Developments in advanced manufacturing have promoted the miniaturization of semiconductor electronic devices to a near-atomic scale,which continuously follows the‘top-down’construction method.However,huge challenges...Developments in advanced manufacturing have promoted the miniaturization of semiconductor electronic devices to a near-atomic scale,which continuously follows the‘top-down’construction method.However,huge challenges have been encountered with the exponentially increased cost and inevitably prominent quantum effects.Molecular electronics is a highly interdisciplinary subject that studies the quantum behavior of electrons tunneling in molecules.It aims to assemble electronic devices in a‘bottom-up’manner on this scale through a single molecule,thereby shedding light on the future design of logic circuits with new operating principles.The core technologies in this field are based on the rapid development of precise fabrication at a molecular scale,regulation at a quantum scale,and related applications of the basic electronic component of the‘electrode-molecule-electrode junction’.Therefore,the quantum charge transport properties of the molecule can be controlled to pave the way for the bottom-up construction of single-molecule devices.The review firstly focuses on the collection and classification of the construction methods for molecular junctions.Thereafter,various characterization and regulation methods for molecular junctions are discussed,followed by the properties based on tunneling theory at the quantum scale of the corresponding molecular electronic devices.Finally,a summary and perspective are given to discuss further challenges and opportunities for the future design of electronic devices.展开更多
Metallic clusters,ranging from 1 to 2 nm in size,have emerged as promising candidates for creating nanoelectronic devices at the single-cluster level.With the intermediate quantum properties between metals and semicon...Metallic clusters,ranging from 1 to 2 nm in size,have emerged as promising candidates for creating nanoelectronic devices at the single-cluster level.With the intermediate quantum properties between metals and semiconductors,these metallic clusters offer an alternative pathway to silicon-based electronics and organic molecules for miniaturized electronics with dimensions below 5 nm.Significant progress has been made in studies of single-cluster electronic devices.However,a clear guide for selecting,synthesizing,and fabricating functional single-cluster electronic devices is still required.This review article provides a comprehensive overview of single-cluster electronic devices,including the mechanisms of electron transport,the fabrication of devices,and the regulations of electron transport properties.Furthermore,we discuss the challenges and future directions for single-cluster electronic devices and their potential applications.展开更多
Charge transport characterization of single-molecule junctions is essential for the fundamental research of single-molecule physical chemistry and the development towards single-molecule electronic devices and circuit...Charge transport characterization of single-molecule junctions is essential for the fundamental research of single-molecule physical chemistry and the development towards single-molecule electronic devices and circuits. Among the single-molecule conductance characterization techniques,the single-molecule break junction technique is widely used in tens of worldwide research laboratories which can generate a large amount of experimental data from thousands of individual measurement cycles. However,data interpretation is a challenging task for researchers with different research backgrounds,and the different data analysis approaches sometimes lead to the misunderstanding of the measurement data and even reproducibility issues of the measurement. It is thus a necessity to develop a user-friendly all-in-one data analysis tool that automatizes the basic data analysis in a standard and widely accepted way. In this work,we present the XMe Code (Xiamen Molecular Electronics Code),an intelligent all-in-one data analysis tool for the comprehensive analysis of single-molecule break junction data. XMe code provides end-to-end data analysis that takes in the original experimental data and returns electronic characteristics and even charge transport mechanisms. We believe that XMe Code will promote the transparency of the data analysis in single-molecule electronics and the collaborations among scientists with different research backgrounds.展开更多
Folding of molecules is an essential process in nature,and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations.The electric field offers a unique...Folding of molecules is an essential process in nature,and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations.The electric field offers a unique strategy to drive the folding of molecular conformation and to control charge transport through single molecules but remains unexplored.The single-molecule break junction technique provides access to detect the conformational changes via the monitoring of single-molecule conductance,and the electric field between two metal electrodes with nanoscale spacing can provide an extremely strong to achieve in-situ control and detection of molecular folding at the single-molecule level.Here,we use the electric field to control the single-molecule folding using the scanning tunneling microscope break junction(STM-BJ)technique.The electric fields induced folding could lead to a∼1400%conductance change of the single-molecule junctions,and the folding/unfolding process can be in-situ switched at the scale of milliseconds.DFT calculations suggest the conformational control originates from the electric fieldinduced charge injection,and the formation of homoconjugated conformation with the overlapped orbitals.This work provides the first demonstration of electric field-driven molecular folding,which is essential for the understanding of molecular machines in nature and for the design of artificial molecular machines.展开更多
