氮掺杂对石墨烯摩擦学特性影响的分子动力学模拟

刘青阳; 徐青松; 李瑞

doi:10.7498/aps.71.20212309

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摘要

掺氮石墨烯具有良好的应用前景, 但对其摩擦学特性的研究仍较为缺乏. 本文采用分子动力学方法研究了氮掺杂对石墨烯摩擦学特性的影响. 结果表明在公度、非公度的界面结构下, 氮掺杂对石墨烯摩擦特性的影响呈现相反的趋势. 界面结构为公度状态时, 氮原子的引入导致了局部非公度状态, 因而界面势垒降低、摩擦减小. 界面公度性的改变、层间氮原子和碳原子的范德瓦耳斯力作用对界面摩擦的影响相反, 在二者的共同作用下, 随氮掺杂比例的升高, 掺氮石墨烯体系的界面摩擦力呈现先增大再减小的趋势. 界面结构为非公度状态时, 氮原子的引入对界面摩擦的影响主要体现在原子类型的变化, 界面摩擦随氮掺杂比例的增大而增大. 存在空位缺陷的石墨烯体系的摩擦最大, 掺杂氮原子对于降低缺陷石墨烯体系的摩擦具有积极意义.

关键词:

Abstract

Graphene has attracted a lot of attention due to its excellent electrical properties, however, the gapless nature of graphene limits its further applications. Doping is an effective way to open the bandgap, in which nitrogen-doped (N-doped) graphene has potential applications, but the study of its tribological properties is still lacking. In this work, the effects of nitrogen doping on the tribological properties of graphene under different interfacial structures are investigated by molecular dynamics simulation. The simulation models include a hexagonal graphene sheet, graphene or N-doped graphene substrate. The results show that the nitrogen doping has different effects on friction when interface structure is in a commensurate state and an incommensurate state. In a commensurate state, N-doping reduces the friction between interfaces in all cases, but the friction first goes up and then decreases with the increase of doping ratio of nitrogen. The local maximum value of friction occurs at a doping ratio of 7.5%. This phenomenon results from the interface structure and the change of van de Waals force between interfaces. The introduction of nitrogen atoms causes the lattice of graphene to distort, which results in the formation of local incommensurate state, thus reducing the interfacial potential barrier and friction. However, the van der Waals force between nitrogen atom and carbon atom between layers is stronger than that between carbon atoms and carbon atoms, which causes the friction to increase. When the doping ratio is low or high, lattice distortion plays more important role. The friction of N-doped graphene shows much smaller increase with load than that of ideal graphene, which indicates that the N-doped graphene possesses a better performance under high load. When the interface structure is in an incommensurate state, the introduction of nitrogen atoms shows slight influence on lattice mismatch, therefore, the change of atomic type plays a dominant role in determining the friction between interfaces, which goes up with the increase of N-doping ratio. When the substrate is graphene with vacancy defects, the value of friction between interfaces is larger than the ideal graphene substrate or N-doped graphene substrate, which indicates that the doping of nitrogen atoms has positive effect on reducing the friction of graphene with defects.

Keywords:

作者及机构信息

北京科技大学机械工程学院, 北京　100083

通信作者: 李瑞, lirui@ustb.edu.cn

基金项目: 中央高校基本科研业务费专项资金(批准号: FRF-IDRY-20-008)和国家自然科学基金(批准号: 51475039)资助的课题.

Authors and contacts

School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China

Corresponding author: Li Rui, lirui@ustb.edu.cn

Funds: Project supported by the Fundamental Research Funds for the Central Universities of the Ministry of Education of China (Grant No. FRF-IDRY-20-008) and the National Natural Science Foundation of China (Grant No. 51475039)

