Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs wit...Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.展开更多
Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Her...Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Here,we study modulations of the electronic structure induced by the interlayer coupling in theγ-phase of indium selenide(γ-InSe)using scanning probe techniques.We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction,which are attributed to strong interlayer coupling.In addition,the moirépatterns observed inγ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns.This suggests that modulation of the electronic structure induced by the moirépotential is smeared out,indicating the presence of a significant interlayer coupling.Our theoretical calculations confirm that the interlayer coupling inγ-InSe is not only of the van der Waals origin,but also exhibits some degree of hybridization between the layers.Strong interlayer coupling might play an important role in the performance ofγ-InSe-based devices.展开更多
Scanning tunneling microscopy/spectroscopy(STM/STS)at 4.8 K has been used to examine the growth of a double-decker bis(phthalocyaninato)yttrium(YP_(c2))molecule on a reconstructed Au(111)substrate.Local differential c...Scanning tunneling microscopy/spectroscopy(STM/STS)at 4.8 K has been used to examine the growth of a double-decker bis(phthalocyaninato)yttrium(YP_(c2))molecule on a reconstructed Au(111)substrate.Local differential conductance spectra(dI/dV)of a single YPc2 molecule allow the characteristics of the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)to be identified.Furthermore,lateral distributions of the local density of states(LDOS)have also been obtained by dI/dV mapping and confirmed by first principles simulations.These electronic feature mappings and theoretical calculations provide a basis for understanding the unique STM morphology of YPc2,which is usually imaged as an eight-lobed structure.In addition,we demonstrate that bias-dependent STM morphologies and simultaneous dI/dV maps can provide a way of understanding the stability of two-dimensional YP_(c2) films.展开更多
Two-dimensional(2D)semiconductors,such as lead selenide(PbSe),locate at the key position of next-generation devices.However,the ultrathin PbSe is still rarely reported experimentally,particularly on metal substrates.H...Two-dimensional(2D)semiconductors,such as lead selenide(PbSe),locate at the key position of next-generation devices.However,the ultrathin PbSe is still rarely reported experimentally,particularly on metal substrates.Here,we report the ultrathin PbSe synthesized via sequential molecular beam epitaxy on Ag(111).The scanning tunneling microscopy is used to resolve the atomic structure and confirms the selective formation of ultrathin PbSe through the reaction between Ag5Se2 and Pb,as further evidenced by the theoretical calculation.It is also found that the increased accumulation of Pb leads to the improved quality of PbSe with larger and more uniform films.The detailed analysis demonstrates the bilayer structure of synthesized PbSe,which could be deemed to achieve the 2D limit.The differential conductance spectrum reveals a metallic feature of the PbSe film,indicating a certain interaction between PbSe and Ag(111).Moreover,the moirépattern originated from the lattice mismatch between PbSe and Ag(111)is observed,and this moirésystem provides the opportunity for studying physics under periodical modulation and for device applications.Our work illustrates a pathway to selectively synthesize ultrathin PbSe on metal surfaces and suggests a 2D experimental platform to explore PbSe-based opto-electronic and thermoelectric phenomena.展开更多
Voltage-controlled conductance and switching induced by single molecules or atoms are ideally studied in scanning tunneling microscope （STM） tunnel junctions. While the objects under consideration are mostly used in...Voltage-controlled conductance and switching induced by single molecules or atoms are ideally studied in scanning tunneling microscope （STM） tunnel junctions. While the objects under consideration are mostly used in their original form, little is known of the possibilities of in situ adjustments of their properties. Here, we evidence properties of a tunnel junction made of a Ce atom/cluster built by atomic manipulation on Au（111） at a temperature of 4.6 K in the presence of H2. The conductance through the object is characterized by a switching voltage corresponding to an opening or closing of an inelastic electron tunneling conductance channel at 50 mV for a Ce atom and 140 mV for a Ce cluster and by charging. We demonstrate that the electronic properties of an STM junction can be engineered in a simple way by in situ guiding of the H2 pinning at an atomic cluster.展开更多
Achieving superior performance of nanoparticle systems is one of the biggest challenges in catalysis.Two major phenomena,occurring during the reactions,hinder the development of the full potential of nanoparticle cata...Achieving superior performance of nanoparticle systems is one of the biggest challenges in catalysis.Two major phenomena,occurring during the reactions,hinder the development of the full potential of nanoparticle catalysts:sintering and contamination with carbon containing species,sometimes called coking.Here,we demonstrate that Ir nanocrystals,arranged into periodic networks on hexagonal boron nitride(h-BN)supports,can be restored without sintering after contamination by persistent carbon.This restoration yields the complete removal of carbon from the nanocrystals,which keep their crystalline structure,allowing operation without degradation.These findings,together with the possibility of fine tuning the nanocrystals size,confer this nanoparticle system a great potential as a testbed to extract key information about catalysis-mediated oxidation reactions.For the case of the CO oxidation by O2,reaction of interest in environmental science and green energy production,the existence of chemical processes not observed before in other nanoparticle systems is demonstrated.展开更多
