Showing papers in "Surface and Interface Analysis in 2004"
TL;DR: In this paper, the authors investigated the usefulness of calculated multiplet peaks to fit high-resolution iron 2p3/2 spectra from high-spin compounds. And they found that the multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake-up satellites were included.
Abstract: Ferrous (Fe2+) and ferric (Fe3+) compounds were investigated by XPS to determine the usefulness of calculated multiplet peaks to fit high-resolution iron 2p3/2 spectra from high-spin compounds. The multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake-up satellites were included. This information was useful for fitting of the complex Fe 2p3/2 spectra for Fe3O4 where both Fe2+ and Fe3+ species are present. It was found that as the ionic bond character of the iron —ligand bond increased, the binding energy associated with either the ferrous or ferric 2p3/2 photoelectron peak also increased. This was determined to be due to the decrease in shielding of the iron cation by the more increasingly electronegative ligands. It was also observed that the difference in energy between a high-spin iron 2p3/2 peak and its corresponding shake-up satellite peak increased as the electronegativity of the ligand increased. The extrinsic loss spectra for ion oxides are also reported; these are as characteristic of each species as are the photoelectron peaks. Copyright © 2004 John Wiley & Sons, Ltd.
2,637 citations
TL;DR: In this article, a suite of chromium oxides and other compounds were studied under high spectral resolution conditions chosen to reduce the possibility of differential charging, and the fine structure observed for compounds such as chromium (III) chloride had a distinctly different pattern.
Abstract: Photoelectron spectra of a number of chromium oxides and other compounds were studied under high spectral resolution conditions chosen to reduce the possibility of differential charging. Some of the suite of Cr(III) compounds chosen for study produced Cr 2p spectra containing fine structure that could be identified with multiplet splitting. The splitting patterns produced were similar for all trivalent binary and ternary oxides and sulphides whose patterns closely reproduced the splitting predicted for the Cr(III) free ion by Gupta and Sen. The fine structure observed for compounds such as chromium (III) chloride had a distinctly different pattern. A number of other chromium (III) compounds were studied that did not exhibit the fine structure described above; nonetheless, well-defined line shapes and reproducible peak centroids were obtained by fitting protocols. The use of such information to determine surface chemistry on chromated steels is described, based on the spectral knowledge of chromium (III) oxides and hydroxides and the chromium (VI) oxide systems.
404 citations
TL;DR: This paper will present a simple method for weighting the data to account for Poisson noise and it will be demonstrated that PCA, when applied to the weighted data, leads to results that are more interpretable, provide greater noise rejection and are more robust than standard PCA.
Abstract: Recent years have seen the introduction of many surface characterization instruments and other spectral imaging systems that are capable of generating data in truly prodigious quantities. The challenge faced by the analyst, then, is to extract the essential chemical information from this overwhelming volume of spectral data. Multivariate statistical techniques such as principal component analysis (PCA) and other forms of factor analysis promise to be among the most important and powerful tools for accomplishing this task. In order to benefit fully from multivariate methods, the nature of the noise specific to each measurement technique must be taken into account. For spectroscopic techniques that rely upon counting particles (photons, electrons, etc.), the observed noise is typically dominated by ‘counting statistics’ and is Poisson in nature. This implies that the absolute uncertainty in any given data point is not constant, rather, it increases with the number of counts represented by that point. Performing PCA, for instance, directly on the raw data leads to less than satisfactory results in such cases. This paper will present a simple method for weighting the data to account for Poisson noise. Using a simple time-of-flight secondary ion mass spectrometry spectrum image as an example, it will be demonstrated that PCA, when applied to the weighted data, leads to results that are more interpretable, provide greater noise rejection and are more robust than standard PCA. The weighting presented here is also shown to be an optimal approach to scaling data as a pretreatment prior to multivariate statistical analysis. Published in 2004 by John Wiley & Sons, Ltd.
284 citations
TL;DR: In this paper, the authors report XPS experiments of cellulosic natural fiber materials, discussing the effects of sample storage, UHV exposure, radiation doses, charging and data analysis.
