Biomass-H_(2)O gasification is a complex thermochemical reaction,including three processes of volatile removal:homogeneous/heterogeneous reforming,biochar gasification and etching.The rate-determining step is biochar-...Biomass-H_(2)O gasification is a complex thermochemical reaction,including three processes of volatile removal:homogeneous/heterogeneous reforming,biochar gasification and etching.The rate-determining step is biochar-H_(2)O gasification and etching so the DFT is carried out to see the catalytic role of different metal elements(K/Ni)in the zigzag biochar model.The calculation results show that the gasification of biochar-H_(2)O needs to go through four processes:dissociative adsorption of water,hydrogen transfer(hydrogen desorption,hydrogen atom transfer),carbon dissolution and CO desorption.The energy barrier indicated that the most significant step in reducing the activation energy of K is reflected in the hydrogen transfer step,which is reduced from 374.14 kJ/mol to 152.41 kJ/mol;the catalytic effect of Ni is mainly reflected in the carbon dissolution step,which is reduced from 122.34 kJ/mol to 84.8 kJ/mol.The existence of K causes the edge to have a stronger attraction to H and does not destroy theπbonds of biochar molecules.The destruction ofπbonds is mainly due to the role of H free radicals,while the destruction ofπbonds will lead to easier C-C bond rupture.Ni shows a strong attraction to O in OH,which forms strong Ni-O chemical bonds.Ni can also destroy the aromatic structure directly,making the gasification easier to happen.This study explored the catalytic mechanism of K/Ni on the biochar-H_(2)O gasification at the molecular level and looked forward to the potential synergy of K/Ni,laying a foundation for experimental research and catalyst design.展开更多
This paper reviews the development of Meleis transition theory,explores the trajectory of the development of transition theory,analyses of the transition theory at home and abroad and research status,discusses the res...This paper reviews the development of Meleis transition theory,explores the trajectory of the development of transition theory,analyses of the transition theory at home and abroad and research status,discusses the research prospect of transition theory,in order to better apply Meleis transition theory to clinical nursing work,provide a certain basis for discipline development and nursing research.展开更多
Purpose: To explore the effect of comprehensive intervention based on transition theory in enhancing the readiness for discharge of post-operative breast cancer patients. Method: In a non-simultaneous controlled study...Purpose: To explore the effect of comprehensive intervention based on transition theory in enhancing the readiness for discharge of post-operative breast cancer patients. Method: In a non-simultaneous controlled study test, 99 post-operative breast cancer patients hospitalized between August 2019 and February 2020 were selected as the control group and 93 post-operative breast cancer patients hospitalized between March and August 2020 were selected as the test group at a Grade A tertiary tumor hospital. While the control group used the conventional care model, the test group added a comprehensive intervention based on transition theory to the routine nursing, which focused on stimulating patients’ awareness of health transitions, assisting patients to identify health critical events, strengthening social support and promoting self-management. The differences between the two groups were compared in terms of patient readiness for discharge and patient evaluation of the quality of discharge teaching. Result: The total score of readiness for discharge was higher in the test group than in the control group (171.7 ± 24.5 vs. 155.9 ± 28.9) and the scores for “Self-condition” (55.6 ± 8.2 vs. 50.8 ± 9.7), “Disease Knowledge” (64.7 ± 13.1 vs. 57.7 ± 13.8), “Coping Ability after Discharge” (24.6 ± 4.8 vs. 22.2 ± 5.6), “Expected Social Support after Discharge” (26.8 ± 4.5 vs. 25.2 ± 4.8) were higher than those of the control group, and all differences were statistically significant (p < 0.05). The total score of the test group on the quality of discharge teaching scale was higher than that of the control group (162.1 ± 19.9 vs. 152.6 ± 28.7), and the scores for “Content that Patients Self-perceived they required before discharge” (53.2 ± 9.5 vs. 49.4 ± 12.1), “Content that Patients Actually Acquired before Discharge” (51.2 ± 9.2 vs. 48.3 ± 11.3) and “Guiding Skills and Effects of Discharge for Nurses” (110.9 ± 12.6 vs. 104.3 ± 19.00) were also higher than those of the control group (p Conclusion: Comprehensive intervention based on transition theory for post-operative breast cancer patients is beneficial to improve the quality of discharge nursing guidance, thereby improving the readiness for discharge of patients and enhancing the sense of control and identity of patients after discharge.展开更多
