M. Faiz

High resolution XPS study of oxide layers grown on Ge substrates

High resolution X-ray Photoelectron Spectroscopy (XPS) was used to analyze thin layers of germanium oxide grown on germanium substrates under various conditions. The results reveal the presence of high density of electron states located at the oxide/germanium interface that lead to the energy band bending. The surface of native oxide layers and that of thin oxide layer grown under dry oxygen correspond to GeO2 composition. Under Ar etching, lower oxidation states were revealed. Short in-situ heat treatment at T=400 degrees C under ultra high vacuum leads to the removal of the oxide layer. In addition, the analysis of the layer grown at T=380 degrees C under dry oxygen suggest that carbides form at the oxide/substrate interface.

Experimental results obtained with the positron-annihilation-radiation telescope of the Toulouse-Argonne collaboration

We present laboratory measurements obtained with a ground-based prototype of a focusing positron-annihilation-radiation telescope developed by the Toulouse-Argonne collaboration. This balloon-borne telescope has been designed to collect 511-keV photons with an extremely low instrumental background. The telescope features a Laue diffraction lens and a detector module containing a small array of germanium detectors. It will provide a combination of high spatial and energy resolution (15 arc sec and 2 keV, respectively) with a sensitivity of -3x10-5 photons cm-2s-1. These features will allow us to resolve a possible narrow 511-keV line both energetically and spatially within a Galactic center “microquasar” or in other broad-class annihilators.

Crystal diffraction lens telescope for focusing nuclear gamma rays

A crystal diffraction lens was constructed at Argonne National Laboratory for use as a telescope to focus nuclear gamma rays. It consists of 600 single crystals of germanium arranged in 8 concentric rings. The mounted angle of each crystal was adjusted to intercept and diffract the incoming gamma rays with an accuracy of a few arcsec. The performance of the lens was tested in two ways. In one case, the gamma rays were focused on a single medium size germanium detector. In the second case, the gamma rays were focused on the central germanium detector of a 3 multiplied by 3 matrix of small germanium detectors. The efficiency, image concentration and image quality, and shape were measured. The tests performed with the 3 by 3 matrix detector system were particularly interesting. The wanted radiation was concentrated in the central detector. The 8 other detectors were used to detect the Compton scattered radiation, and their energy was summed with coincident events in the central detector. This resulted in a detector with the efficiency of a large detector (all 9 elements) and the background of a small detector (only the central element). The use of the 3 multiplied by 3 detector matrix makes it possible to tell if the source is off axis and, if so, to tell in which direction. The crystal lens acts very much like a simple convex lens for visible light. Thus if the source is off to the left then the image will focus off to the right illuminating the detector on the right side: telling one in which direction to point the telescope. Possible applications of this type of crystal lens to balloon and satellite experiments are discussed.

Effect of gamma-irradiation on the electronic structure of (Bi1.65Pb0.35)Sr2Ca2Cu3O10 superconductor

Abstract An XPS investigation was carried out on (Bi 1.65 Pb 0.35 )Sr 2 Ca 2 Cu 3 O 10 superconductors, in an effort to study the effect of gamma-irradiation. There is no significant change in the binding energies of Bi 4f, Ca 2p, Cu 2p, O 1s, Pb 4f, and Sr 3p core levels up to the gamma dose of 50 Mrad. However, for the gamma dose of 60 Mrad, the Bi 4f region shows two sets of spin-orbit split levels, one set at about 1.3 eV lower and the other at about 1.7 eV higher binding energies than that of the low-dose samples. Furthermore, for this high-dose sample, (i) the O 1s region clearly shows the evidence of the removal of O by gamma irradiation and (ii) the Cu 2p region shows no satellite, which is typical of Cu 2+ valence states and a low energy shoulder that is a signature of Cu 1+ valence states, in contrast to the low-dose samples. These observations suggest a reduction of hole-concentration in the Cu–O planes through the O removal at a gamma dose between 50 and 60 Mrad.

