The CO poisoning of metal nanocrystals (NCs) in the methanol oxidation reaction (MOR) is one major hurdle toward the commercial uses of fuel cells. In this work, Fe1-xPtRux NCs with different alloy extents were synthesized by a cation redox reaction in a solution phase. The sizes and structures of the NCs were examined, and also their compositions and alloying extents were carefully analyzed by X-ray absorption spectroscopy (XAS). Measurements of ternary Fe35Pt40Ru25, Fe31Pt40Ru29, Fe17Pt40Ru43, binary Fe58Pt42 and PtRu NCs showed that the ternary Fe1-xPtRux NCs exhibit superior catalytic ability to withstand CO poisoning in MOR among all NCs. Also, the Fe31Pt40Ru29 NCs had the highest alloy extent and the lowest onset potential among the ternary NCs. Furthermore, the origin for the superior CO resistance of ternary Fe1-xPtRux NCs was investigated by determining the adsorption energy of CO on the NCs surfaces and the charge transfer from Fe/Ru to Pt using a simulation based on density functional theory. The simulation results suggested that by introducing a new metal into binary PtRu/PtFe NCs, the anti-CO poisoning ability of ternary Fe1-xPtRux NCs was greatly enhanced because the bonding of CO-Pt on the NC&’s surface was weakened. Overall, our experimental and simulation results have indicated a simple route for the discovery of new metal alloyed catalysts for fuel cell applications.

Supported catalyst materials are critical components in a variety of energy conversion and storage applications. In particular, there is an great amount of interest in nanoscale support structures due to a dramatic increase in surface area, leading to improved charge-transfer kinetics. For example, in the field of photoelectrochemical water splitting, high-surface area structures such as nanowire arrays are being explored to reduce the overpotential associated with the electrochemical reaction. On the photocathode side, noble-metal catalysts such as platinum are known as excellent catalysts for the hydrogen evolution reaction (HER). However, due to high costs and low elemental abundance, there is a significant effort to search for alternate catalyst materials. Another approach to reduce costs would be to dramatically reduce the amount of Platinum loaded on the surface, while maintaining catalytic activity.
In this study, we explore the lower limits of platinum loading by utilizing Atomic Layer Deposition (ALD) to deposit highly conformal Pt nanoparticles on the surface of Si nanowires. Nucleation and growth of Pt nanoclusters during the initial ALD cycles facilitates control of the size and density of the Pt particles uniformly along the entire NW surface. The catalytic performance of small Pt particles for photoelectrochemical hydrogen evolution is evaluated, and the properties of the catalyst particles are further characterized by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The results suggest that ultra-low loading of Pt nanoclusters during the initial ALD cycles can provide sufficient catalytic performance for the HER, which could dramatically reduce the overall material cost while maintaining the desirable catalytic properties of Pt.

Gold nanoparticles exhibit a catalytic activity in many chemical processes.1 Most of the reactions are size-dependant, i. e. the specific activity depends on the average gold particle size. Generally, the activity increases when the particle size decreases, with a marked increase below 5 nm, which strongly supports the role of surface gold atoms in the reactions. But for sub-2 nm particles, the origin of the catalytic power is still unclear and under intense debate. Fundamental investigations on the structure-catalytic activity relationships still lag behind, partly due to the polydispersity issue of gold nanoparticles. Indeed, polydisperse particles obscure the interesting size-dependent catalytic activity of nanogold and preclude an in-depth understanding of the origin of this size dependence.
Recently, atomically well defined thiolate-capped Au nanoclusters (denoted as Aun(SR)m) have been successfully isolated and their catalytic properties have been demonstrated.2 These monodispersed functionalized clusters, with gold core between less than 1 nm and more than 2 nm, hold promises as a new generation of catalysts. More importantly, these nanoclusters permit in-depth studies on the subtle correlation of structure and catalytic activity, since they are well defined and their crystallographic structures start to be solved.3
To investigate the influence of the size, the type of ligands at the surface and also the support effect, different nanoclusters have been synthesized. New clusters made of 4-aminothiophenol (HSPhNH2) have been synthesized, such as Au25(SPhNH2)17, and fully characterized by mass spectrometry, X-ray diffraction and XPS.4 Moreover these clusters exhibit absorption bands and paramagnetic behaviour related to their molecular state. Catalytic activity for oxidation of alkene and alcohol derivatives of these colloidal or supported clusters were investigated and compared to the commonly used Aun(SCH2CH2Ph)m nanoclusters. At the opposite of the bare gold nanoparticles, the presence of the ligands around the clusters leads to a much better selectivity of the product.
(1) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem.-Int. Edit. 2006, 45, 7896.
(2) Jin, R. C.; Zhu, Y.; Qian, H. Chem. Eur. J. 2011, 17, 6584.
(3) Zhu, Y.; Qian, H. F.; Zhu, M. Z.; Jin, R. C. Adv. Mater. 2010, 22, 1915.
(4) Lavenn, C.; Albrieux, F.; Bergeret, G.; Chiriac, R.; Delichère, P.; Tuel, A.; Demessence, A. Nanoscale DOI: 10.1039/C2NR32367B.

The size of the NPs is one of the critical parameters affecting the overall photo-oxidation rate. Nobel metal nanoparticles (NPs) in subnanometer size range may greatly enhance the photocatalytic reactions. We have developed novel catalysts based on noble metal-semiconductor systems, as a new approach to improving the photocatalytic activity to address both environmental and energy issues. Both gas phase and liquid phase oxidation reactions were studied to assess the photoactivity enhancement by noble metal NPs in several size ranges. In particular, the subnanometer range of noble metal NPs (e.g. Au and Pt) was explored for phenol degradation, NO2 oxidation and hydrogen production reactions. The structure of the deposited NPs was characterized by combining microscopy (TEM, STEM, STM) and first-principles electronic structures calculations. We have also explored a correlation between the photocatalytic activity enhancement and the size and shape of the NPs in various oxidation reactions.

The H2-O2 and Li-O2 systems are generating a great deal of interest because they are the key to developing new alternative energy systems - fuel cells and batteries that theoretically possesses a specific energy 5-10 times that of a conventional Li-ion battery. We begin by drawing analogies between the oxygen electrode reactions in the aqueous electrolyte, in particular alkaline electrolyte, and the aprotic (Li+ free) non-aqueous electrolytes. Employing well-characterized single crystal surfaces we will demonstrate that the ORR in these electrolytes is governed by the same principles that dictate the reaction mechanisms in protic solvents. We will employ in situ and ex situ techniques to both quantitatively and qualitatively determine the reaction products; namely the superoxide and peroxide intermediates. In the case of Li-O2 this will be used to determine the stability of the various ethers and carbonate solvents toward the superoxide species. Extending this study to Li+ based solvents will be used to further determine the products formed, their stability, their strength of adsorption to the electrode surface, and the measure of reversibilities. In addition, to bridge the gap between the “water battery” (fuel cell harr; electrolyzer) and the Li-air battery systems we demonstrate that this would require fundamentally new knowledge in several critical areas. We conclude that understanding the complexity (simplicity) of electrochemical interfaces would open new avenues for design and deployment of alternative energy systems. This is only a beginning of our challenging but exciting journey on the “energy highway,” and continued progress will require further innovations in the study of electrified liquid/solid interfaces.

