Yuping Bao The University of Alabama
Andrew M. Dattelbaum Los Alamos National Laboratory
Joseph B. Tracy North Carolina State University
Yadong Yin University of California-Riverside
O1: Energy Applications
Tuesday PM, April 06, 2010
Room 2014 (Moscone West)
9:00 AM - **O1.1
Hybrid Colloidal Nanostructures; From Architecture to Function.
Uri Banin 1 Show Abstract
1 Institute of Chemistry & Center for Nanoscience and Nanotechnology, Hebrew University of Jerusalem, Jerusalem Israel
An important frontier in nano-materials research concerns nanoparticles with different materials in the same nanostructure as means of increasing functionality. One particularly interesting combination of materials is that of a metal and semiconductor in the same nanoparticle where metal tips grown on a semiconductor rod can provide anchor points for electrical connections and for self assembly. We developed the growth of metal (Au) tips on the apexes of semiconductor (CdSe) rods, forming 'nano-dumbbells' (NDB's), via a simple chemical reaction. From the viewpoint of self-assembly they are equivalent to bi-functional molecules such as the di-thiols manifesting two sided chemical connectivity and the use of the tips for assembly with biomolecular linking is demonstrated. By increasing the concentration of gold in the reaction, rods with a metal tip on one side are formed. This occurs by a unique electrochemical ripening mechanism as substantiated by experimental work and model calculations. The Au-CdS system shows a similar behavior but requires different reaction conditions for Au growth. Moreover, using a light-induced reaction, highly selective one-sided growth was achieved and the competition with a thermal route for Au growth on defect sites was studied. Upon reacting Au with InAs nanoparticles a completely different behavior of diffusion of the gold into the nanoparticle was observed. Other growth modes of metal-semiconductor hybrid particles will be discussed, showing the richness of the reaction possibilities of metals and semiconductor nanoparticles. Such systems manifest a unique model for a metal-semiconductor nanoscale junction. A fundamental and intriguing problem associated with such systems is its optical and electronic properties. The electronic properties of metal-semiconductor nanojunctions were investigated by several methods including optical means, scanning tunneling spectroscopy of the gold-tipped CdSe rods and by electrostatic force microscopy. The potential use of metal-semiconductor hybrid nanoparticles as novel photocatalysts will also be discussed.
9:30 AM - O1.2
Photocatalytic Hydrogen Production With Tunable Nanorod Heterostructures.
Lilac Amirav 1 2 , Paul Alivisatos 1 2 Show Abstract
1 Department of Chemistry, University of California at Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Photocatalytic production of hydrogen from water using solar energy is a potentially clean and renewable source for hydrogen fuel, but there are still many materials-related obstacles to its widespread use. It is particularly difficult to find a stable semiconductor system with suitable band gap and electron affinity for visible light absorption and for driving the subsequent redox chemistry. Additional challenges facing the photocatalytic process include the quick recombination of photoinduced charge carriers, back reaction of intermediates on the catalyst surface and the back reaction of the products. With advances in size, shape, and composition control, colloidal synthesis of inorganic nanostructures is now developing toward more sophisticated construction, where multicomponent structures can be tailored in a predictable manner for a particular demand. We report herein the design of a multi-component nanoheterostructure aimed at photocatalytic production of hydrogen. Our nanoheterostructure is composed of a platinum-tipped cadmium sulfide rod with an embedded cadmium selenide seed. In such structure holes are three-dimensionally confined to the cadmium selenide, whereas the delocalized electrons are transferred to the metal tip. Consequently, the electrons are now separated from the holes over three different components, and by a tunable physical length. This enables efficient long lasting charge carriers' separation, and the formation of distinct reaction sites which are further apart, thus minimizing back reaction of intermediates. This structure was found to be highly active for hydrogen production, with an apparent quantum yield of 20% at 450 nm, was active under orange light illumination, and demonstrated improved stability.
9:45 AM - **O1.3
On the Design of High Performance Metallic Nanostructures for Electrocatalysis.
Rongyue Wang 1 2 , Caixia Xu 1 2 , Xiaohu Gu 1 , Xingbo Ge 1 , Yi Ding 1 2 Show Abstract
1 School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong, China, 2 Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan, Shandong, China
Extensive studies have been devoted to the development of new catalysts for energy-saving technologies, such as fuel cells. Currently, the most common materials design strategy is based on mixing/loading Pt-based nanoparticles onto high surface catalyst supports such as carbon black. However, this method has two common problems, i.e. non-uniform dispersion and self-agglomeration of nanoparticles during catalyst processing, which will bury considerable Pt surface atoms and decrease the catalyst durability. In this presentation, we will describe a rational route to the construction of novel metallic nanostructures with designed functions at molecular level, with an ultimate goal of simultaneously fulfilling three key issues involved in the successful implementation of a practical electrocatalyst: ultra-low Pt loading, great poisoning resistance, and high stability. We will discuss the fabrication of a series of hollow and/or porous metallic nanostructures, based on a combination of processing techniques including wet-chemical synthesis, surface modification, and selective etching. These nanostructures are characterized by high surface area open porosity, excellent structure integrity and uniformity, which allow further functionalization for their implementation as highly efficient anode and cathode materials. In a particular example, we will discuss the formation and characterization of a sandwich type layer-structured nanoporous Au-Pt-Au structure. In a probe electro-catalytic reaction of formic acid oxidation, it is able to achieve over 100-fold increase in mass specific catalytic activity as compared with the commercial Pt nanoparticle catalysts, while its catalytic durability is also significantly better. In-situ spectroscopic studies show that the radically improved performance is not merely based on the increased Pt utilization, rather it is mainly achieved by changing the reaction pathways that suppresses the formation of poisoning CO-like species. Preliminary results regarding their performance in actual PEM fuel cells will also be discussed.
10:15 AM - O1.4
Silver/Gold Heterometallic Nanostructures and Their Surface Plasmon-related Behaviors.
Hyunjoon Song 1 Show Abstract
1 Chemistry, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Heterostructured nanocrystals containing multiple components attract much attention due to not only their multifunctional properties but also new features arising from the effective coupling of distinct domains. Metallic heterostructures are particularly interesting because optical and catalytic properties of the different components are readily hybridized due to the rapid transfer of conducting electrons. Most of the metallic heterostructures have been grown on hard templates such as anodic aluminum oxides by electrochemical deposition. There have been few reports of the synthesis of multimetallic nanostructures without hard templates, despite the fact that this approach is advantageous in terms of structural variety and controllability. Silver and gold are representative noble metals in Group 11, and have similar physical and chemical properties. Their lattice mismatch is only 0.2%, resulting in the epitaxial growth in solid states. However, the distinct electrochemical properties in silver and gold lead to interesting phenomena, such as underpotential deposition and Galvanic replacement. Using these properties, we have successfully grown silver nanorods and nanowires from gold decahedral seeds. Hierarchical gold@silver polyhedrons have also been prepared through an epitaxial seeded growth. Anisotropic hollow structures were generated by the Galvanic replacement reaction with the silver-gold-silver heterometallic nanorods. In this presentation, we demonstrate the synthesis of various silver/gold heterometallic nanostructures and their surface plasmon related behaviors by coupling of the silver and gold components.
10:30 AM - **O1.5
Shape Controlled Nanocrystals for Nanoelectronics and Energy Science.
