Adatom and dimer migration in heteroepitaxy: Co/Pt(1 1 1)

By means of tight-binding molecular-dynamics simulations, Co adatom and dimer migration on a Pt(1 1 1) surface is investigated. Combining static and dynamic calculations, activation energies associated to these processes are determined. Since the size mismatch between Co and Pt is large, the presented simulations provide an illustration of the way in which growth can be affected by size effects in heteroepitaxy. In particular an increase of the mobility is found for Co dimers (heteroepitaxy) relatively to Pt ones (homoepitaxy).     

Nano-structuration of CoO film by misfit dislocations

We have studied the nano-patterning of CoO film induced by misfit dislocation network at the interface with the Ag(0 0 1) substrate. Grazing incidence diffraction (GIXD), X-ray photoemission spectroscopy (XPS) and low energy electron diffraction (LEED) have been used to characterize chemistry and structure of the CoO layers. The XPS spectrum of the Co 2p core level permitted to establish the stoichiometric growth of CoO. The structure of the CoO film together with the absorption sites of cobalt and oxygen atoms was determined, thanks to GIXD measurements. Moreover we have followed the evolution of the in-plane lattice constant of the CoO as a function of the film thickness. It turns out that the CoO film growth starts with the same in-plane lattice constant of the Ag(0 0 1) substrate up to 3-4 ML; afterwards the in-plane parameter of CoO steadily increases before reaching a stable value of 2.98 Å at 23 ML. During the relaxation process, at about 8 ML of film thickness, we observe the formation of a buried misfit dislocation network. These dislocations, that have a period of 9.2 nm for a film thickness of 23 ML, induce mosaicity in the CoO film which then appears as a regular distribution of tilted domains.     

GaAs/Ge的MOCVD生长研究

用常压MOCVD在Ge衬底上外延生长了GaAs单晶层,研究了GaAs和6e的极性与非极性材料异质外延生长,获得了质量优良的GaAs/Ge外延片,GaAs外延层X射线双晶衍射回摆曲线半高宽达16弧秒.10K下PL谱半峰宽为7meV.讨论了极性与非极性外延的界面反相畴问题和GaAs-Ge界面的Ga、Ge原子互扩散问题.