Surface and in-depth characterization of TiC/C and Ti(C,N) layers by means of AES and Factor Analysis

Magnetron sputtered TiC/C multilayers and Plasma Vapour Deposited Ti(C,N) layers have been investigated by AES. The carbon sensivity factor has been calibrated for the correct composition of a TiC standard sample. Nitrogen has been measured indirectly based on the Ti_L3M23M23/Ti_L3M23V peak area ratio in the direct EN(E) spectrum using Ti, TiC and TiN standard samples. The influence of Tougaard background removal has been tested. As the less accurate method taking the Ti peak-to-peak ratio has been found to give adequately good results. It has been possible to recalculate AES depth profiles, where only peak-to-peak values and no peak areas in the direct spectrum are available. Factor Analysis has been applied to AES depth profiling results. The data matrix in each column contains the linked experimental spectra of the measured elements. Based on the standard spectra the main components of a TiN layer on silicon have been identified by Factor Analysis. The structure of a TiC/C multilayer system has been resolved by the characteristic C_KLL peak shape in C and TiC. Factor Analysis enables to calculate the individual profiles for Ti, TiC and C.     

Analysis of thin solid films and surfaces by infrared spectroscopy

Thin solid films and surfaces are characterized by IR spectroscopy, based on reflectance and transmittance measurements, in particular with polarized light at oblique incidence. Thus two independent data sets fors- andp-polarization are available. Atp-polarization additional absorption lines at the zeros of the dielectric function are observed (Berreman-mode). The interpretation of the measured spectra is carried out by a fit procedure to simulate the observed spectra. As a result the specimens are characterized in terms of vibronic resonances and their oscillator strengths or concentration, thicknesses of various films in a stack of layers, profiles of depth depending chemical composition, or concentration and mobility of conduction electrons.All examples are relevant for application in technology, as microelectronics, thin film technology, catalysis, e.g. The results of the IR analysis are compared with those of other analytical methods as SIMS, RBS, and AES. The agreement is very good. One important advantage of the IR analysis, however, is the fact that it is a non-destructive method.     

Comparative composition analysis of SiOx and SiNx thin films by AES, EDX and RBS

The chemical composition of thin films in SiO_x and SiN_x systems (SIPOS) have been analyzed by comparative AES, EDX, and RBS of the same samples to assess the extent of possible errors introduced by the weak points of each method. These exist for EDX in the necessity of a thickness correction, for AES in a possible composition dependence of the sensitivity factors, and for RBS in the low sensitivity in detecting light elements. Linear correlations between the data obtained by RBS and EDX have been revealed over the whole range of x. Therefore, EDX can be calibrated by appropriate standards of pure SiO₂ or Si₃N₄ films. For AES analysis a calibration curve is needed. Using RBS data for calibration the content of the light components O and N might be slightly overestimated by this method.     

AES and XPS investigations for the topochemical characterization of dope elements on WC powders

Summary Trace elements bias the hard metal production and can deteriorate the technological and mechanical properties of sintered tools. Therefore, within the COST 503 action, the surface enrichment of the dope elements Ca, Si, Al, P on 1.5 m WC milling grade starting powders has been investigated by AES and XPS. AES depth profiles and high resolution AES (HRAES) elemental maps describe the microscopic distribution of traces. XPS spectra are compared with the AES results and contribute to the understanding of the topochemical structure of doped WC-powder grains.     

Characterization of the stoichiometry of coevaporated FeSix films by AES, EDX, RBS, and electron microscopy

The composition of FeSi_x films on Si coevaporated from separate sources of Fe and Si was analyzed comparatively by AES, EDX, RBS, and electron microscopy. Cross-checks between EDX and RBS reveal systematic errors originating from the spectra background subtraction in RBS and from the thickness correction of the EDX signals. PCA (principal component analysis) assisted AES was successfully applied to the characterization of different Si bonding states in nonstoichiometric FeSi_x films. For the growth of β-FeSi₂ films by means of molecular beam epitaxy (MBE) the adjustment of the atomic beam intensities is reported in order to illustrate the capabilities of the various techniques.     

Surface characterisation of laser irradiated SiC ceramics by AES and XPS

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.     