Abstract: The development of 'user-friendly' surface analytical instrumentation has expanded the application of x-ray photoelectron spectroscopy (XPS) towards softer and more complex composite materials. However, the knowledge of fundamental phenomena in practical, interdisciplinary applications is dearly needed. In the case of polymers and polymer-based or -reinforced composites, the analytical problems are not only related to detection limits and resolution; indeed, the effects of contamination and experimental artefacts on interpretation of the carbon signal are often the more crucial challenge. As a biopolymer, natural cellulose fibres provide an interesting model system for polymer studies. Numerous published XPS studies on lignocelluloses highlight both the possibilities and the problems of the surface analytical probes in analysis of air-exposed organic materials. We report XPS experiments of cellulosic natural fibre materials, discussing the effects of sample storage, UHV exposure, radiation doses, charging and data analysis. Based on a large body of experimental data we also propose that clean paper specimens could be used as an in-situ reference in polymer studies.
260 citations
TL;DR: In this paper, the NiO overstoichiometry (x > 1) was investigated using XPS depth profiling and it was concluded that the stability of NiO films decreases with increasing deviation from stoichiometry.
Abstract: Antiferromagnetic NiO films used for pinning layers in spin valve systems were prepared by reactive sputtering from an NiO target with variation of the oxygen/argon mixture in the sputter gas. Using XPS depth profiling we investigated the NiOx overstoichiometry (x > 1) in the films that was found by other methods and the chemical changes in the films during annealing. A direct detection of Ni3+ failed because of strong preferential sputtering with the formation of metallic Ni during sputtering. By means of factor analysis a qualitative description of the overstoichiometry is possible. Indirectly it could be shown that metallic Ni is already formed in the oxide layers during annealing. It can be concluded that the stability of the NiOx films decreases with increasing deviation from stoichiometry (x > 1). Copyright © 2004 John Wiley & Sons, Ltd.
236 citations
TL;DR: XPS MultiQuant as discussed by the authors is a program for quantitative evaluation of x-ray photoelectron spectra that uses the classic approach of quantification and requires as input the integrated intensities of the measured XPS lines.
Abstract: A program for quantitative evaluation of x-ray photoelectron spectra has been developed to serve as a practical tool for surface chemists. The program uses the ‘classic’ approach of quantification and requires as input the integrated intensities of the measured XPS lines. The usual correction methods and factors can be applied and controlled independently. All necessary basic data for calculations are integrated into the main library of the program. Besides the usual ‘infinitely thick homogeneous sample’ geometry model, the program is able to calculate models for layered structures, both on flat and curved surfaces. Calculation for several samples or experimental data sets can be done together. Results can be presented in several forms, such as atomic %, atomic ratio, oxide molar ratio, etc., and can be stored, printed and charted. Data can be labelled and annotated. XPS MultiQuant is equipped with a user-friendly interface, full text help system and a ‘wizard’ for easy set-up of calculations. Copyright © 2004 John Wiley & Sons, Ltd.
196 citations
TL;DR: In this article, a home-built device for low (9%) and high (95%) relative humidity for shorter (450 min) and longer (1800 min) time periods was used to measure the viscosity of GaInSn alloys.
Abstract: Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device for low (9%) and high (95%) relative humidity for shorter (450 min) and longer (1800 min) time periods. At constant exposure time a characteristic increase of viscosity is observed with increasing humidity. For high humidity, high viscosity is obtained after a short time. Assuming that the measured viscosity change is strongly related to the absorption of oxygen, XPS was applied to the chemical and quantitative analysis of differently prepared samples. In all cases, Ga is predominantly oxidized at the surface whereas Ga atoms in the metallic state are located deeper inside. Besides Ga 2 O 3 (the most stable oxide phase), the less stable Ga 2 O is detected. Indium and tin are almost stable in their metallic state. With increasing humidity the thickness of the oxide film increases in our case from about 19 A to 25 A, assuming a layer-by-layer model. The presented results confirm our assumption of the increase in viscosity of the GaInSn system as a consequence of the preferential oxidation of gallium in the near-surface region.
