The ultrahigh vacuum scanning tunneling microscope(STM)was used to characterize the GaSb_(1-x)Bi_(x) films of a few nanometers thickness grown by the molecular beam epitaxy(MBE)on the GaSb buffer layer of 100 nm with ...The ultrahigh vacuum scanning tunneling microscope(STM)was used to characterize the GaSb_(1-x)Bi_(x) films of a few nanometers thickness grown by the molecular beam epitaxy(MBE)on the GaSb buffer layer of 100 nm with the GaSb(100)substrates.The thickness of the GaSb_(1-x)Bi_(x) layers of the samples are 5 and 10 nm,respectively.For comparison,the GaSb buffer was also characterized and its STM image displays terraces whose surfaces are basically atomically flat and their roughness is generally less than 1 monolayer(ML).The surface of 5 nm GaSb_(1-x)Bi_(x) film reserves the same terraced morphology as the buffer layer.In contrast,the morphology of the 10 nm GaSb_(1-x)Bi_(x) film changes to the mound-like island structures with a height of a few MLs.The result implies the growth mode transition from the two-dimensional mode as displayed by the 5 nm film to the Stranski-Krastinov mode as displayed by the 10 nm film.The statistical analysis with the scanning tunneling spectroscopy(STS)measurements indicates that both the incorporation and the inhomogeneity of Bi atoms increase with the thickness of the GaSb_(1-x)Bi_(x) layer.展开更多
The microstructure of(CrFe)_7C_3 has been studied with scanning tunneling microscopy.It shows that a carbide consists of colonies which are full of stacking faults. The stacking faults in one colony are parallel while...The microstructure of(CrFe)_7C_3 has been studied with scanning tunneling microscopy.It shows that a carbide consists of colonies which are full of stacking faults. The stacking faults in one colony are parallel while those in different colonies lie at angle with each other.展开更多
Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy is...Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh(111). That is, when graphene is formed on Rh(111), the substrate remains fiat and does not develop a SUPPorting nail structure.展开更多
The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail. Upon molecular depositi...The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail. Upon molecular deposition at low temperature, Gd@C82 molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage. Further annealing treatment leads some of the Gd@C82 molecules to assemble into bright and dim patches, which are correlated to the adsorption induced substrate reconstruction. Upon sufficient thermal activation, Gd@C82 molecules sink into the Cu(111) surface one-copper-layer-deep, forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns. By considering the commensurability between the Gd@C82 nearest-neighbor distance and the lattice of the underlying Cu(111), we clearly identified two kinds of in-plane molecular arrangements as (19(1/2)×19(1/2))R23.4°and (19(1/2)×19(1/2))R36.6°with respect to Cu(111). Within the assembled Gd@C82 molecular, island molecules with dim–bright contrast are spatially distributed, which may be modulated by the preexisted species on Cu(111).展开更多
Our recent scanning tunneling microscopy (STM) studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie...Our recent scanning tunneling microscopy (STM) studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe l-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with supercon- ductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFel_xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.展开更多
Simultaneous measurements of surface pressure and surface potential and scanning tunneling microscopy study for N-docosylpyridinium- TCNQ monolayer were carried out.These methods allow us to get more informations on p...Simultaneous measurements of surface pressure and surface potential and scanning tunneling microscopy study for N-docosylpyridinium- TCNQ monolayer were carried out.These methods allow us to get more informations on properties of the monolayer.The molecules at the final stage of compression are really in compact stack although a voluminous hydrophilic head exists in the molecule.展开更多
We propose an interferometer composing of a scanning tunneling microscope(STM),double quantum dots(DQDs),and a semiconductor nanowire carrying Majorana bound states(MBSs)at its ends induced by the proximity effect of ...We propose an interferometer composing of a scanning tunneling microscope(STM),double quantum dots(DQDs),and a semiconductor nanowire carrying Majorana bound states(MBSs)at its ends induced by the proximity effect of an s-wave superconductor,to probe the existence of the MBSs in the dots.Our results show that when the energy levels of DQDs are aligned to the energy of MBSs,the zero-energy spectral functions of DQDs are always equal to 1/2,which indicates the formation of the MBSs in the DQDs and is also responsible for the zero-bias conductance peak.Our findings suggest that the spectral functions of the DQDs may be an excellent and convenient quantity for detecting the formation and stability of the spatially separated MBSs in quantum dots.展开更多
