for the removal of metal ions. It is therefore of our interest to investigate the feasibility of using a nanofiber membranes modified with amine groups on its surface as an adsorbent of metal ions.

Firstly, PAN nanofiber membranes were successfully prepared by electrospinning of PAN/DMF solutions, then the PAN membranes were modified with amine oxime in the aqueous of hydroxylamine hydrochloride. These results showed that as the increase of reaction temperature, reaction time and the concentration of the hydroxylamine hydrochloride, the -CN conversion ratio also increased obviously. However PAN chelating nanofiber membranes size shrinked a little with the increasing of temperature and hydroxylamine hydrochloride concentration, moreover the membranes’ color was getting pale yellow. By combining with FTIR, SEM characterization, the optimum reaction conditions parameters were finally determined.

The adsorption effectiveness of Cu(II), Pb (II), Fe (III) , after 10h equilibria were 35.8, 75.2, and 90.0mg/g, respectively. Results showed that Langmuir adsorption isotherm curve could fits well adsorption data of chelating fiber, and the coefficients were above 0.990, showing that the metal ion chelating nanofibers surface achieved monolayer adsorption. Adsorption process of chelating fiber on metal ion can be described by secondary dynamics equations, and kinetic studies have shown that oxime amine groups on metal ions adsorption processes were controlled by the diffusion of metal ions and coordination reaction. Adsorption and desorption of chelating fiber membranes on Cu (II) experiments suggested that amine oxime PAN chelating fiber membrane can be facilely regenerated with hydrochloric acid solution. Thus Amidoxime PAN chelating nanofibers could have a potential application in these areas of heavy metal ions pollution treatment, the enrichment and recovery of precious metals.

Upon absorption of light, free electrons in metal nanoparticles can be excited to become hot. The hot electrons can travel to the surface of the nanoparticles to react with the species adsorbed on the metal surface. Decreasing the size of metal nanoparticles will eliminate the energy loss of traveling hot electrons, resulting in hot electrons carrying high energy to drive surface reactions efficiently. However, the efficiency of light absorption in small metal nanoparticles becomes low, which is not beneficial for the population of hot electrons. In this talk, quantum-sized nanoparticles made of transition metals will be discussed to highlight a unique strategy for increasing optical absorption cross sections of metal nanoparticles and enhancing the efficiency of hot carrier generation. In this strategy, quantum-sized metal nanoparticles will be assembled on the surface of dielectric silica spheres, and the resulting composites exhibit a significant enhancement in light absorption.

Nanosphere lithography (NSL) is a widely used and convenient technique for large-area patterning of solid surfaces with periodic arrays of nano-features. In NSL a mono- or doublelayer of hexagonally close-packed nanospheres from a colloidal suspension is used as a shadow mask in order to modify the substrate underneath at the openings between each triple of spheres. This can be done by either removing or depositing material, using a big variety of materials combinations, mask opening shape modifications and materials deposition or removal techniques in order to tailor surface nanopatterns.
Among the techniques applied to obtain the nanosphere mono- or double-layer masks, methods based on the convective self-assembly are most important. Convective self-assembly (CSA) of colloidal nanospheres into ordered thin sphere layers takes place at the solid-liquid-gas triple phase boundary of a drying droplet of a colloidal suspension on a solid substrate surface by evaporation of the liquid phase. CSA happens at the triple-phase boundary of any drying droplet as well as during dip coating or when a droplet is moved across a surface using a doctor blade.
Since the latter technique is particularly useful for creating nanomasks, the transport processes occurring in a colloidal suspension droplet pulled by a doctor blade were analyzed for the first time numerically. Both the in-plane and the out-of-plane arrangement of spheres are studied as a function of experimental conditions such as the doctor blade velocity (triple phase boundary velocity), suspension evaporation flux, colloidal particle concentration, colloidal sphere size fluctuations, variations of the flux direction and the presence and crystallographic orientation of nuclei at which the 2d growth of a colloidal mask can start. The resulting arrangements of colloidal spheres are statistically evaluated using Delaunay triangulation procedures.
The simulations reproduce well experimentally observable stripe patterns of mono- and double-layer areas and a method is derived to suppress double-layer formation. Grain boundaries in the 2d sphere monolayers are found parallel to the doctor blade direction of motion as in corresponding experiments using polystyrene spheres. In addition the simulations reveal that a certain finite width of the particle size distribution is beneficial for the crystalline quality of a monolayer mask. The simulations allow to identify stable and less stable growth directions on seed monolayers. Last but not least the mechanism of vacancy formation in monolayer sphere masks can be observed in the simulations. It is expected that the simulation results will largely contribute to bring the convective self-assembly of colloidal nanomasks to perfection.

Assembly of nanoparticles (NPs) into complex architectures across length scales is of paramount importance in nanoscience and nanotechnology, especially for the bottom-up fabrication of electronic and photonic devices, chemical and biological sensors, solar energy conversion and storage devices. Such self-assembly can be driven by entropy-dictated maximization of the packing density of NPs, as well as interparticle interactions. Despite these advances, NP assembly has not achieved the accuracy of atomic/molecular levels as in biological systems. Recent progress in nanochemistry has led to a new class of materials—atomically precise nanoparticles (e.g., gold), and more excitingly, their total structures (i.e., metal core plus surface ligands) have been fully determined by X-ray crystallography. Such perfect nanoparticles (without any interior or surface defects) provide a unique platform for in-depth understanding of the nanoparticle assembly mechanism at the atomic/molecular levels. This talk will present the attainment of the atomically precise, 2.2 nm Au₂₄₆(p-MBT)₈₀ NPs (where p-MBT is p-methylbenzenethiolate). The total structure of Au₂₄₆(p-MBT)₈₀ and the Ångström-level structure of macroscopic crystals that are self-assembled from such NPs are fully resolved by X-ray crystallography. The precise structural information across the Ångström to micron scale reveals that the protecting ligands can generate complex patterns on the NP surface, and the symmetry and density of the surface patterns further guide the packing of NPs into 3D lattices with orientational, rotational, and translational order. This work demonstrates that self-assembly of NPs can indeed reach the same level of hierarchy, complexity and accuracy as biomolecules.