Zhong Wang 1 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Two examples will be presented about shape control of nanocrystals. The first example is about the formation of spherical ceria nanocrystals. For chemical-mechanical planarization of advanced integrated circuits, the polyhedral shaped nanoparticles scratch the silicon wafers and increase defect concentrations. We present here an innovative approach for large-scale synthesis of single-crystal ceria nanospheres , which can reduce the polishing defects by 80% and increase the silica removal rate by 50%. The second example is about shape controlled Pt nano nanocrystals . Platinum NCs of very unusual tetrahexahedral (THH) shape were prepared at high yield by an electrochemical treatment of Pt nanospheres supported on glassy carbon by a square-wave potential, which has a much improved catalytic properties.  X.D. Feng, D.C. Sayle, Z.L. Wang et al., Science, 312, 1504 (2006). Na Tian, Zhi-You Zhou, Shi-Gang Sun, Yong Ding, and Zhong Lin Wang, Science, 316, 732 (2007). The work presented here was also contributed by Na Tian, Zhiyou Zhou, Shigang Sun, Xiangdong Feng, Dean C. Sayle, M. Sharon Paras, Brian Santora, Anthony C. Sutorik, Thi X. T. Sayle, Yi Yang, Yong Ding, Xudong Wang, and Yie-Shein Her.  more details at: http://www.nanoscience.gatech.edu/zlwang/
11:30 AM - **O1.6
Multifunctional Pt-based Nanostructures for Electrocatalytic Applications.
Hong Yang 1 Show Abstract
1 Chemical Engineering, University of Rochester, Rochester, New York, United States
This presentation will cover the synthesis and electrocatalytic properties of multifunctional Pt-on-M and PtM alloy nanostructures. I will discuss several structurally diverse Pt bi- and multi-metallic nanostructures ranging from M-on-M (or nano-dendrite) to yolk-shell and hollow spheres. These structures can either be directly synthesized in solution or through post-synthesis dealloying treatments. The design of element and structure can now be guided by the requirement for a property. For instance, Pt-on-Pd heterogeneous bimetallic nanocrystals have been developed to integrate excellent activity with other different functionalities including particle stability. Noticeably, at the nanometer scale, the macroscopic miscibility gap for metals can disappear when particles are made from molecular precursors and the size is small, and thus new opportunities for a broader selection of metal elements become plausible. Using Pt-Ag as an example, I will discuss a composition-dependent shape control in nanowires and several de-alloying based post synthetic treatment for the generation of complex core-shell like structures and a high-degree of control on catalytic oxidation of organics High-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) analysis, high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and X-ray diffraction (XRD) are among the techniques used to characterize the nanostructures.
12:00 PM - O1.7
Pd-Pt Bimetallic Nanoparticles Supported on TiO2. Characterization and Application to Photocatalysis.
Olivier Rosseler 1 2 , Sergey Pronkin 1 , Antoine Bonnefont 1 , Corinne Ulhaq-Bouillet 3 , Alain Louvet 2 , Elena Savinova 1 , Valerie Keller 1 , Nicolas Keller 1 Show Abstract
1 CNRS, LMSPC, Strasbourg France, 2 DGA, CEB, Vert-Le-Petit France, 3 CNRS, IPCMS, Strasbourg France
In catalytic applications, adsorption of the reactants is a key step. A lot of bi- or multifunctional catalytic systems are constituted of metal and oxide nanoparticles, the first adsorption step occurring generally on the metallic sites. In some cases, both adsorbing (metallic) and oxidizing (TiO2) sites are required: this is the case for carbon monoxide photocatalytic oxidation at room temperature, because TiO2 adsorbs CO very poorly. Adsorption properties of transition metals are mostly dependent on the position of the centre of their d-band , which also means that tuning the position of the center of the d-band by alloying metals allows to control adsorption properties of the metallic nanoparticles, or, in other word, to create a "new" metal.Coupling the catalytic properties of metal nanoparticles with the photocatalytic functions of TiO2 can lead to very interesting synergies: both the catalytic and photocatalytic functions are improved . Preparation and characterization of Pt, Pd and PdPt alloys, deposited on TiO2 will be presented along with some photocatalytic results for simultaneous oxidation of a mixture of pollutants (CO + acetone) in humid atmosphere. Among all samples, only PdPt alloys proved to be very good co-catalysts, demonstrating stronger CO adsorption, very low water sensitivity, and therefore lower water deactivation compared to other monometallic (Au, Pd, Pt, ...) and bimetallic (AuPt, AgPt, NiPt, CoPt, FePt, ...) co-catalysts. Alloying Pd and Pt results in an increased electron density around Pt, enhancing the Pt 5d-CO 2π* back-donation. Therefore, CO adsorption on the alloy is stronger than on the pure metals and CO oxidation is less affected by the presence of other molecules (water, acetone) which would otherwise act as poisons. Those improved results have yet to be explained on the basis of structural, surface and electronic effects affecting the alloy adsorption properties. The structure and surface properties of the alloys have been studied by XPS, HAADF-STEM, and FTIR using CO as a probe molecule. Their electronic properties have been characterized by XPS, TPR/TPD and electrocatalysis towards CO oxidation. Some examples of applications for these metal-semiconductor composites will be given for multi-pollutant indoor air depollution.  E. Christoffersen, P. Liu, H. Skriver, et J.K. Norskov, “Anode Materials for Low-Temperature Fuel Cells: A Density Functional Theory Study,” Journal of Catalysis, vol. 199, 2001, pp. 123-131.  A.V. Vorontsov, I. Stoyanova, D. Kozlov, V. Simagina, et E.N. Savinov, “Kinetics of the Photocatalytic Oxidation of Gaseous Acetone over Platinized Titanium Dioxide,” Journal of Catalysis, vol. 189, 2000, pp. 360-369.
12:15 PM - **O1.8
Electrochemical Synthesis of Core/Shell Dendrimer-encapsulated Nanoparticles.
Richard Crooks 1 , Emily Carino 1 Show Abstract
1 Department of Chemistry & Biochemistry, The University of Texas at Austin, Austin, Texas, United States
We have previously reported a chemical approach for preparing core/shell dendrimer-encapsulated nanoparticles (DENs) in the size range of 1.5 to 2.0 nm. In this case, a core is prepared within a PAMAM dendrimer, and then the shell is added in a second step. In many cases, these materials are catalytically active. Our new results show that similar materials can be prepared by underpotential deposition of the shell onto preformed cores. Results of electrochemical, TEM, and in-situ EXAFS experiments will be discussed.
12:45 PM - O1.9
Size and Composition Controlled Synthesis of Monodispersed Core-shell Nanoparticle Catalysts.
Vismadeb Mazumder 1 , Shouheng Sun 1 Show Abstract
1 Chemistry, Brown University, Providence, Rhode Island, United States
The need to limit the use of Pt in catalysis, has promoted the search for an effective way to increase their catalytic efficiency. Construction of core-shell structures is believed to be one of the ways forward. Here we report a generalized seed-mediated synthetic approach towards the creation of a bimetallic alloy, as well as, a noble metal on a Pd core in the sub-10 nm size range. The mono-disperity of the ~5nm Pd seeds , was critical to the accurate construction of the shells. These surfactant coated core-shell NPs were supported on the Ketjen carbon, and were found to be readily “cleaned” by a 99% acetic acid wash. To demonstrate their usage in catalysis, these core-shell/C NPs were evaluated for the oxygen reduction reaction in both an acidic, as well as base electrolyte – reactions having direct implications in polymer electrolyte membrane fuel cells. The catalysts show no obvious activity degradation after 8000 cyclic voltammetry cycles in the oxygen saturated electrolyte. The synthesis can be extended to create other novel Pt-based nanosystems, which would have implications in myriad fields like optical sensors, hydrogen storage and detection, besides catalysis.Reference: Mazumder, V.; Sun, S.; J. Am. Chem. Soc.,2009, 131, 4588.
O2: Optical Probes for Medical Applications
Tuesday PM, April 06, 2010
Room 2014 (Moscone West)
2:30 PM - **O2.1
Combining Multiple Functions in Single Optically Responsive Nanoparticles for Theranostics.