Neural network pruning is a popular approach to reducing the computational complexity of deep neural networks.In recent years,as growing evidence shows that conventional network pruning methods employ inappropriate pr...Neural network pruning is a popular approach to reducing the computational complexity of deep neural networks.In recent years,as growing evidence shows that conventional network pruning methods employ inappropriate proxy metrics,and as new types of hardware become increasingly available,hardware-aware network pruning that incorporates hardware characteristics in the loop of network pruning has gained growing attention,Both network accuracy and hardware efficiency(latency,memory consumption,etc.)are critical objectives to the success of network pruning,but the conflict between the multiple objectives makes it impossible to find a single optimal solution.Previous studies mostly convert the hardware-aware network pruning to optimization problems with a single objective.In this paper,we propose to solve the hardware-aware network pruning problem with Multi-Objective Evolutionary Algorithms(MOEAs).Specifically,we formulate the problem as a multi-objective optimization problem,and propose a novel memetic MOEA,namely HAMP,that combines an efficient portfoliobased selection and a surrogate-assisted local search,to solve it.Empirical studies demonstrate the potential of MOEAs in providing simultaneously a set of alternative solutions and the superiority of HAMP compared to the state-of-the-art hardware-aware network pruning method.展开更多
Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed du...Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed due to the more rapid decay of the tunneling conductance in theσ-system compared to that in theπ-system.Here,we demonstrate that dominantσ-transport can be observed inπ-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique(STM-BJ).We have found that the conductance of meta-connected picolinic acid,which mainly occurs byσ-transport,is∼35 times higher than that of its para-isomer,which is entirely different from what is expected fromπ-transport through these systems.Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory(DFT)shows that theσ-system provides the dominant transport path.These results reveal that theσ-electrons,rather than theπ-electrons,can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale,and this provides a new avenue toward the future miniaturization of molecular devices and materials.展开更多
Benefiting from the development of molecular electronics and molecular plasmonics, the interplay of light and electronic transport in molecular junctions has attracted growing interest among researchers in both fields...Benefiting from the development of molecular electronics and molecular plasmonics, the interplay of light and electronic transport in molecular junctions has attracted growing interest among researchers in both fields, leading to a new research direction of "single-molecule optoelectronics". Here, we review the latest developments of photo-modulated charge transport,electroluminescence and Raman spectroscopy from single-molecule junctions, and suggest future directions for single-molecule optoelectronics.展开更多
In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By emp...In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.展开更多
Molecular rectifier, as a basic function of molecular electronic devices, has attracted extensive attention for the opportunity in constructing sub-nanometer electronic devices. However, tunneling leakage current has ...Molecular rectifier, as a basic function of molecular electronic devices, has attracted extensive attention for the opportunity in constructing sub-nanometer electronic devices. However, tunneling leakage current has a significant contribution as electronic devices shrink in size, which leads to a challenge in fabricating molecular rectifiers at the sub-nanometer scale. Here, we experimentally demonstrate a sub-nanometer molecular rectifier based on the supramolecular junction assembled between water and 1,4-diazabicyclo[2.2.2]octane (DABCO) molecule. The charge transport through DABCO and corresponding supramolecular junctions exhibits destructive σ-interference, ensuring a sharp conductance variation for transmission modulation. The supramolecular interaction between DABCO and water readily introduces the asymmetric electrode-molecule interaction, which combines with the destructive σ-interference to support the sub-nanometer rectification.展开更多
