Controlling catalytic activities through surface strain engineering remains a hot topic in electrocatalysis studies.Herein,ab initio molecular dynamics(AIMD)simulation associated with free energy sampling technology w...Controlling catalytic activities through surface strain engineering remains a hot topic in electrocatalysis studies.Herein,ab initio molecular dynamics(AIMD)simulation associated with free energy sampling technology were performed to study the energetics of the key step of producing C2 products in electrocatalytic reduction of CO or CO_(2),i.e.CO dimerization,on strained Cu(100)with an explicit aqueous solvent model.It is worth mentioning that when compressive strain reaches a certain extent,the surface of Cu(100)will undergo reconstruction.We showed that,from tensile to compressive strain,the free energy barrier of CO dimerization decreased,suggesting that the activity of CO dimerization increases.It was also found that some of the reconstructed surfaces showing the lowest free energy barriers but might be less stable can be stabilized in the presence of adsorbed O or CO.Upon detailed quantitative analysis on the charges of surface Cu atoms,we found that the free energy barriers were strongly correlated with the charge of Cu atoms where the OCCO intermediate adsorbs.When the surfaces structures of Cu(100)were altered under compressive strain,the electronic structure of surface Cu atoms was monitored and thus the activity of electrocatalytic CO dimerization can be tuned.展开更多
Understanding of metal oxidation is very critical to corrosion control,catalysis synthesis,and advanced materials engineering.Metal oxidation is a very complex phenomenon,with many different processes which are couple...Understanding of metal oxidation is very critical to corrosion control,catalysis synthesis,and advanced materials engineering.Metal oxidation is a very complex phenomenon,with many different processes which are coupled and involved from the onset of reaction.In this work,the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics(MD)simulations using a reactive force field(ReaxFF).We show that oxygen transport is the dominant process during the initial oxidation.Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titanium(0001)surface and further prevented oxidation in the deeper layers.The mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation.展开更多
This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 （001） by using classical molecular dynamics. It is found that these three surfaces re...This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 （001） by using classical molecular dynamics. It is found that these three surfaces relax instead of reconstruction at 0 K, and have little possibility to reconstruct below 40 K. Above 40 K, surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain. Several reconstruction patterns with approximate surface energies are found, and electrostatic potentials on them are also provided in comparison with possible microscopic results.展开更多
DNA/GO composite plays a significant role in the research field of biotechnology and nanotechnology,and attracts a great deal of interest.However,it is still unclear how the oxidation degree of the graphene-based surf...DNA/GO composite plays a significant role in the research field of biotechnology and nanotechnology,and attracts a great deal of interest.However,it is still unclear how the oxidation degree of the graphene-based surface affects the adsorption process of single-strand DNA(ssDNA).In this paper,based on the molecular dynamics simulations,we find that ssDNA molecule is absorbed on the GO surface in the most stable state with the oxidation degree around 15%.The microscopic mechanism is attributed to the van Der Walls and the electrostatic interactions between the ssDNA molecule and the graphene-based surface,which is accompanied with theπ-πstacking and hydrogen bond formation.The number ofπ-πstacking between ssDNA and GO reaches the maximum value when the oxidation degree is around 15%among all the GO surfaces.Our simulation results also reveal the coexistence of stretched and curved configurations as well as the adsorption orientation of ssDNA on the GO surface.Furthermore,it is found that the absorbed ssDNA molecules are more likely to move on the graphene-based surface of low oxidation degree,especially on pristine graphene.Our work provides the physics picture of ssDNA’s physisorption dynamics onto graphene-based surface and it is helpful in designing DNA/GO nanomaterials.展开更多
Main observation and conclusion In this paper,a series of ReaxFF molecular dynamic simulations were performed to study the oxidation of chemical passivated silicon(100)surface,which was terminated with different n-alk...Main observation and conclusion In this paper,a series of ReaxFF molecular dynamic simulations were performed to study the oxidation of chemical passivated silicon(100)surface,which was terminated with different n-alkyl chains.The simulated results showed that the oxidant species diffuse into Si substrate through peroxy-like structures during the oxidation process.During the oxidation process,the Si-alkyl(Si-C)covalent bond was stable and there is no occurrence of decomposition of the n-alkyl chains.In addition,the existence of n-alkyl monolayers on silicon surface did not change the initial reaction pathway of the oxidation process.The simulations indicated that the chemical passivation mechanism includes two parts,one is about the Si-C covalent bond occupying the active site of the reaction on Si(100)surface,and the other is about the oxygen penetrating Si-alkyl layers.The simulations also indicated that the chemical passivation of Si-alkyl is better for longer alkyl chains,which is consistent with the experimental observation.Our results have investigated the oxidation of chemical passivated silicon(100)surface at the atom level,which is helpful to comprehend the manufacture of semiconductor devices like metal-oxide-semiconductor(MOS)devices in the experiments.展开更多
