Due to the intriguing anisotropic optical and electrical properties, low‐symmetry 2D materials are attracting a lot of interest both for fundamental studies and fabricating novel electronic and ...optoelectronic devices. Identifying new promising low‐symmetry 2D materials will be rewarding toward the evolution of nanoelectronics and nano‐optoelectronics. In this work, germanium diarsenide (GeAs2), a group IV–V semiconductor with novel low‐symmetry puckered structure, is introduced as a favorable highly anisotropic 2D material into the rapidly growing 2D family. The structural, vibrational, electrical, and optical in‐plane anisotropy of GeAs2 is systematically investigated both theoretically and experimentally, combined with thickness‐dependent studies. Polarization‐sensitive photodetectors based on few‐layer GeAs2 exhibit highly anisotropic photodetection behavior with lineally dichroic ratio up to ≈2. This work on GeAs2 will excite interests in the less exploited regime of group IV–V compounds.
A new 2D material, GeAs2, with high anisotropy is introduced. A strong interlayer interaction is revealed through large, thickness‐dependent Raman frequency shifts. The structural, vibrational, electrical, and optical in‐plane anisotropy of GeAs2 is investigated theoretically and experimentally. Moreover, a remarkable anisotropic photoresponsivity with linearly dichroic ratio up to ≈2 is realized in a polarization‐sensitive photodetector based on few‐layer GeAs2.
Metallic delafossites ABO2, as the new benchmark of ultra‐high conductive oxides, have recently attracted great interest. The harsh processing conditions and dimensional sizes obviously limit the ...fundamental sciences and technological applications. Here, a low‐cost and facile solution approach is realized to synthesize epitaxial metallic ABO2 thin films including PtCoO2, PdCoO2, and PdCrO2 with a dimension up to two‐inches in diameter, showing ultra‐high room temperature conductivity. The electrical properties, growth mechanisms, and potential technical applications including transparent conducting films and hydrogen evolution reaction activity are unveiled. The achievements of epitaxial metallic delafossites ABO2 thin films through solution methods will pave the route to producing wafer‐scaled ultra‐high conductive metallic delafossites.
Large area and high‐quality metallic delafossite epitaxial thin films including PtCoO2, PdCoO2, and PdCrO2 are successfully synthesized via a facile and low‐cost solution route. All these thin films show ultra‐high room temperature conductivity. Thin film growth mechanisms and potential technical applications including transparent conducting performance and hydrogen evolution reaction activity are unraveled.
Abstract
Magnetic skyrmions, whose shapes are ellipse due to the presence of anisotropic Dzyaloshinskii–Moriya interaction (DMI), have already been discovered in experiments recently. By using ...micromagnetic simulations, we discuss the ground state and the spin-wave modes of a single elliptical skyrmion in a confined nanodot. It is found that the shapes of skyrmion are stretched into a horizontal ellipse, vertical ellipse, or stripe shape under different strengths of anisotropic DMI. When elliptical skyrmions are excited by in-plane ac magnetic fields, the spin-wave mode contains a counterclockwise rotation mode at high frequencies and a clockwise (CW) rotation mode at low frequencies, and the CW mode depends on the strength of anisotropic DMI. When elliptical skyrmions are excited by out-of-plane ac magnetic fields, the spin-wave mode is split from a simple breathing mode into two complex breathing modes, including a mixed mode of CW rotation and breathing, and another anisotropic breathing mode. Our results provide an understanding of the rich spin-wave modes for skyrmions, which may contribute to the applications in magnonics.
Abstract
We report the resonance excitations and the spin-wave modes of a single bimeron in a confined nanodot by using micromagnetic simulations. Magnetic bimerons can be considered as in-plane ...topological spin textures of magnetic skyrmions, which means that the spin-wave modes of bimerons also rotate in-plane compared to skyrmions, for example, through the application of out-of-plane microwave magnetic fields, the spin-wave mode of bimerons is no longer a breathing mode but contains a counterclockwise mode at low frequencies and a clockwise mode at high frequencies. When in-plane microwave magnetic fields rotated at different angles are applied, the spin-wave mode of bimerons has an anisotropic property, i.e., the spin-wave mode presents as a breathing mode for the microwave magnetic field applied along the
x
-direction, and a couple of azimuthal modes for the microwave magnetic field applied along the
y
-direction. Moreover, we demonstrate that the breathing mode, the counterclockwise rotation mode, and the clockwise rotation mode can simultaneously appear together when the microwave magnetic field is applied at a specific angle in the plane. In addition to the three typical spin-wave modes, two high-phase counterclockwise rotation modes lead to the periodic deformation of bimerons due to the broken rotational symmetry of the spin texture. Our results reveal the rich spin-wave modes of bimerons, which may contribute to the applications in spintronics and magnonics.
Low-symmetry two-dimensional (2D) materials have exhibited novel anisotropic properties in optics, electronics, and mechanics. Such characteristics have opened up new avenues for fundamental research ...on nano-electronic devices. In-plane thermal conductivity plays a pivotal role in the electronic performance of devices. This article reports a systematic study of the in-plane anisotropic thermal conductivity of PdSe2 with a pentagonal, low-symmetry structure. An in-plane anisotropic ratio up to 1.42 was observed by the micro-Raman thermometry method. In the Raman scattering spectrum, we extracted a frequency shift from the Ag3 mode with the most sensitivity to temperature. The anisotropic thermal conductivity was deduced by analyzing the heat diffusion equations of suspended PdSe2 films. With the increase in thickness, the anisotropy ratio decreased gradually because the thermal conductivity in the x-direction increased faster than in the y-direction. The anisotropic thermal conductivity provides thermal management strategies for the next generation of nano-electronic devices based on PdSe2.
