Au(111) surface structures induced by adsorption: LEED I(E) analysis of (1 × 1) and (5 × 5) Au(111)–S phases

We report on the various phases formed by sulfur adsorbed on Au(111), at less than 1 monolayer (ML) coverage, as monitored by low-energy electron diffraction (LEED). The phases transform from one to another via coexistence regions. The observation of ordered phases was matched to the coverage information obtained from Auger measurements, using as a calibration point the S coverage of 0.28 ML, corresponding to the sharpest (5 × 5) LEED pattern observed. The influence of emitting filaments (the Auger beam, ion gauge, or LEED electron beam) upon the adsorption itself is discussed. LEED structural investigations were performed on two particular S–Au phases. The analysis of the Au(1 × 1)–S structure provided the values for the first four gold interlayer spacings, showing a 1% expansion of the top layer, interpreted as a remnant of the expansion of the Au(111)–(22 × √3) reconstructed phase. The analysis of the Au(5 × 5)–7S phase confirmed the fcc adsorption site of the S atoms reported previously, and resulted in an average S–Au distance of 1.57 ± 0.10 Å, and an S–Au bond length of 2.29 ± 0.07 Å.