1,721,014 research outputs found
PLVV Auger lineshape modulation by incident beam diffraction in InP
No full textThe electron excited PL2,3VV Auger spectrum of InP has been investigated as a function of the incident beam direction. Phosphorus lineshape has been found to be modulated by the scattering-interference of primary electrons via changes in the relative intensity of surface- and bulk-specific spectral features
Diffraction effects in Auger quantitative analysis on III–V compounds
No full textThe anisotropy in surface and subsurface ionization due to the primary electron diffraction has been conflictually reported to play a minor or major role in Auger spectroscopy, and the influence of instrumental and physical parameters has been discussed. We report on the effects of incoming beam diffraction on the quantitative analysis of cleaved, sputtered and Cs covered III-V compounds. We show that measurements must be taken into account for crystalline specimen orientation with respect to the incident beam direction
Focusing-defocusing of keV electrons along [001] and [101] Fe atomic chains
No full textWe have investigated the focusing and defocusing process of a primary electron wave along Fe atomic chains. To this end, we measured the intensity of the LVV Auger signal, as a function of the incidence angle of the primary beam, from a Co him buried in a Fe matrix. We found that maximum focusing efficiency takes place for six scatterers along [001]Fe atomic chains, then defocusing starts to set in. However, a significant anisotropy is still detectable at eleven scatterers deep in the bulk. The anisotropy depth profile we measured has been used to evaluate the anisotropy in more complex situations, such as thin films and multilayers
Oxygen-dosage effect on the structure and composition of ultrathin NiO layers reactively grown on Ag(001)
No full textNiO ultrathin films have been prepared under UHV conditions on Ag(001) substrate by metal deposition inO2 atmosphere. The films were prepared by deposition of the amount of metal correspondent to 1 ML monolayerof NiO in the presence of different oxygen-to-metal flux ratios, to investigate the oxygen dosage effecton the structure and composition of the growing layer and on the stoichiometry of Ni oxide. Thicker films (upto 20 ML) were also prepared. The structure has been monitored both in reciprocal and direct space bylow-energy electron diffraction and primary-beam diffraction-modulated electron emission. Core-level x-rayphotoemission spectroscopy has been used to study film chemistry and composition. At low coverage (below2 ML) a dramatic dependence of structure and composition on the oxygen-to-nickel flux ratio has beenobserved. Low oxygen dosage induces a (231) reconstruction in the 1-ML films that evolves to a (131)phase as the dosage and/or the film thickness increases. In the layers prepared at low oxygen dosage a largefraction of metallic Ni coexists with the Ni oxide, but the oxidized fraction largely prevails for high oxygendosage. The oxygen dosage during the growth also affects thicker films. The mosaic formation, which has beenascribed to misfit strain relaxation, is related to a low oxygen-to-nickel flux ratio
Magnetic anisotropies in Focused Ion Beam sculpted arrays of submicrometric magnetic dots
No full textThanks to its high sputtering efficiency and high spatial resolution, Focused Ion Beam (FIB) apparatus has been proved to be effective in isolating magnetic units by direct removal of selected portions of a thin film, at variance with the lithographic process, which involve resist process, etching and cleaning steps. The results is an extremely flexible, reproducible and clean fabrication process. we present a systematic study of the dependence of the surface morphology and geometric shape of Fe square elements and ferromagnetic/antiferromagnetic Fe/NiO bilayer square elements on the FIB parameters. We shown that the final quality of the geometries that can be obtained by FIB milling as well as the residual damage strictly depend on beam parameters (like spot size and pixel dwell time) and on the swelling properties of the patterned materials
Focusing and defocusing in electron scattering along atomic chains
No full textWe investigated the degree of forward focusing and of multiple-scattering-induced defocusing for electrons in the keV range along regular chains of different atomic density in GaAs and GaP single crystals. The intensity angular anisotropy of elastic and inelastic (losses) Auger electrons was measured in the primary-beam diffraction-modulated electron-emission approach. In variance to the photoelectron-diffraction (PD) case, the possible influence of the energy-loss mechanism on the observed anisotropy can be disregarded and the in-depth distribution of the scattered intensity is independently determined. Both the focusing and defocusing lengths were found to be significantly larger than in previously reported PD results, and strongly dependent on the interatomic spacing. A comparative study of defocusing along the Ga [110] chains in GaAs and GaP gives experimental evidence of the influence of nearest-neighbor atomic rows (As and P, respectively) on the scattering processes
Angular anisotropy of electron-excited secondary electron emission
No full textWe studied the influence of the crystalline structure of III-V compound semiconductors on the intensity of the energy distribution of secondary electrons. Modulation of the amplitude of the primary electron waves within the crystal by electron-atom scattering results in a dependence of secondary emission intensity on the incidence angle. We measured the intensity anisotropy of the electron energy distribution in a wide energy range on either GaAs(110) and InP(110) surfaces, for different values of the primary beam energy between 0.6 and 5 keV. We focused our attention on the elastic and inelastic Auger emission and on the background intensity. The Monte Carlo method was used to simulate the sequences of events experienced by the primary and secondary electrons in the material. Anisotropy was assumed to arise in electron elastic focusing on atomic sites. The calculated anisotropy dependence on the electron kinetic energy is consistent with experimental results. Differences in anisotropy of electrons with different probing depth is related to the different relative importance of surface and bulk contributions to the overall emission intensity. Defocusing along forward scattering directions does not occur over a depth of several tens of angstrom, indicating that the defocusing length is longer than had been usually assumed for close-packed directions
Structural and compositional stability of Co oxide grown on (001) bct Co
No full textRoom temperature (RT) adsorption of oxygen on the (001) surface of metastable, cubic Co film epitaxially grown on a Fe substrate results in the formation of about 7 monolayers (ML) crystalline CoO film, in the typical rocksalt structure 45 degrees rotated with respect to the square unit mesh of the underlying Co film. We investigated the stability of this oxide layer upon annealing in the RT-620 K temperature range, by means of primary-beam diffraction modulated electron emission (PDMEE), and X-ray photoelectron spectroscopy (XPS). For temperatures up to 570 K, film thickness and local order are preserved, in spite of an increasing number of Co and O atoms bonded in sites of reduced coordination For larger temperatures, thickness also reduces, but the oxide film is still characterized by a high degree of CoO-like local order. (C) 1999 Elsevier Science B.V. All rights reserved
Fe epitaxial layers on Cu3Au(001): a structural study by primary-beam diffraction modulated electron emission
No full text
- …
