LINESHAPE ANALYSIS OF THE SI-H STRETCHING MODE OF THE IDEALLY H-TERMINATED SI(111) SURFACE - THE ROLE OF DYNAMIC DIPOLE COUPLING

The chemically prepared, ideally H-terminated Si(111) surfaces are characterized by a single Si-H stretching vibration with a remarkably small inhomogeneous broadening (almost-equal-to 0.05 cm-1). The lineshape associated with this inhomogeneous broadening is analyzed here by considering two effects, both closely related to finite size effects of an array of coupled dipoles: influence on the spectrum of (a) normal modes other than the commonly observed in-phase vibration and (b) the domain size distribution. Both effects lead to asymmetric lineshapes with a low frequency tail, in agreement with the data. A quantitative analysis reveals that the best samples have perfect (1 x 1) domains containing 5 X 10(3) Si-H units (almost-equal-to 6 X 10(4) angstrom 2) on average with a 30% distribution. The dynamical coupling between adjacent domains and its influence on the quantitative analysis is also briefly addressed.