XPS Study (xp + study)

Distribution by Scientific Domains

Selected Abstracts

Ethanol Adsorption, Decomposition and Oxidation on Ir(111): A High Resolution XPS Study,

CHEMPHYSCHEM, Issue 6 2007
Cornelis J. Weststrate Dr.
Abstract Ethanol (C2H5OH) adsorption, decomposition and oxidation is studied on Ir(111) using high-energy resolution, fast XPS and temperature-programmed desorption. During heating of an adsorbed ethanol layer a part of the C2H5OHad desorbs molecularly, and another part remains on the surface and decomposes around 200 K; these two decomposition pathways are identified, as via acetyl (H3CCO) and via COad+CH3ad, respectively. Acetyl and CH3ad decompose around 300 K into CHad (and COad). CHad decomposes forming Cx and H2 around 520 K. In the presence of Oad an acetate intermediate is formed around 180 K, as well as a small amount of CH3ad and COad. Acetate decomposes between 400,480 K into CO2, H2(/H2O) and CHad. [source]

Electrochemistry and XPS study of an imidazoline as corrosion inhibitor of mild steel in an acidic environment

O. Olivares-Xometl
Abstract The effect of 2-(2-heptadec-8-enyl-4,5-dihydro-imidazol-1-yl)-ethylamine on the corrosion behavior of mild steel in aqueous hydrochloric acid was investigated using weight loss measurements, polarization scans, electrochemical impedance, and X-ray photoelectron spectroscopy (XPS). The inhibition efficiencies and coverage degrees increased with the concentration of inhibitor but decreased proportionally with temperature. It appears that the steric hindrance of the aliphatic chain on the imidazoline ring adsorption may affect inhibitor efficiency. Polarization curves showed that the oleic imidazoline (OI) acted essentially as a mixed type inhibitor, in which the blocking of active sites occurred. As a result of film formation, impedance spectra revealed a considerable increase in the charge transfer resistance as indicated by the second capacitive loop. XPS depth profile analysis observed the presence of nitrogen and carbon species on the inhibitor film, which were associated to the OI. [source]

XPS study of surface potential in AlGaN/GaN heterostructure with Cat-CVD SiN passivation

N. Onojima
Abstract AlGaN surface potentials in AlGaN/GaN heterostructures with and without SiN passivation were investigated using x-ray photoelectron spectroscopy (XPS). SiN films were formed on AlGaN surfaces by catalytic chemical vapor deposition (Cat-CVD), which has already been found to increase two-dimensional electron gas (2DEG) density. Based on a simple electrostatic analysis, the 2DEG density is expected to increase as the AlGaN surface potential decreases. This study experimentally demonstrates that a reduction in the AlGaN surface potential is actually induced by Cat-CVD SiN passivation. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Towards a Molecular Understanding of Cation,Anion Interactions,Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy, X-ray Photoelectron Spectroscopy and Theoretical Calculations

Till Cremer
Abstract Ten [C8C1Im]+ (1-methyl-3-octylimidazolium)-based ionic liquids with anions Cl,, Br,, I,, [NO3],, [BF4],, [TfO],, [PF6],, [Tf2N],, [Pf2N],, and [FAP], (TfO=trifluoromethylsulfonate, Tf2N=bis(trifluoromethylsulfonyl)imide, Pf2N=bis(pentafluoroethylsulfonyl)imide, FAP=tris(pentafluoroethyl)trifluorophosphate) and two [C8C1C1Im]+ (1,2-dimethyl-3-octylimidazolium)-based ionic liquids with anions Br, and [Tf2N], were investigated by using X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While 1H,NMR spectroscopy is found to probe very specifically the strongest hydrogen-bond interaction between the hydrogen attached to the C2 position and the anion, a comparative XPS study provides first direct experimental evidence for cation,anion charge-transfer phenomena in ionic liquids as a function of the ionic liquid's anion. These charge-transfer effects are found to be surprisingly similar for [C8C1Im]+ and [C8C1C1Im]+ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions. [source]