The Stability of Polar Oxide Surfaces

The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and (0001̅ )-O surfaces is 4.0J/m2 comparable to 2.32J/m2 for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications

On resonant scatterers as a factor limiting carrier mobility in graphene

We show that graphene deposited on a substrate has a non-negligible density of atomic scale defects. This is evidenced by a previously unnoticed D peak in the Raman spectra with intensity of about 1% with respect to the G peak. We evaluated the effect of such impurities on electron transport by mimicking them with hydrogen adsorbates and measuring the induced changes in both mobility and Raman intensity. If the intervalley scatterers responsible for the D peak are monovalent, their concentration is sufficient to account for the limited mobilities achievable in graphene on a substrate.Comment: version 2: several comments are taken into account and refs adde

Employment Among People With Spinal Cord Injury in 22 Countries Across the World:Results From the International Spinal Cord Injury Community Survey

Objectives: To describe the employment situation of individuals with spinal cord injury (SCI) in 22 countries participating in the International Spinal Cord Injury community survey, to compare observed and predicted employment rates, to estimate gaps in employment rates among people with SCI compared with the general population, and to study differences in employment between men and women. Design: Cross-sectional survey. Setting: Community. Participants: People of employable age (N=9875; 18-64 y) with traumatic or non-traumatic SCI (including cauda equina syndrome) who were at least 18 years of age at the time of the survey, living in the community, and able to respond to one of the available language versions of the questionnaire. Interventions: Not applicable Main Outcome Measures: The observed employment rate was defined as performing paid work for at least 1 hour a week, and predicted employment rate was adjusted for sample composition from mixed logistic regression analysis. Results: A total of 9875 participants were included (165-1174 per country). Considerable differences in sample composition were found. The observed worldwide employment rate was 38%. A wide variation was found across countries, ranging from 10.3% to 61.4%. Some countries showed substantially higher or lower employment rates than predicted based on the composition of their sample. Gaps between the observed employment rates among participants with SCI and the general population ranged from 14.8% to 54.8%. On average, employment rates were slightly higher among men compared with women, but with large variation across countries. Employment gaps, however, were smaller among women for most countries. Conclusions: This first worldwide survey among people with SCI shows an average employment rate of 38%. Differences between observed and predicted employment rates across countries point at country-specific factors that warrant further investigation. Gaps with employment rates in the general population were considerable and call for actions for more inclusive labor market policies in most of the countries investigated. (C) 2020 by the American Congress of Rehabilitation Medicin

Cascaded Optical Field Enhancement in Composite Plasmonic Nanostructures

Copyright © 2010 The American Physical SocietyWe present composite plasmonic nanostructures designed to achieve cascaded enhancement of electromagnetic fields at optical frequencies. Our structures were made with the help of electron-beam lithography and comprise a set of metallic nanodisks placed one above another. The optical properties of reproducible arrays of these structures were studied by using scanning confocal Raman spectroscopy. We show that our composite nanostructures robustly demonstrate dramatic enhancement of the Raman signals when compared to those measured from constituent elements

Impurity-assisted tunneling in graphene

The electric conductance of a strip of undoped graphene increases in the presence of a disorder potential, which is smooth on atomic scales. The phenomenon is attributed to impurity-assisted resonant tunneling of massless Dirac fermions. Employing the transfer matrix approach we demonstrate the resonant character of the conductivity enhancement in the presence of a single impurity. We also calculate the two-terminal conductivity for the model with one-dimensional fluctuations of disorder potential by a mapping onto a problem of Anderson localization.Comment: 6 pages, 3 figures, final version, typos corrected, references adde

Structural correlations in heterogeneous electron transfer at monolayer and multilayer graphene electrodes

As a new form of carbon, graphene is attracting intense interest as an electrode material with widespread applications. In the present study, the heterogeneous electron transfer (ET) activity of graphene is investigated using scanning electrochemical cell microscopy (SECCM), which allows electrochemical currents to be mapped at high spatial resolution across a surface for correlation with the corresponding structure and properties of the graphene surface. We establish that the rate of heterogeneous ET at graphene increases systematically with the number of graphene layers, and show that the stacking in multilayers also has a subtle influence on ET kinetics. © 2012 American Chemical Society