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Analytical and Bioanalytical Chemistry (v.365, #1-3)

10th Working Conference on Applied Surface Analysis (AOFA 10) Kaiserslautern, 6–10 September 1998 by H. Oechsner; Hubert Gnaser (pp. 1-2).

Characterisation of biomaterials using ToF-SIMS by D. Léonard; H. J. Mathieu (pp. 3-11).

In the field of biomaterials and biological compounds, ToF-SIMS has exhibited large interest due to high surface sensitivity, an information depth limited to the top-surface and molecular imaging capabilities. Selected examples given in this review concern recent applications like characterisation of engineered heterogeneous bioactive surfaces (including biosensors), combinatorial synthesis of peptides, molecular imaging of cells and quantification of biomolecules in real biological samples. These examples illustrate advantages and possible limitations of ToF-SIMS in this research field. Recent improvement with focus on these limitations is also briefly reviewed.

Recent instrumental developments in magnetic sector SIMS by M. Schuhmacher; B. Rasser; E. De Chambost; F. Hillion; Th. Mootz; H.-N. Migeon (pp. 12-18).

The recent developments in magnetic sector SIMS are reviewed. It is not aimed at a detailed description of these instruments which, for several of them, can be found elsewhere [1–8] but reviews the driving forces making necessary the development of magnetic sector SIMS for all types of analysis (single instrument alternative) as well as instruments dedicated to ultimate lateral resolution (50 nm), to isotopic ratio measurements with multicollection of all isotopes, to depth profiling at high depth resolution using an impact energy of 250 eV, and instruments allowing better flexibility about the amount of cesium incorporated in the specimen to optimize the formation of MCs clusters for the analysis of complex materials.

Applications of total reflection X-ray fluorescence spectrometry in trace element and surface analysis by H. Schwenke; P. A. Beaven; J. Knoth (pp. 19-27).

Total reflection X-ray fluorescence spectrometry (TXRF) is presented as a genuine surface analytical technique. Its low information depth is shown to be the characteristic feature differentiating it from other energy dispersive X-ray fluorescence methods used for layer and surface analysis. The surface sensitivity of TXRF and its analytical capability together with the limitations of the technique are discussed here using typical applications including the contamination control of silicon wafers, thin layer analysis and trace element determination. For buried interfaces and implantation depth profiles in silicon a combination of TXRF and other techniques has been applied successfully. The TXRF method has the particular advantage of being calibrated without the need for standards. This feature is demonstrated for the example of the element arsenic.

Electron spectroscopy applied to metastable ceramic solution phases by R. Cremer; Mirjam Witthaut; Dieter Neuschütz (pp. 28-37).

Due to its high surface sensitivity, electron spectroscopy has proven to be a powerful tool for the determination of binding states and electronic structures of thin films. The principal processes of electrons and photons interacting with a surface are briefly discussed. Special attention is paid to the determination of binding states, near range orders and the electronic structures in ceramics by Auger- and Photoelectron Spectroscopy (AES and XPS) as well as Electron Energy Loss Spectroscopy (EELS). The particularities of electron spectroscopy of metastable ternary ceramic solution phases which have been deposited by means of reactive magnetron sputtering are described. Because of their continuous change in composition and, thus, in chemical environment, these solution phases are attractive systems for the analysis of the effects of chemical environment upon binding states and the electronic structure of ceramics.

Combined atom probe and STM study of tip-substrate interactions by A. Fian; Ch. Ernst; M. Leisch (pp. 38-42).

A combination of an imaging atom probe (field ion microscope with a time-of-flight mass spectrometer) and a scanning tunneling microscope (STM), which are integrated in the UHV-system, has been used to study the tip-substrate interactions after electrical contact and mechanical indentation. After “jump-to-contact” experiments with tungsten tips on a gold substrate ad-atom clusters has been observed in the FIM-images. The imaged clusters can be identified by time-of-flight mass analysis as Au and give evidence for material transfer in sub-monolayer range. The image contrast in the micrographs gives almost no reference to induced lattice defects after this contact experiments. In additional indentation-experiments clearly induced plastic deformation of the tip crystallite can be observed as well as material transfer of several monolayers. The FIM micrographs after field desorption of consecutive atomic layers show the features of these deformations typically into a depth up to 20–25 atomic layers.

Quantitative comparison of ATR-IR spectra of LB and bulk layers of 22-tricosenic acid on inorganic supports by G. Müller; C. Riedel (pp. 43-47).

The availability of ATR devices equipped with a diamond internal reflection element makes it possible to obtain IR absorption spectra of organic substances deposited on inorganic substrates, for example, metals, glass or quartz. The quantitative comparison of these spectra performing mass calibration by Langmuir-Blodgett (LB) layers are reported. The measurements were made in the common configuration with the specimen placed between the internal reflection element and the non-transparent support and in a second configuration with a thin transparent substrate (silicon) placed between the specimen and the internal reflection element. The band areas of the CH₂ bands near 2900 cm^–1 measured for the two ATR configurations were compared with those obtained from transmission measurements. The results can be partially interpreted by the equation for the effective thickness of thin layers on internal reflection elements. The relative absorbances of several bands of the TSE spectra obtained under different measuring conditions were also investigated.

Peak shape analysis of core level photoelectron spectra using UNIFIT for WINDOWS by R. Hesse; T. Chassé; R. Szargan (pp. 48-54).

Several approaches used in the peak shape analysis of core level spectra for the purpose of modelling of both peak shapes and background profiles will be discussed. A universal program is presented, which combines options for adequate modelling of the peak shapes and background, implementation of a successful numerical algorithm for an iterative non-linear parameter estimation procedure, and a flexible as well as convenient data handling. The performance of this program code is demonstrated by fitting a synthesized model spectrum. An example for analysis of a complex experimental spectrum is presented, too. An S 2p spectrum recorded from a MBT-treated pyrite surface is successfully analyzed using the presented software and is found to be characterized by five different S 2p contributions.

Investigations to calibrate reference standards for the thickness of coatings by T. Ahbe; K. Hasche; K. Herrmann; K.-P. Hoffmann; K. Thiele (pp. 55-58).

