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采用分子动力学方法模拟了碳在晶体硅基底上的沉积过程, 并分析计算了所沉积的类金刚石薄膜的面向及法向热导率. 对沉积过程的模拟表明, 薄膜密度及sp3杂化类型的碳原子所占比例均随沉积高度的增加而减小, 在碳原子以1 eV能量垂直入射的情况下, 在硅基底上沉积的薄膜密度约为2.8 g/cm3, sp3杂化类型的碳原子所占比例约为22%, 均低于碳在金刚石基底上沉积的情况. 采用Green-Kubo方法, 计算了所沉积类金刚石薄膜的热导率, 其面向热导率可以达到相同尺寸规则金刚石晶体的50%左右, 并且随着薄膜密度与sp3杂化类型碳原子所占比例的升高而升高.Diamond-Like Carbon (DLC) is thought to be a potential material in solving heat dissipation problems in light emitting diode module packages. It is of vital importance in evaluating the thermal conductivity of DLC film deposited on a silicon substrate. In this paper, the molecular dynamics method is used to simulate the formation of a DLC film by the deposition of carbon atoms on a isilicon substrate. Tersoff potential is adopted to reproduce the structures and densities of silicon, carbon, and SiC. A silicon substrate consisting of 544 atoms is located at the bottom of the simulation domain. The substrate is kept at a temperature of 600 K through a Noose-Hover thermostat. Carbon atoms are injected into the substrate individually every 0.5 ps at an energy of 1 eV. After a 7.5 ns deposition process, a 4 nm amorphous film containing 15000 carbon atoms is formed. Injected carbon atoms and substrate silicon atoms are intermixed at the bottom layer of the deposited film while the rest of the film contains only carbon atoms. The density of the film decreases slightly with the increase of the height of the deposited film and the average density is 2.8 g/cm3. Analysis of the coordination number shows that the sp3 fraction of carbon atoms in the film also decreases with the increase of the height of the deposited film, with a maximum value of 22%. It might be caused by the continuous impacts of the subsequently injected carbon atoms on the previously formed DLC film. The thermal conductivities of the DLC film in the planar and normal directions are calculated by the Green-Kubo method. The thermal conductivity of pure diamond film is also calculated for comparison. The results show that the planar thermal conductivity of the deposited DLC film is approximately half of that of the pure diamond film with the same size. It is higher than the normal thermal conductivity of the deposited film. The thermal conductivities of the DLC film in both planar and normal directions increase with the increase of film density and sp3 fraction in the DLC film. The results indicate that the local tetrahedral structure of sp3 carbon atoms contributes to the improvement of thermal conductivity in the DLC film.
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Keywords:
- diamond like carbon film /
- chemical deposition /
- thermal conductivity /
- molecular dynamics
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[1] Wang J, Liu G C, Li H L, Hou B R 2012 Acta Phys. Sin. 61 058102 (in Chinese) [王静, 刘贵昌, 李红玲, 侯保荣 2012 物理学报 61 058102]
[2] Song J M, Gan M J, Cai B Y 2012 J. Eng. Mater. Taiwan 304 124 (in Chinese) [宋健民, 甘明吉, 蔡百扬 2012 工业材料杂志(台湾) 304 124]
[3] Balandin A A 2011 Nat. Mater. 10 569
[4] Hu M H, Bi N, Li S S, Su T C, Zhou A G, Hu Q, Jia X P, Ma H A 2015 Chin. Phys. B 24 038101
[5] Kaukonen H P, Nieminen R 1992 Phys. Rev. Lett. 68 620
[6] Ma T B, Hu Y Z, Wang H 2007 Acta Phys. Sin. 56 480 (in Chinese) [马天宝, 胡元中, 王慧 2007 物理学报 56 480]
[7] Kim K S, Lee S H, Kim Y C, Lee S C, Cha P R, Lee K R 2008 Met. Mater. Int. 14 347
[8] Murakami Y, Horiguchi S, Hamaguchi S 2010 Phys. Rev. E 81 041602
[9] Joe M, Moon M W, Oh J, Lee K H, Lee K R 2012 Carbon 50 404
[10] Wang N, Komvopoulos K 2014 J. Phys. D: Appl. Phys. 47 245303
[11] Huang D M, Pu J B, Lu Z B, Xue Q J 2012 Surf. Interface Anal. 44 837
[12] Li Z J, Pan Z Y, Wei Q, Du A J, Huang Z, Zhang Z X, Ye X S, Bai T, Wang C, Liu J R 2003 Eur. Phys. J. D 23 369
[13] Li Z J 2004 Ph. D. Dissertation (Shanghai: Fudan University) (in Chinese) [李之杰2004 博士学位论文(上海: 复旦大学)]
[14] Tersoff J 1989 Phys. Rev. B 39 5566
[15] Brenner D W 1990 Phys. Rev. B 42 9458
[16] Brenner D W, Shenderova O A, Harrison J A, Stuart S J, Ni B, Sinnott S B 2002 J. Phys. Condes. Matter 14 783
[17] Duin A C T V, Dasgupta S, Lorant F, Goddard W A 2001 J. Phys. Chem. A 105 9396
[18] Verlet L 1967 Phys. Rev. 159 98
[19] Plimpton S 1995 J. Comput. Phys. 117 1
[20] Evans D J, Hoover W G, Failor B H, Moran B, Ladd A J C 1983 Phys. Rev. A 28 1016
[21] Frenkel D, Smit B 1996 Phys. Today 50 7
[22] Lifshitz Y 1990 Phys. Rev. B 41 10468
[23] Li X B, Tang D W, Zhu J 2008 J. Univ. Chin. Acad. Sci. 25 598 (in Chinese) [李小波, 唐大伟, 祝捷 2008 中国科学院大学学报 25 598]
[24] Wu G Q, Kong X R, Sun Z W, Wang Y H 2006 J. Astrona. 27 751 (in Chinese) [吴国强, 孔宪仁, 孙兆伟, 王亚辉 2006 宇航学报 27 751]
[25] Wang Y H, Liu L H, Kong X R 2006 J. Harbin Inst. Technol. 38 708 (in Chinese) [王亚辉, 刘林华, 孔宪仁 2006 哈尔滨工业大学学报 38 708]
[26] Xu N, Li J F, Huang B L, Wang B L 2015 Chin. Phys. B 25 016103
[27] Shamsa M, Liu W, Balandin A, Casiraghi C, Milne W, Ferrari A 2006 Appl. Phys. Lett. 89 161921
[28] Ferrari A C, Libassi A, Tanner B K, Stolojan V, Yuan J, Brown L M, Rodil S E, Kleinsorge B, Robertson J 2000 Phys. Rev. B 62 11089
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