Magnetically operated nanorelay based on two single-walled carbon nanotubes filled with endofullerenes Fe@C20

Structural and energy characteristics of the smallest magnetic endofullerene Fe@C20 have been calculated using the density functional theory approach. The ground state of Fe@C20 is found to be a septet state, and the magnetic moment of Fe@C20 is estimated to be 8 Bohr magnetons. Characteristics of an (8,8) carbon nanotube with a single Fe@C20 inside are studied in the framework of the semiempirical approach. The scheme of a magnetic nanorelay based on cantilevered nanotubes filled with magnetic endofullerenes is elaborated. The proposed nanorelay is turned on as a result of bending of nanotubes by a magnetic force. Operational characteristics of such a nanorelay based on (8,8) and (21,21) nanotubes fully filled with Fe@C20 are estimated and compared to the ones of a nanorelay made of a (21,21) nanotube fully filled with experimentally observed (Ho3N)@C80 with the magnetic moment of 21 Bohr magnetons. Room temperature operation of (21,21) nanotube based nanorelays is shown.Comment: 18 pages, 9 figure

Interlayer interaction, shear vibrational mode, and tribological properties of two-dimensional bilayers with a commensurate moir\'e pattern

The potential energy surface (PES) of interlayer interaction of infinite twisted bilayer graphene is calculated for a set of commensurate moir\'e patterns using the registry-dependent Kolmogorov-Crespi empirical potential. The calculated PESs have the same shape for all considered moir\'e patterns with the unit cell size of the PES which is inversely related to the unit cell size of the moir\'e pattern. The amplitude of PES corrugations is found to decrease exponentially upon increasing the size of the moir\'e pattern unit cell. An analytical expression for such a PES including the first Fourier harmonics compatible with the symmetries of both layers is derived. It is shown that the calculated PESs can be approximated by the derived expression with the accuracy within 1%. This means that different physical properties associated with relative in-plane motion of graphene layers are interrelated and can be expressed analytically as functions of the amplitude of PES corrugations. In this way, we obtain the shear mode frequency, shear modulus, shear strength and barrier for relative rotation of the commensurate twisted layers to a fully incommensurate state for the considered moir\'e patterns. This barrier may possibly lead to the macroscopic robust superlubricity for twisted graphene bilayer with a commensurate moir\'e pattern. The conclusions made should be valid for diverse 2D systems of twisted commensurate layers.Comment: 9 pages, 3 figures; Supplemental Material: 2 pages, 1 figur

Высокочастотный конденсатор с рабочим веществом «изолятор нелегированный кремний изолятор»

The study of the parameters of capacitors with various working substances is of interest for the design and creation of electronic elements, in particular for the development of high-frequency phase-shifting circuits.The purpose of the work is to calculate the high-frequency capacitance of a capacitor with the working substance "insulator-undoped silicon-insulator" at different applied to the capacitor direct current (DC) voltages, measuring signal frequencies and temperatures.A model of such the capacitor is proposed, in which 30 µm thick layer of undoped (intrinsic) crystalline silicon (i-Si) is separated from each of the capacitor electrodes by 1 µm thick insulator layer (silicon dioxide).The dependences of the capacitor capacitance on the DC electrical voltage U on metal electrodes at zero frequency and at the measuring signal frequency of 1 MHz at absolute temperatures T = 300 and 400 K are calculated. It is shown that the real part of the capacitor capacitance increases monotonically, while the imaginary part is negative and non-monotonically depends on U at the temperature T = 300 K. An increase in the real part of the capacitor capacitance up to the geometric capacitance of oxide layers with increasing temperature is due to a decrease in the electrical resistance of i-Si layer. As a result, with an increase in temperature up to 400 K, the real and imaginary parts of the capacitance take constant values independent of U. The capacitance of i-Si layer with an increase in both temperature T and voltage U is shunted by the electrical conductivity of this layer. The phase shift is determined for a sinusoidal electrical signal with a frequency of 0.3, 1, 10, 30, 100, and 300 MHz applied to the capacitor at temperatures 300 and 400 K.Исследование параметров электрических конденсаторов с различными рабочими веществами представляет интерес для проектирования и создания элементов электроники, в частности для разработки высокочастотных фазосдвигающих цепей.Цель работы рассчитать высокочастотную электрическую емкость конденсатора с рабочим веществом «изолятор нелегированный кремний изолятор» при различных подаваемых на конденсатор постоянных напряжениях, частотах измерительного сигнала и температурах.Предложена модель такого конденсатора, в которой слой нелегированного (собственного) кристаллического кремния (i-Si) толщиной 30 мкм отделен от каждого из электродов конденсатора слоем изолятора (диоксида кремния) толщиной 1 мкм.Рассчитаны зависимости емкости конденсатора от постоянного электрического напряжения U на металлических электродах на нулевой частоте и на частоте измерительного сигнала 1 МГц при абсолютных температурах T = 300 и 400 К. Показано, что действительная часть емкости конденсатора монотонно возрастает, а мнимая часть отрицательна и немонотонно зависит от U при температуре T = 300 К. Увеличение действительной части емкости конденсатора до геометрической емкости оксидных слоев при увеличении температуры обусловлено уменьшением электрического сопротивления слоя i-Si. Вследствие этого с увеличением температуры до 400 К действительная и мнимая части емкости принимают постоянные значения, независящие от U. Емкость слоя i-Si при увеличении как температуры T, так и напряжения U шунтируется электрической проводимостью этого слоя. Определен сдвиг фаз для синусоидального электрического сигнала с частотой 0,3; 1; 10; 30; 100 и 300 МГц, подаваемого на конденсатор при температурах 300 и 400 К

