Interlayer Overlap Research Articles

Photoinduced Long-Distance Charge Transfer in Silicanes: The Stacking Matters.

The generation of interlayer charge transfer excitons upon photoexcitation is strongly desirable for two-dimensional (2D) materials stacked through van der Waals interactions. In this work, we investigate photoinduced charge transfer in silicanes (SiH) with three typical stackings. A concept of the regional natural hole orbital and its conjugated particle orbital is developed to characterize excited states in solids. This method delivers bonding information about excited states and explains the formation of certain types of states in nanomaterials. Utilizing this tool, we demonstrate that SiH in the 1H and 6R stackings exhibits an interlayer charge transfer distance that reaches ∼10 Å under violet and near-ultraviolet radiation. The charge transfer is attributed to the interlayer overlap between orbitals at the conduction band minimum, which is disfavored by the 3R stacking. Our findings suggest a new and feasible approach for tuning the optoelectronic properties of Group 14 2D materials by altering their stackings.

Interlayer coupling modulated for thermoelectric transport characterization of black arsenic nanoscale devices

Modulating interlayer coupling modes can effectively enhance the thermoelectric properties of nanomaterials or nanoscale devices. By using density functional theory combined with non-equilibrium Green’s function method, we investigate the thermoelectric properties of zigzag-type black arsenic nanoscale devices with varying interlayer coupling modes. Our results show that altering the interlayer coupling mode significantly modulates the thermoelectric properties of the system. Specifically, we consider four coupling modes with different strengths, by modulating different interlayer overlap patterns. Notably, in the weaker interlayer coupling mode, the system exhibits enhanced thermoelectric properties due to increased interface phonon scattering, for example, the M4 reaching a peak value of 2.23 at μ = −0.73 eV. Furthermore, we explore the temperature-dependent behavior of each coupling model. The results suggest that the thermoelectric characteristics are more sensitive to temperature variations in the weaker coupling modes. These insights provide valuable guidance for enhancing the thermoelectric performance of nanoscale devices through precise interlayer coupling modulation.

The structure of overlapped epitropic LC

The proposed model of the structure of the wall-adjacent epitropic liquid crystalline layer considers it as an oligomeric system of thread-like associates in a non-associated liquid. The results of ELC studies of layers of aliphatic hydrocarbon - n-hexadecane are analyzed. The study of the ELC phase in n-alkanes is important both for the modification of the quantitative physical theory of this phenomenon, and in a practical sense, as it allows to solve practical problems related to the control of boundary friction in mechanisms and parts of machines. Previously, the results of rheological and structural-optical studies of the properties of these systems were considered separately, and the results obtained in the molecular-statistical model were not correlated in detail with the results of rheological measurements for the case of overlapped near-surface layers. To interpret the results of studies (by rheological and optical methods) of such a layer in interlayers of n-hexadecane, symmetrically limited by conductive substrates, it is proposed to take into account the increase in the concentration of the ordered component ("pile") under the condition that the wall layers of epitropic liquid crystals in the interlayer overlap. It will also allow to take into account the results obtained in the molecular statistical model in the processing of rheological data.

A Consistent Representation of Cloud Overlap and Cloud Subgrid Vertical Heterogeneity

AbstractMany global climate models underestimate the cloud cover and overestimate the cloud albedo, especially for low‐level clouds. We determine how a correct representation of the vertical structure of clouds can fix part of this bias. We use the 1D McICA framework and focus on low‐level clouds. Using Large Eddy Simulations results as reference, we propose a method based on exponential‐random overlap that represents the cloud overlap between layers and the subgrid cloud properties over several vertical scales, with a single value of the overlap parameter. Starting from a coarse vertical grid, representative of atmospheric models, this algorithm is used to generate the vertical profile of the cloud fraction with a finer vertical resolution, or to generate it on the coarse grid but with subgrid heterogeneity and cloud overlap that ensures a correct cloud cover. Doing so we find decorrelation lengths are dependent on the vertical resolution, except if the vertical subgrid heterogeneity and interlayer overlap are taken into account coherently. We confirm that the frequently used maximum‐random overlap leads to a significant error by underestimating the low‐level cloud cover with a relative error of about 50%, that can lead to an error of SW cloud albedo as big as 70%. Not taking into account the subgrid vertical heterogeneity of clouds can cause a relative error of 20% in brightness, assuming the cloud cover is correct.

