Use of C60 cluster projectiles for sputter depth profiling of polycrystalline metals

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.     

High resolution depth profiling of non-conducting samples with SNMS

Beat-like signal modulations in sputter depth profiles of multilayer structures are shown to enable an estimation and the optimization of the homogeneity of the sputter erosion process. Using W-Si multilayer structures of 69 doublelayers with a thickness of 40 Å, it is shown that the high-frequency mode (HFM) of electron-gas SNMS (e^–-gas SNMS) for the analysis of insulators provides the same high depth resolution as the conventional direct-bombardment mode (DBM) of this technique.     

Ion-beam analysis of CuInSe<Subscript>2</Subscript> solar cells deposited on polyimide foil

CuInSe₂ (CIS) solar cells deposited on polyimide foil by the Solarion company in a web-coater-based process using sputter and evaporation techniques were investigated in the ion beam laboratory LIPSION of the University of Leipzig by means of Rutherford backscattering spectrometry (RBS) and particle-induced X-ray emission (PIXE) using high-energy broad ion beams and microbeams. From these measurements the composition of the absorber and the lateral homogeneity and film thicknesses of the individual layers could be determined on the basis of some reasonable assumptions. For the first time, quantitative depth profiling of the individual elements was performed by microPIXE measurements on a beveled section prepared by ion-beam etching of a CIS solar cell. Within the CIS absorber layer no significant concentration–depth gradients were found for Cu, In, and Se, in contrast with results from secondary neutral mass spectrometry (SNMS) depth profiling, which was applied to the same samples for comparison. Furthermore, both PIXE and SNMS showed the presence of a remarkable amount of Cd from the CdS buffer layer in the underlying absorber.     

A combination of atomic force microscopy and secondary ion mass spectrometry for investigation of AlxGa1?xAs/GaAs superlattices

Summary Atomic Force Microscopy (AFM) has been used to characterize the topography of crater bottoms obtained during Secondary Ion Mass Spectrometry (SIMS) investigations of an Al_0.35Ga_0.65As/GaAs multilayer system. A linear relation between the roughness of the bottoms, which leads to a drop in the dynamic range of the SIMS-signal and in the depth resolution, and the sputter depth of SIMS has been found. The topography found by AFM also supports a mechanism for the ripple formation proposed recently by W. H. Gries. AFM imaging of cleaved cross sections through this multilayer system allowed to determine evenness and thickness of individual layers, which opens up the possibility to improve the depth scale for sputter techniques like SIMS.     

Depth profile analysis of thin film solar cells using SNMS and SIMS

SNMS (sputtered neutrals mass spectrometry) and SIMS (secondary ion mass spectrometry) are used for the depth profile analysis of thin film solar cells based on amorphous silicon. In order to enhance depth resolution, model systems are analyzed only representing parts of the layered system. Results concerning the TCO (transparent conducting oxide)/p interface and the n/i interface are presented. To minimize matrix effects, SNMS is used when the sample consists of layers with different matrices. Examples are the TCO/p interface (where the transition lengths of the depth profiles are found to be sharper when ZnO is used as TCO compared to SnO₂) and SnO₂/ZnO interfaces in coated TCO layers (where a Sn contamination inside the ZnO layer is found depending on the plasma pressure during the ZnO deposition). SIMS is used when the limits of detection reached by SNMS are not sufficient. Examples are H depth profiles in ZnO layers or P depth profiles near the n/i-interface.     

Quantitative depth profile analysis of high-Tc-superconductors with sputtered neutral mass spectrometry (SNMS)

Summary SNMS, a new surface sensitive as well as a bulk analysis technique, has been applied to the quantitative compositional depth profiling analysis of conductive and insulating thin films. Its performance is demonstrated by investigation of YBCO superconductor bulk analysis and sputter deposited layers on single crystalline substrates of SrTiO₃ and Al₂O₃. A stable stoichiometric volume has been observed in bulk material and thin films respectively. Inside a range of 500 nm from the surface, the composition deviates strongly from the stoichiometric concentration of Y and Ba. Comparative measurements with a freshly cleaved piece of YBCO bulk material which was immediately loaded into the ultrahigh vacuum analysis chamber show constant and stoichiometric concentration of all faced elements (Y, Ba, Cu, O) from the beginning of surface etching. The ratio of Y to Ba and Cu varied by less than 2%, the ratio Cu to oxygen by less than 5% from the nominal composition 1-2-3 (4).

