Microscopic and Macroscopic Surface Dynamics of Highly Anisotropic Crystals

Zadanie pt. Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę

Nonlinear rotor dynamics of 2D molecular array: topology reconstruction

Molecular layers with rotational degrees of freedom and quadrupolar interaction between linear molecules are investigated theoretically. We found earlier that alternative orientation of the molecules along and perpendicular to an axis of the rectangular lattice is preferable. Here we find the integral of motion and give the topology analysis of the possible dynamical phases and special points in the long-wave limit. We find the strong anisotropy in the angle space: directions of easy excitation ("valleys'') exist. We show the potential relief reconstruction in dependence on the adsorbed lattice anisotropy.Теоретически исследованы молекулярные слои с вращательными степенями свободы и квадрупольным взаимодействием между линейными молекулами. Мы нашли ранее, что предпочтительным является альтернативное упорядочение молекул с ориентацией вдоль и перпендикулярно оси прямоугольной решетки. Выведены уравнения движения, найден их интеграл и проведен топологический анализ возможных динамических фаз и особых точек в длинноволновом пределе. Показана сильная анизотропия в плоскости углов: существуют направления легкого возбуждения ("долины''). Мы показываем реконструкции потенциального рельефа в зависимости от анизотропии адсорбированной решетки.Теоретично досліджені молекулярні шари з обертальними ступенями свободи і квадрупольною взаємодією між лінійними молекулами. Ми знайшли раніше, що кращим є альтернативне впорядкування молекул з орієнтацією вздовж і перпендикулярно осі прямокутної гратки. Виведено рівняння руху, знайдено їх інтеграл і проведено топологічний аналіз можливих динамічних фаз і особливих точок для довгохвильової межі. Показано сильну анізотропію в площині кутів: існують напрями легкого збудження ("долини''). Ми показуємо реконструкцію потенційного рельєфу в залежності від анізотропії адсорбованої решітки

Functionalized Semiconducting Carbon Nanotubes: Three Models for Carrier Spectra

Electronic spectra in functionalizing semiconducting carbon nanotube (CNT) are researched theoretically. The soft degrees of freedom are considered in the molecular system: radial deformation, misfit dislocations, and conformation. For each model the selfconsistent system of equations is derived. A system describes a charge carrier longitudinal quantization in CNT, interaction of a carrier in CNT and molecular electric dipoles, material equations for a soft degree of freedom and its reconstruction. It is shown that the functionalization reconstructs the CNT electronic spectra and creates different conditions of localization or tunneling for holes and electrons.Теоретично досліджено електронні спектри функціоналізованої напівпровідникової вуглецевої нанотрубки (НТ). В молекулярній системі розглянуто наступні м’які ступені свободи: радіальна деформація, дислокації невідповідності і конформації. Для кожної моделі отримана самоузгоджена система рівнянь. Кожна система описує поздовжне квантування носія заряду в НТ, взаємодію носія в НТ з електричними диполями молекул, матеріальні рівняння для м'якого ступеня свободи і його реконструкції. Показано, що функціоналізація модифікує електронні спектри НТ і створює різні умови для локалізації або тунелювання дірок й електронів.Теоретически исследованы электронные спектры функционализированной полупроводниковой углеродной нанотрубки (НТ). В молекулярной системе рассматриваются следующие мягкие степени свободы: радиальная деформация, дислокации несоответствия и конформации. Для каждой модели получена самосогласованная система уравнений. Каждая система описывает продольное квантование носителя в НТ, взаимодействие носителя в НТ с электрическими диполями молекул, материальные уравнения для мягкой степени свободы и ее реконструкции. Показано, что функционализация модифицирует электронные спектры НТ и создает различные условия для локализации или туннелирования дырок и электронов

Resonance absorption, reflection, transmission of phonons and heat transfer through interface between two solids

The different mechanisms of resonant transport of phonons between two media in the presence of impurity intermediate layer are described. Particular attention is focused on the resonance interaction of elastic waves with a two-dimensional defect on the contact boundary between two solids, on the multichannel interface phonon scattering and on the experimentally observed nonmonotonic temperature dependence of the reduced heat flux. In the cases when there is a direct interaction between edge atoms of the matrix as non-nearest neighbors or when the impurities do not fill completely the 2D interface layer, the additional channel for the transmission of phonons through the interface opens. This additional transmission channel manifests itself as a transmission (or reflection or absorption) peak with an asymmetric line shape (the so-called Fano resonance for phonons due to interference between the two transmission channels). Some applications of the Fano effect in magnon heat conductivity are also discussed

