Band offsets and point-defect charges of the aluminum and hafnium oxides in contact with the Cu(In,Ga)Sechalcopyrite.

Surface passivation of CuInSe(CIS) and related Cu(In,Ga)Se(CIGS) chalcopyrite materials by depositing selected dielectric layers has been a major research activity aiming to reduce interface recombination and increase the electrical efficiency of chalcopyrite-based thin-film solar cells. The present study reports calculations based on density-functional theory andthermodynamics that examine the origin of field-effect passivation from alumina and hafnia two wide-gap, predominantly ionic insulators that have exhibited promising passivation qualities in silicon-based microelectronics. The source of fixed charges within the bulk lattices of both oxides was studied by determining the thermodynamically most favorable charge states of their native defects within the admissible ranges of the metal and oxygen chemical potentials.

Cytokine induced 3-D organotypic psoriasis skin model demonstrates distinct roles for NF-κB and JAK pathways in disease pathophysiology.

Psoriasis vulgaris is an inflammatory skin disease that affects 2%-3% of the population worldwide. One of the major challenges in discovering novel therapies is the poor translatability of animal models to human disease. Therefore, it is imperative to develop human preclinical models of psoriasis that are amenable to pharmacological intervention.

Optimization of decalcification techniques for histologic examination of the rat maxillary and mandibular incisors for toxicity studies.

The objective of this study was to provide optimized processing for examination of rat incisors in nonclinical toxicity studies that enables analysis using immunohistochemistry (IHC). Rat maxillas and mandibles were decalcified in Immunocal, a formic acid decalcifier, and Decal Stat, a hydrochloric acid decalcifier, to evaluate tissue quality when with hematoxylin and eosin (H&E) stain and an IHC. Following necropsy of 10 to 13-week-old male Sprague Dawley rats, tissues were collected, trimmed, fixed in neutral buffered formalin (NBF), and placed into the corresponding decalcifying solution.

Positron lifetimes of bare and hydrogenated zirconium vacancies in cubic yttria-stabilized zirconia: an ab initio study.

Recent studies by positron-annihilation spectroscopy (PAS) in single-crystal and nanostructured yttria-stabilized zirconia (YSZ) revealed extensive positron trapping at vacancy-type point defects and other structural imperfections. The present work reports first principles calculations of formation energies and positron lifetimes of Zr vacancies in 10.3 mol% cubic YSZ.

Electronic structure and migration of interstitial hydrogen in the rutile phase of TiO.

The formation and migration energies of interstitial hydrogen in rutile TiO are obtained from first principles calculations. The computational approach was based on density functional theory with a semilocal generalised-gradient approximation functional, supplemented with an on-site Hubbard term to account for correlation among the Ti 3d electrons. Charge-transition levels are calculated and compared to previous theoretical studies.

First-principles study of hydrogen configurations at the core of a high-angle grain boundary in cubic yttria-stabilized zirconia.

Hydrogen is a common impurity in oxides and has been studied extensively by first-principles electronic structure methods. From the calculated charge-transition levels and their position with respect to the conduction-band edge, definitive conclusions can be drawn concerning the electrical activity of hydrogen either as an isolated defect or as part of a defect complex with intrinsic defects of the host lattice. For those oxides such as yttria-stabilized zirconia, which in many cases are used in polycrystalline or nanocrystalline forms, the interaction of hydrogen with grain boundaries needs to be better understood.

First principles study of segregation to the Σ5(310) grain boundary of cubic zirconia.

While yttrium and impurity segregation at interfaces of yttria-stabilized zirconia (YSZ) has been intensively studied experimentally, the mechanisms governing the propensity for segregation are still not fully understood. The segregation energetics of yttrium and aluminum, another common segregant at interfaces of YSZ, were studied by means of first principles calculations based on density functional theory. Site-dependent formation energies were calculated following the substitutional incorporation of yttrium and aluminum in the near-interface region of the Σ5(310) grain boundary in cubic zirconia, for which recent experimental data revealed strong yttrium enrichment.

Anomalous angular dependence of the dynamic structure factor near Bragg reflections: graphite.

The electron energy-loss function of graphite is studied for momentum transfers q beyond the first Brillouin zone. We find that near Bragg reflections the spectra can change drastically for very small variations in q. The effect is investigated by means of first principle calculations in the random phase approximation and confirmed by inelastic x-ray scattering measurements of the dynamic structure factor S(q, omega).

Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene.

We have measured a strictly linear pi plasmon dispersion along the axis of individualized single-wall carbon nanotubes, which is completely different from plasmon dispersions of graphite or bundled single-wall carbon nanotubes. Comparative ab initio studies on graphene-based systems allow us to reproduce the different dispersions. This suggests that individualized nanotubes provide viable experimental access to collective electronic excitations of graphene, and it validates the use of graphene to understand electronic excitations of carbon nanotubes.

Optical and loss spectra of carbon nanotubes: depolarization effects and intertube interactions.

We performed ab initio calculations of the anisotropic dielectric response of small-diameter single-walled carbon nanotubes in the framework of time-dependent density-functional theory. The calculated optical spectra are in very good agreement with experiment, both concerning absolute peak positions and anisotropy effects. The latter can only be described correctly when crystal local-field effects ("depolarization" effects) are fully taken into account.

Anisotropy and interplane interactions in the dielectric response of graphite.

We determined the anisotropic dielectric response of graphite by means of time-dependent density-functional theory and high-resolution valence electron energy-loss spectroscopy. The calculated loss function was in very good agreement with the experiment for a wide range of momentum-transfer orientations with respect to the graphitic basal planes, provided that local-field effects were included in the response. The calculations also showed strong effects of the interlayer Coulomb interaction on the total pi+sigma plasmon.

Quantitative atomic-scale analysis of interface structures: transmission electron microscopy and local density functional theory.

Transmission electron microscopy (TEM) and local density functional theory (LDFT) are combined to analyze the microscopic structure of the rhombohedral twin interface in alpha-Al2O3. LDFT provides interfacial energetics and atomic and electronic structures for three competing models. With high-resolution TEM the atomic structure at the interface is imaged quantitatively along two orthogonal zone axes.