Graphene nanoribbons(GNRs)have attracted great research interest because of their widely tunable and unique electronic properties.The required atomic precision of GNRs can be realized via on-surface synthesis method.I...Graphene nanoribbons(GNRs)have attracted great research interest because of their widely tunable and unique electronic properties.The required atomic precision of GNRs can be realized via on-surface synthesis method.In this work,through a surface assisted reaction we have longitudinally fused the pyrene-based graphene nanoribbons(pGNR)of different lengths by a pentagon ring junction,and built a molecular junction structure on Au(111).The electronic properties of the structure are studied by scanning tunneling spectroscopy(STS)combined with tight binding(TB)calculations.The pentagon ring junction shows a weak electronic coupling effect on graphene nanoribbons,which makes the electronic properties of the two different graphene nanoribbons connected by a pentagon ring junction analogous to type I semiconductor heterojunctions.展开更多
Ultrathin ZnO nano structures prese nt in teresti ng two-dimensi on al(2D)graphene-like structure in contrast to wurtzite structure in bulk ZnO.Growth on Au(111)has been regarded as a well-established route to the 2D ...Ultrathin ZnO nano structures prese nt in teresti ng two-dimensi on al(2D)graphene-like structure in contrast to wurtzite structure in bulk ZnO.Growth on Au(111)has been regarded as a well-established route to the 2D ZnO layers while controlled growth of uniform ZnO nano structures remains as a challe nge.Here,reactive deposition of Zn in O3 and NO2 was employed,which is investigated by sea nning tunneling microscopy and X-ray photoelectr on spectroscopy(XPS).We dem on strate that uniform ZnO mono layer nanoislands and films can be obtained on Au(111)using O3 and uniform ZnO bilayer nanoislands and films form on Au(111)using NO2,respectively.Formation of atomic oxyge n overlayers on Au(111)via exposure to O3 is critical to the formatio n of uniform ZnO mono layer nano structures atop.Near ambient pressure XPS studies revealed that n early full hydroxy lati on occurs on mono layer ZnO structures upon exposure to near ambient pressure water vapor or atomic hydrogen species,while partial surface hydroxylation happens on bilayer ZnO under the same gaseous exposure conditions.展开更多
On-surface synthesis never fails to fascinate chemists by producing new functional polymers which can hardly been prepared via traditional solution chemistry.Among those newly prepared polymers,graphene nanoribbons(GN...On-surface synthesis never fails to fascinate chemists by producing new functional polymers which can hardly been prepared via traditional solution chemistry.Among those newly prepared polymers,graphene nanoribbons(GNRs),featured with tunable band gap,have attracted substantial attention because they are considered as promising candidates for next generation carbon-based semiconductors.Here,we summarize the recent advances of GNRs prepared on single crystal surfaces with emphasis on the structural tuning and electronic properties of GNRs.Moreover,critical developments toward the application of GNRs have also been reviewed including the mass fabrication and the performance of GNRs as field effect transistors.展开更多
Graphene nanoribbons(GNRs)not only share many superlative properties of graphene but also display an exceptional degree of tunability of their electronic properties.The bandgaps of GNRs depend greatly on their widths,...Graphene nanoribbons(GNRs)not only share many superlative properties of graphene but also display an exceptional degree of tunability of their electronic properties.The bandgaps of GNRs depend greatly on their widths,edges,etc.Herein,we report the synthesis path and the physical properties of atomic accuracy staggered narrow N=8 armchair graphene nanoribbons(sn-8AGNR)with alternating"Bite"defects on the opposite side.The intermediate structures in the surface physicochemical reactions from the precursors to the sn-8AGNR are characterized by scanning tunneling microscopy.The electronic properties of the sn-8AGNR are characterized by scanning tunneling spectroscopies and 6//6V mappings.Compared with the perfect N=8 armchair graphene nanoribbons(8AGNR),the sn-8AGNR has a larger bandgap,indicating that the liB\Xen edges can effectively regulate the electronic structures of GNRs.展开更多
基金Project supported by the National Key R&D Program of China (Grant No.2022YFA1204302)the National Natural Science Foundation of China (Grant Nos.52022029,52221001,92263107,U23A20570,62090035,U19A2090,and 12174098)+1 种基金the Hunan Provincial Natural Science Foundation of China (Grant Nos.2022JJ30142 and 2019XK2001)in part supported by the State Key Laboratory of Powder Metallurgy,Central South University。
文摘Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51772087,11804089,11574350,11904094,and 51972106)the Natural Science Foundation of Hunan Province,China(Grant Nos.2018JJ3025,2019JJ50034,and 2019JJ50073)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB30000000)the Fundamental Research Funds for the Central Universities of China.
