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Ion beam mixing has been used to produce a silicon carbide (SiC)-rich nanolayer for protective coating. Different C/Si/C/Si/C/Si(substrate) multilayer structures (with individual layer thicknesses falling in the range of 10–20 nm) have been irradiated by Ar+and Xe+ions at room temperature in the energy and fluence ranges of 40–120 keV and 1–6 × 1016ion/cm2, respectively. The effects of ion irradiation, including the in-depth distribution of the SiC produced, was determined by Auger electron spectroscopy depth profiling. The thickness of the SiC-rich region was only some nanometers, and it could be tailored by changing the layer structure and the ion irradiation conditions. The corrosion resistance of the layers was investigated by potentiodynamic electrochemical test in 4 M KOH solution. The measured corrosion resistance of the SiC-rich layers was orders of magnitude better than that of pure silicon, and a correlation was found between the corrosion current density and the effective areal density of the SiC.

Recently, we have shown that the protecting layer of nanosize can be produced by means of ion beam mixing (IBM) of a Si/C multilayer system. The corrosion resistance of the layer correlated with the SiC amount and distribution, determined by Auger electron spectroscopy depth profiling. It has also been shown that the IBM of the Si/C system can be well described by TRIDYN simulation. By combining these two findings, it is possible to design protective layers for various arrangements of layer structure and irradiation conditions. Three different multilayer structures (with individual layer thicknesses falling in the range of 10–20 nm) have been irradiated by Ar+and Xe+ions at room temperature in the energy and fluence ranges of 40–120 keV and 0.25 × 1016to 6 × 1016ion/cm2, respectively. The carbon and silicon depth distributions have been calculated by TRIDYN simulation. From these profiles applying a simple rule for compound formation, the SiC in-depth distributions were calculated. The resulting corrosion resistance has been measured by potentiodynamic corrosion test in 4 M KOH solution. Excellent correlation between these results and the in-depth distribution (calculated by TRIDYN simulation) of SiC has been found. Thus, the design of a protective SiC coatings operating in harsh environments is possible by applying fast and cheap simulation techniques.

Calmodulin plays a role in several life processes, its flexibility allows binding of a number of different ligands from small molecules to amphiphilic peptide helices and proteins. Through the diversity of its functions, it is quite difficult to find new drugs, which bind to calmodulin as a target. We present available structural information on the protein, obtained by X-ray diffraction, nuclear magnetic resonance spectroscopy and molecular modeling and try to derive some conclusions on structure-activity relationships.

Surface-sensitive electron spectroscopies, like Auger electron spectroscopy, X-ray photoelectron spectroscopy and elastic peak electron spectroscopy (EPES) are suitable techniques to investigate surfaces and thin layers. A theoretical model for electron transport is needed to process the observed electron spectra. Electron transport descriptions are based on the differential elastic cross sections for the sample atoms and the inelastic mean free path (IMFP) of backscattered electrons. An electron impinging on the sample can lose energy either due to surface or volume excitations. In the present work a Monte Carlo (MC) simulation of the elastic peak of Si, Ag, Ni, Cu, and Au for surface analysis is presented. The IMFP of Si was determined applying the EPES method. The integrated elastic peak ratio of Si with the standard metal reference samples corrected for surface excitation provided IMFP values of Si in the energy range E = 0.2–2.0 keV. Experiments were made with the ESA 31 HSA (ATOMKI) and with the DESA-100 (Staib) spectrometers. Surface correction was based on the application of Chen's model and material parameters. The Monte Carlo simulations of elastically backscattered electron trajectories were made using new EPESWIN software of Jablonski. An improvement of IMFP experimental results was achieved applying the presented procedure.

A new Monte Carlo method has been developed for simulating backscattered electron spectra, and this was applied for determining the surface excitation parameter (SEP). The simulation is based on direct tracking of electron trajectories in the solid, taking into account elastic and inelastic events. The elastic scattering cross sections are taken from literature, while inelastic cross section data are obtained by a fitting procedure. After some iterations, the program produces electron spectra fitting well to the experimental ones. Si and Ge electron spectra were simulated and SEP values were calculated. The SEP values are compared to other ones from literature.