We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide (CuSe2 ) films on SrTiO3 (001). Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-...We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide (CuSe2 ) films on SrTiO3 (001). Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov (layer-plus-island) mode with a preferential orientation of (111). Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.展开更多
Highly oriented pyrolytic graphite (HOPG) is the substrate often used in scanningtunneling Ancroscopy (STM). It is well known that STM images of the basal plane of HOPG showsome unusual structUral patterns. In this le...Highly oriented pyrolytic graphite (HOPG) is the substrate often used in scanningtunneling Ancroscopy (STM). It is well known that STM images of the basal plane of HOPG showsome unusual structUral patterns. In this letter, we present in situ STM images of some unusualfeatures on HOPG in solutions, including normal or abnormal chain-like featUres and hexagonal oroblique superPeriodic structures. These features emerge both next to and apart from the step ofHOPG.展开更多
Herein,we discovered that the surface-confined condensation of boronic acid can happen spontaneously at room temperature,by comparing the kinetics of condensation of boronic acids with and without the negative sample ...Herein,we discovered that the surface-confined condensation of boronic acid can happen spontaneously at room temperature,by comparing the kinetics of condensation of boronic acids with and without the negative sample bias,we found that the negative sample bias indeed accelerates the self-condensation reaction of boronic acid.Combining with in-situ STM images and ultraviolet photoemission spectrum(UPS)analysis,a reversible adsorption mechanism model was proposed and reasonably explains the reversible electric-field-induced phase transformation.展开更多
CaKFe_(4)As_(4) is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morp...CaKFe_(4)As_(4) is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morphology and electronic structure of CaKFe_(4)As_(4) single crystal were systematically investigated. The cleaved CaKFe_(4)As_(4) showed various morphologies, such as atomically resolved 1×1, 1×2, and √2×√2 lattices. By analyzing the geometrical correlations of these morphologies, the 1×1 and 1×2 lattices were identified as the original and reconstructed As layers, respectively, whereas the √2×√2 lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer. The superconducting energy gap of 7.3 me V and bosonic mode of 12.7 me V were resolved in the scanning tunneling spectra. In addition, the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques, indicating that the electronic structures of CaKFe_(4)As_(4) were insensitive to the surface reconstructions. Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.展开更多
In this review we describe a family of organic-based host frameworks which can accommodate guest molecules. The aim of the study is to test the adjustability of this class of mimic structures that may lead to new inte...In this review we describe a family of organic-based host frameworks which can accommodate guest molecules. The aim of the study is to test the adjustability of this class of mimic structures that may lead to new interesting functions. Emphasis of our research is placed upon four aspects: 1) thermal properties, 2) surface photochemistry, 3) fullerene adsorption, and 4) guest inclusion. It is envisioned that such approach of nanoporous molecular networks might be developed into a new family of useful soft frameworks for studies toward shape-selective catalysis, molecular recognition, self-assembly, and host-guest supramolecular chemistry.展开更多
Graphene nanoribbons(GNRs)attract a growing interest due to their tunable physical properties and promise for device applications.A variety of atomically precise GNRs have recently been synthesized by on-surface and s...Graphene nanoribbons(GNRs)attract a growing interest due to their tunable physical properties and promise for device applications.A variety of atomically precise GNRs have recently been synthesized by on-surface and solution approaches.While on-surface GNRs can be conveniently visualized by scanning tunneling microscopy(STM),and their electronic structure can be probed by scanning tunneling spectroscopy(STS),such characterization remains a great challenge for the solution-synthesized GNRs.Here,we report solution synthesis and detailed STM/STS characterization of atomically precise GNRs with a meandering shape that are structurally related to chevron GNRs but have a reduced energy band gap.The ribbons were synthesized by Ni0-mediated Yamamoto polymerization of specially designed molecular precursors using triflates as the leaving groups and oxidative cyclodehydrogenation of the resulting polymers using Scholl reaction.The ribbons were deposited onto III-V semiconducting InAs(110)substrates by a dry contact