Local Phase Transitions in a Model of Multiplex Networks with Heterogeneous Degrees and Inter-Layer Coupling.

Multilayer networks represent multiple types of connections between the same set of nodes. Clearly, a multilayer description of a system adds value only if the multiplex does not merely consist of independent layers. In real-world multiplexes, it is expected that the observed inter-layer overlap may result partly from spurious correlations arising from the heterogeneity of nodes, and partly from true inter-layer dependencies. It is therefore important to consider rigorous ways to disentangle these two effects. In this paper, we introduce an unbiased maximum entropy model of multiplexes with controllable intra-layer node degrees and controllable inter-layer overlap. The model can be mapped to a generalized Ising model, where the combination of node heterogeneity and inter-layer coupling leads to the possibility of local phase transitions. In particular, we find that node heterogeneity favors the splitting of critical points characterizing different pairs of nodes, leading to link-specific phase transitions that may, in turn, increase the overlap. By quantifying how the overlap can be increased by increasing either the intra-layer node heterogeneity (spurious correlation) or the strength of the inter-layer coupling (true correlation), the model allows us to disentangle the two effects. As an application, we show that the empirical overlap observed in the International Trade Multiplex genuinely requires a nonzero inter-layer coupling in its modeling, as it is not merely a spurious result of the correlation between node degrees across different layers.

Helical Trilayer Nanographenes with Tunable Interlayer Overlaps

The synthesis of well-defined nanocarbon multilayers, beyond the bilayer structure, is still a challenging goal. Herein, two trilayer nanographenes were synthesized by covalently linking nanographene layers through helicene bridges. The structural characterization of the trilayer nanographenes revealed a compact trilayer-stacked architecture. The introduction of a furan ring into the helicene linker modulates the interlayer overlap and π-conjugation of the trilayer nanographenes, enabling the tuning of the interlayer coupling, as demonstrated by optical, electrochemical, and theoretical analyses. Both synthesized trilayer nanographenes are rigid chiral nanocarbons and show a chirality transfer from the helicene moiety to the stacked nanographene layers. These helical trilayer nanographenes reported here represent the covalently linked multilayer nanographenes rather than bilayer ones, showing the tunable multilayer stacking structure.

Pattern Development and Control of Strained Solitons in Graphene Bilayers

Engineering strain and interlayer registry in 2D crystals have been demonstrated as effective controls of their properties. Separation of domains with different interlayer registries in graphene bilayer has been reported, but the pattern control of strained solitons has not yet been achieved. We show here that, by pulling a graphene bilayer apart, soliton structures with a regularly modulated interlayer registry arise from the competition between elastic deformation in monolayers and local slip at the van der Waals interfaces. The commensurate-incommensurate transition with strain localization is identified as the interlayer overlap exceeds a critical size, where the continuum description of load transfer through the tension-shear chain breaks down. Birth, development and annihilation processes of the strained solitons can be controlled by the loading conditions. The effects of lattice symmetry and mechanical constraints are also discussed, completing the picture for microstructural evolution processes in the homo- or heterostructures of 2D crystals.

Angle Dependence of Interlayer Coupling in Twisted Transition Metal Dichalcogenide Heterobilayers

We reveal by first-principles calculations that the interlayer binding in a twisted MoS2/MoTe2 heterobilayer decreases with the increasing twist angle, due to the increase of the interlayer overlap...