Investigations on the traceability of coating thickness measurements to the national standard of length were carried out by topographical and lateral methods. The topographical method used an interference-optical microscope and a modified scanning force microscope to measure the coating thickness as the height of a step on partially coated samples. For the lateral method, a scanning electron microscope was equipped with additional components to measure the coating thickness on cross sections as the distance of material boundary lines. Standards with a coating thickness of about h = 10 nm to 50 μm may be calibrated. The achievable uncertainty depended strongly on the specimen preparation and the specimens themselves.

Factor analysis and XPS-data preprocessing for non-conducting samples by S. Oswald; S. Baunack (pp. 59-62).

The use of factor analysis for automatic interpretation of electron spectra needs in some cases a special data preprocessing. It was shown for x-ray photoelectron spectroscopy that in the case of non-conducting samples in addition to experimental methods (low energy electron flooding) a shift of the measured spectra with respect to a reference peak was useful. Thus, the residual energy shift due to sample charging, especially if the surface conductivity changes during measurement, could be removed. Several shift methods and the influence of different reference peaks were discussed.

Robust automated three-dimensional segmentation of secondary ion mass spectrometry image sets by M. Wolkenstein; T. Stubbings; H. Hutter (pp. 63-69).

Three-dimensional (3-D) element distributions generated by scanning secondary ion mass spectrometry (SIMS) are usually noisy and blurred and contain objects which do not usually have sharp edges or may have noise induced boundaries. Additionally, there are local intensity differences due to sensitivity differences of the channelplate. As a result, traditional segmentation techniques become difficult and yield rather poor results. We present a novel methodology which combines a restoration process (using a combination of channelplate sensitivity compensation with a 3-D de-noising technique based on the wavelet transform) with a fuzzy logic 3-D gray level segmentation which can be used to successfully segment 3-D SIMS image sets. The restoration algorithm removes the artifacts produced by the channelplate inhomogeneities as well as noise aberrations from the image sets and the gray level thresholding algorithm segments their features. The algorithm is designed for minimal user interaction to achieve a high automation level. The methodology is discussed and experimental results using real 3-D images are presented.

Operation and application of a laser mass analyser (LASMA) for multielement analysis by D. M. Woll; M. Wahl; H. Oechsner (pp. 70-75).

The design and the operation of the LASMA instrument combining laser ablation with time-of-flight mass analysis is briefly described. The application to the analysis of multielement metal samples and non-conducting powder mixtures of known composition reveals the LASMA technique to be a semi-quantitative method for elemental bulk analysis with a detection limit around 50 μg/g in a mass range up to 250 amu.

Bombardment-induced silicide formation at rhenium-silicon interfaces studied by XPS and TEM by R. Reiche; S. Oswald; D. Hofman; J. Thomas; K. Wetzig (pp. 76-82).

For further evaluation of photoemission properties of argon ion bombarded rhenium-silicon thin films pure element Re(21 nm) / Si(39 nm) / Re(21 nm) layer sandwiches were investigated on Si(111) substrates. TEM cross sectioning revealed abrupt interfaces between the polycrystalline Re layers and the amorphous Si layer in the as-deposited sample. In XPS sputter depth profiling the interfaces were severely broadened. This is not just a result of the finite electron escape depth together with atomic mixing and preferential sputtering which was demonstrated with the dynamic Monte Carlo simulation program T-DYN, but mainly caused by topographic effects and silicide formation. Factor analysis of XPS spectra results in two Re-Si principal components which can be ascribed to silicide bonding. Accordingly the valence band changes are caused by different bonding configurations. Bombardment-induced silicide formation is proved by TEM investigations of a selected cross-sectioned sandwich. Due to preferential bombardment-induced effects Re₂Si is formed at the Re/Si interfaces in contrast to the ReSi₂ growth on thermal heating. This is discussed in terms of the interface composition and the effective heat of formation (EHF) model.

Ultra thin film sputter depth profiling by J. F. Moulder; S. R. Bryan; U. Roll (pp. 83-84).

As semiconductor device geometry continues to shrink, new ultra thin material systems are developed. One such structure is a thin silicon oxy-nitride (ONO) film used in memory devices. Secondary Ion Mass Spectrometry (SIMS), because of its extreme surface sensitivity (small sampling depth), is routinely used to study thin ONO structures. However, interpretation and quantification of SIMS data is often difficult because of matrix effects that impact the secondary ion yield of different chemical species. With the Quantum 2000 Scanning ESCA Microprobe^TM, it is possible to obtain surface sensitivity equivalent to SIMS, using a low (20°) photoelectron take-off angle. The resulting ESCA data contain quantitative chemical state information that is difficult to obtain by other methods.

Quantitative analysis of silicon- and aluminium-oxynitride films with EPMA, SIMS, hf-SNMS, hf-GD-OES and FT-IR by S. Dreer (pp. 85-95).

A precise and economic way for quantitative bulk analysis of silicon/aluminium, oxygen and nitrogen in the technological important silicon- and aluminium oxynitride thin films based on FT-IR and EPMA is presented and the use of data gained by the latter method is discussed for the calculation of relative sensitivity factors for SIMS and hf-SNMS. Advantages and disadvantages of SIMS, hf-SNMS and hf-GD-OES were compared. The combination FT-IR/EPMA/SIMS offers at present the best possibility for a quantitative bulk and in-depth distribution analysis of such films in the range of 20 to 1000 nm thickness. Alternatively for thicker films, combinations of FT-IR/EPMA/hf-SNMS or FT-IR/EPMA/hf-GD-OES are easier to apply but their use is restricted to oxygen concentrations higher than 10 wt%.

Investigations of local electrical surface characteristics by dynamical scanning force microscopy by M. Hietschold; F. Müller; A.-D. Müller; H. J. Engelmann; E. Zschech (pp. 96-98).

A technique is presented that allows to obtain information about sample surface topography and local electrical surface properties simultaneously. A scanning electrical force microscope is used for that purpose which is based on an atomic force microscope (AFM) working in the dynamical mode. Different information channels contained in the cantilever excitation spectrum are separated by a lock-in technique. The physical content of the technique is discussed in detail and the influence of surface topography on the non-topographic imaging is demonstrated. Finally, the real advantages of cross-sectional sample preparation (as known from electron microscopy) for this kind of scanning probe microscopy with respect to various applications is presented.

Stepped current electromigration test of multilevel aluminum metallizations on wafer level by M. Strasser; M. Schneegans; H. Hammer; R. Frahm (pp. 99-102).