Density functional theory calculations were carried out to explore the potential energy surface(PES) associated with the gas-phase reaction of Ni L2(L=SO3CH3) with acetone. The geometries and energies of the react...Density functional theory calculations were carried out to explore the potential energy surface(PES) associated with the gas-phase reaction of Ni L2(L=SO3CH3) with acetone. The geometries and energies of the reactants, intermediates, products and transition states of the triplet ground potential energy surfaces of [Ni, O, C2, H4] were obtained at the B3LYP/6-311++G(d,p) levels in C,H,O atoms and B3LYP/ Lanl2 dz in Ni atom. It was found through our calculations that the decabonylation of acetaldehyde contains four steps including encounter complexation, C-C activation, aldehyde H-shift and nonreactive dissociation. The results revealed that C-C activation induced by Ni L2(L=SO3CH3) led to the decarbonylation of acetaldehyde.展开更多
The gas phase reaction mechanism of Cl2 + I2 = 2ICl has been theoretically investigated by DFF method at the B3LYP/3-21 G* level. Transition states of three reaction channels were consequently given. The results ind...The gas phase reaction mechanism of Cl2 + I2 = 2ICl has been theoretically investigated by DFF method at the B3LYP/3-21 G* level. Transition states of three reaction channels were consequently given. The results indicate that in the title reaction the least activation energy of bi-molecular reaction was smaller than the dissociation energies of I2 and Cl2, and thus the reaction mechanism was the course of molecule-molecule interaction at low reaction rate. If other factors such as illumination were taken into account, I2 could dissociate into I atoms and then react with Cl2, or Cl2 dissociates into CI atoms and reacts with I2. These were photochemical reactions with high reaction speed. The theoretical results were further validated with absorbance measurement at 516 nm.展开更多
The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory(DFT). Varying from 3D to 2D four VSe2 structures, bulk 2H-...The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory(DFT). Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.展开更多
A simple model based on the statistics of single atoms is developed to predict the diffusion rate of thermal atoms in (or on) bulk materials without empirical parameters. Compared with vast classical molecular-dynam...A simple model based on the statistics of single atoms is developed to predict the diffusion rate of thermal atoms in (or on) bulk materials without empirical parameters. Compared with vast classical molecular-dynamics simulations for predicting the self-diffusion rate of Pt, Cu, and Ar adatoms on crystal surfaces, the model is proved to be much more accurate than the Arrhenius law and the transition state theory. Applying this model, the theoretical predictions agree well with the experimental values in the presented paper about the self-diffusion of Pt (Cu) adatoms on the surfaces.展开更多
A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 (2011)] or molecules [Chin. Phys. Lett. 29 080504 (2012)] was used to predict chemical reaction rates without empirical paramete...A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 (2011)] or molecules [Chin. Phys. Lett. 29 080504 (2012)] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.展开更多
The transit time difference of fluid particles moving along the upper and lower surfaces of a lift-producing airfoil is studied here both theoretically and numerically.We show that,under thin airfoil assumption and fo...The transit time difference of fluid particles moving along the upper and lower surfaces of a lift-producing airfoil is studied here both theoretically and numerically.We show that,under thin airfoil assumption and for potential flow,the transit time difference is equal to the circulation divided by the square of the inflow velocity and the lift coefficient is equal to half of the number of chords travelled by the airfoil during the transit time difference.An analysis of transit time difference for very thick airfoil(c.f.very large angle of attack)suggests the transit time may change sign beyond thin airfoil assumption,a conclusion supported by an example of flow with an attached vortex.Thus,fluid particles may transit the upper surface with less,equal and more time than those transiting the lower surface for lift producing airfoils,depending on the configuration of flow structure and geometry.展开更多
Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of ge...Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of generalized transition state and other kinetic features on the bottleneck of the po- tential energy surface are obtained. We point out that the location of generalized transition state tends to the direction in which the two atoms with larger reduced mass separate off. It can be determined whether a potential energy surface is accurate or not by a fine analysis of its bottleneck region and a comparison of kinetic calculation with experimental result. This is helpful for building a more accurate potential energy surface.展开更多
