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In this paper, we report a new optical data storage method: photomodification of hollow gold nanoparticle (HGN) monolayers induced by one-shot deep-ultraviolet (DUV) KrF laser recording. As far as we are aware, this study is the first to apply HGNs in optical data storage and also the first to use a recording light source for the metal nanoparticles (NPs) that is not a surface plasmon resonance (SPR) wavelength. The short wavelength of the recording DUV laser improved the optical resolution dramatically. We prepared HGNs exhibiting two absorbance regions: an SPR peak in the near-infrared (NIR) region and an intrinsic material extinction in the DUV region. A single pulse from a KrF laser heated the HGNs and transformed them from hollow structures to smaller solid spheres. This change in morphology for the HGNs was accompanied by a significant blue shift of the SPR peak. Employing this approach, we demonstrated its patterning ability with a resolving power of a half-micrometer (using a phase mask) and developed a readout method (using a blue-ray laser microscope). Moreover, we prepared large-area, uniform patterns of monolayer HGNs on various substrates (glass slides, silicon wafers, flexible plates). If this spectral recording technique could be applied onto thin flexible tapes, the recorded data density would increase significantly relative to that of current rigid discs (e.g., compact discs).
ACS Nano 2010 Jan 26
PMID:One-shot deep-UV pulsed-laser-induced photomodification of hollow metal nanoparticles for high-density data storage on flexible substrates. 1996 94

A promising route for the synthesis of large-area graphene, suitable for standard device fabrication techniques, is the sublimation of silicon from silicon carbide at elevated temperatures (>1200 degrees C). Previous reports suggest that graphene nucleates along the (110n) plane, known as terrace step edges, on the silicon carbide surface. However, to date, a fundamental understanding of the nucleation of graphene on silicon carbide is lacking. We provide the first direct evidence that nucleation of epitaxial graphene on silicon carbide occurs along the (110n) plane and show that the nucleated graphene quality improves as the synthesis temperature is increased. Additionally, we find that graphene on the (110n) plane can be significantly thicker than its (0001) counterpart and appears not to have a thickness limit. Finally, we find that graphene along the (110n) plane can contain a high density of structural defects, often the result of the underlying substrate, which will undoubtedly degrade the electronic properties of the material. Addressing the presence of non-uniform graphene that may contain structural defects at terrace step edges will be key to the development of a large-scale graphene technology derived from silicon carbide.
ACS Nano 2010 Jan 26
PMID:Nucleation of epitaxial graphene on SiC(0001). 2000 Apr 39

Boron nitride (BN) is a promising semiconductor with a wide band gap ( approximately 6 eV). Here, we report the synthesis of vertically aligned BN nanosheets (BNNSs) on silicon substrates by microwave plasma chemical vapor deposition from a gas mixture of BF(3)-N(2)-H(2). The size, shape, thickness, density, and alignment of the BNNSs were well-controlled by appropriately changing the growth conditions. With changing the gas flow rates of BF(3) and H(2) as well as their ratio, the BNNSs evolve from three-dimensional with branches to two-dimensional with smooth surface and their thickness changes from 20 to below 5 nm. The growth of the BNNSs rather than uniform granular films is attributed to the particular chemical properties of the gas system, mainly the strong etching effect of fluorine. The alignment of the BNNSs is possibly induced by the electrical field generated in plasma sheath. Strong UV light emission with a broad band ranging from 200 to 400 nm and superhydrophobicity with contact angles over 150 degrees were obtained for the vertically aligned BNNSs. The present BNNSs possess the properties complementary to carbon nanosheets such as intrinsically semiconducting, high temperature stability, and high chemical inertness and may find applications in ultraviolet nanoelectronics, catalyst supports, electron field emission, and self-cleaning coatings, etc., especially those working at high temperature and in harsh environments.
ACS Nano 2010 Jan 26
PMID:Vertically aligned boron nitride nanosheets: chemical vapor synthesis, ultraviolet light emission, and superhydrophobicity. 2004 71

Field-effect transistor-based chemical sensors fall into two broad categories based on the principle of signal transduction-chemiresistor or Schottky-type devices and MOSFET or inversion-type devices. In this paper, we report a new inversion-type device concept-fully depleted exponentially coupled (FDEC) sensor, using molecular monolayer floating gate fully depleted silicon on insulator (SOI) MOSFET. Molecular binding at the chemical-sensitive surface lowers the threshold voltage of the device inversion channel due to a unique capacitive charge-coupling mechanism involving interface defect states, causing an exponential increase in the inversion channel current. This response of the device is in opposite direction when compared to typical MOSFET-type sensors, wherein inversion current decreases in a conventional n-channel sensor device upon addition of negative charge to the chemical-sensitive device surface. The new sensor architecture enables ultrahigh sensitivity along with extraordinary selectivity. We propose the new sensor concept with the aid of analytical equations and present results from our experiments in liquid phase and gas phase to demonstrate the new principle of signal transduction. We present data from numerical simulations to further support our theory.
ACS Nano 2010 Feb 23
PMID:Molecular sensing using monolayer floating gate, fully depleted SOI MOSFET acting as an exponential transducer. 2008 85

Using thermal CVD, the synthesis of multi-walled carbon nanotubes exhibiting roots anchored directly onto alpha-alumina supports, rather than the catalyst particle, is reported. At such roots, the alignment of the graphitic planes with the support lattice fringes depends on the support crystal structure and orientation. Surface defects may alter the reactivity of the surface or control the anchoring of supported atoms or nanoparticles. We argue this surface defect is provided by the catalyst particle's edge interaction with the support, in other words its circumference. The development of oxide-based catalysts is attractive in that they potentially provide an appropriate solution to directly integrate the synthesis of carbon nanotubes and graphene into silicon-based technology.
ACS Nano 2010 Feb 23
PMID:Investigating the outskirts of Fe and Co catalyst particles in alumina-supported catalytic CVD carbon nanotube growth. 2008 96

