Bulk graphene oxide (GO) shows great potential in a variety of applications, such as sensors,photodetectors, supercapacitors, lithium ion batteries and catalysts. However, its thermal conductivity,one of the most important and fundamental physical properties, is still less known. Herein, we havesystematically investigated the thermal conductivity of bulk GOs and find that it can be tailored by tuningtheir oxidation degree during preparation process. Notably, the cross-plane thermal conductivity of bulkGO, in comparison with its precursor graphite, exhibits more than 100 times decrease at roomtemperature. The dependence of thermal conductivity of GO on oxidation degree is attributed to thechemical and structural changes by introducing oxygen atoms and oxygen-containing functional groups,which can lead to a significant enhancement in atomic- and nano-scale phonon scattering. Furthermore,we reveal that the thermal conductivity of bulk GOs exhibits evident anisotropic behavior. These resultsprovide fundamental understanding and valuable information on thermal transport properties of bulkGOs for various practical applications.
Qing-Long MengHengchang LiuZhiwei HuangShuang KongPeng JiangXinhe Bao
Vertical heterostructures based on two-dimensional(2D)materials have attracted widespread interest for their numerous applications in electronic and optoelectronic devices.Herein,we report the direct construct!on of an abnormal graphene/ReSe2 stack on Au foils by a two-step chemical vapor deposition(CVD)strategy.During the second growth stage,mono layer ReSe2 is found to prefere ntially evolve at the irUerface between the first-grown graphene layer and the Au substrate.The unusual stacking behavior is unraveled by in-situ"cutting open"the upper graphene from the defects to expose the lower ReSe2 using scanning tunneling microscopy(STM).From combination of these results with density functional theory calculations,the domain boundaries and edge sites of graphene are proposed to be adsorption sites for Re and Se precursors,further facilitating the growth of ReSe2 at the van der Waals gap of graphene/Au.This work hereby offers an intriguing strategy for obtaining vertical 2D heterostructures featured with an ultra-clean interface and a designed stacking geometry.
Direct growth of large area uniform graphene on functional insulating materials is essential for engineering versatile applications of graphene. However, the existing synthesis approaches can hardly avoid the generation of non-uniform multilayer graphene along the gas flow direction, affording huge challenges for further scaling up. Herein, by exploiting the molten state of soda-lime glass, we have accomplished the direct growth of large area uniform (up to 30 cm × 6 cm) graphene via a facile chemical vapor deposition route on low cost soda-lime glass. The use of molten glass eliminates the chemically active sites (surface corrugations, scratches, defects), and improves the mobility of carbon precursors, affording uniform nucleation and growth of monolayer graphene. Intriguingly, thus-obtained graphene acts as an ideal coating layer for the surface crystallographic modification of soda-lime glass, making it epitaxy substrates for synthesizing high-quality PbI2 nanoplates and continues films. Accordingly, a prototype photodetector was fabricated to present excellent photoelectrical properties of high responsivity (~ 600 on/off current ratio) and fast response speed (18 μs). This work hereby paves ways for the batch production and the direct applications of graphene glass as platforms for constructing high performance electronic and optoelectronic devices.
Exploring high-efficient catalysts for hydrogen evolution reaction(HER)has become very urgeht for resolving the energy related issues.Recently,two-dimensional layered MoS2 and its heterostructures with graphene or other traditional photocatalysts have presented great potentials for electrocatalytic and photocatalytic HER applications.On-site investigations of the atomic-scale structures and local electronic properties of the catalytically active sites are the key points for understanding the internal mechanisms,which however are hard to be achievec from the practical systems.Hereby,this review focuses on the recent progresses on the on-site scanning tunneling microscopy/spectroscopy investigations of the atomic structures and electronic properties of the ultrahigh-vacuum deposited and chemical vapor deposition(CVD)synthesized monolayer MoS2 and MoSz/graphene vertical stacks on the electrodes of Au(111)and Au foils.The correlations between the respective HER activities,edge types and edge electronic states are comparatively introduced.Secondly,this review also introduces thephotocatalytic HER applications of CVD-grown MoS2/WS2 and WS/MoS2 vertical stacks on Au foils,mainly considering of their type-ll band.alignments and the novel interlayer charge transfer behaviors.Finally,future research directions are also proposed for in-depth understanding of the catalytic mechanism,as well as for exploring more efficient HER catalysts.
Min HongJianping ShiYahuan HuanQin XieYanfeng Zhang
Revealing the structural/electronic features and interfacial interactions of monolayer MoS2 and WS2 on metals is essential to evaluating the performance of related devices.In this study,we focused on the atomic-scale features of monolayer WS2 on Au(001) synthesized via chemical vapor deposition.Scanning tunneling microscopy and spectroscopy reveal that the WS2/Au(001) system exhibits a striped superstructure similar to that of MoS2/Au(001) but weaker interfacial interactions,as evidenced by experimental and theoretical investigations.Specifically,the WS2/Au(001) band gap exhibits a relatively intrinsic value of ~ 2.0 eV.However,the band gap can gradually decrease to ~ 1.5 eV when the sample annealing temperature increases from ~370 to 720 ℃.In addition,the doping level (or Fermi energy) of monolayer WS2/Au(001) varies little over the valley and ridge regions of the striped patterns because of the homogenous distributions of point defects introduced by annealing.Briefly,this work provides an in-depth investigation into the interfacial interactions and electronic properties of monolayer MX2 on metal substrates.