The semi-classical model is used to simulate the three-dimensional trajectory and deposition distribution of the chromium atoms in the Gaussian laser standing wave field using the Runge-Kutta method, and then the thre...The semi-classical model is used to simulate the three-dimensional trajectory and deposition distribution of the chromium atoms in the Gaussian laser standing wave field using the Runge-Kutta method, and then the three-dimensional deposition stripes are also given, besides, the effects of atomic beam divergence, chromatic aberration and spherical aberration on deposition structure are also analyzed.展开更多
Single atoms are the ultimate minimum size limit for catalysts. Graphene, as an exciting, ultimately thin （one atom thick） material can be imaged in a transmission electron microscope with relatively few imaging art...Single atoms are the ultimate minimum size limit for catalysts. Graphene, as an exciting, ultimately thin （one atom thick） material can be imaged in a transmission electron microscope with relatively few imaging artefacts. Here, we directly observe the behavior of single Cr atoms in graphene mono- and di-vacancies and, more importantly, at graphene edges. Similar studies at graphene edges with other elemental atoms, with the exception of Fe, show catalytic etching of graphene. Fe atoms have been shown to both etch and grow graphene. In contrast, Cr atoms are only observed to induce graphene growth. Complementary theoretical calculations illuminate the differences between Fe and Cr, and confirm single Cr atoms as superior catalysts for sp^2 carbon growth.展开更多
The microstructural evolution of the gas atomized Fe-25Cr-3.2C powders was investigated by using optical microscope, scanning electron microscope, and X-ray diffraction. The experimental results showed that the atomiz...The microstructural evolution of the gas atomized Fe-25Cr-3.2C powders was investigated by using optical microscope, scanning electron microscope, and X-ray diffraction. The experimental results showed that the atomized Fe-25Cr-3.2C powders were mainly composed of austenite and （Fe,Cr）7 C3 carbide. Eutectic microstructure was developed in the larger particles, whereas dendritic microstrueture was obtained in the particles with diameter less than 38 μm. The reason for microstructure change should be the difference of nucleation undercooling for particles.展开更多
The properties of all materials depend largely on their chemical compositions.Compositional analysis by using the atom probe suggests that it is necessary to invent new parameters to describe some aspects of microstru...The properties of all materials depend largely on their chemical compositions.Compositional analysis by using the atom probe suggests that it is necessary to invent new parameters to describe some aspects of microstructures.Experimental and calculation work indicates that fractal dimension can be used to describe structural aspects not readily expressible with normal parameters.The application of fractal concept in mate- rials studies will enable us to understand from a brand-new angle the ultra-fine microstructures of materials.展开更多
文摘The semi-classical model is used to simulate the three-dimensional trajectory and deposition distribution of the chromium atoms in the Gaussian laser standing wave field using the Runge-Kutta method, and then the three-dimensional deposition stripes are also given, besides, the effects of atomic beam divergence, chromatic aberration and spherical aberration on deposition structure are also analyzed.
基金The following are gratefully acknowledged. The National Natural Science Foundation of China （No. 51672181）, the National Science Center for the financial support within the frame of the Sonata Program （No. 2014/13/D/ST5/02853） and the Opus program （No. 2015/19/B/ST5/03399）.
文摘Single atoms are the ultimate minimum size limit for catalysts. Graphene, as an exciting, ultimately thin （one atom thick） material can be imaged in a transmission electron microscope with relatively few imaging artefacts. Here, we directly observe the behavior of single Cr atoms in graphene mono- and di-vacancies and, more importantly, at graphene edges. Similar studies at graphene edges with other elemental atoms, with the exception of Fe, show catalytic etching of graphene. Fe atoms have been shown to both etch and grow graphene. In contrast, Cr atoms are only observed to induce graphene growth. Complementary theoretical calculations illuminate the differences between Fe and Cr, and confirm single Cr atoms as superior catalysts for sp^2 carbon growth.
基金Item Sponsored by National Natural Science Foundation of China (50701030)National Basic Research Program of China(2010CB630802)
文摘The microstructural evolution of the gas atomized Fe-25Cr-3.2C powders was investigated by using optical microscope, scanning electron microscope, and X-ray diffraction. The experimental results showed that the atomized Fe-25Cr-3.2C powders were mainly composed of austenite and （Fe,Cr）7 C3 carbide. Eutectic microstructure was developed in the larger particles, whereas dendritic microstrueture was obtained in the particles with diameter less than 38 μm. The reason for microstructure change should be the difference of nucleation undercooling for particles.
文摘The properties of all materials depend largely on their chemical compositions.Compositional analysis by using the atom probe suggests that it is necessary to invent new parameters to describe some aspects of microstructures.Experimental and calculation work indicates that fractal dimension can be used to describe structural aspects not readily expressible with normal parameters.The application of fractal concept in mate- rials studies will enable us to understand from a brand-new angle the ultra-fine microstructures of materials.
