Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConfinement Heteroepitaxy: Realizing Atomically Thin, Half-van der Waals Materials
75
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Three-dimensional epitaxial heterostructures are based on covalently-bonded interfaces, whereas those from 2-dimensional (2D) materials exhibit van der Waals interactions. Under the right conditions, however, material structures with mixed interfacial van der Waals and covalent bonding may be realized. Atomically thin layers formed at the epitaxial graphene (EG)/silicon carbide (SiC) interface indicate that EG/SiC interfaces provide this unique environment and enable synthesis of a rich palette of 2D materials not accessible with traditional techniques. Here, we demonstrate a method termed confinement heteroepitaxy (CHet), to realize air-stable, structurally unique, crystalline 2D-Ga, In, and Sn at the EG/SiC interface. The first intercalant layer is covalently-bonded to the SiC, and is accompanied by a vertical bonding gradient that ends with van der Waals interactions. Such structures break out of plane centrosymmetry, thereby introducing atomically thin, non-centrosymmetric 2D allotropes of 3D materials as a foundation for tunable superconductivity, topological states, and plasmonic properties.
rate research
Read More
The exfoliation of two naturally occurring van der Waals minerals, graphite and molybdenite, arouse an unprecedented level of interest by the scientific community and shaped a whole new field of research: 2D materials research. Several years later, the family of van der Waals materials that can be exfoliated to isolate 2D materials keeps growing, but most of them are synthetic. Interestingly, in nature plenty of naturally occurring van der Waals minerals can be found with a wide range of chemical compositions and crystal structures whose properties are mostly unexplored so far. This Perspective aims to provide an overview of different families of van der Waals minerals to stimulate their exploration in the 2D limit.
2D intercorrelated ferroelectrics, exhibiting a coupled in-plane and out-of-plane ferroelectricity, is a fundamental phenomenon in the field of condensed-mater physics. The current research is based on the paradigm of bi-directional inversion asymmetry in single-layers, which restricts 2D intercorrelated ferroelectrics to extremely few systems. Herein, we propose a new scheme for achieving 2D intercorrelated ferroelectrics using van der Waals (vdW) interaction, and apply this scheme to a vast family of 2D vdW materials. Using first-principles, we demonstrate that 2D vdW multilayers-for example, BN, MoS2, InSe, CdS, PtSe2, TI2O, SnS2, Ti2CO2 etc.- can exhibit coupled in-plane and out-of-plane ferroelectricity, thus yielding 2D intercorrelated ferroelectricsferroelectric physics. We further predict that such intercorrelated ferroelectrics could demonstrate many distinct properties, for example, electrical full control of spin textures in trilayer PtSe2 and electrical permanent control of valley-contrasting physics in four-layer VS2. Our finding opens a new direction for 2D intercorrelated ferroelectric research.
Most of the studied two-dimensional (2D) materials have been obtained by exfoliation of van der Waals crystals. Recently, there has been growing interest in fabricating synthetic 2D crystals which have no layered bulk analogues. These efforts have been focused mainly on the surface growth of molecules in high vacuum. Here, we report an approach to making 2D crystals of covalent solids by chemical conversion of van der Waals layers. As an example, we use 2D indium selenide (InSe) obtained by exfoliation and converted it by direct fluorination into indium fluoride (InF3), which has a non-layered, rhombohedral structure and therefore cannot be possibly obtained by exfoliation. The conversion of InSe into InF3 is found to be feasible for thicknesses down to three layers of InSe, and the obtained stable InF3 layers are doped with selenium. We study this new 2D material by optical, electron transport and Raman measurements and show that it is a semiconductor with a direct bandgap of 2.2 eV, exhibiting high optical transparency across the visible and infrared spectral ranges. We also demonstrate the scalability of our approach by chemical conversion of large-area, thin InSe laminates obtained by liquid exfoliation into InF3 films. The concept of chemical conversion of cleavable thin van der Waals crystals into covalently-bonded non-cleavable ones opens exciting prospects for synthesizing a wide variety of novel atomically thin covalent crystals.
Quantum Monte Carlo (QMC) methods have been used to obtain accurate binding-energy data for pairs of parallel thin metallic wires and layers modeled by 1D and 2D homogeneous electron gases. We compare our QMC binding energies with results obtained within the random phase approximation, finding significant quantitative differences and disagreement over the asymptotic behavior for bilayers at low densities. We have calculated pair-correlation functions for metallic biwire and bilayer systems. Our QMC data could be used to investigate van der Waals energy functionals.
Rattling motion of fillers in cage materials has been of great interest for their import roles in superconductivity and thermoelectric applications. The standing waves of the rattling oscillations are normally lower in energy than the propagating waves of the acoustic phonons, thus exert large influences on the configuration of phonon dispersions as well as the associated thermal and electrical properties. Although it has been extensively studied, the origin of the low energy soft modes is still not clear. In the present paper, we show that van der Waals-type interactions are predominant between fillers and their surrounding cage frameworks, which explains the origin of the low energy modes in cage materials as a universal rule. Mass, free space and chemical environment of guest atoms are shown to be the most important factors to determine the three dimensional van der Waals-type interactions. The present work is mainly focused on type-I clathrates, skutterudites and pyrochlores.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