Electromigration is the phenomenon of electron flux induced mass transport resulting in damage of metal lines and interconnect structures of microelectronic devices. The drift process in aluminum metallizations is studied in order to specify quality and to predict reliability of multilevel systems for application in integrated circuits. In contrast to conventional constant current electromigration experiments, stepped current tests are used to investigate the mechanisms of resistance variations of aluminum lines and via chains. In the experiment which is performed on wafer level, aluminum filled via interconnects are compared to tungsten plugs. The measurements are interpreted using a basic model of mass flux including the influence of Joule heating. Activation energies of the dominating diffusion processes are determined and explained considering effects of short length, near-bamboo crystal structure, copper alloying and interfacial barrier layers.

Application of infrared reflection spectroscopy for the analysis of hard coatings on metallic substrates by P. Heger; G. Marx (pp. 103-105).

A method is presented for calculating the absorption spectrum, the film thickness and the index of refraction from IR reflection spectra. Considering real test conditions (partial incoherence, scattering) a routinely usable instrument was created with this direct calculation of the absorption spectrum, which provides a very good correspondence between the measurement and simulation also without any initial information about the expected spectrum. This method is applied to characterize hard coatings deposited on iron substrates by glow discharge assisted CVD processes with organic silicon and boron compounds as precursors. In addition to the qualitative microstructural characterization of these coatings, this method is suitable for a rapid, exact and non-destructive determination of the film thickness and the index of refraction.

XPS analysis of the degradation of Nafion by M. Schulze; M. Lorenz; N. Wagner; E. Gülzow (pp. 106-113).

In polymer membrane fuel cells (PEFC) Nafion^® is frequently used as electrolyte membrane. Nafion^® is an ion exchange polymer based on a PTFE backbone with added sulfonic acid groups. Before using in PEFC the Nafion^® membrane is cleaned by a chemical pretreatment. The influence of this chemical pretreatment of Nafion^® membranes was investigated with XPS measurements as well as the influence of electrochemical stressing. The Nafion^® membrane will be decomposed during XPS measurements. X-ray exposure as well as ion etching induces a degradation of Nafion^®. The change is related to a disintegration of the basis polymer PTFE as well as the sulfonic acid groups containing side chains. The decomposition of the side chains is faster than that of the PTFE backbone.

Water uptake of quartz investigated by means of ion-beam analysis by O. Dersch; F. Rauch (pp. 114-116).

The diffusion of water into quartz was studied by measuring depth profiles of hydrogen and oxygen in hydrothermally treated samples using ion-beam analysis methods. Diffusion data were obtained in the temperature range 60 to 200 °C. It was found that the initial H content of the individual quartz specimen plays a crucial role for the diffusion rate, which also depends on the orientation of the sample surface relative to the quartz c-axis. External factors which possibly influence the diffusion data were examined. Hydrogen depth profiles measured on a prehistoric quartz artifact were found to be compatible with an extrapolation of the diffusion data to ambient temperature.

SIMS depth profiling, line scanning and imaging analyses of the oxide layer on in-reactor corroded cladding specimens with high lateral resolution by O. Gebhardt (pp. 117-122).

The distribution of the reactor water components lithium and boron in the oxide layer of in-reactor corroded Zircaloy fuel rod cladding specimens was investigated by depth profiling, line scanning and imaging analyses using secondary ion mass spectrometry (SIMS). The exact thickness of the oxide layer on the specimens was measured by scanning electron microscopy (SEM). The SIMS analyses showed that lithium and boron were not homogeneously distributed in the oxide layer. The peak concentration of lithium was found close to the reactor water/oxide interface of the specimens whereas boron showed no relevant variations in the bulk of the oxide layers investigated. The concentration of both elements decreased rapidly at a significant distance close to the oxide/metal interface. Conclusions were drawn to improve the understanding of the in-reactor corrosion process of fuel rod claddings consisting of zirconium based alloys.

Characterization of polymers in PEFC-electrodes with EDX and XPS by M. Schulze; M. v. Bradke; R. Reissner; M. Lorenz; E. Gülzow (pp. 123-132).

In polymer electrolyte fuel cells (PEFC) preferably Nafion^® (Du Pont) is used as electrolyte material. The electrodes contain polytetrafluoroethylene (PTFE) as organic binder and the electrolyte Nafion^® as additive to enlarge the three phase boundary zone. Since Nafion^® is chemically related closely to PTFE, using surface analytical methods the two polymers can only be distinguished by the sulfonic acid groups in Nafion^®. XPS measurements give information about the chemical composition of the electrode surface. By electron microscopy and EDX analysis it is possible to image the surface structure and to determine the local elements distribution, but hereby the distinction of the different polymers is a problem. In EDX spectra the sulfur peak induced from the sulfonic acid in the Nafion^® is overlayed by a platinum peak from the catalyst component in the electrodes. Consequently, the distribution of the pure Nafion^® cannot be determined by EDX. To make Nafion^® distinguishable from PTFE and platinum the Nafion^® in the electrode has to be marked, e.g. by exchange of the conducting protons in Nafion^® by alkali ions like sodium. After having marked Nafion^® its spatial distribution in fuel cell electrodes can be determined by EDX mapping of fluorine and sodium.

Raman spectroscopy of C-, BN-, SiC-layers deposited on multifilament substrates by N. Meyer; K. Nestler; S. Stöckel; G. Marx (pp. 133-135).

The analytic characterisation of various layers and layer systems on fibrous materials are presented. The layers, deposited by an isothermal CVD process, consisting mainly of pyrolytic carbon, hexagonal boron nitride and silicon carbide were characterised by different analytical methods, especially by Raman spectroscopy [1]. The surface enhanced Raman spectroscopy (SERS) was used first time for the investigation of boron nitride (BN) coatings on fibres.

Surface analytical investigation of the electrochemical and corrosion behaviour of nanocrystalline FeAl8 by A. John; W. Zeiger; D. Scharnweber; H. Worch; S. Oswald (pp. 136-141).

