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Молекулярно-динамічне моделювання масоперенесення у твердому тілі під дією іонів низьких енергій

Предмет: 
Тип роботи: 
Автореферат
К-сть сторінок: 
44
Мова: 
Українська
Оцінка: 

також маркера з низькою концентрацією Al в Ni (ІП). Результати моделювання порівнюються з даними літератури.

Ключові слова: молекулярно-динамічне моделювання, іонне бомбардування, перемішування, радіаційно-прискорена дифузія, вакансія, міжвузловий атом, радіаційно-адсорбований атом, атомний каскад зіткнень, іонне розпилення.
 
SUMMARY
 
Kornich G. V. Molecular Dynamics simulation of mass transfer in solids under effect of low energy ions. – Manuscript.
Thesis for scientific degree of the doctor of physics and mathematics on speciality 01. 04. 07 – physics of solids. – Donetsk Physico-Technical Institute of National Academy of Sciences of Ukraine, Donetsk, 2002.
The dissertation is devoted to a molecular dynamics (MD) simulation of elementary modification of solid surfaces by atomic cascade relocations, generations of vacancies, interstitial and radiation-adsorbed atoms (ad-atoms) in pure Al, Ni, Cu crystals as well as in two layer Al/Ni and Ni/Al crystals, which were simulated by many body tight binding (TB) atomic potentials under low energy ion bombardment at different crystal temperatures. The second aim of the work is the using the MD simulation of atomic cascade relocations and generations of stable defects for calculation of external parameters of the ion mixing (IM) and radiation-enhanced diffusion (RED) models: sputtering coefficients, coefficients of IM, mean drift velocities of recoils, depth distributions of vacancy and interstitial productions and an ion elastic energy loss. Depth concentration profiles were calculated using mass transport models with MD simulated parameters. The results were compared with literature data.
Two stage calculating method of the low energy IM was created with a quasistable two and three dimension Cu crystal with pure Born-Mayer atomic potential and stable three dimension Cu and Ni crystals with TB potentials. Two stage method with TB potentials for Cu and Ni was applied to calculate a mixing distortion of a pseudo marker at temperatures of 0 K, 300 K, 500 K for Cu and 0 K, 300 K, 750 K for Ni. The mixing broadening of a pseudo marker as solution of the transport IM equation decreases with a temperature increase in Cu and Ni crystals. In both Cu and Ni crystals the diffusion approximation shows a smaller mixing broadening than the solution of transport IM equation.
Two stage method was developed for binary crystals for a case of a low impurity concentration of substitution for Al atoms in a Ni crystal. The general function of atomic relocations of impurity atoms was created as a double sum of local functions of atomic relocations for a single-Al atom location in either of the 1st-8th atomic layer of crystals and for six regions of ion impact. The solving of the IM equation in the diffusion approximation was performed with MD simulated parameters at 100 eV Ar ion bombardment and 300 K. The effective convective flux of impurity atoms in the IM equation increases the broadening and the maximum depth impurity concentration of the marker’s profile. The preferential sputtering of Al atoms minimizes the influence of effective convective flux. The depth periodicity of the mixing coefficient, mean square displacements (MSD) and a number of relocations of impurity atoms in a Ni crystal with a single Al atom of substitution in different atomic layers has been simulated as a result of a crystal lattice order. The depth periodicity of the mixing coefficient has been simulated in a pure Ni crystal too at 0 K and 300 K. The temperature growth results in a growth of number of atomic relocations, MSD as well as in a disappearance of the depth periodicity of the mixing coefficient at 750 K in Ni crystal and disappearance of the depth periodicity of atomic relocations in Al crystal at 500 K.
The combined calculating method of RED via vacancies and interstitial atoms with the MD simulation of depth distributions of vacancy and interstitial atom productions and solving RED equations was applied to pure Cu and Ni crystals at 100 eV Ar ion bombardment and the crystal temperatures of 500 K and 750 K, respectively. The distortion of a pseudo marker in Ni and Cu occurs mainly due to RED via both vacancy and interstitial mechanisms, which create the similar contributions to the general mass transfer effect and not collisional mixing. An efficiency of surface sinks of point defects has considerable influence on near surface diffusion fluxes and the pseudo marker’s depth concentration profile. A bulk recombination and annihilation of defects on external bulk sinks were taken into account too.
In all cases stable vacancies were simulated in the near surface range (1st-4th layers), while stable interstitial atoms were located in the crystal bulk (5th-12th layers). Both the depth of an interstitial atom generation and mixing range are larger than the depth of ion penetration to crystals at ion energies of 40-100 eV. Generations of surface vacancies and ad-atoms in Cu and Ni crystals increase with a temperature change from 0 K to 300 K, while in Al crystal they do not change. Generation of bulk vacancies in Cu crystal does not change, but it decreases in Al and Ni crystals, as well as the generation of interstitial atoms in all pure crystals, with temperature growth. The generation of ad-atoms is larger and generation of interstitial atoms is smaller in Cu crystal at 500 K and in Ni crystal at 750 K as compared to 300 K, while the generation of vacancies does not change in all cases. The defect generation in Al/Ni crystal does not noticeably change with the crystal temperature growth from 0 K to 300 K.
Considerable increase of intensity of atomic relocations through the component interface of Al/Ni and Ni/Al crystals as compared with respect pure crystals as well as of surface vacancy and ad-atom productions at temperatures of 0 K and 300 K and ion energies of 25-100 eV were obtained due to decrease of the general crystal potential energy at exchange relocations of atoms of different types at 0 K. An increase of MSD during the thermal stage of cascades in Al, Ni, Cu crystals is 1. 1-1. 4 of MSD during 0. 2-0. 3 ps. For Al/Ni and Ni/Al crystals MSD increases by 1. 4-3 times due to a difference of Al and Ni lattice constants and exchange relocations through the components interface. Ad-atoms give considerable contribution to an increase of MSD in course of the thermal stage of cascades.
Key words: molecular dynamics simulation, ion mixing, radiation-enhanced diffusion, vacancy, interstitial atom, radiation-adsorbed atom, atomic collision cascade, ion sputtering.
 
