A series of hydrogenated silicon thin films were prepared by the radio frequency plasma enhanced chemical vapor deposition method (RF-PECVD) with various si-lane concentrations. The influence of silane concentration o...A series of hydrogenated silicon thin films were prepared by the radio frequency plasma enhanced chemical vapor deposition method (RF-PECVD) with various si-lane concentrations. The influence of silane concentration on structural and elec-trical characteristics of these films was investigated to study the phase transition region from amorphous to microcrystalline phase. At the same time,optical emis-sion spectra (OES) from the plasma during the deposition process were monitored to get information about the plasma properties,Raman spectra were measured to study the structural characteristics of the deposited films. The combinatorial analysis of OES and Raman spectra results demonstrated that the OES can be used as a fast method to diagnose phase transition from amorphous to microcrystalline silicon. At last the physical mechanism,why both OES and Raman can be used to diagnose the phase transition,was analyzed theoretically.展开更多
Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers no...Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers normally yields a microscopic phase-segregated structure consisting of pure C and BN domains. Further, growing the truly ternary B-C-N phase layers with homogenous atomic arrangements has proven to be very challenging. Here, in designing a better- controlled process for the chemical vapor deposition （CVD） growth of B-C-N atomic layer films with the minimized C and BN phase segregation, we selected trimethyl borane （TMB）, a gaseous organoboron compound with pre-existing B--C bonds, as the molecular precursor to react with ammonia （NH3） gas that serves as the nitrification agent. The use of this unique B-C delivery precursor allows for the successful synthesis of high-quality and large-area B-C-N atomic layer films. Moreover, the TMB/NH3 reactant combination can offer a high level of tunability and control of the overall chemical composition of B-C-N atomic layers by regulating the relative partial pressure of two gaseous reactants. Electrical transport measurements show that a finite energy gap can be opened in the as-grown B-C-N atomic layers and its tunability is essentially dependent on the relative C to BN atomic compositions. On the basis of carefully controlled experiments, we show that the pre-existing B-C bonds in the TMB molecular precursor have played a crucial role in effectively reducing the C and BN phase segregation problem, thereby facilitating the formation of truly ternary B-C-N phase atomic layers.展开更多
We demonstrate the synthesis of a novel self-anchored catalyst structure containing a Fe-Ni alloy nanosheet generated by phase separation for the substrate-free synthesis of carbon nanostructures. Fast Fourier transfo...We demonstrate the synthesis of a novel self-anchored catalyst structure containing a Fe-Ni alloy nanosheet generated by phase separation for the substrate-free synthesis of carbon nanostructures. Fast Fourier transform analysis was carried out in order to investigate both the phase and structural evolution of the alloy nanosheet during reduction and chemical vapor deposition （CVD） growth. y-Fe-Ni （Feo.64Nio.36） and a-Fe-Ni （kamacite） phases were formed and separated on the NiFe204 nanosheet catalyst precursor during H2 reduction, forming selfanchored mono-dispersed y-Fe-Ni nanocrystals on a a-Fe-Ni matrix. The Fe-Ni alloy nanosheet serves both as a catalyst for growing metal-encapsulated carbon nano-onions （CNOs）, and as a support for anchoring these preformed nano- particles, yielding mono-dispersed catalyst nanoparticles with no requirement of additional substrates for the CVD growth. This synthesis is capable of mitigating the coalescence and Ostwald ripening without the assistance of an additional substrate. This structure allows for the growth of uniform-sized CNOs despite the aggregation, crumbling, and stacking of the alloy sheet. This study provides a promising design for novel catalyst structures by phase separation towards the substrate-free synthesis of carbon nanostructures in large scale. Finally, the ferromagnetic Feo.64Ni0.36@#CNOs particles demonstrate their application in both magnetic storage and water purification, as a non-toxic water treatment material.展开更多
The dependence of temperature on diamond growth region in ternary C-H-O phase diagram for diamond growth is calculated on the basis of the non-equilibrium thermodynamiccoupling model. With the rising of temperature, o...The dependence of temperature on diamond growth region in ternary C-H-O phase diagram for diamond growth is calculated on the basis of the non-equilibrium thermodynamiccoupling model. With the rising of temperature, on the whole the diamond growth region inisotherm phase diagram seems to rotate anti-clockwise around its core. In the meantime, itsshape gradually changes from an arch to a triangle via a transition shape like trapezium. Apossible diamond growth region in a projective ternary C-H-O phase diagram is also conducted, and is in agreement with the experimental data reported by Marinelli et al.展开更多
GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si（111） substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional （3D...GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si（111） substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional （3D） mode to the 2I） one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy （TEM） measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.展开更多
B2CN precursor is prepared by a mechanical vibration-milling process using amorphous boron, graphite and h-BN powders with mole ratio of 1：1：1. A mixture of precursor and Ca3B2N4 catalyst is treated under high press...B2CN precursor is prepared by a mechanical vibration-milling process using amorphous boron, graphite and h-BN powders with mole ratio of 1：1：1. A mixture of precursor and Ca3B2N4 catalyst is treated under high pressure and high temperature. A boron rich cubic B（CxN1-x） phase is obtained after removing the catalyst by acid treatment. The average C content of the boron-rich cubic phase is about 6 at.% detected by energy-dispersive x-ray analysis spectroscopy. It is found that the highest carbon content in the cubic phase is as large as 16 at.%.展开更多
The gas phase process of diamond film deposition from CH4/H2 gas mixture by electron-assisted chemical vapor deposition is simulated by the Monte-Carlo method. The electron velocity distribution under different E/P (t...The gas phase process of diamond film deposition from CH4/H2 gas mixture by electron-assisted chemical vapor deposition is simulated by the Monte-Carlo method. The electron velocity distribution under different E/P (the ratio of the electric field to gas pressure) is obtained, and the velocity profile is asymmetric. The variation of the number density of CH3 and H with different CH4 concentrations and gas pressure is investigated, and the optimal experimental parameters are obtained: the gas pressure is in the range of 2.5 kPa - 15 kPa and the CH4 concentration is in the range of 0.5% - 1%. The energy carried by the fragment CH3 as the function of the experiment parameters is investigated to explain the diamond growth at low temperature. These results will be helpful to the selection of optimum experimental conditions for high quality diamond films deposition in EACVD and the modeling of plasma chemical vapor deposition.展开更多
Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was ...Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.展开更多
The thermodynamic phase stability area diagrams of BCl3-NH3-Si Cl4-H2-Ar system were plotted via Factsage software to predict the kinetic experimental results. The effects of parameters(i e, partial pressure of reacta...The thermodynamic phase stability area diagrams of BCl3-NH3-Si Cl4-H2-Ar system were plotted via Factsage software to predict the kinetic experimental results. The effects of parameters(i e, partial pressure of reactants, deposition temperature and total pressure) on the distribution regions of solid phase products were analyzed based on the diagrams. The results show that:(a) Solid phase products are mainly affected by deposition temperature. The area of BN+Si3N4 phase increases with the temperature rising from 650 to 900 ℃, and decreases with the temperature rising from 900 to 1 200 ℃;(b) When temperature and total pressure are constants, BN+Si3N4 phase exists at a high partial pressure of NH3;(c) The effect of total system pressure is correlated to deposition temperature. The temperature ranging from 700 to 900 ℃ under low total pressure is the optimum condition for the deposition.(d) Appropriate kinetic parameters can be determined based on the results of thermodynamic calculation. Si–B–N coating is obtained via low pressure chemical vapor deposition. The analysis by X-ray photoelectron spectroscopy indicates that B–N and Si–N are the main chemical bonds of the coating.展开更多
基金Supported by the National Basic Research Program of China (Grant Nos. 2006CB202602 and 2006CB202603)
文摘A series of hydrogenated silicon thin films were prepared by the radio frequency plasma enhanced chemical vapor deposition method (RF-PECVD) with various si-lane concentrations. The influence of silane concentration on structural and elec-trical characteristics of these films was investigated to study the phase transition region from amorphous to microcrystalline phase. At the same time,optical emis-sion spectra (OES) from the plasma during the deposition process were monitored to get information about the plasma properties,Raman spectra were measured to study the structural characteristics of the deposited films. The combinatorial analysis of OES and Raman spectra results demonstrated that the OES can be used as a fast method to diagnose phase transition from amorphous to microcrystalline silicon. At last the physical mechanism,why both OES and Raman can be used to diagnose the phase transition,was analyzed theoretically.
