Application Of External Strain Research Articles

Synergetic Improvement of Flexoelectric Coefficient in Liquid Crystal Embedded Flexible PVDF Polymer Composite for Energy Harvesting Applications.

Flexoelectricity is the universal electric polarization of dielectrics upon exertion of a non-uniform strain gradient. With the advancement of nano-technology and miniaturization of electronic devices, flexoelectricity holds the promise to address the power requirements for such device operation. The direct flexoelectric effect in liquid crystal (LC) embedded poly(vinylidene fluoride) (PVDF) polymer films is examined for the first time by the application of external strain on the films. Physical characterizations such as Differential Scanning Calorimetry (DSC), dielectric spectroscopy, X-ray diffraction, and field emission scanning electron microscopy (FESEM) are carried out to study the composite films' intrinsic and extrinsic properties like dielectric, crystallinity, and morphologies. The value of the flexoelectric coefficient (μ12) increases with the concentration of LC incorporation. At 3wt%, μ12 attains a maximum value of 68nCm-1, which is more than a threefold increase compared to that of the pure PVDF film. The role of Maxwell-Wagner-Sillars (MWS) polarization in determining flexoelectric polarization in polymer composites is also discussed. Moreover, the influence of the microstructure and domain size formation in determining the flexoelectric response are discussed in detail to infer the behavior of the flexoelectric coefficients of the films. Potential device applications based on this phenomenon have been proposed for future research in sensing and actuation.

Strong spin-orbital coupling induced tunable electronic structures and enhanced visible-light absorption in one-dimensional RhTe6I3 systems.

Considering the demand for device miniaturization, low-dimensional materials have been widely employed in various fields due to their unique and fascinating physical and chemical properties. Here, based on first-principles calculations, we predict a novel one-dimensional (1D) RhTe6I3 chain system. Our calculations indicate that a 1D RhTe6I3 single chain can be prepared from its bulk counterpart by an exfoliation method and exists stably at room temperature. The 1D RhTe6I3 single chain is a direct semiconductor with a moderate bandgap of 1.75 eV under a strong spin-orbital coupling (SOC) effect dominated by Te. This bandgap can be modulated by the chain number and the application of external strain. Notably, the 1D RhTe6I3 single chain has a high electron mobility (1093 cm2 V-1 s-1), which is one to two orders of magnitude higher than those of most previously reported 1D materials. The strong SOC effect can also enhance the visible-light absorption capacity of the 1D RhTe6I3 single chain. The moderate direct bandgap, high electron mobility, excellent visible-light absorption, and strong spin-orbital coupling make 1D RhTe6I3 systems ideal candidates in electronic and optoelectronic devices.

Tunable excitons in rhombohedral trilayer graphene

Trilayer graphene is receiving an increasing level of attention due to its stacking--dependent magnetoelectric and optoelectric properties, and its more robust ferromagnetism relative to monolayer and bilayer variants. Additionally, rhombohedral stacked trilayer graphene presents the possibility of easily opening a gap via either an external electric field perpendicular to the layers, or via the application of external strain. In this paper, we consider an external electric field to open a bandgap in rhombohedral trilayer graphene and study the excitonic optical response of the system. This is done via the combination of a tight binding model with the Bethe--Salpeter equation, solved semi--analytically and requiring only a simple numerical quadrature. We then discuss the valley--dependent optical selection rules, followed by the computation of the excitonic linear optical conductivity for the case of a rhombohedral graphene trilayer encapsulated in hexagonal boron nitride. The tunability of the excitonic resonances via an external field is also discussed, together with the increasing localization of the excitonic states as the field increases.