Axial heterostructured silicon nanowires with varying n- and p-doping were synthesized using a vapor-liquid-solid approach. The nanowire sidewalls exhibit periodic nanofaceting in the silicon deposited directly on the sidewalls when diborane dopant gas is introduced during growth. For such nanofaceting, a model predicting the distance between facets (the facet period) is developed. For a nanowire structure, an extra energy cost term arising from the formation of apexes between facets is considered, and the facet size is predicted to decrease as the wire diameter increases. It is found that the model fits the experimental data well, and the fitted parameters in the model lie within the ranges of their expected values.
ACS Nano 2010 Feb 23
PMID:Dependence of surface facet period on the diameter of nanowires. 2011 64

The fabrication of patterned polymer brushes has attracted considerable attention as these structures can be exploited in devices on the nano- and microscale. Patterning of polymer brushes is typically a complex, multistep process. We report the direct patterning of poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(isobutyl methacrylate) (PIBMA), poly(neopentyl methacrylate) (PNPMA), and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) brushes in a single step by electron beam (e-beam) lithography, to obtain nanopatterned polymer brush surfaces. PMMA, PHEMA, PIBMA, PNPMA, and PTFEMA brushes were grown on silicon substrates via surface-initiated atom transfer radical polymerization. Surface analysis techniques including ellipsometry, contact angle goniometry, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the thickness, hydrophilicity, roughness, and chemical composition of the polymer brushes. Tapping-mode AFM imaging confirmed the successful electron beam patterning of these brushes. Using this direct patterning method, highly resolved nanostructured polymer brush patterns down to 50 nm lines were obtained. This direct patterning of brushes eliminates the need for complex lithographic schemes. The sensitivity of these polymer brushes toward direct patterning with e-beam was studied and compared. The sensitivity curves indicate that the structure of the e-beam degradable methacrylate polymer has a significant effect on the sensitivity of the polymer brush toward e-beam patterning. In particular, the effect of the chemical functionality at the beta-position to the carbonyl group on the polymer brush sensitivity toward direct patterning was studied using groups of varying size and polarity.
ACS Nano 2010 Feb 23
PMID:Direct patterning of intrinsically electron beam sensitive polymer brushes. 2012 Dec 28

Block polymers offer an attractive route to densely packed, monodisperse nanoscale pores. However, their fragility as thin films complicates their use as membranes. By integrating a block polymer film with a thin (100 microm) silicon substrate, we have developed a composite membrane providing both nanoscale size exclusion and fast transport of small molecules. Here we describe the fabrication of this membrane, evaluate its mechanical integrity, and demonstrate its transport properties for model solutes of large and small molecular weight. The ability to block large molecules without hindering smaller ones, coupled with the potential for surface modification of the polymer and the microelectromechanical system style of support, makes this composite membrane an attractive candidate for interfacing implantable sensing and drug-delivery devices with biological hosts.
ACS Appl Mater Interfaces 2009 Apr
PMID:Composite block polymer-microfabricated silicon nanoporous membrane. 2016 Aug 82

Microporous carbons, produced by selective etching of metal carbides in a chlorine-containing environment, offer narrow distribution of micropores and one of the highest specific capacitances reported when used in electrical double layer capacitors (EDLC) with organic electrolytes. Previously, the small micropores in these carbons served as an impediment to ion transport and limited the power storage characteristics of EDLC. Here we demonstrate, for the first time, how the preparation and application of templated carbide-derived carbon (CDC) can overcome the present limitations and show the route for dramatic performance enhancement. The ordered mesoporous channels in the produced CDC serve as ion-highways and allow for very fast ionic transport into the bulk of the CDC particles. The enhanced transport led to 85% capacitance retention at current densities up to approximately 20 A/g. The ordered mesopores in silicon carbide precursor also allow the produced CDC to exhibit a specific surface area up to 2430 m(2)/g and a specific capacitance up to 170 F/g when tested in 1 M tetraethylammonium tetrafluoroborate solution in acetonitrile, nearly doubling the previously reported values.
ACS Nano 2010 Mar 23
PMID:High-rate electrochemical capacitors based on ordered mesoporous silicon carbide-derived carbon. 2018 May 59

The formation of well-oriented cylinders with perpendicular morphology for polystyrene-b-polydimethylsiloxane (PS-PDMS) thin films was achieved by spin coating. The self-assembled PS-PDMS nanostructured thin films were used as templates for nanopatterning; the PDMS blocks can be oxidized as silicon oxy carbide microdomains, whereas the PS blocks were degenerated by a simple oxygen plasma treatment for one-step oxidization. As a result, freestanding silicon oxy carbide thin films with hexagonally packed nanochannels were directly fabricated and used as masks for pattern transfer to underlying polymeric materials by oxygen reaction ion etching (RIE) to generate topographic nanopatterns. By taking advantage of robust property and high etching selectivity of the SiOC thin films under oxygen RIE, this nanoporous thin film can be used as an etch-resistant and reusable mask for pattern transfer to various polymeric materials. This approach demonstrates a simple, convenient, and cost-effective nanofabrication technique to create the topographic nanopatterns of polymeric materials.
ACS Nano 2010 Apr 27
PMID:Robust block copolymer mask for nanopatterning polymer films. 2020 44


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