Comparative study of harmonic oscillations of tunneling current on partially oxidized Si(100) and Si(111) surfaces by scanning tunneling microscopy and spectroscopy

The harmonic oscillations of the tunneling current on partially oxidized Si(100) and Si(111) surfaces and at Au clusters deposited on these surfaces were observed by scanning tunneling spectroscopy (STS) and scanning tunneling microscopy (STM). For both surfaces, the frequencies determined by STS and Fourier analysis of STM current images are roughly multiples of a basic frequency of 30 Hz. The consistency of the basic frequencies indicates that the oscillations of the tunneling current in the STS spectra and STM current images come from the same source. The basic frequency is assumed to be determined by local defects. The dependence of the oscillation frequencies, f(N), on the multiplication factor, N, is not very different for both surfaces. The frequency distributions derived from the STS spectra show two maxima, N=22 (661.6 Hz) and 36 (1077.3 Hz), for Si(100) and one maximum, N=70 (2099.6 Hz), for Si(111). The frequency distribution seems to be dependent on the long-range order of Si surfaces.