Tunable and sizeable band gaps in strained SiC3/hBN vdW heterostructures: A potential replacement for graphene in future nanoelectronics

In this work, we perform first-principles density functional theory calculations to study siligraphene (SiC3)/hexagonal boron nitride (hBN) vdW-heterostructures. Siligraphene has comparable electronic properties to graphene, including the presence of a Dirac-like cone, thus we investigate its potential as a replacement for graphene. We find that, when internal strains induced by the high lattice mismatch between the SiC3 and hBN layers are reduced, a very small and non-tunable gap is induced in a hybrid bilayer heterostructure. However, the picture becomes quite different when structures with higher internal strains are considered. In this scenario, the compressive strain induces a buckling in the SiC3 sheet, resulting in larger band gaps. Additionally, in many configurations, the gaps are found to be quite tunable by the application of external strains or an electrical field. Such tunability is absent in graphene/hBN heterostructures, thus giving SiC3/hBN heterostructures a clear edge. The origin of this gap and its tunability are discussed in terms of the buckling in the SiC3 layer and the interlayer charge transfer. Finally, the optical properties of these heterostructures were also investigated. Strong absorption peaks in both visible and deep UV regions were found, which could be explored for applications in future optoelectronic devices.

Flexible Substrate Based Few Layer MoS2 Electrode for Passive Electronic Devices and Interactive Frequency Modulation Based on Human Motion

This paper reports the demonstration of human integrated electronic devices, such as oscillators and RC filters, by utilizing flexible capacitor fabricated using few layer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> grown on Al foil via hydrothermal method as electrodes and cellulose paper as a dielectric material. There are no reports of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on flexible substrate being utilized as capacitor electrode and further applied human interactive devices. Advantage of using MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on Al foil is the enhanced capacitance upon strain due to the piezoelectric property of few layered MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> over monolayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . As the applied strain increases, increase in the capacitance was observed, which is systematically explained by piezoelectric property of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , change in physical dimensions, and air gap between MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Al foil and cellulose paper. Upon application of external strain on capacitor, range of frequencies can be generated by oscillator circuit and the mathematical operations such as differentiation and integration are observed for different input signal using RC filter circuits. Further, the fabricated flexible MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> capacitor was integrated to human hand and the corresponding frequency modulation with hand movement was recorded. Such a simple technique for fabrication of flexible variable capacitor is a major step ahead in wearable electronics having applications in digital electronics and sensors.

Biaxial strain tuning of the optical properties of single-layer transition metal dichalcogenides

Since their discovery, single-layer semiconducting transition metal dichalcogenides have attracted much attention, thanks to their outstanding optical and mechanical properties. Strain engineering in these two-dimensional materials aims to tune their bandgap energy and to modify their optoelectronic properties by the application of external strain. In this paper, we demonstrate that biaxial strain, both tensile and compressive, can be applied and released in a timescale of a few seconds in a reproducible way on transition metal dichalcogenides monolayers deposited on polymeric substrates. We can control the amount of biaxial strain applied by letting the substrate expand or compress. To do this, we change the substrate temperature and choose materials with a large thermal expansion coefficient. After the investigation of the substrate-dependent strain transfer, we performed micro-differential spectroscopy of four transition metal dichalcogenides monolayers (MoS2, MoSe2, WS2, WSe2) under the application of biaxial strain and measured their optical properties. For tensile strain, we observe a redshift of the bandgap that reaches a value as large as 95 meV/% in the case of single-layer WS2 deposited on polypropylene. The observed bandgap shifts as a function of substrate extension/compression follow the order MoSe2 < MoS2 < WSe2 < WS2. Theoretical calculations of these four materials under biaxial strain predict the same trend for the material-dependent rates of the shift and reproduce well the features observed in the measured reflectance spectra.

Strain-induced change of surface reconstructions for InAs(001)

The effect of strain on the stability of different surface reconstructions on InAs(001) is investigated with density-functional theory calculations. The effects of isotropic as well as anisotropic tensile and compressive strain is investigated, and the results are presented in corresponding equilibrium phase diagrams. I find that the range of stability for any of the relevant reconstructions can be changed significantly, and, in fact, a reconstruction that is unstable in an unstrained system might be stabilized upon application of external strain.