Upconversion nanoparticles (UCNPs) are a unique class of inorganic phosphors capable of absorbing near-infrared light (NIR) and converting it, through the sequential absorption of photons, to ultraviolet (UV) and visible emissions. UCNPs are especially promising for biomedical applications due to their high photostability, and high signal to noise ratio due to the weak autofluorescent response and deep tissue penetration of NIR; however, UCNPs suffer from low upconversion efficiencies leading to the need for high excitation power densities, severly heating the UCNPs' environment, causing a high degree of thermal toxicity. Therefore, developing upconversion nanoparticles (UCNPs) capable of emitting intense visible light emissions in response to low power density NIR excitations is essential for their functional utility in applications including sub-cellular labeling, bioimaging, and biosensing. To this end, we have rationally designed a single-crystal core-shell-shell “sandwich” structured UCNP capable of minimizing deleterious energy back transfer, yielding intense visible emissions in response to low power density 980 nm NIR excitations. This core-shell-shell “sandwich” structured UCNP shows a remarkable enhancement of 63 times for total visible luminescence region, as well as an 80 times enhancement in the green emission range (510nm - 570nm) relative to typical β-NaYF₄:Yb 20 mol%, Er 2 mol% co-doped UCNPs. As a proof of concept, we have constructed a highly sensitive biosensor for the detection of dopamine at pico-molar level concentrations. The exceptional upconversion luminescence endows “sandwich” structured UCNPs with great potential for biosensing, as well as other material and biological applications.

Biliverdin is a naturally-occurring pigment in bile that exhibits high UV-Vis absorbance in the near-IR region, providing a potential platform for photoacoustic imaging with minimal background interference from biological tissue. Biliverdin nanoparticles (BVNPs) were synthesized in a variety of solvents, and were characterized using transmission electron microscopy (TEM), UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS), zeta potential measurements, fluorescence spectroscopy, fluorescence imaging, and photoacoustic imaging. The nanoparticles exhibited high absorbance at 365 nm and 680 nm, fluorescence when excited at 365 nm, and photoacoustic properties when excited at 680 nm. Nanoparticles were shown to form as early as ten minutes into the synthesis, and their properties varied based on the synthesis solvent. Nanoparticles synthesized in water and 0.9% NaCl solution were found to exhibit higher absorbance and lower fluorescence compared to the nanoparticles synthesized in MES. Additionally, nanoparticles synthesized in MES exhibited a red-shifted fluorescence over time compared to the other nanoparticles. The potential of these nanoparticles for use as photoacoustic agents in lymph node imaging was demonstrated in nude mice.

Results are presented for two in-situ synchrotron-based studies: (i) ultra-small-angle X-ray
scattering (USAXS) of the solution-mediated formation and growth of nano-ceria (n-CeO2) using a flow cell. (ii) wide angle x-ray diffraction (WAXRD) of the amorphous-to-cubic crystallization of nano-ZrO₂ in a reducing environment . In the first study, the flow cell has enabled in situ monitoring of characteristics from 1nm to a few micrometers as a function of the
temperature. The nanoparticle formation and growth component has been identified.
Monitoring of flow rate, temperature and pH suspension conditions have permitted real-time studies of the formation and growth of the individual n-CeO2 particles from homogeneous dilute solution over several hours. Incubation times for each temperature and minimum size of critical nucleus-size of 6nm have been identified which has implication of the interfacial energy of n-CeO2 in the aqueous solution. Activation energy for growth has been measured to be ~0.5eV. In the second study, pair distribution function and reverse Monte Carlo simulation were applied to provide details of the local structure during the crystallization. The local structure of the amorphous phase bears resemblance to the short-range arrangement of cubic ZrO₂. The amorphous-to-cubic (a−c) crystallization of nanoZrO₂ in a reducing environment was studied. A reverse Monte Carlo (RMC) simulation was applied to provide details of the local structure during the crystallization process as well as to calculate partial PDFs of Zr−Zr and Zr−O during the crystallization. The number of Zr's next-nearest neighbors of Zr remains 12, whereas the number of O's as nearest neighbors of Zr increases from 6.7 to 7.3 as the material evolves from an amorphous into a cubic structure, suggesting the persistence of a high concentration of oxygen vacancies. The simulated atomic local structure of the amorphous phase bears resemblance to the short-range arrangement of cubic ZrO₂, consistent with the results of X-ray absorption near edge spectroscopy (XANES) at Zr L_II and L_III. The amorphous-to-crystalline phase transformation is affected by the environment. Under an oxidizing condition, the amorphous phase crystallizes directly to tetragonal and subsequently to monoclinic zirconia.

1 J.Appl.Cryst. (2008). 41, 918–929 DOI:10.1107/S0021889808023078
2 Chem. Mater., 2007, 19 (13), pp 3118–3126 DOI: 10.1021/cm061739w

Developing nanocrystals with precisely controlled size, shape, and structure is of great importance for understanding their properties. Although significant developments have been achieved in colloidal synthesis in the past two decades, it remains challenging to synthesize nanocrystals in a predictive way due to a lack of mechanistic understanding of their formation. Here we use synchrotron-based X-ray scattering to probe the formation of nanocrystals in situ under typical colloidal synthetic conditions.

By coupling the small angle X-ray scattering with the wide angle X-ray scattering, we were able to quantitatively analyze the nucleation and growth kinetics of nanocrystals and understand the evolution of their atomic crystalline structures. Using PtSn as a model system, we observed a unique formation mechanism of PtSn nanocrystals in a one-pot synthesis through sequential diffusion of the Sn component inside pre-formed Pt nanocrystals. The in situ characterization provides a general strategy for the synthesis of bimetallic nanocrystals. Moreover, the in situ X-ray scattering enabled the unprecedented discovery of crystallization of various nanocrystals (i.e., metallic, and semiconducting) into three-dimensional superlattices in solution, even at very high temperatures (up to 300 ^oC), providing new insights on interparticle interactions during colloidal synthesis. These studies demonstrate new opportunities offered by in situ X-ray scattering techniques in understanding not only the formation mechanisms of nanocrystals, but also the interparticle interactions for creating diverse nanocrystal superlattices.