Naomi Halas 1 Show Abstract
1 ECE Dept.- MS-366, Rice University, Houston, Texas, United States
Plasmonic nanoparticles provide a straightforward and practical approach to the incorporation of multiple functions into the same nanoparticle. These functions can be both passive and active in nature, providing modified or enhanced optical properties, and light driven, optical actuation processes. For diagnostic imaging, enhancing multiple complementary modalities provides new methods for increasing both sensitivity and spatial resolution. Nanoshell-based nanoparticle complexes where near-IR fluorescent imaging and MRI imaging are enhanced simultaneously, to achieve this combination, will be described. Light-driven therapeutics can be photothermal in nature, for inducing hyperthermic cell death, and at lower incident light intensities can also be developed for light-triggered gene therapy. We examine the photophysical properties of light-triggered oligonucleotide release from plasmonic nanoparticles, quantifying this response in terms of releasable molecules per nanoparticle, and evaluating its efficiency in protein downregulation in living cells.
3:00 PM - **O2.2
Gold Nanocages: A Multifunctional Platform for Biomedical Applications.
Younan Xia 1 Show Abstract
1 Biomedical Engineering, Washington University, Saint Louis, Missouri, United States
Gold nanocages can be readily synthesized via the galvanic replacement reaction between silver nanocubes and gold chlodide in an aqueous solution. By controlling the molar ratio of silver to gold chloride, the surface plasmon peaks of gold nanocages can be continuously tuned from the blue (400 nm) to the near infrared (1200 nm). These hollow and porous gold nanostructures have extraordinarily large cross-sections for both absorption and scattering, typically more than five orders of magnitude larger than those of conventional organic dyes. Exposure of gold nanocages to a laser resulted in the effective conversion of light into heat through the photothermal effect. Gold nanocages can be easily bioconjugated with antibodies to target any specific cancer cells. This novel class of nanostructures is being developed as both a contrast agent for optical imaging in early-stage detection of cancer and a therapeutic agent for photothermal treatment of cancer, and as nanoscale capsules for targeted drug delivery.
3:30 PM - **O2.3
Cooperative Nanomaterials to Image, Sensitize, Target, and Treat Tumors.
Michael Sailor 1 , Ji-Ho Park 1 , Luo Gu 1 , Geoffrey von Malzahn 2 5 , Sangeeta Bhatia 2 5 , Erik Ruoslahti 3 4 Show Abstract
1 Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, United States, 2 Harvard - MIT Division of Health Sciences and Technology and Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Boston, Massachusetts, United States, 5 Division of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, United States, 3 Cancer Research Center, Burnham Institute for Medical Research, La Jolla, California, United States, 4 Vascular Mapping Center, Burnham Institute for Medical Research, Santa Barbara, California, United States
There is a growing need for non-toxic alternatives to II-VI and III-V semiconductors that have a chance to make it into the clinic for imaging and diagnosis of human diseases. In this presentation, we will report the synthesis and characterization of non-toxic, brightly luminescent porous silicon-based quantum dots that can circulate through the blood, lodge themselves in tumors long enough to be imaged, and then degrade into harmless by-products.Cooperative nanosystems consisting of two or more discrete nanomaterial classes will also be presented. The addition of a targeting ligand that selectively interacts with cancer cells can improve the therapeutic efficacy of a nanomaterial, although these systems have met with only limited success due to inefficient targeting. A two- component system that enhances overall targeting efficiency will be presented. The first component is gold nanorod NR) "activators" that populate the porous tumor vessels and act as photothermal antennas to specify tumor heating via remote near-infrared (NIR) laser irradiation. We find that local tumor heating accelerates the recruitment of the second component consisting of a (Lyp1) targeted nanoparticle. Mice containing xenografted MDA-MB-435 tumors that are treated with the combined therapeutic system display significant reductions in tumor volume compared with individual nanoparticles or the untargeted ombination.
4:30 PM - **O2.4
Colloidal Nanocomposites for Surface Plasmon-based Sensing.
Luis Liz-Marzan 1 , Ramon Alvarez-Puebla 1 , Isabel Pastoriza-Santos 1 , Jorge Perez-Juste 1 Show Abstract
1 Departamento de Quimica Fíisica, Universidade de Vigo, Vigo Spain
Metal nanoparticles display very interesting optical properties, related to localized surface plasmon resonances (LSPR), which give rise to well-defined absorption and scattering peaks in the visible and near-IR spectral range. Such resonances can be tuned through the size and shape of the nanoparticles, but are also extremely sensitive towards dielectric changes in the near proximity of the particles surface. Therefore, metal nanoparticles have been proposed as ideal candidates for biosensing applications. Additionally, surface plasmon resonances are characterized by large electric fields at the surface, which are responsible for the so-called surface enhanced Raman scattering (SERS) effect, which has rendered Raman spectroscopy a powerful analytical technique that allows ultrasensitive chemical or biochemical analysis, since the Raman scattering cross sections can be enhanced up to 10 orders of magnitude, so that very small amounts of analyte can be detected. In this talk, recent results of our group will be presented, concerning the synthesis of gold nanoparticles with optimized morphology for LSPR biosensing, as well as their assembly within various platforms for SERS-based ultra-detection. First, a survey will be given of wet-chemistry based techniques recently developed to synthesize noble metal nanoparticles with controlled size and shape, including spheres, core-shells, rods, flat prisms and other polyhedra, which can be prepared in a wide (nano)size range. The resulting optical properties will be discussed for the various shapes and sizes, using several theoretical models, with increasing in complexity as the particles deviate from the spherical shape.The final part of the talk will be devoted to describe some recent efforts to design efficient substrates for SERS detection, including the application of a recently developed core-shell colloidal material, comprising gold nanoparticles coated with a thermally responsive poly-(N-isopropylacrylamide) (pNIPAM) microgel, which we denote Au@pNIPAM. While the gold cores provide the necessary enhancing properties, the pNIPAM shells can be swollen or collapsed as a function of temperature, which can be exploited as a means to trap molecules and get them sufficiently close to the metal core for providing the SERS signal.Additionally, we have devised and fabricated a magnetic+optical, bifunctional colloidal system that combines flexible handling and efficient SERS analytical capabilities . This system comprises silica-coated magnetic γ-Fe2O3 (maghemite) cores, coated with a dense monolayer of gold nanorods presenting long-term optical stability and a high density of hot spots per area unit. The magnetic functionality allows for the use a small number of capsules that can be later concentrated under a magnetic field for SERS analysis thereby increasing the detection limits.
5:00 PM - O2.5
Nanoparticle Size Series for in vivo Imaging.
Zoran Popovic 1 , Wenhao Liu 1 , Cliff Wong 1 , Andrew Greytak 1 , Moungi Bawendi 1 , Vikash Chauhan 2 3 , Dai Fukumura 2 3 , Rakesh Jain 2 3 Show Abstract
1 Chemistry, MIT, Cambridge, Massachusetts, United States, 2 Department of Radiation Oncology, Massachusetts General Hospital , Boston, Massachusetts, United States, 3 , Harvard Medical School, Boston, Massachusetts, United States
We report construction and in vivo application of a size series of fluorescent particles spanning 10-150 nm. The particles are based on semiconductor nanocrystals, quantum dots. For the smallest sizes, 10-20 nm, we used polymer coated quantum dots; for 20-70 nm regime we used single quantum dots embedded in silica spheres, while for sizes above 100 nm silica spheres to which multiple quantum dots were electrostatically assembled were prepared. The obtained particles are pegylated, have high emission quantum yield in aqueous solutions and are non-aggregated under physiological conditions. By embedding quantum dots of distinct emission wavelengths in each domain of the size series we were able to simultaneously administer and track particles (in space and time) in vivo. The simultaneous tracking of different size particles enabled us to follow a size dependant particle distribution within the same solid tumor.
5:15 PM - **O2.6
Optical Properties of Shape-controlled Metal Nanostructures and Applications.
