Aligned carbon nanotube (CNRT) films exhibit excellent electron emission properties at very low fields. This has been attributed to the high aspect ratio of CNTs, I.e. Their emitting surface can have high local field ...Aligned carbon nanotube (CNRT) films exhibit excellent electron emission properties at very low fields. This has been attributed to the high aspect ratio of CNTs, I.e. Their emitting surface can have high local field due to geometrical enhancement. It is found that a new mechanism can be responsible for the enhancement of the local field on the emitting surface of CNTs. This results from the space charge in the vacuum gap, which is readily generated due to the high emission current density of CNTs. Details are given of both experimental and theoretical studies of this effect. The mechanism also accounts for the distinct nonlinearity in Fowler-Nordheim plots often observed with CNTs. The implication of the technical application of our findings is also included.展开更多
Significant field emission has been observed from thin(<1000Å)amorphous-carbon-nitride(a-CN)films.X-ray photoelectron spectroscopy,infrared spectrometry,and UV-visible optical absorption spectrometry have been...Significant field emission has been observed from thin(<1000Å)amorphous-carbon-nitride(a-CN)films.X-ray photoelectron spectroscopy,infrared spectrometry,and UV-visible optical absorption spectrometry have been used to characterize the films.The field emission properties of the thin film have been studied by using a transparent anode imaging system.It is proposed that this class of films should be studied as candidates of coating material for cold cathode emitter,in order for one to benefit from their very high thermal conductivity and super hardness.展开更多
Amorphous CN:Ti films deposited by using the reactive magnetron sputtering method were annealed in vacuum under 200 to 600℃. Incorporation of Ti (less than 3at.%) has brought some new perspectives to the material. El...Amorphous CN:Ti films deposited by using the reactive magnetron sputtering method were annealed in vacuum under 200 to 600℃. Incorporation of Ti (less than 3at.%) has brought some new perspectives to the material. Electron-energy-loss spectrum indicates improved conductivity in CN:Ti films as in the insulating CN films. The high-resolution core-level x-ray photoelectron spectroscopy (XPS) studies show that most carbon atoms form homeopolar bonding in as-deposited CN:Ti film. While the N Is line always shrinks with increasing annealing temperature, the total full width at half maximum of C Is line decreases only at annealing temperature over 300℃ when the broadening due to heterobonding formation is outdone by the effect of increasing order. An enhanced π-band feature in the valence-XPS spectra at high annealing temperatures confirms the graphitization tendency of this material.展开更多
Fick's first law is modified with an additional term df(x)/dx to describe the segregation phenomenon,f(x)is a local,analytical function related to the depth profile at equilibrium.It thus can be determined experim...Fick's first law is modified with an additional term df(x)/dx to describe the segregation phenomenon,f(x)is a local,analytical function related to the depth profile at equilibrium.It thus can be determined experimentally by depth profiling technique.Segregation starting in an initially homogeneous solid is described by an inhomogeneous diffusion equation on the half-infinite domain.Segregation with and without formation of overlayer suggests different boundary conditions.The solution for the Ansatz f(x)=as exp(-x/d_(s))is in perfect agreement with experimental results on sulphur segregation to the surface of titanium.Independent from the detailed kinetics,activation energy can be inferred from the surface concentration evolution under different temperatures.For sulphur segregation in titanium,E_(act)=718 meV/atom.展开更多
Diamond thin films are grown with microwave plasma chemical vapor deposition method on silicon(100)substrates from methane/hydrogen gas mixture,and characterized with atomic force microscopy The results show that most...Diamond thin films are grown with microwave plasma chemical vapor deposition method on silicon(100)substrates from methane/hydrogen gas mixture,and characterized with atomic force microscopy The results show that most of the diamond crystallites are highly oriented with the(100)planes parallel to the silicon substrate.Layer structures are found in the film,indicating a combination of layer-by-layer and island growth.Raman spectrum and x-ray diffraction also confirm the present results.展开更多
A new molecular-dynamics method at constant pressure has been proposed.As the three edge vectors of a crystal cell as well as the position vectors of all particles are taken as independent variables,this method allows...A new molecular-dynamics method at constant pressure has been proposed.As the three edge vectors of a crystal cell as well as the position vectors of all particles are taken as independent variables,this method allows the crystal to relax fully.Furthermore,the effect of pressure on the crystal structure is explicitly given in this approach.As an example,the evolution process of cobalt from a structure far from the final one to the ideal hexagonal close packing structure was given.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.59525206the Education Ministry of China and the Higher Education Bureau,the Science and Technology Commission of Guangdong Province.
