Abstract: The electronic properties of a set of intrinsic and extrinsic point defects in gamma-Al2O3 are investigated using quasiparticle calculations within the G(0)W(0) approximation. We find that the electronic signature of atomic vacancies lie deep in the band gap, close to the top of the valence band edge. The introduction of C, Si, and N impurities induces defective levels that are located close to the conduction band edge and near the middle of the band gap of the oxide. The comparison with electrical measurements reveals that the energy levels of some of these defects match with the electronic fingerprint of the defects reported in gamma-Al2O3 based nonvolatile memories. (C) 2010 American Institute of Physics. [doi:10.1063/1.3507385]

Abstract: The origin of the ferroelectric polarization switching in orthorhombic HfO2 has been investigated by first principles calculations. The phenomenon can be regarded as being the coordinated displacement of four O ions in the orthorhombic unit cell, which can lead to a saturated polarization as high as 53 mu C/cm(2). We show the correlation between the computed polarization reversal barrier and the experimental coercive fields. (C) 2014 AIP Publishing LLC.

Abstract: In this letter, we investigate the effect of various levels of nitrogen impurity on the electrical performance of an atmospheric pressure dielectric barrier discharge in helium. We illustrate the different current profiles that are obtained, which exhibit one or more discharge pulses per half cycle and evaluate their performance in ionizing the discharge and dissipating the power. It is shown that flat and broad current profiles perform the best in ionizing the discharge and use the least amount of power per generated charged particle.

Abstract: In this paper, we quantitatively investigate with atom probe tomography, the effect of temperature on the interfacial transition layer suboxide species due to the thermal oxidation of silicon. The chemistry at the interface was measured with atomic scale resolution, and the changes in chemistry and intermixing at the interface were identified on a nanometer scale. We find an increase of suboxide (SiOx) concentration relative to SiO2 and increased oxygen ingress with elevated temperatures. Our experimental findings are in agreement with reactive force field molecular dynamics simulations. This work demonstrates the direct comparison between atom probe derived chemical profiles and atomistic-scale simulations for transitional interfacial layer of suboxides as a function of temperature.

Abstract: A study of ns-laser ablation is presented, which focuses on the transient behavior of the physical processes that act in and above a copper sample. A dimensionless multiphase collisional radiative model describes the interplay between the ablation, collisional, and radiative mechanisms. Calculations are done for a 6 ns-Nd:YAG laser pulse operating at 532 nm and fluences up to 15 J/cm2. Temporal intensity profiles as well as transmissivities are in good agreement with experimental results. It is found that volumetric ablation mechanisms and photo-processes both play an essential role in the onset of ns-laser induced breakdown.

Abstract: The structural and vibrational properties of amorphous germanium oxide (a-GeO₂) are investigated using first-principles calculations based on density functional theory. We first generate an a-GeO₂ structure by first-principles molecular dynamics and analyze its structural properties. The vibrational spectra is then calculated within a density-functional approach. Both static and dynamic properties are in good agreement with experimental data. We next generate defects in our structure (oxygen vacancies with several density and charge states) and consider the most stable atomic configurations, focusing on the vibrational features of threefold coordinated O and divalent Ge centers.

Abstract: The impact of the scaling of the channel length on the performances of metal-oxide-semiconductor field effect transistors, based on two-dimensional (2D) channel materials, is theoretically investigated, using density functional theory combined with the non-equilibrium Green's function method. It is found that the scaling of the channel length below 10nm leads to strong device performance degradations. Our simulations reveal that this degradation is essentially due to the tunneling current flowing between the source and the drain in these aggressively scaled devices. It is shown that this electron tunneling process is modulated by the effective mass of the 2D channel material, and sets the limit of the scaling in future transistor designs. (C) 2016 AIP Publishing LLC.

Abstract: Cold atmospheric pressure plasma jets (plasma) operated in ambient air provide a rich source of reactive oxygen and nitrogen species (RONS), which are known to influence biological processes important in disease. In the plasma treatment of diseased tissue such as subcutaneous cancer tumors, plasma RONS need to first traverse an interface between the plasma-skin surface and second be transported to millimeter depths in order to reach deep-seated diseased cells. However, the mechanisms in the plasma generation of RONS within soft tissues are not understood. In this study, we track the plasma jet delivery of RONS into a tissue model target and we delineate two processes: through target delivery of RONS generated (primarily) in the plasma jet and in situ RONS generation by UV photolysis within the target. We demonstrate that UV photolysis promotes the rapid generation of RONS in the tissue model target’s surface after which the RONS are transported to millimeter depths via a slower molecular process. Our results imply that the flux of UV photons from plasma jets is important for delivering RONS through seemingly impenetrable barriers such as skin. The findings have implications not only in treatments of living tissues but also in the functionalization of soft hydrated biomaterials such as hydrogels and extracellular matrix derived tissue scaffolds.