From the higher fraction of grain boundaries in nanocrystalline substances a different corrosion behaviour in comparison to the conventional polycrystalline material can be expected, which may be utilised for the development of new corrosion resistant alloys. Therefore, the oxidation behaviour of these two different crystallisation states of FeAl8 was compared by means of electrochemical and surface analytical experiments. The oxide films formed after electrochemical passivation were investigated by Auger Electron Spectroscopy. The application of inelastic peak shape analysis by the method of Tougaard showed, that for both materials the oxide layer may be described by a model of a (below the contamination) buried layer with a thickness of only a few nanometers depending on the preparation conditions. Factor Analysis was applied for the evaluation of the differentiated low energy Auger electron spectra (20–100 eV) as a function of depth profiling sputtering time. For both, the nanocrystalline and the polycrystalline material, the inner part of the oxide layer was enriched in Al, whereas the very outer part (surface region) was enriched in Fe. No differences concerning the sputtering time for removal of the oxide layers were found for the two alloys.

SIMS Analysis of the wear of boron nitride tools for the machining of compacted graphite iron and grey cast iron by M. Gastel; U. Reuter; H. Schulz; H. M. Ortner (pp. 142-146).

Cubic boron nitride (cBN) is a common material for tools for the machining of cast irons at high cutting speed. During the machining of compacted graphite iron (CGI) in continuous cutting the wear of the cBN tools was found to be significantly higher compared to the machining of grey cast iron. This is possibly a result of a heating of the tool surface during the cutting of CGI. One possible reason for the wear is diffusion of some elements from the cutting tool into the CGI or from the CGI into the cutting tool. SIMS measurements were carried out which prove the existence of such diffusion processes. A static model experiment has been performed by heating cBN tools to 700 °C while in contact with CGI or cast iron (CI). SIMS depth profiles of the cBN tools and of CGI/CI show that there is a diffusion of several elements in both directions (B, W and Ti from the cBN tools into the CGI or CI, Fe and Si from the CGI or CI samples into the cBN) up to a depth of 20 μm.

A photoelectrochemical study of anodic oxides on lead selenide surfaces in alkaline solutions by H. Meincke; D. G. Ebling; J. Heinze; M. Tacke; H. Böttner (pp. 147-149).

Lead selenide is a narrow gap semiconductor material. It finds applications in infrared emitting and detecting devices. Their performance is closely related to charge carrier recombination at the surface, which can be reduced by passivation, e.g. due to PbSeO₃ formation by anodic oxidation in alkaline solutions. In dependence on the pretreatment of the surface, two different types of oxide formation were observed. To determine the electronic properties of the anodic oxide, the wavelength dependence of the photocurrent was investigated. The energy of the band gap of both types of anodic oxide on PbSe has been determined to be 2.4 eV for the direct and 1.8 eV for the indirect band gap. A weakening of the photocurrent generated in the bulk (PbSe) due to scattering or absorption within the oxide confirms the potential dependence of the oxide thickness for a high field growth mechanism.

Study of the surface composition of vanadyl pyrophosphate catalysts by XPS and ISS – Influence of Cs+ and water vapor on the surface P/V ratio of (VO)2P2O7 catalysts by F. Richter; H. Papp; G. U. Wolf; Th. Götze; B. Kubias (pp. 150-153).

The investigation of the surface composition of vanadyl pyrophosphate catalysts and the influence of Cs ions and of water vapor on the surface P/V ratio were described and discussed. The characterization was carried out by XPS (X-ray Photoelectron Spectroscopy) and ISS (Ion Scattering Spectroscopy). It was concluded that the P/V ratio on the surface of equilibrated and non equilibrated (VO)₂P₂O₇ catalysts prepared in aqueous solution was between 1.3 and 1.4 (XPS) based on calibrations with different VPO glasses as standard materials having uniform composition of surface and bulk. In the outermost layer of the catalyst the P/V ratio was much higher and laid between 2 and 3 as verified by ISS. Different influences, i.e. addition of alkali metall ions (Cs⁺) or a treatment with water vapor of the catalyst, caused a further increase in the concentration of phosphorus on the surface.

XPS analysis of electrochemically oxidized nickel surfaces by M. Lorenz; M. Schulze (pp. 154-157).

Nickel, commonly used in electrochemical systems like batteries, fuel cells or as catalyst in alkaline water electrolysis can occur in different oxidation states. With surface analytical methods like X-ray photoelectron spectroscopy (XPS), it is possible to determine the oxidation state of metals. The application of this method requires that the sample is in an ultrahigh vacuum (UHV)-system. Therefore in-situ XPS-measurements of electrochemically oxidized samples are not possible. To avoid transfer through atmosphere one has to mount an electrochemical cell directly into a surface analytical system. By means of such an unit, nickel was polarized in potassium hydroxide solution (KOH) at different potentials. After that the different oxidation states were examined with XPS. The interpretation of these experiments is complicated because water is adsorbed after the electrochemical preparation. This can cause an additional surface layer. Ion-beam etching will not only remove this additional surface layer, it also changes the electrochemically prepared layer beyond. Comparing an electrochemically prepared single crystal with polycrystalline samples shows that the electrochemically prepared oxide layer is more clearly visible on the single crystal than on the polycrystalline material.

Surface and interface analysis of PVD Al-O-N and γ-Al2O3 diffusion barriers by R. Cremer; M. Witthaut; K. Reichert; D. Neuschütz (pp. 158-162).

The suitability of PVD films of γ-Al₂O₃ and of ternary Al-O-N as diffusion barriers between a nickel based superalloy CMSX-4 and NiCoCrAlY for a possible application in gas turbines was investigated. Therefore, an Al₂O₃ film and, alternatively, an Al-O-N film were deposited on CMSX-4 at 100 °C substrate temperature by means of reactive magnetron sputtering ion plating (MSIP). After characterization of composition and structure of the films by X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray diffraction (XRD), a NiCoCrAlY coating was deposited onto the diffusion barriers and, for comparison, directly onto CMSX-4 by MSIP as well. The composites were annealed for 4 h at 1100 °C under inert atmosphere. Wavelength dispersive X-ray (WDX) element mappings and line-scans of the cross-sectional cut served to evaluate the suitability of the films as diffusion barriers. After detachment of the coatings from the substrate, the phase stabilities of the two metastable phases γ-Al₂O₃ and Al-O-N were determined by means of grazing incidence XRD. Without a diffusion barrier, enhanced interdiffusion was observed. Analyses of the composite with the γ-Al₂O₃ interlayer revealed diffusion of Ti and Ta from the substrate into the NiCoCrAlY coating. No interdiffusion of Ni, Ti, Ta, and Cr could be detected in case of the ternary Al-O-N film. Whereas the ternary Al-O-N film remained in the as-deposited X-ray amorphous structure after annealing, a phase change from the γ to the α modification could be observed in case of the Al₂O₃ film, presumably responsible for its lower efficiency as a diffusion barrier.