Jin Zhang 1 , Adam Schwartzberg 1 , Chun Li 2 Show Abstract
1 Chemistry, UC Santa Cruz, Santa Cruz, California, United States, 2 MD Anderson Cancer Center, University of Taxes, Houston, Texas, United States
Metal nanomaterials have interesting properties and potential applications in various fields. We have studied the optical and structural properties of different metal nanostructures including aggregates, nanorods, and hollow nanospheres with the goal to optimize their optical properties including SERS (surface-enhanced Raman scattering) activities. We have recently demonstrated SERS from single, hollow gold nanostructures and found that exceptional sample homogeneity leads to a nearly tenfold increase in signal consistency over standard silver substrates. SERS offers a unique combination of molecular specificity and extremely high sensitivity for analytical applications. The rationally designed hollow gold nanospheres (HGNs) have turned out to be useful for cancer imaging and therapy applications through a process called photothermal ablation therapy (PTA), with performance significantly improved over conventional solid gold nanoparticles or other metal nanostructures. This has been demonstrated in both in vitro and in vivo PTA of carcinoma and melanoma cancer cells. The success is mainly due to the unique combination small size (30-50 nm), spherical shape, as well as strong, narrow, and tunable surface plasmon absorption of the HGNs.
5:45 PM - O2.7
Gold Nanorods for In Vivo Cancer SERS Detection and Photothermal Therapy.
Andrea Centrone 1 , Geoffrey Von Maltzahn 2 , Ji-Ho Park 3 , Michael J. Sailor 3 , Sangeeta N. Bhatia 2 , T. Alan Hatton 1 Show Abstract
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Chemistry and Biochemistry, University of California, San Diego, San Diego, California, United States
In this work we show for the first time that the near-infrared plasmon resonance of gold nanorods (NRs) may be exploited to provide an integrated platform for in vivo multiplexed SERS detection and cancer photothermal heating. Particular emphasis will be given on in vivo SERS imaging and it will be shown how this technology can be integrated with photothermal cancer therapy and in situ drug delivery. By screening mixed-monolayer NRs, coated with polyethyleneglycol polymers alongside SERS active molecules, we identified three NR formulations that can be uniquely distinguished in vivo over a spectral bandwidth of only 6 nm, a spectral multiplexing density over an order of magnitude greater than semiconductor quantum dots and fluorescence. Such dense multiplexing is fundamental for in vivo applications and allows Raman scattering to be efficiently excited and detected within the near-infrared optical window, where endogenous tissue absorption coefficients are minimal. In addition to their applications in diagnosis and imaging, plasmonic materials have recently attracted attention for their potential to serve as targeted nano-antennas for selective tumor ablation. Unluckily, traditional means for delivering external energy into tumors lack selectivity over surrounding normal tissues. Plasmonic nanoantennas offer an opportunity to alter this paradigm by imparting their optical properties to tumor tissue and enabling deposition of otherwise harmless near-infrared energy into tumors. We utilized gold nanorods with peak plasmon resonance at 790nm, designed to match our SERS excitation source (785 nm) and still provide strong optical absorption at 810nm for photo-thermal heating.Given the characteristic Raman fingerprint of the molecular labels on the NRs, we named to them SERS-coded NRs. SERS-coded NRs are found to be highly stable, to be detectable down to attomolar particle concentrations, and to have low baseline cytoxicity in vitro. In vivo, they were efficiently detected following subcutaneous, intratumoral or intravenous injection and enabled remote photothermal tumor heating to ablative temperatures. Moreover, the NRs or a saline solution was injected intravenously into mice bearing two tumors on opposite flanks. Once the NRs had cleared from circulation, the right flank of each mouse was irradiated for 5 min and all tumors were measured at regular intervals. Within 10 days all the irradiated, NR-targeted tumors completely disappeared, while all other tumors continued to grow. We also combined SERS imaging and photo-thermal therapy with in situ cancer drug delivery, using SERS- coded NRs and thermo-responsive liposomes loaded with anticancer drugs. Both nanomaterials passively accumulate into the tumor tissues. The heat generated via the NRs’s surface plasmon was exploited for direct cancer destruction but also for triggering the selective release of drugs from the liposomes and increasing the therapy efficacy.
O3: Poster Session
Tuesday PM, April 06, 2010
Exhibition Hall (Moscone West)
6:00 PM - O3.10
Enhanced Laser Mark Contrast Pigments from Core-Shell Nanoparticles.
Leonard Radzilowski 1 , Jian Wang 1 , Laura Gurevich 1 , Mark Ellsworth 1 Show Abstract
1 , Tyco Electronics Corporation, Menlo Park, California, United States
Our laboratory has developed a number of methods for encapsulating inorganic nanoparticles such as titanium dioxide in silsesquioxanes. In particular, two solution-based methods have been developed that deposit as much as 50% wt. silsesquioxane. In one method, a silsesquioxane shell is grown on the nanoparticle surface starting from an alkoxysilane. Titanium dioxide nanoparticles are dispersed in water with ammonium hydroxide, which creates a charged titanium dioxide surface that stabilizes the dispersion and which catalyzes the polymerization of the silane through hydrolysis and dehydrative polycondensation. In a second method a silicone polymer such as polyphenyl silsesquioxane (PPSQ) is adsorbed onto the surface of titanium dioxide nanoparticles from a toluene-water emulsion. After removing the toluene, ammonium hydroxide is added to catalyze crosslinking of PPSQ and produce an insoluble shell. Core-shell nanoparticles prepared by either of these methods are then directly formulated into coatings. With proper choice of the silsesquioxane shell, such nanoparticles are used, for example, as a pigment in a coating that yields irreversible black marks when irradiated with a laser. The degree of blackening is enhanced by the presence of the PPSQ shell compared to uncoated titanium dioxide particles.
6:00 PM - O3.11
Long Range Ferromagnetic Ordering in Nano Crystallite (BiFeO3)1-x (PbTiO3)x Multiferroic Systems at Room Temperature.
Kuldeep Singh 1 , Ashish Gautam 1 , K. Sen 1 , M. Singh 1 Show Abstract
1 Physics, Himachal Pradesh University, Shimla, Himachal Pradesh, India
In recent years, more attention has been paid to multiferroic materials which possess the combined properties of ferromagnetism, ferroelectric or ferroelasticity, owing to their physical mechanism and have potential application for the design of multifunctional devices. The perovskite BiFeO3 (BFO) is one of the few known magnetoelectric multiferroic materials in which ferroelectric (Tc~830oC) and antiferromagnetic (AF) (TN~370 oC) order parameters coexist up to quite high temperature. Four samples (BiFeO3)1-x (PbTiO3)x (called PFPTx) were prepared through solution combustion technique Particle size calculated using Scherrer formula lie in range 7- 8 nm. The transmission electron micrograph of BPFT0 showing spherical particles, with a narrow particle size distribution in the range 3- 12 nm.Particle size is in close agreement with that obtained from XRD. Differential scanning calorimetry (DSC) data, showing the magnetic transition temperature ( Tn = 370oC) of BPFT0 and XPS is used to identify the valence numbers of Fe ion in BPFT0. It has been known that the binding energies of Fe2+ and Fe3+ are slightly different, which can be separated from the XPS spectra. The measured Fe 2p3/2 peaks were not able to deconvolute into two peaks, corresponding to Fe2+ and Fe3+ states, which suggests that the concentration ratio between Fe2+ and Fe3+ is not comparable. The Fe 2p3/2 spectra have been fitted with a single peak. The centre of the peak was calculated to be 711.2 eV, which reflects that the valence number of Fe ion in BPFT0 ceramics is close to trivalent Fe3+. The long range ferromagnetic ordering as evident from well defined Mössbauer sextets exists at room temperature. The magnetic hyperfine splitting spectra indicate that the Neel temperature of BPFT0 nano particles is above room temperature as confirmed from DSC measurement. Mössbauer spectra of BPFT0 yield six line spectra with an isomer shift of 0.24mm/s and a hyperfine field (H) of 49.6mm/s which clearly shows the presence of Fe3+ state only; as observed from XPS. A doublet with isomer shift 0.19 mm/s and Q.S 0.51mm/s is also observed which (correspond to Fe3+) indicates the super paramagnetic behaviour of BPFT0 nano particles. Doping of Pb2+ for Bi3+ should force trivalent iron either in to tetravalent state or intermediate valence state between trivalence and tetravalence or result in the oxygen vacancies in the system. However, the observed Mössbauer spectra rules out the possibility of either intermediate valence or the tetravalence of iron. This may be due to compensation of charge by substituting Ti4+ for Fe3+. Quadrupole splitting 0.14mm/s observed for BPFT0 nano particles clearly indicates rhombohedral structure as observed from XRD. Hyperfine interaction field decreases from 49.9 T for BPFT0 to 44.2 T for BPFT2 which may be due to substitution of non-magnetic ions (Ti4+) for Fe3+.
