For evaporation-deposited Ti films, face-centred cubic structure was observed at the initial stage of film growth, then transited to the hexagonal close-packed structure during film growing (less than 50 nm thick). Wh...For evaporation-deposited Ti films, face-centred cubic structure was observed at the initial stage of film growth, then transited to the hexagonal close-packed structure during film growing (less than 50 nm thick). While. for ion-beam sputter-deposited films. the structure of films always kept the fcc structure during all stages of film formation. The structure of film at initial growth stages relates with the substrate. It is discussed that different film processes and different growth stages provide different thermodynamic condition of film formation and result in the different crystal structures of films during the film formation展开更多
Crystal growth and solute precipitation is a Stefan problem. It is a free boundary problem for a parabolic partial differential equation with a time-dependent phase interface. The velocity of the moving interface betw...Crystal growth and solute precipitation is a Stefan problem. It is a free boundary problem for a parabolic partial differential equation with a time-dependent phase interface. The velocity of the moving interface between solute and crystal is a local function. The dendritic structure of the crystal interface, which develops dynamically, requires high resolution of the interface geometry. These facts make the Lagrangian front tracking method well suited for the problem. In this paper, we introduce an upgraded version of the front tracking code and its associated algorithms for the numerical study of crystal formation. We compare our results with the smoothed particle hydrodynamics method （SPH） in terms of the crystal fractal dimension with its dependence on the Damkohler number and density ratio.展开更多
Crystal growth processes of poly（ethylene oxide） were followed from the original nucleation sites by using atomic force microscopy. Two distinct quasi-2-dimensional crystals about 4 nm thick were obtained from as-sp...Crystal growth processes of poly（ethylene oxide） were followed from the original nucleation sites by using atomic force microscopy. Two distinct quasi-2-dimensional crystals about 4 nm thick were obtained from as-spun polymer ultrathin films： fibrous crystals, generated by the sheafing field via spin-coating, coexist with con- ventional dendrites. The growth of the two structures is dominated by diffusion limited aggregation, though the growth rate of the fibrous crystals is around one order of magnitude faster than that of the dendrites. The fibrous crystals are more stable than the dendritic ones.展开更多
The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is propo...The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is proposed.展开更多
The formation process of crystal polymorphs of titania under hydrothermal condition is studied.According to the experimental results and theoretic analysis,the formation process of crystal polymorphs can be described ...The formation process of crystal polymorphs of titania under hydrothermal condition is studied.According to the experimental results and theoretic analysis,the formation process of crystal polymorphs can be described as a unit process.It includes the formation of growth units,the formation of nuclei through the polymerization of growth unit,and the growth of crystallites.The influence of the environmental phase and growth conditions on the formation of polymorphs is reflected in the changes of the structures of growth units.For example,when changing the pH of the reaction medium,the structure of growth unit with the highest stable energy in the hydrothermal system changes.Then different titania polymorphs can be prepared.The absorption,movement,crystallization or desorption of the growth unit are related to crystalline structure.On the other hand,the formation of crystal inner defects is related to the disturbance of the crystallizing process.展开更多
文摘For evaporation-deposited Ti films, face-centred cubic structure was observed at the initial stage of film growth, then transited to the hexagonal close-packed structure during film growing (less than 50 nm thick). While. for ion-beam sputter-deposited films. the structure of films always kept the fcc structure during all stages of film formation. The structure of film at initial growth stages relates with the substrate. It is discussed that different film processes and different growth stages provide different thermodynamic condition of film formation and result in the different crystal structures of films during the film formation
基金supported in part by the ITAPS Award from US Department of Energy DEFC0206ER25770the ARO Award W911NF0910306+1 种基金supported in part by the DOE subaward through RPI with the Prime Award DEFG0707ID14889supported in part by NSF Award DMS0809285
文摘Crystal growth and solute precipitation is a Stefan problem. It is a free boundary problem for a parabolic partial differential equation with a time-dependent phase interface. The velocity of the moving interface between solute and crystal is a local function. The dendritic structure of the crystal interface, which develops dynamically, requires high resolution of the interface geometry. These facts make the Lagrangian front tracking method well suited for the problem. In this paper, we introduce an upgraded version of the front tracking code and its associated algorithms for the numerical study of crystal formation. We compare our results with the smoothed particle hydrodynamics method （SPH） in terms of the crystal fractal dimension with its dependence on the Damkohler number and density ratio.
基金Supported by the National Natural Science Foundation of China(21176065,21136004)the 111 Project(B08021)the Fundamental Research Funds for the central Universities of China
文摘Crystal growth processes of poly（ethylene oxide） were followed from the original nucleation sites by using atomic force microscopy. Two distinct quasi-2-dimensional crystals about 4 nm thick were obtained from as-spun polymer ultrathin films： fibrous crystals, generated by the sheafing field via spin-coating, coexist with con- ventional dendrites. The growth of the two structures is dominated by diffusion limited aggregation, though the growth rate of the fibrous crystals is around one order of magnitude faster than that of the dendrites. The fibrous crystals are more stable than the dendritic ones.
文摘The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is proposed.
基金This work work was supported by the National Natural Science Foundation of China (Grant Nos. 59772002 and 59832080).
文摘The formation process of crystal polymorphs of titania under hydrothermal condition is studied.According to the experimental results and theoretic analysis,the formation process of crystal polymorphs can be described as a unit process.It includes the formation of growth units,the formation of nuclei through the polymerization of growth unit,and the growth of crystallites.The influence of the environmental phase and growth conditions on the formation of polymorphs is reflected in the changes of the structures of growth units.For example,when changing the pH of the reaction medium,the structure of growth unit with the highest stable energy in the hydrothermal system changes.Then different titania polymorphs can be prepared.The absorption,movement,crystallization or desorption of the growth unit are related to crystalline structure.On the other hand,the formation of crystal inner defects is related to the disturbance of the crystallizing process.