Scanning electrochemical microscopy of enzymes immobilized on structured glass-gold substrates by T. Wilhelm; G. Wittstock; R. Szargan (pp. 163-167).

Scanning electrochemical microscopy (SECM) was used to characterize enzyme-modified glass-gold specimens. The exposed gold surface was functionalized with an aminothiol and reacted with carbodiimide-activated glucose oxidase. The specimen surface was examined with SECM, using a 25 μm platinum electrode. Images were acquired showing the topography, electric conductivity, and enzymatic activity of the composite surface. It was found that the hydroxy-groups of the glass surface are as likely to bind to the activated enzyme as the amino-groups on the gold surface.

The dependence of fractal dimension on measuring conditions of scanning probe microscopy by W. Zahn; A. Zösch (pp. 168-172).

The fractal dimension of sputtered thin film surfaces was determined. Topography was measured using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). It can be shown that measuring conditions have an important influence on the topographic data and the obtained fractal dimension. This influence was investigated systematically. The results of STM- and AFM-measurements have been compared. The results for surfaces imaged with AFM give lower values for the fractal dimension than with STM. Measurements were carried out with a standard cantilever and so the data have been filtered. Dynamic behavior of the measuring system is influenced by scanning speed and loop gain factor. During measurement of topographic signal high scanning speed and low loop gain factor produce a low pass behavior and the fractal dimension will be varied. If there is a disturbance in addition to the topographic signal (e.g. a noise) we found power spectra with more than one linear part. The calculated fractal dimension especially depended on the density of measuring points in the profile. The experimental results were verified by calculated Weierstrass-Mandelbrot functions.

Surface characterisation of laser irradiated SiC ceramics by AES and XPS by S. Baunack; S. Oswald; H. K. Tönshoff; F. von Alvensleben; T. Temme (pp. 173-177).

Samples of sintered silicon carbide (SSiC) were irradiated with a KrF excimer laser (λ = 248 nm) at energy densities of 10, 15 and 25 J/cm² in He atmosphere. The composition of the near surface region was investigated by Auger electron spectroscopy (AES) and photoelectron spectroscopy (XPS) after lapping, laser irradiation and tribological treatment, respectively. By laser irradiation a surface layer is formed which contains about 30% oxygen. The existence of different bonding states of Si, C and O was established by factor analysis of the AES depth profiles and by XPS. By laser irradiation SiC is decomposed and a siliconoxycarbide with the average composition SiC_3.5O_1.5 is formed. Beneath the oxidised surface layer the nominal elemental composition SiC is found but the sample represents a mixture of Si, graphite and siliconoxycarbide with a small amount of SiC only. Obviously, the decomposition zone exceeds in a depth > 300 nm.

Potassium and oxygen diffusion and segregation in nickel by M. Schulze; R. Reissner; M. Lorenz (pp. 178-182).

Nickel is used as catalyst in alkaline electrochemical systems like batteries, electrolyzers and fuel cells. Adsorption experiments from potassium on a thin NiO(100) epitactic layer on an Ag(100)-single crystal substrate showed that potassium intrudes in that NiO-layer where at a temperature of 350 K a mixed oxide phase was built. At 120 K metallic potassium was adsorbed on the NiO surface. A symmetric K2p-peak showed that potassium is in the oxidized state compared to the asymmetric peak of metallic potassium. No potassium diffused into metallic nickel at a temperature of 450 K. The electrochemically oxidized surface layer consisted of nickel, oxygen and also potassium. After heating and ion-etching no more potassium was detectable by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX). But it was visible again after oxidizing and heating of the sample to 670 K. Therefore, the potassium must have been in the bulk. It diffused to the surface if there was oxygen at sufficiently high temperatures. Further heating reduces the surface and the potassium also disappeared.

Material removal and chemical and structural changes induced by irradiation of polymer surfaces with KrF-excimer laser radiation by D. A. Wesner; M. Aden; J. Gottmann; A. Husmann; E. W. Kreutz (pp. 183-187).

Holes in polypropylene (PP) and polymethylmethacrylate (PMMA) plates, 0.5 mm in thickness were drilled by irradiation with up to 3000 pulses of KrF-excimer laser radiation (λ = 248 nm) at fluences per pulse ɛ in the range 0.1–10 J/cm², conditions which yield a laser-induced plasma/vapor plume. The process was analyzed experimentally in terms of material removal rate, optical emission of the laser-induced plasma, hole geometry, debris production at the hole edge, and chemical changes in the polymer induced by the laser irradiation. Additionally, the process was simulated using a model based on degradation of the polymer induced by optical absorption and heating, leading to gas-phase products. Such characteristics as the material removal rate as a function of fluence, the nature of the gas phase products and the deposition of debris were calculated.

Application of scanning SIMS techniques for the evaluation of the oxidation behavior of high-purity molybdenum by M. Gritsch; C. Brunner; K. Piplits; H. Hutter; P. Wilhartitz; A. Schintlmeister; H. P. Martinz (pp. 188-194).

Refractory metals are primarily characterized by a high melting point combined with a rather poor corrosion resistance under oxidizing atmosphere and therefore are mainly used in high temperature processes under reducing atmosphere or in vacuum. Exposure to an atmosphere of high humidity can lead to oxidation of the material even at room temperature. Different methods of surface pre-treatment have been applied to investigate their influence on the oxidation behavior of high-purity molybdenum. Within the scope of this work molybdenum foils and molybdenum discs consisting of the same base material were investigated. Since lateral surface structure as well as the in-depth distribution of contaminants are expected to play an important role in the oxidation process, both the in-depth distribution of the constituents within the oxide layer and the lateral distribution at the surface level of the oxide have been analyzed. Scanning SIMS has been engaged to analyze the uppermost structures of the oxide layer. In order to achieve maximum detection power and to gain the in-depth information, stigmatic SIMS has been applied to investigate the in-depth distribution of the interesting specimen constituents.