We introduce anisometric plates as a new class of colloidal building blocks which combine micron length and nanoscale thickness. Such plates act against gravity and assemble into 3D lattices of controllable and transformational geometry, from hexagonal lattice of plate-stacked columns to honeycomb lattice of columns. Based on real-time tracking of the rotational and translational motions using optical microscopy, we resolve the self-assembly and transformation of the final lattices, which reveals a mechanism of rotational entropy-driven transformation.

Metal chalcogenice nanocrystal synthesis relies heavily on control over solute supply kinetics. We have developed libraries of substituted thiourea and selenourea precursors whose conversion, and therefore, solute supply kinetics are determined by the nature of their substituents. With these libraries, we observe well-defined relationships between solute supply and number of crystals, enabling quantitative study of the nucleation and growth processes. By making kinetic measurements in situ using optical spectroscopy and synchrotron X-ray scattering, we have begun to make estimates of the solute concentration at nucleation, the first stable nucleus size, and per-particle growth rates. This synthetic platform is broadly applicable to other sulfides and selenides, including luminescent quantum dots used in commercial displays, representing a paradigm shift in colloidal synthesis.

Anisotropic micro and nanoscale building blocks provide new opportunities for significantly extending the scope of colloidal self-assembly, and enabling the formation of interesting crystalline superstructures that are otherwise inaccessible. Due to the complexity of these building blocks, however, it is not evident what type of superstructures can be targeted from different types of building blocks. The high-dimensional parameter space that defines the geometric and interaction properties of such systems poses an obstacle to assembly design and optimization. Specifically, a system with multiple types of anisotropic building blocks can self-assemble into complex structures that are hard to predict, but at the same time, could possess interesting transport properties such as tunable phononic or photonic bandgaps.

Here, we present a theoretical and computational study of the interactions and self-assembly behavior of superstructures of colloidal clusters. These units are experimentally synthesized from a number of spherical particles that are permanently bonded together and form various cluster shapes such as cubes or tetrahedra. We use molecular dynamics (MD) and Brownian dynamics (BD) simulations to investigate the interactions of colloidal clusters with different shapes through their complex surfaces and interfaces. Geometric constraints are also investigated to help determine particle sizes and configurations that can result in the design of ordered superstructures. Finally, MD and BD simulations are used to predict thermodynamics and kinetics of self-assembly for a variety of binary and ternary configurations. This theoretical/computational study provides a direct insight into various parameters that affect the interactions between colloidal clusters, and leads to a dimensionality reduction and definition of practical design guidelines for future experimental efforts to synthesize high quality superstructures with long-range order.

Colloidal manipulation and assembly are of significant importance for colloidal science and development of novel optical, electrical, and magnetic devices. The response of colloidal particles under external stimuli have been extensively studied in the past decade. Specifically, light driven colloidal manipulation and assembly are attractive due to the flexible management of light for remote non-contact control. Traditional optical manipulation techniques such as optical tweezers suffer from the need for rigorous optics and high operation power, the latter causing irreversible damage on fragile materials. The optical assembly of two-dimensional and even three-dimensional colloidal particles onto solid substrates is still elusive, though it is critical for the development of functional colloidal structures. Herein, we explore the optothermophoretic effect, which arises from the interactions of colloids with the solvent or dissolved molecules and ions under an optothermal field, for low-power and versatile trapping and assembly of colloidal particles.
Thermophoretic trapping and manipulation is enabled by a negative thermophoretic mobility D_T, i.e., the suspended particles should be driven from the cold region to the hot region under an externally applied temperature gradient. Through exploring the interfacial entropy-driven force which arises from the colloid-solvent interactions, we experimentally demonstrate opto-thermophoretic trapping of colloidal particles in various polar solvents, including water, ethanol, isopropyl alcohol and 1-butanol. The interfacial entropy-driven force is mainly determined by the orientation of solvent molecules at the particle-solvent interface, which is a function of the solvent properties, salt concentration, and hydrophilicity of the particle surface. The thermophoretic trapping behavior in different solvents was characterized to verify this hypothesis.
Furthermore, we present a new strategy to assemble colloidal particles on solid substrates via introducing an ionic surfactant, i.e. cetyltrimethylammonium chloride into curable hydrogels. By adding an AC electric field into our system, we enable rapid electrothermal transport of colloidal particles to the laser spot, where the particles are trapped with a thermoelectric field. The colloidal particles are organized into specific patterns followed by the photopolymerization of the hydrogels, which traps the suspended colloidal patterns into place on the solid substrate. This strategy is applicable to colloidal particles from nanoscale to microscale and of various materials including polymeric, dielectric, and metallic particles. For demonstration, we have succeeded in creating various functional structures including plasmonic dimers and chiral optical heterostructures. With low operation power and versatility in colloidal manipulation, the opto-thermophoretic approaches will find applications in future development of colloidal functional devices.

Controlling the surface chemistry of gold nanorods (AuNRs) is critical to many applications, impacting performance as well as processibility, durability, and toxicity. Most methods for AuNR synthesis are aqueous based, and use a large excess of cetyl trimethylammonium bromide (CTAB) to ensure anisotropic growth. While the weakly interacting CTAB bilayer on the AuNR surface provides electrostatic stability and affords subsequent displacement reactions, its removal is challenging, and the inability to transfer stable AuNRs to organic solvents significantly restrict approaches to chemically modify the surface. CTAB exchange to organic solvents by phase transfer agents can be used; however these tightly associated ligands limit subsequent chemistry. Also, prevention of irreversible aggregation during the exchange require multiple centrifugation steps that inevitably causes loss of a large fraction of AuNRs. In this study, we demonstrate that the polarity of colloidal AuNR can be modulated by varying the structure of the CTAB assembly through its bulk concentration. Below the critical micelle concentration, CTAB exists as dissolved molecules and multilayers absorbed on AuNR surface. Reducing the CTAB concentration preferentially removes molecules from the surface assemblies, transforming them from a dense bilayer to a sporadic monolayer – the latter resulting in irreversible aggregation. At a concentration between a bilayer and monolayer however, the aqueous stable AuNRs will phase transfer to various organic solvents without ligand exchange. This is likely due to a structural inversion of the defective CTAB bilayer. The utility of stable organic disperse of AuNRs via a weakly coordinated surfactant is demonstrated by increasing grafting density of functional moieties for targeted surface modification and robust fabrication of polymer nanocomposites.