Reference samples are needed for experimental determination of the inelastic mean free path (IMFP) of electrons by elastic peak electron spectroscopy (EPES). High‐quality (microcrystalline mirror) Ni reference samples were used for IMFP measurements. For surface excitation parameter experiments, new types of reference samples are needed. They should exhibit pronounced surface‐loss spectra, such as amorphous Ge (aGe), Sn and Ag. A new procedure is presented for their preparation. Microcrystalline Ag and Sn reference samples were deposited on highly polished (by Buehler alumina alpha micropolish 1C) brass (60% Cu, 40% Zn) substrates. Electrolytic deposition was used for Ag and for Sn and resulted in excellent surface quality. The average surface roughness ravwas checked by scanning tunnelling microscopy or atomic force microscopy before and after Ar+ion bombardment cleaning. Typical ravvalues were 4–6 nm for Ag, 3–4 nm for Sn and 2–4 nm for brass substrate. The aGe sample was deposited by magnetron sputtering or by evaporation in a high vacuum on an Si substrate. Its ravwas 4–5 nm. The samples were studied by EPES/reflection electron energy‐loss spectroscopy, covering the 0.2–5 keV energy range, with the ESA 31 HSA electron spectrometer. The IMFP of Sn was determined by EPES. The surface excitation parameters for the Si, Ge and Sn samples were determined from their inelastic scattering cross‐section spectra. For Ag the surface excitation parameter was estimated by using the above reference samples. Copyright © 2002 John Wiley & Sons, Ltd.

Reference samples are needed for experimental determination of the inelastic mean free path (IMFP) of electrons by elastic peak electron spectroscopy (EPES). High-quality (microcrystalline mirror) Ni reference samples were used for IMFP measurements. For surface excitation parameter experiments, new types of reference samples are needed. They should exhibit pronounced surface-loss spectra, such as amorphous Ge (aGe), Sn and Ag. A new procedure is presented for their preparation. Microcrystalline Ag and Sn reference samples were deposited on highly polished (by Buehler alumina alpha micropolish 1C) brass (60% Cu, 40% Zn) substrates. Electrolytic deposition was used for Ag and for Sn and resulted in excellent surface quality. The average surface roughness rav was checked by scanning tunnelling microscopy or atomic force microscopy before and after Ar⁺ ion bombardment cleaning. Typical rav values were 4–6 nm for Ag, 3–4 nm for Sn and 2–4 nm for brass substrate. The aGe sample was deposited by magnetron sputtering or by evaporation in a high vacuum on an Si substrate. Its rav was 4–5 nm. The samples were studied by EPES/reflection electron energy-loss spectroscopy, covering the 0.2–5 keV energy range, with the ESA 31 HSA electron spectrometer. The IMFP of Sn was determined by EPES. The surface excitation parameters for the Si, Ge and Sn samples were determined from their inelastic scattering cross-section spectra. For Ag the surface excitation parameter was estimated by using the above reference samples. Copyright © 2002 John Wiley & Sons, Ltd.

The surface excitation produced by impinging or escaping electrons is a competitive process to elastic backscattering. It affects the intensity of Auger and XPS peaks and is characterized by the surface excitation parameter Pse. This appears in the surface loss peak I(Epls), and possibly a surface plasmon. In our work Pseis defined as the ratio of the probability to create a surface plasmon/elastic scattering and is deduced from the integrated surface loss peak and elastic peak, respectively. Our procedure is based on reflection electron energy loss spectroscopy and elastic peak electron spectroscopy spectra and Kλispectra (Kis the inelastic scattering cross‐section and λiis the inelastic mean free path), determined using Tougaard's method. The normalized Kλicurves are fitted to the spectrum at E= 5 keV (primary energy) and EL= Epl1(volume plasmon), approximated with the Lorentzian type three‐parameter formula of Tougaard. For E>Epl1, the normalized curves are overlapping and Pseis deduced from the integrated difference spectra fitted with the Tougaard cross‐sections. The procedure was applied on materials exhibiting surface and volume plasmons: III–V semiconductors (GaAs, InSb) and In and Sb metals. The REELS experiments were carried out with an ESA 31 HSA spectrometer covering the E= 0.2–5 keV energy range. Copyright © 2002 John Wiley & Sons, Ltd.

