We report on the formation of a graphene monolayer on a Ru（0001） surface by annealing the Ru（0001） crystal. The samples are characterized by scanning tunnelling microscopy （STM） and Auger electron spectroscopy ...We report on the formation of a graphene monolayer on a Ru（0001） surface by annealing the Ru（0001） crystal. The samples are characterized by scanning tunnelling microscopy （STM） and Auger electron spectroscopy （AES）. STM images show that the Moire pattern is caused by the graphene layer mismatched with the underlying Ru（0001） surface and has an N × N superlattice. It is further found that the graphene monolayer on a Ru（0001） surface is very stable at high temperatures. Our results provide a simple and convenient method to produce a graphene monolayer on the Ru（0001） surface, which is used as a template for fabricating functional nanostructures needed in future nano devices and catalysis.展开更多
Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional ...Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.展开更多
A1N is used as high power LED package material because of its excellent thermal conductivity. But its poor adhesive with metal is not compatible with the later processing sequence. The properties of the bonding betwee...A1N is used as high power LED package material because of its excellent thermal conductivity. But its poor adhesive with metal is not compatible with the later processing sequence. The properties of the bonding between the deposited palladium, silver, copper and the clean Al-terminated （0001） surface of wurtzite AIN are investigated by using the density-functional the- ory. The results show that the sites of deposited metal atoms on N site are more stable than that on A1 site. Relaxations are found at all the studied interfaces. The bonding energies of Pd/A1N, Ag/A1N and Cu/A1N are respectively 2.75, 1.98, 2.26 eV. Hybridizations of s orbit and p orbit of the deposited metal atoms are observed, which contributes to the bonding energy of interface. The moving to lower energy state of the d orbit and the easier transfer of electrons to semi-empty d orbit in the case of deposited Pd results in the higher bonding energy of Pd/A1N interface.展开更多
ZnO adsorption on sapphire (0001) surface is theoretically calculated by using a plane wave ultrasoft pseudo-potential method based on ab initio molecular dynamics. The results reveal that the surface relaxation in th...ZnO adsorption on sapphire (0001) surface is theoretically calculated by using a plane wave ultrasoft pseudo-potential method based on ab initio molecular dynamics. The results reveal that the surface relaxation in the first layer Al-O is reduced, even eliminated after the surface adsorption of ZnO, and the chemical bonding energy is 434.3(±38.6) kJ·mol?1. The chemical bond of ZnO (0.185 ± 0.01 nm) has a 30° angle away from the adjacent Al-O bond, and the stable chemical adsorption position of the Zn is deflected from the surface O-hexagonal symmetry with an angle of about 30°. The analysis of the atomic populations, density of state and bonding electronic density before and after the adsorption indicates that the chemical bond formed by the O2 of the ZnO ? and the surface Al3+ has a strong ionic bonding characteristic, while the chemical bond formed by the Zn2+ and the surface O2 has an obvious covalent characteristic, which ? comes mainly from the hybridization of the Zn 4s and the O 2p and partially from that of the Zn 3d and the O 2p.展开更多
The microstructures of the oxide layers formed on near （0001） plane of Zircaloy-4 were investigated by autoclave tests at 360 ℃ in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at...The microstructures of the oxide layers formed on near （0001） plane of Zircaloy-4 were investigated by autoclave tests at 360 ℃ in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at the undulating O/M interface, and the inner surface morphology of the oxide layers formed on （0001） was only concave- convex. Monoclinic, tetragonal and cubic phases and a kind of zirconium sub-oxide with bcc structure were detected in the oxide layer near the metal matrix. This zirconium sub-oxide layer had a coherent relationship with a-Zr matrix, and the growth direction of the zirconium sub-oxide layer was nearly parallel to the [0001] direction of a-Zr regardless of the orientation of metal matrix. The orientations scattering of columnar grains formed on near （0001） plane differ from that formed on near （1010） plane.展开更多
The adsorption and decomposition of H2S on the ZnO（0001） surface have been investigated with first-principles calculations.The results reveal that H2S is dissociatively adsorbed on the clean ZnO（0001） surface to g...The adsorption and decomposition of H2S on the ZnO（0001） surface have been investigated with first-principles calculations.The results reveal that H2S is dissociatively adsorbed on the clean ZnO（0001） surface to generate HS-and hydrogen species.To our interest,as indicated by Mulliken charge and density of states of the configuration calculation,the bonding mechanism of H2S on the ZnO（0001） surface can involve the donation of charge from the ＂s lone pairs＂ into the surface and the back donation of surface electrons to H2S.Therefore,the electrons should play an important role in decomposition.Furthermore,the reactivity of H2S adsorption and further thermal decomposition reactions on the ZnO（0001） surface have also been discussed by calculating the possible reaction pathways.As expected,H2 will be easily generated during the decomposition process.展开更多
