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Register a new userTwo ultra-stable novel allotropes of Tellurium few-layers
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At least four two- or quasi-one- dimensional allotropes and a mixture of them were theoretically predicted or experimentally observed for low-dimensional Te, namely the {alpha}, b{eta}, {gamma}, {delta} and chiral-{alpha}+{delta} phases. Among them the {gamma} and {alpha} phases were found the most stable phases for monolayer and thicker layers, respectively. Here, we found two novel low-dimensional phases, namely the {epsilon} and {zeta} phases. The {zeta} phase is over 29 meV/Te more stable than and the {epsilon} phase shows comparable stability with the most stable monolayer {gamma} phase. The energetic difference between the {zeta} and {alpha} phases reduces with respect to the increased layer thickness and vanishes at the four-layer (12-sublayer) thickness, while this thickness increases under change doping. Both {epsilon} and {zeta} phases are metallic chains and layers, respectively. The {zeta} phase, with very strong interlayer coupling, shows quantum well states in its layer-dependent bandstructures. These results provide significantly insight into the understanding of polytypism in Te few-layers and may boost tremendous studies on properties of various few-layer phases.
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Nanoscrolls (papyrus-like nanostructures) are very attractive structures for a variety of applications, due to their tunable diameter values and large accessible surface area. They have been successfully synthesized from different materials. In this work we have investigated, through fully atomistic molecular dynamics simulations, the dynamics of scroll formation for a series of graphenelike carbon nitride (CN) twodimensional systems: gCN, triazinebased gC3N4, and heptazinebased gC3N4. Our results show that stable nanoscrolls can be formed for all of these structures. Possible synthetic routes to produce these nanostructures are also addressed.
The phonon properties, electronic structures and optical properties of novel carbon allotropes, such as monolayer penta-graphene (PG), double-layer PG and T12-carbon, were explored by means of first-principles calculations. Results of phonon calculations demonstrate that these exotic carbon allotropes are dynamically stable. In addition, the bulk T12 phase is an indirect-gap semiconductor having a bandgap of ~4.89 eV. Whereas the bulk material transforms to a 2D phase, the monolayer and double-layer PG become quasi-direct gap semiconductors with smaller band gaps of ~2.64 eV and ~3.27eV, respectively. Furthermore, the partial charge density analysis indicates that the 2D phases retain part of the electronic characteristics of the T12 phase. The linear photon energy-dependent dielectric functions and related optical properties including refractive index, extinction coefficient, absorption spectrum, reflectivity, and energy loss spectrum were also computed and discussed. The structural estimation obtained as well as other findings are in agreement with existing theoretical data. The calculated results are beneficial to the practical applications of these exotic carbon allotropes in optoelectronics and electronics.
The interlayer bonding in two dimensional materials is particularly important because it is not only related to their physical and chemical stability but also affects their mechanical, thermal, electronic, optical, and other properties. To address this issue, we report the direct characterization of the interlayer bonding in 2D SnSe using contact-resonance atomic force microscopy in this study. Site specific CR spectroscopy and CR force spectroscopy measurements are performed on both SnSe and its supporting SiO2 substrate comparatively. Based on the cantilever and contact mechanic models, the contact stiffness and vertical Youngs modulus are evaluated in comparison with SiO2 as a reference material. The interlayer bonding of SnSe is further analyzed in combination with the semi-analytical model and density functional theory calculations. The direct characterization of interlayer interactions using this nondestructive methodology of CR AFM would facilitate a better understanding of the physical and chemical properties of 2D layered materials, specifically for interlayer intercalation and vertical heterostructures.
We report the experimental observation of strong electrical magneto-chiral anistropy (eMChA) in trigonal tellurium (t-Te) crystals. We introduce the tensorial character of the effect and determine several tensor elements and we propose a novel intrinsic bandstructure-based mechanism for eMChA which gives a reasonable description of the principal results.
Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split H4 and H5 and the degenerate H6 valence bands (VB) and the lowest degenerate H6 conduction band (CB) as well as a higher energy transition at the L-point. Surprisingly, the degeneracy of the H6 CB (a proposed Weyl node) is lifted and the spin-split VB gap is reduced upon photoexcitation before relaxing to equilibrium as the carriers decay. Using ab initio density functional theory (DFT) calculations we conclude that the dynamic band structure is caused by a photoinduced shear strain in the Te film that breaks the screw symmetry of the crystal. The band-edge anisotropy is also reflected in the hot carrier decay rate, which is a factor of two slower along c-axis than perpendicular to it. The majority of photoexcited carriers near the band-edge are seen to recombine within 30 ps while higher lying transitions observed near 1.2 eV appear to have substantially longer lifetimes, potentially due to contributions of intervalley processes in the recombination rate. These new findings shed light on the strong correlation between photoinduced carriers and electronic structure in anisotropic crystals, which opens a potential pathway for designing novel Te-based devices that take advantage of the topological structures as well as strong spin-related properties.
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