169 citations
TL;DR: In this paper, a set of five different aluminium oxide layers has been investigated using XPS, and the oxide layers were made by oxidizing aluminium in a vacuum, with an alkaline and acidic pretreatment and in boiling water.
Abstract: A set of five different aluminium oxide layers has been investigated using XPS. The oxide layers were made by oxidizing aluminium in a vacuum, with an alkaline and acidic pretreatment and in boiling water. Hydroxyl fractions of the aluminium oxide layers ranging from 0.0 to 0.5 were determined by constrained curve-fitting of the O 1s peak. The O/Al atomic ratios of the aluminium oxide layers, ranging from 1.5 to 2.0, were determined from the O 1s and Al 2p photoelectron intensities. A method is presented to account for the attenuation of the photoelectron intensities by the contamination overlayer. For the studied oxide layers, a linear relation is observed between the hydroxyl fraction and the O/Al atomic ratio of the aluminium oxide layers. It is concluded that the results obtained by the curve-fitting procedure are reliable. Furthermore, a linear relation is observed between the hydroxyl fraction and the O 1s peak width. The O 1s binding energies of the O 2− and OH − components of the oxide layers correspond to 531.0 ± 0. 1e V and 532.4 ± 0.1 eV, respectively. Only pseudoboehmite showed 0.5 eV lower binding energies for these components. Angle-resolved XPS analysis showed that most of the studied oxides are enriched in hydroxyl groups at their outermost surface. Copyright 2004 John Wiley & Sons, Ltd.
137 citations
National Physical Laboratory1, National Research Council2, University of Paris3, German National Metrology Institute4, Bundesanstalt für Materialforschung und -prüfung5, University of Jena6, Leipzig University7, National Institute of Advanced Industrial Science and Technology8, Utsunomiya University9, National Institute for Materials Science10, Korea Research Institute of Standards and Science11, National University of Singapore12, Council of Scientific and Industrial Research13, Swiss Federal Laboratories for Materials Science and Technology14, Philips15, University of Surrey16, Daresbury Laboratory17, National Institute of Standards and Technology18, Alcatel-Lucent19
TL;DR: In this paper, a study was carried out for the measurement of ultrathin SiO on (100) and (111) orientation silicon wafer in the thickness range 1.5-8 nm.
Abstract: A study was carried out for the measurement of ultrathin SiO on (100) and (111) orientation silicon wafer in the thickness range 1.5-8 nm. XPS, medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), SIMS, ellipsometry, gazing-incidence x-ray reflectometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM) were used for the measurements. Water and carbonaceous contamination about 1 nm were observed by ellipsometry and adsorbed oxygen mainly from water at thickness of 0.5 nm were seen by MEIS, NRA, RBS and GIXRR. The different uncertainty of the techniques for the scaling constant were also discussed.
135 citations
TL;DR: In this article, a non-linear increase in binding energy with increasing oxygen substitution has been demonstrated for polysiloxane polysilicon systems. But the binding energy of a siloxy unit is known to increase when an oxygen atom replaces an alkyl group attached to the silicon atom.
Abstract: A procedure for obtaining reliable binding energies in XPS for the various chemical states of silicon has been described in the literature for some organosilicon compounds. This manuscript describes further development of this work by the analysis of siloxane compounds that model complex polysiloxane systems. The use of accurate and restrained binding energies will allow greater confidence in the curve-fitting of the Si 2p core level of industrially relevant coatings, which are typically featureless. The binding energy of a siloxy unit is known to increase when an oxygen atom replaces an alkyl group attached to the silicon atom. However, whereas previous work had estimated the binding energy shift between the M [(CH3)3SiO1/2], D [(CH3)2SiO2/2], T [(CH3)SiO3/2] and Q [SiO4/2] environments of silicon to be equal, or decreasing, this work has demonstrated a non-linear increase in binding energy with increasing oxygen substitution. Copyright © 2004 John Wiley & Sons, Ltd.
127 citations
TL;DR: XPS analysis of different forms of copper sulfate, including antlerite, brochantite, posnjakite, chalcanthite and anhydrous copper sulfates, as well as pure copper and its oxides cuprite and tenorite, was carried out as discussed by the authors.