Epoxy resin-reinforced graphite composites have found extensive application as bipolar plates in fuel cells for stationary power supplies,valued for their lightweight nature and exceptional durability.To enhance the i...Epoxy resin-reinforced graphite composites have found extensive application as bipolar plates in fuel cells for stationary power supplies,valued for their lightweight nature and exceptional durability.To enhance the interfacial properties between graphite and epoxy resin(EP),surface oxidation of graphite was carried out using diverse functional groups.Experimental assessments illustrated that the composites with graphite oxide resulted in heightened mechanical strength and toughness compared to pristine graphite,which could be attributed to the excellent interface connection.Moreover,these composites displayed remarkable conductivity while simultaneously retaining their mechanical attributes.Furthermore,molecular dynamics simulations outcomes unveiled that the inclusion of oxygen-containing functional groups on the graphite surface augmented the interfacial energy with EP,and the interface morphology between graphite and resin exhibited heightened stability throughout the stretching process.This simple and effective technique presents opportunities for improving composites interfaces,enabling high load transfer efficiency,and opens up a potential path for developing strong and tough composite bipolar plates for fuel cells.展开更多
At heterointerfaces between complex oxides with polar discontinuity, the instability-induced electric field may drive electron redistribution, causing a dramatic change in the interracial charge density. This results ...At heterointerfaces between complex oxides with polar discontinuity, the instability-induced electric field may drive electron redistribution, causing a dramatic change in the interracial charge density. This results in the emergence of a rich diversity of exotic physical phenomena in these quasi-two-dimensional systems, which can be further tuned by an external field. To develop novel multifunctional electronic devices, it is essential to control the growth of polar oxide films and heterointerfaces with atomic preci- sion. In this article, we review recent progress in control techniques for oxide film growth by molecular beam epitaxy （MBE）. We emphasize the importance of tuning the microscopic surface structures of polar films for developing precise growth control techniques. Taking the polar SrTiO3 （110） and （111） surfaces as examples, we show that, by keeping the surface reconstructed throughout MBE growth, high-quality layer-by-layer homoepitaxy can be realized. Because the stability of different reconstruc- tions is determined by the surface cation concentration, the growth rate from the Sr/Ti evaporation source can be monitored in real time. A precise, automated control method is established by which insulating homoepitaxial SrTiO3 （110） and （111） films can be obtained on doped metallic substrates. The films show atomically well-defined surfaces and high dielectric performance, which allows the surface carrier concentration to be tuned in the range of -1013/cm2. By applying the knowledge of microstructures from fundamental surface physics to film growth techniques, new opportunities are provided for material science and related research.展开更多
Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided qu...Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided quantitative evidence of the effect of oxidized surfaces to tribological properties. In the current study on 99.99% pure copper, it is revealed that tribo-oxidation and the resulting increased abrasive wear can be suppressed by processing in an extreme high vacuum (XHV) adequate environment. The XHV adequate atmosphere was realized by using a silane-doped shielding gas (1.5 vol% SiH4 in argon). To analyse the influence of the ambient atmosphere on the tribological and mechanical properties, a ball–disk tribometer and a nanoindenter were used in air, argon, and silane-doped argon atmosphere for temperatures up to 800 ℃. Resistance measurements of the resulting coatings were carried out. To characterize the microstructures and the chemical compositions of the samples, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. The investigations have revealed a formation of η-Cu3Si in silane-doped atmosphere at 300 ℃, as well as various intermediate stages of copper silicides. At temperatures above 300 ℃, the formation of γ-Cu5Si were detected. The formation was linked to an increase in hardness from 1.95 to 5.44 GPa, while the Young’s modulus increased by 46% to 178 GPa, with the significant reduction of the wear volume by a factor of 4.5 and the suppression of further oxidation and susceptibility of chemical wear. In addition, the relevant diffusion processes were identified using molecular dynamics (MD) simulations.展开更多
文摘Controlling catalytic activities through surface strain engineering remains a hot topic in electrocatalysis studies.Herein,ab initio molecular dynamics(AIMD)simulation associated with free energy sampling technology were performed to study the energetics of the key step of producing C2 products in electrocatalytic reduction of CO or CO_(2),i.e.CO dimerization,on strained Cu(100)with an explicit aqueous solvent model.It is worth mentioning that when compressive strain reaches a certain extent,the surface of Cu(100)will undergo reconstruction.We showed that,from tensile to compressive strain,the free energy barrier of CO dimerization decreased,suggesting that the activity of CO dimerization increases.It was also found that some of the reconstructed surfaces showing the lowest free energy barriers but might be less stable can be stabilized in the presence of adsorbed O or CO.Upon detailed quantitative analysis on the charges of surface Cu atoms,we found that the free energy barriers were strongly correlated with the charge of Cu atoms where the OCCO intermediate adsorbs.When the surfaces structures of Cu(100)were altered under compressive strain,the electronic structure of surface Cu atoms was monitored and thus the activity of electrocatalytic CO dimerization can be tuned.
