SNMS Depth Profiling Research Articles

Evolution of concentration profiles in Pd–Cu systems studied by SNMS technique

Interdiffusion in polycrystalline Pd–Cu thin film system was investigated in the temperature range of 120–310 °C, by means of SNMS depth profiling technique. Depending on the annealing parameters, an almost complete homogenization was detected even at temperatures, where the volume diffusion was frozen in. In the Pd layer, the detected Cu profiles and their time evolution were typical C-kinetic regime grain boundary profiles at short annealing times. Because of the much higher grain boundary diffusivity on the Cu-rich side, the saturation of Cu grain boundaries is reached in very short times. In Pd-side, from the time evolution of C-type depth profiles, we determined the Cu grain boundary diffusion coefficients at different temperatures. The high concentration level in Cu-side could be interpreted supposing moving boundaries that leave behind regions with high Pd concentration.Though the intermetallic phase formation in this system under similar conditions was proved, the shape of our depth profiles does not show any effects of a reaction layer formation near the original interface. Our findings remain compatible with the previous results, if we suppose an unconventional type of growth mode: phase formation takes place in and around grain boundaries, by means of transport along moving grain boundaries/interfaces.

Analysis of Co/Cu multilayers by SNMS reverse depth profiling

The overall quality of multilayer thin films prepared by electrodeposition could strongly be influenced by the surface and interface roughness. The roughness, however, may increase with the number of layers. For that very reason the reliable analysis of the first few layers is essential. However, in depth profiling methods based on sputtering techniques the first layer is always found at the bottom of the sputter crater. Since the depth resolution might decrease during sputtering, the analysis of the first few layers is often very difficult. In order to circumvent this problem, we performed SNMS depth profiling in the direction from the substrate. We prepared thin film samples in two ways. First, Co/Cu multilayer stacks were electrodeposited on Si/Cr/Cu substrates and SNMS depth profiling was carried out from the direction of the topmost layer. Secondly, electrodeposited Co/Cu multilayer stacks were coated with a few microns thick Ni layer and detached from the Si substrate in order to study the film structure from the side of the substrate. Using this latter method, which we denote as “reverse depth profiling”, we were able to analyze the first and, probably, the most even layers of the thin film structure with high resolution.

Lithium self-diffusion in some heavy metal fluoride glasses

Li self-diffusion has been studied below T g in a series of ZrF 4–BaF 2–LaF 3–LiF glasses with LiF contents of 10, 20, and 30 mol%, respectively. The D Li ∗ values range between about 10 −12 and 10 −15 cm 2/s and increase with increasing LiF content from 10 to 20% by two orders of magnitude. The stable isotopes 6Li (enriched) and 7Li and an SNMS depth profiling were used. For the precision of the diffusion data an anhydrous vacuum deposition of the 6Li tracer on the highly reactive glass surfaces was essential. In the glass with 30 mol% LiF no Li mobility could be determined yet with the present diffusion method. The Li diffusion is discussed and it is tried to understand why it displays a differing behaviour compared to that of the Na diffusion in respective NaF-containing glasses.

Diffusion of Ga and In in Sequentially Prepared Cu(In, Ga)S2 Thin Films for Photovoltaic Applications

AbstractThis contribution investigates the diffusion of In and Ga in Cu(In1-xGax)S2 thin film absorbers for photovoltaic applications. Sequentially prepared Cu-rich CuGaS2/CuInS2thin film diffusion couples have been annealed at temperatures in the range of 500°C to 600°C. Annealed samples have been examined by XRD and SNMS depth profiling. It was found that despite significant interdiffusion of Ga and In the bilayer retains its two phase structure of two layers of almost homogeneous composition, where the composition of these layers depends on the annealing temperature. Furthermore the interdiffusion process is less effective if the binary copper-sulfide phase is removed before annealing. On the basis of a tentative two dimensional diffusion model, which includes rapid diffusion along path ways of high diffusivity, the Ga-depth distribution could be modeled by numerical fits of calculated XRD-spectra to the experimental data. CuS is proposed as a possible pathway for rapide In-Ga interdiffusion.