The addition reactions of alkenes and alkynes to the H-terminated GaN （0001） surface with a Ga dangling-bond have been studied employing periodic density functional theory （PDFT） calculations. Detailed information...The addition reactions of alkenes and alkynes to the H-terminated GaN （0001） surface with a Ga dangling-bond have been studied employing periodic density functional theory （PDFT） calculations. Detailed information on the reaction pathways of these alkenes and alkynes with H-GaN （0001） surface is provided, which indicates that the reactions contain two steps separated by the metastable intermediates： elementary addition reaction and H-abstraction process. From the energy curves, the reactions are clearly viable in the cases of ethene, styrene and phenylacetylene; while for ethyne, the H-abstraction barrier is higher than the desorption barrier of the intermediate, so the adsorbed C2H2 in intermediate is more likely to be desorbed back into the gas phase than to form a stable adsorbed species. Furthermore, it is obvious that for either alkenes or alkynes, the systems substituted by phenyl have more stable intermediates because π conjugation could improve their stabilities.展开更多
We report on temperature-programmed growth of graphene islands on Ru （0001） at annealing temperatures of 700 ℃, 800 ℃, and 900 ℃. The sizes of the islands each show a nonlinear increase with the annealing tempera...We report on temperature-programmed growth of graphene islands on Ru （0001） at annealing temperatures of 700 ℃, 800 ℃, and 900 ℃. The sizes of the islands each show a nonlinear increase with the annealing temperature. In 700 ℃ and 800 ℃annealings, the islands have nearly the same sizes and their ascending edges are embedded in the upper steps of the ruthenium substrate, which is in accordance with the etching growth mode. In 900 ℃ annealing, the islands are much larger and of lower quality, which represents the early stage of Smoluchowski ripening. A longer time annealing at 900 ℃ brings the islands to final equilibrium with an ordered moire pattern. Our work provides new details about graphene early growth stages that could facilitate the better control of such a growth to obtain graphene with ideal size and high quality.展开更多
Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by ...Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by the optical near field on the surface is measured as the electrostatic force. We demonstrated atomicresolution imaging of the near field on the α-Al2O3 （0001） surface of a prism. We investigated the spatial distribution of the near field by scanning at different tip-sample distances and found that the atomic corrugation of the near-field signal was observed at greater distances than that of the atomic force microscopy signal. As the tip-sample distance increased, the normalized signal-to-noise ratio of the near field is in a gradual decline almost twice that of the frequency shift （Δf）.展开更多
基金Project supported by the National Natural Science Foundation of China （Grant Nos 90406022 and 10674159）.
文摘We report on the formation of a graphene monolayer on a Ru（0001） surface by annealing the Ru（0001） crystal. The samples are characterized by scanning tunnelling microscopy （STM） and Auger electron spectroscopy （AES）. STM images show that the Moire pattern is caused by the graphene layer mismatched with the underlying Ru（0001） surface and has an N × N superlattice. It is further found that the graphene monolayer on a Ru（0001） surface is very stable at high temperatures. Our results provide a simple and convenient method to produce a graphene monolayer on the Ru（0001） surface, which is used as a template for fabricating functional nanostructures needed in future nano devices and catalysis.
基金Supported by the PhD Programs Foundation of Ministry of Education of China(Grant No.200805321032)the Science and Technology Program Project of Hunan Province(Grant No.2008GK3083)the Program for Changjiang Scholars and the Innovative Research Team in university(Grant No.531105050037)
文摘Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.
基金supported by the Foundation of Chongqing Science and Technology Commission (Grant Nos.CSTC2009AC4187,CSTC2008BB4408)
文摘A1N is used as high power LED package material because of its excellent thermal conductivity. But its poor adhesive with metal is not compatible with the later processing sequence. The properties of the bonding between the deposited palladium, silver, copper and the clean Al-terminated （0001） surface of wurtzite AIN are investigated by using the density-functional the- ory. The results show that the sites of deposited metal atoms on N site are more stable than that on A1 site. Relaxations are found at all the studied interfaces. The bonding energies of Pd/A1N, Ag/A1N and Cu/A1N are respectively 2.75, 1.98, 2.26 eV. Hybridizations of s orbit and p orbit of the deposited metal atoms are observed, which contributes to the bonding energy of interface. The moving to lower energy state of the d orbit and the easier transfer of electrons to semi-empty d orbit in the case of deposited Pd results in the higher bonding energy of Pd/A1N interface.