Abstract: XPS analysis of different forms of copper sulfate, including antlerite, brochantite, posnjakite, chalcanthite and anhydrous copper sulfate, as well as pure copper and its oxides cuprite and tenorite, was carried out. These products most often occur when dealing with atmospheric corrosion of copper and bronze in sulfur-bearing environments. These compounds were minerals, commercial products, or grown on pure copper by artificial weathering. Spectral features such as peak energy and line shape for Cu 2p, Cu LMM, O is and S 2p bands were examined. Comparison of the measurements obtained proves the efficiency of XPS in differentiating the various compounds.
TL;DR: In this article, the effects of the deposition temperature and time on the film properties were investigated using X-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy.
Abstract: Iron oxide thin films were grown with gas-phase deposition on a glass substrate in order to study the effects of the deposition temperature and time on the film properties. Characterization of the samples was performed using x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy. It was observed that the film deposited at 350°C consisted of γ-Fe2O3 whereas films produced at temperatures between 400°C and 500°C could be identified as α-Fe2O3. Increasing the deposition temperature resulted in an increase of the grain size at temperatures between 350°C and 450°C. When the deposition time was decreased, a part of the iron ions were observed to be in the divalent state. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, a high-temperature thermal decomposition method was used to synthesize monodisperse cobalt nanoparticles in the presence of oleic acid and triphenylphosphine.
Abstract: Monodisperse cobalt nanoparticles are synthesized via a high-temperature thermal decomposition method in the presence of oleic acid and triphenylphosphine. The as-synthesized nanoparticles are stable against further deep oxidation when they are kept in heptane .C7H16/. Time-dependent XPS studies indicate that oxidation of the as-synthesized cobalt nanoparticles in air is slow. The valence change of cobalt from the nanoparticle sample is not observed after it is kept in heptane under air for 90 days. The cobalt nanoparticles have a b-manganese-type structure (also called e-Co). Annealing the nanoparticles at 500 ◦ C under Ar .95%/ +H 2 .5%/ converts these particles from e-Co to fcc-Co. Two-dimensional and three-dimensional self-assembled superlattices of the passivated cobalt nanoparticles are formed by slow evaporation of the carrier solvent. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles. Copyright 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the adsorption of a range of organic molecules from toluene onto the oxidized surface of magnetron-sputtered aluminium metal was studied using sessile drop water contact angle measurements.
Abstract: The adsorption of a range of organic molecules from toluene onto the oxidized surface of magnetron-sputtered aluminium metal is studied using sessile drop water contact angle measurements. Molecules with different head group functionalities and various chain lengths are considered, including alkyl carboxylic acids, alkyl phosphonic acids, alkyl amines, alkyl trimethoxysilanes, alkyl trichlorosilanes and epoxy alkanes. Alkyl phosphonic and carboxylic acids are identified as readily forming the most well-packed monolayers on the aluminium surface, whereas the others adsorb less well and the chlorosilanes polymerize as a result of combination with moisture to form a thick deposit. The high-adsorption-density monolayers of alkyl phosphonic and carboxylic acids were studied using polarization modulation infrared reflection–absorption spectroscopy (PM-IRRAS) and x-ray photoelectron spectroscopy (XPS): PM-IRRAS reveals relatively poorer ordering of the C10 alkyl carboxylic acid monolayer compared with that formed from the phosphonic acid, and XPS data suggest that this is likely to relate to a lower ability to displace preadsorbed volatile organic compounds. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, a peak-fit analysis of Cr 2p XPS spectra of Cr(III) compounds is proposed, based on the experimental and theoretical work of other authors.
