The Study On The Interface Structure And Properties Of The Singlecrystal Like Polycrystalline Nano-diamond Composite Films

In this paper, a new kind of nano-diamond composite films, in which nano-diamond grains is surrounded by a monolayer heterogeneous interface, is proposed.This composite structure is called single-crystallites like poly-crystallites thin films.Since the composite structure has a regular ordered phase interface, thereby more sp2bond, non-diamond carbon atoms, hydrogen atoms and large vacancies existing in thecurrent nano-diamond films is been reduced or eliminated. This paper based on thedensity functional theory (DFT) of the first-principles methods to calculate the threemain parts, first the total and cohesive energies of pure diamond (001) and (111)supercells were calculated. Then a series of calculations of diamond (001) and (111)with tetravalent (Si), germanium (Ge), trivalent boron (B) and pentavalent phosphorus(P) interfaces were conducted. After that the mechanical properties of the interfacestructure at a steady state were calculated. Finally, the magnetic of the state3d transitionmetal including Cr, Mn, Fe, Co, Ni at the interface structure and the magnetic of thestate3d transition metal adsorption on the diamond (001) surface obtained. Thecalculations present some results:(1) Compared with pure diamond model, the total energies of diamond with aninterface increased and cohesive energies decreased. It indicates that the interface phaseatoms can not be as solid solution in diamond crystals, so that it is possible to staybetween diamond particles to form an interface. After full relaxation, the (001) interfaceand the (111) interface of diamond possess relative low total energy and form a stablestructure. Therefore, the interface could exist between diamond crystallites. In addition,the energy density of (001) interface is larger than that of (111) interface.(2) For the mechanical properties of the interface structure, generally (001)interface is better than (111). The young’s modulus of a direction parallel to the interfaceis slightly larger than the direction perpendicular to the interface. The young’s modulus, bulk modulus and shear modulus of B (001) interface structure is922.231Gpa,412.262Gpa and409.146Gpa, respectively. The young’s modulus of nano-diamondcomposite film interface structure is larger than the current prepared experimentallyNanocrystalline Diamond Films（NCD） or Ultrananocrystalline Diamond Films（UNCD） films. Its hardness is above40Gpa, which are superhard nano-diamondcomposite films. The hardness of B (001) interface structure is about71.1Gpa, close tothe single crystal diamond.(3) Results of the magnetic showed that the Cr and Ni can not induce the interfacestructure of diamond to generate a magnetic. However, the total magnetic moments ofMn, Fe, Co interface structure were9.0399B,4.4919Band1.2829B, respectively.The system was stable ferromagnetic with some metal properties were showed, andturned into diluted magnetic semiconductors. The magnetic and electronic properties ofTM (TM=Cr, Mn, Fe, Co and Ni) adatoms adsorption on diamond (001) surface weremagnetically induced.