High-Frequency Capacitor with Working Substance "Insulator–Undoped Silicon–Insulator"

The study of the parameters of capacitors with various working substances is of interest for the design and creation of electronic elements, in particular for the development of high-frequency phase-shifting circuits. The purpose of the work is to calculate the high-frequency capacitance of a capacitor with the working substance insulator undoped silicon insulator at different applied to the capacitor direct current (DC) voltages, measuring signal frequencies and temperatures. A model of such the capacitor is proposed, in which 30 µm thick layer of undoped (intrinsic) crystalline silicon (i-Si) is separated from each of the capacitor electrodes by 1 µm thick insulator layer (silicon dioxide). The dependences of the capacitor capacitance on the DC electrical voltage U on metal electrodes at zero frequency and at the measuring signal frequency of 1 MHz at absolute temperatures T = 300 and 400 K are calculated. It is shown that the real part of the capacitor capacitance increases monotonically, while the imaginary part is negative and non-monotonically depends on U at the temperature T = 300 K. An increase in the real part of the capacitor capacitance up to the geometric capacitance of oxide layers with increasing temperature is due to a decrease in the electrical resistance of i-Si layer. As a result, with an increase in temperature up to 400 K, the real and imaginary parts of the capacitance take constant values independent of U. The capacitance of i-Si layer with an increase in both temperature T and voltage U is shunted by the electrical conductivity of this layer. The phase shift is determined for a sinusoidal electrical signal with a frequency of 0.3, 1, 10, 30, 100, and 300 MHz applied to the capacitor at temperatures 300 and 400 K

Схема элемента Пельтье на полупроводниках с прыжковым переносом электронов по дефектам

The study of thermoelectric properties of crystalline semiconductors with structural defects is of practical interest in the development of radiation-resistant Peltier elements. In this case, the spectrum of energy levels of hydrogen-like impurities and intrinsic point defects in the band gap (energy gap) of crystal plays an important role.The purpose of this work is to analyze the features of the single-electron band model of semiconductors with hopping electron migration both via atoms of hydrogen-like impurities and via their own point triplecharged intrinsic defects in the c- and v-bands, as well as to search for the possibility of their use in the Peltier element in the temperature range, when the transitions of electrons and holes from impurity atoms and/or intrinsic defects to the c- and v-bands can be neglected.For Peltier elements with electron hopping migration we propose: (i) an h-diode containing |d1)and |d2)-regions with hydrogen-like donors of two types in the charge states (0) and (+1) and compensating them hydrogen-like acceptors in the charge state (−1); (ii) a homogeneous semiconductor containing intrinsic t-defects in the charge states (−1, 0, +1), as well as ions of donors and acceptors to control the distribution of t-defects over the charge states. The band diagrams of the proposed Peltier elements in equilibrium and upon excitation of a stationary hopping electric current are analyzed.A model of the h-diode containing hydrogen-like donors of two types |d1) and |d2) with hopping migration of electrons between them for 50 % compensation by acceptors is considered. It is shown that in the case of the reverse (forward) electrical bias of the diode, the cooling (heating) of the region of the electric double layer between |d1)and |d2)-regions is possible.A Peltier element based on a semiconductor with point t-defects is considered. It is assumed that the temperature and the concentration of ions of hydrogen-like acceptors and donors are to assure all t-defects to be in the charge state (0). It is shown that in such an element it is possible to cool down the metal-semiconductor contact under a negative electric potential and to heat up the opposite contact under a positive potential.Исследование термоэлектрических свойств кристаллических полупроводников с дефектами структуры представляет практический интерес при создании радиационно-стойких элементов Пельтье. При этом важную роль играет спектр уровней энергии водородоподобных примесей и собственных точечных дефектов в энергетической щели (запрещённой зоне) кристалла.Цель работы анализ особенностей одноэлектронной зонной модели полупроводников с прыжковой миграцией электронов как по атомам водородоподобных примесей, так и по собственным точечным трёхзарядным дефектам, а также поиск возможности их использования в элементе Пельтье в области температур, когда переходами электронов и дырок с атомов примесей и/или собственных дефектов в cи v-зоны можно пренебречь.В качестве элементов Пельтье с прыжковой миграцией электронов предложены: 1) h-диод, содержащий |d1)и |d2)-области с водородоподобными донорами двух сортов в зарядовых состояниях(0) и (+1) и компенсирующие их водородоподобные акцепторы в зарядовом состоянии (−1); 2) однородный полупроводник, содержащий собственные t-дефекты в зарядовых состояниях (−1, 0, +1), а также ионы доноров и акцепторов для управления распределением t-дефектов по зарядовых состояниям. Проанализированы зонные диаграммы предлагаемых элементов Пельтье в равновесии  и при возбуждении стационарного прыжкового электрического тока.Рассмотрена модель h-диода, содержащего водородоподобные доноры двух сортов |d1) и |d2) с прыжковой миграцией между ними электронов при компенсации их на 50 % акцепторами. Показано, что при обратном (прямом) электрическом смещении диода возможно охлаждение (нагревание) области двойного электрического слоя между |d1)и |d2)-областями.Рассмотрен элемент Пельтье на основе полупроводника с точечными t-дефектами. Принималось, что температура, а также концентрации ионов водородоподобных акцепторов и доноров таковы, что практически все t-дефекты находятся в зарядовом состоянии (0). Показано, что в таком элементе возможно охлаждение контакта металл-полупроводник, находящегося под отрицательным электрическим потенциалом, и нагревание противоположного контакта, под положительным потенциалом