The demands for materials which integrate more than one functional imaging or therapeutic unit are of increasing interest for biomedical applications. Here, we present the step-by-step preparation of asymmetric and optically active particles, namely Gd₂O₃@Ag, Gd₂O₃@Au, SiO₂-N₃@Au and SiO₂-SH@Au via simple magnetron sputtering approach. Successful attachment of plasmonic nanoparticles to the surface of metal oxide spheres without necessity of a potentially toxic inter-adhesive layer was proven by optical methods as well as X-ray photoelectron spectroscopy. The combination of optical and magnetic properties as present inGd₂O₃@Ag and Gd₂O₃@Au Janus-type particles leads to dual-imaging probes for optical and magnetic resonance imaging. In addition, functional groups, such as azide groups were linked to the surface of silica particles previous to Au nanoparticle attachment. Subsequent side-selective click reactions with 5-FAM were successfully performed as demonstrated by UV-vis measurements. All described systems exhibited excellent long-term stability and can therefore be considered as promising candidates for theranostic applications.

Ratiometric sensing strategy relies on the ratio of the two photoluminescence (PL) signals originating from the same nano-object for detecting the changes in the surrounding media. Recently, such dual-color emission has been demonstrated in semiconductor colloids, where the PL signal from a quantum-confined domain was complemented with the secondary emission from transition metal ions or a bulk-like structure. Here, we report on the development of dual-color nanocrystal colloids featuring a combination of two quantum-confined emitters within the same nano-object. The reported morphology relies on double-well core/barrier/shell arrangement, where zero-dimensional excitons of the core component (PbS) can coexist with two-dimensional excitons of the shell domain (CdSe). As a result, the core and shell emission bands can be independently tuned across 880–1500 nm and 600-650 nm spectral windows, respectively. A CdS potential barrier at the PbS/CdSe interface was designed to suppress the energy and charge diffusion between the two domains allowing both emission bands to exhibit quantum yields over 10%. Fabricated colloids were demonstrated as dual-color probes for sensing the redox environment, where both the energetics and the timing of photoinduced charge transfer to an add-on analyte could be inferred from the ratiometric measurements

The future with functionalized nanoparticles (NP) acting as building blocks depends on the understanding of the nanoparticles behavior in the application process. Some theoretical and experimental studies reveal that the organic layer (OL) around the nanoparticle are able to swollen with good solvents. The dynamic of the OL surrounding the NP can mold the superlattice structure by changing the interparticle forces in the self-assembly process. Actually, the theories to describe the OL behavior use polymer concepts and cannot describe the molecules modifications because of the several mechanisms involved in the assembly process. Generally, the experimental studies are made with transmission election microscopy (TEM) images, however, to fully understand the NP for advanced applications, the NP need to be studied directly in solution. The characterization of NPs in solution is difficult and the techniques used for this purpose are the dynamic light scattering (DLS) and the small angle x-ray diffraction (SAXS). In this work, we track the ZrO2 (5 nm) capped with oleic acid NP volume fraction (φ) changes in solutions with hexane and toluene using a distinct approach, the viscometry and the intrinsic viscosity by the Einstein Viscosity Theory. With this approach we were able to calculate the volume fraction by density and viscosity measurements, the difference in φ are correlated with the organic layer modification. To validate this approach, the NP hydrodynamic radius (Rh) calculated are compared with the SAXS and DLS techniques.

The importance of stabilizing ligands cannot be understated for the colloidal synthesis of nanoparticles as well as their dispersion and assembly into macro-structures such as electrodes for alternative energy applications. We have recently demonstrated a novel all-inorganic ligand approach to pure Pt and Pt-Bi nanoparticle synthesis where surface-adsorbed Sn serves as both reducing agent and stabilizing ligand, producing remarkably monodispersed nanoparticles. By eliminating the need to remove organic surfactants prior to nanoparticle incorporation into electrodes, we were able to use electrostatic assembly to achieve well-defined nanoparticle dispersions in aqueous media in contrast to the aggregated structures and flammable and toxic organic solvents common in the field. The approach has allowed us to elucidate the nature of structure sensitivity for electrocatalytic oxygen reduction reaction in acidic and alkaline media. In this paper, we provide a detailed investigation of the evolution of surface-adsorbed Sn-Pt and Sn-Bi ligand interaction during nanoparticle growth. We show that surface adsorbed SnCl₃^– exists as pyramidally coordinated to the Pt and Bi surface through Sn-Pt and Sn-Bi bond formation, resulting in a distorted tetrahedrally coordinated Sn-moiety.. Furthermore, we show the shift in the bond charge distribution as the Pt and Bi are reduced from salt to their metallic states. Direct evidence for the distorted tetrahedral coordination of M-SnCl₃^- and the shift in Sn-M bond charge emerges from the ¹¹⁹Sn Mossbauer quadrupole splitting (QS) and Isomer-shift (IS) respectively. The evolution of the bond energy corresponds to the growth of the nanoparticle (as measured using using small- and wide-angle x-ray absorption spectroscopy) and its transition from the atomic cluster to single crystal state. Evolution of the structure and chemistry of this surface complex has never before been demonstrated and our work is the first to identify the strength of the Sn-Minteraction in these systems. Such an understanding of nanoparticle surface chemistry will permit extension of this technique to other metals and macro-structures.