Abstract: By using modern XPS systems it is possible to obtain spectra with well-resolved spin orbit, multiplet and field splitting even with powder samples mounted using adhesive tape. Measurement of Cr2O3 powder with the latest generation of XPS spectrometers, which are able to analyse non-conductive powders with ultimate energy resolution, revealed multiplet splitting features and satellite emission in the Cr 2p spectrum. Therefore, peak-fit analysis of Cr 2p XPS spectra of Cr(III) compounds requires a more appropriate approach and common practice has to be reconsidered. One possible way to analyse this spectrum is proposed, based on the experimental and theoretical work of other authors. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, a practical sputter rate of 2.4 nm min−1 for SiO2 was obtained for sputtering an area of 5 mm × 5 mm using a 5 kV C60 ion beam with an energy of 83 eV per carbon atom.
Abstract: We have applied sputtering using a buckminsterfullerene (C60) ion beam for XPS analysis. A practical sputter rate of 2.4 nm min−1 for SiO2 was obtained for sputtering an area of 5 mm × 5 mm using a 5 kV C60 ion beam with an energy of 83 eV per carbon atom. Extremely low sputtering degradation of polytetrafluoroethylene was observed in these conditions. The results were compared with argon ion beam energies of 500 V and 5 kV. These are the first results utilizing a C60 ion beam for XPS analysis with limited sputtering damage. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the Ce-based conversion coatings were applied on a 2024-T3 Al alloy sheet using Rutherford backscattering spectroscopy, scanning electron microscopy, Auger electron spectrography, x-ray photoelectron spectrograms, and atomic force microscopy.
Abstract: The deposition of Ce-based conversion coatings onto 2024-T3 Al alloy sheet was studied using Rutherford backscattering spectroscopy, scanning electron microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy. The Al sheet was pretreated with an alkaline clean followed by treatment in a Ce(IV) and H2SO4-based desmutter. The Ce(IV)-based conversion coating solution contained 0.1 M CeCl3·7H2O and 3% H2O2 and was acidified to pH 1.9 with HCl. Upon immersion, there was an induction period that included activation followed by aluminium oxide growth over the matrix and cerium oxide deposition onto cathodic intermetallic particles and along rolling marks on the surface. After the induction period cerium oxide deposited generally across the whole surface and thickened. The strongest anodic sites initially were adjacent to the intermetallic cathodes and resulted in aluminium dissolution but also oxide thickening. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, an error analysis for numerically evaluating random uncertainties in x-ray photoelectron spectroscopy has been implemented in version 2003 of the spectra treatment and analysis software UNIFIT in order to improve the understanding of the statistical basis and the reliability of the model parameters.
Abstract: An error analysis for numerically evaluating random uncertainties in x-ray photoelectron spectroscopy has been implemented in version 2003 of the spectra treatment and analysis software UNIFIT in order to improve the understanding of the statistical basis and the reliability of the model parameters for photoelectron spectra. The theoretical basis as well as two approaches to obtain error limits of the fit parameters have been considered. Several test spectra have been analysed and discussed. A representative example has been chosen to demonstrate the relevance of the error estimation for practical surface analysis. Suggestions for the minimization of errors in the peak-fitting procedures are presented. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the surface distribution of organic compounds on natural cellulosic fibre materials (cotton, flax and softwood pulps) with XPS was studied using a novel approach introduced by Tougaard.
Abstract: In x-ray photoelectron spectroscopy (XPS), knowledge of elemental depth distributions within the first 10 nm is often essential. However, none of the conventional XPS methods can reliably discern, for example, a thin overlayer from clusters on rough surfaces. Therefore, reliable experimental data on the actual distributions of lignin and extractives on the fibre surfaces is needed, although there are numerous XPS studies on cellulosic fibres and paper. We have studied surface distributions of organic compounds on natural cellulosic fibre materials (cotton, flax and softwood pulps) with XPS, using a novel approach introduced by Tougaard. We were able to model the surface composition of rough fibre surfaces via simple spectral analysis of the O is signal. The simple spectral background analyses used show that in the case of cotton and flax, the non-cellulosic compounds cover the cellulosic fibre surface much more effectively than in softwood pulps, in spite of the smaller amount of non-cellulosic material present.
TL;DR: In this paper, a simulation model is used in order to compute the ion trajectories close to a field emitter, and the model is modified to take into account the unique morphology of the multilayer thin-film structure.
