The Growth Modes of Epitaxial Au/Co/Au Sandwiches
POLISH ACADEMY OF SCIENCES WARSAW INSTOF PHYSICS
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This study investigated the optimum growth conditions of epitaxial GoldCobaltGold AuCoAu sandwiches with a strong perpendicular magnetic anisotropy. The thermally induced evolution of sandwich morphology, which determines its magnetic properties, was studied by means of reflection high-energy electron diffraction RHEED and Auger electron spectroscopy AES. The roughness of Au and Co surfaces, affected by the sample annealing, was evaluated from the length-dependent variance of topography acquired by atomic force microscopy. The AuCoAu sandwiches were grown in a molecular beam epitaxy MBE system with the vacuum level in the range of 10 -10 torr. Glass and sapphire wafers with orientation 11-20 buffered with a Molybdenum Mo layer were used as substrates. Co and Mo were evaporated from electron guns and Au from effusion cells at the rates lower than 0.5 angstroms per second. All deposition processes were performed at room temperature. The bottom Au layer, 200 angstroms thick, was grown either directly on the glass substrate or on the Mo buffer 200 angstroms covering a sapphire substrate. The shape of the Co layer was either flat or wedge-like, and its thickness range was between 0 and 25 angstroms. The top Au layer was kept at 80 angstroms in thickness. The crystalline structure of all grown layers was characterized in situ by RHEED. The AES analysis was carried out to check the chemical composition of the layers and to estimate diffusion processes due to the sample annealing. Ex situ Atomic Force Microscopy AFM measurements Nanoscope III in the Tapping mode were performed for surface roughness investigations. Results show that the sapphire substrate buffered with Mo is ideal for growing smooth AuCoAu sandwiches. The annealing above 170 degrees Centigrade improves the flatness of the Au surface such that atomically smooth areas of a few hundred nanometers in diameter occur. 3 figures, 14 refs.
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