Dipole formation processes at self-assembled monolayers of benzene derivatives chemisorbed on the Si͑111͒ surface are investigated from first principles. The surface dipole is shown to be sensitive to the molecular coverage and dominated by intramolecular charge rearrangement due to long-range, cooperative behavior. This cooperative behavior suppresses substrate contributions to dipole formation.

Electron transfer from sol–gel–prepared TiO2 into adsorbed benzene diazonium compounds has been investigated using cyclic voltammetry, x-ray photoelectron spectroscopy, contact potential difference, and surface photovoltage spectroscopy. The results show that the potential of maximum electron transfer depends strongly on the dipole moment of the benzene compound. Two reactive surface sites at which electron transfer occurs have been identified.

No abstract

A frequency and temperature dependent change of the sign of modulated surface photovoltage signals from metal-free tetraphenyl porphyrin (H2TPP)∕Au junctions has been observed. The sign of the modulated photovoltage signal could be switched by using continuous (bias) illumination, while the sign depends on the wavelength of the bias light. The light induced modulation of the negative and positive charges in the H2TTP layer can be interpreted in terms of internal photoemission of electrons from Au into H2TTP and of hole escape after exciton dissociation at the H2TPP∕Au junction.

The alloy composition of a Cd1−xZnxTe(111) sample and its spatial homogeneity have been determined by surface photovoltage spectroscopy (SPS) and compared to conventional energy dispersive x-ray spectroscopy measurements. Experimental improvements of the former technique yield a contactless, surface sensitive, and highly accurate spectral resolution of the band gap (error<4 meV) and consequently of the Zn concentration (error<0.6% in comparison with the latter technique). In addition, SPS is capable of determining the face and type of the Cd1−xZnxTe as well as identifying gap states at its surface. The electronic structure has been investigated in comparison with n-CdTe(111), before and after various surface chemical treatments. An acceptor surface state has been observed at 1.21 eV below the conduction band edge and attributed to TeO2. A donor surface state (with a lower concentration relative to the corresponding state in CdTe) associated with Cd atom displacement has been found at 1.42 eV above the valence band maximum. A chemically induced surface state at 0.72 eV below the conduction band edge may be due to Zn vacancies, as supported by x-ray photoelectron spectroscopy measurements.