Cu-Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressureassisted sintering. The carbide forming elements Cr and Ti are added to improve interfacial bonding between diam...Cu-Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressureassisted sintering. The carbide forming elements Cr and Ti are added to improve interfacial bonding between diamond and the Cu-Fe matrix. The interfacial reactions between diamond/graphite and Cr or Ti, and diamond graphitization are investigated by thermodynamics/kinetics analyses and experimental methods. The results show that interfacial reactions and graphitization of diamond can automatically proceed thermodynamically. The Cr3C2, Cr7C3, Cr23C6, and TiC are formed at the interfaces of composites by reactions between diamond and Cr or Ti; diamond graphitization does not occur because of the kinetic difficulty at 1093 K under the pressure of 13 MPa.展开更多
Cathode samples of nano-diamond by graphitization pretreatment with different temperatures were fabricated by electrophoresis, then the structures and morphologies of the cathode samples were characterized by scanning...Cathode samples of nano-diamond by graphitization pretreatment with different temperatures were fabricated by electrophoresis, then the structures and morphologies of the cathode samples were characterized by scanning electron microscope(SEM) and X-ray diffraction(XRD), and the field emission tests were conducted. The effects of graphitization pretreatment on the field emission characteristics of nano-diamond cathode surface on titanium substrate are studied. The results indicate that the surface morphologies of nano-diamond cathode samples after graphitization pretreatment change a lot, and the field emission characteristics in low-voltage area are improved obviously. However, in high-voltage area, the curve distortion happens, and it doesn't conform the mechanism of field emission characteristics.展开更多
Large diamonds have successfully been synthesized from FeNiMnCo-S-C system at temperatures of 1255-1393 ℃and pressures of 5.3-5.5 GPa.Because of the presence of sulfur additive,the morphology and color of the large d...Large diamonds have successfully been synthesized from FeNiMnCo-S-C system at temperatures of 1255-1393 ℃and pressures of 5.3-5.5 GPa.Because of the presence of sulfur additive,the morphology and color of the large diamond crystals change obviously.The content and shape of inclusions change with increasing sulfur additive.It is found that the pressure and temperature conditions required for the synthesis decrease to some extent with the increase of S additive,which results in left down of the V-shape region.The Raman spectra show that the introduction of additive sulfur reduces the quality of the large diamond crystals.The x-ray photoelectron spectroscopy（XPS） spectra show the presence of S in the diamonds.Furthermore,the electrical properties of the large diamond crystals are tested by a four-point probe and the Hall effect method.When sulfur in the cell of diamond is up to 4.0 wt.%,the resistance of the diamond is 9.628×105 Ω·cm.It is shown that the large single crystal samples are n type semiconductors.This work is helpful for the further research and application of sulfur-doped semiconductor large diamond.展开更多
Nanocrystalline diamond coatings were deposited by MPCVD on the spheres used for a ball bearing.The nanocrystalline coatings with a grain size of 50 nm were confirmed by the surface morphology and composition analysis...Nanocrystalline diamond coatings were deposited by MPCVD on the spheres used for a ball bearing.The nanocrystalline coatings with a grain size of 50 nm were confirmed by the surface morphology and composition analysis.The hardness of the coating is 20-40 GPa tested by nanoindentation,which is higher than that of tungsten carbide and silicon nitride substrates.The coating around the sphere observed from the Micro CT images is uniform with a thickness of 12 μm.展开更多
Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we p...Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics（MD） simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding（known as energy corrugation） comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces.For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However,for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.展开更多
Artificial graphene structures embedded in semiconductors could open novel routes for studies of electron interactions in 1ow-dimensional systems. We propose a way to manipulate the transport properties of massless Di...Artificial graphene structures embedded in semiconductors could open novel routes for studies of electron interactions in 1ow-dimensional systems. We propose a way to manipulate the transport properties of massless Dirac fermions in an artificial graphene-based tunnel junction. Velocity-modulation control of electron wave propagation in the different regions can be regarded as velocity barriers. Transmission probability of electron is affected profoundly by this velocity barrier. We find that there is no confinement for Dirac electron as the velocity ratio ζ is less than 1, but when the velocity ratio is larger than 1 the confined state appears in the continuum band. These localized Dirac electrons may lead to the decreasing of transmission probability.展开更多
In this paper, the tribological performances of diamond film and graphite/diamond com-posite film were compared on an SRV wear testing machine with paraffin oil lubrication. The sur-face morphologies of specimens and ...In this paper, the tribological performances of diamond film and graphite/diamond com-posite film were compared on an SRV wear testing machine with paraffin oil lubrication. The sur-face morphologies of specimens and wear tracks were observed by SEM. The wear volumes ofwear tracks were measured by profilometer. The influence of load on the tribological performancesof different specimens was studied. The wear mechanism under paraffin oil lubrication was ana-lyzed. The results showed that with paraffin oil lubrication, the friction coefficient and wear volumeof graphite/diamond composite film specimen are lower than diamond film. Under paraffin oil lu-brication, the wear mechanisms of both diamond film and graphite/diamond composite film weremainly sub-micro-fracture.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 51165021)the Science Fund for Distinguished Young Scholars of Gansu Province, China (Grant No. 111RJDA0103)
文摘Cu-Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressureassisted sintering. The carbide forming elements Cr and Ti are added to improve interfacial bonding between diamond and the Cu-Fe matrix. The interfacial reactions between diamond/graphite and Cr or Ti, and diamond graphitization are investigated by thermodynamics/kinetics analyses and experimental methods. The results show that interfacial reactions and graphitization of diamond can automatically proceed thermodynamically. The Cr3C2, Cr7C3, Cr23C6, and TiC are formed at the interfaces of composites by reactions between diamond and Cr or Ti; diamond graphitization does not occur because of the kinetic difficulty at 1093 K under the pressure of 13 MPa.