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参考文献

[1]	Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A A 2004 Science 306 666 Google Scholar
[2]	Geim A K, Novoselov K S 2007 Nat. Mater. 6 183 Google Scholar
[3]	Geim A K 2009 Science 324 1530 Google Scholar
[4]	Martins T B, Miwa R H, da Silva A J R, Fazzio A 2007 Phys. Rev. Lett. 98 196803 Google Scholar
[5]	Dutta S, Manna A K, Pati S K 2009 Phys. Rev. Lett. 102 096601 Google Scholar
[6]	Biel B, Blase X, Triozon F, Roche S 2009 Phys. Rev. Lett. 102 096803 Google Scholar
[7]	Kamal Kandezi M, Shadman Lakmehsari M, Matta C F 2020 J. Mol. Liq. 302 112574 Google Scholar
[8]	林婷婷, 吕秋丰 2015 功能材料 46 5007 Google Scholar Lin T T, Lv Q F 2015 J. Func. Mater 46 5007 Google Scholar
[9]	Wang G, Wang B, Wang X, Park J, Dou S, Ahn H, Kim K 2009 J. Mate. Chem. 19 8378 Google Scholar
[10]	Kwon O S, Park S J, Hong J-Y, Han A R, Lee J S, Lee J S, Oh J H, Jang J 2012 ACS. Nano. 6 1486 Google Scholar
[11]	Dienwiebel M, Verhoeven G S, Pradeep N, et al. 2004 Phys. Rev. Lett. 92 126101 Google Scholar
[12]	Zheng X, Gao L, Yao Q, et al. 2016 Nat. Commun. 7 13204 Google Scholar
[13]	Leven I, Krepel D, Shemesh O, Hod O 2013 J. Phys. Chem. Lett. 4 115 Google Scholar
[14]	Liu S W, Wang H P, Xu Q, et al. 2017 Nat. Commun. 8 14029 Google Scholar
[15]	陈勇, 李瑞 2019 物理学报 68 186801 Google Scholar Chen Y, Li R 2019 Acta Phys. Sin. 68 186801 Google Scholar
[16]	Wang K, Ouyang W, Cao W, Ma M, Zheng Q 2019 Nanoscale 11 2186 Google Scholar
[17]	Liu Y, Grey F, Zheng Q 2014 Sci. Rep. 4 4875 Google Scholar
[18]	Biswas S K 2008 Tribol Lett 30 159 Google Scholar
[19]	Lee C, Li Q, Kalb W, Liu X Z, Berger H, Carpick R W, Hone J 2010 Science 328 76 Google Scholar
[20]	Li S, Li Q, Carpick R W, Gumbsch P, Liu X Z, Ding X, Sun J, Li J 2016 Nature 539 541 Google Scholar
[21]	Ye Z, Martini A 2014 Langmuir 30 14707 Google Scholar
[22]	Guo Y, Guo W, Chen C 2007 Phys. Rev. B 76 155429 Google Scholar
[23]	Dong Y, Wu X, Martini A 2013 Nanotechnology 24 375701 Google Scholar
[24]	Gao L, Chen X, Yan Y, Liu Y, Song A, Ma T, Hu Y, Su Y, Qiao L 2018 Comput. Mater. Sci. 147 28 Google Scholar
[25]	Li R, Song C 2018 Crystals 8 167 Google Scholar
[26]	Shen Y, Wang Y, Zhou Y, Shi A, Hu J, Zhang Y 2016 J. Phys. D 49 415303 Google Scholar
[27]	Stuart S J, Tutein A B, Harrison J A 2000 J. Chem. Phys. 112 6472 Google Scholar
[28]	Kınacı A, Haskins J B, Sevik C, Çağın T 2012 Phys. Rev. B 86 115410 Google Scholar
[29]	Lennard-Jones J E 1931 Proceed. Phys. Soc. 43 461 Google Scholar
[30]	Leven I, Maaravi T, Azuri I, Kronik L, Hod O 2016 J. Chem. Theory Comput. 12 2896 Google Scholar
[31]	Zhang W, Lu W C, Zhang H X, Ho K M, Wang C Z 2016 Carbon 110 330 Google Scholar

施引文献

图 1 石墨烯片在石墨烯基底上的模型

Fig. 1. The illustration of hexagonal graphene sheet on graphene substrate.

