By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrop...By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.展开更多
It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed....It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis（para-pyridyl）acetylene（BPPA） tetramer on Au（111） surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular ＂non-bonded＂ region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy.展开更多
Rutile TiO2 （001） quantum dots （or nano-marks） in different shapes were used to imitate uncleaved material surfaces or materials with rough surfaces. By numerical integration of the equation of motion of cantileve...Rutile TiO2 （001） quantum dots （or nano-marks） in different shapes were used to imitate uncleaved material surfaces or materials with rough surfaces. By numerical integration of the equation of motion of cantilever for silicon tip scanning along the [110] direction over the rutile TiO2 （001） quantum dots in ultra high vacuum （UHV）, scanning routes were explored to achieve atomic resolution from frequency shift image. The tip-surface interaction forces were calculated from Lennard-Jones （12-6） potential by the Hamaker summation method. The calculated results showed that atomic resolution could be achieved by frequency shift image for TiO2 （001） surfaces of rhombohedral quantum dot scanning in a vertical route, and spherical cap quantum dot scanning in a superposition route.2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.展开更多
Furazan macrocyclic compound 3,4:7,8:11,12:15,16-tetrafurazan-1,9-dioxazo-5,13-diazocyclohexadecane(DOATF)is an ideal energetic material with high heat of formation.Here,using scanning tunneling microscopy(STM)and non...Furazan macrocyclic compound 3,4:7,8:11,12:15,16-tetrafurazan-1,9-dioxazo-5,13-diazocyclohexadecane(DOATF)is an ideal energetic material with high heat of formation.Here,using scanning tunneling microscopy(STM)and noncontact atomic force microscopy(nc-AFM),we investigated the adsorption structure of DOATF molecules on Au(111)surface,which shows the four furanzan rings in the STM images and a bright protrusion off the center of the molecule in the nc-AFM images.Combined with density functional theory(DFT)calculations,we confirmed that the bright feature in the nc-AFM images is an N-O coordinate bond pointing upwards in one of the two azoxy groups;while the other N-O bond pointing towards the Au(111)surface.Our work contributes for a deeper understanding of the adsorption structure of macrocyclic compounds,which would promote the designing of DOATF-metal frameworks.展开更多
为了兼顾非接触式原子力显微镜(noncontact atomic force microscope,NC-AFM)更高谐振频率探针的使用需求,并通过提高控制器精度进而提高NC-AFM分辨率,提出了一种基于探针-样品间原子作用力变化的全数字可调谐NC-AFM高分辨率探针起振系...为了兼顾非接触式原子力显微镜(noncontact atomic force microscope,NC-AFM)更高谐振频率探针的使用需求,并通过提高控制器精度进而提高NC-AFM分辨率,提出了一种基于探针-样品间原子作用力变化的全数字可调谐NC-AFM高分辨率探针起振系统。在Simulink环境下对探针起振系统的控制部分进行了设计,通过现场可编程门阵列(FPGA)实现了鉴相,滤波,锁频等功能;采用压电陶瓷片驱动探针振动,设计了操作便捷的探针座。将不同频率正弦信号提供给设计的起振系统进行功能性验证,实验结果表明,系统可以在20 kHz~50 MHz频率范围内跟踪探针谐振频率;最后使用起振系统成功使商用探针在谐振频率处振动,准确测出了探针的谐振频率及振动幅值,系统频率分辨率达到了0.1 Hz。展开更多
Zigzag graphene nanoribbons(ZGNRs)with spin-polarized edge states have potential applications in carbon-based spintronics.The electronic structure of ZGNRs can be effectively tuned by different widths or dopants,which...Zigzag graphene nanoribbons(ZGNRs)with spin-polarized edge states have potential applications in carbon-based spintronics.The electronic structure of ZGNRs can be effectively tuned by different widths or dopants,which requires delicately designed monomers.Here,we report the successful synthesis of ZGNR with a width of eight carbon zigzag lines and nitrogen-boronnitrogen(NBN)motifs decorated along the zigzag edges(NBN-8-ZGNR)on Au(111)surface,which starts from a specially designed U-shaped monomer with preinstalled NBN units at the zigzag edge.Chemical-bond-resolved non-contact atomic force microscopy(nc-AFM)imaging confirms the zigzag-terminated edges and the existence of NBN dopants.The electronic states distributed along the zigzag edges have been revealed after a silicon-layer intercalation at the interface of NBN-8-ZGNR and Au(111).Our work enriches the ZGNR family with a new dopant and larger width,which provides more candidates for future carbonbased nanoelectronic and spintronic applications.展开更多
Topological defects in graphene materials introduce exotic properties with both fundamental importance and technological implications,absent in their defect-free counterparts.Although individual topological defects ha...Topological defects in graphene materials introduce exotic properties with both fundamental importance and technological implications,absent in their defect-free counterparts.Although individual topological defects have been widely studied,collective magnetic behaviors originating from well-organized multiple topological defects remain a great challenge.Here,we examined the collective magnetic properties originating from three pentagon topological defects in truxene-based molecular graphenoids using scanning tunneling microscopy(STM)and non-contact atomic force microscopy.Unpairedπelectrons were introduced into the aromatic topology of truxene molecular graphenoids one by one by dissociating hydrogen atoms at the pentagon defects via atom manipulation.STM measurements,together with density functional theory calculations,suggested that the unpaired electrons were ferromagnetically coupled,forming a collective highspin quartet state of S=3/2.Our work demonstrates that collective spin ordering could be realized through engineering regular patterned topological defects in molecular graphenoids,providing a new platform for designing one-dimensional ferromagnetic spin chains and two-dimensional ferromagnetic networks.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
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
文摘By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.
