Registration Number
0312U003157,
0109U002546
, R & D reports
Title
Influence of surface reactions on phase transformaions and morfology evolution in the nanosystems
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Вивчення кінетики утворення метастабільних нанопористих структур у процесах реакції на поверхні наночастинок
Head
Gusak Andriy Mikhailovich, Доктор фізико-математичних наук
Registration Date
13-02-2012
Organization
B. Khmelnitsky state university in Cherkasy
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1. Mathematical models enabling to understand the mechanism and kinetics of oxide growth at the thin films surfaces under "oxygen pump", are suggested. For various ratio of grin-boundary, bulk and interface "metal-oxide" diffusivities, one can determine the time of reaching the maximal oxide size (thickness) and then, taking into account the grain sizes, predict the time of continuous oxide layer formation at the surface. It is established that the diffusion mechanism influences substantially the shape and size of an oxide layer (in particular, on its effective thickness). Influence of the Mass-transfer parameters on the effective growth exponent has been analyzed. Regularities of the oxide growth for 4 diffusion regimes are found. They demonstrate that at low temperatures an oxygen pump regime is realized by diffusion along triple junctions of the grain boundaries, and at high temperatures - by the bulk diffusion in the oxide. 2. The following model of point contact reaction between silicon nanowires and nickel nanowires or nanoparticles has been elaborated: a) surface diffusion along external surface of silicon nanowire wit distributed sink due to penetration of metal atoms into wire bulk through the nanometric oxide layer; b) formation of the first monosilicide nucleus outside the mechanical contact region; c) "stop-and-go" epitaxial growth of monosilicide along nanowire by fast lateral filling of each new atomic layer leading to depletion of nickel interstitial atoms solution in silicon and respectively, to long waiting time necessary for reanimation of concentration super-saturation via the point contact; d) waiting periods are correlated in time, and this should lead to deviation of waiting time distribution from Poissonian one. 3. New theory FDN (Flux Drive Nucleation) is suggested, as well as models of nucleation in open systems (including surface layers and interfaces) are suggested: Solid state reactions start with formation of nuclei of the product phases. Divergence of external fluxes appears to be essential for nucleation. This influence is expressed in terms of the 5-th or 4-th power of size term in the effective Gibbs potential of nucleation. Characteristic size of diffusion spot around mechanical contact point could be even larger the wire diameter. It explains why a) silicide nucleate outside the contact point, b) why the phase NiSi grows instead of common Ni2Si c) why the average growth velocity is not decreasing with time. 4. Surface reaction of the nanoparticles and nanowires leading to formation and collapse of hollow nanoshells, have been modeled as one "life cycle", taking into account Kirkendall, Frenkel, Gibbs-Thomson effects. Percolation transition of voids in nanowirews is predicted 5. Surface influence on the SHS reaction in multilayers is modeled for Ni-Al system. The threshold of reaction initiation by side thermal flux is found for first time. Slowing down and acceleration of SHS reaction by non-equilibrium defects is described for the first time.
Product Description
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Гладка Л.І.
Грицаєнко Ю.
Дорошенко І.
Запорожець Т.В.
Ковальчук А.О.
Ляшенко О.Ю.
Ляшенко Ю.О.
Солодовник М.
Тютюнник Н.В.
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2020-04-02