The influence of ion beam sputtering on the composition of the near-surface region of silicon carbide layers by G. Ecke; R. Kosiba; J. Pezoldt; H. Rößler (pp. 195-198).

The concentrations and the lattice structure of silicon carbide layers and single crystals are influenced by ion beam sputtering. The influence of ion beam sputtering and primary ion energy on preferential sputtering is investigated by Auger measurements and T-DYN simulations. In dependence on primary ion energy C is enriched. Preferential sputtering increases with decreasing ion energy. Sputtering has a strong influence on the Auger peak shapes of SiC. Except for low ion energy and glancing incidence the peak shapes are independent of the primary ion energy. T-DYN simulations help to explain and understand the near-surface processes during sputtering of SiC. For ion energy dependence of preferential sputtering there is a good agreement of the T-DYN simulation and the Auger measurement.

Characterization of transition metal nitride formation in rapid thermal processing (RTP) by Ivan Galesic; B. O. Kolbesen (pp. 199-202).

The potential of RTP for the preparation of transition metal nitrides by reaction of metal thin films in molecular nitrogen was investigated. The films and the nitridation process were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) in a scanning electron microscope (SEM) and secondary neutral mass spectrometry (SNMS). The chemical states of vanadium at the utmost surface, detected by XPS, are related to V₂O₅ before RTP and to vanadium nitride, oxide and oxynitride after RTP. The deposition of a 3 nm Si top layer prevents V from oxidation and its selective removal before RTP enhances the proportion of nitride determined by XPS after RTP. From comparative experiments in a conventional tube furnace the advantages of RTP became obvious. With short process times of the RTP technique the integral amount of residual oxygen is kept low and oxide formation is largely avoided. The nitrogen content and the different polycrystalline phases formed by varying process time and temperature provide information about reactivity and the nitridation process. The nitrogen to vanadium ratio was determined by EDX and SNMS, revealing that the N content reaches saturation after only 5 seconds at 1100 °C.

Effect of surface oxidation on the solution of hydrogen in vanadium by G. Kiss; H. Paulus; O. Krafcsik; F. Réti; K.-H. Müller; J. Giber (pp. 203-207).

The formation of vanadium surface oxides and their influence on the absorption of hydrogen were studied by XPS and TDMS methods. Vanadium hereby serves as a model system for hydrogen metal interaction. Different stable and unstable oxides indicated by the oxidation number of vanadium have been investigated: oxidation number +5 corresponding to stable V₂O₅; oxidation number +3 corresponding to stable V₂O₃ and lower than +3, corresponding to unstable oxides. Exposure of a cleaned V sample to different oxygen dosages (1 L – 1000 L, p_O2 = 1 × 10^–4 Pa) at room temperature leads to the formation of unstable oxides with oxidation numbers smaller than 3. V-O bondings break up at temperatures higher than 290 °C and oxygen desorbs. Besides the dosage the oxide formation is also influenced by the temperature. All these oxides act as surface barriers and prevent the absorption of hydrogen by vanadium.

Depth profile and microscopic structure of gold-implanted aluminum using X-ray spectroscopies by K. Baur; J. Hormes (pp. 208-211).

Ion-implanted gold in polycrystalline aluminum was studied with energies ranging from 100 keV to 500 keV and a dose density of 1 × 10¹⁶ ions/cm². The centroid depths of the implantation profiles were determined by Angle-Resolved Self-Ratio X-ray Fluorescence Spectrometry using synchrotron radiation of the electron storage ring ELSA at the University of Bonn. A linear correlation between the implantation energy and the centroid depth of the profile was found. Comparing these results to TRIM calculations a range enhancement of the experimental data up to 10% is observed. X-ray Absorption Near Edge Structure (XANES) spectroscopy was used at the Au-L_III edge to investigate surface modification due to the implantation process on a microscopic scale. For all energies the implantation leads to nanocrystalline precipitates of the intermetallic compound AuAl₂.

Studies of polycrystalline materials by Pseudo Kossel technique by E. Langer; S. Däbritz; A. Röder; W. Hauffe (pp. 212-216).

In contrast to the Kossel Technique the Pseudo Kossel Technique (PKT) is mainly used for investigations of single crystals to determine the crystal structure, the crystallographic orientation and lattice parameter of the specimens so far. Though the PKT has yet large possibilities and is well-suited also for micro range investigations, the application for the characterization of polycrystalline materials is not common. The complicated configuration of the reflex sections in polycrystals, caused by grain boundary effects, usually makes it very difficult to evaluate them. The studies have been carried out at Al and BaTiO₃ polycrystals. Thus, for the first time the successful application of the technique to a ceramic was demonstrated. The dependence of the reflex length on the grain size was investigated by simulation. It is shown that this technique allows precise determination of correlation between neighbor grains, since one diffraction pattern contains contributions from several grains. As a result one obtains for example the relative orientations of neighbor grains, which influence among other things the electrical and mechanical properties.

High-resolution analytical transmission electron microscopy of semiconductor quantum structures by R. Schneider; H. Kirmse; I. Hähnert; W. Neumann (pp. 217-220).

Analytical transmission electron microscopy was applied to characterize the size, shape, real structure, and, in particular, the composition of different semiconductor quantum structures. Its potential applicability is demonstrated for heterostructures of III-V semiconducting materials and II-VI ones, viz. (In,Ga)As quantum wires on InP and (In,Ga)As quantum dots on GaAs both grown by metal organic chemical vapor deposition, and CdSe quantum dots on ZnSe grown by molecular beam epitaxy. The investigations carried out show that the element distribution even of some atomic layers can be detected by energy-dispersive X-ray spectroscopy, however, exhibiting a smeared profile. Contrary to that, sub-nanometre resolution has been achieved by using energy-filtered transmission electron microscopy to image quantum dot structures.

EPMA sputter depth profiling of an InGaAs-InP heterostructure by S. Richter; Peter Karduck (pp. 221-226).

