Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A22: Focus Session: Hybrid Organic-Inorganic Nanomaterials I: Patterning and Self Assembly |
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Sponsoring Units: DPOLY Chair: R Kannan, Wayne State Room: Morial Convention Center 214 |
Monday, March 10, 2008 8:00AM - 8:12AM |
A22.00001: Connecting quantum dots and bionanoparticles in hybrid nanoscale ultra-thin films Ravisubhash Tangirala, Yunxia Hu, Qingling Zhang, Jinbo He, Thomas Russell, Todd Emrick Aldehyde-functionalized CdSe quantum dots and nanorods, and horse spleen ferritin bionanoparticles, were co-assembled at an oil-water interface. Reaction of the aldehydes with the surface-available amines on the ferritin particles enabled cross-linking at the interface, converting the assembled nanoparticles into robust ultra-thin films. The cross-linked capsules and sheets thus made by aldehyde-amine conjugation could be disrupted by addition of acid. Reductive amination chemistry could be performed to convert these degradable capsules and sheets into structures with irreversible cross-linking. Fluorescence confocal microscopy, scanning force microscopy and pendant drop tensiometry were used to characterize these hybrid nanoparticle-based materials, and transmission electron microscopy (TEM) confirmed the presence of both the synthetic and naturally derived nanoparticles. [Preview Abstract] |
Monday, March 10, 2008 8:12AM - 8:24AM |
A22.00002: Janus Au Nanoparticle Patterning via Polymer Single Crystals Christopher Li, Bing Li Gold nanoparticles (AuNPs) possess remarkable electrical and optical properties coupled with good chemical stability. Thus, they have wide potential applications in fabrication of advanced optical and electronic devices. In order to efficiently transfer their outstanding properties from nano- to micro-scale, patterned AuNPs are desired. Here, we report a novel method using polymer single crystals as substrates to pattern AuNPs. By using thiol-terminated polyethylene oxide (HS-PEO) as the substrate, we were able to assemble AuNPs into different patterns on the PEO single crystals. Furthermore, these AuNPs are asymmetrically functionalized (Janus NPs). A variety of shapes including chains and sheets were formed, and the size and areal density of the AuNP assemblies can be controlled through the AuNP adding time and the ratio between AuNPs and polymer single crystals, respectively. Because of the asymmetrical nature of the AuNPs, the resultant chains and sheets are both asymmetric (Janus chains and Janus sheets), which could lead to a variety of interesting optic properties. We anticipate that our approach would provide a facile means to pattern AuNPs, and it could be extended to other metal and semiconductor NPs. [Preview Abstract] |
Monday, March 10, 2008 8:24AM - 8:36AM |
A22.00003: Organic-Inorganic Nanocomposites via Directly Grafting Conjugated Polymers onto Quantum Dots Zhiqun Lin, Jun Xu, Jun Wang, Mike Mitchell, Prasun Mukherjee, Malika Jeffries-El, Jacob W. Petrich Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized by \textit{directly} grafting vinyl terminated P3HT onto [(4-bromophenyl)methyl]dioctylphosphine oxide (DOPO-Br)-functionalized CdSe quantum dot (QD) surfaces via a mild palladium-catalyzed Heck coupling, \textit{thereby dispensing with the need for ligand exchange chemistry}. \textit{The resulting P3HT}-\textit{CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components}. The photophysical properties of nanocomposites were found to differ from the conventional composites in which P3HT and CdSe QDs were physically mixed. Solid-state emission spectra of nanocomposites suggested the charge transfer from P3HT to CdSe QDs, while the energy transfer from 3.5-nm CdSe QD to P3HT was implicated in the P3HT/CdSe composites. A faster decay in lifetime further confirmed the occurrence of charge transfer in P3HT-CdSe nanocomposites. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 8:48AM |
A22.00004: Amplification of Self-Assembled Nanopatterns: Bilayer Approach to High Aspect-Ratio Cylindrical Nanopore Arrays and Their Use for Templating Functional Materials Ho-Cheol Kim, Oun-Ho Park, Joy Cheng, Mark Hart, Robert Miller, Hiroshi Ito Thin films containing well-defined nanoscopic cylindrical pores oriented perpendicular to the surface are highly desirable for a variety of applications. Of great interest is to use the porous structures for templating a variety of functional materials into 3D nanostructures. Previous reports employ the porous oxide of anodized aluminum or thin films of block copolymers for generating high aspect-ratio nanoporous films. It is, however, still desirable to develop a generalized, simple and reliable method to fabricate nanoporous templates with controlled pore dimensions, high aspect-ratio, substrate non-selectivity and uniformity over large areas. We report a relatively simple and reproducible method for generating nanoporous templates. The approach we used in this study provides nanoporous films with controlled pore diameters (8nm - 25nm in this study) and high aspect-ratio over large areas of a variety of substrates. We also report the application of the templates for generation of nanostructured copper sulfide and titania and their functional properties. [Preview Abstract] |
Monday, March 10, 2008 8:48AM - 9:00AM |
