11 research outputs found
Tunneling current between graphene layers
The physical model that allows to calculate the values of the tunneling
current be-tween graphene layers is proposed. The tunneling current according
to the pro-posed model is proportional to the area of tunneling transition. The
calculated value of tunneling conductivity is in qualitative agreement with
experimental data.Comment: 4 page
Structure and energetics of carbon, hexagonal boron nitride and carbon/hexagonal boron nitride single-layer and bilayer nanoscrolls
Single-layer and bilayer carbon and hexagonal boron nitride nanoscrolls as
well as nanoscrolls made of bilayer graphene/hexagonal boron nitride
heterostructure are considered. Structures of stable states of the
corresponding nanoscrolls prepared by rolling single-layer and bilayer
rectangular nanoribbons are obtained based on the analytical model and
numerical calculations. The lengths of nanoribbons for which stable and
energetically favorable nanoscrolls are possible are determined. Barriers to
rolling of single-layer and bilayer nanoribbons into nanoscrolls and barriers
to nanoscroll unrolling are calculated. Based on the calculated barriers
nanoscroll lifetimes in the stable state are estimated. Elastic constants for
bending of graphene and hexagonal boron nitride layers used in the model are
found by density functional theory calculations.Comment: 9 pages, 6 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
AA stacking, tribological and electronic properties of double-layer graphene with krypton spacer
Structural, energetic and tribological characteristics of double-layer
graphene with commensurate and incommensurate krypton spacers of nearly
monolayer coverage are studied within the van der Waals-corrected density
functional theory. It is shown that when the spacer is in the commensurate
phase, the graphene layers have the AA stacking. For this phase, the barriers
to relative in-plane translational and rotational motion and the shear mode
frequency of the graphene layers are calculated. For the incommensurate phase,
both of the barriers are found to be negligibly small. A considerable change of
tunneling conductance between the graphene layers separated by the commensurate
krypton spacer at their relative subangstrom displacement is revealed by the
use of the Bardeen method. The possibility of nanoelectromechanical systems
based on the studied tribological and electronic properties of the considered
heterostructures is discussed
ТЕРМИЧЕСКАЯ ЭНЕРГИЯ АКТИВАЦИИ ПРЫЖКОВОЙ ε2-ЭЛЕКТРОПРОВОДНОСТИ ПО АТОМАМ БОРА В СЛАБО КОМПЕНСИРОВАННОМ КРЕМНИИ
The insulating side of the concentration insulator–metal phase transition (Mott’s transition) in p-type silicon crystals doped with acceptor (boron atoms) is considered under the conditions of stationary hopping electrical conduction. The boron atoms substitute silicon atoms in the crystal lattice and can be in one of the three charge states (−1, 0, +1), while the compensating impurity (donors) is in the charge state (+1). The distribution of impurity atoms is supposed to be random (Poisson’s distribution). The A0-band is formed from the energy levels of boron atoms in the charge states (0) and (−1), while the A+-band is formed from the energy levels of boron atoms in the charge states (+1) and (0). The decrease in the activation energy ε2 of thermally assisted tunneling transitions (hops) of holes between electrically neutral boron atoms, i. e. boron atoms that are in the charge state (0), is calculated. The ε2 quantity is approximately equal to an energy gap between A0- and A+-bands, i. e. Hubbard’s gap. In the quasi-classical approximation it is shown that the narrowing of the energy gap between A0- and A+-bands occurs due to: (i) the formation of a quasi-continuous band of allowed energy values for v-band holes from excited quantum states of boron atoms in the charge state (0), thus the value of the v-band shift into the band gap is determined by a maximum radius of the hole orbit in a boron atom, which does not exceed the half of the average distance between the nearest impurity atoms, and (ii) the splitting of the ground (non-excited) energy levels of the “molecular” pairs of boron atoms in the charge states (0) into triplet and singlet states of two holes. Calculations of ε2 without any adjustable parameters are quantitatively agree with the known experimental data on p-Si:B.