The chemical microanalysis of semiconductor heterostructures by electron probe x-ray microanalysis (EPMA) is presented. The great advantage of EPMA is the sensitive detection and accurate quantification of partial mass coverage down to about 0.01 μg/cm². To improve depth resolution of EPMA the surface was sputtered by inert gas ions and x-ray intensities were measured with increasing sputter depth. These intensity-sputter profiles represent a convolution of the structure of the material by the excitation characteristics of the incident electrons. They were interpreted and evaluated with respect to the chemical composition and thickness of each layer. For this purpose a Monte-Carlo-Simulation program package was developed, which can calculate realistic x-ray intensities versus sputter depth for a given material. Additionally, it can reconstruct the structure of the material assuming a laterally homogeneous multilayered system with sharp interfaces and constant composition inside each layer. The results of the reconstruction could be quantified with an accuracy of less than 5% rel.. In spite of the large information depth of x-rays a depth resolution of about 1–3 nm could be determined.

Structural and optical properties of thin silver films deposited on Si(111) by A. Masten; M. Brüggemann; P. Wißmann (pp. 227-230).

Silver films in the thickness range 3–12 nm were deposited on very clean Si(111) substrates at ambient temperature. The annealing up to temperatures of 650 °C was then studied using LEED/Auger, SEM and X-ray diffraction as well as resistivity and ellipsometry measurements. The films crack during annealing and silver islands are formed on the silicon surface. The coagulation results in a steep drop of the ellipsometric parameters Δ and Ψ in the temperature range 150–300 °C which can be attributed to the generation of surface plasmons and Mie plasmon polaritons, respectively.

SEM and AES depth profile studies of thin titanium and titanium oxide films covered by nanoscale evaporated Au layers by A. H. J. van den Berg; W. Lisowski; M. Smithers (pp. 231-235).

Thin titanium and titanium oxide films, both covered by ultra-thin gold layers, have been compared with titanium films after analysis, using a combination of SEM and AES. The Ti films were prepared under UHV conditions by evaporation on a glass substrate. The Ti oxide layers were prepared in situ by precisely controlled oxygen sorption at 298 K on Ti film. Both Ti and Ti oxide films were then covered in situ by a very thin Au layer. Analysis was performed in a separate system after long-term exposure of the films to air. SEM analysis revealed a much smaller size grain on the Au coated Ti films than on Ti films not coated with a Au layer. The thin gold layers covering the Ti surface prevent an extensive air interaction with Ti film. The analysis of the features of the Ti Auger spectra during the sputter profile measurements allow to characterise the chemical nature of Ti-oxide formed in Ti/Au interface region.

Examinations on the morphology of tarnish layers grown on stainless 18–10 chromium nickel steels by G. Pajonk; H. Bubert (pp. 236-243).

18-10 chromium nickel steels are generally valid as well weldable. However, during thermal joining oxides are formed in the heat affected zone, whose structure and composition essentially differs from the morphology of passive layers. The steel qualities X6 CrNiTi 18-10 (materials no. 1.4541) and X5 CrNiMoTi 17-12-2 (materials no. 1.4571) were examined on their tarnish growing behaviour by means of XPS/sputtering, transmission electron microscopy and atomic force microscopy. Information on the pitting corrosion resistance of annealed metal sheets was received by ageing them in iron chloride solution and by measuring the current density-potential curves under quasi-stationary conditions in artificial sea water.

XANES and XPS characterization of hard amorphous CSixNy thin films grown by RF nitrogen plasma assisted pulsed laser deposition by T. Thärigen; D. Mayer; R. Hesse; P. Streubel; D. Lorenz; P. Grau; M. Lorenz; R. Szargan (pp. 244-248).

Amorphous carbon silicon nitride thin films were grown on (100) oriented silicon substrates by pulsed laser deposition (PLD) assisted by an RF nitrogen plasma source. Up to about 30 at. % nitrogen and up to 20 at. % silicon were found in the hard amorphous thin films by XPS in dependence on the composition of the mixed graphite / Si₃N₄ PLD target. The universal nanohardness was measured to be at maximum load force of 0.1 mN up to 23 GPa for thin CSi_xN_y films with reference value of 14 GPa for single crystalline silicon. X-ray photoelectron spectroscopy (XPS) of CSi_xN_y film surfaces showed a clear correlation of binding energy and intensity of fitted features of N 1s, C 1s, and Si 2p peaks to the composition of the graphite / Si₃N₄ target and to nitrogen flow through the plasma source, indicating soft changes of binding structure of the thin films due to variation of PLD parameters. Auger electron spectroscopy (AES) of Si KL₂₃L₂₃;¹D Auger transition gave a detailed view of bonding structure of Si in the CSi_xN_y films. The intensity of π* and σ* resonances at the carbon K-edge X-ray absorption near-edge structure (XANES) of the CSi_xN_y films measured at BESSY I corresponded to the nanohardness of the CSi_xN_y films, thus giving insight into chemical binding structure of superhard amorphous materials.

Investigation of the properties of a-C:H coatings with graded metal interlayers by M. Nöthe; A. Buuron; F. Koch; H. J. Penkalla; W. P. Rehbach; H. Bolt (pp. 249-254).

A combined PVD-/CVD-process was used to deposit Al interlayers with mixed interface to a-C:H coatings on Si (100) and steel substrates. The Al interlayers had a typical thickness of 100 nm to 1 µm with a-C:H layers of 0.5 to 3 µm thickness. As a reference some substrates were coated directly with a-C:H films. TEM element mappings and SIMS analyses showed that the Al- and C-distributions overlap, indicating the formation of a compositionally graded interlayer. SEM fracture cross sections indicated that delamination of a-C:H coatings with metal interlayer occurs preferently near the substrate metal interface. Using a low bias voltage (lower than –100 V) during the a-C:H deposition leads to a columnar structure of the coating, higher bias voltages lead to coatings with amorphous structure by the fracture cross sections.

Characterisation of boron nitride fibre coatings with different crystalline order by TEM and XPS by D. Dietrich; S. Stöckel; K. Weise; K. Nestler; G. Marx (pp. 255-257).

Reinforcement effects in composites are widely influenced by fibre coatings. A detailed understanding of their microstructure and chemical composition is of great interest. Boron nitride films were deposited continuously on fibre rovings of various ceramics in CVD reactors of vertical as well as horizontal position. XPS depth profilings show that the film compositions are close to stoichiometric BN with carbon and oxygen impurities in the range of 10 at%. Cross-sections of separated fibres were investigated by HREM and TEM diffraction. All BN films are hexagonal turbostratic. The (002) layers with an increased distance (about 0.36 nm) showed a mean stacking sequence near to graphite and a characteristic orientation to the fibre in the interface region. We assume the gas flow type and hence the exchange rate of matter and energy determines the film structure in this region. With increasing film thickness the (002) layers fold randomly in all directions or form nanocrystals at elevated temperatures.

