1,810 research outputs found
Atomistic modelling of large-scale metal film growth fronts
We present simulations of metallization morphologies under ionized sputter
deposition conditions, obtained by a new theoretical approach. By means of
molecular dynamics simulations using a carefully designed interaction
potential, we analyze the surface adsorption, reflection, and etching reactions
taking place during Al physical vapor deposition, and calculate their relative
probability. These probabilities are then employed in a feature-scale
cellular-automaton simulator, which produces calculated film morphologies in
excellent agreement with scanning-electron-microscopy data on ionized sputter
deposition.Comment: RevTeX 4 pages, 2 figure
Anisotropy of Growth of the Close-Packed Surfaces of Silver
The growth morphology of clean silver exhibits a profound anisotropy: The
growing surface of Ag(111) is typically very rough while that of Ag(100) is
smooth and flat. This serious and important difference is unexpected, not
understood, and hitherto not observed for any other metal. Using density
functional theory calculations of self-diffusion on flat and stepped Ag(100) we
find, for example, that at flat regions a hopping mechanism is favored, while
across step edges diffusion proceeds by an exchange process. The calculated
microscopic parameters explain the experimentally reported growth properties.Comment: RevTeX, 4 pages, 3 figures in uufiles form, to appear in Phys. Rev.
Let
Hastes florais de cenoura: uma opção para a floricultura.
bitstream/item/33614/1/documento-175.pd
Physics of the Be(101Ì…0) Surface Core Level Spectrum
Photoelectron diffraction has been utilized to confirm the theoretical prediction that the surface core level shifts observed for Be(101̅0) have been improperly assigned. The original assignment based upon the relative intensity of the shifted components was intuitively obvious: the peak with the largest shift of −0.7eV with respect to the bulk was associated with the surface plane, the next peak shifted by −0.5eV stems from the second layer, and the third peak at −0.22eV from the third and fourth layers. First-principles theory and our experimental data show that the largest shift is associated with the second plane, not the first plane
Phonon softening and superconductivity in tellurium under pressure
The phonon dispersion and the electron-phonon interaction for the -Po
and the bcc high pressure phases of tellurium are computed with
density-functional perturbation theory. Our calculations reproduce and explain
the experimentally observed pressure dependence of the superconducting critical
temperature (T) and confirm the connection between the jump in
T and the structural phase transition. The phonon contribution to the
free energy is shown to be responsible for the difference in the structural
transition pressure observed in low and room temperature experiments.Comment: Revtex, 4 Postscript figures, to appear in Phys. Rev. Let
Inhibited Al diffusion and growth roughening on Ga-coated Al (100)
Ab initio calculations indicate that the ground state for Ga adsorption on Al
(100) is on-surface with local unit coverage. On Ga-coated Al (100), the bridge
diffusion barrier for Al is large, but the AlGa {\it exchange
barrier is zero}: the ensuing incorporation of randomly deposited Al's into the
Ga overlayer realizes a percolation network, efficiently recoated by Ga atoms.
Based on calculated energetics, we predict rough surface growth at all
temperatures; modeling the growth by a random deposition model with partial
relaxation, we find a power-law divergent roughness .Comment: 4 pages RevTeX-twocolumn, no figures. to appear in Phys. Rev. Lett.,
July 199
Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces
Electron-hole excitations in the surface bands of GaAs(110) are analyzed
using constrained density-functional theory calculations. The results show that
Frenkel-type autolocalized excitons are formed. The excitons induce a local
surface unrelaxation which results in a strong exciton-exciton attraction and
makes complexes of two or three electron-hole pairs more favorable than
separate excitons. In such microscopic exciton "droplets" the
electron density is mainly concentrated in the dangling orbital of a surface Ga
atom whereas the holes are distributed over the bonds of this atom to its As
neighbors thus weakening the bonding to the substrate. This finding suggests
the microscopic mechanism of a laser-induced emission of neutral Ga atoms from
GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from:
[email protected]
A machine learning pipeline for discriminant pathways identification
Motivation: Identifying the molecular pathways more prone to disruption
during a pathological process is a key task in network medicine and, more in
general, in systems biology.
Results: In this work we propose a pipeline that couples a machine learning
solution for molecular profiling with a recent network comparison method. The
pipeline can identify changes occurring between specific sub-modules of
networks built in a case-control biomarker study, discriminating key groups of
genes whose interactions are modified by an underlying condition. The proposal
is independent from the classification algorithm used. Three applications on
genomewide data are presented regarding children susceptibility to air
pollution and two neurodegenerative diseases: Parkinson's and Alzheimer's.
Availability: Details about the software used for the experiments discussed
in this paper are provided in the Appendix
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