基金Support of this work from the National Natural Science Foundation of China(Grant No.51361009)Work at Ames Laboratory was supported by the US Department of Energy,Basic Energy Sciences,Division of Materials Science and Engineering under Contract No.DE-AC02-07CH11358,including a grant of computer time at the National Energy Research Scientific Computing Centre(NERSC)in Berkeley,CA.
文摘Understanding of metal oxidation is very critical to corrosion control,catalysis synthesis,and advanced materials engineering.Metal oxidation is a very complex phenomenon,with many different processes which are coupled and involved from the onset of reaction.In this work,the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics(MD)simulations using a reactive force field(ReaxFF).We show that oxygen transport is the dominant process during the initial oxidation.Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titanium(0001)surface and further prevented oxidation in the deeper layers.The mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation.
基金supported by the National Natural Science Foundation of China (Grant No. 10964003)the Natural Science Foundation of Gansu Province (Grant No. 096RJZA102)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education (GrantNo. 20096201120002)the China Postdoctoral Science Foundation (Grant No. 20100470886)
文摘This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 （001） by using classical molecular dynamics. It is found that these three surfaces relax instead of reconstruction at 0 K, and have little possibility to reconstruct below 40 K. Above 40 K, surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain. Several reconstruction patterns with approximate surface energies are found, and electrostatic potentials on them are also provided in comparison with possible microscopic results.
基金the National Natural Science Foundation of China，the National High Technology Research and Development Program of China，Key Technology R&D Program of Jiangxi Province，Science and Technology Project of Universities in Jiangxi Province
基金supported by the National Natural Science Foundation of China(Grant Nos.11305237 and 11974366)the Fundamental Research Funds for the Central Universities,China,the Natural Science Foundation of Shanghai,China(Grant No.19ZR1463200)the Key Research Program of Chinese Academy of Sciences(Grant No.QYZDJ-SSW-SLH053).
文摘DNA/GO composite plays a significant role in the research field of biotechnology and nanotechnology,and attracts a great deal of interest.However,it is still unclear how the oxidation degree of the graphene-based surface affects the adsorption process of single-strand DNA(ssDNA).In this paper,based on the molecular dynamics simulations,we find that ssDNA molecule is absorbed on the GO surface in the most stable state with the oxidation degree around 15%.The microscopic mechanism is attributed to the van Der Walls and the electrostatic interactions between the ssDNA molecule and the graphene-based surface,which is accompanied with theπ-πstacking and hydrogen bond formation.The number ofπ-πstacking between ssDNA and GO reaches the maximum value when the oxidation degree is around 15%among all the GO surfaces.Our simulation results also reveal the coexistence of stretched and curved configurations as well as the adsorption orientation of ssDNA on the GO surface.Furthermore,it is found that the absorbed ssDNA molecules are more likely to move on the graphene-based surface of low oxidation degree,especially on pristine graphene.Our work provides the physics picture of ssDNA’s physisorption dynamics onto graphene-based surface and it is helpful in designing DNA/GO nanomaterials.
基金The authors are grateful for funding from the Youth Innovation Group of Shandong University(No.2020QNQT018).
文摘Main observation and conclusion In this paper,a series of ReaxFF molecular dynamic simulations were performed to study the oxidation of chemical passivated silicon(100)surface,which was terminated with different n-alkyl chains.The simulated results showed that the oxidant species diffuse into Si substrate through peroxy-like structures during the oxidation process.During the oxidation process,the Si-alkyl(Si-C)covalent bond was stable and there is no occurrence of decomposition of the n-alkyl chains.In addition,the existence of n-alkyl monolayers on silicon surface did not change the initial reaction pathway of the oxidation process.The simulations indicated that the chemical passivation mechanism includes two parts,one is about the Si-C covalent bond occupying the active site of the reaction on Si(100)surface,and the other is about the oxygen penetrating Si-alkyl layers.The simulations also indicated that the chemical passivation of Si-alkyl is better for longer alkyl chains,which is consistent with the experimental observation.Our results have investigated the oxidation of chemical passivated silicon(100)surface at the atom level,which is helpful to comprehend the manufacture of semiconductor devices like metal-oxide-semiconductor(MOS)devices in the experiments.
