Interdiffusion During the Growth of Fe on Ag/Fe(110)
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Mat. Res. Soc. Symp. Proc. Vol. 399 01996 Materials Research Society
the surface segregation of bulk contaminants. After this initial procedure, it was possible to obtain a clean surface (as determined by AES and RIEED) merely by Ar4 bombardment followed by flash/annealing at 600'C. Temperature measurements were made using a W3%Re-W25%Re thermocouple attached to the sample. The RHEED experiments discussed in this paper were conducted using a beam energy of 60kV incident along of Fe(l 10). RESULTS AND DISCUSSION Our previous studies of Ag/Fe( 110) show that this system follows the Stranski-Krastanov growth mode with Ag islands growing on top of two intermediate Ag layers [4,5]. We also verified that the orientational relationship is of the Nishiyama-Wassermann (NW) type with (11 1 )Ag // 0 1 0 0 0 1 (11 )Fe ; < >Ag //< >Fe . This is in agreement with the results of Synman and Olsen [9]. The RHEED patterns obtained from the first Ag layer (Figure 1) are consistent with a "missing row" model [4] in which the first layer is complete at a coverage of 0.8ML as confirmed by AES [5,7]. RHEED patterns obtained for room temperature (RT) Fe deposition onto 0.8ML AgfFe(l 10) are shown in figure 1. The composite sample was prepared by depositing the Ag with the Fe crystal held at 250TC to minimize surface roughness. It was then allowed to cool to RT prior to deposition of the Fe capping layers. Upon Fe deposition, the Ag-related rods broadened slightly and for coverages > IML (Fe), diffuse 3 dimensional spots related to Fe crystallites growing in a (110) orientation, appear. It should be noted that, although there are three equivalent orientations in the NW relationship [9], only one was observed for the 0,8ML Ag/Fe(1 10) studies. This can be explained by considering the structure of the Ag layer on the surface. In previous publications [4,5] we showed that the first layer is complete at 0.8ML Ag corresponding to a missing row model [4]. The significance of these results is that the Ag layer grown here will not have the full three fold symmetry of the close-packed Ag(l 11) surface and will not fully cover the Fe crystal. This reduction in symmetry and the possibility of Fe atoms nucleating directly onto the Fe crystal are possible reasons for the suppression of the other two orientations. This was supported by results from studies of thicker Ag layers where the three orientations of Fe islands are observed. The pattern for 3ML Fe/5ML Ag/Fe(1 10) obtained after RT deposition is shown in the bottom right of figure 1. The bright hexagonal array of spots is indicative of the coexistence of the three orientations in the NW arrangement. In a previous RHEED study of the Fe/Ag(l 11) system, Gutierrez et al [8] observed a mosaic pattern consisting of two or more orientations for growth at 85TC; two of the orientations were suppressed for growth at 180TC. As can be noted from figures I and 2(a), the central regions of the three dimensional spots become increasingly triangular in shape with increasing Fe coverage. These shapes are consis
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