Negative Poisson's ratio (NPR) materials are functional and mechanical metamaterials that shrink (expand) longitudinally after being compressed (stretched) laterally. By using first-principles ...calculations, we found that Poisson's ratio can be tuned from near zero to negative by different stacking modes in van der Waals (vdW) graphene/hexagonal boron nitride (G/
-BN) superlattice. We attribute the NPR effect to the interaction of
orbitals between the interfacial layers. Furthermore, a parameter calculated by analyzing the electronic band structure, namely, distance-dependent hopping integral, is used to describe the intensity of this interaction. We believe that this mechanism is not only applicable to G/
-BN superlattice but can also explain and predict the NPR effect in other vdW layered superlattices. Therefore, the NPR phenomenon, which was relatively rare in 3D and 2D materials, can be realized in the vdW superlattices by different stacking orders. The combinations of tunable NPRs with the excellent electrical/optical properties of 2D vdW superlattices will pave a novel avenue to a wide range of multifunctional applications.
Encapsulation is critical for devices to guarantee their stability and reliability. It becomes an even more essential requirement for devices based on 2D materials with atomic thinness and far ...inferior stability compared to their bulk counterparts. Here a general van der Waals (vdW) encapsulation method for 2D materials using Sb2O3 layer of inorganic molecular crystal fabricated via thermal evaporation deposition is reported. It is demonstrated that such a scalable encapsulation method not only maintains the intrinsic properties of typical air‐susceptible 2D materials due to their vdW interactions but also remarkably improves their environmental stability. Specifically, the encapsulated black phosphorus (BP) exhibits greatly enhanced structural stability of over 80 days and more sustaining‐electrical properties of 19 days, while the bare BP undergoes degradation within hours. Moreover, the encapsulation layer can be facilely removed by sublimation in vacuum without damaging the underlying materials. This scalable encapsulation method shows a promising pathway to effectively enhance the environmental stability of 2D materials, which may further boost their practical application in novel (opto)electronic devices.
In this work, an effective van der Waals passivation method for 2D materials with inorganic molecular crystal Sb2O3 as the encapsulation layer is developed. The scalable encapsulation method, carried out through a complementary metal‐oxide‐semiconductor‐compatible manufacturing process, opens unprecedented opportunities for 2D materials to be applied in optoelectronic devices toward chip‐level development.
With an increasingly profound understanding of battery materials, strategies designed for interface protection have become more sophisticated. However, it is inherent that different materials used in ...electrodes and electrolytes tend to react with each other. To address this issue, this study proposes an “Electrode‐Electrolyte‐In‐One” (EEIO) concept, where a single energy storage material can serve as both electrode and solid‐state electrolyte (SSE) during its different ion storage stages. The EEIO materials of chloride ion batteries and fluorine ion batteries are preliminarily studied, establishing reasonable screening procedures and predicting their operational mechanisms. The analysis of Cl− and F− affinity indicates that the EEIO system in the anion storage batteries comprises the anode and SSE. Through comprehensive evaluation of ion binding capacity, phase transformation mechanism, electrical conductivity, and ion diffusion kinetic properties, several potential EEIO materials are identified. In the EEIO system, the material interface and the conductive‐insulation interface are separated, which solves the material compatibility problem between the anode and SSE. Furthermore, the EEIO system has an inherent correlation between the anode electrochemical reaction and the SSE decomposition reaction, ensuring that the electrochemical voltage of EEIO batteries never exceeds the decomposition voltage of SSE. Therefore, SSE in the EEIO battery has absolute electrochemical stability.
The single energy storage material such as metal can respectively serve as electrode and SSE during its different ion storage stages, enabling the SSE and one side electrode to form an EEIO system. In anionic batteries, the EEIO consists of anodes and SSE. Conversely, cationic batteries, it consist of cathodes and SSE.
A controllable elemental substitution strategy enables the strain engineering of two-dimensional MoS2 to its limit, which can potentially modulate its physical and chemical properties and broaden its ...applications.
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Strain engineering is a promising method for tuning the electronic properties of two-dimensional (2D) materials, which are capable of sustaining enormous strain thanks to their atomic thinness. However, applying a large and homogeneous strain on these 2D materials, including the typical semiconductor MoS2, remains cumbersome. Here we report a facile strategy for the fabrication of highly strained MoS2 via chalcogenide substitution reaction (CSR) of MoTe2 with lattice inheritance. The MoS2 resulting from the sulfurized MoTe2 sustains ultra large in-plane strain (approaching its strength limit ~10%) with great homogeneity. Furthermore, the strain can be deterministically and continuously tuned to ~1.5% by simply varying the processing temperature. Thanks to the fine control of our CSR process, we demonstrate a heterostructure of strained MoS2/MoTe2 with abrupt interface. Finally, we verify that such a large strain potentially allows the modulation of MoS2 bandgap over an ultra-broad range (~1 eV). Our controllable CSR strategy paves the way for the fabrication of highly strained 2D materials for applications in devices.
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