Showing papers by "Ralph G. Nuzzo published in 2001"
TL;DR: In this article, the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the structural dynamics of supported Pt nanoscale particles was described.
Abstract: In this report, we describe the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the structural dynamics of supported Pt nanoscale particles. We examined several carbon-supported samples. Electron microscopy shows that the particles in these samples (S1−S3) have average particle diameters of roughly 20, 40, and 60 A respectively, while electron microdiffraction data for these particles provided evidence of long-ranged ordering in the form of face centered cubic structures. This study highlights the use of advanced synchrotron X-ray absorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), as powerful tools for studying the structural habits and dynamics of these prototypical nanoscale materials. Using state-of-the-art methods of measurement and computational modeling, we demonstrate that it is possible to deve...
602 citations
TL;DR: The channel outgas technique is compared with previously reported methods in which microfluidic channels are filled either by using capillary forces or by applying a pressure gradient at one or more empty reservoirs, and has proven to be > 90% effective in eliminating the formation of bubbles within microfluidity networks.
Abstract: This paper describes an improved method for filling microfluidic structures with aqueous solutions. The method, channel outgas technique (COT), is based on a filling procedure carried out at reduced pressures. This procedure is compared with previously reported methods in which microfluidic channels are filled either by using capillary forces or by applying a pressure gradient at one or more empty reservoirs. The technique has proven to be >90% effective in eliminating the formation of bubbles within microfluidic networks. It can be applied to many devices, including those containing PDMS-terminated channel features, a single channel inlet, and three-dimensional arrays.
161 citations
TL;DR: Scanning electron microscopy and fluorescence microscopy images of the fabricated porous silicon structures showed that features in the size range of approximately 10-150 microm, and possibly smaller, can be generated by this catalytically amplified soft lithographic patterning method.
Abstract: Photoluminescent, porous silicon pixel arrays were fabricated via a Pt-promoted wet etching of p-type Si(100) using a 1:1:1 EtOH/HF/H2O2 solution. The pixels were fabricated with micrometer-scale design rules on a silicon substrate that had been modified with an octadecyltrichlorosilane (OTS) monolayer patterned using microcontact printing. The printed OTS layer serves as an orthogonal resist template for the deposition of a Pt(0) complex, which preferentially deposits metal species in areas not covered with OTS. The Pt centers generate a localized oxidative dissolution process that pits the Si in the Pt-coated regions, resulting in the formation of a porous silicon microstructure that luminesces around 580 nm upon illumination with a UV source. Scanning electron microscopy and fluorescence microscopy images of the fabricated porous silicon structures showed that features in the size range of ∼10−150 μm, and possibly smaller, can be generated by this catalytically amplified soft lithographic patterning me...
112 citations
TL;DR: In this article, the chemisorption of organosulfur compounds has been studied using FTIR, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surface wetting properties.
Abstract: Alkanethiols HS(CH2)nCH3 (n = 7, 11, 15, 17) and the hydroxy functional thiol HS(CH2)12OH are shown to adsorb from solution onto zinc selenide crystals and form well-organized monolayers. The chemisorption of these organosulfur compounds has been studied using transmission Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surface wetting properties. FTIR indicates that the longer chain alkanethiols (n = 15, 17) form well-defined SAMs with crystalline-like conformations of the chains within the monolayers. As the chain length decreases, there is less conformational order present in the monolayers. The orientation of the largely trans-zigzag alkyl chains on the surface is at a slight tilt off the surface normal direction, as indicated by the dichroism of the infrared spectra and the chain-length-dependent scaling of the mass coverage of the SAM. The structural data obtained by XPS and FTIR are compatible with the inferences derived fro...
58 citations
TL;DR: These development cycles ultimately predict that, in 10 years, the advances made in design and processing methodologies will yield architectures for the most sophisticated integrated circuits that contain more than one billion transistors operating at speeds that are at least a factor of 10 faster than the most capable chips available today.
Abstract: Microelectronic devices are among the most complex structures produced by modern manufacturing technology. A state-of-the-art microprocessor in a personal computer, for example, contains as many as 30 million transistors interconnected by more than one billion discrete electrical junctions (1). To achieve this level of integration, the sizes that define the device components must be small, smaller by several orders of magnitude, for example, than the size of a typical cell found in the human body. The demand for greater performance and capacity in these systems, as famously characterized by Moore's Law (2), has seen the number of individual transistors on a chip increase by a factor of 2 approximately every 18 months. These development cycles ultimately predict that, in 10 years, the advances made in design and processing methodologies will yield architectures for the most sophisticated integrated circuits that contain more than one billion transistors operating at speeds that are at least a factor of 10 faster than the most capable chips available today (International Technology Roadmap for Semiconductors Update, http://public.itrs.net/reports.htm). These devices will possess functionalities that certainly would have been unimaginable in 1947 from the vantage point provided by the characteristics of the original point contact transistor of Brattain, Bardeen, and Shockley.