A22.00005: Nanoparticle Arrays via Self Assembled Peptide Templates Nikhil Sharma, Matthew Lamm, Darrin Pochan The bottom up approach towards nano-scale patterning presents the possibility of creating hierarchical architectures through simple self-assembly strategies. Herein, we demonstrate the use of a peptidic template for the construction of parallel, linear arrays of inorganic nanoparticles. A 20 amino acid peptide, consisting of alternating hydrophilic (lysine) and hydrophobic (valine) residues flanking a central diproline turn sequence (VKVKVKVKVPPTKVKVKVKV-NH$_{2})$ was employed as a nano-scale template for the organization of 2nm gold particles. This peptide self assembles into a laminated fibrillar morphology in solution and has a periodic nanostructure consisting of alternating hydrophobic and hydrophilic layers with a lateral periodicity of 2.5 nm. Negatively charged gold nanoparticles are templated into the positively charged lysine layer through electrostatic interaction and are aligned within the template that itself swells to a periodic spacing of 4.0 nm in order to accommodate the particles. These 1D nanoparticle arrays have potential applications in fields like nano-electronics, and we are currently attempting to create arrays of quantum dots and hetero-structures of metal and semiconductor particles. [Preview Abstract] |
Monday, March 10, 2008 9:00AM - 9:12AM |
A22.00006: Study of Alkanethiol Self-Assembled Structure Grown on Silver Liang Hu, Zishu Zhang, Mikhail Yu. Efremov, Eric A. Olson, Ming Zhang, Lito de la Rama, Leslie H. Allen Alkanethiol self-assembled structures grown on surface-supported Ag clusters (3D) are studied by measuring heat capacity with nanocalorimeter at high scanning rate (40,000 K/s), and compared with the self-assembled monolayer (SAMs) grown on planar Ag surface (2D). There is more amount of alkanethiol assembled on 3D Ag clusters compared with 2D SAMs, and the melting transition occurs at a higher temperature with sharper melting peak. This is due to the formation of layered Ag-alkanethiolate structure demonstrated by X-ray diffraction. IR spectrum indicates this self-assembled structure has a high degree of conformational order. [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:48AM |
A22.00007: Ordered Inorganic/Organic Composites via Novel Templates and Techniques Invited Speaker: The fabrication of well ordered nanocomposite materials offers new opportunities for device applications. Recently we reported that nanostructured templates with sub-10 nm domains can be easily obtained through the blending of disordered polymer surfactants containing poly(ethylene oxide) as the hydrophilic block with homopolymers including poly (acrylic acid), poly (4-vinyl phenol) and poly (styrene sulfonate) that selectively associate with the PEO block through hydrogen bonding. These inexpensive blends are strongly segregated, yielding well ordered domains. Moreover, the functionalities imparted by the homopolymers provide convenient handles for binding active materials such as nanoparticles and for promoting in situ, phase selective reactions to produce hierarchical metal oxide polymer composites. The behavior of the template systems and their use for the fabrication of well ordered polymer/nanoparticle, metal/oxide polymer, and metal oxide/polymer/nanoparticle composites using aqueous routes or via the 3-D replication of the template structure in supercritical fluids will be discussed. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:00AM |
A22.00008: Two-Dimensional Confinement of Nanorods in Block Copolymer Domains Yu Liu, Ranjan Deshmukh, Russell Composto To control their unique electrical and optical properties, one-dimensional metallic/semiconductor nanoparticles need to be aligned and assembled within a host material. In our research, we investigated the assembly of gold nanorods (NRs) in films of a symmetric diblock copolymer, poly(styrene-b-methyl methacrylate), PS-b-PMMA (211kg/mol). The NR length and diameter was 42nm and 13nm, respectively. The NRs were grafted with a short PEG-brush (5kg/mol). During solvent annealing, the NRs become oriented as the PS-b-PMMA chains assemble into a parallel lamellar morphology. The NRs are selectively sequestered and confined in the PMMA domains, which are narrower than the NR length, due to the favorable interaction between the PEG brush and PMMA block. This confinement orients 71{\%} of NRs within $\pm$ 5$^{\circ}$ of the lamella plane. This route to produce alternating layers containing conducting NRs separated by dielectric domains has the potential for fabricating self-assembled nanodevices. The thermal stability of the NRs in PS-b-PMMA and homo PMMA films will also be discussed. [Preview Abstract] |
Monday, March 10, 2008 10:00AM - 10:12AM |
A22.00009: Surfactant Directed Assembly of ZnS Nanocrystals Youli Li, Cyrus Safinya, Jacob Israelachvili, Nataly Belman, Yuval Golan Post-synthesis assembly of nanocrystals into ordered two- and three-dimensional super-structures is an important step in many technological applications. A method was developed to use chain-crystalline surfactants to link nanocrystals into 2D and 3D assemblies with precise control of inter-particle distances as well as crystallographic orientation of the nanocrystals. X-ray diffraction and transmission electron microscopy data revealed that ZnS nanocrystals synthesized in octadecylamine (ODA) self-assemble into a highly ordered structure composed of stacked sheets with in-plane 2D-crystalline order. The unit cell of the nanocrystal superlattice (including type and dimensions) is directly related to the crystal structure of the pure surfactant, and thus can be tuned predictably by varying the surfactant chain length. This method can be used to assemble a broad range of nanocrystals and particles (Work supported by ONR N00014-05-1-0540, DOE DE-FG02-06ER46314, NSF DMR-0619171 and BSF 2002059). [Preview Abstract] |