The inelastic mean free paths (IMFPs) of three AuPd alloys were determined by means of elastic peak electron spectroscopy (EPES) in a round-robin study in four laboratories using different types of electron spectrometers in the energy range 0.5–2 keV. The scatter of the IMFP values was in the range of 25%. Within this accuracy the inverse IMFP of these alloys can be calculated by the weighted sum of the inverse IMFPs of the alloying elements. Reflected electron energy loss spectra also were measured and the Kλ curves, calculated by the method of Tougaard, were used for estimating the inelastic processes in the alloys. The source of the scatter in the IMFPs obtained in the present work is discussed. Copyright © 2002 John Wiley & Sons, Ltd.

The inelastic mean free paths (IMFPs) of three AuPd alloys were determined by means of elastic peak electron spectroscopy (EPES) in a round‐robin study in four laboratories using different types of electron spectrometers in the energy range 0.5–2 keV. The scatter of the IMFP values was in the range of 25%. Within this accuracy the inverse IMFP of these alloys can be calculated by the weighted sum of the inverse IMFPs of the alloying elements. Reflected electron energy loss spectra also were measured and the Kλ curves, calculated by the method of Tougaard, were used for estimating the inelastic processes in the alloys. The source of the scatter in the IMFPs obtained in the present work is discussed. Copyright © 2002 John Wiley & Sons, Ltd.

The recoil effect on quasi-elastic scattering of electrons has been described by Boersch. The Rutherford type scattering on the nucleus produces a shift of the elastic peak maximum of ΔEem, proportional to 1/M(atomic mass) and electron energy. Laser et al. studied the recoil effect for exact calibration of the energy scale for XPS. The other effect is broadening of the elastic peak. Reflection electron energy loss spectra were studied by an electron spectrometer ESA 31 of high energy resolution. Various modifications of C (electrode and reactor graphite, glassy C, powder) and conducting polymers (polyacetylene, polyaniline, polythiophene) have been studied with varying composition of C, O, H, S, Pd etc. In the case of the samples containing different elements the complex nature of the elastic peaks (consisting of the sum of components having different intensities and shifts) was clearly observed. Possible explanations for the recoil effects detected are reviewed.

Analysis for surface chemistry uses electron spectroscopy: AES, XPS and REELS. The excitation and electron emission processes are affected by the competitive surface excitation. Impinging and escaping electrons suffer losses in the solid surface region, producing surface plasmons. The surface excitation is characterized by the surface excitation parameter Pse. A new experimental procedure is described for the determination of Pse. It is based on REELS–EPES, using the elastic peak as reference. The procedure is valid for materials having surface and volume plasmon loss peaks, like Si, In, and Sb. It can be applied for estimating Pseon materials exhibiting a surface loss peak decreasing with energy, like Ag. The ratio of the integrated surface and volume loss peaks is composed and compared with the elastic peak. Experimental results in the E=0.2–5 keV energy range are presented for several solids.

The consistency and accuracy of inelastic electron mean free paths (IMFPs) determined from comparison of the intensity of elastically reflected electrons with theoretical calculations were studied. The variation with experimental geometry, spectrometer energy resolution and the procedure for background subtraction was studied. Four different types of spectrometers— double pass cylindrical mirror analyser (CMA) pre-retarded CMA, hemispherical analyser (HSA) and retarding field analyser (RFA)— with widely different geometries and energy resolutions, placed in four different laboratories in three countries, were used. Four background subtraction methods (Shirley, linear, Tougaard and ELPSEP) were applied to isolate the elastic peak intensity from the reflected electron spectra. It was found that the IMFPs determined with data from the double pass CMA deviated considerably more (by a factor of 2) from the average values as well as from theoretical IMFP values than IMFPs determined with data from the other spectrometers. The data from the double pass CMA were therefore excluded from the statistical analysis. The root mean square (RMS) deviation of the IMFP from a function fitted to the data was 1.6–2.8 Å, depending on the background subtraction method, and it is smallest for the Tougaard method. The RMS deviation from IMFP values calculated by Tanuma et al. is 2.1–3.2 Å, again with the smallest value for the Tougaard method. The percentage deviation of the results using a Tougaard background from Tanuma et al. values is 12.6%. The results point to the conclusion that the major contribution to the inaccuracies in IMFPs determined with this method is not the background subtraction procedure but rather the lack of accuracy of the presently available models for elastic electron scattering, i.e. atomic elastic scattering cross-sections and effects of crystallinity that are not included in the presently applied models. Copyright © 2001 John Wiley & Sons, Ltd.