The reaction mechanism of ozone (O 3) addition to the double bonds of gas phase keto-limonene was investigated using ab initio methods.Two different possibilities for O 3 addition to the double bond were considered ...The reaction mechanism of ozone (O 3) addition to the double bonds of gas phase keto-limonene was investigated using ab initio methods.Two different possibilities for O 3 addition to the double bond were considered and two corresponding van der Waals complexes (Complex 1 and Complex 2) were found for 1-endo and 2-endo.The rate constants were calculated using the transition state theory at the CCSD(T)/6-31G(d)+ CF//B3LYP/6-31G(d,p) level.The high-pressure limit of the total rate constant at 298 K was 3.51×10-16 cm 3/(molecule·sec),which was in a good agreement with the experimental data.展开更多
4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction,heat sink and mechanical sealing.Nucleation plays a critical role in the deposition of the diam...4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction,heat sink and mechanical sealing.Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides.Nevertheless,as a typical polar material,the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet.In this contribution,nucleation of diamond was performed on the carbon-and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device.The nucleation density on the carbon-face is higher by 2-3 orders of magnitude compared to the silicon-face.Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film,which is different from columnar diamond growth structure on the silicon-face.Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals.In addition,kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s)dimers on silicon-faces than carbon-faces,resulting in much lower nucleation densities on silicon-faces.展开更多
Ab initio study of the reactions ofn-heptyl radicals(1-C7H15, 2-C7H15, 3-C7H15, and 4-C7H15) with metha- nol was conducted over the temperature range of 300--1500 K. Transition states for the reaction channels produ...Ab initio study of the reactions ofn-heptyl radicals(1-C7H15, 2-C7H15, 3-C7H15, and 4-C7H15) with metha- nol was conducted over the temperature range of 300--1500 K. Transition states for the reaction channels producing CTH15OH, CH3, C7H15OCH3, H, C7H16, CH2OH and CH30 were identified and the geometries of all stationary points were calculated at BB1K/MG3S level of theory. The potential barrier heights of the corresponding transition states were predicted by the CBS-QB3//BB1K and G4//BB1K methods, indicating that the eight H-abstraction channels are more kinetically favorable than the channels where OH transfers from CH3OH to C7H15 and where the CTHIsOCH3+H products are given. Tile rate constants of H-abstraction channels were calculated with TST and TST/Eck. Both the forward and reverse rate constants have positive temperature dependence and the ttmneling effect is only important at the temperature lower than 700 K. For the reactions of H-atom abstraction from methyl in CH3OH by n-heptyl, a reverse and the corresponding forward rate constant are roughly equal. For the reactions of H-atom abstraction from OH in CH3OH by n-heptyl, a reverse rate constant is larger by several orders of magnitude thin1 the corresponding forward one.展开更多
The stress relaxation of semi-crystalline nylon 1010 cannot be fitted by the Kohlrausch-Williams-Watts formula when the experiments were performed at pre-yielding regime below the glass transition temperature.We study...The stress relaxation of semi-crystalline nylon 1010 cannot be fitted by the Kohlrausch-Williams-Watts formula when the experiments were performed at pre-yielding regime below the glass transition temperature.We study this problem and identify the two-step mechanism of stress relaxation.At short time scale,relaxation is fast,dominated by stress biased thermal fluctuation with a fixed short-range length scale(activation volume).At long time scale,relaxation is slow due to the emergence of a cooperative long-range length scale determined by the stress fluctuation.The cooperative length scale is proportional to the reciprocal of stress and the amplitude of stress fluctuation is the product of stress and activation volume.Based on this two-step mechanism,we propose a new kinetics equation to capture the stress relaxation effectively,where the short time relaxation is described by an Eyring-like local activation and the long-time relaxation is captured by a cooperative excitation process resorting to an extension from the random first order transition theory.Our equation fits the experimental data well and can serve as a model to guide the related experiments of relaxation processes in crystalline solids.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant No.52276180)the Natural Science Foundation of Heilongjiang Province(Grant No.YQ2022E026).