基金the financial supports from the National Key R&D Program of China(No.2020YFB1505901)。
文摘Epoxy resin-reinforced graphite composites have found extensive application as bipolar plates in fuel cells for stationary power supplies,valued for their lightweight nature and exceptional durability.To enhance the interfacial properties between graphite and epoxy resin(EP),surface oxidation of graphite was carried out using diverse functional groups.Experimental assessments illustrated that the composites with graphite oxide resulted in heightened mechanical strength and toughness compared to pristine graphite,which could be attributed to the excellent interface connection.Moreover,these composites displayed remarkable conductivity while simultaneously retaining their mechanical attributes.Furthermore,molecular dynamics simulations outcomes unveiled that the inclusion of oxygen-containing functional groups on the graphite surface augmented the interfacial energy with EP,and the interface morphology between graphite and resin exhibited heightened stability throughout the stretching process.This simple and effective technique presents opportunities for improving composites interfaces,enabling high load transfer efficiency,and opens up a potential path for developing strong and tough composite bipolar plates for fuel cells.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 11474334, 11634016, and 11404381）, the National Key R＆D Program of the Ministry of Science and Technology of China （Grant Nos. 2017YFA0303600 and 2014CB921001）, the Open Re- search Fund Program of the State Key Laboratory of Low- Dimensional Quantum Physics, and the Strategic Priority Re- search Program （B） of the Chinese Academy of Sciences （Grant No. XDB07030100）.
文摘At heterointerfaces between complex oxides with polar discontinuity, the instability-induced electric field may drive electron redistribution, causing a dramatic change in the interracial charge density. This results in the emergence of a rich diversity of exotic physical phenomena in these quasi-two-dimensional systems, which can be further tuned by an external field. To develop novel multifunctional electronic devices, it is essential to control the growth of polar oxide films and heterointerfaces with atomic preci- sion. In this article, we review recent progress in control techniques for oxide film growth by molecular beam epitaxy （MBE）. We emphasize the importance of tuning the microscopic surface structures of polar films for developing precise growth control techniques. Taking the polar SrTiO3 （110） and （111） surfaces as examples, we show that, by keeping the surface reconstructed throughout MBE growth, high-quality layer-by-layer homoepitaxy can be realized. Because the stability of different reconstruc- tions is determined by the surface cation concentration, the growth rate from the Sr/Ti evaporation source can be monitored in real time. A precise, automated control method is established by which insulating homoepitaxial SrTiO3 （110） and （111） films can be obtained on doped metallic substrates. The films show atomically well-defined surfaces and high dielectric performance, which allows the surface carrier concentration to be tuned in the range of -1013/cm2. By applying the knowledge of microstructures from fundamental surface physics to film growth techniques, new opportunities are provided for material science and related research.
基金The project was funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)(No.394563137-SFB 1368).
文摘Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided quantitative evidence of the effect of oxidized surfaces to tribological properties. In the current study on 99.99% pure copper, it is revealed that tribo-oxidation and the resulting increased abrasive wear can be suppressed by processing in an extreme high vacuum (XHV) adequate environment. The XHV adequate atmosphere was realized by using a silane-doped shielding gas (1.5 vol% SiH4 in argon). To analyse the influence of the ambient atmosphere on the tribological and mechanical properties, a ball–disk tribometer and a nanoindenter were used in air, argon, and silane-doped argon atmosphere for temperatures up to 800 ℃. Resistance measurements of the resulting coatings were carried out. To characterize the microstructures and the chemical compositions of the samples, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. The investigations have revealed a formation of η-Cu3Si in silane-doped atmosphere at 300 ℃, as well as various intermediate stages of copper silicides. At temperatures above 300 ℃, the formation of γ-Cu5Si were detected. The formation was linked to an increase in hardness from 1.95 to 5.44 GPa, while the Young’s modulus increased by 46% to 178 GPa, with the significant reduction of the wear volume by a factor of 4.5 and the suppression of further oxidation and susceptibility of chemical wear. In addition, the relevant diffusion processes were identified using molecular dynamics (MD) simulations.