The consistency and accuracy of inelastic electron mean free paths (IMFPs) determined from comparison of the intensity of elastically reflected electrons with theoretical calculations were studied. The variation with experimental geometry, spectrometer energy resolution and the procedure for background subtraction was studied. Four different types of spectrometers— double pass cylindrical mirror analyser (CMA) pre‐retarded CMA, hemispherical analyser (HSA) and retarding field analyser (RFA)— with widely different geometries and energy resolutions, placed in four different laboratories in three countries, were used. Four background subtraction methods (Shirley, linear, Tougaard and ELPSEP) were applied to isolate the elastic peak intensity from the reflected electron spectra. It was found that the IMFPs determined with data from the double pass CMA deviated considerably more (by a factor of 2) from the average values as well as from theoretical IMFP values than IMFPs determined with data from the other spectrometers. The data from the double pass CMA were therefore excluded from the statistical analysis. The root mean square (RMS) deviation of the IMFP from a function fitted to the data was 1.6–2.8 Å, depending on the background subtraction method, and it is smallest for the Tougaard method. The RMS deviation from IMFP values calculated by Tanuma et al.is 2.1–3.2 Å, again with the smallest value for the Tougaard method. The percentage deviation of the results using a Tougaard background from Tanuma et al.values is 12.6%. The results point to the conclusion that the major contribution to the inaccuracies in IMFPs determined with this method is not the background subtraction procedure but rather the lack of accuracy of the presently available models for elastic electron scattering, i.e. atomic elastic scattering cross‐sections and effects of crystallinity that are not included in the presently applied models. Copyright © 2001 John Wiley & Sons, Ltd.

The inelastic mean free path (IMFP) of electrons is a fundamental material parameter needed for surface analysis. The IMFP data of semiconducting III–V compounds have been calculated by Tanuma et al., Kwei et al.and Gries. The present paper completes previous research and reports experimental studies on the IMFPs of GaP and InAs. Elastic peak electron spectroscopy (EPES) was used with Ni, Au and Ag reference samples. Both InAs(100) and GaP(100) have been studied in three laboratories, using different types of electron spectrometer analysers and energy ranges: HSA (0.2–5 keV), DCMA (0.2–2 keV), DESA 100 (0.5–2 keV). The surface of the samples was cleaned and amorphized by Ar+ion bombardment with controlled parameters (energy, dose, etc.) to eliminate crystallinity effects. The surface composition of the ion‐bombarded samples was determined in situby XPS and Auger electron spectroscopy. Their crystallinity and incoherent elastic scattering were tested with Renninger plots of the elastic peak intensity, rotating the sample around its axis perpendicular to the surface. The IMFPs were calculated by a Monte Carlo algorithm using the NIST database of elastic scattering cross‐sections. A reasonable agreement was found with theoretical IMFP values calculated by other authors. Copyright © 2000 John Wiley & Sons, Ltd.

The inelastic mean free path (IMFP) of electrons is a fundamental material parameter needed for surface analysis. The IMFP data of semiconducting III–V compounds have been calculated by Tanuma et al., Kwei et al. and Gries. The present paper completes previous research and reports experimental studies on the IMFPs of GaP and InAs. Elastic peak electron spectroscopy (EPES) was used with Ni, Au and Ag reference samples. Both InAs(100) and GaP(100) have been studied in three laboratories, using different types of electron spectrometer analysers and energy ranges: HSA (0.2–5 keV), DCMA (0.2–2 keV), DESA 100 (0.5–2 keV). The surface of the samples was cleaned and amorphized by Ar⁺ ion bombardment with controlled parameters (energy, dose, etc.) to eliminate crystallinity effects. The surface composition of the ion-bombarded samples was determined in situ by XPS and Auger electron spectroscopy. Their crystallinity and incoherent elastic scattering were tested with Renninger plots of the elastic peak intensity, rotating the sample around its axis perpendicular to the surface. The IMFPs were calculated by a Monte Carlo algorithm using the NIST database of elastic scattering cross-sections. A reasonable agreement was found with theoretical IMFP values calculated by other authors. Copyright © 2000 John Wiley & Sons, Ltd.

