Charge state of the O2_{2} molecule during silicon oxidation through hybrid functional calculations

We study the charge state of the diffusing O$_2$ molecule during silicon oxidation through hybrid functional calculations. We calculate charge transition levels of O$_2$ in bulk SiO$_2$ and use theoretical band offsets to align these levels with respect to the Si band edges. To overcome the band-gap problem of semilocal density fuctionals, we employ hybrid functionals with both predefined and empirically adjusted mixing coefficients. We find that the charge transition level $\epsilon^{0/-}$ in bulk SiO$_2$ occurs at $\sim$1.1 eV above the silicon conduction band edge, implying that the O$_2$ molecule diffuses through the oxide in the neutral charge state. While interfacial effects concur to lower the charge transition level, our estimates suggest that the neutral charge state persists until silicon oxidation.Comment: 4 pages, 3 figure

Gold nanoparticles supported on magnesium oxide for CO oxidation

Au was loaded (1 wt%) on a commercial MgO support by three different methods: double impregnation, liquid-phase reductive deposition and ultrasonication. Samples were characterised by adsorption of N2 at -96°C, temperature-programmed reduction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Upon loading with Au, MgO changed into Mg(OH)2 (the hydroxide was most likely formed by reaction with water, in which the gold precursor was dissolved). The size range for gold nanoparticles was 2-12 nm for the DIM method and 3-15 nm for LPRD and US. The average size of gold particles was 5.4 nm for DIM and larger than 6.5 for the other methods. CO oxidation was used as a test reaction to compare the catalytic activity. The best results were obtained with the DIM method, followed by LPRD and US. This can be explained in terms of the nanoparticle size, well known to determine the catalytic activity of gold catalysts

Neuroendocrine response in acute heart failure and the influence of treatment. Eur Heart

KEY WORDS: Arginine vasopressin, atrial natriuretic peptide, cyclic GMP, heart failure, norepinephrine, renin-angiotensin system, treatment

Insight into fundamental, overtone, and combination IR bands of surface and bulk Ba(NO3)2 by ab initio molecular dynamics

Vibrational characteristics of Ba(NO3)2, one of the key components in an important automotive catalytic technology, NOx storage and reduction (NSR), were investigated by ab initio molecular dynamics. In particular, the fundamental, overtone, and combination bands of surface and bulk Ba(NO3)2 were calculated and compared with experimental infrared (IR) spectra measured by internal and diffuse reflection sampling configurations. Using the densities of characteristic internal vibrational modes, the origins of the experimental IR bands in the regions of fundamental as well as overtone and combination vibrations were clarified. Furthermore, the molecular dynamics based vibrational analysis showed that the bands in the overtone and combination band region (1600?3000 cm?1), typically neglected in NSR studies, contain chemically rich information and can assist in the firm identification of surface nitrates and their adsorption configurations