Epitaxial Iridium Growth on Strontium Titanate
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Epitaxial Iridium Growth on Strontium Titanate Z. Dai, A.P. Li, C. Bednarski, L. I. McCann, and B. Golding Department of Physics & Astronomy and Center for Sensor Materials, Michigan State University, E. Lansing, MI 48824-1116, U. S. A. ABSTRACT Epitaxial (100) iridium films have been grown on (100) SrTiO3 (STO) substrates by electron beam evaporation. The epitaxial relationship between the iridium film and STO substrate was determined to be Ir(001)[100]//STO(001)[100]. A systematic study of the role of STO substrate surface preparation, Ir thickness, and substrate temperature on Ir film crystallinity and morphology has been performed. The best Ir films typically have small Ir(200) XRD linewidths < 0.3 º, surface roughness of 0.2 nm, and low ion channeling yields, χmin ≤ 4%, when deposited at 800 °C. Films generally become smoother with better crystallinity when the film thickness approaches 300 nm. A growth mode with initial island formation and subsequent layer-by-layer appears to take place at higher substrate temperatures, whereas at lower temperatures the film grows in a 3D mode. INTRODUCTION Iridium thin films have many interesting properties that include a very high melting point (Tm = 2450 °C), good mechanical strength, excellent chemical stability, superior oxidation resistance, and low electrical resistivity [1,2]. They have been prepared by several techniques, such as metallorganic chemical vapor deposition (MOCVD) [3,4], radio-frequency magnetron sputtering [5], pulsed laser deposition [6,7], and electron beam evaporation [8]. Iridium films have also been used as a substrate for CVD diamond film growth because of its high melting point, close lattice match to diamond (8%), low carbide formation at CVD diamond growth temperatures (700 °C-800 °C), and low carbon solid solubility [9,10,11]. The cubic perovskite SrTiO3 (a0=0.39050 nm) has been used as a substrate for iridium growth because of the close lattice match to fcc iridium (a0=0.38394 nm). Hörmann et al.[12] reported on iridium film growth as a function of substrate temperature and on film morphology evolution vs. film thickness. In this paper, we study the morphology of epitaxial Ir films grown on (001) STO substrates with special attention to the role of the STO substrate on the crystalline quality of the Ir epilayer. EXPERIMENTAL DETAILS Iridium film deposition was performed in a UHV electron beam evaporation system with a base pressure approaching10-10 Torr. Iridium rods with 99.9% purity were used as the source. Single crystal STO substrates with dimensions 5×5×0.5 mm3 from several vendors were used. Substrates were carefully inspected for growth defects by optical microscopy before ultrasonic cleaning in acetone and methanol, followed by drying in a nitrogen gas flow. Atomically flat substrates with terraced structures were prepared by standard methods [13, 14]. The substrates were loaded into the UHV chamber via a load-lock immediately following cleaning. Before P11.35.1 Downloaded from https://www.cambridge.org/core. University of Warwick, on
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