Ab initio minimal basis set molecular orbital and discretized Poisson−Boltzmann electrostatic potential calculations were carried out on large models of the active site of heme peroxidases (cytochrome C peroxidase and cytosolic ascorbate peroxidase) to rationalize the location of the radical site in Compound I, an intermediate of the enzymatic reaction. Both molecular orbital and electrostatic potential calculations suggest that the spin distribution depends on the protonation state of the proximal His...Asp...Trp triad. If the transferable proton is shifted from the Trp side chain to Asp, the radical localizes on the indole group, while if it remains on the Trp the unpaired electron transfers to the heme group. Therefore, in cytochrome C peroxidase, Trp is deprotonated in Compound I, while it is protonated and neutral in cytosolic ascorbate peroxidase. Protonation state of the proximal residues is influenced by the electrostatic effect of the protein environment that differs in these enzymes, especially in the immediate vicinity of the Asp side chain. In contrast to earlier propositions we did not find evidence for the effect of the neighboring potassium-binding loop on the localization of the free radical. The heme peroxidases studied provide examples for the electrostatic, protonation-mediated modulation of electron transfer.

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Thin‐film structures several monolayers thick can be observed by Auger depth profiling if specimen rotation, grazing angle of incidence and low ion energy are used. To evaluate depth profiles measured on such features, we developed a trial‐and‐error type of evaluation technique. First we simulated the depth profile for an arbitrary in‐depth distribution using a dynamic TRIM code and then the Auger signal was calculated from the output of the TRIM simulation. It will be shown that using a single fitting parameter all depth profiles measured on various layer structures could be properly evaluated. Based on our evaluation technique we can predict that a depth profile taken on a step‐function‐like transition is not sensitive to the quality of the interface. On the other hand, small changes in the interface of thin‐layer structures result in clearly visible changes in the Auger depth profile. © 1998 John Wiley & Sons, Ltd.

Elastic peak depth profiling was carried out on an Mo/Si multilayer system using a rotating specimen, grazing angle of incidence (86° with respect to the surface normal) and 0.5 keV Ar ion energy. The depth profiling was simulated by dynamic TRIM (T‐DYN) code. The T‐DYN code provided the in‐depth distribution of the elements in any moment of the depth profiling process. Direct Monte Carlo calculation was developed to calculate the intensity of the elastic peak emitted from the distribution determined by the T‐DYN code. Good agreement was found between the calculated and measured elastic peak depth profiles, proving that the Monte Carlo routine developed is readily applicable to inhomogeneous layers and the mixing of the Mo/Si layer is well described by the T‐DYN code.© 1997 by John Wiley & Sons, Ltd.

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Dynamic behavior in certain perovskites below the anti-ferrodistortive transition is studied along the longitudinal excitation branch by investigating effects of weak anisotropy for a n = 3 component order parameter field. Exploiting the consequences of small deviations from isotropy and of the relatively high frequencies involved, it is found that the longitudinal excitation frequency ωL may be expected to be proportional to the average value P of the order parameter beyond the static mean-field region of temperatures. Experimental implications of our theory are briefly discussed.

Isothermal stress relaxation tests at fixed displacement on coarse-grained laboratory heats of A508-2-type steel, normally highly susceptible to stress relief cracking (SRC), have established that trace impurities are essential for this phenomenon. An undoped heat made from iron containing ~5 ppm sulphur in a high-purity crucible was found to be extremely resistant to SRC. Subsequent chemical analysis showed that this steel contained 2 ppm boron and an inadvertant 66 ppm nitrogen, which presumably scavenged the boron to some extent. Other high-purity heats were doped with boron, sulphur, and phosphorus, singly and in combinations. Boron and sulphur additions were always deleterious; phosphorus sometimes appeared to have beneficial effects. High-resolution scanning Auger spectroscopy confirmed the role of surface-adsorbed sulphur in the cracking mechanism.MST/564

