Crystalline carbon nitride thin films were prepared on Si (100) substrates by a microwave plasma chemical vapor deposition method, using CH4/N2 as precursor gases. The surface morphologies of the carbon nitride films ...Crystalline carbon nitride thin films were prepared on Si (100) substrates by a microwave plasma chemical vapor deposition method, using CH4/N2 as precursor gases. The surface morphologies of the carbon nitride films deposited on Si substrate at 830℃ are consisted of hexagonal crystalline rods. The effect of substrate temperature on the formation of carbon nitrides was investigated. X-ray photoelectron spectroscopy analysis indicated that the maximum value of N/C in atomic ratio in the films deposited at a substrate temperature of 830℃ is 1 .20, which is close to the stoichiometric value of C3N4. The X-ray diffraction pattern of the films deposited at 830℃ indicates no amorphous phase in the films, which are composed of β- and α-C3N4 phase containing an unidentified C-N phase. Fourier transform infrared spectroscopy supports the existence of C-N covalent bond.展开更多
Periodic nitrogen-doped homoepitaxial nano-multilayers were grown by microwave plasma chemical vapor deposition. The residual time of gases(such as CH4and N2) in the chamber was determined by optical emission spectros...Periodic nitrogen-doped homoepitaxial nano-multilayers were grown by microwave plasma chemical vapor deposition. The residual time of gases(such as CH4and N2) in the chamber was determined by optical emission spectroscopy to determine the nano-multilayer growth process, and thin, nanoscale nitrogen-doped layers were obtained. The highest toughness of 18.2 MPa·m^(1/2)under a Young’s modulus of1000 GPa is obtained when the single-layer thickness of periodic nitrogen-doped nano-multilayers is about 96 nm. The fracture toughness of periodic nitrogen-doped CVD layer is about 2.1 times that of the HPHT seed substrate. Alternating tensile and compressive stresses are derived from periodic nitrogen doping;hence, the fracture toughness is significantly improved. Single-crystal diamond with a high toughness demonstrates wide application prospects for high-pressure anvils and single-point diamond cutting tools.展开更多
Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition(MPCVD)-grown samples.No abnormality has been detected on the apparatus especially the base pressure and fee...Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition(MPCVD)-grown samples.No abnormality has been detected on the apparatus especially the base pressure and feeding gas purity.By a comprehensive investigation including the analysis of the plasma composition,we found that a minor leakage of the system could be significantly magnified by the thermal effect,resulting in a considerable residual nitrogen in the diamond material.Moreover,the doping mechanism of leaked air is different to pure nitrogen doping.The dosage of several ppm of pure nitrogen can lead to efficient nitrogen incorporation in diamond,while at least thousands ppm of leaked air is required for detecting obvious residual nitrogen.The difference of the dosage has been ascribed to the suppression effect of oxygen that consumes nitrogen.As the unintentional impurity is basically detrimental to the controllable fabrication of diamond for electronic application,we have provided an effective way to suppress the residual nitrogen in a slightly leaked system by modifying the susceptor geometry.This study indicates that even if a normal base pressure can be reached,the nitrogen residing in the chamber can be“activated”by the thermal effect and thus be incorporated in diamond material grown by a MPCVD reactor.展开更多
This work proposed to change the structure of the sample susceptor of the microwave plasma chemical vapor deposition(MPCVD)reaction chamber,that is,to introduce a small hole in the center of the susceptor to study its...This work proposed to change the structure of the sample susceptor of the microwave plasma chemical vapor deposition(MPCVD)reaction chamber,that is,to introduce a small hole in the center of the susceptor to study its suppression effect on the incorporation of residual nitrogen in the MPCVD diamond film.By using COMSOL multiphysics software simulation,the plasma characteristics and the concentration of chemical reactants in the cylindrical cavity of MPCVD system were studied,including electric field intensity,electron number density,electron temperature,the concentrations of atomic hydrogen,methyl,and nitrogenous substances,etc.After introducing a small hole in the center of the molybdenum support susceptor,we found that no significant changes were found in the center area of the plasma,but the electron state in the plasma changed greatly on the surface above the susceptor.The electron number density was reduced by about 40%,while the electron temperature was reduced by about 0.02 eV,and the concentration of atomic nitrogen was decreased by about an order of magnitude.Moreover,we found that if a specific lower microwave input power is used,and a susceptor structure without the small hole is introduced,the change results similar to those in the surface area of the susceptor will be obtained,but the spatial distribution of electromagnetic field and reactant concentration will be changed.展开更多
Mo2C was prepared by microwave plasma chemical vapor deposition(MPCVD)technique with the power of 800 W and pressure of 18 kPa.Compared with traditional preparation methods,MPCVD has faster growth rate and higher puri...Mo2C was prepared by microwave plasma chemical vapor deposition(MPCVD)technique with the power of 800 W and pressure of 18 kPa.Compared with traditional preparation methods,MPCVD has faster growth rate and higher purity of the products.The influence of growth time on the morphology and structure of Mo_(2)C was characterized by X-ray diffraction and Scanning Electron Microscopy.The photocatalytic performance of Mo_(2)C was tested.It was found that Mo_(2)C had good photocatalytic performance and the 6 h sample had the highest photodegradation rate,indicating the great potential of Mo_(2)C as photocatalyst.展开更多
基金financed by the National NatUral Science Foundation of China(Grant No.19674009)Beijing Laboratory of Vacuum Physics,Chinese Academy of Sciences.