文摘Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Here,we study modulations of the electronic structure induced by the interlayer coupling in theγ-phase of indium selenide(γ-InSe)using scanning probe techniques.We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction,which are attributed to strong interlayer coupling.In addition,the moirépatterns observed inγ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns.This suggests that modulation of the electronic structure induced by the moirépotential is smeared out,indicating the presence of a significant interlayer coupling.Our theoretical calculations confirm that the interlayer coupling inγ-InSe is not only of the van der Waals origin,but also exhibits some degree of hybridization between the layers.Strong interlayer coupling might play an important role in the performance ofγ-InSe-based devices.
基金The first author acknowledges the financial support of JSPS(Japan Society for the Promotion of Science)This work was also supported by an International Colla-borative Research Grant by the National Institute of Information and Communications Technology of Japan.
文摘Scanning tunneling microscopy/spectroscopy(STM/STS)at 4.8 K has been used to examine the growth of a double-decker bis(phthalocyaninato)yttrium(YP_(c2))molecule on a reconstructed Au(111)substrate.Local differential conductance spectra(dI/dV)of a single YPc2 molecule allow the characteristics of the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)to be identified.Furthermore,lateral distributions of the local density of states(LDOS)have also been obtained by dI/dV mapping and confirmed by first principles simulations.These electronic feature mappings and theoretical calculations provide a basis for understanding the unique STM morphology of YPc2,which is usually imaged as an eight-lobed structure.In addition,we demonstrate that bias-dependent STM morphologies and simultaneous dI/dV maps can provide a way of understanding the stability of two-dimensional YP_(c2) films.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12174096, 51772087, 51972106, 11904094, 11804089 and 12174095)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB30000000)the Natural Science Foundation of Hunan Province, China (Grant Nos. 2019JJ50073 and 2021JJ20026)
文摘Two-dimensional(2D)semiconductors,such as lead selenide(PbSe),locate at the key position of next-generation devices.However,the ultrathin PbSe is still rarely reported experimentally,particularly on metal substrates.Here,we report the ultrathin PbSe synthesized via sequential molecular beam epitaxy on Ag(111).The scanning tunneling microscopy is used to resolve the atomic structure and confirms the selective formation of ultrathin PbSe through the reaction between Ag5Se2 and Pb,as further evidenced by the theoretical calculation.It is also found that the increased accumulation of Pb leads to the improved quality of PbSe with larger and more uniform films.The detailed analysis demonstrates the bilayer structure of synthesized PbSe,which could be deemed to achieve the 2D limit.The differential conductance spectrum reveals a metallic feature of the PbSe film,indicating a certain interaction between PbSe and Ag(111).Moreover,the moirépattern originated from the lattice mismatch between PbSe and Ag(111)is observed,and this moirésystem provides the opportunity for studying physics under periodical modulation and for device applications.Our work illustrates a pathway to selectively synthesize ultrathin PbSe on metal surfaces and suggests a 2D experimental platform to explore PbSe-based opto-electronic and thermoelectric phenomena.
文摘Voltage-controlled conductance and switching induced by single molecules or atoms are ideally studied in scanning tunneling microscope （STM） tunnel junctions. While the objects under consideration are mostly used in their original form, little is known of the possibilities of in situ adjustments of their properties. Here, we evidence properties of a tunnel junction made of a Ce atom/cluster built by atomic manipulation on Au（111） at a temperature of 4.6 K in the presence of H2. The conductance through the object is characterized by a switching voltage corresponding to an opening or closing of an inelastic electron tunneling conductance channel at 50 mV for a Ce atom and 140 mV for a Ce cluster and by charging. We demonstrate that the electronic properties of an STM junction can be engineered in a simple way by in situ guiding of the H2 pinning at an atomic cluster.
基金the Agencia Estatal de Investigación(AEI)and Fondo Europeo de Desarrollo Regional(FEDER)(AEI/FEDER,UE)(project No.MAT2016-77852-C2-2-R)the Comunidad de Madrid and the Universidad Autónoma de Madrid under project No.SI3/PJI/2021-00500,and the CERICERIC Consortium(No.20187040)。
文摘Achieving superior performance of nanoparticle systems is one of the biggest challenges in catalysis.Two major phenomena,occurring during the reactions,hinder the development of the full potential of nanoparticle catalysts:sintering and contamination with carbon containing species,sometimes called coking.Here,we demonstrate that Ir nanocrystals,arranged into periodic networks on hexagonal boron nitride(h-BN)supports,can be restored without sintering after contamination by persistent carbon.This restoration yields the complete removal of carbon from the nanocrystals,which keep their crystalline structure,allowing operation without degradation.These findings,together with the possibility of fine tuning the nanocrystals size,confer this nanoparticle system a great potential as a testbed to extract key information about catalysis-mediated oxidation reactions.For the case of the CO oxidation by O2,reaction of interest in environmental science and green energy production,the existence of chemical processes not observed before in other nanoparticle systems is demonstrated.
