Search

Актуальність теми Отримані результати можуть бути корисними в гнучкій електроніці, де широко використовуються впорядковані ланцюги наночастинок Au та Ag, а також радіально модульовані квазіодновимірні структури. Зв’язок роботи з науковими програмами, планами, темами ФМФ-07 Динаміка та властивості багаточастинкових систем. Об’єкт дослідження Фізичні механізми суттєвого впливу зовнішнього опромінення на динаміку морфології квазіодновимірних наносистем внаслідок інтенсифікації поверхневої дифузії атомів. Предмет дослідження Чисельне моделювання трансформації поверхонь металевих нанодротів внаслідок поверхневої дифузії атомів при підвищених температурах в режимах предплавлення без руйнування внутрішньої кристалічної структури. Мета роботи Знайти можливості контрольованого синтезу періодично модульованих за перерізом квазіодновимірних наноструктур. Методи дослідження Числовий експеримент на основі Монте-Карло моделі. Задачі дослідження. 1. Встановити чутливість різних граней металів з гранецентрованою кристалічною ґраткою до штучної стимуляції поверхневої дифузії. 2. Порівняти отримані результати з випадком, коли поверхнева дифузія посилюється простим підвищенням температури. 3. Виконати моделювання термічного розпаду нанодротів з різною орієнтацією внутрішньої кристалічної структури відносно їх осей і різним рівнем анізотропії густини поверхневої енергії. 4. Розкрити мікроскопічні фізичні фактори, які відповідають за різку зміну в динаміці нанодротів в залежності від рівня інтенсифікації поверхневої дифузії. 5. Провести термодинамічний аналіз явищ, що спостерігаються, та виконати кількісні оцінки їх показових параметрів на основі статистичної динаміки. 6. Розробити рекомендації для методів керованого синтезу квазіодновимірних наносистем з розвиненою морфологією типу «зелена гусениця». Наукова новизна одержаних результатів Розробити рекомендації для методів керованого синтезу квазі-одновимірних наносистем з розвиненою морфологією типу «зелена гусениця»Практичне значення одержаних результатів Збудженні модуляції поверхні товстих нанодротів можна використати як зародки для синтезу впорядкованих ланцюжків вторинних наноголок в дифузійному режимі осадження вільних атомів Апробація результатів дисертації Зроблені доповіді на конференціях: 1. XX Всеукраїнській науково-практичній конференції «Теоретичні і прикладні проблеми фізики, математики та інформатики». 2. Х Міжнародній науково-практичній конференції «Нанотехнології та наноматеріали» (НАНО-2022). Actuality of theme The obtained results may be useful in flexible electronics, where ordered chains of Au and Ag nanoparticles, as well as radially modulated quasione-dimensional structures, are widely used. Relationship of work with scientific programs, plans, themes FPM-07 Dynamics and properties of multiparticle systems. Object of research Physical mechanisms of significant external influence irradiation on the dynamics of the morphology of quasi-one-dimensional nanosystems due to the intensification of the surface diffusion of atoms. Subject of research Numerical modeling of the transformation of the surfaces of metal nanowires due to the surface diffusion of atoms at elevated temperatures in premelting regimes without destruction of the internal crystal structure. Purpose of work To find the possibilities of controlled synthesis of quasi-onedimensional nanostructures periodically modulated in cross-section. Research methods A numerical experiment based on the Monte Carlo method Tasks of research 1. To establish the sensitivity of various faces of metals with a facecentered crystal lattice to artificial stimulation of surface diffusion. 2. Compare the obtained results with the case when surface diffusion is enhanced by a simple increase in temperature. 3. Model the thermal decay of nanowires with different orientations of the internal crystal structure relative to their axes and different levels of surface energy density anisotropy. 4. To reveal microscopic physical factors that are responsible for a sharp change in the dynamics of nanowires depending on the level of intensification of surface diffusion. 5. Conduct a thermodynamic analysis of the observed phenomena and perform quantitative assessments of their indicative parameters based on statistical dynamics. 6. Develop recommendations for methods of controlled synthesis of quasi-onedimensional nanosystems with a developed morphology of the "green caterpillar" type. Scientific novelty of the results Develop recommendations for methods of controlled synthesis of quasi-one-dimensional nanosystems with developed "green caterpillar" morphology. The practical significance of the results Excitation modulations of the surface of thick nanowires can be used as seeds for the synthesis of ordered chains of secondary nanoneedles in the diffusion mode of deposition of free atomsApprobation of the results of the dissertation. Reports made at conferences: 1. XX All-Ukrainian Scientific and Practical Conference "Theoretical and Applied Problems of Physics, Mathematics and Informatics". 2. X International Scientific and Practical Conference "Nanotechnologies and Nanomaterials" (NANO-2022).