基金supported by the Ministry of Science and Technology(MOST)of China(Nos.2012CB932704,2012CB933001)the National Natural Science Foundation of China(NSFC,Nos.11274380,91433103,21173058,11622437,61674171 and 21203038)supported by the Outstanding Innovative Talents Cultivation Funded Programs 2015 of Renmin University of China
文摘It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis（para-pyridyl）acetylene（BPPA） tetramer on Au（111） surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular ＂non-bonded＂ region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy.
文摘Rutile TiO2 （001） quantum dots （or nano-marks） in different shapes were used to imitate uncleaved material surfaces or materials with rough surfaces. By numerical integration of the equation of motion of cantilever for silicon tip scanning along the [110] direction over the rutile TiO2 （001） quantum dots in ultra high vacuum （UHV）, scanning routes were explored to achieve atomic resolution from frequency shift image. The tip-surface interaction forces were calculated from Lennard-Jones （12-6） potential by the Hamaker summation method. The calculated results showed that atomic resolution could be achieved by frequency shift image for TiO2 （001） surfaces of rhombohedral quantum dot scanning in a vertical route, and spherical cap quantum dot scanning in a superposition route.2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.
基金the National Key Research and Development Projects of China(Grant No.2019YFA0308500)the National Natural Science Foundation of China(Grant No.61888102)the Funds from the Chinese Academy of Sciences(Grant Nos.XDB30000000 and YSBR-003)。
文摘Furazan macrocyclic compound 3,4:7,8:11,12:15,16-tetrafurazan-1,9-dioxazo-5,13-diazocyclohexadecane(DOATF)is an ideal energetic material with high heat of formation.Here,using scanning tunneling microscopy(STM)and noncontact atomic force microscopy(nc-AFM),we investigated the adsorption structure of DOATF molecules on Au(111)surface,which shows the four furanzan rings in the STM images and a bright protrusion off the center of the molecule in the nc-AFM images.Combined with density functional theory(DFT)calculations,we confirmed that the bright feature in the nc-AFM images is an N-O coordinate bond pointing upwards in one of the two azoxy groups;while the other N-O bond pointing towards the Au(111)surface.Our work contributes for a deeper understanding of the adsorption structure of macrocyclic compounds,which would promote the designing of DOATF-metal frameworks.
基金The work was supported by grants from the National Key Research and Development Program of China(No.2019YFA0308500)the National Natural Science Foundation of China(No.61888102)+5 种基金the Chinese Academy of Sciences(Nos.XDB30000000 and YSBR-003)the EU Graphene Flagship(Graphene Core 3,No.881603)the H2020-MSCA-ITN(ULTIMATE,No.813036)the Center for Advancing Electronics Dresden(CfAED)the H2020-EU.1.2.2.-FET Proactive Grant(LIGHT-CAP,No.101017821)the DFG-SNSF Joint Switzerland-German Research Project(EnhanTopo,No.429265950).
文摘Zigzag graphene nanoribbons(ZGNRs)with spin-polarized edge states have potential applications in carbon-based spintronics.The electronic structure of ZGNRs can be effectively tuned by different widths or dopants,which requires delicately designed monomers.Here,we report the successful synthesis of ZGNR with a width of eight carbon zigzag lines and nitrogen-boronnitrogen(NBN)motifs decorated along the zigzag edges(NBN-8-ZGNR)on Au(111)surface,which starts from a specially designed U-shaped monomer with preinstalled NBN units at the zigzag edge.Chemical-bond-resolved non-contact atomic force microscopy(nc-AFM)imaging confirms the zigzag-terminated edges and the existence of NBN dopants.The electronic states distributed along the zigzag edges have been revealed after a silicon-layer intercalation at the interface of NBN-8-ZGNR and Au(111).Our work enriches the ZGNR family with a new dopant and larger width,which provides more candidates for future carbonbased nanoelectronic and spintronic applications.
基金S.W.acknowledges the financial support from the National Key R&D Program of China(grant no.2020YFA0309000)the National Natural Science Foundation of China(grant nos.11874258 and 12074247)+5 种基金the Shanghai Municipal Science and Technology Qi Ming Xing Project(grant no.20QA1405100)Fok Ying Tung Foundation for young researchers and SJTU(grant no.21X010200846)This work is also supported by the Ministry of Science and Technology of China(grant nos.2019YFA0308600,2016YFA0301003,and 2016YFA0300403)NSFC(grants nos.21925201,11521404,11634009,92065201,11874256,11790313,and 11861161003)the Strategic Priority Research Program of Chinese Academy of Sciences(grant no.XDB28000000)the Science and Technology Commission of Shanghai Municipality(grants nos.20ZR1414200,2019SHZDZX01,19JC1412701,and 20QA1405100)for partial support.
文摘Topological defects in graphene materials introduce exotic properties with both fundamental importance and technological implications,absent in their defect-free counterparts.Although individual topological defects have been widely studied,collective magnetic behaviors originating from well-organized multiple topological defects remain a great challenge.Here,we examined the collective magnetic properties originating from three pentagon topological defects in truxene-based molecular graphenoids using scanning tunneling microscopy(STM)and non-contact atomic force microscopy.Unpairedπelectrons were introduced into the aromatic topology of truxene molecular graphenoids one by one by dissociating hydrogen atoms at the pentagon defects via atom manipulation.STM measurements,together with density functional theory calculations,suggested that the unpaired electrons were ferromagnetically coupled,forming a collective highspin quartet state of S=3/2.Our work demonstrates that collective spin ordering could be realized through engineering regular patterned topological defects in molecular graphenoids,providing a new platform for designing one-dimensional ferromagnetic spin chains and two-dimensional ferromagnetic networks.
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.
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.