Revolutionary as graphene, the inorganic two-dimensional (2D) nanostructures intrigue the scientific community, by offering large variability of chemical compositions, mechanical rigidity, possible engineering of electronic structure and tunability of energy band-gap. Thus, the inorganic 2D nanostructures are potentially useful for various opto-electronic applications. The current research focuses on the development of synthetic procedures for the growth and phase control of 2D semiconductor nanostructures, In₂X₃ (X=S) in a shape of nanoplatelets (NPLs). The materials were prepared using one step colloidal synthesis process. Metal-thiolate forms in the initial stage of reaction, which effectively acts as the precursors to decompose into γ-In₂S₃ nanocrystals. The size and shape of the γ-In₂S₃ NPLs can be easily controlled by varying the reaction growth temperature and the decomposition rate of Indium-thiolate. Additional heat supply lead to phase transition obtaining the defect spinel phase β-In₂S₃. The crystal structure and phase identities were confirmed by X-ray diffraction and HR-TEM analyses. The possible formation mechanism for γ-In₂S₃ NPLs with two anisotropic shapes is presented on the basis of the nanocrystals growth directions and the synthesis conditions. The HR-TEM images recorded at various synthesis stages indicated that the synthesized individual NPLs naturally restacked owing to mutual van der Waals (vdW) forces, and eventually led to moiré patterns with lattice fringes. Analysis of the FFT data supplied the number restacked hexagonal NPLs and the relative rotation angle between adjacent layers.
The absorption spectra and the Tauc analysis proposed the existence of a direct wide band-gap in both γ-In₂S₃ and β-In₂S₃ NPLs around ~ 3.5 eV -3.7 eV, in contradiction to a situation found in the analogous bulk materials. Furthermore, emission spectra were dominated by an intense exciton band slightly Stokes shifted from the absorption band-edge, with additional contribution from a defect radiative recombination at lower energies. The relative defects emission intensity change greatly during the reaction progress and especially in the course of phase transition due to defects migration and atomic rearrangement. The Raman spectra of the γ-In₂S₃ and β-In₂S₃ showed seven and sixteen resonance modes respectively, compatible with predicted transitions based on the corresponding crystal lattice symmetry. Overall, the preliminary results mentioned here revealed the phase transition process of γ-In₂S₃ to β-In₂S₃, and the formation of high quality and shape controlled 2D NPLs with unique optical properties emanated from the size confinement and morphology, like, direct band-gap, radiative exciton recombination and defects photoluminescence, with direct benefit for their for their integration in new and emerging solar cells, light sources and photodetector devices.

The current study invastigates the magneto-optical properties of CdSe/CdMnS core/shell colloidal nanoplatelets (NPs). Replacing a single or a few cations of the host semiconductor nanocrystal with magnetic dopants introduces new physical properties (e.g., giant magnetization and g-factor), which are of potential value for a spin-based applications. The studied NPs consisted of a CdSe core, covered by four monolayers of CdMnS shell, creating a quasi-type-II electronic nanostructure. The material's design enabled the alignment of the dopant ground and first excited states nearly in resonance with the band-edge levels of the host semiconductor,thus, inducing a strong sp-d spin exchange interaction. The magneto-optical properties were investigated by probing the single exciton recombination emission, using a micro-photoluminescence in the presence of an external magentic field (B₀), as well as continous-wave and time-resolved optically detected magnetic resonance (ODMR) spectroscopy. The ODMR spectrum was characterized by a sextet manifold, revealing the existence of a single Mn⁺² dopant in the vicinity of a single photo-generated exciton.
The ODMR observations were supported by a theoretical model, based on the effective mass approximation of the NPs electronic states, perturbed by the relevant exchange interactions: electron-Mn⁺², hole- Mn⁺² and electron-hole, with a dependence on the core/shell heterostructure design. The simulation revealed the physical constants, such as the g-factor of the electron and hole, g_e,xx= g_e,yy= 1.94, g_e,zz=2.1, and g_h,xx= g_h,yy= -0.88, g_h,zz=-1.0, respectively. The host-guest exchange energies are also extracted, being J_s-d = 1.8975 meV and J_p-d = -1.8942 meV. To the best of our knowledge the ODMR method was never been applied before for the study of magnetically doped colloidal nanostructures, while the information about selective coupling of specific carrier with magnetic spins is of a paramount importance in the engineering the magneto-optical properties.

Biomolecules are central to their extraordinary effectiveness for biological functions in life. These natural nanotools reinforce the rational fabrication of nanomaterials for many applications in fields, such as plasmonics and biomedicine. Scientists have utilized DNA beyond its biological roles for the preparation of a myriad of self-assemblies or metalized materials while there are issues of mutual concern: the self-assemblies of biomolecules have limited practical uses even though they look fantastic. Moreover, the metallization of the self-assemblies into applicable inorganic materials is currently limited by cost and difficulty, as keeping materials into patterns smaller than 100 nm in size. We aimed to develop groundbreaking technology of highly facile preparation of nanometals with direction-following, shape- and size-controlled architectures via regulation of metallic atom crystallization by DNA. This technology unlocks the toolbox full of smart biomolecules for the synthesis of architecture-programmable metallic nanomaterials. Importantly, the technology will solve one of the most fundamental but difficult problems of bottom-up synthesis: how to tailor nanomaterial’s structure with molecular level precision of design. Hereby, unprecedented nanostructures (e.g. asymmetric metallic nanoparticles) can be generated in extremely specific properties, which holds broad appeal for material scientists and nanotechnologists.

A suspended particle device adapted for controlling the transmission of electromagnetic radiation has become an area of considerable focus for smart window technology, due to their desirable properties such as instant and precise light control and cost-effectiveness. Here, we demonstrate transparency tunable device in response to electric stimuli using spherical colloidal nanoparticles and their assemblies. The observed transparency is dynamically tunable in response to simple and relatively small (1-5 V) external electrical voltage with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby to modified photonic band structures, confirmed by finite-difference time-domain simulations of Maxwell’s equations. Interestingly, in addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe₂O₃/SiO₂ core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe₂O₃/SiO₂ nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli. The use of colloidal nanoparticles along with variation in the material composition, the particle size, and device thickness provided multiple pathways to tune the transparency as well as color spectrum.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The advantages of quantum dots (quantum-confinement effects) and perovskites (high emission efficiencies and low production costs) are combined in all-inorganic cesium lead halide perovskite nanocrystals (IP-NCs, CsPbX₃ with X = Cl, Br, I) – a new promising material for photovoltaic and optoelectronic applications. CsPbX₃ colloidal nanocrystals dispersed in non-polar solvents show high quantum photoluminescence yields of 50-90%, narrow emission bands, and emission tunability along the whole visible spectrum. However, this material presents two main drawbacks: (i) IP-NCs are breakable in polar solvents, and (ii) different emission color IP-NCs cannot be mixed or exposed together because they suffer halide exchange which brings to composition homogenization. In order to enhance their properties, we report on the successful encapsulation of IP-NCs in solid lipid structures of stearic acid. The encapsulated IP-NCs remain stable for a period longer than 2 months and anion-exchange is fully arrested. In this way, an easy-to-handle material, with a non-toxic carrier and free from organic solvents has been obtained, increasing the application fields for IP-NCs toward, e.g., ink-jet printing for optoelectronics or security markers and imaging applications with different colors to cover the human eye spectral range.

