X-Ray and Electron Diffraction Studies of As-Deposited Rf Sputtered Thin Films of IrO 2
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EXPERIMENTAL The Iridium oxide films were produced by d.c. magnetron reactive sputtering of an Ir target in an argon:oxygen atmosphere. Details of the sample preparation and characterization procedures have been reported elsewhere [4]. In addition, Electron Probe Microanalysis on a typical sample showed negligible contamination and, within the accuracy of the technique, gave the stoichiometry of IrO2 . Single crystal Si, A12 0 3 , MgO and NaCl were used as substrates with the substrate temperature being held to approximately 400 C using a temperature controlled heat sink during the deposition process. As-deposited SIROF's made using similar methods have a density of -~1g/cm-3 [2]. Film thicknesses (t) were found by stylus measurements and in the study reported here ranged from 1 to 101gm. All the films were strongly adhered to their substrates (excepting those deposited on NaCI substrates). The crystalline rutile powder sample was 99.99% of purity with respect to metallic impurities and was supplied by Aldrich. For the diffraction measurements itwas pressed into a 0.5mm thick pellet. The x-ray diffraction experiments were performed on a Rigaku 2-circle diffractometer with a sealed tube source and a graphite (002) monochromator. Measurements were taken using Mo Kox and Cu Ka radiation with wavelengths of X=0.7098A and 1.54188A, respectively. The Transmission Electron Mircoscopy (TEM) measurements were made with a JEOL 2000FX operated at 200keV. Diffraction pattems were recorded both in conventional selected area (SAD) mode and microdiffraction mode. Several high resolution images were also recorded. Suitable pieces of a film deposited on a NaCI substrate were chosen for these measurements. RESULTS The x-ray patterns for the films on all of the substrates were essential the same. Due to the
presence of exposed substrate and a film thickness of 1l.m thick for the sample deposited on the NaCI strong substrate scattering was observed. This made quantitative measurements from this sample difficult. The patterns presented here were taken from a 10;.im thick film deposited on a sapphire (A1 2 0 3 ) substrate using the Cu x-ray source. In this case the value of Itt, where gt is absorption coefficient, was high enough to neglect substrate scattering. The data taken with Mo radiation showed continuous "diffuse" scattering to beyond Q(=4rsin0/?)=l 0A-1. The x-ray diffraction pattern for the sputtered film, shown in Fig. 1, has peaks at approximately the positions for the reported rutile powder pattern [7]. The profile of the first peak could be approximated to a Lorentzian with a full width at half maximum (FWHM) A 0=0.1 7P1. The Scherrer equation may be used to get a particle size: 0(20) = 0.94k / Lcos0
(1)
where 0(20), the FWHM in the scattering angle, was used to estimate the particle size L=34A. Grain sizes for the films on all of the substrates were inthe range 25A to 35A. In the case of the films deposited on NaCI, the widths of the IrO2 peaks between the substrate Bragg peaks was consistent with this small particle
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