6:00 PM - O3.13
Novel Solid Nanohybrids that Stabilize Oil/Water Emulsions and Catalyze Reactions at the Interface.
Jimmy Faria 1 2 , Min Shen 1 2 , Steven Crossley 1 2 , Daniel Resasco 1 2 Show Abstract
1 School of Chemical, Biological, and Materials Engineering, University of Oklahoma, Norman, Oklahoma, United States, 2 Center for Biomass Refining, University of Oklahoma, Norman, Oklahoma, United States
A novel system has been developed to catalyze reactions at the oil/water interface of a biphasic liquid system. Stabilization of emulsions was accomplished through the use of nanohybrids composed of hydrophilic oxide particles and hydrophobic Carbon Nanotubes (SWNT), generated in the CoMoCAT process (1-4). These nanohybrids are inherently amphiphilic, and tend to adsorb at the interface of a biphasic water/oil liquid system. When enough energy is added to the system, these particles stabilize emulsions by suppressing the coalescence of the droplets (5). Depending on whether the particles are more hydrophilic or more hydrophobic they tend to stabilize oil-in-water or water-in-oil emulsions, respectively. The resulting emulsions are remarkably stable against coalescence and sedimentation, and can be easily separated by filtration or centrifugation, which make them suitable for applications in interfacial catalytic processes in which the catalyst can be easily recovered after reaction. The catalytic activity was provided by the deposition of transition metals onto the nanohybrids. Which allow the selective catalysis of reactions at the Oil/Water interface. The proof-of-concept of the biphasic hydrogenation and condensation catalysis was performed in three substrate classes of interest in biorefining. The first example was the hydrodeoxygenation of vanillin (4-hydroxy-3-methoxybenzaldehyde). The next one was the conversion of molecules that were exclusively soluble in the aqueous or the organic phase, like glutaraldehyde (water phase) and octanal (oil phase). Finally we explored a tandem reaction sequence in which Pd-catalyzed hydrogenation was paired with a preceding Aldol-condensation of 5-methylfurfural and acetone. The results show that with these nanohybrids is possible to perform selectively hydrodeoxygenation and condensation reactions at the water/oil interface of a biphasic system, followed by migration of the products to the oil phase. This contribution provides a proof-of-concept for a very promising catalytic system with many potential applications in the liquid phase, such as bio-oil upgrading, specialty chemicals, and pharmaceutical applications where selective reaction and separation based on water solubility are desirable.References:(1) W. E. Alvarez, B. Kitiyanan, A. Borgna, D. E. Resasco, Carbon 39, 547 (2001). (2) W. E. Alvarez et al. , Chem. Mater. 14, 1853 (2002). (3) D. E. Resasco et al. J. Nanopart. Res 4, 131 (2002).(4) D. E. Resasco, B. Kitiyanan, J. H. Harwell, W. Alvarez. U.S. Patent No. 6,333,016 (2001)(5) M. Shen, D.E. Resasco, Langmuir 25, 10843 (2009).
6:00 PM - O3.14
Multifunctional Nanoparticle Networks as Transparent Conducting Electrodes for Solar Cells.
Dennis Callahan 1 , Jeremy Munday 1 , Harry Atwater 1 Show Abstract
1 Applied Physics, Caltech, Pasadena, California, United States
There has been increased interest recently in the use of metallic nanoparticles to enhance the absorption in thin film solar cells. These studies mainly focus on the increased scattering efficiency of metallic nanoparticles in the visible region with the aim of redirecting long wavelength incident photons into guided modes within the solar cell, resulting in an increased path length. This would allow for much thinner active layers, leading to many advantages such as decreased dark current, relaxation of material quality requirements and reduction in material consumption. A previous study  has suggested the possibility that such nanoparticle arrays may also improve the cell’s fill factor by as much as 18%. Here, we explain this previous result by demonstrating that metallic nanoparticle arrays may also decrease the sheet resistance along the top of the solar cell, in addition to increasing the photocurrent. Thin films of various metals (Ag, Au, Cu) were deposited by thermal evaporation at 5x10-6 Torr with thicknesses varying from 2-30 nm on both GaAs and fused quartz substrates. These films were then annealed at various temperatures in 2.5 LPM of H2/N2 atmosphere to break up the metal layers into nanoparticles. Nanoparticle densities were studied ranging from sparse (~3x109 particles/cm2) to moderate (~7x1010 particles/cm2), until eventually resembling interpenetrating networks of continuous metal. 4-point probe measurements were performed on the samples to extract the effective sheet resistance of the nanoparticle-decorated surfaces. Scanning electron microscopy and atomic force microscopy were performed to determine the nanoparticle size, density and overall coverage. Identical experiments were performed on transparent fused quartz substrates to determine the transparency of the nanoparticle arrays with various surface coverage. Sheet conductance was found to increase by 10-30%, depending on initial Ag film thickness, eventually approaching that of bulk silver upon the onset of continuous metal film. A simple resistor network model is presented to explain the observed results. This study suggests the multifunctionality of metallic nanoparticle arrays for solar cell modification in that they may have the potential to simultaneously improve all relevant solar cell parameters, including short circuit current, open circuit voltage, fill factor and overall conversion efficiency.  Nakayama et al. Applied Physics Letters. 93, 121904 (2008).
6:00 PM - O3.15
CuInS2/Au Heterostructured Nanoparticles: Plasmonic Properties and Their Photocatalytical Applications.
Yeming Xu 1 , Quan Li 1 Show Abstract
1 physics department, the Chinese University of Hong Kong, Hong Kong China
Recent demonstration of increased light absorption in a number of semiconductors as a result of scattering from noble metal nanoparticles have suggested promising application of semiconductor/Au heterojunctioned nanostructures in the field of both energy and photocatalysis. I-III-VI2 chalcopyrite compounds, in particular, nanostructured Cu(In1-xGax)(SySe1-y) are one of the most promising semiconductor candidates for photovoltaic and visible-light-driven photocatalytic applications due to their excellent optical properties—this family of material has direct band-gap and high optical absorption coefficient with desirable absorption range that matches the solar spectrum. In the present study, the heterostructured CuInS2-Au nanoparticles were synthesized with two controllable morphologies, i.e., CuInS2 nanocrystal surface decorated with multiple Au nanoparticles, and core/shell nanocrystals (Au@CuInS2). Their microstructure, electronic and optical properties were investigated in detail. In particular, the change of the Au surface plasmon (SPR) is carefully investigated using single heterstructured nanoparticles. Obvious red shift of the Au SPR energy (from ~520 nm to ~620 nm) was only observed in nanoparticles with¬ core/shell configuration. The core/shell Au@CuInS2 nanoparticles also demonstrate excellent photocatalytic response under visible light, being improved when comaring to the reported gold-loaded CuInS2 photocatalyst. This work is supported by grants from the GRF of HKSAR under project No. 414908, 414709, and CUHK Focused Investment Scheme C.
