ICMCTF2000 Session F3-2: Surface and Thin Film Analysis

Recently a phase, known as 'S phase', based on an alloy of austenic stainless steel and nitrogen, has shown potential for simultaneously improving wear and corrosion resistance. Stainless steel coatings were deposited on low carbon steel and mono-crystalline silicon substrates by DC-magnetron sputtering in a reactive atmosphere of nitrogen. The total mass flow of argon and nitrogen was kept constant (20 sccm) for all depositions and the nitrogen mass flow was varied between 0 and 10 sccm with increments of 1 sccm while argon mass flow was decreased for the same amount.

The elemental composition of coatings and the deposition rates were studied by Rutherford backscattering (RBS), by X-ray emission induced by charge particles (PIXE) and by nuclear reactions (NRA). The nitrogen content is found to increase with increasing mass flow up to saturation value of 45 atomic percent.

A structural analysis by means of conversion electron Mössbauer spectroscopy (CEMS) and grazing incidence X-ray diffraction (GXRD) was also performed. The results indicate that the lattice expands as the nitrogen mass flow increases and that this expansion is caused by the incorporation of nitrogen into interstitial sites. Moreover, the presence of the so-called S-phase is detected. The latter is probably due to nitrogen in solid solution at vacancies in the stainless steel. This phase is particularly interesting for industrial applications because it increases the resistance to wear without compromising the corrosion resistance of the steel.

The optical and electrical properties of ITO films are found to be sensitive to preparation conditions. The sol-gel method is an attractive one due to the ability to coat on large areas and easy control of the doping level without using expensive and complicated equipment when compared with other methods. In general, the sol-gel process uses metal alkoxides as raw materials, but it is expensive to obtain indium and tin alkoxides, therefore we prepared ITO thin films from the sol-gel process using metal salts as raw materials and organic solvents. The films have been deposited onto glass substrates from a starting solution prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. ITO thin films containing 0-20 mol % SnO₂ were successfully prepared by heat-treatment at above 400⁰ C. The resistivity of ITO films has been minimised by optimizing the amount of tin doping.

The electrical, optical and structural properties of ITO thin films were investigated. The thickness of ITO film was measured by ellipsometer. The electrical resistivity was measured by using four-point probe method. The ITO thin films containing 10 mol % SnO₂ showed the minimum resistivity of 1.5 X10-3 ohm-cm. Transmittance of ITO thin films were measured by a UV-vis spectrometer. The ITO film has high transmittance above 80 % over the wavelength range 400 to 900 nm and has an absorption edge at 280 nm. This is high enough for applying ITO thin film as transparent electrodes. Grazing incidence X-ray diffraction showed that the sol-gel films heat treated up to 700⁰ C are polycrystalline with a cubic structure. XPS analysis has shown that Sn was incorporated into the In₂O₃ structure substitutionally.

X-ray absorption spectroscopy (XAS) has been widely used to study many different types of compounds and materials in gas, solid or liquid forms. This technique presents an obvious interest when the materials to be investigated have a poor crystallographic order or are amorphous. Depending on the deposition method and type of material, it is very often found that many thin films do not have a well-crystallised structure. In these cases XAS can be an interesting alternative for their structural characterisation.

This paper wants to give a general overview of the possibilities of this technique to study thin films and of the problems that may be encountered for its systematic use as a tool of thin film characterisation. Thus, it is recognised that a versatile and simple collection method of XAS spectra for thin films is the so called "conversion electron yield" (CEY) detection. The information depth provided by this method depends on the element to be investigated and on the type of constituent material of the film. From the calibration curves obtained for a series of oxide materials it can be concluded that thickness around 100 nm are typical for this type of analysis with oxide materials.

The possibilities of the XAS methodology for thin film characterisation are illustrated with a series of examples of nitrogen implanted layers and oxide thin films prepared by Ion Beam Induced CVD. This method consists of the bombardment of a suitable substrate with accelerated oxygen ions in the presence of a volatile precursor. As an effect of the ion bombardment, structural effects such as amorphisation, preferential growth of certain crystallographic planes, etc. can be induced in the films. The chosen examples illustrate the possibilities of XAS for a structural and chemical characterisation of the layers as an alternative and/or complement to the conventional X-ray diffraction technique (XRD). The advantages of using an approach based on these two techniques are clearly illustrated with the presented examples