文摘Aligned carbon nanotube (CNRT) films exhibit excellent electron emission properties at very low fields. This has been attributed to the high aspect ratio of CNTs, I.e. Their emitting surface can have high local field due to geometrical enhancement. It is found that a new mechanism can be responsible for the enhancement of the local field on the emitting surface of CNTs. This results from the space charge in the vacuum gap, which is readily generated due to the high emission current density of CNTs. Details are given of both experimental and theoretical studies of this effect. The mechanism also accounts for the distinct nonlinearity in Fowler-Nordheim plots often observed with CNTs. The implication of the technical application of our findings is also included.
基金Supported by the National Natural Science Foundation for Outstanding Youth of China under Grant No.59525206the Higher Education Bureau of Guangdong Province.
文摘Significant field emission has been observed from thin(<1000Å)amorphous-carbon-nitride(a-CN)films.X-ray photoelectron spectroscopy,infrared spectrometry,and UV-visible optical absorption spectrometry have been used to characterize the films.The field emission properties of the thin film have been studied by using a transparent anode imaging system.It is proposed that this class of films should be studied as candidates of coating material for cold cathode emitter,in order for one to benefit from their very high thermal conductivity and super hardness.
基金the Volkswagen-Foundation,Germany,under the grant number 174701the K.C.Wong Education Foundation,Hong Kong.
文摘Amorphous CN:Ti films deposited by using the reactive magnetron sputtering method were annealed in vacuum under 200 to 600℃. Incorporation of Ti (less than 3at.%) has brought some new perspectives to the material. Electron-energy-loss spectrum indicates improved conductivity in CN:Ti films as in the insulating CN films. The high-resolution core-level x-ray photoelectron spectroscopy (XPS) studies show that most carbon atoms form homeopolar bonding in as-deposited CN:Ti film. While the N Is line always shrinks with increasing annealing temperature, the total full width at half maximum of C Is line decreases only at annealing temperature over 300℃ when the broadening due to heterobonding formation is outdone by the effect of increasing order. An enhanced π-band feature in the valence-XPS spectra at high annealing temperatures confirms the graphitization tendency of this material.
基金Supported by the Volkswagen Foundation,Hannover,Germany.
文摘Fick's first law is modified with an additional term df(x)/dx to describe the segregation phenomenon,f(x)is a local,analytical function related to the depth profile at equilibrium.It thus can be determined experimentally by depth profiling technique.Segregation starting in an initially homogeneous solid is described by an inhomogeneous diffusion equation on the half-infinite domain.Segregation with and without formation of overlayer suggests different boundary conditions.The solution for the Ansatz f(x)=as exp(-x/d_(s))is in perfect agreement with experimental results on sulphur segregation to the surface of titanium.Independent from the detailed kinetics,activation energy can be inferred from the surface concentration evolution under different temperatures.For sulphur segregation in titanium,E_(act)=718 meV/atom.
基金Supported by State Education Committee of China,and Chinese Academy of Sciences。
文摘Diamond thin films are grown with microwave plasma chemical vapor deposition method on silicon(100)substrates from methane/hydrogen gas mixture,and characterized with atomic force microscopy The results show that most of the diamond crystallites are highly oriented with the(100)planes parallel to the silicon substrate.Layer structures are found in the film,indicating a combination of layer-by-layer and island growth.Raman spectrum and x-ray diffraction also confirm the present results.
基金Supported by the National Natural Science Foundation of China under Grant No.69525409,and by the Chinese Outstanding Young Investigator Foundation by the Chinese Academy of Sciences.
文摘A new molecular-dynamics method at constant pressure has been proposed.As the three edge vectors of a crystal cell as well as the position vectors of all particles are taken as independent variables,this method allows the crystal to relax fully.Furthermore,the effect of pressure on the crystal structure is explicitly given in this approach.As an example,the evolution process of cobalt from a structure far from the final one to the ideal hexagonal close packing structure was given.