Deposition and characterization of thin boron-carbide coatings

Summary Thin boron-carbide films were deposited using a PACVD process on Si substrates at room temperature. Various mixtures of B₂H₆/He and CH₄, as well as the less hazardous B(CH₃)₃, have been used as process gases. The composition of the deposited films has been correlated with the B₂H₆/He/CH₄ mixture used. When using B(CH₃)₃, the coatings were found to be slightly boron enriched compared to the gas phase stoichiometry. In both cases oxygen contaminants were additionally found (up to 5 at %) in the films. Most of the oxygen was incorporated from the residual gas at the beginning of the deposition. The coatings were hard and showed good adherence to the substrate; no film peel-off was observed after exposure to air. The films have been characterized, in-situ, by electron spectroscopy (XPS, UPS, AES), and by other methods (AES depth profiling, SEM, -step).     

29Si NMR spectra of methylphenylcyclotri-and -tetrasilazanes

²⁹Si NMR spectra of various methylphenyl-substituted cyclotri- and -tetrasilazanes, composed of different combinations of the units d = Me₂SiNH, d^ph = MePhSiNH and d = Ph₂SiNH, have been investigated. For most of the compounds having more than one asymmetric centre, the spectra of both the individual isomers and their mixtures have been studied, and the signals of the individual isomers have been assigned. The effect of a different arrangement of phenyl groups in the rings, and the influence of the stereochemistry of the isomers on the ²⁹Si chemical shifts in cyclotri- and -tetrasilazanes have been studied. The ²⁹Si chemical shifts in cyclotrisilazanes are additive and can be represented as the sum of increments corresponding to the number and positions of the phenyl groups in the rings. In these compounds, the spatial structure of the isomers does not exert any noticeable effect on the spectra. On the contrary, chemical shifts are not simply additive in cyclotetrasilazanes: a pronounced stereochemical dependence is apparent.     

Investigation on structure and morphology of the thermally treated glassy alloy (Fe,Cr)80(P,C,Si)20 by means of ESCA and SEM/EDXA

Metallic glass ribbons of the chemical composition (Fe,Cr)₈₀(P,C,Si)₂₀ have been thermally treated in the region between 530 and 980°C for 72 h. The SEM/EDXA investigations indicate that a phase transformation takes place between 575 and 980°C in a surface layer of 5 m thickness. Thus, a Cr-rich phase occurs between 760 and 800°C which is converted into an open-pore system between 850 and 900°C. The oxidation process reaches its maximum at 760°C. The ESCA spectra of the material in the as received state and of the thermally treated samples indicate that different oxygen species are formed within the analysed surface layer of 10 nm. The oxygen of the original material is incorporated as hydroxyl groups in species such as FeO(OH) and CrO(OH). After thermal treating the hydroxyl content decreases and the oxide content increases. Species of Si exist in the surface layer as SiO_x-like compounds (peak at BE=102.0 eV). A majority phase of transition metal phosphide species is coexisting with oxidised phosphate species.     

Effects of electron polarization on the auger spectra of lanthanum oxide

The SCF-X scattered-wave method has been used in the quasirelativistic approximation to calculate the energies and relative intensities of the transitions in the M₄, ₅N₄,₅V and N₄,₅VV Auger electron spectra AES of lanthanum in the LaO ₆ ^9– cluster, which is taken as a model for crystalline La₂O₃. A study has been made of the influence of relaxation effects on the AES. The AES intensity distribution is largely determined by the population of the 4f states of La in the initial state of the Auger process. The AES for lanthanum in La₂O₃ are interpreted from the calculations.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 207–210, March–April, 1986.     

Comparative surface and bulk analysis of oxygen in Si3N4 powders

Summary Five commercially available -Si₃N₄ powders and one in the modification were subjected to Auger electron spectroscopy (AES) and carrier-gas-heat extraction (CGHE) analysis.AES depth profiles of the oxygen/nitrogen ratio could be obtained, from which total oxygen contents were calculated and compared to CGHE data. It is demonstrated that by the latter method also dissolved oxygen in -Si₃N₄ is detected, whereas by AES only chemically bound oxygen can semiquantitatively be analyzed. Evidence is found for the existence of water, adsorbed or present as hydroxyl groups, near the surface.

