Stefan Flege

Characterization of tellurium layers for back contact formation on close to technology treated CdTe surfaces

We have studied the contact formation on CdTe surfaces following the technologically applied procedure. The electronic properties of wet chemically etched CdTe surfaces has been investigated with photoelectron spectroscopy. For the characterization of the morphology, structure, and elemental distribution in the etched layer atomic force microscopy, scanning electron microscopy, grazing incidence x-ray diffraction, and secondary ion mass spectroscopy have been used. Etching of the samples has been performed in air and in an electrochemistry chamber directly attached to the UHV system. In both cases the formation of an elemental polycrystalline Te layer with a thickness of about 80 A is detected. For comparison, a thin Te layer has been deposited by physical vapor deposition onto a CdTe substrate. We determine a valence-band offset of ΔEVB=0.5±0.1 eV, independent of the preparation of the interface.

Preparation and Properties of Ag-Containing Diamond-Like Carbon Films by Magnetron Plasma Source Ion Implantation

The doping effect of silver on the structure and properties of diamond-like carbon (DLC) films was investigated. The samples were prepared by a process combining acetylene plasma source ion implantation (high-voltage pulses of −10 kV) with reactive magnetron sputtering of an Ag disc. A mixture of two gases, argon, and acetylene was introduced into the discharge chamber as working gas for plasma formation. A negative high-voltage pulse was applied to the substrate holder, thus, accelerating ions towards the substrate. The chemical composition of the deposited films was modified by the respective gas flows and determined using X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The silver concentration within the DLC films influenced the structure and the tribological properties. The surface roughness, as observed by scanning electron microscopy, increased with silver concentration. The film structure was characterized by Raman spectroscopy and X-ray diffractometry (XRD). The DLC films were mainly amorphous, containing crystalline silver, with the amount of silver depending on the process conditions. The tribological properties of the films were improved by the silver doping. The lowest friction coefficient of around 0.06 was derived at a low silver content.

Oxygen vacancy kinetics in ferroelectric PbZr0.4Ti0.6O3

Oxygen vacancy kinetics in ferroelectric PbZr0.4Ti0.6O3 were studied by oxygen18 (O18) tracer self-diffusion in epitaxial thin films as well as bulk polycrystalline samples. O18 exchange annealing was carried out at an oxygen partial pressure of 250mbar and temperatures between 250 and 400°C. Isotope depth profiling was performed by secondary ion mass spectrometry as well as neutral secondary mass spectrometry. The observed concentration depth profiles of the polycrystalline samples show two distinct diffusion paths, namely, bulk diffusion and grain boundary (GB) diffusion. It appears to be of type B-kinetics in the investigated temperature range, with DGB∕Dbulk⪢100. Donor doped samples with different levels of Nb5+ (1–4mol.%) were also investigated. The effect on the diffusion depth profiles, however, were negligible and can solely be attributed due to the change in the samples microstructure as induced by the dopants. A diffusion coefficient for the bulk diffusion of the O18 isotope, Dbulk=10±5×10−8cm2∕...

Temperature dependent properties of silicon containing diamondlike carbon films prepared by plasma source ion implantation

Silicon containing diamondlike carbon (Si-DLC) films were prepared on silicon wafer substrates by a plasma source ion implantation method with negative pulses superposed on a negative dc voltage. A mixture of acetylene and tetramethylsilane gas was introduced into the discharge chamber as working gases for plasma formation. Ions produced in the plasma are accelerated toward a substrate holder because of the negative voltage applied directly to it. After deposition, the films were annealed for 0.5 h in ambient air at temperatures up to 923 K in order to evaluate the thermal stability of the Si-DLC films. The films were analyzed by x-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy, and Raman spectroscopy. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The mechanical and tribological properties were investigated by an indentation method and a ball-on-disk test. The results show the si...

