1,721,166 research outputs found
Auger electron emission by ion impact on solid surfaces
No full textIn this review, we examine recent work on the emission of Auger electrons by energetic ion collisions on solid surfaces. We give a detailed presentation of the results concerning the interpretation of the Auger lineshape, the identification and separation of different spectral contributions, and the evaluation of the relative importance of symmetric and asymmetric collisions in ionization and sputter-ejection processes. We stress the relevance of the excitation and detection geometry, and discuss the angular and energetic dependence of the Auger lineshape in terms of the Doppler effect. Emission from multi-elemental targets and from singly or multiply charged projectiles is also reviewed. Finally, a brief survey of computational studies in this area is presented
LIQUID-LIKE LAYER AT ICE SURFACE - DIRECT EXPERIMENTAL-EVIDENCE
No full textDirect experimental proof of the existence of a liquid-like layer on the surface of ice crystals were obtained from measurements of the coefficient of thermal expansion of ice, by eans of strain gauges frozen on the surface. The liquid-like layer was found to exist in an appreciable temperature range below melting point
ION BEAM-STIMULATED AUGER-ELECTRON EMISSION FROM CR AND CR-SILICIDES
No full textThe emission of Auger electrons induced by energetic ions impact on Cr and Cr-silicides of different stoichiometry (Cr3Si and CrSi2) was investigated. Attention was focused on the origin, nature and characteristics of the metal peaks and on the role of asymmetric metal-silicon collision for the Cr and Si atom excitation. The ion excited, M23-related, low energy Cr spectrum essentially originates in the decay of slow sputtered Cr atoms. The Cr autoionization satellite almost completely vanishes, while interatomic transitions involving Cr and Ar atoms occur. Cr-Si collisions have been found to be efficient for the ionization of either Si and Cr atoms, indicating that excitation can also occur in the heavier partner
Modulated electron emission by scattering-interference of primary electrons
No full textWe review the effects of scattering-interference of the primary, exciting beam on the electron emission from ordered atomic arrays. The yield of elastically and inelastically backscattered electrons, Auger electrons and secondary electrons shows a marked dependence on the incidence angle of primary electrons. Both the similarity and the relative importance of processes experienced by incident and excident electrons are discussed. We also present recent studies of electron focusing and defocusing along atomic chains. The interplay between these two processes determines the in-depth profile of the primary electron intensity anisotropy. Finally, the potential for surface-structural studies and limits for quantitative analysis are discussed, in comparison with the Anger electron diffraction (AED) and photoelectron diffraction (PD) techniques
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
ION-BEAM EFFECTS ON SURFACE AND SUBSURFACE COMPOSITION OF NEAR-NOBLE SILICIDES
No full textModifications of Cr–silicide (Cr3Si and CrSi2) and Ni–silicide (NiSi2) surface and subsurface regions induced by an Ar ion beam were investigated by angle integrated Auger electron spectroscopy. The dependence of the surface modification on the ion beam energy and density was investigated between −80 and 400 °C. At room temperature (RT) Cr–silicides are metal enriched in the surface and subsurface region. Ion bombardment of a CrSi2 surface at high temperature (HT) produces Si enrichment with respect to RT, resulting in the formation of a CrSi layer. The Si enrichment occurs at a temperature lower than the temperature characteristic of purely thermal segregation. On the contrary, the Cr3Si surface composition is independent of the temperature. The NiSi2 surface is stoichiometric at RT; ion bombardment at HT produces a Si surface segregation in two distinct steps. On the basis of a careful line‐shape analysis of the Si core–valence–valence Auger transitions, we attribute the first step to the formation of an ordered, ∼1.4 Å thick, Si overlayer, the second one to the growth of a thicker (∼3 Å) amorphous Si layer
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
AES and EELS study of alkali-metal adsorption kinetics on either cleaved or sputtered GaAs and InP (110) surfaces
No full textA detailed study at room temperature of the interfaces between thin alkali films and cleaved or sputtered processed (110) surfaces of GaAs and InP has been performed using Auger and electron energy loss spectroscopy. Attention has been focused on the interface growth kinetics, and on subsurface intermixing and segregation processes in the presence of different metals (Cs, Na and K) and substrates. The most relevant features in the interface formation are very similar in all cases. Alkali adatoms partially diffuse in the semiconductor subsurface. For K and Na on GaAs, this intermixing also results in an As outdiffusion. On sputter-prepared substrates, the interface formation rate is lower, the As outdiffusion on the contrary is larger and occurs also in the Cs/GaAs case. A comparison with high and low electronegativity metals on III–V semiconductors is made and the results are discussed. As far as interfacial reaction and products are concerned, we found that cations and anions are predominantly involved in the chemical bonding with the adatoms in GaAs and in InP, respectively
Structural and morphological modifications of thermally reduced cerium oxide ultrathin epitaxial films on Pt(111)
No full textThe modifications of the stoichiometry, morphology and surface structure of cerium oxide ultrathin films
induced by thermal treatments under vacuum and oxygen partial pressure were studied using in situ X-ray
photoemission spectroscopy, scanning tunnelling microscopy and low energy electron diffraction. The
effect of the film nominal thickness, heating temperature and heating time on the degree of reduction of
the film was investigated. The reduction is more relevant on the film surface, where different ordered
surface structures were observed at different degrees of reduction for very thin films. The obtained results
are discussed taking into account the dimensionality of the oxide and the effects of the proximity of the Pt
substrate. After reduction it was always possible to re-oxidize the films back to their original oxidation
state by thermal treatment under oxygen-rich conditions
Interfacial interaction between cerium oxide and silicon surfaces
No full textAbstract The interaction of cerium oxide films with Si substrates is investigated by means of X-ray photoelectron spectroscopy. Cerium oxide films of different thickness have been grown at room temperature by reactive deposition on different Si surfaces, namely Si(111), Si(100) and thermally oxidized Si(100). We show that cerium oxide and silicon form a silicate phase of subnanometric thickness and that the interfacial phase composition and thickness is similar on the (111) and (100) Si surfaces. The silicate phase formed at the interface contains cerium in the 3+ oxidation state, while silicon presents different oxidation states up to 4+. With a thermal annealing in O2 at 1040K the interface reaction proceeds and the silicate phase evolves in stoichiometry. We demonstrate the stability of the silicate phase towards oxidation after exposure to atomic or molecular oxygen or air. The presence of a thick thermal oxide layer on the Si surface partially limits the extent of the reaction.
Highlights ► A subnanometric silicate phase forms at the interface between cerium oxide and Si. ► The silicate phase evolves in thickness and composition after thermal treatments. ► The interfacial reaction has the same extent on the (111) and (100) Si surfaces. ► The interfacial reaction is partially limited by the presence of a silicon oxide. ► The silicate phase is stable towards oxidizing treatments
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