Analysis of Co and Cr dopants in epitaxial films of β-FeSi2 by ERDA, RBS, EDX and AES by W. Bohne; G.-U. Reinsperger; J. Röhrich; A. Schöpke; B. Selle; I. Sieber; P. Stauß; I. Urban (pp. 258-262).

Thin films of β-FeSi₂ doped with Co or Cr were grown on Si substrates by molecular beam epitaxy. The matrix components Fe and Si and the dopant were co-evaporated from three separately controlled sources. The dopant concentration was measured concurrently by ERDA, RBS, EDX and AES. Ion scattering spectrometry using heavy-ion beams of high energy (ERDA with 250 MeV ¹²⁹Xe, RBS with 15 MeV ¹⁴ N) proved to be most powerful in providing a high mass resolution (1 amu) and a low detection limit for Co and Cr (about 0.2 at %). Although the sensitivity of standard RBS (with 1.4 MeV ⁴He), EDX and AES is limited to a level of about 1 at% these methods allow to assess essential trends caused by variation of the deposition parameters.

Morphology and structure of nanoscale Co-Cu multilayers by J. Thomas; K. Brand; A. A. Gorbunov; K. Wetzig (pp. 263-268).

Nanoscale cobalt-copper multilayers prepared by pulsed laser deposition on oxidized silicon substrate were investigated by means of transmission electron microscopic (TEM) methods combined with energy dispersive X-ray spectroscopy. The multilayers proved to be polycrystalline with grain sizes between some nanometers and the stack thickness. The topmost copper layer was incomplete with droplets up to 1 μm. For single layer thicknesses greater than 4 nm it could be shown that the structure of the layer stacks was face centred cubic with hexagonal close packed parts in the cobalt layers.

Nitrogen incorporation into WTi films by J. Burschik; B. Adolphi (pp. 269-271).

The nitrogen incorporation into WTi films for diffusion barrier applications in microelectronics was investigated. Reactive sputtering and ion implatation were used to obtain nitrogen containing films. XPS depth profiling and peak deconvolution yielded chemical composition and information on the reactions involving N. No reaction between W and N was observed, whereas Ti and N did react. The ratio of Ti metal to TiN formed was determined. However, the interpretation of these results is uncertain.

Mixed self-assembled monolayers of terminally functionalized thiols at gold surfaces characterized by angle resolved X-ray photoelectron spectroscopy (ARXPS) studies by J. Heeg; U. Schubert; F. Küchenmeister (pp. 272-276).

The adsorption of non-reactive alkanethiols and cyano-terminated thiols possessing the same chain length as well as their mixtures were examined on polycrystalline gold surfaces by angle resolved X-ray photoelectron spectroscopy (ARXPS). The adsorption behavior was investigated based on the chemical shift of the S 2p peak components. Besides the expected bound state of the thiols at the surface, non-bound molecules were detected with an increasing intensity at lower take-off angles. The layer composition does not entirely reflect the solution composition and the degree of adsorption is independent of the solution composition. A preferential adsorption of the methyl-terminated alkanethiol at the polycrystalline gold surface was measured.

Chemical interaction and diffusion on interface cathode/electrolyte of SOFC by A. Naoumidis; A. Ahmad-Khanlou; Z. Samardzija; D. Kolar (pp. 277-281).

The high-temperature solid oxide fuel cell (SOFC) is suited for the environmentally acceptable and efficient conversion of chemical into electric energy. A prerequisite for introducing this technology on the market is the controlled formation of the interface between electrodes and the electrolyte. In the case of using an electrolyte based on LaGaO₃ the formation of third phases and the diffusion of individual metallic cations from and to the electrolyte was investigated with the aid of point analyses on micrographs of the environment of the interface using quantitative EDS analysis. In case of an anode of Ni-CeO₂ cermet the mixed oxide SrLaGa₃O₇ is formed and, in addition, a relatively pronounced transport of La from the electrolyte into the CeO₂ phase was observed. A relatively strong diffusion of Mn and an even stronger diffusion of Co into the electrolyte took place between the cathode of, e.g., La_0.75Sr_0.2Mn_0.8Co_0.2O₃ and the La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte, whereas a weak transport of Ga to the cathode was identified.

The influence of an epitaxial CoSi2 layer on diffusion of B and Sb in underlying Si during oxidation by A. K. Tyagi; U. Breuer; H. Holzbrecher; J. S. Becker; H.-J. Dietze; L. Kappius; H. L. Bay; S. Mantl (pp. 282-285).

The effect of an epitaxial 20 nm thick CoSi₂ layer on the diffusion of B and Sb in Si is investigated during oxidation and is compared to thermal diffusion in Si. B and Sb doping superlattices (DSLs) were grown by molecular beam epitaxy (MBE). They consisted of six spikes with peak concentrations of about 10¹⁸ cm^–3 (B) and about 10¹⁹ cm^–3 (Sb) and peak centres spaced 100 nm apart. The shallowest spike was capped with 100 nm of Si followed by 20 nm of CoSi₂ grown by molecular beam allotaxy (MBA). Oxidation in dry O₂ and annealing in pure N₂ were performed at temperatures of 800 °C to 1200 °C. Concentration depth profiles were measured by secondary ion mass spectrometry (SIMS). The results showed that the diffusion of B and Sb in Si was markedly different for specimens with or without a CoSi₂ layer. Oxidation enhanced diffusion (OED) of B and oxidation retarded diffusion (ORD) of Sb was observed for specimens without a CoSi₂ layer. The effect of CoSi₂ layer was a strong retardation of B diffusion and an enhancement of Sb diffusion. The B diffusivity was retarded by a factor of 2–10 as compared to the thermal diffusivity and by a factor of 20–100 as compared to the corresponding diffusivity for oxidation of Si without a CoSi₂layer. Sb diffusivity was enhanced by a factor of 2 with respect to thermal diffusivity and by about a factor of 5 as compared to the case without a CoSi₂ layer.

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Analytical and Bioanalytical Chemistry (v.365, #1-3)

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Analytical and Bioanalytical Chemistry (v.365, #1-3)