Naturally occurred folding and unfolding systems such as 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 govern 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 target function. To date, fabrications of active nanostructures have been conducted at ambient pressure and largely relied on these specific chemical or physical interactions. Here we show using stress-induced assembly method as an artificial tool, we recently demonstrated, we can emulate natural folding and unfolding processes to explore energy landscaping that govern local interactions, to design new classes of active materials with structure and function that are not attainable for current materials, and to investigate new property resulted 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, CdSe, etc) including nanorod, nanowire, nanosheet, and nanoporous network can be fabricated. Guided by computational simulations, we are able to rationalize the PDA of nanoparticle arrays for predictable nanostructures. PDA method mimics embossing and imprinting manufacturing processes and opens exciting new avenues for study folding and unfolding of active materials during compression (folding) and pressure release (unfolding). Exerting pressure-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.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Zinc Oxide (ZnO) is one of transparent conducting oxides that have received a lot of recent attention due to its wide direct band gap (~3.37 eV), large exciton energy (60 meV), good thermal and chemical stability, low toxicity and high biocompatibility. Its nanostructures have a wide range of potential applications including optoelectronic devices, sensors, nanogenerators and transistors. Various deposition techniques have been used to deposit ZnO nanostructures but none has directly produced single-unit-cell thick nanosheets.
Here, we report single-unit-cell thick (0.56 nm) ZnO nanosheets electrochemically deposited on a Si substrate. The surface morphology and thickness of single-unit-cell thick ZnO nanosheets were investigated by field emission scanning electron microscopy and atomic force microscopy. Transmission electron microscopy and X-ray photoelectron spectroscopy were also performed to study the growth mechanism and chemical composition of ZnO nanosheets, respectively. UV-Vis spectroscopy was employed to determine the effect of quantum confinement on the energy band gap of single-unit-cell thick ZnO nanosheets (4.4 eV). In particular, stacking of nanosheets has been found to lead to band gaps over a substantial range (4.4-3.4 eV), which suggests nanosheets with controllable stack thicknesses could potentially produce new optoelectronic applications.

Alzheimer&’s disease (AD) is a progressive neurodegenerative disorder affecting large number of the aging population. The major clinical manifestation of AD is memory loss resulting in behavioral deficits, disorientation in time and space, and impairments in language skills. It is widely accepted that AD results from amyloid-β accumulation in extracellular regions and neurofibrillary tangles in neurons. In the presence of amyloid-β accumulation surrounded by degenerating neurites, these abnormal deposits would be the source of some neurotoxic effect. Here, we designed and realized a model system that allows a systematic study on amyloid β deposition and its toxicity to neuron cells. In this system, the supported lipid layer (SLB) was used as a substrate that mimics in-vivo-like neuron cell membrane environment. On the SLB, amyloid-β assemblies were induced by injecting spherical Au nanoparticles (AuNPs) and Au nanorods (AuNRs), and then neuroblastoma cells were seeded for the neurotoxicity test. The size and shape (aspect ratio for AuNRs in this case) effects of nanostructures on the formation of various amyloid β aggregates were studied on this template using dark-field light scattering from plasmonic Au nanostructures.

Atomic Layer Deposition (ALD) is a technique that allows depositing materials layer by layer. Due to its important step coverage and the high conformality of the obtained films, the ALD technique has the capability to coat complex structures. This characteristic of ALD makes it one of the most essential gas phase vapour deposition methods. Despite the enormous progress reported so far, the deposition of metals remains challenging with this method and are based on strong hydrogen-assisted reduction of complex Ni-precursors. The investigation regarding the ALD deposition is today driven by the variety of applications in modern technologies in which metal thin film are indispensable. Furthermore metal particles are particularly interesting for the heterogeneous catalysis and also for the catalysed growth of other materials.
Here we investigate an ALD process using cobalt acetylacetonate and nickel acetylacetonate as precursors and ethanol as a mild reducing agent at temperature above 250°C. In this study we demonstrate the efficiency of alcohol molecules at reducing these well-know and inexpensive organometallic compounds. Therefore, alcohols are discussed as an alternative to the conventionally used hydrogen reduction. The investigation of the growth parameters as a function of the deposition temperature and the surface exposure time to the precursors as well as the comparison of different alcohols as reducing agent will be discussed.
The combination of the X-Ray Photoelectron Spectroscopy and X-Ray Diffraction analysis confirms the absence of oxygen in the films despite its significant fraction in both precursors. An important incorporation of carbon was noticed however and is strongly dependent on the process parameters. Materials phases are identified by complementary Transmission Electron Microscopy analysis.

The synthesis of metallic nanoparticles of pure Cu, Co and alloyed Cu-Co by means of a mechanochemical process is reported. The entire range of possible chemical compositions is investigated. High energy mechanical milling is used to promote chemical reduction of metallic chlorides with Na in a dispersive medium (NaCl). Such an environment hinders agglomeration of the chemically reduced alloyed metallic nanoparticles producing a single or bimodal size distribution depending on the milling time. In all cases measurement of magnetic properties shows a behavior that can only be explained for extremely small domains. The measurement of magnetic properties by electron paramagnetic resonance EPR shows the variation of composition and the development of a solid solution (during milling) on the basis of a quantum mechanics equation. Transmission electron microscopy is used to image and show the size distribution of the synthesized particles. Thermal treatment of these nanoparticles gives rise to separation of the metallic elements forming a core-shell morphology with the corresponding variation of magnetic properties as measured by vibrating sample magnetometry and electron microscopy.

The study of the 2D-3D structural transition in Au₇⁺ nanocluster as a function of the number of gold atoms has been a long standing problem due to contradictory results between experiments, that show a 2D structure, and some theoretical results predicting 3D. We present a theoretical analysis, based on the pseudo Jahn-Teller effect that explains the origin of the 2D-3D structural transition controversy. It is shown that the usually assumed 2D non-degenerate ground state cluster structure with D_6h symmetry is unstable due to a vibronic coupling between the ground state and two quasi-degenerate excited states, producing a puckering effect ending in a 3D stable structure with D_3d symmetry. This structure presents the same surface area than the 2D, being therefore compatible with ion mobility experimental results. We discuss the effects of the symmetry breaking due to the puckering effect in the Raman, IR and UV-vis spectra that might point to possible sensor capabilities for this subnanometric cluster. The study is based on a scalar, spin orbit relativistic and time-dependent DFT calculations in the zero order approximation (ZORA). The authors acknowledge to the DIRECCIOacute;N GENERAL DE COacute;MPUTO Y DE TECNOLOGÍAS DE LA INFORMACIOacute;N (DGTIC-UNAM). B. Molina acknowledges support by PAPIIT-DGAPA, UNAM IN119811.