transfer technique.High-resolution STM/STS characterization not only confirmed the GNR geometry,but also revealed details of electronic structure including energy states,electronic band gap,as well as the spatial distribution of the local density of states.The experimental STS band gap of GNRs is about 2 eV,which is very close to 2.35 eV predicted by the density functional theory simulations with GW correction,indicating a weak screening effect of InAs(110)substrate.Furthermore,several aspects of GNR-InAs(110)substrate interactions were also probed and analyzed,including GNR tunable transparency,alignment to the substrate,and manipulations of GNR position by the STM tip.The weak interaction between the GNRs and the InAs(110)surface makes InAs(110)an ideal substrate for investigating the intrinsic properties of GNRs.Because of the reduced energy band gap of these ribbons,the GNR thin films exhibit appreciably high electrical conductivity and on/off ratios of about 10 in field-effect transistor measurements,suggesting their promise for device applications.展开更多
The assembly of amyloid peptides into highly organized fibrils is one of the major characteristics of many de-generative diseases such as Alzheimer’s disease and type II diabetes.Assembly structures of amyloid peptid...The assembly of amyloid peptides into highly organized fibrils is one of the major characteristics of many de-generative diseases such as Alzheimer’s disease and type II diabetes.Assembly structures of amyloid peptides at liquid-solid interface can be visualized by scanning tunneling microscopy(STM)with site-specific resolution.The STM analysis can provide valuable information on the folding mechanism of amyloid peptides based on the corre-lation of surface assembly structures and fibrillation behaviors.Cases on mutational analysis of amyloid peptides by STM are also reviewed which illustrate the capacities of STM studies on amyloid assemblies.展开更多
Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF...Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF(n=1,2)/PC71BM donor-acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy(STM),scanning tunneling spectroscopy(STS),density functional theory(DFT)calculations,and transient absorption(TA)spectroscopy.The results show that BTID-1F and BTID-2F form bright strip structures,whereas BTID-nF(n=1,2)/PC71BM form ridge-like structures with each complex composed of one BTID-nF(n=1,2)molecule and four PC71BM molecules which adsorbed around the BTID-nF(n=1,2)molecule by S···πinteraction.With the assistance of S···πinteraction between BTID-nF(n=1,2)and PC71BM,BTID-nF(n=1,2)/PC71BM co-assembled ridge-like structures are more stable than the BTID-nF(n=1,2)ridge structures.To investigate the charge transfer of BTID-nF(n=1,2)/PC71BM system,STS measurements,DFT calculation,and TA spectroscopy are further performed.The results show that charge transfer occurs in BTID-nF(n=1,2)/PC71BM system with the electron transferring from BTID-nF(n=1,2)molecules to PC71BM.展开更多
The peptide assembly structures of polyglutamine (PolyQ) have been studied by using scanning tunneling microscopy (STM) with high spatial resolution in ambient conditions. 4,4'-Bipyridyl (4Bpy) was introduced i...The peptide assembly structures of polyglutamine (PolyQ) have been studied by using scanning tunneling microscopy (STM) with high spatial resolution in ambient conditions. 4,4'-Bipyridyl (4Bpy) was introduced into the PolyQ7 and PolyQ8 peptide assemblies for labeling the C-termini of the peptides. The fine structures of the 4Bpy-PolyQ7 and 4Bpy-PolyQ8 co-assemblies are observed, and the statistics of the apparent peptide strand length reveal different length distributions for PolyQ7 and PolyQs. One predominant apparent peptide strand length is ob- served for PolyQ7 reflecting one predominant peptide conformation in assembly structures, while three major ap- parent strand lengths can be identified with PolyQ8 reflecting three co-existing peptide conformations in peptide as- semblies. Such drastic difference in assembling characteristics can be considered as a reflection of asymmetric ad- sorption effect ofpeptides relating to odd-even residue numbers of PolyQ7 and PolyQ8,展开更多
The assembling behavior and electronic properties of asymmetric tris(phthalocyaninato)lutetium triple-decker sandwich complex molecules(Lu2Pc3)on highly oriented pyrolytic graphite(HOPG)surfaces have been studied by s...The assembling behavior and electronic properties of asymmetric tris(phthalocyaninato)lutetium triple-decker sandwich complex molecules(Lu2Pc3)on highly oriented pyrolytic graphite(HOPG)surfaces have been studied by scanning tunneling microscopy/spectroscopy(STM/STS)methods.Phase transitions were observed at different bias polarities,involving an ordered packing arrangement with fourfold symmetry at negative bias and an amorphous arrangement at positive bias.Molecular switching behaviour for individual Lu2Pc3 molecules was reported here according to the bias-polarity-induced flipping phenomena and the peak shift in dI/dV versus V curves at different voltage scanning directions.The sensitive response of the strong intrinsic molecular dipole to an external electric field is proposed to be responsible for molecular switching of Lu_(2)Pc_(3)at the solid/liquid interface.展开更多