The conductance through single-molecule junctions characterized by the break junction techniques consists of the through-space tunneling and through-molecule tunneling conductance, and the existence of through-space t...The conductance through single-molecule junctions characterized by the break junction techniques consists of the through-space tunneling and through-molecule tunneling conductance, and the existence of through-space tunneling between the electrodes makes the quantitative extraction of the intrinsic molecular signals of single-molecule junctions challenging. Here, we established an analytic model to describe the evolution of the conductance of a single molecule in break junction measurements. The experimental data for a series of oligo(aryleneethynylene) derivatives validate the proposed model, which provides a modeling insight into the conductance evolution for the opening process in a "real" break junction experiment. Further modulations revealed that the junction formation probability and rupture distance of the molecular junction, which reflect the junction stability, will significantly influence the amplitude and position of the obtained conductance peak. We further extend our model to a diffusion and a chemical reaction process, for which the simulation results show that the break junction technique offers a quantitative understanding of these time-dependent systems, suggesting the potential of break junction techniques in the quantitative characterization of physical and chemical processes at the single-molecule scale.展开更多
Single-molecule devices,which are fabricated by the single molecule bridged through electrodes,provide a promising approach to investigate the intrinsic chemical or physical properties of individual molecules.Beyond t...Single-molecule devices,which are fabricated by the single molecule bridged through electrodes,provide a promising approach to investigate the intrinsic chemical or physical properties of individual molecules.Beyond the studies of single-molecule wires,a large number of responsive single-molecule junctions or devices with unique chemical or physical properties have been designed and fabricated by introducing the external field,which further offers the chance to explore conductive materials at the molecular level.Here,we summarized the latest studies on the behaviors of single-molecule devices based on the photon,thermal,electric,or magnetic responses,and discussed the development of responsive single-molecule devices in prospect.展开更多
The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level,but also brings opportunities for ...The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level,but also brings opportunities for the development of single-molecule optoelectronic devices.Understanding the interaction mechanisms between molecules and nanocavities is essential to obtain ondemand properties in devices by artificial design,since molecules in junctions exhibit unique behaviors of excited states benefited from the structures of metallic nanocavities.Here,we review the excitation mechanisms involved in the interplay between molecules and plasmonic nanocavities,and reveal the influence of nanostructures on excited-state properties by demonstrating the differences in excited state decay processes.Furthermore,vibronic transitions of molecules between nanoelectrodes are also discussed,offering a new single-molecule characterization method.Finally,we provide the potential applications and challenges in single-molecule optoelectronic devices and the possible directions in exploring the underlying mechanisms of photophysical and photochemical processes.展开更多
Charge transport across the peptide chains is one of the vital processes in the biological systems,so understanding their charge transport properties is an indispensable prerequisite to explain the complex biochemical...Charge transport across the peptide chains is one of the vital processes in the biological systems,so understanding their charge transport properties is an indispensable prerequisite to explain the complex biochemical phenomenon.Here,we review the charge transport mechanism,the influence of the special groups and the experimental conditions on the charge transport through the peptide backbone by employing the single-molecule electrical measurements.Besides,we further review the recent progresses in charge transport properties of supramolecular interaction among the adjacent peptide chains.Finally,we discuss some experimental and theoretical contradictions existing in the charge transport through peptides and provide new inspiration for the future development of the bioelectronics at the single-molecule scale.展开更多
Plasmonic optical manipulation has emerged as an affordable alternative to manipulate single chemical and biological molecules in nanoscience.Although the theoretical models of sub-5 nm single-molecule trapping have b...Plasmonic optical manipulation has emerged as an affordable alternative to manipulate single chemical and biological molecules in nanoscience.Although the theoretical models of sub-5 nm single-molecule trapping have been considered promising,the experimental strategies remain a challenge due to the Brownian motions and weak optical gradient forces with significantly reduced molecular polarizability.Herein,we address direct trapping and in situ sensing of single molecules with unprecedented size,down to∼5Åin solution,by employing an adjustable plasmonic optical nanogap and single-molecule conductance measurement.The theoretical simulations demonstrate that local fields with a high enhancement factor,over 103,were generated at such small nanogaps,resulting in optical forces as large as several piconewtons to suppress the Brownian motion and trap a molecule of length sub-1 nm.This work demonstrates a strategy for directly manipulating the small molecule units,promising a vast multitude of applications in chemical,biological,and materials sciences at the single-molecule level.展开更多
