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Herein, we report on the production of nanoelectrode arrays by attaching colloidal gold on silicon-bound mixed self-assembled monolayers of TFA-protected alkenylthiol (C(11)-S-TFA) and undecylenic acid (acid). Effective modification of the surface, tethering of the nanoparticles, and the direct influence of the deprotected alkenylthiol (C(11)-SH) /acid ratio on the number of adherent particles were demonstrated using X-ray photoelectron spectroscopy, electrochemistry, and atomic force microscopy. Cyclic voltammetry showed that the enhancement of electron transfer to the silicon surface by the presence of nanoparticles is influenced by the number of tethered nanoparticles.
ACS Appl Mater Interfaces 2009 Nov
PMID:Electrochemical behavior of gold colloidal alkyl modified silicon surfaces. 2035 17

Silica aerogels are sol-gel-derived materials consisting of interconnected nanoparticle building blocks that form an open and highly porous three-dimensional silica network. Flexible aerogel films could have wide applications in various thermal insulation systems. However, aerogel thin films produced with a pure sol-gel process have inherent disadvantages, such as high fragility and moisture sensitivity, that hinder wider applications of these materials. We have developed synthesis and manufacturing methods to incorporate electrospun polyurethane nanofibers into the cast sol film prior to gelation of the silica-based gel in order to reinforce the structure and overcome disadvantages such as high fragility and poor mechanical strength. In this method, a two-stage sol-gel process was employed: (1) acid-catalyzed tetraethyl orthosilicate hydrolysis and (2) base-catalyzed gelation. By precisely controlling the sol gelation kinetics with the amount of base present in the formulation, nanofibers were electrospun into the sol before the onset of the gelation process and uniformly embedded in the silica network. Nanofiber reinforcement did not alter the thermal conductivity and rendered the final composite film bendable and flexible.
ACS Appl Mater Interfaces 2009 Nov
PMID:Flexible nanofiber-reinforced aerogel (xerogel) synthesis, manufacture, and characterization. 2035 19

Silver galvanic displacement on silicon has been employed to produce large-area reproducible substrates, with morphology similar to that of the natural desert rose but on the micrometer scale. The process is based on an extremely simple wet chemistry approach using only AgF and KF, as silver and fluoride sources. A key element is the absence of HF in the deposition solution, which has been commonly used in previous silver galvanic displacement processes. The new process affords a higher degree of control in the redox reaction than those reported previously. The structures formed in this manner possess a large area-to-volume ratio with a high density of rough silver flakes uniformly distributed across the substrate. The silver morphology on the nanometer scale is shown to provide an excellent platform for surface-enhanced Raman spectroscopy (SERS), yielding detection levels for trans-1,2-bis(4-pyridyl)ethylene, 4-mercaptopyridine, and Rhodamine 6G in solution down to ppb, ppt, and ppq limits, respectively. The SERS reproducibility on the substrate was verified by monitoring the signal intensity variations across the sample. The simplicity of the substrate fabrication process, as well as the excellent uniformity, opens up opportunities for the quantitative and in-field chemical trace analysis using these substrates.
ACS Appl Mater Interfaces 2009 Nov
PMID:Silver nanodesert rose as a substrate for surface-enhanced Raman spectroscopy. 2035 26

Pulsed plasma enhanced chemical vapor deposition (PECVD) was used to deliver digital control of SiO(2), TiO(2), and SiO(2)-TiO(2) composites at room temperature. Alloy formation was investigated by maintaining constant delivery of TiCl(4) while varying the SiCl(4) flow. Film composition was assessed by spectroscopic ellipsometry, XPS, and FTIR. It is shown that the alloy composition and refractive index can be tuned continuously over a broad range using pulsed PECVD. The two precursors were found to be highly compatible, with the alloy growth rate simply reflecting the sum of the contributions from the two individual precursors. Digital control over both thickness and composition was demonstrated through the production of antireflection (AR) coatings for crystalline silicon. AR coatings were synthesized on the basis of optimized designs, and in each case the measured optical performance was found to be in excellent agreement with model predictions. The average reflectance across the visible spectrum was reduced from 39% for uncoated wafers to 2.5% for the three-layer AR coating.
ACS Appl Mater Interfaces 2009 Nov
PMID:Digital control of SiO(2)-TiO(2) mixed-metal oxides by pulsed PECVD. 2035 31

This paper presents the fabrication of poly(ferrocenylmethylphenylsilane) (PFMPS) patterns by step-and-flash imprint lithography for use as high-contrast etch masks in dry etch processes. PFMPS was spin-coated onto a resist template made by UV nanoimprint lithography to create a reactive ion etch resist layer with a thickness variation corresponding to the imprinted pattern. Etching back the excess of PFMPS by argon sputtering revealed the imprinted organic resist material, which was subsequently removed by oxygen plasma. PFMPS lines down to 30 nm were obtained after removal of the organic resist by oxygen plasma. Because PFMPS contains iron and silicon atoms in its main chain, it possesses a high resistance to oxygen reactive ion etching and, e.g., CHF(3)/O(2) or SF(6)/O(2) reactive ion etch processes. PFMPS patterns formed after imprinting were subsequently transferred into the underlying silicon substrate, and etch rates of 300 nm/min into Si and around 1 nm/min into the PFMPS layer were achieved, resulting in an etch contrast of approximately 300.
ACS Appl Mater Interfaces 2009 Nov
PMID:Nanoscale patterning by UV nanoimprint lithography using an organometallic resist. 2035 38