The self-assembly of L-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope(STM) at 4.4 K.When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer,molecu...The self-assembly of L-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope(STM) at 4.4 K.When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer,molecular trimers,tetramers,hexamers,and chains coexist on Cu(111).Then almost all molecules self-assemble into chiral hexamers after being annealed at room temperature.When increasing molecular coverage to the full layer,a new type of chain is observed on the surface.Based on the high-resolution STM images at sub-molecular level,we suggest that the L-tryptophan molecules are present in neutral,zwitterionic or anionic states in these structures.展开更多
In this review, supramolecular coordination processes on two-dimensional (2D) surfaces or interfaces observed by scanning tunneling microscopy (STM) are discussed. Four parts are mainly involved, which include (1) rec...In this review, supramolecular coordination processes on two-dimensional (2D) surfaces or interfaces observed by scanning tunneling microscopy (STM) are discussed. Four parts are mainly involved, which include (1) recognition of Fe^(3+) through functional molecular networks, (2) K^(+)-induced switching of valinomycin, (3) supramolecular coordination happened in a nano-reactor, (4) reversible 2D supramolecular spring driven by coordination. The direct insight of the coordination phenomena provided by STM supplements our knowledge of its mechanism. Since different building blocks can be connected into a whole part through coordination, the understanding of its mechanism will be beneficial to the future design of molecular 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
基金supported by the National Natural Science Foundation of China(Nos.61474073,61874069 and 61804157).
文摘The ultrahigh vacuum scanning tunneling microscope(STM)was used to characterize the GaSb_(1-x)Bi_(x) films of a few nanometers thickness grown by the molecular beam epitaxy(MBE)on the GaSb buffer layer of 100 nm with the GaSb(100)substrates.The thickness of the GaSb_(1-x)Bi_(x) layers of the samples are 5 and 10 nm,respectively.For comparison,the GaSb buffer was also characterized and its STM image displays terraces whose surfaces are basically atomically flat and their roughness is generally less than 1 monolayer(ML).The surface of 5 nm GaSb_(1-x)Bi_(x) film reserves the same terraced morphology as the buffer layer.In contrast,the morphology of the 10 nm GaSb_(1-x)Bi_(x) film changes to the mound-like island structures with a height of a few MLs.The result implies the growth mode transition from the two-dimensional mode as displayed by the 5 nm film to the Stranski-Krastinov mode as displayed by the 10 nm film.The statistical analysis with the scanning tunneling spectroscopy(STS)measurements indicates that both the incorporation and the inhomogeneity of Bi atoms increase with the thickness of the GaSb_(1-x)Bi_(x) layer.
文摘The microstructure of(CrFe)_7C_3 has been studied with scanning tunneling microscopy.It shows that a carbide consists of colonies which are full of stacking faults. The stacking faults in one colony are parallel while those in different colonies lie at angle with each other.
基金Supported by the National Natural Science Foundation of China under Grant No 51402026the Basic Research Program of Jiangsu Province under Grant No BK20130236the High Technology Research Key Laboratory of Changzhou under Grant No CM20133007
文摘Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh(111). That is, when graphene is formed on Rh(111), the substrate remains fiat and does not develop a SUPPorting nail structure.
基金the National Natural Science Foundation of China(Grant No.11004219)MOST of China(Grant No.2013CBA01600)
文摘The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail. Upon molecular deposition at low temperature, Gd@C82 molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage. Further annealing treatment leads some of the Gd@C82 molecules to assemble into bright and dim patches, which are correlated to the adsorption induced substrate reconstruction. Upon sufficient thermal activation, Gd@C82 molecules sink into the Cu(111) surface one-copper-layer-deep, forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns. By considering the commensurability between the Gd@C82 nearest-neighbor distance and the lattice of the underlying Cu(111), we clearly identified two kinds of in-plane molecular arrangements as (19(1/2)×19(1/2))R23.4°and (19(1/2)×19(1/2))R36.6°with respect to Cu(111). Within the assembled Gd@C82 molecular, island molecules with dim–bright contrast are spatially distributed, which may be modulated by the preexisted species on Cu(111).
