1,511 research outputs found
Effects of impurities on radiation damage of silicon solar cells
Impurities effects on radiation damage of silicon solar cell
Thiol density dependent classical potential for methyl-thiol on a Au(111) surface
A new classical potential for methyl-thiol on a Au(111) surface has been
developed using density functional theory electronic structure calculations.
Energy surfaces between methyl-thiol and a gold surface were investigated in
terms of symmetry sites and thiol density. Geometrical optimization was
employed over all the configurations while minimum energy and thiol height were
determined. Finally, a new interatomic potential has been generated as a
function of thiol density, and applications to coarse-grained simulations are
presented
Nondestructive Inspection and Evaluation of Metal Matrix Composites
A review is presented of work performed in our laboratory on the nondestructive inspection of metal matrix composites. In order to obtain damage representative of that which occurs in service, the specimens were mechanically loaded to intermediate load levels below that which causes final, catastrophic failure. Various nondestructive techniques were used both during and after the applied loadings to follow damage initiation and progress.</p
Anchored phosphatases modulate glucose homeostasis.
Endocrine release of insulin principally controls glucose homeostasis. Nutrient-induced exocytosis of insulin granules from pancreatic β-cells involves ion channels and mobilization of Ca(2+) and cyclic AMP (cAMP) signalling pathways. Whole-animal physiology, islet studies and live-β-cell imaging approaches reveal that ablation of the kinase/phosphatase anchoring protein AKAP150 impairs insulin secretion in mice. Loss of AKAP150 impacts L-type Ca(2+) currents, and attenuates cytoplasmic accumulation of Ca(2+) and cAMP in β-cells. Yet surprisingly AKAP150 null animals display improved glucose handling and heightened insulin sensitivity in skeletal muscle. More refined analyses of AKAP150 knock-in mice unable to anchor protein kinase A or protein phosphatase 2B uncover an unexpected observation that tethering of phosphatases to a seven-residue sequence of the anchoring protein is the predominant molecular event underlying these metabolic phenotypes. Thus anchored signalling events that facilitate insulin secretion and glucose homeostasis may be set by AKAP150 associated phosphatase activity
Conductance statistics from a large array of sub-10 nm molecular junctions
Devices made of few molecules constitute the miniaturization limit that both
inorganic and organic-based electronics aspire to reach. However, integration
of millions of molecular junctions with less than 100 molecules each has been a
long technological challenge requiring well controlled nanometric electrodes.
Here we report molecular junctions fabricated on a large array of sub-10 nm
single crystal Au nanodots electrodes, a new approach that allows us to measure
the conductance of up to a million of junctions in a single conducting Atomic
Force Microscope (C-AFM) image. We observe two peaks of conductance for
alkylthiol molecules. Tunneling decay constant (beta) for alkanethiols, is in
the same range as previous studies. Energy position of molecular orbitals,
obtained by transient voltage spectroscopy, varies from peak to peak, in
correlation with conductance values.Comment: ACS Nano (in press
High on-off conductance switching ratio in optically-driven self-assembled conjugated molecular systems
A new azobenzene-thiophene molecular switch is designed, synthesized and used
to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio
up to 7x1E3 (with an average value of 1.5x1E3) is reported. The "on"
conductance state is clearly identified to the cis isomer of the azobenzene
moiety. The high "on/off" ratio is explained in terms of photo-induced,
configuration-related, changes in the electrode-molecule interface energetics
(changes in the energy position of the molecular orbitals with respect to the
Fermi energy of electrodes) in addition to changes in the tunnel barrier length
(length of the molecules). First principles DFT calculations demonstrate a
better delocalization of the frontier orbitals, as well as a stronger
electronic coupling between the azobenzene moiety and the electrode for the cis
configuration over the trans one. Measured photoionization cross-sections for
the molecules in the SAM are close to the known values for azobenzene
derivatives in solution.Comment: 1 file with main text, figure and suppementary informatio
Ultrafast Relaxation of Photoexcited Carriers: The Role of Coherence in the Generation Process
A self-consistent description of the ultrafast dynamics of photoexcited carriers in semiconductors based on a generalized Monte Carlo solution of the semiconductor Bloch equations is presented. The problem of photogeneration and its theoretical description are discussed. We show that some of the approaches commonly used fail in describing correctly the effect of carrier-carrier interaction in the low-density limit. By including terms which have the structure of ‘‘in-scattering'' terms (vertex corrections) for the interband polarization, the experimentally observed features in the carrier dynamics are well described in the whole density range
Theory of electrical rectification in a molecular monolayer
The current-voltage characteristics in Langmuir-Blodgett monolayers of
\gamma-hexadecylquinolinium tricyanoquinodimethanide (C16H33Q-3CNQ) sandwiched
between Al or Au electrodes is calculated, combining ab initio and
self-consistent tight binding techniques. The rectification current depends on
the position of the LUMO and HOMO relative to the Fermi levels of the
electrodes as in the Aviram-Ratner mechanism, but also on the profile of the
electrostatic potential which is extremely sensitive to where the electroactive
part of the molecule lies in the monolayer. This second effect can produce
rectification in the direction opposite to the Aviram-Ratner prediction
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