基金Acknowledgements We acknowledge financial support from the National Natural Science Foundation of China （Nos. 21322304 and 51472267） and the National Basic Research Program of China （Nos. 2012CB933003 and 2013CB932603） and the Strategic Priority Research Program B of the Chinese Academy of Sciences （No. XDB07030100） of China.
文摘Graphene-like, ternary system B-C-N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B-C-N atomic layers normally yields a microscopic phase-segregated structure consisting of pure C and BN domains. Further, growing the truly ternary B-C-N phase layers with homogenous atomic arrangements has proven to be very challenging. Here, in designing a better- controlled process for the chemical vapor deposition （CVD） growth of B-C-N atomic layer films with the minimized C and BN phase segregation, we selected trimethyl borane （TMB）, a gaseous organoboron compound with pre-existing B--C bonds, as the molecular precursor to react with ammonia （NH3） gas that serves as the nitrification agent. The use of this unique B-C delivery precursor allows for the successful synthesis of high-quality and large-area B-C-N atomic layer films. Moreover, the TMB/NH3 reactant combination can offer a high level of tunability and control of the overall chemical composition of B-C-N atomic layers by regulating the relative partial pressure of two gaseous reactants. Electrical transport measurements show that a finite energy gap can be opened in the as-grown B-C-N atomic layers and its tunability is essentially dependent on the relative C to BN atomic compositions. On the basis of carefully controlled experiments, we show that the pre-existing B-C bonds in the TMB molecular precursor have played a crucial role in effectively reducing the C and BN phase segregation problem, thereby facilitating the formation of truly ternary B-C-N phase atomic layers.
基金The authors acknowledge the finance support by the National Natural Science Foundation of China （Nos. 51531004 and 51272173） and Foundation for SinoEuro Cooperative Project from Chinese Ministry of Science and Technology （No. SQ2013ZOA100006）. The authors also acknowledge helpful discussion with Dr. Jiancan Yu in Nanyang Technological University in Singapore.
文摘We demonstrate the synthesis of a novel self-anchored catalyst structure containing a Fe-Ni alloy nanosheet generated by phase separation for the substrate-free synthesis of carbon nanostructures. Fast Fourier transform analysis was carried out in order to investigate both the phase and structural evolution of the alloy nanosheet during reduction and chemical vapor deposition （CVD） growth. y-Fe-Ni （Feo.64Nio.36） and a-Fe-Ni （kamacite） phases were formed and separated on the NiFe204 nanosheet catalyst precursor during H2 reduction, forming selfanchored mono-dispersed y-Fe-Ni nanocrystals on a a-Fe-Ni matrix. The Fe-Ni alloy nanosheet serves both as a catalyst for growing metal-encapsulated carbon nano-onions （CNOs）, and as a support for anchoring these preformed nano- particles, yielding mono-dispersed catalyst nanoparticles with no requirement of additional substrates for the CVD growth. This synthesis is capable of mitigating the coalescence and Ostwald ripening without the assistance of an additional substrate. This structure allows for the growth of uniform-sized CNOs despite the aggregation, crumbling, and stacking of the alloy sheet. This study provides a promising design for novel catalyst structures by phase separation towards the substrate-free synthesis of carbon nanostructures in large scale. Finally, the ferromagnetic Feo.64Ni0.36@#CNOs particles demonstrate their application in both magnetic storage and water purification, as a non-toxic water treatment material.