Ag-doped double-sided PLD-YBCO thin films for passive microwave devices in future communication systems

Pulsed laser deposited (PLD) Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films on both sides of 3-inch diameter sapphire wafers are used routinely for development of microwave filters for future communication systems. The reproducibly deposited YBCO:Ag films of about 250 nm thickness show critical current densities of 4 MA/cm/sup 2/ at 77 K and laterally homogeneous maps of microwave surface resistance R/sub s/ of about 45 m/spl Omega/ at 145 GHz and 77 K measured by an open resonator technique. The R/sub s/ at 8.4 GHz and 77 K determined in the center position of the YBCO:Ag films with a sapphire resonator technique remains constant at about 380 /spl mu//spl Omega/ up to a microwave surface magnetic field of 7-10 mT. Correlations of transport and microwave properties to the film microstructure are shown in terms of in-plane epitaxy, size of particulates on the films, and composition ratios Cu/O and Y/O, and growth defects like stacking faults as shown by Raman spectroscopy, SEM, and SNMS depth profiling, and TEM cross sections, respectively. The optimum Ag-content of the PLD-YBCO target was determined to be about 4 weight -%. The results demonstrate that Ag-doping supports the PLD process for YBCO in terms of reliability and cost effectiveness.

Formation and development of aluminium inhibition layers during galvanizing/galvannealing

Inhibition layers formed in zinc baths with aluminium levels and immersion times relevant to commercial continuous strip galvanizing and galvannealing have been studied. The changes in layer thickness and composition, as a function of immersion time, have been studied using the novel application of SNMS depth profiling. This approach has allowed to study the growth kinetics of the inhibition layer. Interesting information has been collected on the distribution of various elements which influence the quality of the coating layers.

Improved Ti1–xAlxN PVD Coatings for Dry High Speed Cutting Operations

Titanium aluminium nitride (Ti1–xAlxN) has been shown to enhance the performance of cutting tools in dry, high speed machining of cast iron and die steels when compared with TiN and TiCN coatings. The ultimate benefit of Ti1–xAlxN coatings depends on two main criteria: the microroughness of the coating surface has to be minimised, and the oxidation resistance has to be maximised. The microroughness is governed by the choice of deposition method whereas the oxidation resistance is controlled by the composition of the coating. In particular, the generation of macroparticles during the PVD process has to be suppressed and the Al content of the film metallic constituents has to be kept between 40 and 60 at.-%. To achieve these demands supplementary to excellent adhesion, a PVD deposition process has been developed based on combined steered arc and unbalanced magnetron sputtering techniques. Using Cr in the steered arc sustained metal ion etching process the desired adhesion criteria may be exceeded and the surface roughness is kept as low as Ra = 0·04 μm. Unbalanced magnetronsputtering takes place from 50: 50 (at.-%) TiAI alloy targets. Further improvement has been achieved by incorporation of 3 at.-%Cr and, in particular, about 2 at.-% Y into the TiA1N coating, leading to an optimised film composition of Ti0·42Al0.53Cr0.03 Y0.02N. Cross-sectional TEM analysis, SNMS depth profiling, and thermogravimetric evaluation reveal grain refinement, interface stabilisation, and reduced oxidation at temperatures up to 950°C. These coatings allow enhanced dry drilling performance in GG 25 grey cast iron at a cutting speed of 60 m min–1 and feed of 0·2 mm rev–1, and dry milling of 56 HRC die steel with a 300 m min–1 (12000 rev min–1) cutting speed and linear feeds up to 6 m min–1, with a total lifetime of more than 20 h for this latter application.

Plasma SNMS investigations on powder metallurgical Cr and Ti-48Al-2Cr after oxidation in air and 15 N 2 / 18 O 2 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 Y 2 O 3 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 15 N 2 / 18 O 2 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.

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-Tc 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.

RTA-Treated Ohmic Contacts To GaAs Containing WSiN Barriers

AbstractFor III-V device operation at 300 °C or above ohmic contacts have to consist of multilayered systems comprising an amorphous diffusion barrier. The contact system Au/Pt/Ti/WSiN/ Au/Ge/Ni-n-GaAs (n ≈ 5.1017 cm−3) has been developed and optimized with respect to the parameters of the barrier as well as the internal Au/Ge/Ni layers. The WSiN layer was deposited via reactive dc magnetron sputtering, the other layers by electron beam evaporation without breaking the vacuum. Annealing has been performed in a halogen lamp furnace. The contact resistance Rc as determined by TLM structures was measured as function of the annealing temperature and time. It was found that short-time annealings lead to a broad Rc minimum at 0.1 ωmm. For such Rc's the Au/Ge/Ni layer thicknesses must be ≥ 20/10/6 nm. Extended microstructural analysis was accomplished by XTEM/EDS and by AES and SNMS depth profiling. The typical alloying depth of the contact in the GaAs has been found to be about 50 nm, i.e. smaller than for the conventional Au/Ni/AuGe contact. The secondary phases formed (Au(Ga), NiGe(As)) are similar. With annealing conditions producing the desired Rc value, both Au(Ga) and NiGe(As) were observed in a bamboo-like arrangement at the metal-semiconductor interface. Degradation of Rc could be attributed to burying of the nickel-rich phases beneath gold-rich phases. This contact system is stable up to ≈ 300°C.

