Local atomic environment of Si suboxides at the SiO2/Si(111) interface determined by angle-scanned photoelectron diffraction

Local environments of Si suboxides at the interface between a thermally grown SiO2 film and Si(111) were studied by angle-scanned photoelectron diffraction. Si 2p core-level spectra containing chemically shifted components were recorded. The components were deconvoluted by least squares fitting and assigned to different Si oxidation states. The obtained diffraction patterns of the various suboxides exhibit different features. Comparison of these patterns with multiple scattering calculations including a multipole R-factor analysis shows that a simple chemical abrupt interface model describes well the environment of the suboxides and indicates ordered SiO2 close to the interface.     

Nonlinear optical study of amorphous SiN:H films on the Si(111) substrate

A correlation between the resistivity-voltage dependences of the hydrogenated SiN/Si(111) films and the photo-induced third-harmonic generation (PITHG) at λ = 1064 nm in the reflected light regime was found. The contribution to the PITHG is both due to linear photo-induced surface changes as well as due to the hydrogen dopants. When the fundamental power density increases to higher than 1.2 GW/cm², there occurs a drastic decrease of the PITHG. Maximal PITHG changes are observed at a pump-probe delay time about 18 ps and the value of the PITHG slightly increases with the enhanced applied dc-electric field during illumination by a third-harmonic laser beam as a photo-inducing one. The deviation from the tripled frequency wavelength to higher wavelengths substantially suppresses the output PITHG signal. The crucial role of the interface trapping levels and silicon-hydrogen charge transfer is shown.     

Bistability in scanning tunneling spectroscopy of Ga-terminated Si(111)

Bistable electron transport, a phenomenon usually associated with double-barrier structures, has been observed with a conventional STM junction formed between a metal tip and a Ga-terminated Si(111) surface at 77 K. Large hysteresis loops appear in the current-voltage characteristics when electrons are injected from the tip to the surface. The turn-on bias varies from -3.1 to -4.0 V and shows an inverse dependence on the tip-sample distance, indicating a strong field effect. The turn-off bias, however, is essentially pinned at a conductance threshold of -2.7 V.     

Ultraviolet photoemission spectroscopy of HCl on Si(111) surfaces

Chemisorption of HCl on thermally cleaned Si(111) surfaces has been studied by ultraviolet photoemission spectroscopy. HCl chemisorption, both at 300K and 850 K, induces two main peaks in the photoemission spectrum which are attributed to Cl lone pair p_x, p_y orbitals and Si: sp³?Cl:p_z bonding orbital, respectively. This strongly suggests that HCl molecules dissociate on Si(111) surfaces already at room temperature.     

Lattice vibrations at ideal Si(111) surfaces

Surface vibrations at an ideal (111) silicon surface with vanishing wavevector components parallel to the surface are calculated within the shell-model for a simple model of surface force constants.