A polygonal double-layer coil design for high-efficiency wireless power transfer

In this work, we present a novel coil structure for the design of Wireless Power Transfer (WPT) systems via magnetic resonant coupling. The new coil consists of two layers of flat polygonal windings in square, pentagonal and hexagonal shapes. The double-layer coil can be conveniently fabricated using the print circuit broad (PCB) technology. In our design, we include an angle between the two layers which can be adjusted to change the area of inter-layer overlap. This unique structure is thoroughly investigated with respect to the quality factor Q and the power transfer efficiency (PTE) using the finite element method (FEM). An equivalent circuit is derived and used to explain the properties of the angularly shifted double-layer coil theoretically. Comparative experiments are conducted from which the performance of the new coil is evaluated quantitatively. Our results have shown that an increased shift angle improves the Q-factor, and the optimal PTE is achieved when the angle reaches the maximum. When compared to the pentagonal and hexagonal coils, the square coil achieves the highest PTE due to its lowest parasitic capacitive effects. In summary, our new coil design improves the performance of WPT systems and allows a formal design procedure for optimization in a given application.

Thermal transport in MoS2/Graphene hybrid nanosheets

Heat dissipation is a very critical problem for designing nano-functional devices, including MoS2/graphene heterojunctions. In this paper we investigate thermal transport in MoS2/graphene hybrid nanosheets under various heating conditions, by using molecular dynamics simulation. Diverse transport processes and characteristics, depending on the conducting layers, are found in these structures. The thermal conductivities can be tuned by interlayer coupling, environment temperature, and interlayer overlap. The highest thermal conductivity at room temperature is achieved as more than 5 times of that of single-layer MoS2 when both layers are heated and 100% overlapped. Different transport mechanisms in the hybrid nanosheets are explained by phonon density of states, temperature distribution, and interlayer thermal resistance. Our results could not only provide clues to master the heat transport in functional devices based on MoS2/graphene heterojunctions, but are also useful for analyzing thermal transport in other van der Waals hybrid nanosheets.

Monolayer behaviour in bulk ReS2 due to electronic and vibrational decoupling

Semiconducting transition metal dichalcogenides consist of monolayers held together by weak forces where the layers are electronically and vibrationally coupled. Isolated monolayers show changes in electronic structure and lattice vibration energies, including a transition from indirect to direct bandgap. Here we present a new member of the family, rhenium disulphide (ReS2), where such variation is absent and bulk behaves as electronically and vibrationally decoupled monolayers stacked together. From bulk to monolayers, ReS2 remains direct bandgap and its Raman spectrum shows no dependence on the number of layers. Interlayer decoupling is further demonstrated by the insensitivity of the optical absorption and Raman spectrum to interlayer distance modulated by hydrostatic pressure. Theoretical calculations attribute the decoupling to Peierls distortion of the 1T structure of ReS2, which prevents ordered stacking and minimizes the interlayer overlap of wavefunctions. Such vanishing interlayer coupling enables probing of two-dimensional-like systems without the need for monolayers.

Nuclear exchange coupling and electronic structure of low-dimensional semiconductors

We review the nuclear magnetic resonance (NMR) studies of the indirect nuclear exchange coupling and electronic structure of the chain and layered semiconductors Tl(I)M(III)X2 (M = Tl, Ga, In, X = Se, S, Te) and some other low-dimensional Tl-contained semiconducting compounds. Both univalent and trivalent Tl atoms in these compounds show essential chemical shielding anisotropy despite their formal spherically symmetric 5d106s2 and 5d10 electron configurations. Such a behavior results from the sp-hybridization of the Tl electron wave functions. Strong exchange coupling among the spins of Tl1+ and M3+ ions, which reside in neighboring chains or layers, is observed. Such coupling is realized due to the overlap of the Tl1+ and M3+ electron wave functions across the intervening chalcogen atom. This overlap is the important mechanism in the formation of the valence and conduction bands and determines the electronic structure and properties of the compounds. The long-range indirect nuclear exchange coupling via a chalcogen atom is an analog of the Kramers mechanism of electron spin exchange via a nonmagnetic bridge ion. Recent photoemission spectroscopy studies and band-structure calculations of several aforementioned compounds have confirmed the NMR results on the interchain and interlayer overlap.