基金supported by the National Basic Research Program of China(Grant Nos.2009CB929400 and 2010CB923003)
文摘Our recent scanning tunneling microscopy (STM) studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe l-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with supercon- ductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFel_xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.
文摘Simultaneous measurements of surface pressure and surface potential and scanning tunneling microscopy study for N-docosylpyridinium- TCNQ monolayer were carried out.These methods allow us to get more informations on properties of the monolayer.The molecules at the final stage of compression are really in compact stack although a voluminous hydrophilic head exists in the molecule.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11564029 and 11675023)the Natural Science Foundation of Inner Mongolia,China(Grant No.2017MS0112)+3 种基金the Science Foundation for Excellent Youth Scholors of Inner Mongolia University of Science and Technology,China(Grant No.2017YQL06)the Initial Project of UEST of China,Zhongshan Institute(Grant No.415YKQ02)the Science and Technology Bureau of Zhongshan City,China(Grant Nos.2017B1116 and 2017B1016)the Innovation Team of Zhongshan City,China(Grant No.180809162197886).
文摘We propose an interferometer composing of a scanning tunneling microscope(STM),double quantum dots(DQDs),and a semiconductor nanowire carrying Majorana bound states(MBSs)at its ends induced by the proximity effect of an s-wave superconductor,to probe the existence of the MBSs in the dots.Our results show that when the energy levels of DQDs are aligned to the energy of MBSs,the zero-energy spectral functions of DQDs are always equal to 1/2,which indicates the formation of the MBSs in the DQDs and is also responsible for the zero-bias conductance peak.Our findings suggest that the spectral functions of the DQDs may be an excellent and convenient quantity for detecting the formation and stability of the spatially separated MBSs in quantum dots.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11374336 and 61176078
文摘We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide (CuSe2 ) films on SrTiO3 (001). Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov (layer-plus-island) mode with a preferential orientation of (111). Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.
文摘Highly oriented pyrolytic graphite (HOPG) is the substrate often used in scanningtunneling Ancroscopy (STM). It is well known that STM images of the basal plane of HOPG showsome unusual structUral patterns. In this letter, we present in situ STM images of some unusualfeatures on HOPG in solutions, including normal or abnormal chain-like featUres and hexagonal oroblique superPeriodic structures. These features emerge both next to and apart from the step ofHOPG.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.21872103,52073208).
文摘Herein,we discovered that the surface-confined condensation of boronic acid can happen spontaneously at room temperature,by comparing the kinetics of condensation of boronic acids with and without the negative sample bias,we found that the negative sample bias indeed accelerates the self-condensation reaction of boronic acid.Combining with in-situ STM images and ultraviolet photoemission spectrum(UPS)analysis,a reversible adsorption mechanism model was proposed and reasonably explains the reversible electric-field-induced phase transformation.
基金supported by the National Key Basic Research Program of China(Grant Nos.2017YFA0302902,2016YFA0300301,2017YFA0303003,and 2018YFB0704102)the National Natural Science Foundation of China(Grant Nos.11927808,11834016,118115301,119611410,11961141008,11822411,and 11961160699)+5 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant Nos.QYZDBSSW-SLH008,and QYZDY-SSW-SLH001)the Strategic Priority Research Program(B)of Chinese Academy of Sciences(Grant Nos.XDB25000000,and XDB33000000)the Beijing Natural Science Foundation(Grant Nos.Z190008,and JQ19002)the Key-Area Research and Development Program of Guangdong Province(Grant No.2020B0101340002)the CAS Interdisciplinary Innovation Teamsupport from the Youth Innovation Promotion Association of CAS(Grant No.Y202001)。
文摘CaKFe_(4)As_(4) is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morphology and electronic structure of CaKFe_(4)As_(4) single crystal were systematically investigated. The cleaved CaKFe_(4)As_(4) showed various morphologies, such as atomically resolved 1×1, 1×2, and √2×√2 lattices. By analyzing the geometrical correlations of these morphologies, the 1×1 and 1×2 lattices were identified as the original and reconstructed As layers, respectively, whereas the √2×√2 lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer. The superconducting energy gap of 7.3 me V and bosonic mode of 12.7 me V were resolved in the scanning tunneling spectra. In addition, the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques, indicating that the electronic structures of CaKFe_(4)As_(4) were insensitive to the surface reconstructions. Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.