基金supported by the PH.D Start-up Foundation of Yan’an University(No.YD 2010-04)the Special Foundation of Yan’an University(No.YDZD 2011-01)+3 种基金the 2014 Education and Innovation Project of Yan’an University for Graduate Studentthe 2014 Local University National Training Project of Innovation and Entrepreneurship for Undergraduates(No.201410719023)the Special Research Funds for Discipline Construction of High Level University Construction(No.2015SXTS02)the Natural Science Foundation of Shaanxi Province(No.2014JM2-5058)
文摘Cathode samples of nano-diamond by graphitization pretreatment with different temperatures were fabricated by electrophoresis, then the structures and morphologies of the cathode samples were characterized by scanning electron microscope(SEM) and X-ray diffraction(XRD), and the field emission tests were conducted. The effects of graphitization pretreatment on the field emission characteristics of nano-diamond cathode surface on titanium substrate are studied. The results indicate that the surface morphologies of nano-diamond cathode samples after graphitization pretreatment change a lot, and the field emission characteristics in low-voltage area are improved obviously. However, in high-voltage area, the curve distortion happens, and it doesn't conform the mechanism of field emission characteristics.
基金Project supported by the National Natural Science Foundation of China(Grant No.51172089)the Education Department of Henan Province,China(Grant No.12A430010)the Fundamental Research Funds for the Universities of Henan Province,China(Grant No.NSFRF140110)
文摘Large diamonds have successfully been synthesized from FeNiMnCo-S-C system at temperatures of 1255-1393 ℃and pressures of 5.3-5.5 GPa.Because of the presence of sulfur additive,the morphology and color of the large diamond crystals change obviously.The content and shape of inclusions change with increasing sulfur additive.It is found that the pressure and temperature conditions required for the synthesis decrease to some extent with the increase of S additive,which results in left down of the V-shape region.The Raman spectra show that the introduction of additive sulfur reduces the quality of the large diamond crystals.The x-ray photoelectron spectroscopy（XPS） spectra show the presence of S in the diamonds.Furthermore,the electrical properties of the large diamond crystals are tested by a four-point probe and the Hall effect method.When sulfur in the cell of diamond is up to 4.0 wt.%,the resistance of the diamond is 9.628×105 Ω·cm.It is shown that the large single crystal samples are n type semiconductors.This work is helpful for the further research and application of sulfur-doped semiconductor large diamond.
文摘Nanocrystalline diamond coatings were deposited by MPCVD on the spheres used for a ball bearing.The nanocrystalline coatings with a grain size of 50 nm were confirmed by the surface morphology and composition analysis.The hardness of the coating is 20-40 GPa tested by nanoindentation,which is higher than that of tungsten carbide and silicon nitride substrates.The coating around the sphere observed from the Micro CT images is uniform with a thickness of 12 μm.
基金support from the National Natural Science Foundation of China (Grants 11272177, 11422218, 11432008)the National Basic Research Program of China (Grants 2013CB933003, 2013CB934201 and 2015CB351903)+2 种基金the Tsinghua University Initiative Scientific Research Programthe Thousand Young Talents Program of Chinathe financial support from China Postdoctoral Science Foundation (Grant 2014M562055)
文摘Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics（MD） simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding（known as energy corrugation） comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces.For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However,for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.
基金Supported by the National Natural Science Foundation of China under Grants Nos.10174024 and 10474025
文摘Artificial graphene structures embedded in semiconductors could open novel routes for studies of electron interactions in 1ow-dimensional systems. We propose a way to manipulate the transport properties of massless Dirac fermions in an artificial graphene-based tunnel junction. Velocity-modulation control of electron wave propagation in the different regions can be regarded as velocity barriers. Transmission probability of electron is affected profoundly by this velocity barrier. We find that there is no confinement for Dirac electron as the velocity ratio ζ is less than 1, but when the velocity ratio is larger than 1 the confined state appears in the continuum band. These localized Dirac electrons may lead to the decreasing of transmission probability.
文摘In this paper, the tribological performances of diamond film and graphite/diamond com-posite film were compared on an SRV wear testing machine with paraffin oil lubrication. The sur-face morphologies of specimens and wear tracks were observed by SEM. The wear volumes ofwear tracks were measured by profilometer. The influence of load on the tribological performancesof different specimens was studied. The wear mechanism under paraffin oil lubrication was ana-lyzed. The results showed that with paraffin oil lubrication, the friction coefficient and wear volumeof graphite/diamond composite film specimen are lower than diamond film. Under paraffin oil lu-brication, the wear mechanisms of both diamond film and graphite/diamond composite film weremainly sub-micro-fracture.
