Effect of Processing Parameters on the Chemistry of Magnetron Sputtered Ti-Al Thin Films
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temperatures about 1100K. 7 They are potentially light weight and heat-resistant materials for future structural applications in space technology.8 The properties of Ti 3AI thin films are strongly dependent on the deposition technique and its process parameters. In this paper dc-sputtering technique is used for the fabrication of TiAI thin films on 316-L stainless steel substrate. Ti3AI thin films were deposited at varying sputtering parameters such as plasma power and the argon flow rate. The surface morphology (scanning electron microscopy (SEM)), thin film surface chemistry (X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES)) and mechanical properties were analyzed as a function of sputtering power. Finally, a cold trap experiment was tried to observe any physical/chemical property changes between depositions at room and liquid nitrogen temperature. EXPERIMENTAL Single layers of Ti 3AI were deposited from a Ti (70%): Al (30%) target by a conventionally built DC planar magnetron sputtering system onto I"x 1/2" rectangular 316 type stainless steel substrates at ambient temperature. The stainless steel substrates were mechanically polished to ensure large number of nucleation sites and a better adhesion of the film. Small strips of 7059 Corning Glass of the same dimensions were also employed as substrates for measuring the film thickness. The sputtering conditions were: (i) power - 83, 120, 175 watts, (ii) deposition time - 1 hour, (iii) background pressure - 5 x 10-5 and (iv) argon flow rate - 7.5 - 15 sccm. The micro-Vickers hardness of the films was measured under a constant load of 25mN and a holding time of 10-15 s at room temperature. Film thickness was measured using an optical interferometer. For structural identification, x-ray diffraction was performed on a conventional Rigaku D/max-2400 diffiractometer using a Cu Ka radiation equipped with a monochromator. Surface chemical analysis was performed using a 5400 PHI ESCA (XPS) spectrometer having a base pressure of 1010 torr using AlKoc X-radiation (1486 eV, line width 0.7 eV) with a power of 350 watts. The spectrometer scale was calibrated using gold (4f 7 2 ) = 84 + 0.2 eV. The charging shifts produced by the insulating oxide samples were removed by using a binding energy scale by fixing the C (Is) binding energy of the hydrocarbon part of the adventitious carbon line at 284.6 eV.9 Non linear backgrounds were removed from the spectra using a method described by Sherwood.10 Non-linear least square curve fitting was performed using a Gaussian/Lorentzian peak shape,1'0 11 which include x-radiation satellites in the fitting routine. Additionally, variable take-off angle XPS has been utilized to obtain information on depth distribution of the thin film atomic concentrations. Sputter depth profiling was carried out using a PHI 600 Scanning auger microprobe by sputtering the thin films by high purity (99.999%) argon ions. The following ion gun parameters were used during etching: ion beam energy 3 keV, emission current 25 mA. The cold tr
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