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Quantitative Tiefenprofilanalyse von HT_c-Supraleitern mit SNMS

     

Atom probe mass spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O₂⁺ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.     

Depth profiling of Irganox‐3114 nanoscale delta layers in a matrix of Irganox‐1010 using conventional Cs+ and O2+ ion beams

Depth profiling of an organic reference sample consisting of Irganox 3114 layers of 3 nm thickness at depths of 51.5, 104.5, 207.6 and 310.7 nm inside a 412 nm thick Irganox 1010 matrix evaporated on a Si substrate has been studied using the conventional Cs⁺ and O₂⁺ as sputter ion beams and Bi⁺ as the primary ion for analysis in a dual beam time‐of‐flight secondary ion mass spectrometer. The work is an extension of the Versailles Project on Advanced Materials and Standards project on depth profiling of organic multilayer materials. Cs⁺ ions were used at energies of 500 eV, 1.0 keV and 2.0 keV and the O₂⁺ ions were used at energies of 500 eV and 1.0 keV. All four Irganox 3114 layers were identified clearly in the depth profile using low mass secondary ions. The depth profile data were fitted to the empirical expression of Dowsett function and these fits are reported along with the full width at half maxima to represent the useful resolution for all the four delta layers detected. The data show that, of the conditions used in these experiments, an energy of 500 eV for both Cs⁺ beam and O₂⁺ beam provides the most useful depth profiles. The sputter yield volume per ion calculated from the slope of depth versus ion dose matches well with earlier reported data. Copyright © 2013 John Wiley & Sons, Ltd.     

Multilayer thin-film coatings based on chromium nitride and aluminum nitride: Comparative depth profiling by secondary ion mass spectrometry and glow-discharge optical emission spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O ₂ ⁺ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.     

A statistical approach to delta layer depth profiling

We present a simple statistical model describing the removal and relocation of material during a sputter depth profiling experiment. All input parameters are determined from low‐fluence molecular dynamics simulations, making the model de facto parameter free. The model can be used to extrapolate data from the molecular dynamics simulations to projectile fluences relevant to sputter depth profiling experiments. As a result, the erosion of the surface is calculated in terms of fluence‐dependent filling factors of different sample layers. Using input data determined for the 20‐keV C₆₀ cluster bombardment of silicon, it is found that a steady‐state erosion profile is reached after removal of approximately 20 monolayer equivalents of material. Plotting the contribution of particles from a specific layer to the instantaneous sputtered flux, one can directly determine the delta layer response function predicted from such a model. It is shown that this function can be parameterized by the semiempirical Dowsett response function, and the resulting fitting parameters are compared with published depth profile data. The model is then used to study the role of different processes influencing the observed depth resolution. We find that the statistical nature of the sputtering process suffices to explain many features of experimentally measured delta layer depth profiles. Copyright © 2012 John Wiley & Sons, Ltd.     

Optimization of large area pulsed laser deposition of YBaCuO thin films by SNMS depth profiling and rutherford backscattering

The scaling up of established deposition techniques like pulsed laser deposition (PLD) to larger substrate diameter is a main condition for the technological application of high-T_c superconducting (HTSC) thin films. SNMS depth profiling and RBS have been used to control the homogeneity of film thickness and stoichiometry of Au/YBaCuO/CeO₂ thin film systems deposited on 3-inch sapphire wafers by PLD. A systematic dependence has been found for the relative SNMS sensitivity factors (RSF) on the structural state of YBaCuO. Therefore, a calculation of the composition of the epitaxial YBaCuO thin films is not possible using RSF determined from polycrystalline YBaCuO target material. The interdiffusion of thin films and substrate has been investigated in dependence on the deposition temperature by SNMS depth profiling. The obtained homogeneity of film thickness and stoichiometry over the entire 3-inch diameter proofs the suitability of PLD for in-situ deposition of 3-inch wafers by YBaCuO thin film systems for microwave applications.     