Theory and improvements for SNMS depth profiling with INA3

Optimization of SNMS depth profiling using the direct bombardment mode (DBM) is possible by improvement of the ion current density distribution, reduction of bombardment energy and independent choice of current density. A model for primary ion extraction is presented and ion current density distributions have been calculated for different sample holder arrangements. Using the simulation procedure optimal extraction conditions can be predicted for conventional arrangements and suggestions for new ones can be made. The best depth resolution has been obtained using a new extraction arrangement with an additional aperture.

Investigation of thin fluoride films for optical applications by surface analytical methods and electron microscopy

Impurity contents of loosely packed CaF2 and LaF3 films are analysed by SNMS depth-profiling. On the basis of TEM investigations a quantitative description of the structure of the films is given. The irreversibly incorporated oxygen contents of the films are nearly independent of the film structures. In contrast, the irreversibly incorporated carbon contents are proportional to the inner surfaces of the loosely packed films and to the C-contaminations of appropriate surfaces of compact fluoride samples. It is concluded that the irreversibly incorporated C covers the grain surfaces and the irreversibly incorporated O is located preferably within the grains.

Transformation of amorphous glassy metal/zirconium alloys into CO2 hydrogenation catalysts: an XPS, SIMS, and SNMS investigation

Active catalysts for hydrogenation reactions starting from CO2 have been obtained from amorphous Cu70Zr30, Au25Zr75, Pd25Zr75 and Ni64Zr36 alloys. During in situ activation of these metallic glasses, oxidation and segregation phenomena are occurring, which lead to dispersed metal/zirconia catalysts. A combination of XPS and SNMS depth profiling is applied to examine changes in the oxidation state, as well as in the relative concentrations of the metal and of the zirconium components. From the chemical shifts of the metal 3d/Zr3p doublets analyzed as a function of sputtering time, the removal of an inactive surface ZrO2 layer by Ar ion bombardment, and the concomitant appearance of metallic Zr are demonstrated. Experiments on model substrates with defined layer structures show that the interpretation of depth profiles is most straightforward from the SNMS data. For Au25Zr75 and Pd25Zr75, the ZrO/Zr ratio at sputtering equilibrium increases significantly during transformation of the precursors into the respective metal/zirconia catalysts. The Ni64Zr36 alloy is not fully activated under identical conditions of pretreatment, such that the composition of the original bulk alloy is reached after prolonged sputtering. In situ activation experiments with Cu70Zr30 reveal a pronounced surface enrichment of metallic copper during exposure to CO2 hydrogenation conditions.

Excimer Laser Induced Deposition of Bisrcacuo Htsc Thin Films and Buffer Layers -Depth Profiling by SNMS

ABSTRACTSecondary Neutrals Mass Spectrometry SNMS was used to investigate interdiffusion processes in laser deposited BiSrCaCuO HTSC thin films on various substrate materials. The in-situ deposition of epitaxial Bi2Sr2Ca1Cu2O8+x films requires a substrate temperature just below the decomposition temperature of the 2212 -phase of BiSrCaCuO. This high substrate temperature of about 850°C seems to be the reason for interdiffusion processes of BiSrCaCuO films and MgO(100), YSZ(100) and Si(100) with YSZ or SrTiO3 buffer layers as substrate materials. Therefore, Tc(R=0) of BiSrCaCuO films on silicon with buffer layer is not higher than 70 K at present. SNMS depth profiling gives a more detailed insight into interdiffusion phenomena than other analytical techniques.

InSb/CdTe heterostructures grown by MBE

InSb/CdTe heterostructures were grown by MBE, including a 10 layer “superlattice”. The structures were characterized by X-ray diffraction, van der Pauw measurements, and SNMS depth profiling. The interfaces widen because of interdiffusion and through the formation of an interface compound from the reaction of Te with the InSb surface. The interface compound is identified as strained InTe(II). The interfaces are still too wide for practical devices. Thermochemical analysis indicates that the reaction can be suppressed by applying a Cd overpressure. The diffusion of In and Sb in CdTe is very fast and will necessitate a MEE growth scheme at lower temperatures.

VAMAS surface chemical analysis technical working party—an overview of project objectives, progress and the requirements for further work

AbstractAn update for 1989 is given for the VAMAS Surface Chemical Analysis Technical Working Party. The overall programme now has 26 projects targeted to solve key problems in the enabling base of AES, XPS, SIMS, SNMS and sputter depth profiling. Increased coordination of projects is leading to stronger project databases. Eleven of the projects have involved round robins, and details are provided of results where the analysis is complete and of project leaders where new participants are invited.