The quantum interference effect in the charge transport through single-phenyl molecules received intensive interests from theory but remained as an experimental challenge. In this paper, we investigated the charge tra...The quantum interference effect in the charge transport through single-phenyl molecules received intensive interests from theory but remained as an experimental challenge. In this paper, we investigated the charge transport through single-molecule benzene dithiol （BDT） junction with different connectivities using mechanically controllable break.junction （MCB]） technique. By further improving the mechanical stability and the electronic measuring component of the MCBJ set-up, we obtained the conductance histograms of BDT molecules （BDTs） from the statistical analysis of conductance-distance traces without data selection. By tuning the connectivity, the conductance of BDTs is determined to be 10-12Go, 10-22Go and 10-10Go for pcra, meta, and ortho connectivity, following the trend that ortfio-BDT 〉 para-BDT 〉 meta-BDT. Furthermore, the displacements of the junctions followed the trend that para 〉 meta 〉 ortho, suggesting the charge transport through the molecules via the gold-thiol bond. The different trends between conductance and displacement for different connectivities suggests the presence of destructive quantum interference effect on meta-BDT, which provides the experimental evidence for the quantum interference effect through single-phenyl molecular junctions.展开更多
Electronic coupling between individual building blocks plays an essential role in charge transport through molecular materials and devices.However,the investigation of the transmission mechanism in charge transport vi...Electronic coupling between individual building blocks plays an essential role in charge transport through molecular materials and devices.However,the investigation of the transmission mechanism in charge transport via intramolecular coupling remains challenging.Herein,we demonstrate the transition of the intramolecular through-bond and through-space coupling in a single-molecule junction with a family of diketopyrrolopyrrole(DPP)derivative by varying intramolecular donor–acceptor(D–A)interactions.The transition is accomplished by regulating D–A interactions by inserting different aromatic rings inside,leading to two orders of magnitude difference of the single-molecule conductance.The flicker noise analysis demonstrates that the conductance difference arises from the control of the contribution between through-bond and through-space coupling.These findings are further supported by the calculation that the intramolecular coupling among molecular building blocks correlates with the D–A interaction,providing a promising way to regulate the contribution between through-bond and through-space coupling in the charge transport through molecular materials and devices.展开更多
State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level.Experimentally, molecular electronics face two primary challenges. One challenge is th...State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level.Experimentally, molecular electronics face two primary challenges. One challenge is the reliable construction of single-molecule junctions, and the second challenge is the arbitrary modulation of electron transport through these junctions. Over the past decades, electrochemistry has been widely adopted to meet these challenges, leading to a wealth of novel findings. This review starts from the application of electrochemical methods to the fabrication of nanogaps, which is an essential platform for the construction of single-molecule junctions. The utilization of electrochemistry for the modification of molecular junctions,including terminal groups and structural backbones, is introduced, and finally, recent progress in the electrochemical modulation of single-molecule electron transport is reviewed.展开更多
Recent years have witnessed the fabrication of various non-covalent interaction-based molecular electronic devices.In the noncovalent interaction-based molecular devices,the strength of the interfacial coupling betwee...Recent years have witnessed the fabrication of various non-covalent interaction-based molecular electronic devices.In the noncovalent interaction-based molecular devices,the strength of the interfacial coupling between molecule and electrode is weakened compared to that of the covalent interaction-based molecular devices,which provides wide applications in fabricating versatile molecular devices.In this review,we start with the methods capable of fabricating graphene-based nanogaps,and the following routes to construct non-covalent interaction-based molecular junctions with graphene electrodes.Then we give an introduction to the reported non-covalent interaction-based molecular devices with graphene electrodes equipped with different electrical functions.Moreover,we summarize the recent progress in the design and fabrication of new-type molecular devices based on graphene and graphene-like two-dimensional(2D)materials.The review ends with a prospect on the challenges and opportunities of non-covalent interaction-based molecular electronics in the near future.展开更多
基金supported by the National Natural Science Foundation of China(Nos.22173075,21933012,31871877)the National Key Research and Development Program of China(2017YFA0204902)the Fundamental Research Funds for the Central Universities(Nos.20720200068,20720190002).
