Molecular Dynamics And First-principles Study On Diamond-like Carbon Thin Films

Diamond-like Carbon films, the properties of which range from diamond to graphite,are metastable amorphous materials, containing a certain amount sp~3hybrid atoms. Theproperties of DLC films are adjustable in a large range: refractive index can be adjustedbetween1.8and2.5, the optical band gap between0.8eV and4.1eV, resistivity range upto10orders of magnitude class, hardness upper limit95GPa. Friction coefficient is lessthan0.20, much smaller than the average super hard materials (between0.35and0.7).Soin terms of scientific research or in applications the DLC films are hot spot.In this paper, the methods of classical Molecular Dynamics and First-Principles,considering the electron spins,were used to calculate five amorphous carbon structureswith different densities:2.0g/cm~3,2.3g/cm~3,2.6g/cm~3,2.9g/cm~3,3.2g/cm~3. Also westudied the influence of quenching time on the disordered structures with density of2.9g/cm~3.Comparing the radial distribution function, it indicated that the simulatedamorphous structures are consistent with experimental data. We also studied the bondlengths, angles distribution and coordination of each structure, which conclude that thecontent of non-sp~3hybrid bonds is linear relationship with density of amorphous carbon.And then the influence produced by three or four-atom rings on the structure was studied.Found that inner-stress is non–linear relationship with the content of sp~3hybrid bonds.By the mean square displacement, the diffusions of carbon atoms in the differentquenching time were discussed, the results of which show the shorter time of thequenching time and the higher content of sp~3hybrid bonds, with higher energy ofstructure. Meanwhile, TDOS, PDOS of the amorphous carbon structures and three andfour-atom rings' LDOS were discussed in this paper. The defect structures were emergedin our models. The results show that defect density in highly density structures is higherthan that in lower density structures. And what' more, most defect structures exist in formof isolated sp~3dangling bonds in highly density structures. The electronic density ofstates near Fermi level in the high-density amorphous carbon structures are mainly resulted from the defect states.Finally, the DLC film preparation methods were introduced briefly. Based on theexisting conditions in our laboratory, we have designed and reformed the machine so thatit can deposited films by magnetron sputtering, chemical vapor deposition and electricfield assisted chemical deposition.