It is well known that Au-Ag bimetallic nanoparticles have better performance in catalytic processes compared to their counterpart pure clusters. This improvement in their catalytic properties has been attributed to a kind of synergy between the gold and silver atoms that has not been fully understood. Unlike pure clusters, there are very few studies on the catalytic behavior of the Au-Ag binary nanoparticles. From the theoretical point of view, in the subnanometer regimen, the bimetallic Au-Ag clusters present a challenging problem, since by combining the different gold and silver relativistic effects, a variety of skeletal geometric structures and homotopic distributions are obtained. In particular, pure gold has favorable planar structure even up to 16 atoms, while silver begins to favor 3D arrangements from 5-7 atoms. This dissimilar behavior produces a diverse population of 2D and 3D coexisting binary clusters, whose properties strongly depend of the Au/Ag mixing ratio. In this work we use the relativistic approach ZORA-DFT to model the AunAgm (with 4 le; (n + m )le; 12) binary nanoclusters in selected proportions (1:1, 3:1, 5:1) in the gas-phase and we study their reactivity from the descriptors based in the condensed Fukui indexes obtained from an electronic population analysis.The authors acknowledge to the GENERAL COORDINATION OF INFORMATION AND COMMUNICATIONS TECHNOLOGIES (CGSTIC) at CINVESTAV for providing HPC resources on the Hybrid Cluster Supercomputer "Xiuhcoatl" and the DIRECCIOacute;N GENERAL DE COacute;MPUTO Y DE TECNOLOGÍAS DE LA INFORMACIOacute;N (DGTIC-UNAM). B. Molina acknowledges support by PAPIIT-DGAPA, UNAM IN119811.

A novel fullerene derivative (C60RM) was newly synthesized. Its chemical structure and phase behavior were investigated with spectroscopic, scattering and microscopic techniques. The self-assembled striped C60RM patterns with regular intervals were successfully prepared via the one-dimensional (1D) pattern-forming state of an elastically anisotropic cholesteric liquid crystal (LC) as a template. This work was supported by the Human Resource Training Project for Regional Innovation and the Converging Research Center Program (2012K001428) of Korean government.

Precise measuring of nanocrystal sizes and their distributions is very important for both fundamental size-dependent property characterizations and many technological applications because they exhibit characteristic size-dependent electrical, optical, magnetic, and chemical properties. Although TEM is the most popularly employed technique to measure the size of nanocrystals, obtaining TEM images and subsequent extraction of size information is a laborious and time-consuming process. Herein, we report on the accurate characterization of nanocrystal sizes and size distributions of sub-5-nm-sized iron oxide nanocrystals using MALDI-TOF mass spectrometer. The mass of particles could be readily converted to the size by devised equation and it is well matched with the TEM data. The size distribution from mass spectrum is highly resolved and detecting the difference of only few angstrom in the size. We used this mass spectrum technique to investigate the formation process of iron oxide nanocrystals. From ex situ measurement during growth of iron oxide nanocrystals, it was found that the particles proceeded via discrete growth in size, the result showing magic size nanocrystals.

Recently, a high-performance battery is expected to be developed for the energy storage. In particular, lithium-air and fuel batteries are potential candidates for the next generation battery. Platinum nanoparticles are usually used as a catalyst in the cathode for these batteries. It is the best catalyst for oxygen reduction reaction (ORR). However, platinum is expensive, scarce metal which limited the practical use of these batteries.
Many researchers have studied novel catalyst composed of non-rare metals. Unfortunately, it has not been succeeded yet as we do not have a clear concept to develop new catalyst. Recently, metal nanocluster catalyst with less than 2 nm in diameter has been investigated since the electronic structure can be drastically varied by the control of diameter. For example, it inhabits the property of semiconductor or insulator, not of metal. Metal-insulator transition nanoparticle is defined as nanocluster. And it is distinguished from nanoparticle.
In this study, we analyzed the catalytic reaction mechanism of nanocluster. Au, Pt nanocluster were evaluated as the model catalysts. Ab-initio MO calculation was conducted by Gaussian03 program. All calculations were used by a level of UB3LYP. The basis sets for Au and Pt atoms were LanL2DZ basis sets, and the basis sets of O and H atoms were 6-311+G(2df,2p). We discuss the ORR on Au13, Pt13 cluster from a potential diagram. In this case, especially in Au13, the desorption process of OH has a large activation energy, which is one of the back-donation process of electrons. Compared with Pt13, back-donation process of charged Pt13 is lower. We also calculated the reaction on charged Pt13 cluster. Throughout this reaction, energy difference against initial structure of charged Pt13 is smaller than that of neutral Pt13. This system is closer to reality. After reaction, Pt13 structure changed to more stable one which is low symmetry. We can get essential mechanism of ORR by using this stable and low symmetry structure as an initial structure.

Ion channels have attracted great attentions of scientists worldwide because of their crucial roles in many biological activities, such as nerve conduction, muscle contraction, heart beating, bioelectric generation, photosynthesis, etc. Polymeric single nanochannel built by track-etched method serves as one kind of the biomimetic ion channels become a new research focus due to their robust mechanical properties, better controlled geometry and the reactive surface compared to other materials. It can mimic not only the shape of their biological counterpart, but also the ion selective and rectified properties. In this thesis, by using track-etched PET single nanochannels and several different intelligent molecules, we prepared biomimetic ion channels which show zinc activated, photo/pH dual-responsive and also ionic rectified properties, respectively.
(1) Bio-inspired by the biological zinc activated ion channels, we prepare a biomimetic zinc activated ion channel by integrating a zinc responsive protein-zinc finger into the conical single PET nanochannels. The results show that the biomimetic ion channels could be activated after zinc ions binding, which is induced by the folding of zinc fingers, yielding an increase of the effective channel diameter. As the sophisticated protein was introduced to the single nanochannels, this work offers a new research platform for more complicated biomimetic intelligent system.
(2) By integrating one of the most popular light responsive molecules-spiropyran into PET single nanochannels, we prepared a light/pH dual controlled biomimetic intelligent nanochannel. Spiropyran could undergo ring-opening reaction after irradiating by UV light, and resulting two charged groups. They can adopt different charges depending on the pH. As a result, the biomimetic ion channel could be endowed light/pH dual-responsive property under the coactions of UV light and pH. Moreover, the ring-opened charged molecules could change back to ring-closed state under visible light, leading to the reversibility of the system. The biomimetic intelligent reversible system could achieve complicated function only by modifying a simple molecule, which might provide a research basis for preparing novel photo-electric conversion system.
(3) Based on the symmetric hour glass-shape single polymeric nanochannel, we prepared a novel biomimetic rectified system using ion sputtering of Au and Pt. Four different composed nanochannels were prepared with either symmetric or asymmetric sputtering method. The results show that only the asymmetric composed nanochannels could rectify ionic current effectively. This work provides a basic platform to obtain rectifications in symmetric nanochannels. Furthermore, the channels would also have promising applications in sophisticated bio-nanodevices because of convenience to be modified further.