文摘Developments in advanced manufacturing have promoted the miniaturization of semiconductor electronic devices to a near-atomic scale,which continuously follows the‘top-down’construction method.However,huge challenges have been encountered with the exponentially increased cost and inevitably prominent quantum effects.Molecular electronics is a highly interdisciplinary subject that studies the quantum behavior of electrons tunneling in molecules.It aims to assemble electronic devices in a‘bottom-up’manner on this scale through a single molecule,thereby shedding light on the future design of logic circuits with new operating principles.The core technologies in this field are based on the rapid development of precise fabrication at a molecular scale,regulation at a quantum scale,and related applications of the basic electronic component of the‘electrode-molecule-electrode junction’.Therefore,the quantum charge transport properties of the molecule can be controlled to pave the way for the bottom-up construction of single-molecule devices.The review firstly focuses on the collection and classification of the construction methods for molecular junctions.Thereafter,various characterization and regulation methods for molecular junctions are discussed,followed by the properties based on tunneling theory at the quantum scale of the corresponding molecular electronic devices.Finally,a summary and perspective are given to discuss further challenges and opportunities for the future design of electronic devices.
基金supported by the National Natural Science Foundation of China(Nos.22250003,22173075,21933012,and 22003052)the Fundamental Research Funds for the Central Universities(Nos.20720220020,20720220072,and 20720200068).
文摘Metallic clusters,ranging from 1 to 2 nm in size,have emerged as promising candidates for creating nanoelectronic devices at the single-cluster level.With the intermediate quantum properties between metals and semiconductors,these metallic clusters offer an alternative pathway to silicon-based electronics and organic molecules for miniaturized electronics with dimensions below 5 nm.Significant progress has been made in studies of single-cluster electronic devices.However,a clear guide for selecting,synthesizing,and fabricating functional single-cluster electronic devices is still required.This review article provides a comprehensive overview of single-cluster electronic devices,including the mechanisms of electron transport,the fabrication of devices,and the regulations of electron transport properties.Furthermore,we discuss the challenges and future directions for single-cluster electronic devices and their potential applications.
基金supported by the National Natural Science Foundation of China(22325303,21973079,22032004)the National Key R&D Program of China(2017YFA0204902)+2 种基金the Fundamental Research Funds for the Central Universities in China(Xiamen University,20720190002)IRTSTFJ,National Science Foundation of Fujian Province(2018J06004)Beijing National Laboratory for Molecular Sciences(BNLMS202005).
文摘Charge transport characterization of single-molecule junctions is essential for the fundamental research of single-molecule physical chemistry and the development towards single-molecule electronic devices and circuits. Among the single-molecule conductance characterization techniques,the single-molecule break junction technique is widely used in tens of worldwide research laboratories which can generate a large amount of experimental data from thousands of individual measurement cycles. However,data interpretation is a challenging task for researchers with different research backgrounds,and the different data analysis approaches sometimes lead to the misunderstanding of the measurement data and even reproducibility issues of the measurement. It is thus a necessity to develop a user-friendly all-in-one data analysis tool that automatizes the basic data analysis in a standard and widely accepted way. In this work,we present the XMe Code (Xiamen Molecular Electronics Code),an intelligent all-in-one data analysis tool for the comprehensive analysis of single-molecule break junction data. XMe code provides end-to-end data analysis that takes in the original experimental data and returns electronic characteristics and even charge transport mechanisms. We believe that XMe Code will promote the transparency of the data analysis in single-molecule electronics and the collaborations among scientists with different research backgrounds.
基金the National Natural Science Foundation of China(Nos.22250003 and 22205084)National Key R&D Program of China(No.2017YFA0204902).
