Influence of oxygen flow on the microstructure, resistivity, and Faraday rotation of reactive RF sputtered NiO and Fe-doped NiO thin films
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The effect of oxygen flow during deposition on the crystallinity, resistivity, and magneto-optical properties was studied for reactive sputtered thin NiO and Fe-doped NiO films. A series of NiO and Fe-doped NiO samples with different oxygen concentration were made using the RF sputtering technique at room temperature on different types of substrates. In terms of deposition pressure two types of sample were made: one type was sputtered at -1mTorr and the other at -7-8mTorr. Film thickness and roughness were measured using the variable angle spectroscopic ellipsometry and the XRR technique. Thickness values determined with both techniques are found to be close to each other. From the XRD peak analysis of both type of samples crystal size was calculated using the Scherrer equation and the inhomogeneous micro-strain was calculated using the Stokes and Wilson approximation. A Pole Figure Analysis method which shows the dominating textures in the thin film was also done. A near surface analysis was done to get a true idea of the defects i.e. oxygen or metal vacancies in the thin films by using the Rutherford Backscattering Spectrometry (RBS). To measure the electrical properties, specifically the resistivity, the four-point probe method was used. The magneto-optical (MO) hysteresis loop were measured to determine the magnetic properties of the films. The MO Faraday data on the samples confirm preliminary results obtained by Twagirayezu using VSM  on these types of samples. As the magnetic signal on these samples was expected to be very small if at all present, a large effort was spent on improving the magneto-optical measurement setup. A thorough analysis was done to better understand the Fabry-Perot interference in the Photo-elastic modulator (PEM) and the effect on the measurement method.
When using a Photo-elastic modulator (PEM) in combination with a coherent light source, in addition to the modulation of the phase, Fabry-Perot interference in the PEM's optical head induces large offsets in the 1ω and 2ω detector signals. A Jones matrix which describes both the phase and amplitude modulations simultaneously, was derived and used to find an expression for the detector signal for two different MO Kerr setups. The effect of the PEM tilt angle, polarizer angle, analyzer angle, and retardation, on the detector signal offsets show that offsets can be zeroed by adjusting PEM tilt angle, polarizer angle, and retardation. This strategy will allow one to avoid large offset drifts due to the small retardation, intensity, and beam direction fluctuations caused by lab temperature fluctuations. In addition, it will enable one to measure in the most sensitive range of the lock-in amplifiers and to adjust measurement parameters to optimize S/N ratio.