As the length scale of devices keeps shrinking, the critical layer thicknesses are steadily declining for large scale integrated circuits. Atomic layer deposition (ALD) is one of the widely used methods to fabricate ultrathin films with atomic thickness control on the thickness .Among many nano metrology tools, Spectroscopic ellipsometry (SE) is a powerful one for transparent or semi-transparent thin film thickness measurement.
Conventional thin-film analysis by SE is based on Cauchy model which treats the film as an ideal smooth film. It shows great accuracy for thin films above 3nm, which has been calibrated by TEM in many reports. However how to accurately measure the thickness of ultrathin films in a few nanometers, remains to be a big challenge. In such ultrathin film system, the interface and surface roughness both played an important role, and the island structures also affect the results. Therefore, using refractive index n from bulky film to fit thickness is inaccurate, while fitting n and thickness at the same time usually gives n with no physical meaning. The thicknesses measured by Effective Medium Approximation (EMA) are more accurate than those fitted by Cauchy model. Unlike Cauchy model which treats thin film as an ideal smooth layer, EMA model gives the void percentage and thickness measurement simultaneously. It takes non-ideal situations into account and treats the uneven surface as a smooth film with air. Here we have compared the results from both Cauchy model and EMA model on Al2O3 thin films grown by ALD. The results show that when thicknesses are above 3nm, there is no big differences by these two methods, while EMA can tell the void percentage of the thin films which related to the surface situation and interface roughness state. For films less than 3nm, Cauchy model is not suitable. Only the EMA can practically reflect the non-ideal ultrathin film and/or island thickness.
While Al2O3 ALD is an ideal layer-by-layer growth process with minimal island growth, EMA would be well suitable model to explain other non-ideal ALD processes, especially on transition metal oxides and metals that tend to form island growth. EMA showed great potential for exploring ALD growth mechanism and a powerful real-time monitoring technique for material properties.

Metallic or semiconducting nanoclusters (NCs) can be characterized as atomic agglomerates with a small number n of constituent atoms (typically n < 100). As distinct to larger atomic aggregates referred as nanoparticles, NCs do not tend to mimic the lattice structure of the corresponding bulk material or present a melting point depression behavior smoothly varying with n. Instead, their thermal stability seems to rely on the development of specific atomic arrangements and/or on the enhancement of the strength of chemical binding energies, usually rendering fluctuations in their physical and chemical properties such as of the melting temperature (even exceeding the bulk value) with small variations of n. Because of their specific nature, NCs are usually synthesized or detected as freestanding structures in vacuum, or stabilized by ligand molecules when produced by chemical routes. In this contribution we demonstrate that thermally stable Pb or Sn NCs can be synthesized as embedded structures in dielectric SiO2 and Si3N4 films. They are produced via ion implantation followed by particular thermal aging treatments described elsewhere [1,2]. The films and their atomic constituents are characterized by Rutherford backscattering spectrometry (RBS) and the NCs dimensions by conventional transmission electron microscopy (TEM) as well as by high resolution scanning transmission electron microscopy using high angle annular dark field Z contrast imaging conditions (STEM-HAADF). Our investigations show that the NCs structures maintain their integrity even when the samples are submitted to high temperature thermal treatments up to about 1400 K (i.e. more than 750 K above the melting temperature of the corresponding bulk materials). We also suggest a novel explanation for the observed superheating behavior considering that the aging treatment leads to the formation of covalently bonded nanostructures presenting low free cluster/matrix interface energies. A phenomenological model based on the transition from covalent to metallic bounds as a function of size consistently fits the existing experimental data of melting point depression and superheating behavior for Sn and Pb particles.
[1] F. Kremer, F. P. Luce, Z. E. Fabrim, D. F. Sanchez, R. Lang, F. C. Zawislak, P. F. P. Fichtner; Journal of Physics. D, Applied Physics 45 095304 (2012)
[2] F. P. Luce, F. Kremer, S. Reboh, Z. E. Fabrim, D. F. Sanchez, F. C. Zawislak and P. F. P. Fichtner, J. Appl. Phys. 109, 014320 (2011)

Sub-nanometer nanoparticles (NPs) are very intriguing for the scientific community due to numerous characteristics they possess. Size control and homogeneity of metal NPs during synthesis and characterization are extremely important parameters to consider. A general method is proposed to generate nanoparticles with a defined number of atoms in the metal core by incorporating “atomic metrons” as the macromolecules with defined number of binding sites as the matrix. Synthesis, characterization, and purification of the atomic metrons with known binding sites will be discussed. Furthermore, filling all the binding sites with metal atoms and transformation to NPs will be demonstrated.

