FTIR Ellipsometry Study on RF sputtered Permalloy-Oxide Thin Films
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FTIR Ellipsometry Study on RF sputtered Permalloy-Oxide Thin Films
Md Abdul Ahad Talukder1, Yubo Cui1, Maclyn Compton1, Wilhelmus Geerts1, Luisa Scolfaro1, Stefan Zollner2 1 Department of Physics, Texas State University, San Marcos, TX 78666 2 Department of Physics, New Mexico State University, Las Cruces, NM 88003
ABSTRACT The optical properties of RF sputtered polycrystalline permalloy oxide (PyO) thin films were studied in the infrared by variable angle ellipsometry. The dispersion of PyO shows a Lorentzian dispersion peak at 381.5 cm-1. We attribute this peak to the transverse optical phonon of PyO. This peak is consistent with a rocksalt crystal structure for the Ni0.81Fe0.19O1-G thin films. INTRODUCTION The transition metal-oxides of Ni [1] and Fe [2] are currently being investigated for application in radiation-hard, low-energy, high-speed logic and resistive RAM devices (RRAM). Combining both oxides in a single device might allow in a mean to adjust atom mobility, morphology and texture, to optimize switching properties. We therefore investigate the properties of Fe doped NiO [3]. This material maintains the rocksalt crystal structure up to about 2 at. % at atmospheric pressure [4,5]. At lower oxygen pressure the solubility of Fe increases though up to 40 at. % at 1000oC [4]. Dual ion beam sputtered permalloy-oxide (PyO) thin films were shown to have a rocksalt crystal structure [6]. The texture of thin oxygen-depleted doped NiO films is poor and very sensitive on deposition parameters such as oxygen flow rate, substrate temperature, and deposition power, and often only one diffraction peak is observed in an XRD 2T scan. Therefore in this paper we report on the far infrared phonon spectrum of RF sputtered PyO films to confirm the crystal structure found by XRD. EXPERIMENTAL PROCEDURE Fused quartz purchased from Pella and SiO2 covered Si wafers that were roughened at the back with a bead-blaster were used as substrates. Prior to loading them into an AJA sputter system they were cleaned ultrasonically in water, acetone, and IPA. Deposition was done by reactive RF magnetron sputtering (240 Watt) from a Permalloy target (Ni0.81Fe0.19) using a sputter gas of 80% Ar and 20% O2 (p=10-3 Torr). The films were deposited at different substrate temperatures using a heater powered by a halogen lamp. The heater was switched off immediately after deposition and then let to cool down in the vacuum system over several hours. The time it took for the 588oC and 513oC samples to cool down below 400oC was less than 5 and 3 minutes. X-ray powder diffraction patterns were measured with a Panalytical Empyrean X-ray
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diffractometer. Films deposited at room temperature on glass confirm the rocksalt crystal structure with equal height (111) and (200) peaks and smaller but visible (220), (311
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