Plasma SNMS investigations on powder metallurgical Cr and Ti-48Al-2Cr after oxidation in air and 15N2/18O2 atmosphere

Oxidation experiments at 800°C and 900°C, partly in atmospheres enriched in isotope tracers, with subsequent SNMS depth profiling confirmed that two well-known oxidation mechanisms are also valid for the title materials: In powder metallurgical Cr, Y addition shows the reactive element effect, most completely by means of Y implantation and to a lesser extent by the addition of Y₂O₃ dispersion, classical fast Cr outward transport dominated kinetics is replaced by kinetics that is governed by slow inward diffusion of oxygen. In γ-TiAl with 2 at-% Cr, N is identified as the “frontline” oxidizing element being able to penetrate existing oxide and nitride layers inward towards the bulk metal. These results exemplify that the combination of plasma SNMS depth profiling with oxidation experiments, especially in ¹⁵N₂/¹⁸O₂ tracer atmosphere, and with reactive element implantation is an excellent method to obtain basic insights into corrosion mechanisms. Especially advantageous is the use of SNMS because of its much lesser matrix dependence compared to SIMS which has more frequently been used for this kind of experiments.     

Vertical random variability of the distribution coefficient in the soil and its effect on the migration of fallout radionuclides

In the field, the distribution coefficient, K _d, for the sorption of a radionuclide by the soil cannot be expected to be constant. Even in a well defined soil horizon, K _d will vary stochastically in horizontal as well as in vertical direction around a mean value. The horizontal random variability of K _d produce a pronounced tailing effect in the concentration depth profile of a fallout radionuclide, much less is known on the corresponding effect of the vertical random variability. To analyze this effect theoretically, the classical convection-dispersion model in combination with the random-walk particle method was applied. The concentration depth profile of a radionuclide was calculated one year after deposition assuming (1) constant values of the pore water velocity, the diffusion/dispersion coefficient, and the distribution coefficient (K _d = 100 cm^3.g^-1), and (2) exhibiting a vertical variability for K _d according to a log-normal distribution with a geometric mean of 100 cm^3.g^-1 and a coefficient of variation of CV = 0.53. The results show that these two concentration depth profiles are only slightly different, the location of the peak is shifted somewhat upwards, and the dispersion of the concentration depth profile is slightly larger. A substantial tailing effect of the concentration depth profile is not perceivable. Especially with respect to the location of the peak, a very good approximation of the concentration depth profile is obtained if the arithmetic mean of the K _d-values (K _d = 113 cm^3.g^-1) and a slightly increased dispersion coefficient are used in the analytical solution of the classical convection-dispersion equation with constant K _d. The evaluation of the observed concentration depth profile with the analytical solution of the classical convection-dispersion equation with constant parameters will, within the usual experimental limits, hardly reveal the presence of a log-normal random distribution of K _d in the vertical direction in contrast to the horizontal direction.     

Interaction of Pd-overlayers with SnO2: comparative XPS, SIMS, and SNMS studies

Summary We report about interaction processes between palladium (Pd) and tin dioxide (SnO₂) studied with various surface spectroscopic techniques. Total sputter yields necessary for absolute depth calibration in SIMS are determined for SnO₂. Clustering of palladium occurs at low temperatures. Small changes in the XPS relative core level intensities of Pd and Sn allow to determine cluster sizes. Oxidation of Pd in the presence of oxygen at T470 K is a prerequisite for diffusion of Pd²⁺ ions into SnO₂ layers. The latter process is confirmed and described quantitatively by evaluating the SIMS and SNMS measurements.     