The joint experimental and theoretical studied are based the deposition of size-selected subnanometer clusters on carbon- and oxide-based supports, in situ and ex situ synchrotron X-ray characterization of the hybrid nanostructures under catalytically and electrochemically relevant reaction conditions. Series of clusters sizes of various metals such as Ag, Co, Ni were studied, and the oxidation state, thermal stability under heterogeneous catalytic (e.g. Fischer-Tropsch synthesis, dehydrogenation) and electrochemical conditions exploited as a function of cluster composition and size, as well as support composition. As will be shown on select examples, using clusters prepared with atomic precision, the combination of experiment and theoretical modelling provides detailed insights in the structure-function relationship at the subnanometer scale.
References:
(1) Y. Lei, F. Mehmood, S. Lee, J. P. Greeley, B. Lee, S. Seifert, R. E. Winans, J. W. Elam, R. J. Meyer, P. C. Redfern, D. Teschner, R. Schlögl, M. J. Pellin, L. C. Curtiss, and S. Vajda, Science 328, 224-228 (2010)
(2) S. Vajda, M. J. Pellin, J. P. Greeley, C. L. Marshall, L. A. Curtiss, G. A. Ballentine, J. W. Elam, S. Catillon-Mucherie, P. C. Redfern, F. Mehmood and P. Zapol, Nat. Mater. 8, 213-216 (2009)
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Nanoparticles less than 1 nm in size have recently attracted attention because of their unique properties which lie somewhere between larger nanostructures and molecules. In general, gas-phase approaches to the synthesis of subnanometer nanoparticles are desired because of their high purity. However, unlike wet chemical methods where surfactants are used to prevent agglomeration, particle coagulation can occur in the gas phase and mass selection is usually required to obtain uniformly-sized clusters.1
Here, we present a novel plasma-based approach to produce subnanometer particles in the gas phase.2,3 Vapors of bis(cyclopentadienyl)nickel, a metal-organic precursor for Ni, are sublimed at room temperature in a flow of Ar and continuously introduced into an atmospheric-pressure microplasma. To precisely control the vapor concentration of the Ni precursor, this flow is diluted with pure Ar. Particles are homogeneously nucleated near room temperature in the microplasma by electron- or Ar metastable-induced dissociation of the vapor precursor. As the particles exit the microplasma, growth is rapidly quenched by a N2 gas flow. The particles are characterized in situ by aerosol size classification which shows that we are able to produce particles less than 2 nm in size when the precursor vapor concentration is below ~1 ppm. To more carefully characterize the particles, the aerosol flow is deposited onto freshly cleaved mica (RMS roughness < 0.15 nm) by electrostatic precipitation to carry out atomic force microscopy (AFM). AFM characterization confirms that we are able to produce sub-1 nm nanoparticles with a clear trend of smaller particles at lower precursor vapor concentrations. The smallest particles observed to date are ~0.3 nm (in height). Overall, our approach to gas-phase synthesis of subnanometer particles is unique as it avoids mass selection and is at atmospheric pressure, thus enabling scale up.
1. S. Lee, C. Fan, T. Wu, and S. L. Anderson, J. Am. Chem. Soc. 126, 5682 (2004).
2. W-H. Chiang and R. M. Sankaran, Appl. Phys. Lett. 91, 121503 (2007).
3. P. A. Lin, A. Kumar, and R. M. Sankaran, Plasma Proc. Poly., doi: 10.1002/ppap.201100216.

Diamondoids are nanometer-size hydrogenated diamond nanocrystals built up from diamond cages [1]. Interestingly, contrary to other semiconducting nanocrystals, their structure is exactly known, thus they are ideal test-beds for experiments and theory [1,2,3]. Their small size, easily controllable surface structure and unique stability due to strong sp3 bonds make them prototype materials for several applications. We found very simple structure-property relationship rules by using density functional theory based calculations (time-dependent density functional theory and many-body perturbation theory in the GW-BSE approximation). For example, hydroxyl termination may allow tuning the ionization potential, while double bonded sulfur atom coverage turns the optical gap from ultraviolet to visible and even to the infrared spectral range [3,4]. Our results provide guidance how to use these diamondoids as alternative in vivo biomarkers [4].
[1] J. E. Dahl, S. G. Liu, and R. M. K. Carlson, Science 299, 96 (2003).
[2] A. Fokin and P. Schreiner, Mol. Phys. 107, 823 (2009).
[3] Marton Voros and Adam Gali, Physical Review B 80, 161411(R) (2009).
[4] Marton Voros, Tamas Demjen, Tibor Szilvasi, Adam Gali, Physical Review Letters 108, 267401 (2012).

Ion capturing is currently achieved through chelating molecules that typically have a cage-like structure capable of ‘locking&’ the targeted ion in place. This mechanism of molecular recognition requires a set of complex interactions, yet it can be trivialized as a lock-and-key mechanism. Recently, we have shown that gold nanoparticles coated with mixture of alkyl-thiols and oligo ethyleneglycol-terminated alkyl thiols are capable of remarkable ion chelation. We have evidence that the mixture of ligand molecules forms stripe-like domains on the ligand shell of the nanoparticles. Simulations show that at the edge of the ethelyneglycol domains ions are trapped by multiple ethylene glycols coming together and forming a flexible cage for the trapped ions. The astonishing part is that this chelation mechanism, apparently flexible in the cage forming molecules as well as in the number of molecules coming together to form a cage, is actually truly selective. This talk will show that the entropy of the system does play a role in the selectivity. In fact, particles whose binding constant to potassium increases as temperature increase will be shown and their binding mechanism discussed. An attempt at understanding the selectivity of this supramolecular system will be presented.

Using first-principles density functional theory, we investigated the chemical bonding and electronic structure of OFe₄(CO₂Ph)₆, which is regarded as a functional unit in a metal-organic-framework(MOF). The calculations show that the structure of OFe₄(CO₂Ph)₆ is very similar to that of the experimentally synthesized OZn₄(CO₂Ph)₆, which ensures the substitutability of the center metal atom in MOF-5. In order to see why the cluster OFe₄(CO₂Ph)₆ is stable, the binding nature among the atoms in the system was examined. The calculated deformation charge density exhibits that electrons are transferred from Fe to O sites. Whereas, excess electrons are gathered at the central regions between the C, O and H atoms. Furthermore, the partial density of states shows that, d orbital of Fe atoms and p orbital of O atoms are strongly hybridized, giving rise to the HOMO, while the hybridization between the p orbital of the C atoms and O atoms and the s orbital of the H atoms contributes to the states in a very large energy range below the HOMO level. The above results indicate that, the bonding nature between Fe atoms and O atoms is ionic-covalent, with the ionic bonding interaction dominating over the covalent interaction. Meanwhile, the bonding between C and H atoms is typically covalent. Our investigation has provided theoretical evidences for the possibility of synthesizing MOF-5 materials with the central Zinc being substituted by other metal atoms.

In this paper we present fast a single-step synthesis for CaS nanoparticles using
several different approaches, including dissolution of bulk sample, classic double
ion exchange reaction and we compare the results with a novel, microwave-assisted
synthesis in DMSO. We also propose this material as an alternative to cadmium based
quantum dots. Optical properties, such as fluorescence and absorbance are presented
as well. Theoretical calculations using density functional theory (DFT/B3LYP/DGTZVP)
were performed in order to determine the optimal geometrical configuration as well
as the cluster energies for (CaS)n for 1 le; n le; 5. Also configuration interaction singles
method (CIS/DGTZVP) using Gaussian 09® software was used to compare against our
optical spectroscopy data and confirm our findings.