6:00 PM - O3.16
Enhanced Semiconductor Nanocrystal Conductance via Solution Phase Growth of Metal Contacts.
Mathew Sheldon 1 4 , Brandon Beberwyck 1 4 , Taleb Mokari 2 , Lin-Wang Wang 3 , Paul Alivisatos 1 4 Show Abstract
1 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States, 4 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Single nanostructure electrical measurements directly probe the fundamental limits of semiconductor device miniaturization, providing precise characterization of electronic structure resulting from quantum confinement and dimensional control. When employed to study individual colloidal semiconductor nanocrystals, the technique can also determine the ultimate transport efficiencies of these materials, essential for optimizing their performance in energy harvesting and other electronic and optoelectronic applications. Crucially, single particle experiments elucidate the semiconductor-metal interface between the nanoparticle and the device electrode, which determines the barrier physics to charge injection and thereby overall device performance. Here we show that direct solution phase growth of contact metals onto the semiconductor decreases the interface barrier, giving over 100,000 times conductivity enhancement per particle. Further, we systematically vary the contact metal and semiconductor nanoparticle to understand trends in electronic response. Our results emphasize the importance of nanoscale interface structure for robust device performance and the advantage of this contact method.
6:00 PM - O3.21
Au Nanocages: Promising Catalysts for Redox Reactions.
Jie Zeng 1 , Qiang Zhang 1 , Jingyi Chen 1 , Younan Xia 1 Show Abstract
1 Department of Biomedical Engineering, Washington University in St Louis, St Louis, Missouri, United States
We have evaluated the catalytic properties of Au-based nanostructures (including nanocages, nanoboxes, and solid nanoparticles) using a model reaction based on the reduction of p-nitrophenol by NaBH4. From the average reaction rate constants at three different temperatures, we determined the activation energy, the entropy of activation, and the pre-exponential factor for each type of Au nanostructure. The kinetic data indicates that Au-based nanocages exhibit the highest catalytic activity relative to either nanoboxes or nanoparticles. The considerable enhancement in catalytic activity for the Au nanocages can be probably attributed to the following two factors: i) the nanocage could provide a much larger surface (per particle) than a small solid nanoparticle to simultaneously accommodate both the oxidation and reduction half reactions; and ii) the ultrathin walls of the nanocage could provide a much higher activity than a big solid nanoparticle due to the size effect. In other words, the superior catalytic activity of the Au nanocages is a result of two effects -- good electrical connection and small size -- related to their ultrathin and highly porous walls. In addition, a compensation effect was observed in this catalytic system, which can be primarily interpreted by a model based on kinetic regime switching. Key words: gold nanostructures, catalysis, redox, compensation effectReferences(1) Skrabalak, S. E.; Au, L.; Li, X. D.; Xia, Y. Nat. Protoc. 2007, 2, 2182.(2) Zeng, J.; Huang, J.; Lu, W.; Wang, X.; Wang, B.; Zhang, S.; Hou, J. Adv. Mater. 2007, 19, 2172.(3) Schrinner, M.; Ballauff, M.; Talmon, Y.; Kauffmann, Y.; Thun, J.; Moller, M.; Breu, J. Science 2009, 323, 617.(4) Esumi, K.; Isono, R.; Yoshimura, T. Langmuir 2004, 20, 237.
6:00 PM - O3.22
Heat Generation in Illuminated Gold Nanoparticles on a Flat Surface.
Nan Zeng 1 , Anthony Murphy 1 Show Abstract
1 CSIRO Materials Science and Engineering, CSIRO, Sydney, New South Wales, Australia
Gold nanoparticles strongly absorb visible light of wavelength near520 nm through surface plasma resonance. The energy absorbed by the nanoparticles is converted to heat and thus increases the nanoparticles' temperature. Applications of this effect include modifying the shape of the nanoparticles, as well as using them as nanoscale heat sources to heat surrounding materials, such as polymers, ice, or biological cells. The aim is usually to use the heat generated to change the phase of the surrounding materials. We have previously studied heat transport problem for nanoparticles embedded in a homogeneous dielectric material, and identified the concentration of nanoparticlesas a major factor in determining the substrate temperature increase. For a porous system, where nanoparticles reside on the interface between the substrate and the voids, additional factors need to be considered. Air convection and conduction become important, as does their relation to the porosity of the system and the size of the pores.In this paper, we studied a model with gold nanoparticles adsorbed onto the surfaces of a porous polymer substrate. They are connected to the substrate through linker molecules. A flashlamp is used to irradiate the nanoparticles. The absorption efficiency of a cluster of nanoparticles is calculated using the T-matrix method. The heat transport equation is solved using the finite element method. Our results allow us to estimate the heating efficiency of gold nanoparticles in such a system.
6:00 PM - O3.23
Polycrystalline Semiconductor Nanowires: Controlling Electronic Coupling and Waveguiding.
Jianhong Zhang 1 , Andrey Lutich 1 , Christian Mauser 1 , Jessica Rodriguez-Fernandez 1 , Andrei Susha 1 2 , Markus Doeblinger 3 , A. Govorov 4 , Andrey Rogach 1 2 , Frank Jaeckel 1 , Jochen Feldmann 1 Show Abstract
1 Department of Physics and CeNS, Ludwig-Maximilians-University Munich, Munich Germany, 2 Department of Physics and Materials ScienceDepartment of Physics and Materials Science, University of Hong Kong, Hong Kong China, 3 Department of Chemistry, Ludwig-Maximilians-University Munich, Munich Germany, 4 Department of Physics and Astronomy, Ohio University, Athens, Ohio, United States
Polycrystalline semiconductor nanowires prepared from colloidal semiconductor nanocrystals display an array of extraordinary optical properties. Single nanowires display optical waveguiding over distances of several micrometers rendering them promising for nanoscale optical interconnects. The photoluminescence peak wavelength of individual nanowires can be controlled thermomechanically via the distances between the nanocrystals in the wire at different temperatures . Furthermore, strong anisotropic absorption, photoluminescence and Rayleigh scattering of both single nanowires and macroscopically aligned films are observed. J. Zhang, A.A. Lutich, A.S. Susha, M.Döblinger, A.O. Govorov, A.L. Rogach, F. Jäckel, J. Feldmann, submitted
6:00 PM - O3.25
Design and Fabrication of Nanostructured Particles Exhibiting Enhanced Optical Functionality.
Robin Klupp Taylor 1 5 , Monica Distaso 1 5 , Volodymyr Lobaz 1 5 , Mathias Hanisch 1 5 , Huixin Bao 1 , Wolfgang Peukert 1 5 , Oleksandr Zhuromskyy 2 5 , Ulf Peschel 2 5 , Dina Ibragimova 4 5 , Andreas Hirsch 4 5 , Frantisek Seifrt 3 5 , Guenter Leugering 3 5 Show Abstract
1 Institute of Particle Technology, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 5 Cluster of Excellence "Engineering of Advanced Materials", Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 2 Institute of Optics, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 4 Institute of Organic Chemistry 2, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 3 Insititute of Applied Mathematics, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany
The optical properties of small particles are key to many applications including pigments, cosmetics, optoelectronic devices, radiation control etc. In general due to the synthesis techniques available, such functional particles are usually single phase with simple or disperse morphologies. It is also known qualitatively from the literature that certain particle morphologies (spheres, rods etc.) and compositions can often lead to more favourable properties. In this paper we will summarize the work of an interdisciplinary industrial collaboration in the framework of the Cluster of Excellence “Engineering of Advanced Materials – Hierarchical Structure Formation for Functional Devices” situated at the University of Erlangen-Nuremburg, Germany. The goal of this work is to demonstrate a process chain for the design and synthesis of functional optical particles. The chain begins with 3D finite element method-based topology and shape optimization techniques. These provide suggestions for non-intuitive particle morphologies and compositions. These designs are being used as signposts for the development of real particle systems with enhanced properties. Our experimental work uses a range of colloidal techniques to synthesize nanostructured particles e.g. by “oriented attachment” assembly, sol-gel nanocoating and seeded growth. Areas of particular interest that will be introduced include particles which are designed to be transparency in one part of the optical spectrum but have strong extinction in another part as well as multifunctional magneto-optical particles. Since mathematical optimization often leads to reduced-symmetry particles, our work on the synthesis of asymmetrically coated particles (Janus particles) via modified colloidal techniques will also be presented.Product optical properties are often modified by particle-particle interactions. Hence, the use of simulation techniques such as the t-matrix method, which are being utilized to handle aggregates of the complex particles developed in this project, will be discussed.It is hoped that this paper will provide an overview of the progress of a broadly applicable strategy for the discovery and development of novel highly-functional optical particle systems.