Secondary ion mass spectrometry depth profiling of ultrathick films using an argon gas cluster source: Crater shape implications on the analysis area as a function of depth

Argon cluster ions have enabled molecular depth profiling to unprecedented depths, with minimal loss of chemical information or changes in sputter rate. However, depth profiling of ultrathick films (>100 μm) using a commercial ion source oriented at 45° to the surface causes the crater bottom to shrink in size because of a combination of the crater wall angle, sputter rate differences along the trailing-edge crater wall, and undercutting on the leading-edge. The shrinking of the crater bottom has 2 immediate effects on dual-beam depth profiling: first is that the centering of the analysis beam inside the sputter crater will no longer ensure the best quality depth profile because the location of the flat crater bottom progressively shifts toward the leading-edge and second, the shifting of the crater bottom enforces a maximum thickness of the film that could be depth profiled. Experiments demonstrate that a time-of-flight secondary ion mass spectrometry instrument equipped with a 20 keV argon cluster source is limited to depth profiling a 180 μm-thick film when a 500 μm sputter raster is used and a 100 μm square crater bottom is to be left for analysis. In addition, depth profiling of a multilayer film revealed that the depth resolution degrades on trailing-edge side of the crater bottom presumably because of the redeposition of the sputtered flux from the crater wall onto the crater bottom.     

Nonlinear optical (NLO) polymers. IV. Second‐order optical nonlinearity of NLO polyurea and copolyurea with NLO dipole moments aligned transverse to the main backbone

This article presents the molecular orientation and second‐order optical nonlinearity of newly prepared polyureas and copolyurea with dipole moments aligned transverse to the main backbone. Nonlinear optical (NLO) polyureas, TPU and TPU2, were prepared from 2,4‐diamino‐4′‐nitroazobenzene (2R‐DIAMINE) with 4,4′‐diphenylmethane diisocyanate (DMDI) and tolylene 2,4‐diisocyanate, respectively. NLO copolyurea was prepared from DMDI with 2R‐DIAMINE and m‐phenylene diamine. TPU and TPU2 gave d₃₃ values of 12.5 and 9.8 pm/V, respectively, under optimum poling conditions. A time‐dependent decay curve of second‐order nonlinear susceptibility was fitted well with a Kohlrausch–Williams–Watts stretched exponential function. The relaxation time of TPU2 was 4.2 × 10⁸ s at 100 °C. Copolyurea was uniaxially drawn in ratios of 1.5 and 2.0. The average molecular angles Φ_X , Φ_Y , and Φ_Z in three laboratory frames were evaluated from the refractive indices. Φ_Y decreased and Φ_X and Φ_Z increased with an increasing draw ratio. The dependence of the second‐order harmonic intensity on the incidence angle, that is, the Maker fringe pattern, was fitted with two independent tensor components, d₃₃ and d₃₁, for undrawn film and five independent tensor components, d₃₃, d₃₂, d₃₁, d₁₅, and d₂₄, for drawn films. For drawn films, Kleinman symmetry was not satisfied: d₃₁ ≠ d₁₅ and d₃₂ ≠ d₂₄. An increase in the draw ratio gave rise to a large increase in the tensor component d₃₃. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 247–255, 2001     

On nd bonding in the transition metal trimers: comparison of Sc3 and Y3

CASSCF/CCI calculations are presented for the low-lying states of Y₃. Comparison of the wave functions for Y₃ and Sc₃ indicates substantial 4d-5p hybridization in Y₃, but little 3d-4p hybridization in Sc₃. The increased 4d-5p hybridization leads to stabilization of 4d bonding with respect to 4d bonding for equilateral triangle Y₃, and also leads to 4d-5p bonding for linear geometries. These effects lead to a different ordering of states for equilateral triangle geometries and a smaller excitation energy to the linear configuration for Y₃ as compared to Sc₃.     