We describe internal structure of a fluorescent probe comprising CdSe quantum dots(QDs) in nano scale calculated by ab-initio calculation. Energetic and structural properties of wurtzite and zincblend structures were discussed depending on shape and size, also quantum dots(0D), quantum rods(1D), and quantum well(include quantum disk)(3D) were compared. It is shown that the simulation results are consistent with the experimental results on the various previous studies. It is also found that the optimal shape of CdSe quantum dots could be determined by surface energy. Theoretical predictions for the optimal shape (aspect ratio) were presented by the anisotropic surface energy analysis. It is shown that the anisotropic surface energy can be utilized to control the shape of the quantum dots realizing from 0D to 2D, which can provide different optical properties (spectra) in the nano length scales

When binary mixture of dislike ligand molecules are used as components of the ligand shell of gold nanoparticles, stripe-like domains spontaneously form. These domains have characteristic dimensions in the sub-nanometer range. As a consequence these mixed monolayer protected nanoparticles present a complex outside surface, characterized by the sub-nanometer alternation of domains of varying wetting properties. Here, the role of these domains in determining the interfacial energy, the catalytic activity, and the biological activity of these particles will be discussed. In particular novel results about the dynamic properties of these domains will be presented.

The controlled tailoring of nano-porosity in metallic thin films of several 100 nm thickness using dealloying has gained renewed attention in recent years, as such nanoporous thin films are candidates for applications in sensors, plasmonics, micro-fuel cells and super-capacitors. In this contribution, the physical mechanism of nanoporosity formation during the dealloying process of binary PtAl- and ternary PtYAl-alloy thin films is examined using focused ion beam (FIB) nanotomography and Rutherford backscattering spectrometry (RBS). The selective dissolution of Al from the Pt-alloy compound results in a branched nanoporosity with a mean branch thickness below 10 nm and a pore intercept length of 10 nm. The dynamics of nanoporosity formation is found to obey to a superposition of a reaction diffusion equation describing the linearly propagating diffusion front¹ and a secondary slower dissolution process away from the moving interface. An increased Al content as well as a partial substitution of Pt by Y result in a slower dealloying kinetics with a slower linearly propagating diffusion front. The resulting nanoporous Pt thin films perform exceptionally well as oxygen reduction electrodes in a micro-solid oxide fuel cell setup in the temperature range from 473 to 1073 K² and allow for up to 93% absorption of light in the visible spectrum.
¹ PRL 107, 225503 (2011), ² PRB 84, 184111 (2011)

This talk will focus on our recent demonstrations of new methods for the preparation of ultrathin Au and Pd nanowires. When AuCl was mixed with oleylamine, linear chains will be formed from [(oleylamine)AuCl] complex via aurophilic interaction. The linear chains, with AuI-AuI bonds as the backbone and surrounded by oleylamines, couldn assemble together to form bundles of polymeric strands. When the AuI was reduced to Au0 by reacting with Ag nanoparticles in hexane, the polymeric strands functioned as both the source of Au and the template to mediate the nucleation and growth of Au nanowires. Using this method, we were able to produce Au nanowires with an average diameter of ~1.8 nm and an aspect ratio of >1000 in high yields (~70%). Most recently, we have developed a new method based on oriented atatchment for genrating Pd nanowires with ultrathin thickness. I will discuss the reaction mechanisms for these two different types of syntheses.

Gallium nitride (GaN) nanowires exist in a myriad of cross-sectional shapes. In this study, a series of classical molecular dynamics simulations is performed to investigate the strain-phononics-structure relationship in rectangular and triangular wurtzite (Wz) - GaN nanowires. The thermal conductivity of the nanowires is linearly dependent on the uniaxial strain in both compressive and tensile regimes, and shows no significant dissimilitude for the same amount of strain exerted on the two types of nanowire. This is coherent with an analytical approach using the Boltzmann transport theory. However, the thermomechanical behaviour at the vertex regions shows palpable differences between the two subfamilies, relative to the non-vertex faceted regions, as the structural morphology is most disparate at the vertices. Furthermore the degree of strain asymmetry is a strong determinant of the vibrational response and consequently thermal conductance.

Due to the size- and shape-dependent properties, nanomaterials such as nanoparticles have been successfully fabricated multi-dimensional (D) ordered assemblies for the development of ‘artificial solids&’ (e.g., metamaterials) with potential applications in nanoelectronics and nanophotonics. Synthesis and assembly of nanomaterials have been relied on specific chemical or physical forces such as van der Waals interactions, dipole-dipole interaction, chemical reactions, and DNA-templating, etc. In this presentation, I will discuss our recent discovery that an external stress can be utilized to engineer nanomaterial assemblies and to fabricate new nanomaterial architectures without relying on these specific forces. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink, allowing fine-tuning of interparticle separation distance to interrogate collective physical properties, 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, CdSe, etc) including nanorod, nanowire, nanosheet, and nanoporous network can be fabricated. Guided by computational simulations, we are able to rationalize the necessary stress for predictable nanostructures. Exerting stress-dependent control over the structure and property provides a unique and robust system to understand collective chemical and physical characteristics of nanomaterials. This method mimics embossing and imprinting manufacturing processes and opens exciting new avenues for large-scale fabrication of novel active nanomaterials during applying and releasing of stress.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

In the past 20 years, one of best catalytic material for hydrodesulphurization reactions of crude oil has been the transition sulfides MoS2, known also as the “workhorse” of refinery industry. It has been proved by this and other research groups that the MoS2 laminar structure can increase its catalytic activity when is promoted with cobalt or nickel. The location of active sites seems to be at rim and edge sites on that particular laminar structure, as demonstrated using Mossbauer spectroscopy and x-ray techniques. However, due to maximum capability of this promoted systems Co(Ni)/MoS2 to remove heterogeneous atoms (S, N, O); a search for new catalytic materials has been an ongoing activity nowadays in the HDS community. In here, we present the new family of ternary phase catalyst with special emphasis on their structural aspects as revealed by aberration corrected (Cs) high-resolution transmission electron microscopy techniques in an attempt to describe the nature of active sites on this porous nano-rod like catalytic materials.

Hybrid nanomaterials represent a new class of materials that could potentially display properties beyond those of constituent nanocomponents. For instance, hybrid nanomaterials consisting of nanoparticles (NPs) distributing on the surface of graphene could display not only unique properties of NPs and those of graphene, but also additional novel properties due to electronic interactions between the NP and the graphene. This talk will introduce several methods to produce such hybrid graphene-NP structures, which include an electrostatic method to assemble aerosol and colloidal NPs onto graphene to produce flat graphene-NP hybrids, an ultrasonic nebulization or aerosolization method to produce crumpled graphene-NP hybrid balls, and a polymerization method to produce nitrogen-doped graphene-NP hybrids. Example applications of resulting hybrid nanomaterials will be presented for the detection of chemical (graphene-SnO2 NP hybrids) and biological (graphene-Au NP hybrids) species and for energy storage (crumpled graphene-Mn3O4 and crumpled graphene-SnO2 NP hybrids) and conversion (graphene-TiN NP hybrids). Rational design of such hybrid nanomaterials can lead to sensitive and selective detection of low-concentration chemical (NO2 and NH3) and biological (various proteins and E. coli bacteria) species at room temperature, high performance electrochemical supercapacitors and lithium-ion batteries, and low-cost counter electrodes for dye-sensitized solar cells.