The rate of crack growth by apparent intergranular decohesion of a statically loaded MnMoNiCr steel at 535–600°C in vacuum was measured using the d.c. potential-drop method. Slow-displacement-rate testing of notched tensile bars at the same temperatures in an inert atmosphere was also carried out. The steel had been air-cooled from 1300°C to simulate a weld heat-affected zone. Interrupted tests followed by low-temperature brittle fracture were used to clarify the details of the cracking process, which occurred more rapidly in some grain boundaries than in others, giving rise to oscillations in the measured crack velocity. Striations on the intergranular facets were consistent with crack growth in steps of about 0.1 μm. SEM observations indicated that the tip of the main crack had a radius on the sub-micron scale. The cracking behavior of the tensile bars was qualitatively similar to that of the CT specimens and was found to have a temperature dependence of about 55 kcal/mol. The similarity of this phenomenon to cracking in other alloy systems is pointed out. The three contending models for the brittle mode of stress-relief cracking are compared in the light of the present results; a detailed treatment of a proposed theory is given in a separate paper.

AES depth profiling was carried out on a Ge-Si multilayer structure using rotated specimen and grazing incidence angle. Under these sputtering conditions the depth resolution is determined mainly by atomic mixing. The dependence of the experimentally measured atomic mixing on incidence angle and energy was compared with the simulation results obtained from TRIM code. It was found that the trends of the dependencies were the same, but the TRIM predicted weaker atomic mixing than that of the experimental one. Thus we concluded that consideration of the thermal processes is also important in the description of the atomic mixing in the Ge-Si system.

Elastic peak depth profiling was carried out on an Mo/Si multilayer system using a rotating specimen, grazing angle of incidence (86° with respect to the surface normal) and 0.5 keV Ar ion energy. The depth profiling was simulated by dynamic TRIM (T-DYN) code. The T-DYN code provided the in-depth distribution of the elements in any moment of the depth profiling process. Direct Monte Carlo calculation was developed to calculate the intensity of the elastic peak emitted from the distribution determined by the T-DYN code. Good agreement was found between the calculated and measured elastic peak depth profiles, proving that the Monte Carlo routine developed is readily applicable to inhomogeneous layers and the mixing of the Mo/Si layer is well described by the T-DYN code. © 1997 by John Wiley & Sons, Ltd.

Thin-film structures several monolayers thick can be observed by Auger depth profiling if specimen rotation, grazing angle of incidence and low ion energy are used. To evaluate depth profiles measured on such features, we developed a trial-and-error type of evaluation technique. First we simulated the depth profile for an arbitrary in-depth distribution using a dynamic TRIM code and then the Auger signal was calculated from the output of the TRIM simulation. It will be shown that using a single fitting parameter all depth profiles measured on various layer structures could be properly evaluated. Based on our evaluation technique we can predict that a depth profile taken on a step-function-like transition is not sensitive to the quality of the interface. On the other hand, small changes in the interface of thin-layer structures result in clearly visible changes in the Auger depth profile. © 1998 John Wiley & Sons, Ltd.

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A one-dimensional system of electrons interacting via a BCS-type interaction is investigated by renormalization group techniques in two successive approximations atT=0, keeping only a single energy variable ?. The first approximation is equivalent to the summation of leading logarithmic terms carried out by Bychkovet al., and correspondingly the vertex function displays a singularity at a finite value of ?. The second approximation accounts for the next leading logarithmic terms as well, and by this means the singularity is shown to be pushed down to ?=0. Due to important self-energy contributions, however, the invariant couplings behave differently and tend to a saturation value at ?=0.

In this research we investigated a new ceramic forming process. The technology is based on a concentrated ceramic suspension with ethylene acrylic acid copolymer binder system. After the forming procedure to get the final products, the samples were dried, debinded and sintered on high temperature. The samples were studied by different ways during the process: rheological studies, surface properties (optical and scanning electron microscopy), mercury porosimetry.

Measurements of the arsenic losses during alloying of the usual evaporated metal contact systems of GaAs Gunn diodes are given. The results were obtained by making in situ alloying processes in a mass spectrometer. Curves of As2 yields are given as functions of temperature and time.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.