6:00 PM - O3.26
Charge-selective Raman Scattering and Fluorescence Quenching by Metal Nanoparticle Monolayers on Semiconductor Substrates.
Karthik Bhatt 1 , Susheng Tan 1 , Kaan Kalkan 1 Show Abstract
1 , Oklahoma State University, Stillwater, Oklahoma, United States
An interesting attribute of monolayers of metal nanoparticles (NP) synthesized on semiconductor substrates is charging of NP induced by the Fermi level difference. This charging can be tapped in self-assembly, as well as selective adsorption of ions on NP, which augments the application of NP in surface plasmon resonance (SPR) sensors, surface-enhanced Raman scattering (SERS) substrates and other plasmonic devices. Although charging of NP is demonstrated in the literature by using surfactants, surfactant molecules cause signal interference. Further, surfactants form a physical barrier between analyte and metal, attenuating or completely eliminating surface-enhanced effects. In the present work, silver nanoparticles (AgNP) were synthesized on high conductivity Si wafers (p- and n-type) employing the electroless reduction of AgNO3 by Si, as well as vapor deposition. Electric force microscopy (EFM) confirms the presence of NP charge and its expected variation (charge and magnitude) with the Fermi level difference. The electric potential measured 100 nm from the NP, shows a monotonous increase with the nanoparticle size that we explain by a simple dipole approximation for the NP-semiconductor charge couple and depletion assumption for the semiconductor space charge region. Using our charged, surfactant free nanoparticles, we demonstrate charge selective Raman scattering and fluorescence quenching for ionic fluorophores (fluorescein(-), rhodamine-6G(+) and acridine orange(+)). Furthermore, we infer from atomic force microscopy (AFM) and optical absorption, that this charging phenomenon plays an important role in self-inhibiting growth of Ag nanoparticles (AgNP) during chemical reduction. In particular, the positively charged AgNP do not coalesce despite a few nm interparticle spacing. Therefore, strong electromagnetic interactions between the particles develop, resulting in well resolved hybrid plasmon modes as inferred from optical extinction. On the contrary, self-inhibition does not occur with negatively charged AgNP, resulting in the loss of surface plasmon resonance.
6:00 PM - O3.28
The Synthesis of Cu Nano Ink Using an Electrolysis Method and Application of Inkjet Printing.
Jin-min Cheon 1 , Jongryoul Kim 1 , Yong-Ho Choa 2 Show Abstract
1 Materials Engineering, Hanyang Unv., Ansan Korea (the Republic of), 2 Chemical Engineering, Hanyang Unv., Ansan Korea (the Republic of)
Increasing productivity of conductive nano-metal powder ink is recognized as a critical issue for the production of electro-magnetic devices using ink-jet printing. This paper presents a new synthesis method of Cu nano-particles mass-production using an electrolysis method. Compared with previous chemical methods, the electrolysis method makes it possible to fabricate Cu nano-particles directly from Cu plate. This can both reduce the production cost and increase productivity of Cu nano-particles. When voltage flows at Cu plate, Cu ions spring up to electrolyte and then change into Cu nano-particles by reduction agent and dispersion agent. Electrolyte containing the Cu nano-particles can be directly used as Cu conductive ink. In the electrolysis method, Cu nano-particles what having a variety size distribution are obtained by controlling voltage, dispersion agent, and reduction agent. Voltage is too high (ex. 300V), hydrolysis is rapidly occurred. In consequence, water is evaporated and electrolyte’s concentration is changed. Therefore 100~200V is suitable. Cu nano-particles are expected to form high-angle boundaries because of high surface-diffusion rate. So oxidation is critical problem of copper nano-particles. We obstruct oxidation by controlling electrolyte (ph control agent, dispersion agent, solvent, etc.). We print a pattern using inkjet printer (piezo-type single nozzle). After drying the pattern in vacuum oven at 60°C during 24hr, it is sintered in air, H2. And then the pattern is measured whether it is oxidized or not. To confirm low temperature sintering possibility for applying to flexible substrate, the pattern is sintered at 150°C, 200°C and 250°C. After that, we analyze sintering behavior by SEM image and measure resistivity of the pattern.
6:00 PM - O3.29
Dynamics of Electronic Relaxation in PbSe Quantum Dot Films.
Jesse Engel 1 2 , Matt Sheldon 1 2 , Wanli Ma 1 2 , Paul Alivisatos 1 2 Show Abstract
1 Materials Science, UC Berkeley, Berkeley, California, United States, 2 Materials Science, Lawerence Berkeley National Lab, Berkeley, California, United States
Films of colloidally synthesized quantum dots, with their size-tunable bandgaps and solution-based processing, show promise for use as electronic and optoelectronic devices such as solar cells, photodiodes, and transistors. However, charge transport through a quantum dot film is distinctly different from that through an extended crystalline solid. The films exhibit an energy landscape of localized states disordered in both their onsite energies, due to size polydispersity, and there structural periodicity, due to film packing. Hopping models have proven very effective in describing the conduction of these systems in the steady state, however much is still unknown about their dynamics. Electron localization leads to poor screening, allowing for long range coulomb interactions to play an important role. In terms of variable range hopping, this manifests itself by the creation of a “coulomb gap” in the density of states near the Fermi level due to carrier-carrier repulsion. Such systems are often referred to as coulomb glasses, as correlated electron dynamics and many-electron hopping events that arise from these interactions can lead to “glassy behavior”, such as long relaxation times due to the frustration of the minimization of configurational energy.Here, we present results on the time evolution of the resistance of PbSe quantum dot films, indicative of the relaxation of the coulomb glass. Thin film nanocrystal transistors were fabricated by evaporating patterned electrodes, with channel lengths and widths varying from 1-10um and 25-750um respectively, on n-doped Si wafers, with 100nm of dry oxidized silicon dioxide as a gate insulator. PbSe quatum dots 5 nm in diameter were colloidally synthesized and deposited on the transistor substrates via spincoating. To reduce particle spacing and increase interparticle coupling, films were then soaked in solutions of benzenedithiol in acetonitrile, to allow for ligand exchange with the native oleic acid ligands. Films were kept air-free in an argon environment for the entire course of the experiment. We observe distinctive power law decays on the order of thousands of seconds, which vary with voltage and temperature. Transient peak heights and power law decay exponents are found to increase for higher applied fields, with peak heights reaching an order of magnitude higher than the steady state at electric field values of 100kV/cm. The decay transients for increasing fields are also found to turn into growth transients (exponent > 0) for decreasing fields, leading to pinched hysteresis loops in I-V characteristics for sweep rates greater than 0.01V/s. Steady state conductance values are found to correspond to predictions for space charge limited transport with traps. Our results emphasize the correlation of the nonlinear features in the transient decay of film resistance and its equilibrium values to the dynamics of relaxation in the coulomb glass.
6:00 PM - O3.3
Synthesis and Characterization of TiO2 Nanoparticles: A Potential Adsorbent for As(III) Removal from Water/Wastewater.