Untersuchung des Sputter‐Ätzens auf die Eigenschaften von PVD‐CrN Hartstoffschichten auf Magnesium AZ91hp

Eine gangige Methode, zu beschichtende Oberflachen von Verunreinigungen zu befreien und die Adhasionseigenschaften von PVD-Schichten zu verbessern, ist das sogenannte Sputter-Atzen vor dem eigentlichen PVD-Beschichtungsprozess. Beim Sputter-Atzen wird der Beschichtungsprozess umgekehrt und die Oberflache des Substrates selbst wird gesputtert. Im Rahmen dieser Veroffentlichung wurden vor der Abscheidung von PVD-CrN Schichten die Substrate der Magnesium Druckgusslegierung AZ91 unterschiedlichen Atzzeiten unterzogen und deren jeweiliger Einfluss auf die Grenzflache Schicht-Grundwerkstoff, auf die Schichtoberflache und auf die mechanischen Eigenschaften des beschichteten Systems hin untersucht. Die Grenzflachenuntersuchungen wurden mit tiefenaufgeloster XPS und mit SIMS durchgefuhrt. Die Oberflachen wurden mit hochauflosender Rasterelektronenmikroskopie und AFM untersucht. Die Charakterisierung der mechanischen Eigenschaften beinhaltet Schichtdicke, Schichtharte, Hartetiefenprofile, Schichthaftung, Schichteigenspannungen und die Schichtstruktur. Es wurden zum Teil sehr starke Eigenschaftsanderungen mit zunehmender Atzzeit festgestellt. Dies betrifft vor allem einige mechanische Eigenschaften sowie die Oberflachenrauheit der beschichteten Systeme. Beim Schichtsystem AZ91-Cr/CrN fuhren langere Atzzeiten zu einer Verbesserung der Schichtqualitaten. Investigating the Influence of the Sputter Etching Process on the Properties of PVD-CrN Coatings on Magnesium Die Cast Alloy AZ91hp A common method prior to the PVD deposition is the sputter etching process of the substrate itself to clean the surface from adhesion products and to improve the coating adhesion. This report deals with the sputter etching of magnesium die cast alloy AZ91hp to investigate the influences on the coating-substrate interface, the surface properties and the mechanical properties of PVD-CrN hard coatings. The coating-substrate interface of the Cr-AZ91 coating systems was investigated with XPS and SIMS. Surface studies were carried out by high resolution electron microscopy and AFM. The characterization of the mechanical properties of the CrN-AZ91 compound systems includes thickness, coating hardness and hardness depth profiles, coating adhesion, structure and residual stresses. Some properties show a strong dependency of the etching time, especially the mechanical properties and the coating roughness. Increasing etching times lead to an improvement of the coating quality.

Nano- and microstructured silver films synthesised by halide-assisted electroless plating

Electroless silver plating baths were modified with different amounts of chloride and bromide, and the effect on the deposition kinetics and the morphology of the resulting silver films was evaluated. The baths were based on silver nitrate and tartrate as the metal source and the reducing agent. Ethylenediamine was used as the complexing agent to suppress silver halide precipitation. With increasing halide concentration, a reduction in the deposition rate and a decreased tendency towards three-dimensional nucleation was found. Bromide affected the plating reaction more strongly than chloride. The deposit morphologies range from coarse-grained, compact particle aggregates over bimodal structures composed of island-like microparticles and smaller particles of varying geometry to shape-controlled films dominated by plates with a triangular or hexagonal shape. The fabrication of silver films of adjustable micro- and nanostructure is relevant for various applications such as heterogeneous catalysis, sensing and plasmonics. As an example for structural tailoring enabled by the outlined reaction system, we created a biomimetic, self-cleaning coating possessing a static contact angle of 165 ± 3° and a tilt angle of <3°. To this end, a hydrophobic metal surface was designed which exhibits a superimposed roughness on the micrometre and submicron scale. The former was defined by the silver deposition, the latter by consecutive galvanic replacement. To achieve superhydrophobic properties, the metal surface was coated with an alkanethiol self-assembled monolayer.

Synthesis and Characterization of (Na0.5K0.5)NbO3 (NKN) Thin Films Formed by a Diol-based Sol-gel Process

Lead-free (Na 0.5 K 0.5 )NbO 3 (NKN) thin films were fabricated by spin coating on Pt/Ti/SiO 2 /Si substrates by a diol-based sol-gel process. Na-acetate, K-acetate, Nb-pentaethoxide and 1,3 propanediol were used to prepare the NKN precursor solution. Thermal analysis showed two characteristic temperatures of 360 and 600 °C. Based on these temperatures, a heat treatment program with pyrolysis at 360 °C and calcination at 600 °C after every layer was used. To avoid inhomogeneities and secondary phases, an excess of sodium and potassium was necessary. To evaluate the proper excess amount of sodium and potassium secondary ion mass spectrometry (SIMS) lateral element maps and X-ray diffraction (XRD) patterns were recorded. An excess amount of 20% led to homogeneous distribution of the elements and to single phase perovskite NKN films with random crystal orientation. Scanning electron microscopy (SEM) images showed a pore free surface with 100 nm grains. The leakage current measurements showed a current of 1×10 −3 A/cm 2 at 150 kV/cm.