文摘Folding of molecules is an essential process in nature,and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations.The electric field offers a unique strategy to drive the folding of molecular conformation and to control charge transport through single molecules but remains unexplored.The single-molecule break junction technique provides access to detect the conformational changes via the monitoring of single-molecule conductance,and the electric field between two metal electrodes with nanoscale spacing can provide an extremely strong to achieve in-situ control and detection of molecular folding at the single-molecule level.Here,we use the electric field to control the single-molecule folding using the scanning tunneling microscope break junction(STM-BJ)technique.The electric fields induced folding could lead to a∼1400%conductance change of the single-molecule junctions,and the folding/unfolding process can be in-situ switched at the scale of milliseconds.DFT calculations suggest the conformational control originates from the electric fieldinduced charge injection,and the formation of homoconjugated conformation with the overlapped orbitals.This work provides the first demonstration of electric field-driven molecular folding,which is essential for the understanding of molecular machines in nature and for the design of artificial molecular machines.
基金the National Natural Science Foundation of China(62106098)the Stable Support Plan Program of Shenzhen Natural Science Fund(20200925154942002)the M0E University Scientific-Technological Innovation Plan Program.
文摘Neural network pruning is a popular approach to reducing the computational complexity of deep neural networks.In recent years,as growing evidence shows that conventional network pruning methods employ inappropriate proxy metrics,and as new types of hardware become increasingly available,hardware-aware network pruning that incorporates hardware characteristics in the loop of network pruning has gained growing attention,Both network accuracy and hardware efficiency(latency,memory consumption,etc.)are critical objectives to the success of network pruning,but the conflict between the multiple objectives makes it impossible to find a single optimal solution.Previous studies mostly convert the hardware-aware network pruning to optimization problems with a single objective.In this paper,we propose to solve the hardware-aware network pruning problem with Multi-Objective Evolutionary Algorithms(MOEAs).Specifically,we formulate the problem as a multi-objective optimization problem,and propose a novel memetic MOEA,namely HAMP,that combines an efficient portfoliobased selection and a surrogate-assisted local search,to solve it.Empirical studies demonstrate the potential of MOEAs in providing simultaneously a set of alternative solutions and the superiority of HAMP compared to the state-of-the-art hardware-aware network pruning method.
基金supported by the National Natural Science Foundation of China(21722305,21673195,21973079,and 21703188)the National Key R&D Program of China(2017YFA0204902)the Guangdong Basic and Applied Basic Research Foundation(2020A151511106).
文摘Quantum tunneling conductance of molecular junctions originates from the charge transport through theπ-orbitals(π-transport)and theσ-orbitals(σ-transport)of the molecules,but theσ-transport can not be observed due to the more rapid decay of the tunneling conductance in theσ-system compared to that in theπ-system.Here,we demonstrate that dominantσ-transport can be observed inπ-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique(STM-BJ).We have found that the conductance of meta-connected picolinic acid,which mainly occurs byσ-transport,is∼35 times higher than that of its para-isomer,which is entirely different from what is expected fromπ-transport through these systems.Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory(DFT)shows that theσ-system provides the dominant transport path.These results reveal that theσ-electrons,rather than theπ-electrons,can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale,and this provides a new avenue toward the future miniaturization of molecular devices and materials.
基金supported by the National Key R&D Program of China (2017YFA0204901, 2017YFA0204902)the National Natural Science Foundation of China (21673195, 61571242, 21503179, 21727806, 21722305)the Young Thousand Talent Project of China
文摘Benefiting from the development of molecular electronics and molecular plasmonics, the interplay of light and electronic transport in molecular junctions has attracted growing interest among researchers in both fields, leading to a new research direction of "single-molecule optoelectronics". Here, we review the latest developments of photo-modulated charge transport,electroluminescence and Raman spectroscopy from single-molecule junctions, and suggest future directions for single-molecule optoelectronics.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （Nos. 21503179, 21403181, 61573295, 21522508, 21673195, 21533006, and 61071010）, the National Basic Research Program of China （No. 2015CB932300）, the Natural Science Foundation of Fujian Province （No. 2016J05162）, the Fundamental Research Funds for the Central Universities in China （Xiamen University, Nos. 20720170035 and 20720160092）, and the Young Thousand Talent Project of China.