基金Financial support from the National Natural Science Foundation of China (Grant Nos. 20473097 and 20573116)the National Key Project for Basic Research (Grant Nos. 2007CB936503 and 2007CB936802)
文摘In this review we describe a family of organic-based host frameworks which can accommodate guest molecules. The aim of the study is to test the adjustability of this class of mimic structures that may lead to new interesting functions. Emphasis of our research is placed upon four aspects: 1) thermal properties, 2) surface photochemistry, 3) fullerene adsorption, and 4) guest inclusion. It is envisioned that such approach of nanoporous molecular networks might be developed into a new family of useful soft frameworks for studies toward shape-selective catalysis, molecular recognition, self-assembly, and host-guest supramolecular chemistry.
基金The work was supported by the Office of Naval Research(No.N00014-19-1-2596)the National Science Foundation(NSF)through CHE-1455330Some experiments were performed with the support of Nebraska Materials Research Science and Engineering Center(NSF DMR-1420645)using the instrumentation at Nebraska Nanoscale Facility,which is supported by the NSF(ECCS-1542182)and the Nebraska Research Initiative.All the simulations were performed on the Blue Water computation resources provided by the University of Illinois at Urbana-Champaign.
文摘Graphene nanoribbons(GNRs)attract a growing interest due to their tunable physical properties and promise for device applications.A variety of atomically precise GNRs have recently been synthesized by on-surface and solution approaches.While on-surface GNRs can be conveniently visualized by scanning tunneling microscopy(STM),and their electronic structure can be probed by scanning tunneling spectroscopy(STS),such characterization remains a great challenge for the solution-synthesized GNRs.Here,we report solution synthesis and detailed STM/STS characterization of atomically precise GNRs with a meandering shape that are structurally related to chevron GNRs but have a reduced energy band gap.The ribbons were synthesized by Ni0-mediated Yamamoto polymerization of specially designed molecular precursors using triflates as the leaving groups and oxidative cyclodehydrogenation of the resulting polymers using Scholl reaction.The ribbons were deposited onto III-V semiconducting InAs(110)substrates by a dry contact transfer technique.High-resolution STM/STS characterization not only confirmed the GNR geometry,but also revealed details of electronic structure including energy states,electronic band gap,as well as the spatial distribution of the local density of states.The experimental STS band gap of GNRs is about 2 eV,which is very close to 2.35 eV predicted by the density functional theory simulations with GW correction,indicating a weak screening effect of InAs(110)substrate.Furthermore,several aspects of GNR-InAs(110)substrate interactions were also probed and analyzed,including GNR tunable transparency,alignment to the substrate,and manipulations of GNR position by the STM tip.The weak interaction between the GNRs and the InAs(110)surface makes InAs(110)an ideal substrate for investigating the intrinsic properties of GNRs.Because of the reduced energy band gap of these ribbons,the GNR thin films exhibit appreciably high electrical conductivity and on/off ratios of about 10 in field-effect transistor measurements,suggesting their promise for device applications.
基金supported by the National Natural Science Foundation of China (Nos.91127043,21273051,20911130229)the National Basic Research Program of China (Nos.2011CB932800,2009CB930100)the Chinese Academy of Sciences (No.KJCX2-YW-M15).
文摘The assembly of amyloid peptides into highly organized fibrils is one of the major characteristics of many de-generative diseases such as Alzheimer’s disease and type II diabetes.Assembly structures of amyloid peptides at liquid-solid interface can be visualized by scanning tunneling microscopy(STM)with site-specific resolution.The STM analysis can provide valuable information on the folding mechanism of amyloid peptides based on the corre-lation of surface assembly structures and fibrillation behaviors.Cases on mutational analysis of amyloid peptides by STM are also reviewed which illustrate the capacities of STM studies on amyloid assemblies.
基金the National Basic Research Program of China(Nos.2017YFA0205000 and 2016YFA0200700)the National Natural Science Foundation of China(Nos.21773041,21972031,21301092,and 20962002)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB36000000).