27 citations
TL;DR: In this article, the authors examined the mechanisms and energy involved in the activation and thermal decomposition of tungsten nitride precursors and found that the activation energies for each of these processes were ∼30 kcal/mol for the process leading to the evolution of tert-butylamine and ∼40 kcal/mol for the various reactions which lead to the fragmentation of the precursor ligands.
Abstract: The chemical vapor deposition (CVD) of tungsten nitride from a single source reagent, bis(tertbutylimido)bis(tertbutylamido)tungsten ((t-BuN)2W(NHBu-t)2), is examined with particular focus placed on the mechanisms and energetics involved in the activation and thermal decomposition of this CVD precursor. The main reactions that take place are (1) activated adsorption of the precursor, (2) hydrogen addition/exchange, leading to the evolution of tert-butylamine, (3) ligand activation via both γ-hydride activation and β-methyl elimination processes, and (4) ligand decomposition via C−N bond rupture. The activation energies for each of these processes were examined and found to be ∼30 kcal/mol for the process(es) leading to the evolution of tert-butylamine and ∼40 kcal/mol for the various reactions which lead to the fragmentation of the precursor ligands (pathways which appear to involve both C−H and C−C bond activation as well as the rupture of the ligand C−N bonds). The growth surface of the deposited film c...
24 citations
TL;DR: In this paper, the authors examined the desorption processes of dihydrogen and aluminum hydride in the presence of a xenon beam at 1.6, 2.8, and 3.6 eV with a hydrogen covered surface.
Abstract: We examine the recombination and desorption of hydrogen from an aluminum(111) surface focusing on desorption processes that lead to the formation of dihydrogen and aluminum hydride (presumably alane). In addition to simple temperature-programmed reaction spectroscopy (TPRS), we examine the perturbations which occur to the desorption kinetics of these species as a result of the energy transfer due to collisions of a xenon beam at 1.6, 2.8, and 3.6 eV with a hydrogen covered surface. Whereas the recombinative desorption of dihydrogen from an Al(111) surface nominally follows an unusual zero-order rate law, bombardment of a hydrogen-covered surface with an energetic xenon atom leads to a kinetic profile more closely modeled by a higher reaction order. It also was found that upon exposure to the beam, the peak area (and thus the desorption yield) for the H2 desorption was reduced 5−25% depending on the length of exposure whereas for the aluminum hydride the percent reduction ranged from 10−80%. This suggests ...
13 citations
TL;DR: In this article, a soft-lithography-based methodology for generating nanoscale structures on Si(100) substrates via wet chemical etching is presented, which apparently results from the phase dynamics of a multicomponent resist ink which phase separates on the Si surface.
Abstract: We demonstrate a novel soft-lithography-based methodology for generating nanoscale structures on Si(100) substrates via wet chemical etching. The feature generation apparently results from the phase dynamics of a multicomponent resist ink which phase separates on the Si surface. The monolayers formed from inks comprised of different mole fractions of docosyltrichlorosilane and octyltrichlorosilane contact printing are annealed in air and then placed into KOH etching solutions to generate dense textures of nanoscale features. We examine the resulting etch structures via atomic force microscopy and find that the different mole fractions of the model inks used here influence the nanoscale textures of the structures obtained. The photoluminescence of the etched samples was examined, both for the samples obtained from the etching and following a subsequent treatment in a buffered HF solution.
10 citations
TL;DR: In this article, spontaneous dewetting was used to generate mesoscopically patterned features of polyfluoropolyether (PFPE) films on SiO2.
Abstract: Polyfluoropolyether (PFPE) films have long been used as lubricant coatings for magnetic recording media. In this paper, we demonstrate that the unique wetting properties of PFPEsmore specifically, the dynamical organizations that result from spontaneous dewettingcan be harnessed to generate mesoscopically patterned features of these materials on SiO2. In this work, a functionalized PFPE amphiphile with the formula CF3CF2CF2O(CF(CF3)CF2O)nCF(CF3)CONHCH2CH2CH2Si(OCH3)3 (Krytox SA, DuPont) was deposited on a SiO2 surface by both spin-casting and contact printing. Both methods produce complex surface structures comprised of beaded domains and depletion regions (and in the case of spin-casting, also thin films) that result from dewetting processes. Spontaneous dewetting was used to generate self-organizing PFPE bead patterns by microcontact printing. The wetting transitions in this latter case occur directly on the printing tool and, via the bias provide by the topography of the stamp, provide a means for gene...
7 citations
TL;DR: In this article, the authors present several representative studies of thin-film growth by chemical vapor deposition, with particular emphasis given to elucidating the mechanistic, energetic, and structural aspects of nucleation and growth.
Abstract: In this Account, we present several representative studies of thin-film growth by chemical vapor deposition, with particular emphasis given to elucidating the mechanistic, energetic, and structural aspects of nucleation and growth. These understandings have allowed us to develop new methods to deposit patterned, as opposed to blanket, thin films. We show how such procedures can be exploited to effect the directed assembly (i.e., the additive fabrication) of a device architecture.