文摘In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.
基金This work was supported by the National Natural Science Foundation of China(21673195,21722305,21703188,U1705254,21933012,31871877)the National Key R&D Program of China(2017YFA0204902),the Fundamental Research Funds for the Central Universities(20720200068)the Fundamental Research Funds for Xiamen University(20720190002).
文摘Molecular rectifier, as a basic function of molecular electronic devices, has attracted extensive attention for the opportunity in constructing sub-nanometer electronic devices. However, tunneling leakage current has a significant contribution as electronic devices shrink in size, which leads to a challenge in fabricating molecular rectifiers at the sub-nanometer scale. Here, we experimentally demonstrate a sub-nanometer molecular rectifier based on the supramolecular junction assembled between water and 1,4-diazabicyclo[2.2.2]octane (DABCO) molecule. The charge transport through DABCO and corresponding supramolecular junctions exhibits destructive σ-interference, ensuring a sharp conductance variation for transmission modulation. The supramolecular interaction between DABCO and water readily introduces the asymmetric electrode-molecule interaction, which combines with the destructive σ-interference to support the sub-nanometer rectification.
基金supported by the National Key R&D Project of China(2017YFA0204902)the National Natural Science Foundation of China(21722305,21673195,21703188,21790360)the Youth Innovation Promotion Association CAS(2015024)
文摘The conductance through single-molecule junctions characterized by the break junction techniques consists of the through-space tunneling and through-molecule tunneling conductance, and the existence of through-space tunneling between the electrodes makes the quantitative extraction of the intrinsic molecular signals of single-molecule junctions challenging. Here, we established an analytic model to describe the evolution of the conductance of a single molecule in break junction measurements. The experimental data for a series of oligo(aryleneethynylene) derivatives validate the proposed model, which provides a modeling insight into the conductance evolution for the opening process in a "real" break junction experiment. Further modulations revealed that the junction formation probability and rupture distance of the molecular junction, which reflect the junction stability, will significantly influence the amplitude and position of the obtained conductance peak. We further extend our model to a diffusion and a chemical reaction process, for which the simulation results show that the break junction technique offers a quantitative understanding of these time-dependent systems, suggesting the potential of break junction techniques in the quantitative characterization of physical and chemical processes at the single-molecule scale.
基金This work was supported by the National Natural Science Foundation of China(Nos.21722305,21673195)the National Key R&D Program of China(2017YFA0204902)the Fundamental Research Funds for the Central Universities in China(Xiamen University)(20720190002).
文摘Single-molecule devices,which are fabricated by the single molecule bridged through electrodes,provide a promising approach to investigate the intrinsic chemical or physical properties of individual molecules.Beyond the studies of single-molecule wires,a large number of responsive single-molecule junctions or devices with unique chemical or physical properties have been designed and fabricated by introducing the external field,which further offers the chance to explore conductive materials at the molecular level.Here,we summarized the latest studies on the behaviors of single-molecule devices based on the photon,thermal,electric,or magnetic responses,and discussed the development of responsive single-molecule devices in prospect.
基金supported by the National Natural ScienceFoundation of China (Nos. 22173075, 21933012 and 31871877)the National Key R&D Program of China (No. 2017YFA0204902)+1 种基金the Fundamental Research Funds for the Central Universities(Nos. 20720200068 and 20720190002)the Beijing NationalLaboratory for Molecular Sciences (No. BNLMS202005).
文摘The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level,but also brings opportunities for the development of single-molecule optoelectronic devices.Understanding the interaction mechanisms between molecules and nanocavities is essential to obtain ondemand properties in devices by artificial design,since molecules in junctions exhibit unique behaviors of excited states benefited from the structures of metallic nanocavities.Here,we review the excitation mechanisms involved in the interplay between molecules and plasmonic nanocavities,and reveal the influence of nanostructures on excited-state properties by demonstrating the differences in excited state decay processes.Furthermore,vibronic transitions of molecules between nanoelectrodes are also discussed,offering a new single-molecule characterization method.Finally,we provide the potential applications and challenges in single-molecule optoelectronic devices and the possible directions in exploring the underlying mechanisms of photophysical and photochemical processes.
