In-plane optical anisotropy of two-dimensional VOCl single crystal with weak interlayer interaction

Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic and magnetic properties.However,the intrinsic in-plane anisotropic properties of 2D VOCl still lacks in-depth re-search,especially optical anisotropy.Herein,a systematic Raman spectroscopic study is performed on VOCl single-crystal with different incident laser polarization at various temperatures.The polarized-dependent Raman scattering spectra reveal that the Ag mode of VOCl show a 2-lobed shape in parallel polarization configuration while a 4-lobed shape in vertical configuration.In addition,the temperature-dependent and thickness-dependent Raman scattering spectra confirm a rela-tively weak van der Waals interaction between each layers among VOCl single crystal.These findings might provide better understanding on the in-plane anisotropic phenomenon in VOCl layers,thus will accelate further application of 2D single crystals for nanoscale angle-dependent optoelectronics.

Persistence of charge density wave against variation of band structures in V_(x)Ti_(1−x)Se_(2)(x=0–0.1)

Charge density wave(CDW)is a phenomenon that occurs in materials,accompanied by changes in their intrinsic electronic properties.The study of CDW and its modulation in materials holds tremendous significance in materials research,as it provides a unique approach to controlling the electronic properties of materials.TiSe_(2) is a typical layered material with a CDW phase at low temperatures.Through V substitution for Ti in TiSe_(2),we tuned the carrier concentration in V_(x)Ti_(1-x)Se_(2) to study how its electronic structures evolve.Angle-resolved photoemission spectroscopy(ARPES)shows that the band-folding effect is sustained with the doping level up to 10%,indicating the persistence of the CDW phase,even though the band structure is strikingly different from that of the parent compound TiSe_(2).Though CDW can induce the band fold effect with a driving force from the perspective of electronic systems,our studies suggest that this behavior could be maintained by lattice distortion of the CDW phase,even if band structures deviate from the electron-driven CDW scenario.Our work provides a constraint for understanding the CDW mechanism in TiSe_(2),and highlights the role of lattice distortion in the band-folding effect.

Biomass-derived hard carbon microtubes with tunable apertures for high-performance sodium-ion batteries

Sodium-ion batteries(SIBs)are considered the most up-and-coming complements for large-scale energy storage devices due to the abundance and cheap sodium.However,due to the bigger radius,it is still a great challenge to develop anode materials with suitable space for the intercalation of sodium ions.Herein,we present hard carbon microtubes(HCTs)with tunable apertures derived from low-cost natural kapok fibers via a carbonization process for SIBs.The resulted HCTs feature with smaller surface area and shorter Na+diffusion path benefitting from their unique micro-nano structure.Most importantly,the wall thickness of HCTs could be regulated and controlled by the carbonization temperature.At a high temperature of 1,600℃,the carbonized HCTs possess the smallest wall thickness,which reduces the diffusion barrier of Na+and enhances the reversibility Na+storage.As a result,the 1600HCTs deliver a high initial Coulombic efficiency of 90%,good cycling stability(89.4%of capacity retention over 100 cycles at 100 mA·g^(−1)),and excellent rate capacity.This work not only charts a new path for preparing hard carbon materials with adequate ion channels and novel tubular micro-nano structures but also unravels the mechanism of hard carbon materials for sodium storage.