文摘Crystalline carbon nitride thin films were prepared on Si (100) substrates by a microwave plasma chemical vapor deposition method, using CH4/N2 as precursor gases. The surface morphologies of the carbon nitride films deposited on Si substrate at 830℃ are consisted of hexagonal crystalline rods. The effect of substrate temperature on the formation of carbon nitrides was investigated. X-ray photoelectron spectroscopy analysis indicated that the maximum value of N/C in atomic ratio in the films deposited at a substrate temperature of 830℃ is 1 .20, which is close to the stoichiometric value of C3N4. The X-ray diffraction pattern of the films deposited at 830℃ indicates no amorphous phase in the films, which are composed of β- and α-C3N4 phase containing an unidentified C-N phase. Fourier transform infrared spectroscopy supports the existence of C-N covalent bond.
基金financially supported by the National Key Research and Development Program of China (No.2018YFB0406501)the European Union’s Horizon 2020 Research and Innovation Staff Exchange (RISE) Scheme (No. 734578)the Beijing Natural Science Foundation (No. 4192038)。
文摘Periodic nitrogen-doped homoepitaxial nano-multilayers were grown by microwave plasma chemical vapor deposition. The residual time of gases(such as CH4and N2) in the chamber was determined by optical emission spectroscopy to determine the nano-multilayer growth process, and thin, nanoscale nitrogen-doped layers were obtained. The highest toughness of 18.2 MPa·m^(1/2)under a Young’s modulus of1000 GPa is obtained when the single-layer thickness of periodic nitrogen-doped nano-multilayers is about 96 nm. The fracture toughness of periodic nitrogen-doped CVD layer is about 2.1 times that of the HPHT seed substrate. Alternating tensile and compressive stresses are derived from periodic nitrogen doping;hence, the fracture toughness is significantly improved. Single-crystal diamond with a high toughness demonstrates wide application prospects for high-pressure anvils and single-point diamond cutting tools.
基金Project supported by the National Key R&D Program of China(Grant Nos.2018YFB0406502,2017YFF0210800,and 2017YFB0403003)the National Natural Science Foundation of China(Grant Nos.61974059,61674077,and 61774081)+1 种基金the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20160065)the Fundamental Research Funds for the Central Universities
文摘Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition(MPCVD)-grown samples.No abnormality has been detected on the apparatus especially the base pressure and feeding gas purity.By a comprehensive investigation including the analysis of the plasma composition,we found that a minor leakage of the system could be significantly magnified by the thermal effect,resulting in a considerable residual nitrogen in the diamond material.Moreover,the doping mechanism of leaked air is different to pure nitrogen doping.The dosage of several ppm of pure nitrogen can lead to efficient nitrogen incorporation in diamond,while at least thousands ppm of leaked air is required for detecting obvious residual nitrogen.The difference of the dosage has been ascribed to the suppression effect of oxygen that consumes nitrogen.As the unintentional impurity is basically detrimental to the controllable fabrication of diamond for electronic application,we have provided an effective way to suppress the residual nitrogen in a slightly leaked system by modifying the susceptor geometry.This study indicates that even if a normal base pressure can be reached,the nitrogen residing in the chamber can be“activated”by the thermal effect and thus be incorporated in diamond material grown by a MPCVD reactor.
基金financial support from the National Natural Science Foundation of China(Grant Nos.61974059,61674077,and 61774081)the Fundamental Research Funds for the Central Universities,China。
文摘This work proposed to change the structure of the sample susceptor of the microwave plasma chemical vapor deposition(MPCVD)reaction chamber,that is,to introduce a small hole in the center of the susceptor to study its suppression effect on the incorporation of residual nitrogen in the MPCVD diamond film.By using COMSOL multiphysics software simulation,the plasma characteristics and the concentration of chemical reactants in the cylindrical cavity of MPCVD system were studied,including electric field intensity,electron number density,electron temperature,the concentrations of atomic hydrogen,methyl,and nitrogenous substances,etc.After introducing a small hole in the center of the molybdenum support susceptor,we found that no significant changes were found in the center area of the plasma,but the electron state in the plasma changed greatly on the surface above the susceptor.The electron number density was reduced by about 40%,while the electron temperature was reduced by about 0.02 eV,and the concentration of atomic nitrogen was decreased by about an order of magnitude.Moreover,we found that if a specific lower microwave input power is used,and a susceptor structure without the small hole is introduced,the change results similar to those in the surface area of the susceptor will be obtained,but the spatial distribution of electromagnetic field and reactant concentration will be changed.
基金Hubei Provincial Department of Education(Q20201512)。
文摘Mo2C was prepared by microwave plasma chemical vapor deposition(MPCVD)technique with the power of 800 W and pressure of 18 kPa.Compared with traditional preparation methods,MPCVD has faster growth rate and higher purity of the products.The influence of growth time on the morphology and structure of Mo_(2)C was characterized by X-ray diffraction and Scanning Electron Microscopy.The photocatalytic performance of Mo_(2)C was tested.It was found that Mo_(2)C had good photocatalytic performance and the 6 h sample had the highest photodegradation rate,indicating the great potential of Mo_(2)C as photocatalyst.