АННОТАЦИЯ
 
Корнич Г. В. Молекулярно-динамическое моделирование массопереноса в твердом теле под действием ионов низких энергий. – Рукопись.
Диссертация на соискание ученой степени доктора физико-математических наук по специальности 01. 04. 07 – Физика твердого тела. – Донецкий физико-технический институт НАН Украины, Донецк, 2002.
Диссертация посвящена молекулярно-динамическому (МД) моделированию перемещений атомов в каскадах столкновений, образованию вакансий, междоузельных и радиационно-адсорбированных атомов в однокомпонентных Al, Ni, Cu и двухслойных кристаллах Al/Ni и Ni/Al, которые описываются многочастичными атомными потенциалами, при бомбардировке ионами Ar и Xe с энергиями 15-100 эВ и температурах 0 К – 750 К, а так же использованию стабильного и квазистабильного МД методов для расчетов параметров моделей ионного перемешивания (ИП) и радиационно-ускоренной диффузии (РУД) : коэффициентов распыления и ИП, средней скорости дрейфа атомов отдачи, распределения генерации вакансий и междоузельных атомов по глубине кристаллов. Расчитываются послойные профили концентрации псевдомаркера (ИП и РУД) в Cu и Ni, а так же маркера с низкой концентрацией Al в Ni (ИП). Результаты моделирования сравниваются с данными литературы.
Ключевые слова: молекулярно-динамическое моделирование, перемешивание, радиационно-ускоренная диффузия, вакансия, междоузельный атом, радиационно-адсорбированный атом, атомный каскад столкновений, ионное распыление.
 
Список використаних джерел
 
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