下载: 全尺寸图片幻灯片

图 2 (a) 石墨烯在0.5 nN载荷下的黏滑摩擦力曲线; (b)不同载荷下界面平均摩擦力随N掺杂比例的变化

Fig. 2. (a) Viscous slip friction curve of graphene under 0.5 nN load; (b) the average friction between interfaces with nitrogen-doped (N-doped) ratio under different loads.

下载: 全尺寸图片幻灯片

图 3 公度时两种体系界面的PES　(a) 基底为石墨烯; (b) 基底为氮掺杂石墨烯

Fig. 3. PES between interfaces of two simulation systems in a commensurate state: (a) The substrate is graphene; (b) the substrate is N-doped graphene.

下载: 全尺寸图片幻灯片

图 4 (a) 氮掺杂石墨烯的原子结构; (b) 理想石墨烯的原子结构

Fig. 4. (a) Atomic structure of N-doped graphene; (b) atomic structure of ideal graphene.

下载: 全尺寸图片幻灯片

图 5 (a) 非公度时不同载荷下石墨烯的平均摩擦力随氮掺杂比例的变化; (b) 存在5%空位缺陷的石墨烯与N掺杂石墨烯的平均摩擦力

Fig. 5. (a) Average friction on N-doped graphene with different N-doping ratio under different loads when interface is in incommensurate state; (b) average friction on graphene with 5% vacancy defects compared with N-doped graphene.

下载: 全尺寸图片幻灯片

图 6 非公度时两种体系界面的PES　(a) 基底为石墨烯; (b) 基底为N掺杂的石墨烯

Fig. 6. PES between interfaces of two simulation systems in an incommensurate state: (a) The substrate is graphene; (b) the substrate is N-doped graphene.

下载: 全尺寸图片幻灯片

[1]	Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A A 2004 Science 306 666 Google Scholar
[2]	Geim A K, Novoselov K S 2007 Nat. Mater. 6 183 Google Scholar
[3]	Geim A K 2009 Science 324 1530 Google Scholar
[4]	Martins T B, Miwa R H, da Silva A J R, Fazzio A 2007 Phys. Rev. Lett. 98 196803 Google Scholar
[5]	Dutta S, Manna A K, Pati S K 2009 Phys. Rev. Lett. 102 096601 Google Scholar
[6]	Biel B, Blase X, Triozon F, Roche S 2009 Phys. Rev. Lett. 102 096803 Google Scholar
[7]	Kamal Kandezi M, Shadman Lakmehsari M, Matta C F 2020 J. Mol. Liq. 302 112574 Google Scholar
[8]	林婷婷, 吕秋丰 2015 功能材料 46 5007 Google Scholar Lin T T, Lv Q F 2015 J. Func. Mater 46 5007 Google Scholar
[9]	Wang G, Wang B, Wang X, Park J, Dou S, Ahn H, Kim K 2009 J. Mate. Chem. 19 8378 Google Scholar
[10]	Kwon O S, Park S J, Hong J-Y, Han A R, Lee J S, Lee J S, Oh J H, Jang J 2012 ACS. Nano. 6 1486 Google Scholar
[11]	Dienwiebel M, Verhoeven G S, Pradeep N, et al. 2004 Phys. Rev. Lett. 92 126101 Google Scholar
[12]	Zheng X, Gao L, Yao Q, et al. 2016 Nat. Commun. 7 13204 Google Scholar
[13]	Leven I, Krepel D, Shemesh O, Hod O 2013 J. Phys. Chem. Lett. 4 115 Google Scholar
[14]	Liu S W, Wang H P, Xu Q, et al. 2017 Nat. Commun. 8 14029 Google Scholar
[15]	陈勇, 李瑞 2019 物理学报 68 186801 Google Scholar Chen Y, Li R 2019 Acta Phys. Sin. 68 186801 Google Scholar
[16]	Wang K, Ouyang W, Cao W, Ma M, Zheng Q 2019 Nanoscale 11 2186 Google Scholar
[17]	Liu Y, Grey F, Zheng Q 2014 Sci. Rep. 4 4875 Google Scholar
[18]	Biswas S K 2008 Tribol Lett 30 159 Google Scholar
[19]	Lee C, Li Q, Kalb W, Liu X Z, Berger H, Carpick R W, Hone J 2010 Science 328 76 Google Scholar
[20]	Li S, Li Q, Carpick R W, Gumbsch P, Liu X Z, Ding X, Sun J, Li J 2016 Nature 539 541 Google Scholar
[21]	Ye Z, Martini A 2014 Langmuir 30 14707 Google Scholar
[22]	Guo Y, Guo W, Chen C 2007 Phys. Rev. B 76 155429 Google Scholar
[23]	Dong Y, Wu X, Martini A 2013 Nanotechnology 24 375701 Google Scholar
[24]	Gao L, Chen X, Yan Y, Liu Y, Song A, Ma T, Hu Y, Su Y, Qiao L 2018 Comput. Mater. Sci. 147 28 Google Scholar
[25]	Li R, Song C 2018 Crystals 8 167 Google Scholar
[26]	Shen Y, Wang Y, Zhou Y, Shi A, Hu J, Zhang Y 2016 J. Phys. D 49 415303 Google Scholar
[27]	Stuart S J, Tutein A B, Harrison J A 2000 J. Chem. Phys. 112 6472 Google Scholar
[28]	Kınacı A, Haskins J B, Sevik C, Çağın T 2012 Phys. Rev. B 86 115410 Google Scholar
[29]	Lennard-Jones J E 1931 Proceed. Phys. Soc. 43 461 Google Scholar
[30]	Leven I, Maaravi T, Azuri I, Kronik L, Hod O 2016 J. Chem. Theory Comput. 12 2896 Google Scholar
[31]	Zhang W, Lu W C, Zhang H X, Ho K M, Wang C Z 2016 Carbon 110 330 Google Scholar