Nondestructive characterization of nanoscale layered samples

Multilayered samples consisting of Al, Co and Ni nanolayers were produced by MBE and characterized nondestructively by means of SRXRF, μ-XRF, WDXRF, RBS, XRR, and destructively with SIMS. The main aims were to identify the elements, to determine their purity and their sequence, and also to examine the roughness, density, homogeneity and thickness of each layer. Most of these important properties could be determined by XRF methods, e.g., on commercial devices. For the thickness, it was found that all of the results obtained via XRR, RBS, SIMS and various XRF methods (SRXRF, μ-XRF, WDXRF) agreed with each other within the limits of uncertainty, and a constant deviation from the presets used in the MBE production method was observed. Some serious preliminary discrepancies in the results from the XRF methods were examined, but all deviations could be explained by introducing various corrections into the evaluation methods and/or redetermining some fundamental parameters.

Deposition of Diamond-Like Carbon Films on Inner Wall Surfaces of Millimeter-Size-Diameter Steel Tubes by Plasma Source Ion Implantation

Diamond-like carbon (DLC) film deposition on the interior surfaces of steel tubes was carried out by plasma source ion implantation. SUS304 austenitic-type stainless steel tubes with inner diameters of 9, 5, and 4 mm were used as substrate tubes. Acetylene was the working gas for the plasma that was generated by applying a negative pulse voltage of -18 kV to the substrates. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The composition within the film and at the interface was examined by depth profiling with Auger electron spectroscopy and secondary ion mass spectrometry. The film structure was characterized by Raman spectroscopy. The friction coefficient of the untreated substrate and the DLC films was evaluated by a reciprocating sliding test. The DLC film surfaces were smooth, and no special structure was observed on the surface. The DLC film thicknesses, structure, and composition on the interior surface of the steel tube depend, on the one hand, on the gas and pulse conditions and, on the other hand, on the distance from the end of the tube, as well as on the diameter of the tube. A low friction coefficient of 0.2 was derived for the deposited DLC films.

PVD‐CrN Beschichtungen auf Magnesium AZ91hp und Stahl 100Cr6 – Untersuchung des Substrateinflusses auf die Schichteigenschaften

An PVD-Chromnitrid beschichteten Proben der Magnesiumlegierung AZ91hp und dem Walzlagerstahl 100Cr6 wurden vergleichende Untersuchungen hinsichtlich Struktur, mechanischen Eigenschaften, Haftfestigkeit und Eigenspannungen durchgefuhrt. Fur die Beschichtungen wurden die Parameter Schichtdicke und Substrat-BIAS variiert. Beide Substratwerkstoffe wurden in einer Charge zusammen beschichtet. Bei der rontgenographischen Analyse der Eigenspannungen in den Schichten zeigten sich signifikante Unterschiede zwischen dem beschichteten Magnesium und dem beschichteten Stahl. Beim Stahl war eine Abhangigkeit der Eigenspannungen vom Substrat-BIAS erkennbar, beim Magnesium war dies nicht der Fall. Die Schichtstruktur wurde im Rasterelektronenmikroskop untersucht. An den beschichteten Substraten wurden mit SIMS Element-Tiefenprofile aufgenommen. PVD-CrN coated magnesium alloy AZ91hp and steel 100Cr6 – Investigation on the influence of the substrate material on coating properties PVD-chromium-nitride coated samples of substrates of the magnesium alloy AZ91hp and the roller and ball bearing steel 100Cr6 were investigated regarding structure, mechanical characteristics, adhesion and internal stresses. For the coatings the parameters layer thickness and substrate BIAS voltage were varied. Both substrate materials were coated in one lad. Results of the x-ray analysis of the internal stresses show significant differences between the coated magnesium and the coated steel substrates. In the case of the variation of the substrate BIAS voltage, for the coated steel a dependency of the internal stresses to coating parameters could be obtained. For the coated magnesium no dependency was recognizable. The coating structure was examined with scanning electron microscopy. Element depth profiles of the coated samples were performed with SIMS.