Imidazolines containing single-, twin- and triple-tailed hydrophobes and hydrophilic pendants (CH2CH2NH)nH as inhibitors of mild steel corrosion in CO2–0.5 M NaCl

Inhibition of mild steel corrosion in CO2–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar) by a new series of imidazolines having single-, twin- and triple-tailed phenyl substituents at C(2) and N(1) pendants of CH2CH2NH2 and (CH2CH2NH)2CH2CH2NH2 have been examined. Imidazolines containing twin-tailed (3,5-dioctyloxyphenyl) hydrophobes outperformed their single- and triple-tailed counterparts as well as two commercial imidazolines. The triamine pendant imparted better inhibition at higher temperature and pressure. The XPS study confirmed the presence of an imidazoline film covering the metal surface. The imidazolines prefer to be adsorbed on the metal surface rather than micellization.

GROWTH OF ZnO NANOSTRUCTURES ON ZINC AND Pt SUBSTRATES

Nanocrystalline ZnO of various shapes was obtained without the use of catalysts by dry oxidation of metallic zinc. Oxidation treatments performed below the melting point of Zn(Tm = 419°C) led to the formation of flakes-type structure. At 500°C, long nanofibers of circular and uniform cross section covering the surface of the oxidized samples were observed. At 600°C, large density of cone-shape needles covered the oxidized surface. High quality nanocrystals of hexagonal shape were obtained by vapor deposition on Pt substrate. XRD results showed that the lattice parameters of the needles are 1% smaller than those of microcrystalline ZnO.

Assignment of fluorine sites in (Tl0.5Pb0.5)Sr1.6Ba0.4Ca2Cu3Oy/Fx

Abstract Fluorine 1s and Cu 2 p core level binding energies of (Tl 0.5 Pb 0.5 )Sr 1.6 Ba 0.4 Ca 2 Cu 3 O y /F x for nominal x =0.0, 1.0, 2.2 and 3.0 were measured by X-ray photoelectron spectroscopy (XPS) in order to identify the F site in the overdoped superconductors. Detailed data analysis indicate that about two thirds of the incorporated F replace O in Cu–O planes of the Tl-1223 structure. Most of the remaining one third of F replaces O in the Ba/Sr–O planes and a small amount of F substitutes for O in the Tl/Pb–O planes of Tl-1223 structure. Cu 2 p 3/2 binding energy was found to be decreasing with increasing x . This indicates that the valency of Cu in Tl-1223/F x decreases as x increases. The reduction of charge carriers in the overdoped high temperature superconductors is discussed in terms of anion substitution.

Micro-PIXE analysis of a single crystal of Y1Ba2Cu3O7−δ superconductor

Abstract A single crystal sample of Y1Ba2Cu3O7−δ superconductor was analyzed using a scanning proton microbeam and the PIXE technique. Micrographs of the crystal surface obtained by SEM revealed a small secondary crystal overgrowth on the main crystal. Micro-PIXE measurements of elemental composition and distribution profiles were carried out on the main base crystal, the smaller crystal overgrowth and in the interface region between them. In addition to Y, Ba and Cu, Au and traces of Cr and Fe were also detected in all three areas. Distributions of Y, Ba, Cu and Au were found to be uniform over both the main crystal and its overgrowth. However, the interface region exhibited strong anomalies in the distribution patterns of these elements.

Crystal diffraction telescopes for nuclear astrophysics

Until recently, focusing of gamma-radiation was regarded as an impracticable task. Today, gamma-ray lenses have become feasible and present promising perspectives for future instrumentation. For the first time in high energy astronomy the signal/noise ratio will be dramatically improved as gamma-rays are collected on the large area of a lens from where they are focused onto a small detector. Besides an unprecedented sensitivity, such instruments feature very high angular and energy resolution.

A space bourne crystal diffraction telescope for the energy range of nuclear transitions

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