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氮掺杂对石墨烯摩擦学特性影响的分子动力学模拟

北京科技大学机械工程学院, 北京　100083

通信作者: 李瑞, lirui@ustb.edu.cn

基金项目: 中央高校基本科研业务费专项资金(批准号: FRF-IDRY-20-008)和国家自然科学基金(批准号: 51475039)资助的课题.

收稿日期: 2021-12-14

修回日期: 2022-03-09

上网日期: 2022-07-08

刊出日期: 2022-07-20

摘要: 掺氮石墨烯具有良好的应用前景, 但对其摩擦学特性的研究仍较为缺乏. 本文采用分子动力学方法研究了氮掺杂对石墨烯摩擦学特性的影响. 结果表明在公度、非公度的界面结构下, 氮掺杂对石墨烯摩擦特性的影响呈现相反的趋势. 界面结构为公度状态时, 氮原子的引入导致了局部非公度状态, 因而界面势垒降低、摩擦减小. 界面公度性的改变、层间氮原子和碳原子的范德瓦耳斯力作用对界面摩擦的影响相反, 在二者的共同作用下, 随氮掺杂比例的升高, 掺氮石墨烯体系的界面摩擦力呈现先增大再减小的趋势. 界面结构为非公度状态时, 氮原子的引入对界面摩擦的影响主要体现在原子类型的变化, 界面摩擦随氮掺杂比例的增大而增大. 存在空位缺陷的石墨烯体系的摩擦最大, 掺杂氮原子对于降低缺陷石墨烯体系的摩擦具有积极意义.

关键词:

Effect of N-doping on tribological properties of graphene by molecular dynamics simulation

School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China

Corresponding author: Li Rui, lirui@ustb.edu.cn

Fund Project: Project supported by the Fundamental Research Funds for the Central Universities of the Ministry of Education of China (Grant No. FRF-IDRY-20-008) and the National Natural Science Foundation of China (Grant No. 51475039)

