Two-dimensional materials having a layered structure comprise a monolayer or multilayers of atomic thickness and ultra-low shear strength.Their high specific surface area,in-plane strength,weak layer-layer interaction...Two-dimensional materials having a layered structure comprise a monolayer or multilayers of atomic thickness and ultra-low shear strength.Their high specific surface area,in-plane strength,weak layer-layer interaction,and surface chemical stability result in remarkably low friction and wear-resisting properties.Thus,2D materials have attracted considerable attention.In recent years,great advances have been made in the scientific research and industrial applications of anti-friction,anti-wear,and lubrication of 2D materials.In this article,the basic nanoscale friction mechanisms of 2D materials including interfacial friction and surface friction mechanisms are summarized.This paper also includes a review of reports on lubrication mechanisms based on the film-formation,self-healing,and ball bearing mechanisms and applications based on lubricant additives,nanoscale lubricating films,and space lubrication materials of 2D materials in detail.Finally,the challenges and potential applications of 2D materials in the field of lubrication were also presented.展开更多
The electrical performance of two-dimensional transition metal dichalcogenides （TMDs） is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization appr...The electrical performance of two-dimensional transition metal dichalcogenides （TMDs） is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe2 devices. Low-temperature photoluminescence （PL） spectra of electron-beam-lithography- processed WSe2 exhibit a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an electron-beam-free transfer-electrode technique, we successfully prepared a backgated WSe2 device containing a limited amount of defects. A maximum hole mobility of approximately 200 cm2.V -1.s-1 was achieved because of the reduced scattering sources, which is the highest reported value for this type of device. This work provides not only a versatile and nondestructive method to monitor the defects in TMDs but also a new route to approach the room-temperature phonon-limited mobility in high-performance TMD devices.展开更多
Angle-resolved polarized Raman（ARPR） spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropi...Angle-resolved polarized Raman（ARPR） spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropic materials.However, polarized Raman measurements can be implemented by several different configurations and thus lead to different results. In this work, we systematically analyze three typical polarization configurations： 1） to change the polarization of the incident laser, 2） to rotate the sample, and 3） to set a half-wave plate in the common optical path of incident laser and scattered Raman signal to simultaneously vary their polarization directions. We provide a general approach of polarization analysis on the Raman intensity under the three polarization configurations and demonstrate that the latter two cases are equivalent to each other. Because the basal plane of highly ordered pyrolytic graphite（HOPG） exhibits isotropic feature and its edge plane is highly anisotropic, HOPG can be treated as a modelling system to study ARPR spectroscopy of twodimensional materials on their basal and edge planes. Therefore, we verify the ARPR behaviors of HOPG on its basal and edge planes at three different polarization configurations. The orientation direction of HOPG edge plane can be accurately determined by the angle-resolved polarization-dependent G mode intensity without rotating sample, which shows potential application for orientation determination of other anisotropic and vertically standing two-dimensional materials and other materials.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51505442)Guangxi Natural Science Foundation(Grant No.2018GXNSFAA138174)
文摘Two-dimensional materials having a layered structure comprise a monolayer or multilayers of atomic thickness and ultra-low shear strength.Their high specific surface area,in-plane strength,weak layer-layer interaction,and surface chemical stability result in remarkably low friction and wear-resisting properties.Thus,2D materials have attracted considerable attention.In recent years,great advances have been made in the scientific research and industrial applications of anti-friction,anti-wear,and lubrication of 2D materials.In this article,the basic nanoscale friction mechanisms of 2D materials including interfacial friction and surface friction mechanisms are summarized.This paper also includes a review of reports on lubrication mechanisms based on the film-formation,self-healing,and ball bearing mechanisms and applications based on lubricant additives,nanoscale lubricating films,and space lubrication materials of 2D materials in detail.Finally,the challenges and potential applications of 2D materials in the field of lubrication were also presented.
基金This work was supported by National Natural Science Foundation of China （Nos. 61422503, 21541013 and 61376104）, Natural Science Foundation of Jiangsu Province （No. BK20150596）, Jiangsu key laboratory for advanced metallic materials （No. BM2007204）, the open research funds of Key Laboratory of MEMS of Ministry of Education （SEU, China）, and the Funda- mental Research Funds for the Central Universities. The authors would like to thank Prof. Zhenhua Qiao from USTC, China for helpful discussions.
文摘The electrical performance of two-dimensional transition metal dichalcogenides （TMDs） is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe2 devices. Low-temperature photoluminescence （PL） spectra of electron-beam-lithography- processed WSe2 exhibit a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an electron-beam-free transfer-electrode technique, we successfully prepared a backgated WSe2 device containing a limited amount of defects. A maximum hole mobility of approximately 200 cm2.V -1.s-1 was achieved because of the reduced scattering sources, which is the highest reported value for this type of device. This work provides not only a versatile and nondestructive method to monitor the defects in TMDs but also a new route to approach the room-temperature phonon-limited mobility in high-performance TMD devices.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFA0301204)the National Natural Science Foundation of China(Grant Nos.11604326,11434010,11474277,and 11225421)
文摘Angle-resolved polarized Raman（ARPR） spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropic materials.However, polarized Raman measurements can be implemented by several different configurations and thus lead to different results. In this work, we systematically analyze three typical polarization configurations： 1） to change the polarization of the incident laser, 2） to rotate the sample, and 3） to set a half-wave plate in the common optical path of incident laser and scattered Raman signal to simultaneously vary their polarization directions. We provide a general approach of polarization analysis on the Raman intensity under the three polarization configurations and demonstrate that the latter two cases are equivalent to each other. Because the basal plane of highly ordered pyrolytic graphite（HOPG） exhibits isotropic feature and its edge plane is highly anisotropic, HOPG can be treated as a modelling system to study ARPR spectroscopy of twodimensional materials on their basal and edge planes. Therefore, we verify the ARPR behaviors of HOPG on its basal and edge planes at three different polarization configurations. The orientation direction of HOPG edge plane can be accurately determined by the angle-resolved polarization-dependent G mode intensity without rotating sample, which shows potential application for orientation determination of other anisotropic and vertically standing two-dimensional materials and other materials.