Bio-inspired smart materials should be a “live” material with various functions like organism in Nature, they must have three essential elements as sense, drive and control. The studies on lotus and rice leaves reveal that a super-hydrophobic surface with both a large CA and small sliding angle needs the cooperation of micro- and nanostructures. Considering the arrangement of the micro- and nanostructures, the surface structures of the water-strider&’s legs were studied in detail. Accordingly, super-hydrophobic surfaces of aligned carbon nanotube films, aligned polymer nanofibers and differently patterned aligned carbon nanotube films have been fabricated. Many methods had been applied in making superhydrophobic films with multi-functional properties, such as structural colored, transparent and/or conductive superhydrophobic films. Under certain circumstances, a surface wettability can switch between superhydrophilicity and superhydrophobicity, just like in Chinese ancient Taiji philosophy that “Yin” and “Yang”, the two opposing fundamental properties of nature, are switchable. The cooperation between surface micro- and nanostructures and surface modification of poly (N-isopropylacrylamide) gave reversible switching. By grafting the copolymer of temperature-sensitive and pH-sensitive components, a dual-responsive surface can be controlled by either or both of temperature and pH was fabricated. Besides organic surfaces, a series of inorganic switchers were also made. UV light stimulated transition between superhydrophobic and superhydrophilic by aligned ZnO, TiO2, and SnO2 films are successfully prepared respectively. Most recently, we developed a superoleophobic and controllable adhesive water/solid interface which opens up a new strategy to control self-cleaning properties in water. To expand the “switching” concept of the smart 2D surface, we also did a lot of interesting work in 1D system. For example, we discovered the water collection ability of capture silk of the cribellate spider Uloborus walckenaerius and then prepared artificial spider silk which will have great applications in water collection. In addition, we developed the novel biomimetic ion channel systems with a variety of intelligent properties (pH responsive, temperature responsive, potassium responsive, zinc activated, and dual-responsive single nanochannels), which were controlled by our designed biomolecules or smart polymers responding to the single external stimulus, provided an artificial counterpart of switchable protein-made nanochannels (highlight by Nature, and Nature China). These intelligent nanochannels could be used in energy-conversion system, such as photoelectric conversion system inspired by rhodopsin from retina or bR, and concentration-gradient-driven nanofluidic power source that mimic the function of the electric eels.

Metal nanocrystals (MNCs) are gaining interest, particularly for bioimaging and sensing applications, due to their small size, environmental sensitivity, as well as facile and solution-based synthesis. Furthermore, luminescence quantum yields and photostability have improved considerably in recent years. By virtue of the fact that multiple metals have shown fluorescence (Ag, Au, Cu, Pt) and because quantum confinement effects are very strong at the subnanometer to nanometer size range, emission tunability throughout the visible and near infrared spectrum has been demonstrated.
Light emitting diodes (LEDs) are establishing themselves as an important element in emerging displays and lighting solutions. Materials such as III-V semiconductors are often used, but with growing popularity of both molecular- and quantum dot-based emitters. While the emission of MNCs has been demonstrated both in solution as well as solid-state, electroluminescence of MNCs within a thin film structure has never been shown. Here, we make use of a synthetic phase-transfer strategy for preparing glutathione-coated MNCs in organic solvents [Yuan et al., ACS Nano, 2011, 5, 8800] to demonstrate a thin film MNC LED with either Au or Ag MNCs as the emitting element. In both cases, the electroluminescence peak of the LED corresponds with the photoluminescence of the MNCs in solution, and we are able to observe spectrally pure emission without parasitic emission from other materials making up the LED structure. Specifically, the Ag NCs feature an emission peak at 695 nm, whereas the Au NCs emit at 750 nm. The Au and Ag emission onsets at low voltages of 1.74 V and 2.21 V, respectively. This is therefore the first time that electroluminescence of a MNC thin film has been observed.
Ultimately, we show that MNCs represent an additional option for an emitter within the thin film LED research domain, and with continued improvements in spectral narrowing, quantum yield, and stability, that these emitters could find future applications.

Fluorescence imaging in biological and medical sciences is often hindered by significant depth-dependent signal attenuation and high fluorescent backgrounds. Nanotechnology offers significant opportunities for signal gains when using, for example, quantum dots or plasmon-enhanced emitters, but significant size, bioconjugation, toxicity, and aggregation concerns become paramount. We have addressed the limited brightness and biocompatibility issues in fluorescence imaging by encapsulated highly fluorescent metal nanoclusters, consisting of fewer than 12 silver atoms. These species show excellent brightness and great promise in both single molecule and bulk imaging, while maintaining small overall size. Still, these species are insufficiently bright for the most demanding applications. Their unique photophysics, however, has enabled optical modulation of their emission that not only increases total emission, but, more importantly, greatly reduces background. Demodulation of nanodot signals enables fluorescence image recovery from within high backgrounds, resulting in order-of-magnitude sensitivity increases. Our detailed studies of the states enabling low-energy optical modulation have enabled us to both approach biosensing and biolabeling applications and translate these concepts to more standard organic fluorophores. These general concepts of removing background through selective fluorescence modulation are applicable to a wide variety of systems, with Ag nanodots and modulatable organic dyes being used for a variety of biological imaging applications.

Au nanoparticles (NPs) have been reported to be ferromagnetic when coated with organic layers like dodecanethiol. However there are also conflicting reports that suggest magnetism is intrinsic in gold based nanostructures. We have used pulsed laser deposition (PLD) to prepare Au- indium tin oxide (ITO) composites through ablating gold and ITO targets on sapphire substrates without any organic binders. The formation of Au-In alloy from oxide composites will be discussed. We report that nanostructured Au-ITO composites are ferromagnetic due to an intrinsic contribution from Au. In this talk we will discuss the sample synthesis and unique magnetic properties along with x-ray magnetic circular dichroism (XMCD) data, which will be collected soon.

