The initial formation of the Au-Si(111) 7 × 7 interface has been examined by ARUPS, LEED and AES techniques. At room temperature, strong interactions between Au and Si atoms occur for coverages as low as 0.2 monolayer. This is related to the existence of a 1 × 1 LEED structure, to the suppression of the intrinsic silicon surface states and to the appearance of prominent Au 5d bands. The energy position of the latter structures is compatible with a significant gold-silicon interdiffusion. For increasing coverages, an amorphous Au-Si layer with a more metallic character gradually grows. This is supported by the removal of the 1 × 1 LEED pattern, the lack of influence of polar angle on the photoemission features and the substantial increase of the density of states near the Fermi level, E F . At the same time, the shift of the Au 5d emission towards E F is clearly related to the existence of a gold-rich Si alloy. The effects of annealing on one gold monolayer are presented. A sharp 3 1/2 × 3 1/2 R(30 degrees ) LEED pattern is obtained, whereas normal photoemission spectra reveal the existence of electronic states at -1 and -2.6 eV below E F . Their insensitivity to polarisation and their strong dispersion along the Gamma K'M' direction of the surface Brillouin zone show that they correspond to new interface states. These results are discussed in terms of structural models proposed for 3 1/2 × 3 1/2 ordered surfaces.
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Houzay et al. (1982) studied this question.