文摘Biomass-H_(2)O gasification is a complex thermochemical reaction,including three processes of volatile removal:homogeneous/heterogeneous reforming,biochar gasification and etching.The rate-determining step is biochar-H_(2)O gasification and etching so the DFT is carried out to see the catalytic role of different metal elements(K/Ni)in the zigzag biochar model.The calculation results show that the gasification of biochar-H_(2)O needs to go through four processes:dissociative adsorption of water,hydrogen transfer(hydrogen desorption,hydrogen atom transfer),carbon dissolution and CO desorption.The energy barrier indicated that the most significant step in reducing the activation energy of K is reflected in the hydrogen transfer step,which is reduced from 374.14 kJ/mol to 152.41 kJ/mol;the catalytic effect of Ni is mainly reflected in the carbon dissolution step,which is reduced from 122.34 kJ/mol to 84.8 kJ/mol.The existence of K causes the edge to have a stronger attraction to H and does not destroy theπbonds of biochar molecules.The destruction ofπbonds is mainly due to the role of H free radicals,while the destruction ofπbonds will lead to easier C-C bond rupture.Ni shows a strong attraction to O in OH,which forms strong Ni-O chemical bonds.Ni can also destroy the aromatic structure directly,making the gasification easier to happen.This study explored the catalytic mechanism of K/Ni on the biochar-H_(2)O gasification at the molecular level and looked forward to the potential synergy of K/Ni,laying a foundation for experimental research and catalyst design.
文摘This paper reviews the development of Meleis transition theory,explores the trajectory of the development of transition theory,analyses of the transition theory at home and abroad and research status,discusses the research prospect of transition theory,in order to better apply Meleis transition theory to clinical nursing work,provide a certain basis for discipline development and nursing research.
文摘Purpose: To explore the effect of comprehensive intervention based on transition theory in enhancing the readiness for discharge of post-operative breast cancer patients. Method: In a non-simultaneous controlled study test, 99 post-operative breast cancer patients hospitalized between August 2019 and February 2020 were selected as the control group and 93 post-operative breast cancer patients hospitalized between March and August 2020 were selected as the test group at a Grade A tertiary tumor hospital. While the control group used the conventional care model, the test group added a comprehensive intervention based on transition theory to the routine nursing, which focused on stimulating patients’ awareness of health transitions, assisting patients to identify health critical events, strengthening social support and promoting self-management. The differences between the two groups were compared in terms of patient readiness for discharge and patient evaluation of the quality of discharge teaching. Result: The total score of readiness for discharge was higher in the test group than in the control group (171.7 ± 24.5 vs. 155.9 ± 28.9) and the scores for “Self-condition” (55.6 ± 8.2 vs. 50.8 ± 9.7), “Disease Knowledge” (64.7 ± 13.1 vs. 57.7 ± 13.8), “Coping Ability after Discharge” (24.6 ± 4.8 vs. 22.2 ± 5.6), “Expected Social Support after Discharge” (26.8 ± 4.5 vs. 25.2 ± 4.8) were higher than those of the control group, and all differences were statistically significant (p < 0.05). The total score of the test group on the quality of discharge teaching scale was higher than that of the control group (162.1 ± 19.9 vs. 152.6 ± 28.7), and the scores for “Content that Patients Self-perceived they required before discharge” (53.2 ± 9.5 vs. 49.4 ± 12.1), “Content that Patients Actually Acquired before Discharge” (51.2 ± 9.2 vs. 48.3 ± 11.3) and “Guiding Skills and Effects of Discharge for Nurses” (110.9 ± 12.6 vs. 104.3 ± 19.00) were also higher than those of the control group (p Conclusion: Comprehensive intervention based on transition theory for post-operative breast cancer patients is beneficial to improve the quality of discharge nursing guidance, thereby improving the readiness for discharge of patients and enhancing the sense of control and identity of patients after discharge.
