First-principles Inverstigation On The Interfaces For Nanomultilayers Ti/TiN, TiN/CrN, And TiN(NbN)/SiNx

Nanomultilayer films have special structure and physical property, which make them highly attractive from the technological as well as the scientific point of view. Many factors contribute to the hardness enhancement of multilayer film, of which deposition condition is the most important one. There are still problems remained to be solved, for example, the preparation method, the structure and characterization of property, and the application, and more investigations should be done about its growth mechanism and microcosmic interface properties. In addition, even though some mechanisms of superhardness effects of nanomultilayer films have been suggested according to the research results of some multilayer films systems, these mechanisms cannot entirely explain the phenomena observed in all experiments. The relationships between the mechanical properties and the microstructure of superhardness ceramic multilayer films need to be further researched.The properties of materials are determined by their atomic and electronic structures, and the quantum chemistry provides a viable method to compute the behavior of the electrons and atomic nuclei under arbitrary circumstances. The first-principles density function theory (DFT) is always the most powerful tool for calculating the electronic structures and the characteristics in the field of condensed state physics.In this paper, according to the interfacial microstructure, lattice mismatch and the elastic modulus difference have been considered through first-principles density functional theory and three kinds of nanomultilayer films have been manufactured. The relationships within modulation structures, lattice parameters, microstructure and superhardness effects of the films have been studied, three kinds model including TiN/Ti,TiN/CrN and TiN(NbN)/SiNx were constructed, first-principles plane-wave method provided by CASTEP code is utilized to systemically investigate the geometrical and electronic structures of nanomultilayers interface.Firstly, we have studied the bulk properties of TiN and Ti, such as the lattice parameters, elastic constants. In the calculation of the lone film TiN and Ti, we gained surface structures and data of surface energy of the lone film of TiN and Ti. With the increase in thickness of TiN film, surface energy of TiN decreased, which shows that the structure becomes more stable. Before we begin the detailed study of interfaces, we considered the adsorption properties of a single Ti atom on the TiN (100) and N-terminated TiN (111) surface with periodicity in order to check the convergence with respect to the thickness of TiN slab. We found that the hollow place of the TiN (100) surface, which titanium atom deposits, is the most stable position. For the TiN (111) surface, Ti atoms could occupy the site which is the top of N atoms or on the bridge site between two N atoms, also there are two kinds of hollow sites. The bridge site is unstable, and the two kinds of hollow sites are stable, the hollow site on the top of the N atom of the third layer is more stable.The results are in good agreement with the experimental and other calculational results.We constructed several models of TiN (111)/Ti (001) interface, and gained two kinds of the stable models of the interface, adhesion energies of interface and the interfacial separations. In addition, we also gained difference charge density of two stable interface systems. In the first system, the extent of accumulation and depletion is from 0.2500e/?3 to -0.2200 e/?3, in another system, the extent is from 0.2771e/?3 to -0.2720e/?3. In addition, we also analysed the LDOS of different sites of Ti and N.Secondly, we have studied the bulk properties of CrN, such as the lattice parameters, elastic constants. we mainly studied the structure of lone CrN film, the results indicate that the surface energy decreases with the increasing in thickness of CrN film. We constructed two kinds of the TiN (100)/CrN (100) interface systems, and calculated the data of interface adhesion energies and the interfacial separations, with the coherent boundary growing; the interface system is more stable. In addition, the interface adhesion energies and the interfacial separations of the different thickness of CrN (100) and the same thickness of TiN film are obtained. At the same time, we analysed the charge density and LDOS of the different systems of TiN (100)/CrN (100) interfacial models.Thirdly, we performed extensive first-prinples DFT calculations using CASTEP in order to shed light on the atomic structure and associated physical properties of TiN/SiNx and NbN/SiNx nanomultilayer interfaces. We predicted the optimized atomic structure and bulk modulus of the sixα-Si3N4(P31c),β-Si3N4(P63/M),γ-Si3N4 (FD-3M), SiN(fcc) phases of bulk,TiN and NbN, which are in excellent agreement with available experimental results.For the lone slab of TiN, NbN and SiN, we calculated the different thickness systems ,and gained surface structures and surface energy ,the results indicated that the two SiN(100) atom layers is stable but three or over three atom layers is unstable.For the interface syetems of TiN/SiNx, we constructed the TiN (100)/ SiN (100), TiN (111)/SiN (111)/TiN (111) TiN/SiN models, according to the interface syetems of TiN/SiNx, NbN/SiNx models were constructed, and we gained the interface atomic structure and electron structure of the models constructed.In conclusion, we constructed three kinds interface systems, we perform first-principles DFT calculations of the electronic structure and properties of nanomultilayers interface. These findings will be helpful in the study and the design of nanomultilayers.