Abstract: Owing to their giant magnetoresistance properties, multilayer thin-film materials are widely used in information storage technology. However, because this magnetic behaviour is highly sensitive to interface roughness and diffusivity on a subnanometre scale, the structural characterization of these materials with high spatial resolution is of fundamental importance. The three-dimensional atom probe is one of the instruments that theoretically can provide chemical analyses in three dimensions with the highest spatial resolution. However, because three-dimensional reconstructions can be subject to strong artefacts due to trajectory aberrations, it is important to combine experimental analyses with theoretical investigations of the evaporation and reconstruction process in order to obtain the most accurate data on interface structure.
In this paper, a simulation model is used in order to compute the ion trajectories close to a field emitter. The model is modified to take into account the unique morphology of the multilayer thin-film structure. This model gives a sound interpretation of the three-dimensional atom probe images of multilayer thin films. The three-dimensional atom probe reconstructions of NiFe/FeCo/Cu multilayer structures are found to be degraded by strong artefacts owing to the difference in evaporation field between the FeCo layer and the Cu layer. By using simulation, these aberration effects are interpreted as errors in the calculation of the z-dimension within three-dimensional images. A correction procedure has been developed to improve the reconstruction of multilayer thin films in the three-dimensional atom probe. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors developed a software called QUANTitative analysis of Electron Energy Losses at Surfaces (QUEELS) that can be used to perform surface energy loss analysis in a user-friendly way.
Abstract: Surface analysis based on the interpretation of electron spectroscopy such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, or reflection electron energy loss spectroscopy are influenced by the inelastic scattering processes that take place when an electron moves in the region near a solid surface. The actual energy losses depend on the particular experimental situation. Thus, an electron is attracted by its image charge when it is moving in the vacuum. It will therefore lose energy even after it has left the surface and, similarly, an electron that moves in the vacuum towards the solid surface gains energy. Likewise, the scattering properties for an electron moving close to the surface are different from those of an electron moving in the bulk of the solid. In photoemission and Auger experiments the effect of the static hole will also affect the scattering probabilities of the electron in the first few Angstroms as it moves away from the point of excitation. These effects will also cause the 'effective' inelastic mean free path to depend on the position of the electron with respect to the surface and with respect to the point of excitation. In the past years, we have developed models to describe these effects within a dielectric response theory for different cases of electrons moving near surfaces in general geometries with or without a static core hole. The formulas are quite involved with many infinite integrals and this is a major barrier for people to apply them in practice. With the purpose of making the calculations easier to perform, we have developed software (QUEELS: QUantitative analysis of Electron Energy Losses at Surfaces) that will do this in a user-friendly way. It is hoped that with this tool at hand, we will be able to more effectively and quickly get a more complete understanding of the importance of these different effects for quantitative analysis of surface electron energy spectra.
TL;DR: In this article, low-energy ion scattering was used to determine the surface impurity fraction and to observe which groups at the surface are shielded by the segregated species in polydialkoxy phenylenevinylene (PPV), polycarbonate and dendrimer macromolecules.
Abstract: The present revolution in novel organic materials is driven by the synthesis of new materials exhibiting specific functional properties. Traces of silicon compounds are often present in these materials and, although the bulk concentrations of these impurities may be low, segregation can seriously modify the surface composition. Surfaces and interfaces play an important role in many applications, and the intrinsic properties of the materials are thus often obscured by the presence of segregated impurities. By studying silicon impurity segregation in poly-dialkoxy phenylenevinylene (PPV), polycarbonate and dendrimer macromolecules, we demonstrate how low-energy ion scattering may be used to determine the surface impurity fraction and to observe which groups at the surface are shielded by the segregated species. We demonstrate that the performance of PPV- based light-emitting diodes is significantly reduced for submonolayer coverages of siloxanes. We find that the kinetics of the segregation process depend strongly on the materials and the sample preparation conditions. We find that the presence of solvents is needed to enable segregation at room temperature. Heating does enable siloxane impurity segregation in polycarbonate in the solid phase, whereas for polydimethylsiloxane in PPV films we find that segregation in the solid phase does not occur up to 200°C. The siloxane molecules are found to segregate to preferential sites at the surface, shielding the polar groups. Finally, we demonstrate that purification of the surface is often possible through simple procedures that provide an easy way to study the intrinsic properties of the materials.