Received Date: 14 December 2021

Accepted Date: 09 March 2022

Available Online: 08 July 2022

Published Online: 20 July 2022

Abstract: Graphene has attracted a lot of attention due to its excellent electrical properties, however, the gapless nature of graphene limits its further applications. Doping is an effective way to open the bandgap, in which nitrogen-doped (N-doped) graphene has potential applications, but the study of its tribological properties is still lacking. In this work, the effects of nitrogen doping on the tribological properties of graphene under different interfacial structures are investigated by molecular dynamics simulation. The simulation models include a hexagonal graphene sheet, graphene or N-doped graphene substrate. The results show that the nitrogen doping has different effects on friction when interface structure is in a commensurate state and an incommensurate state. In a commensurate state, N-doping reduces the friction between interfaces in all cases, but the friction first goes up and then decreases with the increase of doping ratio of nitrogen. The local maximum value of friction occurs at a doping ratio of 7.5%. This phenomenon results from the interface structure and the change of van de Waals force between interfaces. The introduction of nitrogen atoms causes the lattice of graphene to distort, which results in the formation of local incommensurate state, thus reducing the interfacial potential barrier and friction. However, the van der Waals force between nitrogen atom and carbon atom between layers is stronger than that between carbon atoms and carbon atoms, which causes the friction to increase. When the doping ratio is low or high, lattice distortion plays more important role. The friction of N-doped graphene shows much smaller increase with load than that of ideal graphene, which indicates that the N-doped graphene possesses a better performance under high load. When the interface structure is in an incommensurate state, the introduction of nitrogen atoms shows slight influence on lattice mismatch, therefore, the change of atomic type plays a dominant role in determining the friction between interfaces, which goes up with the increase of N-doping ratio. When the substrate is graphene with vacancy defects, the value of friction between interfaces is larger than the ideal graphene substrate or N-doped graphene substrate, which indicates that the doping of nitrogen atoms has positive effect on reducing the friction of graphene with defects.

Keywords:

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1. 引　言

自2004年Geim等^[1]剥离出石墨烯以来, 石墨烯因其优异的力学、电学特性、大比表面积等特点吸引了众多研究者的关注^[2,3]. 目前的研究表明石墨烯零带隙的性质制约了其应用, 采用原子级修饰进行化学掺杂是调控石墨烯性质的一种有效手段. 通过化学掺杂, 例如氮(N)、硼(B)元素的掺杂, 能够有效地调节石墨烯费米面的位置. 一些研究者已经开展了此方面的研究. 如Martins等^[4]研究了B原子掺杂石墨烯纳米带的电子结构和输运性质. Dutta等^[5]和 Biel 等^[6]分别研究了N, B共掺杂后石墨烯纳米带的电子结构. Kandezi等^[7]采用通过分子动力学(MD)方法研究了在电场辅助下N, B掺杂的纳米多孔石墨烯片选择性分离离子的特性. N掺杂石墨烯也已用于超电容器^[8]、锂电池^[9]和场效应晶体管^[10]等.