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Vergleichende Oberflächen- und Bulkanalyse von Sauerstoff in Si₃N₄-Pulvern

List of Symbols A Surface area of an idealized Si₃N₄ grain - c _o ^AES Bulk concn. (by wt.) of oxygen in Si₃N₄ as estimated from AES depth profiles - C _O ^GHE Bulk concn. (by wt.) of oxygen in Si₃N₄ as obtained using CGHE in the fixed temperature mode - C _pr Bulk concn. (by wt.) of oxygen in Si₃N₄ as obtained using CGHE in the temperature programme mode - C_surf Bulk concn. (by wt.) of oxygen in Si₃N₄, tentatively assigned to superficial oxygen on Si₃N₄ particles, as obtained using CGHE in the temperature programme mode - C _U c _o ^AES as recalculated from X_U - d Diameter of an idealized Si₃N₄ grain (1 m) - M_index Formula mass of the species named in the index (O, 2 SiO₂, Si₃N₄) - m _o Mass of oxygen in the Si₃N₄ material - M_x Estimated formula mass of a (SiO₂)_2XSi₃N₄ compound as detected by AES via X - r Radius of an idealized Si₃N₄ grain (0.5 m) - V Volume of an idealized Si₃N₄ grain - X atomic oxygen-to-nitrogen ratio (AES) - X_a X values obtained in the scanning beam (area) mode - X_dec X values obtained in the fixed beam (point) mode after about 30 min measuring time (i.e., in some cases, severe decomposition) - X_p X values obtained in the fixed beam (point) mode within about 2 min measuring time (before severe decomposition) - X_U Background value for X in the AES depth profiles - xxps Atomic oxygen-to-nitrogen ratio as obtained from XPS data - Z Sputter depth - Z _E End value for the integration below the depth profile curves - _O Oxygen mass per unit area - _O Oxygen mass per unit volume (recalculated bulk concentration) - _U Oxygen mass per unit volume as recalculated from X_U.     

Comparative bulk, surface and depth profile analyses on AlN and SiC-coated B4C powders

Summary On thin layers of m sized AIN particles, superficial enrichment of O, probably caused by atmospheric hydrolysis and/or oxidation, was detected by means of Auger Electron Spectroscopy (AES) combined with sputter depth profiling. By comparing the O/N ratio found at the surface with that of the bulk, determined by means of the carrier gas heat extraction (CGHE) method, surface enrichment appeared to be more pronounced for lower O coverages. Chemical speciation of O (H₂O, CO₂) was feasible using appropriate CGHE techniques. — Similarly, using AES and Secondary Ion Mass Spectrometry as depth profiling methods, surface enrichment of Si, C and O was found for two B₄C powders, which had been coated by the sintering additive SiC. For this system, Laser Mass Microanalysis yielded additional information about chemical species. Combination of all applied methods led to comprehensive models of the natural and prepared particle coatings.     

In-depth compositional analysis of ceramic (Bi2O3)0.75(Er2O3)0.25 by AES and XPS

The chemical composition of dense ceramics of erbia-stabilized -Bi₂O₃ was analyzed by Auger electron spectroscopy (AES) depth profiling using Ar⁺ ion sputtering. The relative sensitivity factors (rsf) and sputter rates of bismuth and erbium in this material have been determined by electron probe microanalysis (EPMA) and chemical analysis. These results, supplemented by data from angle resolved X-ray photoelectron spectroscopy (ARXPS), shows a bismuth enrichment at the surface. Evidence has been found for reduction of the bismuth-oxide at the outermost part of the surface layer.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

A Raman study on the coordination sites and stability of the [Al(formamide)5]Cl3 complex

Raman experiments of aluminum chloride and formamide (FA) solutions in different compositions and temperatures were carried out. Spectral changes provoked by the increase of the salt concentration were observed in different regions. The ν_CO and ν_CN modes of FA upon complexation were upshifted and suggest that the CONH hybrid (II) is stabilized by Al(III). Bands at 547 and 295 cm⁻¹, which are assigned to the ν_AlO and ν_AlN vibrations, respectively, evidence coordination through both O and N atoms of FA. The quantitative analysis performed at the carbonyl stretching region found 5 FA molecules around this cation, resulting in the formation of the [Al(FA)₅]Cl₃ complex. Its stability is maintained by whole studied concentration range and up to around 100 °C. At higher temperatures, distortions in the FA shell begin occurring and a new component at 356 cm⁻¹ is then observed and assigned to the [AlCl₄]⁻ complex.     

Depth profiles of Ta2O5/SiO2/Si structures: a combined X-ray photoemission, Auger electron, and secondary ion mass spectroscopic study

Summary We prepared thin films of tantalum oxide on SiO₂/Si substrates by thermal oxidation of tantalum. The different oxide layers and their interfaces were characterized by SIMS, AES, and XPS. Characteristic structures were obtained after different oxidation procedures. The comparative discussion of AES and SIMS depth profiles makes possible an unequivocal characterization of the reactive interfaces between the oxides of Ta and Si. The Ta₂O₅/SiO₂ interface in particular shows non-stoichiometries which depend on the oxidation procedures and which determine the performance characteristics of pH-sensitive Ta₂O₅ field-effect transistors.