TL;DR: In this article, three pretreatments were used to prepare the aluminium surface before the deposition of thin non-functional silane films, and the generated surfaces were characterized before and after the silane film deposition by IRSE and by the combination of SEM, AES and spectroscopic ellipsometry (SE), respectively.
Abstract: This paper focuses on the effect of aluminium surface pretreatment on the formation of thin non-functional silane films. Three pretreatments were used to prepare the aluminium surface before the deposition of silane films. The generated surfaces were characterized before and after the silane film deposition by infrared spectroscopic ellipsometry (IRSE) and by the combination of SEM, AES and spectroscopic ellipsometry (SE), respectively. It is demonstrated that the amounts of hydroxyl groups at the aluminium surface provided by the different pretreatments strongly influence the initiation and the formation of the silane films.
TL;DR: In this paper, the extrinsic loss structures for XPS spectra of oxide films grown on iron in such a way that their thickness and structure could be determined using Generate and Analyze.
Abstract: QUASES Analyze and Generate were used to model the extrinsic loss structures for XPS spectra of oxide films grown on iron in such a way that their thickness and structure could be determined. The Generate program used in conjunction with spectra of model iron oxides allowed for both magnetite (Fe 3 O 4 ) and maghaemite (γ-Fe 2 O 3 ) structures to be identified in all films studied. These structures were identified as overlying layers in the oxide films and were usually intermixed at their interface. The absence of other iron oxide structures within the film could be tested based on their goodness of fit to the experimental spectrum. Comparison of the thickness values obtained using Generate with those found using nuclear reaction analysis suggested that the Generate results were higher by 20%. This difference likely resulted from the use of a calculated inelastic mean free path value for Fe 2p electrons in the Generate calculation rather than using the real attenuation length. For oxide films whose thickness approached 10 nm, the QUASES results for photoelectron spectra obtained with a Zr achromatic x-ray source were compared with those from the standard Al monochromatic source. In this particular case, the oxide thicknesses obtained using Generate and Analyze were found to be more consistent when the Zr source was used.
TL;DR: In this article, the authors derived geometry correction factors, based on pure geometrical considerations, to determine the thickness of oxide and carbonaceous contaminant layers on Si 3 N 4 powder and Al foil.
Abstract: Accurate determination of overlayer thickness on samples with curved surfaces is of growing importance, especially in connection with nanometric materials systems. In this work two simple geometries are treated; closely packed spheres, well representing powder samples, and close-packed cylinders, modelling fibrous samples. In the case of the powder samples (the arrangement is similar to the structure of the closest packed spheres) in addition to the intensity originating from curved layers of the top row of the spheres, the contribution of the partially visible spheres of the second and third rows below the top row are also considered, enhancing the accuracy of the calculations. As is shown, the method of calculation for spheres and cylinders is similar but the values of the geometry correction factors are different. The applicability of the derived geometry correction factors, based on pure geometrical considerations, is supported with experimental data obtained in two material systems: the thickness of oxide and carbonaceous contaminant layers on Si 3 N 4 powder and Al foil were determined. These types of calculations were conveniently performed by the XPS MultiQuant program providing not only the geometry correction factors but also other parameters, such as cross-sections, asymmetry parameters, etc.
TL;DR: In this paper, the authors studied the siloxane, SiOSi, film formation on a Ti substrate by using mono-, bis-and tris-aminosilanes.