虽然氮掺杂石墨烯的电学特性已经得到了研究者的关注, 但氮掺杂对石墨烯摩擦行为的影响研究鲜见报道. 近年来对石墨烯摩擦行为的研究主要集中于石墨烯界面间的超滑行为, 以及层数、层间距和表面基团等对石墨烯摩擦的影响. 在石墨烯超滑行为的研究方面, Dienwiebel等^[11]研究了石墨烯与石墨基底间摩擦, 结果表明当界面结构为非公度状态时, 摩擦力几乎为零, 表现出结构超滑的现象. Zheng等^[12]发现通过摩尔纹晶格失配可实现石墨烯的超低摩擦. Leven等^[13]研究了石墨烯在六方氮化硼(h-BN)表面的滑动行为, 结果表明足够大的石墨烯片在h-BN表面滑动时将出现稳定的超滑行为. Liu等^[14]实现了微米尺度石墨烯与h-BN异质界面在大气环境下的可靠超低摩擦. 陈勇等^[15]发现石墨烯与硼烯体系的势能起伏小于石墨烯与六方氮化硼, 表明石墨烯与硼烯界面摩擦力可能更小. Wang等^[16]通过在石墨烯基底上施加单轴或双轴应变实现了超滑, 并将其归因于拉伸后石墨烯基底晶格常数的变化导致了界面的不相称结构. Liu等^[17]采用分子动力学模拟研究了石墨烯片在石墨表面的超滑行为, 结果表明石墨烯片在滑动过程的旋转破坏了超滑状态, 原因在于界面的晶格适配增大了摩擦^[11,18]. 在层数、间距对石墨烯摩擦的影响方面, Lee等^[19]发现随着石墨烯层数的减少, 界面摩擦力增大, 原因在于皱褶效应^[20]. Ye 等^[21]研究了底层固定的双层石墨烯及悬空单层石墨烯表面的摩擦行为, 发现双层石墨烯的摩擦力随载荷近似线性增大, 而悬空石墨烯表面的摩擦力却为非单调函数. Guo等^[22]模拟了层间距对石墨烯摩擦的影响, 指出随着层间距的减小, 摩擦力增大. 化学改性对石墨烯的摩擦行为影响显著, 目前研究者主要研究了H、F、羟基等表面基团对石墨烯摩擦行为的影响, 如Dong等^[23]指出氢化导致的原子级粗糙度的增加是氢化石墨烯摩擦力增大的主要原因. Li 等^[24]比较了氟化石墨烯和石墨烯的摩擦学性能, 指出氟化石墨烯的摩擦大于石墨烯的原因在于官能团的引入导致了界面相互作用的增强和表面粗糙度的增大. Li等^[25]通过分子动力学模拟研究了接枝羟基对石墨烯摩擦的影响, 明确了氢键作用、范德瓦耳斯力和库仑力对摩擦力的贡献. Shen等^[26]通过引入不同的官能团改变石墨烯电子的分配状态, 调控层间或者层与对副间的相互作用力, 成功调控了材料的摩擦学性能.

由上述研究可以看出, 研究者对基团影响石墨烯的探讨主要集中在面上基团的引入, 仅Zhang等^[27]采用第一性原理方法研究了面内掺杂对石墨烯摩擦性能的影响, 但也只考虑了公度情况, 面内掺杂对石墨烯摩擦的影响仍需进一步探讨. 氮掺杂石墨烯具有良好的应用前景, 有必要对其摩擦学行为开展研究. 因此本文采用分子动力学方法建立了石墨烯与掺氮石墨烯组成的模拟体系, 探讨了氮掺杂对石墨烯摩擦行为的影响, 以期推动石墨烯摩擦的研究进程.

4. 结　论

本文采用分子动力学模拟方法, 研究了界面结构为公度、非公度状态下掺杂N原子对石墨烯摩擦性能的影响, 主要结论如下.

1)在界面结构为公度状态时, 掺杂N原子后界面摩擦力比理想石墨烯体系小, 并且随N掺杂比例的增大摩擦力呈现先增大后减小的趋势. 原因在于掺杂N原子后, N原子周围的六边形晶格产生了畸变, 进而导致了界面间的局部非公度结构, 降低了摩擦. 界面间摩擦受晶格失配和原子类型由C变为N两方面的影响. 晶格失配的增强将降低摩擦, 而层间N—C原子的范德瓦耳斯力作用增大摩擦, 二者对摩擦的影响趋势相反. 当N掺杂比例很低或较高时, 界面公度性状态的变化占主导作用, 因此摩擦力呈现先增大后减小的趋势. 与理想石墨烯体系相比, 氮掺杂石墨烯体系能够承载大的载荷并保持良好的摩擦性能.

2)当界面结构为非公度状态时, N掺杂石墨烯体系的界面摩擦力大于理想石墨烯体系. 原因在于界面结构为非公度状态时, 影响界面摩擦的主导因素为基底中原子类型的改变, 随着N掺杂比例的增大, 层间相互作用增强, 摩擦变大. 缺陷石墨烯体系的界面摩擦最大, N掺杂倾向于吸附在石墨烯缺陷位置, 对于减小缺陷石墨烯体系的摩擦具有积极意义.

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氮掺杂对石墨烯摩擦学特性影响的分子动力学模拟