Ternary Al_1-xCr_xN hard coatings show significantly increased hardness, wear and oxidation resistance compared to simple binary coatings like TiN or CrN. They are applied to e.g. metal cutting and forming tools at the industrial scale. A further improvement of friction properties is obtained by alloying Al_1-xCr_xN with V, which forms V₂O₅ layers at high-temperatures acting as solid lubricant. The tribological properties of hard coatings are strongly influenced by their structure and chemistry, i.e. phase composition, size and orientation of individual crystallites as well as oxidation and diffusion. Micro-Raman spectroscopy in general is limited to non-destructive analysis of lattice, size, defects, impurities and orientation of the respective crystallites of hard coatings at the µm scale. Combining the spectrometer with a piezo-autofocus, a heating stage and a motorized, computer-controlled X-Y stage enables coating analyses at room and elevated temperatures up to several hundred °C in three dimensions.

Newly grown phases and structural changes of coating and substrate within wear tracks produced by tribological ball-on-disk tests were identified. Electron microprobe X-ray distribution images combined with Raman mappings confirmed the presence of the iron oxides maghemite and hematite in the tracks. Colour coded Raman maps allowed unambiguously identification of coating and underlying substrate. High-temperature mapping at 700°C showed partly removed coating on silicon-wafer substrates due to stress and/or recrystallisation. Oxidations of Al-Cr-V-N coatings to V₂O₅ and AlVO₄ around 650°C were monitored "in situ". In conclusions, Raman mappings are a powerful tool for the analysis of advanced hard coatings in the process of their development.

Cadmium arsenide(Cd₃As₂) is one of the group of II-V semiconductors which posseses a high electron mobility µ_n of up to 1.0 - 1.5 m²V^-1s^-1. Potential applications include magnetoresistors, thermal detectors and photodetectors. Cd₃As₂ thin films may be prepared by thermal evaporation, but require further electrical characterisation over a range of deposition conditions. In previous work¹ it was observed that at high electric fields carrier excitation via the Schottky and Poole-Frenkel effects occurred, followed by destructive electroforming and breakdown effects at an electric field F_b of up to 5 x 10⁷ V m^-1. In the present work these effects are more fully explored. Films were deposited at rates of about 0.5 nm s^-1and with thickness in the range 0.2 - 1.2 µm onto substrates maintained at 293 K using planar Ag electrodes. Some samples were prepared with Al or Au electrodes and substrate temperatures of up to 393 K. At a specific voltage there was a catastrophic decrease in the current from typically several hundred to a few mA. The corresponding field was found to depend on the film thickness, and followed a relation of the form F_b = Ad^-b, where d is the film thickness and A and b are constants. For films with Ag electrodes deposited under the standard conditions a calculated value of b = 0.83 was obtained. Similar behaviour was identified previously in films with wider bandgaps. After the breakdown events the samples showed voltage-controlled differential negative resistivity (VCNR) in their current-voltage characteristics, with a peak current of several mA at an operating voltage of a few volts, characteristic of an electroforming process. It has previously been suggested that this type of process may result in the growth of nanowires within the semiconductor.

¹ M. Din and R.D. Gould, Thin Solid Films 340 (1999) 28-32.

Development of residual stress is an intrinsic phenomenon in thin film deposition experiments, and strongly influences the mechanical properties and stability of thin films.

TiNi films on silicon substrate produced by the magnetron sputtering technique were used to study the relationship between the most relevant deposition parameters and/or annealing conditions and the residual stress level. Mechanical stresses in TiNi films were evaluated from the measured curvature change using the Stoney equation. In situ wafer curvature was measured between room temperature and 530°C using a laser interferometer with an external thermo-chamber.

It was found that the properties of TiNi films could be linked to the residual stress magnitude, which in turn was strongly affected by the deposition process parameters, such as film composition, deposition temperature and working gas pressure. During annealing of as-deposited films, stress evolution is related to residual stress in as-deposited films; thermal stress; tensile stress due to densification crystallization; stress relaxation due to martensite transformation. The stress relaxation and generation behavior was significantly affected by Ti/Ni ratios, annealing temperatures and durations. It should be emphasized that independent from the deposition parameters and annealing conditions after the chemical removal of TiNi films, the silicon substrates return to the initial non deformed state. This result shows the elastic nature of their curvature.