Vibrational dynamical and thermodynamical characteristics of the superlattices based on the metal-hydrogen system

The phonon spectra and vibrational thermodynamical characteristics of the Pd-H superlattices are investigated. Results of our calculations give a possibility to agree the data of neutronographic and calorimetric experiments and explain for the such systems the atomic mean square amplitudes and correlations between ones

Phonon spectrum and vibrational characteristics of linear nanostructures in solid matrices

The atomic dynamics of linear chains embedded in a crystalline matrix or adsorbed on its surface is studied. A linear chain formed by substitutional impurities in a surface layer and at the same time offsetting from this layer was analyzed particularly. This system models the actively studied experimentally structures in which gas molecules are adsorbed on the walls of the bundles of carbon nanotubes located in certain medium. It is shown that the quasi-one-dimensional features are typical for the chains in which the interatomic interaction is higher than the interaction between the atoms of the chain and the atoms of the crystal matrix. On the local phonon density of atoms of the chain the transition to quasi-one-dimensional behavior has the form of the kink. In other words, it is the first (lowest-frequency) van Hove singularity, which in 3D structures (the system under consideration is generally three-dimensional) corresponds to the transition from closed to open constant-frequency (quasi-plane) surfaces. The local phonon densities of atoms in the chain have one-dimensional character at frequencies higher than the frequency of the van Hove singularity. The rms amplitude of embedded chains atoms vibrations is calculated and the behavior of the atomic vibrations contribution in the low-temperature heat capacity of the system is analyzed

Dissipative Interaction and Anomalous Surface Absorption of Bulk Phonons at a Two-Dimensional Defect in a Solid

We predict an extreme sensitivity to the dissipative losses of the resonant interaction of bulk phonons with a 2D defect in a solid. We show that the total resonant reflection of the transverse phonon at the 2D defect, described earlier without an account for dissipation, occurs only in the limit of extremely weak dissipation and is changed into almost total transmission by relatively weak bulk absorption. Anomalous surface absorption of the transverse phonon, when one half of the incident acoustic energy is absorbed at the 2D defect, is predicted for the case of "intermediate" bulk dissipation.Comment: 11 preprint pages, no figure

Theory of rare gas alloys: heat capacity

Low-temperature heat capacity of cryocrystals, which contain impurity clusters has been investigated theoretically and experimentally. Such defects might essentially enrich low-frequency part of the phonon spectrum by introducing both localized and delocalized vibrations. The effect of both types of the vibrations on the temperature dependence of the heat capacity is analyzed. Heat capacity of the disordered solid solution Kr–Ar (Ar concentration is ~25%) is studied as an example of the effect of the light weakly connected impurities on the low-temperature thermodynamic characteristics of the system. The mass defect of such an impurity induces «phonon pumping» from the low-frequency part of the spectrum into the high-frequency part and decreasing the low-temperature heat capacity, while the weakened interaction between the impurity and the host atoms combined with even weaker interaction between the impurities leads to the formation of the low-temperature maximum on the heat capacity temperature dependence. The analysis performed shows that at rather high Ar concentrations, the nonmonotonous temperature dependence of the relative change in the heat capacity of solid Kr₁₋pArp solutions is determined by excitation of delocalized high-dispersion low-frequency phonons

Oscillatory spectra of surface atoms in strongly anisotropic layered crystal (quasi-1D behaviour)

Vibrations localized near the surface have been analyzed using the Jacobian matrix method taking into account discreteness of the lattice. It has been shown that localized surface vibrations in layered crystals have got quasi-one-dimensional character and their properties are described by exact solutions obtained in the framework of the one-dimensional model.Коливання, що локалiзованi поблизу поверхнi, аналiзуються за допомогою методу J -матриць iз врахуванням дискретностi гратки. Показано, що в шаруватих кристалах такi коливання мають одновимiрний характер та можуть задовiльно описуватися за допомогою вiдповiдних точних аналiтичних виразiв, що отриманi для одновимiрної моделi

Evolution of discrete local levels into an impurity band in solidified inert gas solution

The density of states g(w) of disordered solutions of solidified inert gases have been calculated using the Jacobian matrix method. The transformation of a discrete vibrational level into an impurity zone at a growing concentration of light impurity atoms has been investigated. It is shown that a 1–10% change in the impurity concentration leads to smearing the local discrete level into an impurity band. As this occurs, additional resonance levels appear which carry important information about the impurity–impurity and impurity– basic lattice force interactions in such solutions