Рассматривается изоляторная сторона концентрационного фазового перехода изолятор–металл (перехода Мотта) в легированных акцепторами (атомами бора) кристаллах кремния p-типа в условиях стационарной прыжковой электрической проводимости. Атомы бора замещают в кристаллической решетке атомы кремния и могут находиться в одном из трех зарядовых состояний (−1, 0, +1), а компенсирующая примесь (доноры) находится в зарядовом состоянии (+1). Распределение атомов примесей по кристаллу предполагается случайным (пуассоновским). Из уровней энергии атомов бора в зарядовых состояниях (0) и (−1) формируется A0-зона, а из уровней энергии атомов бора в зарядовых состояниях (+1) и (0) формируется A+-зона. Рассчитывается уменьшение энергии активации ε2 термически ассистированных туннельных переходов (прыжков) дырок между электрически нейтральными атомами бора, т. е. находящимися в зарядовых состояниях (0). Величина ε2 примерно равна энергетической ширине щели между A0- и A+-зонами, т. е. щели Хаббарда. В квазиклассическом приближении показано, что сужение энергетической щели между A0- и A+-зонами происходит вследствие: 1) формирования из возбужденных квантовых состояний атомов бора в зарядовом состоянии (0) квазинепрерывной зоны разрешенных значений энергии для дырок v-зоны, так что величина смещения потолка v-зоны в глубь запрещенной зоны определяется максимальным радиусом орбиты дырки в атоме бора, не превышающим половины среднего расстояния между ближайшими атомами примесей, 2) расщепления основных (невозбужденных) уровней энергии «молекулярных» пар атомов бора в зарядовых состояниях (0) на триплетное и синглетное состояния двух дырок. Расчеты ε2 без подгоночных параметров количественно согласуются с имеющимися экспериментальными данными для p-Si:B
Effect of Peierls transition in armchair carbon nanotube on dynamical behaviour of encapsulated fullerene
The changes of dynamical behaviour of a single fullerene molecule inside an
armchair carbon nanotube caused by the structural Peierls transition in the
nanotube are considered. The structures of the smallest C20 and Fe@C20
fullerenes are computed using the spin-polarized density functional theory.
Significant changes of the barriers for motion along the nanotube axis and
rotation of these fullerenes inside the (8,8) nanotube are found at the Peierls
transition. It is shown that the coefficients of translational and rotational
diffusions of these fullerenes inside the nanotube change by several orders of
magnitude. The possibility of inverse orientational melting, i.e. with a
decrease of temperature, for the systems under consideration is predicted.Comment: 9 pages, 6 figures, 1 tabl
Multiscale modeling strategy to solve fullerene formation mystery
Since fullerene formation occurs under conditions where direct observation of atomic-scale reactions is not possible, modeling is the only way to reveal atomistic mechanisms which can lead to selection of abundant fullerene isomers (like C-I). In the present paper we review the results obtained for different atomistic mechanisms by various modeling techniques. Although it seems that atomic-scale processes related to odd fullerenes (such as growth by consecutive insertions of single carbon atoms and rearrangements of the sp structure promoted by extra sp atoms) provide the main contribution to selection of abundant isomers, at the moment there is no conclusive evidence in favor of any particular atomistic mechanism. Thus, the following multiscale modeling strategy to solve the mystery of the high yield of abundant fullerene isomers is suggested. On the one hand, sets of reactions between fullerene isomers can be described using theoretical graph techniques. On the other hand, reaction schemes can be revealed by classical molecular dynamics simulations with subsequent refinement of the activation barriers by ab initio calculations. Based on the reaction sets with the reaction probabilities derived in this way, the different atomistic mechanisms of abundant fullerene isomer selection can be compared using kinetic models.AMP acknowledges the Russian Foundation of Basic Research (Grant No. 20-52-00035). IVL acknowledges the European Union MaX Center of Excellence (EU-H2020 Grant No. 824143). SAV and NAP acknowledge the Belarusian Republican Foundation for Fundamental Research (Grant No. F20R-301) and Belarusian National Research Program “Convergence-2025.