The influence of intrinsic defects of 1T-TaS_(2)on charge density waves(CDWs)is studied using scanning tunneling microscopy and spectroscopy(STM,STS),angle-resolved photoelectron spectroscopy(ARPES),and density functi...The influence of intrinsic defects of 1T-TaS_(2)on charge density waves(CDWs)is studied using scanning tunneling microscopy and spectroscopy(STM,STS),angle-resolved photoelectron spectroscopy(ARPES),and density functional theory(DFT).We identify several types of structural defects and find that most have a local character limited to a single CDW site,with a single exception which effectively behaves as a dopant,leading to band-bending and affecting multiple neighboring sites.While only one type of defect can be observed by STM topographic imaging,all defects are easily resolved in STS mapping.Our results indicate modulation of the Mott band gap commensurate with the CDW and breaking of the three-fold symmetry of electronic states.DFT calculations(with included Coulomb interactions)are used to investigate the electronic structure,focusing on both sulfur vacancy and oxygen-sulfur substitution.The sulfur vacancy system,characterized with a metallic behavior,is identified as the origin of one of the experimentally observed defects.Additionally,the effect of oxidation of 1T-TaS_(2)depends on the substitution site,leading to the heterogeneity of electronic properties.展开更多
The interaction between graphene and germanium surfaces was investigated using a combination of microscopic and macroscopic experimental techniques and complementary theoretical calculations.Density functional theory ...The interaction between graphene and germanium surfaces was investigated using a combination of microscopic and macroscopic experimental techniques and complementary theoretical calculations.Density functional theory (DFT) calculations for different reconstructions of the Ge(001) surface showed that the interactions between graphene and the Ge(001) surface introduce additional peaks in the density of states,superimposed on the graphene valence and conduction energy bands.The growth of graphene induces nanofaceting of the Ge(001) surface,which exhibits well-organized hill and valley structures.The graphene regions covered by hills are of high quality and exhibit an almost linear dispersion relation,which indicates weak graphene-germanium interactions.On the other hand,the graphene component occupying valley regions is significantly perturbed by the interaction with germanium.It was also found that the stronger graphene-germanium interaction observed in the valley regions is connected with a lower local electrical conductivity.Annealing of graphene/Ge(001)/Si(001) was performed to obtain a more uniform surface.This process results in a surface characterized by negligible hill and valley structures;however,the graphene properties unexpectedly deteriorated with increasing uniformity of the Ge(001) surface.To sum up,it was shown that the mechanism responsible for the formation of local conductivity inhomogeneities in graphene covering the Ge(001) surface is related to the different strength of graphene-germanium interactions.The present results indicate that,in order to obtain high-quality graphene,the experimental efforts should focus on limiting the interactions between germanium and graphene,which can be achieved by adjusting the growth conditions.展开更多
基金supported by the National Science Centre,Poland under grants 2015/19/B/ST3/03142 and 2019/32/T/ST3/00487M.L.S.thanks for University of Lodz support under IDUB 6/JRR/2021 project.T.-C.C acknowledges support of the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Division of Materials Science and Engineering,under Grant No.DE-FG02-07ER46383+4 种基金M.G.acknowledges financial support provided by Slovak Research and Development Agency provided under Contract No.APVV-SKCZ-RD-21-0114by the Ministry of Education,Science,Research and Sport of the Slovak Republic provided under Grant No.VEGA 1/0105/20Slovak Academy of Sciences project IMPULZ IM-2021-42project FLAG ERA JTC 20212DSOTECHAuthor acknowledges the provision of the Polish Ministry of Education and Science project(Support for research and development with the use of research infrastructure of the National Synchrotron Radiation Centre SOLARIS”under contract nr 1/SOL/2021/2).
文摘The influence of intrinsic defects of 1T-TaS_(2)on charge density waves(CDWs)is studied using scanning tunneling microscopy and spectroscopy(STM,STS),angle-resolved photoelectron spectroscopy(ARPES),and density functional theory(DFT).We identify several types of structural defects and find that most have a local character limited to a single CDW site,with a single exception which effectively behaves as a dopant,leading to band-bending and affecting multiple neighboring sites.While only one type of defect can be observed by STM topographic imaging,all defects are easily resolved in STS mapping.Our results indicate modulation of the Mott band gap commensurate with the CDW and breaking of the three-fold symmetry of electronic states.DFT calculations(with included Coulomb interactions)are used to investigate the electronic structure,focusing on both sulfur vacancy and oxygen-sulfur substitution.The sulfur vacancy system,characterized with a metallic behavior,is identified as the origin of one of the experimentally observed defects.Additionally,the effect of oxidation of 1T-TaS_(2)depends on the substitution site,leading to the heterogeneity of electronic properties.
文摘The interaction between graphene and germanium surfaces was investigated using a combination of microscopic and macroscopic experimental techniques and complementary theoretical calculations.Density functional theory (DFT) calculations for different reconstructions of the Ge(001) surface showed that the interactions between graphene and the Ge(001) surface introduce additional peaks in the density of states,superimposed on the graphene valence and conduction energy bands.The growth of graphene induces nanofaceting of the Ge(001) surface,which exhibits well-organized hill and valley structures.The graphene regions covered by hills are of high quality and exhibit an almost linear dispersion relation,which indicates weak graphene-germanium interactions.On the other hand,the graphene component occupying valley regions is significantly perturbed by the interaction with germanium.It was also found that the stronger graphene-germanium interaction observed in the valley regions is connected with a lower local electrical conductivity.Annealing of graphene/Ge(001)/Si(001) was performed to obtain a more uniform surface.This process results in a surface characterized by negligible hill and valley structures;however,the graphene properties unexpectedly deteriorated with increasing uniformity of the Ge(001) surface.To sum up,it was shown that the mechanism responsible for the formation of local conductivity inhomogeneities in graphene covering the Ge(001) surface is related to the different strength of graphene-germanium interactions.The present results indicate that,in order to obtain high-quality graphene,the experimental efforts should focus on limiting the interactions between germanium and graphene,which can be achieved by adjusting the growth conditions.