Ag nanowires (AgNWs) hold great promise for applications such as transparent and flexible displays, solar cells, chemical/biological sensors, photonic circuits and scanning probe microscopies, but their susceptibility to damage from oxidation significantly limit their device life-time and commercialization potential. To address this challenge, we developed a single-step, room-temperature, solution-phase, etch-free deposition technique to grow an ultra-thin, epitaxial layer of Au coating on the AgNW surface, which acts as a reliable and economical anti-oxidation barrier to provide long-term device stability. The Ag@Au core-shell NWs are stable in air and in physiological buffer solution for months. Transparent flexible electrodes fabricated from Ag@Au core-shell NWs shows steady performance in air at 80°C and 100% humidity for 2 months, while those fabricated with bare AgNWs died out within 2 weeks. The ultra-thin Au coating did not introduce significant Au fluorescence in the SERS spectrum, making them feasible for SERS and plasmonic sensing applications. It was also demonstrated that the ultra-thin Au coating does not have adverse effects on the propagation and coupling of surface plasmon polaritons (SPPs) in AgNW waveguides, and the device performance remains stable for weeks, a significant improvement against uncoated AgNW. AgNW-AFM probes are low-cost alternatives of high-aspect-ratio, high-resolution AFM probes, but the major drawback is their short shelf-life (typically a couple of weeks). It was demonstrated that the Ag@Au core-shell NWs functions similarly to bare-AgNW, with a much longer shelf-life for at least 4 weeks in the air.

It remains a challenge to synthesize Au@Ag nanocubes in an aqueous system with sharp corners, edges and tunable aspect ratio in the past decade. Here, sharp-featured Au@Ag core/shell nanocuboids have been successfully synthesized in the aqueous system with tunable aspect ratio from 1 to 3. By chaging the solvent polarity, the assembly structure can be tuned from micrometer order 2D structure with different surface roughness to 3D structure. In addition, simulation and experimental results demonstrated that the sharp feature and in-cuboid, out-of-cuboid LSPR coupling of Au@Ag core/shell nanocuboids enabled high SERS activities. The ultrasensitive detection of single-point mutations of TDP-43 and IAPP8-37 proteins was demonstrated at 10 pM for the first time. This could be a general strategy for the single-point mutation detection of proteins.

Radiative cooling is a process where a material loses heat due to strong emission of photons in the mid-infrared spectrum and enhanced light scattering in the solar region. This process would allow cooling of materials below the ambient temperature under the sun without the use of electricity and therefore would significantly reduce energy consumption. In this work, we have demonstrated a passive radiative cooling of disordered silica microsphere coatings below the ambient temperature while exposed to direct sunlight. To fabricate the coatings, silica microspheres are deposited by colloidal sedimentation method and spray coating method. In the first method, silica colloidal stability is disrupted by addition of KCl solution. The instability causes the colloids to sediment, creating a disordered uniform coating. In the second method, much like commercial painting, the colloidal solution is forced through a spray nozzle and deposited onto a substrate. Scanning electron microscopy images and autocorrelation analyses show that the resulting structures are disordered without short- or long-range order. Optical measurements also indicate that the coatings produced under optimal conditions have a short transport photon mean free path of approximately 4-8 μm in the solar spectral region. These coatings also exhibit high emissivity above 95% in the atmospheric transparency window. These results suggest strong photon scattering properties in the visible region, while providing a strong thermal emission. Such films would enable effective radiative cooling. To test the cooling performance, we apply this film on top of a black substrate and expose the material to a direct sunlight during the summer in New Mexico. Temperature measurement of the sample shows that our coating reduces the substrate temperature below that of the ambient air by as much as 12 °C during daytime. Similar testing with a commercial solar-rejection paint indicates that the silica coating performs better than the commercial paint by 4.7 °C on average. We will further discuss plans to improve the performance of the coating using polymer spheres in this presentation.

Copper indium sulfide (CIS) QDs are attractive as labels for biomedical imaging since they have large absorption coefficients across a broad spectral range, size- and composition-tunable photoluminescence from the visible to the near-infrared, and low toxicity. However, the application of NIR-emitting CIS QDs is still hindered by large size and shape dispersions and low photoluminescence quantum yields (PLQYs). In this work, we develop an efficient pathway to synthesize highly luminescent NIR-emitting wurtzite CIS/ZnS QDs, starting from template Cu_2-xS nanocrystals (NCs), which are converted by topotactic partial Cu⁺ for In³⁺ exchange into CIS NCs¹. These NCs are subsequently used as cores for the overgrowth of ZnS shells (≤ 1 nm thick). The CIS/ZnS core/shell QDs exhibit PL tunability from the first- to the second NIR window (750 - 1100 nm), with PLQYs ranging from 75% (at 820 nm) to 25% (at 1050 nm), and can be readily transferred to water upon exchange of the native ligands for mercaptoundecanoic acid. The resulting water-dispersible CIS/ZnS QDs possess good colloidal stability over at least 6 months and PLQYs ranging from 39% (at 820 nm) to 6% (at 1050 nm). These PLQYs are superior to those of commonly available water-soluble NIR-fluorophores (dyes and QDs), making the hydrophilic CIS/ZnS QDs developed in this work promising candidates for further application as NIR-emitters in bioimaging. The hydrophobic CIS/ZnS QDs obtained immediately after the ZnS shelling are also attractive as fluorophores in luminescent solar concentrators.

