Thiolate-induced lateral distortion of the Cu(100) surface

Medium energy ion scattering (MEIS) with 100 keV H+ incident ions has been used to explore adsorbate-induced distortions of the Cu(100) surface in the Cu(100)(2 × 2)–CH3S (methylthiolate) phase. Previous identification of a methylthiolate-induced pseudo-(100) reconstruction of Cu(111) with Cu–Cu spacings 15% larger than on Cu(100) have led to the suggestion that on Cu(100) in the commensurate (2 × 2) phase a lateral radial expansion of the Cu atoms surrounding the thiolate in a four-fold coordinated hollow should occur. Changes in the scattered ion yields for incidence in [ 1 ¯ 10 ] , [ 1 ¯ 00 ] , and [ 2 ¯ 11 ] directions are consistent with such a lateral shift of 0.12 ± 0.04 Å, while changes in the MEIS blocking-curve dips indicate that these lateral shifts are accompanied by an outward expansion of the outermost surface layer spacing of 0.08 ± 0.04 Å. This local strain is attributed to adsorbate-induced compressive stress.