基金Funded by the National Natural Science Foundation of China(No.51174179)
文摘Density functional theory calculations were carried out to explore the potential energy surface(PES) associated with the gas-phase reaction of Ni L2(L=SO3CH3) with acetone. The geometries and energies of the reactants, intermediates, products and transition states of the triplet ground potential energy surfaces of [Ni, O, C2, H4] were obtained at the B3LYP/6-311++G(d,p) levels in C,H,O atoms and B3LYP/ Lanl2 dz in Ni atom. It was found through our calculations that the decabonylation of acetaldehyde contains four steps including encounter complexation, C-C activation, aldehyde H-shift and nonreactive dissociation. The results revealed that C-C activation induced by Ni L2(L=SO3CH3) led to the decarbonylation of acetaldehyde.
基金Project supported by the Chinese Postdoctoral Science Foundation (No. 2003033486)
文摘The gas phase reaction mechanism of Cl2 + I2 = 2ICl has been theoretically investigated by DFF method at the B3LYP/3-21 G* level. Transition states of three reaction channels were consequently given. The results indicate that in the title reaction the least activation energy of bi-molecular reaction was smaller than the dissociation energies of I2 and Cl2, and thus the reaction mechanism was the course of molecule-molecule interaction at low reaction rate. If other factors such as illumination were taken into account, I2 could dissociate into I atoms and then react with Cl2, or Cl2 dissociates into CI atoms and reacts with I2. These were photochemical reactions with high reaction speed. The theoretical results were further validated with absorbance measurement at 516 nm.
基金Funded by the National Natural Science Foundation of China(No.11547115)the Science Research Foundation for Ph D of Liaoning Province(No.201501091)
文摘The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory(DFT). Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.
基金Project supported by the National Natural Science Foundation of China(Grant No.51071048)
文摘A simple model based on the statistics of single atoms is developed to predict the diffusion rate of thermal atoms in (or on) bulk materials without empirical parameters. Compared with vast classical molecular-dynamics simulations for predicting the self-diffusion rate of Pt, Cu, and Ar adatoms on crystal surfaces, the model is proved to be much more accurate than the Arrhenius law and the transition state theory. Applying this model, the theoretical predictions agree well with the experimental values in the presented paper about the self-diffusion of Pt (Cu) adatoms on the surfaces.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274073)the Leading Academic Discipline Project of Shanghai,China(Grant No.B107)
文摘A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 (2011)] or molecules [Chin. Phys. Lett. 29 080504 (2012)] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.
基金supported partly by the National Key Project of China(No.GJXM92579)the National Science and Technology Major Project of China(No.2017-II-003-0015)the National Natural Science Foundation of China(No.11721202)。
文摘The transit time difference of fluid particles moving along the upper and lower surfaces of a lift-producing airfoil is studied here both theoretically and numerically.We show that,under thin airfoil assumption and for potential flow,the transit time difference is equal to the circulation divided by the square of the inflow velocity and the lift coefficient is equal to half of the number of chords travelled by the airfoil during the transit time difference.An analysis of transit time difference for very thick airfoil(c.f.very large angle of attack)suggests the transit time may change sign beyond thin airfoil assumption,a conclusion supported by an example of flow with an attached vortex.Thus,fluid particles may transit the upper surface with less,equal and more time than those transiting the lower surface for lift producing airfoils,depending on the configuration of flow structure and geometry.
基金Project supported by the National Natural Science Foundation of China.
文摘Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of generalized transition state and other kinetic features on the bottleneck of the po- tential energy surface are obtained. We point out that the location of generalized transition state tends to the direction in which the two atoms with larger reduced mass separate off. It can be determined whether a potential energy surface is accurate or not by a fine analysis of its bottleneck region and a comparison of kinetic calculation with experimental result. This is helpful for building a more accurate potential energy surface.
基金supported by the National Natural Science Foundation of China (No.40975073)
文摘The reaction mechanism of ozone (O 3) addition to the double bonds of gas phase keto-limonene was investigated using ab initio methods.Two different possibilities for O 3 addition to the double bond were considered and two corresponding van der Waals complexes (Complex 1 and Complex 2) were found for 1-endo and 2-endo.The rate constants were calculated using the transition state theory at the CCSD(T)/6-31G(d)+ CF//B3LYP/6-31G(d,p) level.The high-pressure limit of the total rate constant at 298 K was 3.51×10-16 cm 3/(molecule·sec),which was in a good agreement with the experimental data.
