Vibration eigenmodes of the Au-(5 × 2)/Si(111) surface studied by Raman spectroscopy and first-principles calculations.

Ordered submonolayers of adsorbate atoms on semiconductor surfaces constitute a playground for electronic correlation effects, which are tightly connected to the local atomic arrangement and the corresponding vibration eigenmodes. We report on a study of the vibration eigenmodes of Au-covered Si(111) surfaces with (5 × 2) reconstruction using polarized Raman spectroscopy and first-principles calculations. Upon Au coverage, the vibration eigenmodes of the clean reconstructed Si(111)- (7 × 7) surface are quenched and replaced by new eigenmodes, determined by the Au- (5 × 2) reconstruction. Several polarization-dependent surface eigenmodes emerge in the spectral range from 25 to 120 cm-1, with the strongest ones at 29, 51, and 106 cm-1. In our first-principles calculations we have determined the vibration frequencies, the corresponding elongation patterns, and the Raman intensities for two different structure models currently discussed in the literature. The best agreement with the experimental results is achieved for a model with 0.7 monolayer coverage and seven Au atoms per unit cell, proposed by S. G. Kwon and M. H. Kang [Phys. Rev. Lett. 113, 086101 (2014)]. [ABSTRACT FROM AUTHOR]