We examine the current response of molecularly controlled semiconductor devices to the presence of weakly interacting analytes. We evaluate the response of two types of devices, a silicon oxide coated silicon device and a GaAs/AlGaAs device, both coated with aliphatic chains and exposed to the same set of analytes. By comparing the device electrical response with contact potential difference and surface photovoltage measurements, we show that there are two mechanisms that may affect the underlying substrate, namely, formation of layers with a net dipolar moment and molecular interaction with surface states. We find that whereas the Si device response is mostly correlated to the analyte dipole, the GaAs device response is mostly correlated to interactions with surface states. Existence of a silicon oxide layer, whether native on the Si or deliberately grown on the GaAs, eliminates analyte interaction with the surface states.
ACS Appl Mater Interfaces 2009 Nov
PMID:The molecularly controlled semiconductor resistor: how does it work? 2035 42

Developing a method to pattern organic molecules, particularly on the sub-100-nm scale, is of wide interest in current nanoscience for a broad range of technological applications. Because of the efficiency and simplicity of soft lithography, here we describe in detail the process for synthesizing and applying catalytic stamp lithography, a process that can easily produce sub-100-nm patterns on surfaces; in this work, the approach is demonstrated on silicon. Catalytic stamps were fabricated through a two-step procedure in which the nanoscale pattern of catalysts is produced via a self-assembled block-copolymer-templated synthesis of metallic nanostructures on SiO(x)/Si supports, followed by the production of the poly(dimethylsiloxane) (PDMS) stamp on top of the as-patterned metals. Simply peeling off the as-formed PDMS stamp removes the metallic nanostructures, leading to the functional stamp. Two different patterns, pseudohexagonal and linear Pt nanoarrays, were produced from a single block copolymer, PS(125000)-b-P2VP(58500), by controlling the morphology of thin-film templates through tetrahydrofuran vapor annealing. When terminal alkenes, alkynes, or aldehydes with different functionalities were used as molecular inks, these Pt nanopatterns on catalytic stamps were translated into corresponding molecular arrays on Si(111)-H and Si(100)-H(x) surfaces because catalytic hydrosilylation took place exclusively underneath patterned Pt nanostructures. With this straightforward approach, the resolution limit of conventional microcontact printing (approximately 100 nm) could be downsized to a sub-20-nm scale, while maintaining the advantages of stamp-based patterning (i.e., large-area, high-throughput capabilities and low cost).
ACS Appl Mater Interfaces 2009 Dec
PMID:Nanoscale patterning of organic monolayers by catalytic stamp lithography: scope and limitations. 2035 48

Silver-nanoparticle-embedded aminosilica colloids synthesized via aminosilane-induced spontaneous reduction reaction exhibit selective adhesion properties on hydrophobic surfaces and have been utilized as a simple and one-step procedure to create patterned nanocomposite film with silver to aminosilica mole ratio at 0.9:1. Substrates that enable self-assembly of the colloids include silicon wafer, polydimethylsiloxane, and microscope slide, where patterns of hydrophilic surface were either created using oxygen plasma treatment or stamped with chemical ink using microcontact printing. Upon substrates being immersed in a solution containing silver-aminosilica colloids, particles attach to hydrophobic surfaces and continuously self-assemble onto the deposited film, allowing us to fabricate nanocomposite patterns with controllable thickness (approximately 200 nm).
ACS Appl Mater Interfaces 2009 Dec
PMID:Self-assembly of silver-aminosilica nanocomposites through silver nanoparticle fusion on hydrophobic surfaces. 2035 56

Chiral polyelectrolyte multilayers (PEMs) consisting of poly(l-lysine) (PLL), poly(N-(S)alkylated 4-vinylpyridinium iodide), or poly(ethyleneimine maltose) (PEI-m) as polycations and poly(styrenesulfonic acid) sodium salt (PSS) or poly(vinyl sulfate) as polyanions, as well as a nonchiral PEM composed of poly(ethyleneimine) (PEI) and PSS were deposited on silicon substrates and poly(tetrafluoroethylene) membranes using the layer-by-layer method. For these PEMs, enantiospecific interaction toward one enantiomer of either l/d-glutamic acid (l/d-GLU), l/d-tryptophan, or l/d-ascorbic acid (l/d-ASC), respectively, was studied under variation of the concentration, pH, and ionic strength. Both deposition and enantiospecific interaction were analyzed by attenuated total reflection Fourier transform infrared spectroscopy. Our results show a significant enantiospecific preference of d-GLU over l-GLU at PEMs containing PLL and of d-ASC over l-ASC at PEMs containing PEI-m. No such enantiospecific preference was found for nonchiral PEMs containing PEI. The enantiospecificity of PEMs of PLL/PSS toward l/d-GLU could be significantly influenced by the ionic strength and pH values, so that increasing attractive electrostatic interactions resulted in higher enantiospecificity.
ACS Appl Mater Interfaces 2009 Dec
PMID:In situ ATR-FTIR investigation on the preparation and enantiospecificity of chiral polyelectrolyte multilayers. 2035 70

This work describes newly structured stacked silicon nanowires (s-SiNWs), consisting of nanosized silicon wires on top of silicon microrods (SiMRs) and exhibiting pronouncedly superior electron field emission (EFE) characteristics to the conventional SiNWs, by using a two-step electroless metal deposition process. Experimental results indicate that for these s-SiNWs, the electrostatic "screen effect" is markedly suppressed and the field enhancement factor (beta-value) is significantly increased ((beta)(s-SiNWs) = 2533). Additionally, the turn-on field (E(0)) for triggering the EFE process is reduced to a level comparable with that of carbon nanotubes, viz. (E(0))(s-SiNWs) = 2.0 V/mum. This simple and robust modified electroless metal deposition approach does not require either a high temperature or an expensive photolithographic process and possesses great potential for applications.
ACS Appl Mater Interfaces 2010 Feb
PMID:Stacked silicon nanowires with improved field enhancement factor. 2035 75


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