Abstract: The aim of this investigation was to study the siloxane, SiOSi, film formation on Ti substrate by using mono-, bis- and tris-aminosilanes. The ultimate goal was to obtain a smooth, well-organized and stable siloxane film with suitable surface energy. Such films are expected to perform well in adhering resins to dental metal alloys when the films contain reactive functional groups. Aminosilanes were prepared as 0.5 vol.% solutions in dilute ethanol (50 vol.% ethanol in deionized water), with their natural pH of ∼ 9. The substrates were silanized in two ways: silane was allowed to react at room temperature or was cured for 1 h at 110°C. The surface characterization was carried out by reflectance–absorbance Fourier transform infrared spectroscopy (RA-FTIR), x-ray photoelectron spectroscopy (XPS), contact angle measurement and atomic force microscopy (AFM). Siloxane film thickness measurements were not made. According to spectral analysis, all silanes indicated covalent bond formation with titanium. SiOTi and SiOSi bonds were clearly seen in the spectra, suggesting that chemical retention had taken place. After curing at elevated temperature, the spectral bands seemed to be stronger than those on samples cured at room temperature. Curing of hydrolyzed silanes at elevated temperature seemed to enhance the siloxane layer formation, derived from aminosilanes, on the Ti substrate. This might have an influence on the hydrolytic stability of organosilane-promoted adhesion between Ti and dental resins. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, an improved method for deriving the equations for cold field electron emission from a free-electron metal was presented, where the derivation of these equations can be presented as a straightforward double integral in a space where the vertical axis represents the total electron energy, and the horizontal axis represented the component of electron kinetic energy parallel to the emitter surface.
Abstract: An improved method is reported for deriving the equations for cold field electron emission from a free-electron metal. It is shown that the derivation of these equations can be presented as a straightforward double integral in a space where the vertical axis represents the total electron energy, and the horizontal axis represents the component of electron kinetic energy parallel to the emitter surface. A general approach is developed that applies to a tunnelling barrier of any shape. It is shown that the temperature-correction factor derived by Murphy and Good for emission through an image-rounded barrier also applies to a more general barrier. For the standard image-rounded barrier the results coincide with those of Murphy and Good, but the derivation is more straightforward mathematically and the physics involved can be visualized more easily. The method developed here should be a good foundation for developing an improved theory of cold field electron emission from semiconductors: the main object of the paper is to lay this foundation. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, an atomic force microscope between polymer balls attached to a cantilever and a silicon wafer under ultra high vacuum conditions was used to measure the adhesion force.
Abstract: Adhesion measurements are presented which were carried out with an atomic force microscope between polymer balls attached to a cantilever and a silicon wafer under ultra high vacuum conditions. In using a silicon surface with a defined structure a correlation between adhesion force and contact area was found. This correlation could partly be explained by the Johnson-Kendall-Roberts model, if a change of the surface energy is assumed as a result of the structuring. For a constant geometric contact area an additional structuring leads to a decrease of the adhesion force.
TL;DR: In this article, low-pressure microwave plasma has been used to incorporate new functionalities onto the surface of cyclic olefin copolymers (COC) to enhance their adhesion to metals.
Abstract: Low-pressure microwave plasma has been used to incorporate new functionalities onto the surface of cyclic olefin copolymers (COC). The main goal of the plasma treatment was to hydrophilize the COC's surface in order to enhance its adhesion to metals. The effect of two plasma parameters (treatment time and type of plasma gas) on the adhesion properties has been investigated. In order to investigate the opportunity for optimization of the adhesive strength in the COC–metal composite, an adhesion-promoting layer of acrylic acid (AA), or inorganic SiO2, has been deposited. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors investigated the merits of fullerene cluster ions as projectiles in time-of-flight secondary neutral mass spectrometry (ToF-SNMS) sputter depth profiling of an Ni:Cr multilayer sample.
Abstract: We have investigated the merits of fullerene cluster ions as projectiles in time-of-flight secondary neutral mass spectrometry (ToF-SNMS) sputter depth profiling of an Ni:Cr multilayer sample similar to the corresponding NIST depth profiling standard. It is shown that sputter erosion under bombardment with C60+ ions of kinetic energies between 10 and 20 keV provides good depth resolution corresponding to interface widths of several nanometres. This depth resolution is maintained during the complete removal of the multilayer stack with a total thickness of 500 nm. This finding is in contrast to the case where atomic Ga+ projectile ions of comparable kinetic energy are used, demonstrating the unique features of cluster projectiles in sputter depth profiling. Copyright © 2004 John Wiley & Sons, Ltd.