基金the National Key Research and Development Project(No.2017YFE0128600)Ningbo 3315 Innovation Team(No.2019A-18-C)+9 种基金Science and Technology Innovation 2025 Major Project of Ningbo(No.2018023)National Defense Key Laboratory Fund(No.6142807180511)Innovation Funding of State Oceanic Administration(No.NBHY-2017-Z3)Ningbo Industrial Technology Innovation Project(No.2016B10038)‘13th Five-Year’Equipment Pre-research Sharing Project(No.E1710161)‘Key Talents’Senior Engineer Project of Ningbo Institute of Materials Technology and Engineeringthe financial support of CONICYT in the project Fondecyt 11180121the financial support given the VID in the framework of U-IniciaUI013/2018 and the academic direction of the University of Chilefinancial support from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University(Faculty Grant SFO Mat LiU No.200900971)the Swedish Research Council(VR)。
文摘4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction,heat sink and mechanical sealing.Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides.Nevertheless,as a typical polar material,the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet.In this contribution,nucleation of diamond was performed on the carbon-and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device.The nucleation density on the carbon-face is higher by 2-3 orders of magnitude compared to the silicon-face.Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film,which is different from columnar diamond growth structure on the silicon-face.Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals.In addition,kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s)dimers on silicon-faces than carbon-faces,resulting in much lower nucleation densities on silicon-faces.
基金Supported by the National Natural Science Foundation of China(No.51576139).
文摘Ab initio study of the reactions ofn-heptyl radicals(1-C7H15, 2-C7H15, 3-C7H15, and 4-C7H15) with metha- nol was conducted over the temperature range of 300--1500 K. Transition states for the reaction channels producing CTH15OH, CH3, C7H15OCH3, H, C7H16, CH2OH and CH30 were identified and the geometries of all stationary points were calculated at BB1K/MG3S level of theory. The potential barrier heights of the corresponding transition states were predicted by the CBS-QB3//BB1K and G4//BB1K methods, indicating that the eight H-abstraction channels are more kinetically favorable than the channels where OH transfers from CH3OH to C7H15 and where the CTHIsOCH3+H products are given. Tile rate constants of H-abstraction channels were calculated with TST and TST/Eck. Both the forward and reverse rate constants have positive temperature dependence and the ttmneling effect is only important at the temperature lower than 700 K. For the reactions of H-atom abstraction from methyl in CH3OH by n-heptyl, a reverse and the corresponding forward rate constant are roughly equal. For the reactions of H-atom abstraction from OH in CH3OH by n-heptyl, a reverse rate constant is larger by several orders of magnitude thin1 the corresponding forward one.
基金financially supported by the National Natural Science Foundation of China (Nos.21873054,21774131 and 21544007)the National Natural Science Foundation of China (Nos.U1862205 and 51673110)China Petroleum & Chemical Corporation for financial support。
文摘The stress relaxation of semi-crystalline nylon 1010 cannot be fitted by the Kohlrausch-Williams-Watts formula when the experiments were performed at pre-yielding regime below the glass transition temperature.We study this problem and identify the two-step mechanism of stress relaxation.At short time scale,relaxation is fast,dominated by stress biased thermal fluctuation with a fixed short-range length scale(activation volume).At long time scale,relaxation is slow due to the emergence of a cooperative long-range length scale determined by the stress fluctuation.The cooperative length scale is proportional to the reciprocal of stress and the amplitude of stress fluctuation is the product of stress and activation volume.Based on this two-step mechanism,we propose a new kinetics equation to capture the stress relaxation effectively,where the short time relaxation is described by an Eyring-like local activation and the long-time relaxation is captured by a cooperative excitation process resorting to an extension from the random first order transition theory.Our equation fits the experimental data well and can serve as a model to guide the related experiments of relaxation processes in crystalline solids.