Zuleyha Kocabas 1 , Yuda Yurum 1 Show Abstract
1 Material Science and Engineering, Sabanci University, Istanbul Turkey
Titanium dioxide, a well-known adsorbent material, has been extensively tested in environmental applications, especially in separation technologies. In the present study, TiO2 nanoparticles were synthesized by using sol-gel method for removing arsenide (As(III)) ions from water/wastewater. Several water/titanium molar ratios were prepared in order to obtain optimum crystalline structure, morphology, and particle size of titanium dioxide nanoparticles. Two types of TiO2 minerals which were rutile and anatese were mainly synthesized at different calcination temperatures. After characterization of synthesized powders by X-ray diffraction and scanning electron microscopy (SEM), batch adsorption experiments were carried out to analyze removal capacity of the titanium nanoparticles. Residual arsenic concentrations of the solutions treated with titanium dioxide nanoparticles were measured with a Varian, Vista-Pro CCD simultaneous inductively coupled plasma ICP-OES spectrophotometer. The adsorption isotherms, kinetic and thermodynamic parameters of batch adsorption experiments were achieved. The maximum % of removal of arsenic was found ~77% at pH 3, respectively when 0.1 g rutile type TiO2 nanoparticles were used at the As0 5 ppm. Anatase type of TiO2 nanoparticles had also closer adsorption capacity which was ~63% at pH 6 with the same initial arsenic concentration. This study proposes the potential adsorbent material for water/wastewater which is contaminated with As(III) species.
6:00 PM - O3.30
Diameter Control and Theoretical Simulation of Ag-Au-Ag Heterometallic Nanowires.
Jongwook Jung 1 , Daeha Seo 1 , Hyunjoon Song 1 Show Abstract
1 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
One dimensional nanostructures have been used as basic and significant parts to fabricate nanodevices as well as an appropriate system to demonstrate quantum size and surface effects of nanomaterials. In this work, we prepared heterometallic nanowires with different thickness by a seed-mediated process using Au decahedral seeds. The thickness of the heterometallic nanowires was controlled by adjusting the size of the Au decahedral seeds, which play important roles to determine the dimension of heterometallic nanostructure. The resulting Ag-Au-Ag heterometallic nanowires have the diameters of 63 nm from small seeds (diameter : 52 nm), 86 nm for medium seeds(81 nm), and 146 nm for large seeds(143 nm), respectively. The Au and Ag segments in the Ag-Au-Ag heterometallic nanowires were analyzed by EDS, line profile, and elemental mapping. This seed-mediated process has advantaged in high yield, template-free, and relatively low reaction temperature.Optical properties of the Ag-Au-Ag heterometallic nanowires were studied to correlate with theoretical results by DDA (discrete dipole approximation) calculations. In UV-vis spectra, the peaks were significantly red-shifted when the nanowire thickness was increased. In this presentation, we demonstrated the synthesis and diameter control of Ag-Au-Ag heterometallic nanowires, and analyze their optical behaviors by DDA simulations.
6:00 PM - O3.31
Synthesis and Characterization of High Quality QDs Based on Thermal Decomposition Mechanism of Single Molecule Precursor Forming Nanoparticles.
Yun Ku Jung 1 , Jin-Kyu Lee 1 Show Abstract
1 Chemistry, Seoul National University, Seoul Korea (the Republic of)
Recently, metal dialkyldithiocarbamates have been used as a single-molecule source for the synthesis of semiconductor QDs and rare-earth metal sulfide (MS) nanoparticles. Zinc diethylthiocarbamate (Zn(DETC)2) has also been used as a single-molecule source for QD synthesis; in this method, ZnS shells are grown around the surface of CdSe QDs in a microfluidic system. We have investigated in order to understand the formation of MS nanoparticles. The major intermediates and side products were isolated under various conditions and characterized by NMR spectroscopy and LC-MS. The analysis results showed that nucleophilic attack of the metal-coordinated amine on the most electron-deficient thiocarbonyl carbon of the alkyldithiocarbamate ligands at a high temperature initiated the decomposition to generate thiourea, hydrogen sulfide, and solid MS nanoparticles. The critical role of the amine in the thermolysis method used for the synthesis of metal sulfide (MS) nanoparticles could be extended to the synthesis of metal oxide (MOx) nanoparticles as well. We have synthesis high quality semiconductor QDs based on the thermal decomposition mechanism of single molecule precursor. Compared to purified QDs, which are removed excess organic ligands such as TOPO, the synthesized high quality semiconductor QDs are air stable for long time and the PL intensity is increased about 20 times. We speculate that thermal decomposition could be extended to many interesting applications such as generation of alloy nanoparticles through consecutive thermolysis of various single molecule precursor.
6:00 PM - O3.32
Probing the Photothermal Effect of Au-based Nanocages With Surface-enhanced Raman Scattering.
Matthew Rycenga 1 , Younan Xia 1 Show Abstract
1 Biomedical Engineering, Washington University, Saint Louis, Missouri, United States
Metal nanoparticles can efficiently generate heat in the presence of electromagnetic radiation. This process, known as the photothermal (PT) effect, has the potential for use in a variety of applications from cancer therapy to lithography. However, characterizing the heat generated by metal nanoparticles is difficult, and fundamental to engineering the PT effect for practical use. To this end, we demonstrate a simple approach to probe the heat generated by Au-based nanocages using surface-enhanced Raman spectroscopy (SERS). The continuous wave lasers of a Raman microscope were used to excite the nanocages for both the SERS and PT effect. Because SERS directly measures the chemical structures of molecules on a metal nanoparticle, this technique can be used to determine the temperature at a nanoparticle's surface by employing probe molecules with measurable, temperature-dependent structural changes. The trans and gauche conformations of well-ordered alkanthiolate self-assembled monolayers (SAMs) chemisorbed to the nanocages were used to determine disorder in the SAMs caused by the heat released from the PT effect. Through controlled studies and molecular dynamic simulations these SAMs were calibrated to act as a ‘thermometer’ for determining the temperature at the nanoparticle surface for different excitation wavelengths, nanoparticle LSPRs, and nanoparticle compositions. Our data confirms the PT effect is greater when the excitation wavelength matches the LSPR of the particles, demonstrates the ability of SERS to monitor the PT effect of metallic nanoparticles, and shows the Au-based nanocage PT effect can increase surface temperatures by as much as 60 degrees.
6:00 PM - O3.33
Synthesis of Au(core)/Ag(shell) Nanoparticles and Their Conversion to AuAg Alloys.
Matthew Shore 1 , Junwei Wang 1 , Aaron Johnston-Peck 1 , Joseph Tracy 1 Show Abstract
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Au(core)/Ag(shell) and AuAg nanoparticles (NPs) with diameters of 10 nm and controlled compositions were synthesized through digestive ripening and annealing. This approach is highly general and is potentially applicable for synthesizing many kinds of core/shell and alloy NPs with novel plasmonic and catalytic properties. Au NPs stabilized by dodecylamine (DDA) were first synthesized through digestive ripening in refluxing toluene, and addition of primary amines and silver acetate under different conditions resulted in Au(core)/Ag(shell) and AuAg alloy NPs when the amine reduced Ag(I) to Ag(0). An advantage of this method is that Au NPs serve as the seeds for forming binary NPs, because growth of monodisperse Ag NPs is usually more challenging than Au. Deposition of Ag on Au requires an additional reducing species (primary amine) and cannot occur through galvanic exchange. Adding silver acetate and DDA in toluene to ripened Au NPs and further refluxing produced Au(core)/Ag(shell) NPs. The structure and composition were analyzed by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Growth of the Ag shell is accompanied by a small blue shift in the surface plasmon resonance absorbance. When annealing the Au(core)/Ag(shell) NPs in oleylamine at 250 °C, they convert to AuAg alloy NPs, and their absorbance b