基金the National Natural Science Foundation of China(No.22072086)The Swiss National Science Foundation(Nos.200020_182015 and 200021_172527)supported this work。
文摘Graphene nanoribbons(GNRs)have attracted great research interest because of their widely tunable and unique electronic properties.The required atomic precision of GNRs can be realized via on-surface synthesis method.In this work,through a surface assisted reaction we have longitudinally fused the pyrene-based graphene nanoribbons(pGNR)of different lengths by a pentagon ring junction,and built a molecular junction structure on Au(111).The electronic properties of the structure are studied by scanning tunneling spectroscopy(STS)combined with tight binding(TB)calculations.The pentagon ring junction shows a weak electronic coupling effect on graphene nanoribbons,which makes the electronic properties of the two different graphene nanoribbons connected by a pentagon ring junction analogous to type I semiconductor heterojunctions.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.21825203,91545204,21688102,and 21621063)the National Key Research and Development Program of China(Nos.2016YFA0200200 and 2017YFB0602205)+1 种基金Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB17020000)The authors thank the support for Nano-X from Suzhou Institute of Nano-Tech and Nano-Bionics(SINANO).The fruitful discussion with Yuemin Wang in Karlsruhe Institute of Technology(KIT)is highly appreciated.
文摘Ultrathin ZnO nano structures prese nt in teresti ng two-dimensi on al(2D)graphene-like structure in contrast to wurtzite structure in bulk ZnO.Growth on Au(111)has been regarded as a well-established route to the 2D ZnO layers while controlled growth of uniform ZnO nano structures remains as a challe nge.Here,reactive deposition of Zn in O3 and NO2 was employed,which is investigated by sea nning tunneling microscopy and X-ray photoelectr on spectroscopy(XPS).We dem on strate that uniform ZnO mono layer nanoislands and films can be obtained on Au(111)using O3 and uniform ZnO bilayer nanoislands and films form on Au(111)using NO2,respectively.Formation of atomic oxyge n overlayers on Au(111)via exposure to O3 is critical to the formatio n of uniform ZnO mono layer nano structures atop.Near ambient pressure XPS studies revealed that n early full hydroxy lati on occurs on mono layer ZnO structures upon exposure to near ambient pressure water vapor or atomic hydrogen species,while partial surface hydroxylation happens on bilayer ZnO under the same gaseous exposure conditions.
文摘On-surface synthesis never fails to fascinate chemists by producing new functional polymers which can hardly been prepared via traditional solution chemistry.Among those newly prepared polymers,graphene nanoribbons(GNRs),featured with tunable band gap,have attracted substantial attention because they are considered as promising candidates for next generation carbon-based semiconductors.Here,we summarize the recent advances of GNRs prepared on single crystal surfaces with emphasis on the structural tuning and electronic properties of GNRs.Moreover,critical developments toward the application of GNRs have also been reviewed including the mass fabrication and the performance of GNRs as field effect transistors.
基金support by the National Natural Science Foundation of China(Nos.11674136,61901200,51662023,and 51861020)The National Recruitment Program for Young Professionals(No.1097816002)+2 种基金Yunnan Province for Recruiting High-Caliber Technological Talents(No.1097816002)reserve talents for Yunnan young and middle aged academic and technical leaders(No.2017HB010)the Yunnan Province Science and Technology Plan Project(No.2019FD041).Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB30010000).
文摘Graphene nanoribbons(GNRs)not only share many superlative properties of graphene but also display an exceptional degree of tunability of their electronic properties.The bandgaps of GNRs depend greatly on their widths,edges,etc.Herein,we report the synthesis path and the physical properties of atomic accuracy staggered narrow N=8 armchair graphene nanoribbons(sn-8AGNR)with alternating"Bite"defects on the opposite side.The intermediate structures in the surface physicochemical reactions from the precursors to the sn-8AGNR are characterized by scanning tunneling microscopy.The electronic properties of the sn-8AGNR are characterized by scanning tunneling spectroscopies and 6//6V mappings.Compared with the perfect N=8 armchair graphene nanoribbons(8AGNR),the sn-8AGNR has a larger bandgap,indicating that the liB\Xen edges can effectively regulate the electronic structures of GNRs.