Few-atom noble metal nanoclusters are collections of small numbers of gold or silver atoms (typically 2-30 atoms) with physical sizes close to the Fermi wavelength of an electron (~0.5 nm for gold and silver). These nanoclusters are a missing link between the atomic and nanoparticle behavior of noble metals - exhibiting fluorescence emissions spanning the UV to near IR range. Fluorescent metal nanoclusters are gaining much interest because of their desirable photophysical properties, smaller size than quantum dots, and biocompatibility. As a compliment to quantum dots and molecular fluorophores, fluorescent metal nanoclusters have been produced using templates of dendrimers and polymers, small molecular ligands, or within biological materials of interest, such as DNA. Recently, we have synthesized and photophysically characterized Ag-nanoclusters (AgNCs), which were templated on DNA, with distinct and narrow excitation and emission profiles tuned to common laser lines. Intrinsically fluorescent recogonition ligands have been created from chimera&’s of DNA that template AgNC and aptamers, for the specific and sensitive detection of proteins. More recently, we have developed a DNA detection probe (NanoCluster Beacon, NCB) that “lights up” upon target binding. In a separation-free assay, a signal-to-background ratio of up to 500 was demonstrated. In addition to eliminating the need to purify DNA nanocluster probes that do not bind targets, there is no need to remove the silver nanocluster precursors used during nanocluster formation. Further, chameleon NanoCluster Beacons have been developed that can identify single-nucleotide polymorphisms. Toward a better understanding of the structure of these families of fluorescent silver nanoclusters, we have begun EXAFS, SANS and SAXS characterization.

The size-tunable optical properties of colloidal quantum dots (QDs), along with their stability and saturated color emission, have made them particularly attractive as the active materials in large-area light-emitting devices (LEDs). To date, efficient red and green LEDs have been realized with (CdSe)ZnS core/shell QDs, but QD-LEDs emitting blue light have remained elusive due to a lack of appropriate materials. Ideally, LEDs for flat panel display applications would have emission at ~ 470 nm with a narrow bandwidth, which may be obtained from CdSe QDs smaller than 2 nm. However, such small QDs are difficult to synthesize with narrow size distributions and good quantum efficiencies. In this work, we report on the synthesis of CdS/CdSe/ZnS nanocrystals with a subnanometer or nanometer CdSe quantum well (QW) layer using the successive ion layer adsorption and reaction technique. As the well thickness was increased from 0.6 nm to 1.8 nm, the photoluminescence peak shifted from 435 nm to 490 nm. Nanocrystals with a QW ~1.2 nm emitted blue light ~467 nm, with a full-width-at-half-maximum ~31 nm. It was found that 2-3 monolayers of ZnS outer shell can effectively passivate the QDQW structures, leading to the suppression of long-wavelength emission and a significant increase in PL quantum yield (QY) to 47%. QDQW-LEDs with blue light emission from the CdSe QW were successfully demonstrated. The LEDs with an emitting layer comprising QDQW nanocrystals embedded in a poly(N-vinylcarbazole) host were five times brighter than LEDs based on closely-packed QDQW nanocrystals. However, all the EL spectra included significant broadband emission from interfacial states due to poor and unbalanced charge injection into the QDQWs. It is expected that the device performance can be further improved to realize color-saturated blue nanocrystal LEDs by bandgap engineering through size variations of the QW and cladding layers.

Nanoparticles allow the combination of a variety of molecular imaging modalities and local treatment of lesions, potentially catalyzing the shift of our current medical paradigm to “earlier detection and prevention”. In the past decade, emergence of molecular gold nanoparticles with discrete and tunable luminescence opens up a new pathway to address many challenges in biomedical imaging (Annu. Rev. Phys. Chem., 2007, 409; Nanoscale, 2012,4073). In this talk, we will present a class of luminescent ~2 nm gold nanoparticles, which behave like molecular fluorophores (J. Phys. Chem. C, 2010;7727). By modifying their surface chemistries, we can make them avidly bind to cancer cell membrane under mild acidic conditions (6.5 -5.3) even in the presence of serum proteins while no interactions were observed with tumor cells at pH 7.4 (J Amer. Chem. Soc, 2011,11014). After introduced into the mice, the luminescent gold nanoparticles have little accumulation in the liver and spleen, and they can be cleared from the body through the kidney with an efficiency of 10~100 times better than the same sized AuNPs (Angew. Chem. Int. Ed., 2011,3168). The detailed pharmacokinetics studies show that these molecular gold nanoparticles can rapidly distribute in the body like many small-molecule based contrast agents but have a relatively long blood circulation half life, making them as promising contrast agents for diagnosis of many diseases (Agnew. Chem. Int. Ed. 2012,10118).

Uniform and extremely small-sized iron oxide nanoparticles (ESIONs) of < 4 nm were synthesized via the thermal decomposition of iron-oleate complex in the presence of oleyl alcohol. We developed a rapid and reliable method to determine the sizes and the size distributions of < 4 nm-sized iron oxide nanocrystals using matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS). The MS data were readily converted to size information using a simple equation. The size distribution converted from the mass spectrum is well matched with the data from TEM which requires long and tedious analysis work. We used this mass spectrum technique to investigate the formation process of iron oxide nanocrystals which is not easy to monitor with other methods. From ex situ measurements, we observed the transition from molecular precursors to clusters, and then finally to nanocrystals, which has not been able for optically inactive nanocrystals.
The 3 nm-sized iron oxide nanoparticles exhibited very low magnetization derived from the spin-canting effect. The hydrophobic nanoparticles can be easily transformed to water-dispersible and biocompatible nanoparticles by capping with the poly(ethylene glycol)-derivatized phosphine oxide (PO-PEG) ligands. The 3 nm-sized nanoparticles exhibited a high r1 relaxivity of 4.78 mM-1s-1 and low r2/r1 ratio of 6.12, demonstrating that ESIONs can be efficient T1 contrast agents. High resolution blood pool MR imaging using ESIONs enabled clear observation of various blood vessels with sizes down to 0.2 mm.

Recent interest in nanomaterial fabrication has gone beyond the production of a single material. Integration of multiple nanocomponents provides the capability of performing multitasks on a single platform. Among various multifunctional nanostructures, magnetic-fluorescent nanoparticles have drawn much attention because of the clinically proven in vivo imaging capability of iron oxide nanoparticles and the high sensitivity of in vitro fluorescent imaging. Here, we report a facile approach to the preparation of magnetic (iron oxides) and fluorescent (gold nanoclusters) bifunctional nanoparticles. The key contributions of this report included: (1) the activated dopamine surface was used for direct conjugation, which eliminated the addition of chemical cross-linkers, (2) the presence of a single nanocluster per BSA molecule was observed from advanced electron microscopy, (3) the fluorescence enhancement was monitored when switching the bifunctional nanoparticle dispersion media to biological buffers.
The integrated nanostructures were systematically characterized with a comprehensive set of tools, which included: transmission electron microscopy (TEM), high angle annular dark field (HAADF) scanning TEM, energy dispersive X-ray spectroscopy (XPS), alternating gradient magnetometer (AGM), Fourier transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). Further, the detailed processes of dopamine activation and nanocluster formation were studied using UV-vis spectroscopy.