1. Xia, C.; Meeldijk, J. D.; Gerritsen, H. C.; de Mello Donega, C. Chem. Mater. 2017, 29 (11), 4940-4951.

Thermal decomposition is a promising route for the synthesis of highly monodisperse magnetite nanoparticles. The simplicity of the synthesis however is counterbalanced by the complex chemistry of the system, e.g. the interplay of the reagents with the reaction variables that determine the final particle size and dispersity.
Control over nanoparticle size can be obtained by adjusting the reaction parameters, namely precursor concentration or heating rate. In this contribution, we show that in the size-controlled synthesis via the precursor concentrate, the size does not monotonically increase with increasing the precursor concentration but passes through a maximum with increasing precursor concentration. The observation of two different size regimes is closely related to the amount of surfactant. Next, we present a combined experimental and theoretical study on the influence of the heating rate on crystal growth, size, and monodispersity of iron-oxide nanoparticles. Monodisperse nanoparticles were synthesized with sizes varying from 6.3 nm to 27 nm simply by controlling the heating rate of the reaction. Using numerical calculations based on the classical nucleation theory and growth model, we identified the relative time scales associated with the heating rate and precursor to monomer (growth species) conversion rate as a decisive factor influencing the final size and dispersity of the nanoparticles. Furthermore, we show that the nanoparticle particles show size-dependent but superior superparamagnetic properties at room temperature.

Germanium (Ge) is one of the extensively studied semiconductors possessing higher absorption coefficient and carrier mobilities than silicon. Because of low-cost and its compatibility with existing CMOS processing methods, germanium has found applications in many electronic and in optoelectronic devices. Recently, it has also been realized that Ge is well suited as an anode for Li and Na ion batteries. However, material’s inherently inefficient light absorbtion or large volume change during lithiation/delithiation process impede its further use in optical and energy storage applications. Although alloying of Ge with Sn was concluded to be potentially beneficial for addressing both issues, the finite solubility (< 1% of Sn in Ge) and large lattice mismatch between Ge and Sn made it challenging to prepare SnGe alloys with any significant degree of element mixing. Exploiting the tolerance of nanosize crystals to withstand large amount of strain, we have developed a facile synthetic approach to Sn_xGe_1-x nanoalloys with almost entire compositional range of alloying, with tin content up to 95 %, while still retaining the cubic phase of the material and the homogeneous distribution of both elements within particles. Some insights in the mechanism for the alloy formation have also been elucidated. The synthesized nanoalloys are moderately thermally stable, with phase segregation starting at temperatures above 200 °C via tin diffusion out of the particle interior. Deliberate and controlled sulfudization of the nanoalloy surface via the deposition of a thin layer of sulfur increases thermal stability of protected particles up to 500 °C. The presence of more cationic Sn and Ge atoms on the particle surface after sulfur treatment enables the ligand exchange from the non-polar long-chain alkyl ligands to shorter and more polar hydrazine or even iodide, thereby rendering particles processible for the preparation of thin films with close interparticle contacts. The details of the synthesis methods, mechanistic studies, structural and optical characterizations will be presented and discussed

To meet requirements of low cost, hole-conductor-free fully printable mesoscopic perovskite solar cells (MPSCs) using carbon counter electrode are invented. Devices with excellent long-term stability and a certified PCE of 12.8% are fabricated by mixing MAPbI₃ with 5-ammoniumvaleric acid iodide (5-AVAI), which make hole-conductor-free fully printable MPSCs have huge potential for industrialization. Different to abundant additives in traditional MPSCs, including butylphosphonic acid 4-ammonium chloride, 1,8-diiodooctane(DIO), MACl, NH₄Cl, and KCl et al., only very few additives, LiCl and tetrafluoroboric acid (HBF₄) are successfully applied in hole-conductor-free fully printable MPSCs. By incorporating iodide benzylamine (BAI) into the methyl ammonium iodide (MAI) solution, a simple and effective method is developed for enhancing the performance and long-term stability of hole-conductor-free fully printable MPSCs. BA-MAPbI₃ based hole-conductor-free fully printable MPSCs achieve a PCE of 12.69%, in comparison with 6.43% of the control devices. The introduction of BAI reduces defect concentration in perovskite films and induces better pore filling and better contact with TiO₂ scaffold, which results longer exciton lifetime and higher quantum efficiency of photo-generate charges in devices. Furthermore, BA-MAPbI₃ perovskite solar cells show excellent stability, they keep 80% of origin power conversion efficiency for over 500 hours in ambient air under continuous light.

Due to efficient and tunable emission properties, semiconductor core/shell nanocrystals (NCs) are of high technological importance for solid-state lighting and bio-medical applications. Optical properties of core/shell nanomaterials can be improved by engineering a graded protective shell. Relaxed lattice interfaces between core and shell materials lead to smaller density of interfacial defects and lower Auger non-radiative recombination. At the same time, the absence of an atomically defined interface makes determination of the atomic structure of graded core/shell NCs a complicated task.
In this work, we demonstrate an experimental approach to quantify nanocrystal structure, selecting graded Ag-In-Se/ZnSe core/shell nanocrystals as a proof-of-concept material. We determine the average radial distribution of elements with sub-nanometer resolution using anomalous small-angle X-ray scattering (ASAXS) analysis, supported by electron microscopy. This information is combined with retrievals of the average shape of NCs obtained from ab initio shape retrieval SAXS model and crystal structure information from wide-angle X-ray scattering (WAXS) to create atomic reconstructions of the NCs. We show that this detailed understanding of structure enables quantitative studies of solid-state diffusion in the NCs and lattice relaxation at the core/shell interface. Finally, we link these results to the luminescence efficiency of graded core/shell NCs and propose design rules for optimal shell structure and record-luminescent core/shell nanocrystals.

Semiconductor nanocrystals – which can behave electronically as quantum dots – are a versatile way to turn incident light into fluorescence, electricity, and storable fuels because of their size-tunable properties. Appropriate surface termination and linking chemistry can be used to control the flow of energy and charge within and among nanocrystals and molecules, as has been demonstrated in the case of ratiometric chemical sensors and optoelectronic devices formed of colloidal quantum dots. Despite this promise, the nanocrystal surface is complex and dynamic, subject to ligand exchange with surrounding medium. Purification methods and characterization techniques that permit assemblies of increasing complexity to be formed in a highly repeatable and verifiable fashion are key to revealing the full potential of colloidal nanocrystals in these and other areas.

