No abstract

The oxidation rate of silicon small particles prepared by a gas-evaporation method and with diameters ranging from about 20 to 500 nm is investigated by high-resolution transmission electron microscopy. It is found that the oxidation rate of silicon small particles is less than the rate for wafers, and decreases with decreasing particle size. This phenomenon cannot be explained by the Deal–Grove model.

In situ synchrotron radiation photoelectron spectroscopy was performed during the oxidation of the Ge(100)-2 × 1 surface induced by a molecular oxygen beam with various incident energies up to 2.2 eV from the initial to saturation coverage of surface oxides. The saturation coverage of oxygen on the clean Ge(100) surface was much lower than one monolayer and the oxidation state of Ge was +2 at most. This indicates that the Ge(100) surface is so inert toward oxidation that complete oxidation cannot be achieved with only pure oxygen (O2) gas, which is in strong contrast to Si surfaces. Two types of dissociative adsorption, trapping-mediated and direct dissociation, were confirmed by oxygen uptake measurements depending on the incident energy of O2. The direct adsorption process can be activated by increasing the translational energy, resulting in an increased population of Ge2+ and a higher final oxygen coverage. We demonstrated that hyperthermal O2 beams remarkably promote the room-temperature oxidation with novel atomic configurations of oxides at the Ge(100) surface. Our findings will contribute to the fundamental understanding of oxygen adsorption processes at 300 K from the initial stages to saturated oxidation.

Adsorptions of alkali metals (such as K and Li) on monolayers of coronene and picene realize the formation of ordered phases, which serve as well-defined model systems for metal-intercalated aromatic superconductors. Upon alkali-doping of the monolayers of coronene and picene, scanning tunneling microscopy and X-ray absorption spectroscopy revealed the rearrangement of the entire molecular layer. The K-induced reconstruction of both monolayers resulted in the formation of a structure with a herringbone-like arrangement of molecules, suggesting the intercalation of alkali metals between molecular planes. Upon reconstruction, a shift in both the vacuum level and core levels of coronene was observed as a result of a charge transfer from alkali metals to coronene. In addition, a new density of states near the Fermi level was formed in both the doped coronene and the doped picene monolayers. This characteristic electronic feature of the ordered monolayer has been also reported in the multilayer picene films, ensuring that the present monolayer can model the properties of the metal-intercalated aromatic hydrocarbons. It is suggested that the electronic structure near the Fermi level is sensitive to the molecular arrangement, and that both the strict control and determinations of the molecular structure in the doped phase should be important for the determination of the electronic structure of these materials.