The growth of carbonaceous materials was studied using a Kinetic Monte Carlo model that captures the growth and oxidation of six-member and partially-embedded five-member rings. A novel algorithm was used to resolve the migration of partially-embedded five-member rings around the edges of molecules. Circumcoronene molecules were grown at 1500 K and 1 atm in the presence of varying mole fractions of atomic and molecular oxygen and constant mole fractions of hydrogen and acetylene. The parameter space of the study covered the mole fraction of atomic and molecular oxygen in the ranges: 10-8 ≤ XO ≤ 10-1 and 10-6 ≤ XO2 ≤ 10-1. Four regions of carbon growth associated with different carbonaceous products were identified. Graphene was formed in the presence of high mole fractions of atomic oxygen (10-4 < XO ≤ 10-2). Fullerenes were formed in the presence of low mole fractions of atomic oxygen and high mole fractions of molecular oxygen (XO ≤ 10-4 and 10-2 < XO2 ≤ 10-1). Low mole fractions of both atomic and molecular oxygen (XO ≤ 10-4 and XO2 ≤ 10-2) resulted in structures that became curved as time progressed. The highest mole fractions of atomic oxygen (XO > 10-2) produced small structures due to oxidation of the molecules. The production and consumption of partially-embedded five-member rings appear to explain the formation of the observed structures. The oxidation of partially-embedded five-member rings leaves behind armchair sites that grow to form large and flat structures that resemble graphene. Formation and subsequent embedding of partially-embedded five-member rings result in curved structures that resemble fullerenes.

This paper uses a Kinetic Monte Carlo model that includes processes to integrate curvature due to the formation of five- and seven-member rings to simulate polycyclic aromatic hydrocarbons (PAHs) growing in lightly sooting ethylene and acetylene counterflow diffusion flames. The model includes new processes to form seven-member rings via hydrogen-a bstraction-acetylene-addition and bay closure reactions on sites containing partially embedded five-member rings. The model additionally includes bay closure and HACA bay capping reactions for the integration of five-member rings. The mass spectra of PAHs predicted by the model are assessed against experimental data, and the distribution of embedded five-member rings and seven-member rings is studied as a function of spatial location, molecule size and frequency of events sampled in the simulation. The simulations show that the formation of seven-member rings and the embedding of five-member rings is a competitive process. Both types of rings are observed more frequently as the simulation proceeds from the fuel outlet towards the stagnation plane. Approximately 15% of the events that integrate curvature resulted in the formation of a seven-member ring coupled to an embedded five-member ring, and the remaining 85% of events embedded five-member rings via the formation of six-member rings. The proportion of PAHs containing embedded five-member rings and/or seven-member rings is observed to be a function of PAH size, passing through a maximum for PAHs containing 15–20 six-member rings. However, the proportion of PAHs containing both types of ring increases with PAH size, where upwards of 10% of PAHs containing at least one five-member ring and 15 or more six-member rings also contain a seven-member ring.

