Er2O3 thin films are grown on oxidized Si （111） substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing...Er2O3 thin films are grown on oxidized Si （111） substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction （GIXRD）, atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er2O3 thin film is a mosaic of single-crystal domains. The interplanar spacing d in-plane residual strain tensor ell and the strain relaxation degree ε are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulk Er2O3. In-plane strains in three sets of planes, i.e. （440）, （404）, and （044）, are isotropic.展开更多
The adsorptions of a series of alkali metal （AM） atoms, Li, Na, K, Rb and Cs, on a Si（001）-2 × 2 surface at 0.25 monolayer coverage have been investigated systematically by means of density functional theory ...The adsorptions of a series of alkali metal （AM） atoms, Li, Na, K, Rb and Cs, on a Si（001）-2 × 2 surface at 0.25 monolayer coverage have been investigated systematically by means of density functional theory calculations. The effects of the size of AM atoms on the Si（001） surface are focused in the present work by examining the most stable adsorption site, diffusion path, band structure, charge transfer, and the change of work function for different adsorbates. Our results suggest that, when the interactions among AM atoms are neglectable, these AM atoms can be divided into three classes. For Li and Na atoms, they show unique site preferences, and correspond to the strongest and weakest AM-Si interactions, respectively. In particular, the band structure calculation indicates that the nature of Li-Si interaction differs significantly from others. For the adsorptions of other AM atoms with larger size （namely, K, Rb and Cs）, the similarities in the atomic and electronic structures are observed, implying that the atom size has little influence on the adsorption behavior for these large AM atoms on the Si（001） surface.展开更多
Direct growth of GaN films on Si(001) substrate at low temperatures (620～720℃) by electron cyclotron resonance (ECR) microwave plasma enhanced metalorganic chemical vapor deposition (PEMOCVD).The crystalline phase s...Direct growth of GaN films on Si(001) substrate at low temperatures (620～720℃) by electron cyclotron resonance (ECR) microwave plasma enhanced metalorganic chemical vapor deposition (PEMOCVD).The crystalline phase structures of the films are investigated.The results of high resolution transmission electron microscopy (HRTEM) and X ray diffraction (XRD) indicate that high c axis oriented crystalline wurtzite GaN is grown on Si(001) but there is an amorphous layer formed naturally at GaN/Si interface.Both faces of the amorphous layer are flat and sharp,and the thickness of the layer is 2nm approximately cross the interface.The analysis supports that β GaN phase is not formed owing to the N x Si y amorphous layer induced by the reaction between N and Si during the initial nucleation stage.The results of XRD and atomic force microscopy (AFM) indicate that the conditions of substrate surface cleaned in situ by hydrogen plasma,GaN initial nucleation and subsequent growth are very important for the crystalline quality of GaN films.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10174081 and 60425411.
文摘Er2O3 thin films are grown on oxidized Si （111） substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction （GIXRD）, atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er2O3 thin film is a mosaic of single-crystal domains. The interplanar spacing d in-plane residual strain tensor ell and the strain relaxation degree ε are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulk Er2O3. In-plane strains in three sets of planes, i.e. （440）, （404）, and （044）, are isotropic.
基金supported by the National Natural Science Foundation of China(21203027)Fuzhou University(2012-XQ-11)
文摘The adsorptions of a series of alkali metal （AM） atoms, Li, Na, K, Rb and Cs, on a Si（001）-2 × 2 surface at 0.25 monolayer coverage have been investigated systematically by means of density functional theory calculations. The effects of the size of AM atoms on the Si（001） surface are focused in the present work by examining the most stable adsorption site, diffusion path, band structure, charge transfer, and the change of work function for different adsorbates. Our results suggest that, when the interactions among AM atoms are neglectable, these AM atoms can be divided into three classes. For Li and Na atoms, they show unique site preferences, and correspond to the strongest and weakest AM-Si interactions, respectively. In particular, the band structure calculation indicates that the nature of Li-Si interaction differs significantly from others. For the adsorptions of other AM atoms with larger size （namely, K, Rb and Cs）, the similarities in the atomic and electronic structures are observed, implying that the atom size has little influence on the adsorption behavior for these large AM atoms on the Si（001） surface.
文摘Direct growth of GaN films on Si(001) substrate at low temperatures (620～720℃) by electron cyclotron resonance (ECR) microwave plasma enhanced metalorganic chemical vapor deposition (PEMOCVD).The crystalline phase structures of the films are investigated.The results of high resolution transmission electron microscopy (HRTEM) and X ray diffraction (XRD) indicate that high c axis oriented crystalline wurtzite GaN is grown on Si(001) but there is an amorphous layer formed naturally at GaN/Si interface.Both faces of the amorphous layer are flat and sharp,and the thickness of the layer is 2nm approximately cross the interface.The analysis supports that β GaN phase is not formed owing to the N x Si y amorphous layer induced by the reaction between N and Si during the initial nucleation stage.The results of XRD and atomic force microscopy (AFM) indicate that the conditions of substrate surface cleaned in situ by hydrogen plasma,GaN initial nucleation and subsequent growth are very important for the crystalline quality of GaN films.