Monday, March 10, 2008 10:12AM - 10:24AM |
A22.00010: End-functionalized triblock copolymers as a robust template for assembly of nanoparticles Rastko Sknepnek, Joshua Anderson, Monica Lamm, Joerg Schmalian, Alex Travesset Polymers with attached end groups with specific affinity for nanoparticles, i.e., functionalized polymers, are shown to provide a robust templating strategy, where the aggregated nanoparticles follow the mesoscopic order imposed by the polymeric matrix. In this talk, we will present a detailed investigation of triblock polymer templating as a function of both nanoparticle size and concentration . Next to phases such as hexagons or gyroids, regularly observed in copolymer solutions and melts, we find a novel square columnar phase of two interpenetrating line-lattices of micellar cylinders and aligned nanoparticles. We argue that this phase is a realization of the packing problem of binary mixtures of disks. Our study suggests that nanoparticle templating with functionalized block copolymers can provide a simple and efficient tool for assembling novel materials with nanometer scale resolution. [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 10:36AM |
A22.00011: Nanoparticle Ordering in Diblock Copolymer-based Supramolecular Systems Thomas Schilling, Ting Xu, Shih-Huang Tung, Yue Wu A well-controlled nanoparticle dispersion within a polymer matrix can have a significant impact on a wide range of material properties. A simple, efficient strategy to direct nanoparticle assembly within nanoscopic domains has been developed. Cadmium selenide (CdSe) nanoparticles were directly blended with diblock copolymer-based supramolecules wherein small molecules were attached to the side chain of one block via hydrogen-bonding. Co-assembly of nanoparticle and supramolecule were examined using SAXS and TEM, confirming fine ordering of the nanoparticles. The influence of nanoparticle concentration on supramolecule microphase separation and nanoparticle ordering was studied. Various functionalities should be readily incorporable into these systems by simply varying the nanoparticle type. The hierarchical assembly of supramolecule and nanoparticles presents many new opportunities for the fabrication of functional nanodevices. [Preview Abstract] |
Monday, March 10, 2008 10:36AM - 10:48AM |
A22.00012: The metal insulator transition in self-assembled gold nanoparticle wires M. E. Reeves, Jianwei Sun, J. A. Hoffmann, Jasper Nijdam, Guebre Tessema We report the temperature dependence of wires assembled from spherical nanoparticles by a relatively new technique, vertical colloidal deposition. This is a simple, one-step method for assembling spherical nanoparticles into wires without the need for lithographic templating. It is effective for a variety of conducting and nonconducting nanoparticles and substrates, and the only material requirement is that the nanoparticles be placed in a colloidal suspension that is wettable on the desired substrate. The shape of the meniscus defines the wire's geometry, and we report the synthesis and physical properties of wires several millimeters long by a few micrometers wide. When wires are formed from 12 nm gold nanoparticles, they exhibit a weak metallic temperature dependence. Those assembled from 6 nm nanoparticles show activated behavior. Post-processing also effects the conductivity of the nanoparticle wires, such as when they are intercalated with proteins or other short organic molecules. Evidence for the metal insulator transition in these materials will be presented and discussed. [Preview Abstract] |
Monday, March 10, 2008 10:48AM - 11:00AM |
A22.00013: Effects of Electric-Magnetic Fields on Hybrid Excitons in a Semiconductor Quantum Dot Coated by an Organic Shell Que Huong Nguyen The effect of electric and magnetic fields on the hybrid exciton of an organic-coated semiconductor spherical quantum dot is considered. Due to dipole-dipole interaction at the semiconductor dot- organic shell interface, a strong mixing of the Wannier-Mott exciton in the quantum dot and the Frenkel exciton of the organic medium occurs, resulting in a new hybrid exciton having priorities of both kinds of excitons as large exciton radius and large oscillator strength. The hybrid excitons are as sensitive to external perturbation as Wannier-Mott excitons. We investigate the effect of mutual presence of electric and magnetic fields on the hybrid exciton of the isolated semiconductor quantum dot such as CdSe (core) clothed by an organic or glass coating for two configuration of fields when the electric and magnetic fields are parallel and orthogonal. The fields affect the eigenfunctions (by a Stark -effect distortion and by the magnetic field-induced distortion) and the Frenkel-Wannier coupling term. Upon the application of the magnetic and electric fields the coupling term between the two kinds of excitons increases. The most important feature of this system is by adjusting the magnetic field and electric field, one can tune the resonance between the two kinds of excitons to get different regions of mixing to obtain the expected high non-linearity. [Preview Abstract] |
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