We formulate and study a stochastic model for the thermally-driven motion of interacting straight screw dislocations in a cylindrical domain with a convex polygonal cross-section. Motion is modelled as a Markov jump process, where waiting times for transitions from state to state are assumed to be exponentially distributed with rates expressed in terms of the potential energy barrier between the states. Assuming the energy of the system is described by a discrete lattice model, a precise asymptotic description of the energy barriers between states is obtained. Through scaling of the various physical constants, two dimensionless parameters are identified which govern the behaviour of the resulting stochastic evolution. In an asymptotic regime where these parameters remain fixed, the process is found to satisfy a Large Deviations Principle. A sufficiently explicit description of the corresponding rate functional is obtained such that the most probable path of the dislocation configuration may be described as the solution of Discrete Dislocation Dynamics with an explicit anisotropic mobility which depends on the underlying lattice structure., Comment: Major revision, including overhaul of notation, additions to Section 6 on Large Deviations, and resolution of conjecture in original version. 45 pages, 2 figures, 1 table

The carbon/sulfur composite cathodes of lithium sulfur batteries undergo mesostructural evolutions during discharge due to the dissolution/precipitation reactions of solid sulfur and Li2S. Furthermore, the cathode design and discharge parameters also impact the mesostructural evolutions of carbon/sulfur composites. In order to compare and study these mesostructural evolutions, we have developed a novel three dimensional kinetic Monte Carlo (kMC) model based on an algorithm called Variable Step Size Method (VSSM). Our model describes mechanisms such as dissolution of solid sulfur, reactions and diffusions of different polysulfides and electrodeposition of Li2S. The initial carbon/sulfur mesostructure used in our model is created based on its desired structural and geometric properties using an in silico method. In this paper, we present the theoretical development of our kMC model and demonstrate its capabilities using discharge simulations of a model carbon/sulfur mesostructure under two different rates (C-rates) namely C/2 and 2C. Furthermore, we also present the impact of initial S8(s) loading on the 2C discharge simulation. Fil: Thangavel, Vigneshwaran. Université de Picardie Jules Verne. Laboratoire de Réactivité et Chimie des Solides; Francia. Centre National de la Recherche Scientifique; Francia Fil: Guerrero, Oscar Xavier. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzados. Departamento de Química; México Fil: Quiroga, Matías Abel Oscar. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina. Centre National de la Recherche Scientifique; Francia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentina Fil: Mikala, Adelphe Matsiegui. Centre National de la Recherche Scientifique; Francia. Université de Picardie Jules Verne. Laboratoire de Réactivité et Chimie des Solides; Francia Fil: Rucci, José Alexis. Centre National de la Recherche Scientifique; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Université de Picardie Jules Verne. Laboratoire de Réactivité et Chimie des Solides; Francia Fil: Franco, Alejandro A.. Université de Picardie Jules Verne. Laboratoire de Réactivité et Chimie des Solides; Francia. Centre National de la Recherche Scientifique; Francia

Microstructural evolution and sintering behavior of powder compacts composed of spherical particles with different particle size distributions (PSDs) were simulated using a kinetic Monte Carlo model of solid state sintering. Compacts of monosized particles, normal PSDs with fixed mean particle radii and a range of standard deviations, and log-normal PSDs with fixed mode and a range of skewness values were studied. Densification rate and final relative density were found to be inversely proportional to initial PSD width. Grain growth was faster during the early stages of sintering for broad PSDs, but the final grain sizes were smaller. These behaviors are explained by the smallest grains in the broader PSDs being consumed very quickly by larger neighboring grains. The elimination of the small grains reduces both the total number of necks and the neck area between particles, which in turn reduces the regions where vacancies can be annihilated, leading to slower densification rates. The loss of neck area causes grain growth by surface diffusion to become the dominant microstructural evolution mechanism, leading to poor densification. Finally, pore size was shown to increase with the width of PSDs, which also contributes to the lower densification rates.