基金Supported by the High Technology Research and Development Programme of Chinathe National Natural Science Foundation of China
文摘The dependence of temperature on diamond growth region in ternary C-H-O phase diagram for diamond growth is calculated on the basis of the non-equilibrium thermodynamiccoupling model. With the rising of temperature, on the whole the diamond growth region inisotherm phase diagram seems to rotate anti-clockwise around its core. In the meantime, itsshape gradually changes from an arch to a triangle via a transition shape like trapezium. Apossible diamond growth region in a projective ternary C-H-O phase diagram is also conducted, and is in agreement with the experimental data reported by Marinelli et al.
基金Supported by the National Natural Science Foundation of China under Grant No 60476021.
文摘GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si（111） substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional （3D） mode to the 2I） one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy （TEM） measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50225207, 50372055 and 50472051, and the National Basic Research Programme of China under Grant No 2005CB724400.
文摘B2CN precursor is prepared by a mechanical vibration-milling process using amorphous boron, graphite and h-BN powders with mole ratio of 1：1：1. A mixture of precursor and Ca3B2N4 catalyst is treated under high pressure and high temperature. A boron rich cubic B（CxN1-x） phase is obtained after removing the catalyst by acid treatment. The average C content of the boron-rich cubic phase is about 6 at.% detected by energy-dispersive x-ray analysis spectroscopy. It is found that the highest carbon content in the cubic phase is as large as 16 at.%.
基金The project supported by the Nature Science Foundation of Hebei Province, China (No 502121)
文摘The gas phase process of diamond film deposition from CH4/H2 gas mixture by electron-assisted chemical vapor deposition is simulated by the Monte-Carlo method. The electron velocity distribution under different E/P (the ratio of the electric field to gas pressure) is obtained, and the velocity profile is asymmetric. The variation of the number density of CH3 and H with different CH4 concentrations and gas pressure is investigated, and the optimal experimental parameters are obtained: the gas pressure is in the range of 2.5 kPa - 15 kPa and the CH4 concentration is in the range of 0.5% - 1%. The energy carried by the fragment CH3 as the function of the experiment parameters is investigated to explain the diamond growth at low temperature. These results will be helpful to the selection of optimum experimental conditions for high quality diamond films deposition in EACVD and the modeling of plasma chemical vapor deposition.
基金the National High-Tech Research and Development Program of China (No.2002AA305508)the National Natural Science Foundation of China (No.50472095)+1 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars (No.2003-14)Beijing Novel Project (No. 2003A13).]
文摘Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.
基金Funded by the National Natural Science Foundation of China(Nos.51002120,51472201)
文摘The thermodynamic phase stability area diagrams of BCl3-NH3-Si Cl4-H2-Ar system were plotted via Factsage software to predict the kinetic experimental results. The effects of parameters(i e, partial pressure of reactants, deposition temperature and total pressure) on the distribution regions of solid phase products were analyzed based on the diagrams. The results show that:(a) Solid phase products are mainly affected by deposition temperature. The area of BN+Si3N4 phase increases with the temperature rising from 650 to 900 ℃, and decreases with the temperature rising from 900 to 1 200 ℃;(b) When temperature and total pressure are constants, BN+Si3N4 phase exists at a high partial pressure of NH3;(c) The effect of total system pressure is correlated to deposition temperature. The temperature ranging from 700 to 900 ℃ under low total pressure is the optimum condition for the deposition.(d) Appropriate kinetic parameters can be determined based on the results of thermodynamic calculation. Si–B–N coating is obtained via low pressure chemical vapor deposition. The analysis by X-ray photoelectron spectroscopy indicates that B–N and Si–N are the main chemical bonds of the coating.
