Papers by Keyword: Auger Electron Spectroscopy (AES)

Abstract: During low-temperature annealing, the segregation of the alloying element leads to a strong enrichment of the surface layer, causing a rearrangement of the surface electron structure. This change in the electron structure is manifested in the characteristic energy loss spectra. Annealing of single crystals at 400–500 K leads to an increase in the density of surface electron states. As shown by the calculations of the surface potential using experimental data on the temperature dependence of the surface concentration, dopant segregation causes a linear increase in the surface potential.

Abstract: Surface and interface properties of Fe-Cr, Fe-Al, and Fe-Cr-Al are studied using Exact Muffin-Tin Orbitals and Monte Carlo methods and with x-ray photoelectron and Auger electron techniques. Surface composition is investigated as a function of oxidation (heating) time. Hard x ray photoelectron spectroscopy (HAXPES) is used to scan non destructively the compositions below the surface. It is found that Cr boosts the Al segregation to the surface.

Abstract: AISI 316L steel, subjected to a low temperature carburizing treatment (kolstering), has been examined by Mechanical Spectroscopy (MS) and nanoindentation to determine the Youngs modulus of the surface hardened layer (S phase). MS results showed that the average value of elastic modulus of S phase is 202 GPa, a little higher than that of the untreated material.Nanoindentation tests, carried out with loads of 5, 15 and 30 mN, evidence a modulus profile vs depth: E is ~ 400 GPa at a distance from the surface of ~ 110 nm, then decreases to reach the value of the steel substrate (190 GPa) at 33 μm.These results, together with X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements of carbon concentration profile, can be explained by considering the presence of a very thin surface layer, different from S phase and consisting of a mixed structure of Diamond-like carbon (DLC) and tetrahedral carbon (taC).Furthermore, the same experiments have been carried out also after heat treatments at 450 °C to correlate the modulus change to the decomposition of the metastable S phase leading to the formation of (Cr,Mo)C and Cr₂₃C₆ carbides in a Cr-depleted austenitic matrix.

Abstract: A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550°C under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.

Abstract: Silicide sequential phase formation during tens-of-nanometer-thick metallic film reaction on Si substrate has been extensively studied. Nevertheless, the reasons of sequential phase formation are still under debate, and have been poorly studied at the atomic scale. Using atomistic kinetic Monte Carlo simulations, we show that considering a binary fcc non-regular solid solution, without diffusion asymmetries, the diffusive reaction of a sub-nanometer-thick film (~5 atomic monolayers) on a semi-infinite substrate leads to the sequential formation of all the phases present in the binary phase diagram, starting with the film atom richest phase. These predictions are supported by experimental observations: the dissolution of a 4 monolayer-thick Si film on a Ni(111) substrate, during in-situ ultra high vacuum Auger electron spectroscopy, shows delays and kinetic changes in the dissolution process that may correspond to the sequential formation of the Ni-Si compounds, i.e. NiSi₂, NiSi, Ni₃Si₂, Ni₂Si, Ni₃₁Si₁₂ and Ni₃Si.

Abstract: Thin films (40-60 nm) prepared by co-evaporation of Sn and TeO2 were studied as ethanol gas sensors. In the as-deposited state, the films thus obtained are amorphous and consist of mixed Te and Sn oxides, doped with Te, Sn, and/or SnTe (depending on the atomic ratio between Sn and Te (RSn/Te)), due to interaction between the two substances during the co-deposition. After stepwise thermal treatment of films with RSn/Te ≈ 2.3 up to 360oC (by 40oC steps, for 15 minutes at each temperature) nanocrystalline films, built up of a mixture of SnO2, TeO2 and unstoichiometric Sn oxide were obtained. The Pt-doping was realized by thermal evaporation in a separate vacuum cycle, after the annealing. To study the film composition and structure as well as the volume distribution of the elements different electron microscopy techniques (TEM, SAED) and analytical methods (EDS in SEM, AES) were applied. The sensitivity towards ethanol vapours was investigated as a function of the substrate temperature (T) in the range from 20oC to 200oC. High sensitivity has been observed for Pt-doped films at T = 120oC. No cross sensitivity to relative humidity (RH [%]) was observed at this temperature. Further improvement of the sensitivity could be obtained by optimization of the thermal processing, Pt-doping and working temperature.

Abstract: Traditionally, the term hard coatings refer to the property of high hardness in mechanical sense with good tribological properties [1]. With the development of modern technology in the areas of optical, optoelectronic, microelectronic and related defense applications, the definition of the term hard coatings can be extended. Thus, a system which operates satisfactorily, in a given environment can be said to be hard with respect to that environment [2]. Most of the hard coatings are ceramic compounds such as oxides, carbides, nitrides (AlN), ceramic alloys, cermets, metastable materials such as Diamond-Like Carbon (DLC). Their properties and environmental resistance depend on the composition, stoichiometry, impurities, microstructure, imperfections, and in the case of coatings, the preferred orientation (texture). In this paper we shall take a look at some characteristics - physicochemical and optical of AlN and DLC layers synthesized by physical vapor deposition – RF magnetron sputtering in an industrial high vacuum deposition system. The influence of the process parameters on the growth rate, morphology, topography and chemical bonding structure will be presented.

Abstract: Diffusion controlled processes play a crucial role in the degradation of technical materials. At low temperatures the most significant of them is the diffusion along grain boundaries. In thin film geometry one of the best methods for determining the grain boundary (GB) diffusion coefficient of an impurity element is the Hwang-Balluffi method, in which a surface sensitive technique is used to follow the surface accumulation kinetics. Results of grain boundary diffusion measurements, carried out in our laboratory by this method in three different materials systems (Ag/Pd, Ag/Cu and Au/Ni) are reviewed. In case of Ag diffusion along Pd GBs the surface accumulation was followed by AES method. The data points can be well fitted by an Arrhenius function with an activation energy Q=0.99eV

Abstract: The development of lapping and polishing technologies for SiC single crystal wafers has realized the fabrication of an extremely flat SiC wafer with excellent surface quality. To improve the SiC wafer flatness, we developed a four-step lapping process consisting of four stages of both-side lapping with different grit-size abrasives. We have applied this process to lapping of 2-inch-diameter SiC wafers and obtained an excellent flatness with TTV (total thickness variation) of less than 3 μm, LTV (local thickness variation) of less than 1 μm, and SORI smaller than 10 μm. We also developed a novel MCP (mechano-chemical polishing) process for SiC wafers to obtain a damage-free smooth surface. During MCP, oxidizing agents added to colloidal silica slurry, such as NaOCl and H2O2, effectively oxidize the SiC wafer surface, and then the resulting oxides are removed by colloidal silica. AFM (atomic force microscope) observation of polished wafer surface revealed that this process allows us to have excellent surface smoothness as low as Ra=0.168 nm and RMS=0.2 nm.

Abstract: Chemical and structural changes at the grain boundaries were investigated to quantify their influence on fracture behaviour of austenitic stainless steels and model ferritic Fe-Si-P alloys. The balance between the size and the area density of intergranular particles was found to be one of the most decisive factors influencing sensitivity of the steels to intergranular fracture. The precise dependence of the energy of intergranular fracture on the phosphorus grain boundary concentration was also determined.