The Growth of Ni Overlayers on Au(100) Buffers Deposited on GaAs(100) and MgO(100) Substrates.
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THE GROWTH OF Ni OVERLAYERS ON Au(100) BUFFERS DEPOSITED ON GaAs(100) AND MgO(100) SUBSTRATES.
B. GILLES*, J. EY.MIERY**, A. MARTY**, J.C. JOUD*, A. CHAMBEROD** * LTPCM, ENSEEG, 38402 St. Martin d'H~res, France. **
CENG, DRFMC, SP2M, MP, 38041 Grenoble, France.
ABSTRACT High quality single-crystal Au(100) buffers have been grown on GaAs(100) or MgO(100) substrates via a thin bcc Fe(100) nucleation layer. Using RHEED, LEED and Auger spectroscopy the growth of Ni overlayers at room temperature was observed to follow an epitaxial layer-by-layer mode for 2 monolayers, after which islanding occured. Detailed analysis of the Auger signal reveals that atomic mixing appears within the first completed layer. Grazing incidence diffraction has been used to investigate the structure of 5-10 nm films. A mixture of (100) and (110) grains have been characterized ; the latter orientation shows a large number of stacking faults along the Ni[ ill] direction in agreement with the Au[001] direction. 1 INTRODUCTION Molecular beam epitaxy (MBE) has become now a widely used method to study the growth of single crystal materials. The sharpness of the interfaces within the atomic scale makes possible the study of the earliest stage of epitaxy. The most effective approach to this has been the use of complementary methods such as reflection high energy electron diffraction (RHEED) or low energy electron diffraction (LEED) associated with Auger electron spectroscopy (AES). In this study, we investigate the growth of Ni on Au(100) surface. Both have a fcc structure with a large difference in lattice parameter (aA,, = .408 nm, aNi = .352 nm) and the phase diagram exhibits a miscibility gap, so that they may be regarded as nearly immiscible in the bulk at room temperature. A recent work has been devoted to the prediction of growth mode by molecular dynamics simulation [1]. 2 EXPERIMENTAL 2.1 Experimental setup Our equipment is a Riber MBE system. The evaporation is performed with the use of e-beam guns and the molecular fluxes are regulated with quartz micro-balances. The RHEED gun is operated at 40 kV and the angle of incidence is set around 1.50. Auger analysis as well as LEED diffraction is carried out in a separated chamber. The base pressure during all the operations is maintained to 5.10-li Torr around the sample. During the time required for our experiments, no significant C or 0 contamination has been detected in Auger measurements. 2.2 The Au buffer layer on GaAs or MgO substrates GaAs wafers having (100) surface were solvent cleaned and then etched in a solution of H2 SO 4 :H2 0 2 :H2 0 = 4:1:1 for 2 mn. They were then rinsed in deionized
Mat. Res. Soc. Symp. Proc. Vol. 237. 01992 Materials Research Society
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running water for 30 mn, rinsed in methanol and transfered to the vacuum chamber. The substrates were heated in UHV at 580 'C for several mn, which leads to the desorption of the native Ga-oxide [2]. A clearly defined c(8x2) and/or (4x2) surface structure is then produced. This reconstruction is known to be a Ga-rich phas
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