Zur Entwicklung der Oberflächenrauhigkeit während des Sputterns

Zusammenfassung Die zeitliche Entwicklung der Mikrorauhigkeit einer Oberfläche während des Sputterns wurde für verschiedene Größen der Oberflächendiffusionskoeffizienten untersucht. Das Modell berücksichtigt die Bedeckungsgradabhängigkeit der Diffusionsweglänge. Effekte der Korrelation zwischen Atomen beim Sputtern wurden diskutiert. Es wurde gezeigt, daß ab einem Schwellenwert des Oberflächendiffusionskoeffizienten die Tiefenauflösung nahezu konstant wird, statt mit der Quadratwurzel der Sputtertiefen anzuwachsen.

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The development of surface roughness during sputtering

Summary The time-dependence of the micro roughness of a surface during sputtering is investigated for various values of the coefficient of surface diffusionD _s using a model of a coverage dependent diffusion length. Effects of correlation between atoms within the sputtered layer are discussed. It is shown that beginning at a threshold value ofD _s the depth resolution of sputtering becomes a constant instead of being proportional to the square root of the sputter depth.

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Vorgetragen beim 10. Kolloquium über metallkundliche Analyse, Wien, 3.-5. November 1980. -Herrn Prof. Dr. Hanns Malissa zum 60. Geburtstag gewidmet.     

Improvement of the oxidation behavior of Ti1-xAlxN hard coatings by optimization of the Ti/Al ratio

The oxidation behavior of cubic Ti_1-xAl_xN films was improved by decreasing the Ti/Al ratio from 50/50 in the direction of the phase transition between cubic and hexagonal structure. Metastable, polycrystalline, single-phase Ti_1-xAl_xN films were deposited on high speed steel (HSS) substrates by reactive magnetron sputtering ion plating (MSIP). The composition of the bulk was determined by electron probe microanalysis (EPMA), the crystallographic structure by thin film X-ray diffraction (XRD). A Ti_1-xAl_xN film with a Ti/Al atomic ratio of 38/62 was deposited in cubic NaCl structure, whereas a further decrease of the Ti/Al ratio down to 27/73 led to a two-phase film with both cubic and hexagonal constituents. The Ti_0.38Al_0.62N film was oxidized in synthetic air for 1 h at 800?°C. The oxidic overlayer was analyzed by X-ray photoelectron spectroscopy (XPS) sputter depth profiling, EPMA crater edge linescan analysis, and secondary neutrals mass spectroscopy (SNMS). Scanning electron microscopy (SEM) micrographs of the cross sectional fracture were taken for morphological examination. With higher Ti content, the Ti_1-xAl_xN formed a TiO_2-x rich sublayer beneath an Al₂O₃ rich toplayer, whereas the oxide layer on the Ti_0.38Al_0.62N film consisted of pure Al₂O₃. The thickness of the oxide layer was determined to 60–80 nm, about a quarter of the oxide layer thickness detected on Ti_0.5Al_0.5N films. The absence of a TiO_2-x sublayer was also confirmed by XRD. The results show a distinct improvement of the oxidation resistance of cubic Ti_1-xAl_xN films by increasing the Al content from x = 0.5 to 0.62, whereas a further increase leads to the hexagonal structure, which is less suitable for tribological applications due to its tendency to form cracks during oxidation.     

Some recent developments in the surface-analytical application of X-ray fluorescence spectrometry

Summary Standard depth profiles of an analyte deposited into (diffusion or ion implantation) or on (thin-film deposition) a plane surface can be analyzed for profile type and centroid depth or film thickness by means of a standardless method in which the matrix-attenuated signals of the fiuorescing analyte measured at two different take-off angles are related to the mathematical distribution moments of the profile. For a binary thin film the element ratio can also be established. Results obtained on phosphorus profiles in silicon and on zinc sulphide optical coatings are referred to.The quantity or concentration level can be determined by use of a reference standard which may contain the analyte in an entirely different distribution. This simplifies the calibration of secondary reference standards.A good lateral resolution in the sub-millimeter range can be achieved with synchrotron radiation. A further improvement of lateral resolution is possible by direct excitation with electron microbeams, though at significantly inferior detection limits.

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Neuere Entwicklungen bei der oberflächen-analytischen Anwendung der Röntgenfluorescenz-Spektrometrie