文摘ZnO adsorption on sapphire (0001) surface is theoretically calculated by using a plane wave ultrasoft pseudo-potential method based on ab initio molecular dynamics. The results reveal that the surface relaxation in the first layer Al-O is reduced, even eliminated after the surface adsorption of ZnO, and the chemical bonding energy is 434.3(±38.6) kJ·mol?1. The chemical bond of ZnO (0.185 ± 0.01 nm) has a 30° angle away from the adjacent Al-O bond, and the stable chemical adsorption position of the Zn is deflected from the surface O-hexagonal symmetry with an angle of about 30°. The analysis of the atomic populations, density of state and bonding electronic density before and after the adsorption indicates that the chemical bond formed by the O2 of the ZnO ? and the surface Al3+ has a strong ionic bonding characteristic, while the chemical bond formed by the Zn2+ and the surface O2 has an obvious covalent characteristic, which ? comes mainly from the hybridization of the Zn 4s and the O 2p and partially from that of the Zn 3d and the O 2p.
基金financially supported by the National Natural Science Foundation of China (Nos. 51171102 and 51271104)
文摘The microstructures of the oxide layers formed on near （0001） plane of Zircaloy-4 were investigated by autoclave tests at 360 ℃ in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at the undulating O/M interface, and the inner surface morphology of the oxide layers formed on （0001） was only concave- convex. Monoclinic, tetragonal and cubic phases and a kind of zirconium sub-oxide with bcc structure were detected in the oxide layer near the metal matrix. This zirconium sub-oxide layer had a coherent relationship with a-Zr matrix, and the growth direction of the zirconium sub-oxide layer was nearly parallel to the [0001] direction of a-Zr regardless of the orientation of metal matrix. The orientations scattering of columnar grains formed on near （0001） plane differ from that formed on near （1010） plane.
基金supported by the Natural Science Foundation of Fujian Province (No. E0510004)
文摘The adsorption and decomposition of H2S on the ZnO（0001） surface have been investigated with first-principles calculations.The results reveal that H2S is dissociatively adsorbed on the clean ZnO（0001） surface to generate HS-and hydrogen species.To our interest,as indicated by Mulliken charge and density of states of the configuration calculation,the bonding mechanism of H2S on the ZnO（0001） surface can involve the donation of charge from the ＂s lone pairs＂ into the surface and the back donation of surface electrons to H2S.Therefore,the electrons should play an important role in decomposition.Furthermore,the reactivity of H2S adsorption and further thermal decomposition reactions on the ZnO（0001） surface have also been discussed by calculating the possible reaction pathways.As expected,H2 will be easily generated during the decomposition process.
基金Supported by the National Natural Science Foundation of China (No 20673019)
文摘The addition reactions of alkenes and alkynes to the H-terminated GaN （0001） surface with a Ga dangling-bond have been studied employing periodic density functional theory （PDFT） calculations. Detailed information on the reaction pathways of these alkenes and alkynes with H-GaN （0001） surface is provided, which indicates that the reactions contain two steps separated by the metastable intermediates： elementary addition reaction and H-abstraction process. From the energy curves, the reactions are clearly viable in the cases of ethene, styrene and phenylacetylene; while for ethyne, the H-abstraction barrier is higher than the desorption barrier of the intermediate, so the adsorbed C2H2 in intermediate is more likely to be desorbed back into the gas phase than to form a stable adsorbed species. Furthermore, it is obvious that for either alkenes or alkynes, the systems substituted by phenyl have more stable intermediates because π conjugation could improve their stabilities.
基金Project supported by the National Basic Research Program of China (Grant Nos. 2011CB932700,2010CB923004,2010CB923004,and 2009CB929103)the National Natural Science Foundation of China (Grant Nos. 10834011 and 60976089)the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences (Grant No. KJCX2-YW-W22)
文摘We report on temperature-programmed growth of graphene islands on Ru （0001） at annealing temperatures of 700 ℃, 800 ℃, and 900 ℃. The sizes of the islands each show a nonlinear increase with the annealing temperature. In 700 ℃ and 800 ℃annealings, the islands have nearly the same sizes and their ascending edges are embedded in the upper steps of the ruthenium substrate, which is in accordance with the etching growth mode. In 900 ℃ annealing, the islands are much larger and of lower quality, which represents the early stage of Smoluchowski ripening. A longer time annealing at 900 ℃ brings the islands to final equilibrium with an ordered moire pattern. Our work provides new details about graphene early growth stages that could facilitate the better control of such a growth to obtain graphene with ideal size and high quality.
文摘Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by the optical near field on the surface is measured as the electrostatic force. We demonstrated atomicresolution imaging of the near field on the α-Al2O3 （0001） surface of a prism. We investigated the spatial distribution of the near field by scanning at different tip-sample distances and found that the atomic corrugation of the near-field signal was observed at greater distances than that of the atomic force microscopy signal. As the tip-sample distance increased, the normalized signal-to-noise ratio of the near field is in a gradual decline almost twice that of the frequency shift （Δf）.