The Greytak group has used gel permeation chromatography (GPC) as a means to separate nanocrystals from small molecules. We have shown that GPC is an effective way to isolate nanocrystals with low and consistent ligand populations without requiring a change in solvent, and to drive nanocrystal ligand exchange reactions in situ through continuous separation of soluble products. Our lab has demonstrated these concepts using cadmium selenide-based nanocrystals. A current challenge is to translate the progress that has been made in CdSe and other II-VI nanocrystal surface chemistry and photophysics to inorganic semiconductors that can meet 21^st century challenges. This includes materials that can be sustainably scaled for efficient solar energy conversion, and materials with diminished use of toxic elements. In this talk I will describe ongoing work, enabled by GPC, to expand the material scope for detailed understanding of nanocrystal surface chemistry.

Controlling the assembly of nanoparticles into devices is a huge field, with approaches ranging from electrostatic, capillary-flows, DNA binding and optical tweezers all showing some efficacy in achieving nanoparticle assembly. Bringing these abilities into an industrial range hinges on building a thorough understanding the driving forces that nanoparticles heed. In our pursuit of more directed methods of nanoparticle assembly, we have discovered that electrostatically charged and hydrophilic nanoparticles will spontaneously assemble onto patterned regions of hydrophobic molecular monolayers on surfaces. We are able to show this is possible with single particle resolution in less than one minute, whilst demonstrating that assembly across more macroscopic length-scales can be achieved simultaneously¹. We also find that the mechanism that drives this can be inhibited through control of the pH in the colloid. Whilst not fully understood, our working hypothesis for this process is that the water is dewetted from between the interface of the nanoparticle and the hydrophobic surface, in spite of the hydrophilic nature of the nanoparticle. This is unanticipated form of nanoparticle assembly, with previous findings determining that hydrophobic-hydrophilic interfaces would not result in breakdown of the hydrophobic barrier², and could indicate a breakdown of common scientific understanding for nanoscale forces.
References:
1. Porter, B. ~F., Pacios, M. & Bhaskaran, H. Hydrophobic-hydrophilic interactions drive rapid nanoparticle assembly. ArXiv e-prints (2017).
2. Zhang, X., Zhu, Y. & Granick, S. Hydrophobicity at a Janus interface. Science 295, 663–666 (2002).

Nanotechnology is of great importance in various fields including biochemistry, catalysis, medical research, semiconductors etc. Synthesis of various nanoparticles through range of routes for different applications have been extensively demonstrated by researchers across the world. Size and shape of the nanoparticles is generally controlled through solution chemistry which involves selection of solvents, surfactants, ligands, reaction conditions, and many more. Semiconducting nanoparticles are also being synthesized and studied for its applications in thermoelectric, photovoltaic, sensor and many other fields.
Amine-thiol chemistry is being extensively used for fabricating thin film photovoltaics. However, in this work we will present a new approach of using this chemistry to synthesize binary, tertiary and quaternary semiconducting nanoparticles. Amine-thiol system can dissolve various metal salts and chalcogens depending on proper selection of amine and thiol pair. Taking advantage of its dissolution capability, we synthesized Copper Indium Gallium Sulfide (CIGS) and Copper Indium Sulfide (CIS) nanoparticles. These specific syntheses are carried out at high temperatures, which allows all metal precursors to react with each other forming desired phase of nanoparticles. Also, the ratio of each metal component in final CIGS or CIS nanoparticle can be varied by just selecting appropriate amount of metal precursors in the starting reaction solution. Various conditions for nanoparticle synthesis have been tested which resulted in either amine or thiol capping on the nanoparticles. Choice of these capping will give a colloidal dispersion of these nanoparticles in either polar or non-polar solvents depending on specific application. Photovoltaic devices fabricated from CIGS and CIS nanoparticles synthesized from this route will also be presented in this talk.
While proposing high temperature route to synthesize CIGS and CIS nanoparticles from amine-thiol system, we also developed a novel room temperature synthesis route for lead chalcogenide nanoparticles. Lead chalcogenide nanoparticles are being used in various applications including quantum dot solar cell (PbS, PbSe) and thermoelectric systems (PbSe, PbTe) since past many years. In our work, we have demonstrated quantum confinement of self-assembled PbS nanoparticles synthesized from this amine-thiol room temperature route. Our work also shows size control for both PbS and PbTe nanoparticles and their self-assembled microstructures. Thermoelectric properties measured for PbSe nanoparticles synthesized through this route has also shown comparable results with those reported in the literature.
In conclusion, we present a novel route to synthesize and tailor an array of semiconducting nanoparticles using amine-thiol chemistry at different temperatures for various applications.

Owing to its excellent visible light absorption, high charge-transport ability and facile modification, porphyrins, especially metalloporphyrins, have extensively been used as light-harvesting antennas or photocatalysts to stimulate nature photosythesis. Subject to easy to photocorrosion and difficult to recover as well as its limited solubility, porphyrin single molecules have always been employed to synthesis self-assembled nanocrystals or coupled with semi-conductors(TiO₂, CdSe) and noble metal nanoparticles(Pt, Au) or to fabricate other porphyrin-based materials-such as metal-organic frameworks, covalent-organic frameworks and porphyrin-linked polymer materials to better its dispersion or to improve the transportation and separation of the light-induced electrons which further enhance its photocatalytic activities.
Graphite carbon nitride (g-C₃N₄), a new type of metal-free organic polymeric semiconductor, by virtue of its suitable bandgap and visible-light absorption, unique electronic structure and chemical stability, which can be easily available by pyrolysis of urea, melamine, dicyandiamide and other CN-containing materials, has been broadly applied to many applications such as water splitting, CO₂ reduction and organic pollutants degradation.
We developed a convenient and efficient method to fabricate the g-C₃N₄ doped with porphyrins via only one simple step copolymerization in which the porphyrin or metalloporphyrins crosslinked with g-C₃N₄ skeleton as single moleculars, forming heterojunctions which was attributed to the rapid interfacial charge transfer and separation of photo induced charge carriers, as evidenced by the PL spectroscopy. In addition, this method can easily introduce different metal atom as the catalytic site to increase the catalytic efficiency. When the hybrid material were employed as visible light photocatalyst for generation of H₂ from water and reduction of CO₂ into CH₄, they all exhibited excellent catalytic activities which more than 3 times higher than pure g-C₃N₄.