The thesis is devoted to investigation of regularities of structural phase transitions at the interfaces of "graphene-metal (Fe, Pt, Ti)" and "metal layer (Fe, Pt, Mn) below 25 nm-Si(100)" systems for formation of scientific bases of next generation microdevices fabrication. The feature of this work is the fact that, in contrast to other studies, combined approach for investigation of structural phase transitions at the interfaces of different types was applied: computer simulation methods of different scale levels were combined with modern experimental investigation methods.
Molecular dynamics approach was used for investigation of "graphene-metal" interfaces. Main part of calculations was realized at Huizhou University (PRC), using TianHe-II supercomputer. The models of pure metal, free graphene, "graphene-metal system" of two different orientations for each metal, two temperatures – 300 K and 400K, three most densely packed metal planes were created in order to determine the impact induced by graphene coating. As a result, more than 70 model systems were analyzed, allowing to determine regularities of structural relaxation and reconstruction processes at the interfaces of systems "graphene-single crystal of metal Fe, Pt, Ti of various surface orientations" as well as impact of temperature factor.
- there are just structural modifications (expansion up to 3%) without reconstruction of graphene at metal surfaces at temperatures below 400 K;
- relaxation and reconstruction rates of surface layer decrease with increase of its crystallographic packing density, and increase with a rise of the temperature.
Based on these regularities, the following criteria were proposed for a first time in order to provide structural stability of the "graphene-metal" interfaces:
- in case of small mismatch between crystal lattice parameters of metal and graphene it is desirable to choose planes with a maximum surface packing density;
- in case of large mismatch between crystal lattice parameters of metal and graphene it is desirable to choose planes with a lowest surface packing density;
Interfaces of the second type "metal-silicon" were investigated by means of continuous approach, using modern nonlinear mathematical analysis methods, theory of differential equations with partial derivatives, integral equations as well modern experimental methods.
The tasks of nucleation and growth of new phase particles (ensemble like) of flat and cylindrical shapes, growing from the area with a limited diffusant source, were considered as well. The solutions of these diffusion tasks in new forms were obtained, allowing to determine the following parameters: growth rate of new particles during heat treatment; maximum size of growing particles and time needed to achieve this size; concentration and time distributions in the area close to these particles; diffusion characteristics.
For experimental study of technically promising “metal-silicon” systems in the temperature range of 723 K – 1273 K the following methods were used: secondary ions mass-spectrometry, X-ray diffraction, transmission electron microscopy, four-point resistivity measurements, etc. It was determined that feature of structural and phase modifications in the investigated layers of silicides (Mn4Si7) and intermetallics (L10-FePt) is a formation of structural elements ensemble of flat shape. Obtained solutions of diffusion tasks in a new form were used to forecast of parameters and evolution of found structural elements.
Computer simulation of growth kinetics of Mn4Si7 silicide phase during co-deposition of Mn and Si, in case of oversaturated Mn-Si solid solution formation during initial diffusion stages, reveled satisfied agreement between calculation parameters and transmission electron microscopy experimental results.
Using Fe-Pt/Si(100) system as an example, it was proved that molecular dynamics is an effective approach to determine temperature dependence of vacancy formation energy, diffusion activation energy, migration energies of Fe and Pt atoms in the L10-FePt intermetallic.
Obtained results are of practical interest for scientific basis formation of modern technologies of micro- and nano- devices creation with layers of graphene, metals and silicon.