文摘Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF(n=1,2)/PC71BM donor-acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy(STM),scanning tunneling spectroscopy(STS),density functional theory(DFT)calculations,and transient absorption(TA)spectroscopy.The results show that BTID-1F and BTID-2F form bright strip structures,whereas BTID-nF(n=1,2)/PC71BM form ridge-like structures with each complex composed of one BTID-nF(n=1,2)molecule and four PC71BM molecules which adsorbed around the BTID-nF(n=1,2)molecule by S···πinteraction.With the assistance of S···πinteraction between BTID-nF(n=1,2)and PC71BM,BTID-nF(n=1,2)/PC71BM co-assembled ridge-like structures are more stable than the BTID-nF(n=1,2)ridge structures.To investigate the charge transfer of BTID-nF(n=1,2)/PC71BM system,STS measurements,DFT calculation,and TA spectroscopy are further performed.The results show that charge transfer occurs in BTID-nF(n=1,2)/PC71BM system with the electron transferring from BTID-nF(n=1,2)molecules to PC71BM.
文摘The peptide assembly structures of polyglutamine (PolyQ) have been studied by using scanning tunneling microscopy (STM) with high spatial resolution in ambient conditions. 4,4'-Bipyridyl (4Bpy) was introduced into the PolyQ7 and PolyQ8 peptide assemblies for labeling the C-termini of the peptides. The fine structures of the 4Bpy-PolyQ7 and 4Bpy-PolyQ8 co-assemblies are observed, and the statistics of the apparent peptide strand length reveal different length distributions for PolyQ7 and PolyQs. One predominant apparent peptide strand length is ob- served for PolyQ7 reflecting one predominant peptide conformation in assembly structures, while three major ap- parent strand lengths can be identified with PolyQ8 reflecting three co-existing peptide conformations in peptide as- semblies. Such drastic difference in assembling characteristics can be considered as a reflection of asymmetric ad- sorption effect ofpeptides relating to odd-even residue numbers of PolyQ7 and PolyQ8,
基金the National Natural Science Foundation of China(90406019,20573116,and 20673029)the National Basic Research Program of China(973 Program,2006CB932100).
文摘The assembling behavior and electronic properties of asymmetric tris(phthalocyaninato)lutetium triple-decker sandwich complex molecules(Lu2Pc3)on highly oriented pyrolytic graphite(HOPG)surfaces have been studied by scanning tunneling microscopy/spectroscopy(STM/STS)methods.Phase transitions were observed at different bias polarities,involving an ordered packing arrangement with fourfold symmetry at negative bias and an amorphous arrangement at positive bias.Molecular switching behaviour for individual Lu2Pc3 molecules was reported here according to the bias-polarity-induced flipping phenomena and the peak shift in dI/dV versus V curves at different voltage scanning directions.The sensitive response of the strong intrinsic molecular dipole to an external electric field is proposed to be responsible for molecular switching of Lu_(2)Pc_(3)at the solid/liquid interface.
基金supported by the Ministry of Science and Technology (Nos.2018YFA0306003,2017YFA0205003)National Natural Science Foundation of China (No.21972002)supported by High-performance Computing Platform of Peking University
文摘The self-assembly of L-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope(STM) at 4.4 K.When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer,molecular trimers,tetramers,hexamers,and chains coexist on Cu(111).Then almost all molecules self-assemble into chiral hexamers after being annealed at room temperature.When increasing molecular coverage to the full layer,a new type of chain is observed on the surface.Based on the high-resolution STM images at sub-molecular level,we suggest that the L-tryptophan molecules are present in neutral,zwitterionic or anionic states in these structures.
基金supported by the National Basic Re-search Program of China (Nos.2011CB932303,2013CB934203)The National Natural Science Foun-dation of China (Nos.51173031,91127043,21472029)is also gratefully acknowledged.
文摘In this review, supramolecular coordination processes on two-dimensional (2D) surfaces or interfaces observed by scanning tunneling microscopy (STM) are discussed. Four parts are mainly involved, which include (1) recognition of Fe^(3+) through functional molecular networks, (2) K^(+)-induced switching of valinomycin, (3) supramolecular coordination happened in a nano-reactor, (4) reversible 2D supramolecular spring driven by coordination. The direct insight of the coordination phenomena provided by STM supplements our knowledge of its mechanism. Since different building blocks can be connected into a whole part through coordination, the understanding of its mechanism will be beneficial to the future design of molecular 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.