Structure and Morphology of Clean and Magnesium - Dosed Sapphire Surfaces
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Diffraction (LEED and RHEED) and Atomic Force Microscopy (AFM). Following heat treatments at 1000 0C in 5x10- 7 torr 02, both surfaces exhibited (lxl) diffraction patterns. Regular step-terrace structure was observed on the (1012) surface with the AFM, but no step structure was visible on the (0001) surface. The initial growth of magnesium overlayers dosed onto the (1012) surface at 25 0 C in ultra-high vacuum was monitored with RHEED and the chemical interactions at the Mg / A120 3 interface were characterized with X-ray Photoelectron Spectroscopy (XPS). During the initial deposition, very little interaction between Mg and the A120 3 substrate occurs and a very abrupt interface is formed. At larger Mg doses, a textured polycrystalline Mg overlayer is produced. Annealing the Mg film above 300 0 C causes some oxidation of Mg at the Mg / A12 0 3 interface, but most of the Mg desorbs from the surface. INTRODUCTION
Advanced ceramic materials are important mechanical, electronic and chemical components in many technologies. An understanding of the structure and chemical interactions at interfaces between ceramics and other materials is required to optimize materials performance. A good review of interface bonding models and general rules for interface reactivity in metal / ceramic systems is given by Ruhle and Evans [1]. Aluminum oxide is the most common oxide ceramic in current technology. In sintered form (alumina), it has been found that MgO solute acts as a sintering aid by enhancing surface diffusion and suppressing grain boundary motion [2]. In single crystal form (sapphire), aluminum oxide is important as an electronic substrate and dielectric layer [3]. Fundamental studies of interface structure and chemistry have been carried out for several metal / sapphire interfaces; for example, these include systems where the metal has been Cu [4], Ti [5], Ni [6] and Nb [7]. In this paper, we first describe the structure and morphology of clean c-axis (0001) and r-axis (1012) sapphire surfaces following annealing treatments. Then, results of Mg dosing experiments on the r-axis sapphire surface to create a welldefined Mg / sapphire interface will be discussed.
583 Mat. Res. Soc. Symp. Proc. Vol. 317. ©1994 Materials Research Society
EXPERIMENTAL C-axis and r-axis oriented sapphire wafers polished to an epitaxial grade finish were obtained from Insaco Inc. [8]. These samples were etched in H3PO 4 acid at 80 0C for 10 minutes and rinsed in deionized water. Following this treatment, the average rms surface roughness was less than 5 A over a 9 ýLm2 area as determined by the AFM. The samples were inserted into a surface analysis and film growth chamber described previously [9] for annealing and oxidation treatments. Indirect sample heating up to 12000 C was accomplished by electron beam bombarding a Ta plate in contact with the back side of the sample. Surface structure was studied with a 4-grid LEED system and a 15 keV RHEED gun. AFM imaging of surface morphology was carried out in air using a Park SFM-BD2 microscope with s
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