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Tiefenprofile von Ta₂O₃/SiO₂/Si-Strukturen: Eine kombinierte Untersuchung mit Röntgen-Photoemissions-, Auger-Elektronen- und Sekundär-Ionen-Massen-Spektrometrie

     

Study of chemical bonds in a-B/C:H films by electron probe microanalysis

This paper describes the study of chemical bonds in amorphous hydrogen rich boron/carbon (a-B/C:H) films by electron probe microanalysis. The films were deposited on Si single crystals by plasma chemical vapour deposition with a precursor-carborane (C₂B₁₀H₁₂) in a laboratory setup. A film thickness and B/C ratio up to a value of 8000 Å and 4, respectively, have been obtained. The analysis of boron and carbon X-ray emission spectra has shown that the nearest order in the films is characterized by the coexistence of C-C, B-C and B-B bonds for B/C 1 and of B-B and B-C bonds for B/C 4. After two years exposure in air the oxygen content in the films increases from 2–5 to 15–20 at.%.     

A spectroscopic study of atomic interactions in aryl derivatives of group iv elements

Spectroscopic features (quantitative IR, Raman, and UV spectra) are discussed for group IV (M=C, Si, Ge, Sn) aryls, mainly R₃MC₆H₅ and R₃MCH₂C₆H₅, in order to distinguish features of the intramolecular interactions. Confirmation is obtained for the existing view on the electron-acceptor behavior of heteroatoms joined to aromatic rings. The effect is seen in the IR and UV spectra, which implies that the ground and excited states are perturbed. The effect of M on the ring is shown to be an over-all one; the positive (induction) component follows the electronegativity of M in a scale close to Gordy's, while the negative one increases somewhat from Si to Ge and Sn.The effects in M aryls are analogous to those in M alkenyls, in particular the - conjugation in a phenyl radical attached to Si, which is already known for M allyls.     

Analytical,structural and electrical characterization of SiGe layers by electron microbeam techniques

k-ratios of Ge-L and Si-K measured at different beam energies allow to evaluate simultaneously composition and thickness of SiGe layers on a Si substrate. A simple technique applying backscattered electrons also enables estimation of composition of bulk SiGe and of composition and thickness of relatively thick (200 nm) SiGe layers on Si. Electron channeling patterns of pseudomorphic SiGe/Si structures and of pure Si substrate show no significant differences whereas in relaxed structures a smearing of the pattern with increasing density of misfit dislocations is observed. Under particular conditions the technique of the electron beam induced current permits imaging of recombination-active misfit dislocations with a spatial resolution around 0.2 m. Moreover, a repulsion of holes due to the valence-band offset in a n-Si/SiGe heterostructure was detected.     

Structure and elemental composition of transparent nanocomposite silicon oxycarbonitride films

Based on thermodynamic simulation on the deposition of condensed phases with the complex composition in the Si–C–N–O–H system in a wide temperature range, using initial gas mixtures of 1,1,3,3-tetramethyldisilazane (HSi(CH₃)₂)₂NH (TMDS), TMDS with a variable mixture of oxygen and nitrogen (O₂+xN₂), a method is developed to obtain SiC _x N _y O _z :H nanocomposite films by the plasma chemical decomposition of this gas mixture in the temperature range of 373-973 K. By FTIR and energy dispersive X-ray spectroscopy the structure of chemical bonds and the elemental composition of the obtained silicon oxycarbonitride films are studied. The in situ composition of the initial gas phase in PECVD processes is examined by optical emission spectroscopy.     

Electronic Structure and Chemical Bonding in β-Sialons

Using the discrete variation procedure we investigated the electronic structure, charge distributions, and chemical bonding in solid solutions of variable composition based on -Si₃N₄ with Si substituted by Al and N substituted by O (the general composition ). The electronic processes at the initial stage of SiAlON formation were studied (x = 1, 2) considering different distributions of Al–O pairs in the lattice of -Si₃N₄. The distribution mode of the dopant is found to be a more significant factor affecting the electronic structure of sialons compared to increased Al–O content; in particular, clusterization of dopant pairs leads to increased forbidden gap and splitting of the upper and lower valence bands. The results of calculations are used to interpret the systematic variations in the functional properties of -sialons depending on their chemical composition.