基金This work was supported by the National Key R&D Program of China(No.2017YFA0204902)the National Natural Science Foundation of China(Nos.21673195,21503179,61573295,21703188,21722305)Post-Doctoral Science Foundation of China(No.2018M632582).
文摘Charge transport across the peptide chains is one of the vital processes in the biological systems,so understanding their charge transport properties is an indispensable prerequisite to explain the complex biochemical phenomenon.Here,we review the charge transport mechanism,the influence of the special groups and the experimental conditions on the charge transport through the peptide backbone by employing the single-molecule electrical measurements.Besides,we further review the recent progresses in charge transport properties of supramolecular interaction among the adjacent peptide chains.Finally,we discuss some experimental and theoretical contradictions existing in the charge transport through peptides and provide new inspiration for the future development of the bioelectronics at the single-molecule scale.
基金supported by the National Natural Science Foundation of China(grant nos.T2222002,21973079,22032004,92161118,12174324,21991130,and 21905238)the Ministry of Science and Technology of the People’s Republic of China(grant no.2021YFA1201502)the Natural Science Foundation of Fujian Province(grant no.2021J06008).
文摘Plasmonic optical manipulation has emerged as an affordable alternative to manipulate single chemical and biological molecules in nanoscience.Although the theoretical models of sub-5 nm single-molecule trapping have been considered promising,the experimental strategies remain a challenge due to the Brownian motions and weak optical gradient forces with significantly reduced molecular polarizability.Herein,we address direct trapping and in situ sensing of single molecules with unprecedented size,down to∼5Åin solution,by employing an adjustable plasmonic optical nanogap and single-molecule conductance measurement.The theoretical simulations demonstrate that local fields with a high enhancement factor,over 103,were generated at such small nanogaps,resulting in optical forces as large as several piconewtons to suppress the Brownian motion and trap a molecule of length sub-1 nm.This work demonstrates a strategy for directly manipulating the small molecule units,promising a vast multitude of applications in chemical,biological,and materials sciences at the single-molecule level.
基金supported by the Ministry of Science and Technology of China(No. SQ2017YFJC020081)the National Natural Science Foundation of China(Nos. 21673195,21503179)+2 种基金Fundamental Research Funds for the Central Universities in China (Xiamen University: No. 20720170035)Natural Science Foundation of Fujian Province(No. 2016J05162)the Young Thousand Talent Project of China
文摘The quantum interference effect in the charge transport through single-phenyl molecules received intensive interests from theory but remained as an experimental challenge. In this paper, we investigated the charge transport through single-molecule benzene dithiol （BDT） junction with different connectivities using mechanically controllable break.junction （MCB]） technique. By further improving the mechanical stability and the electronic measuring component of the MCBJ set-up, we obtained the conductance histograms of BDT molecules （BDTs） from the statistical analysis of conductance-distance traces without data selection. By tuning the connectivity, the conductance of BDTs is determined to be 10-12Go, 10-22Go and 10-10Go for pcra, meta, and ortho connectivity, following the trend that ortfio-BDT 〉 para-BDT 〉 meta-BDT. Furthermore, the displacements of the junctions followed the trend that para 〉 meta 〉 ortho, suggesting the charge transport through the molecules via the gold-thiol bond. The different trends between conductance and displacement for different connectivities suggests the presence of destructive quantum interference effect on meta-BDT, which provides the experimental evidence for the quantum interference effect through single-phenyl molecular junctions.
基金supported by Natural Science Foundation of China(nos.21722305,21673195,21703188,51733004,and 51525303)the National Key R&D Program of China(nos.2017YFA0204902 and 2017YFA0204903)+1 种基金the Beijing National Laboratory for Molecular Sciences(no.BNLMS202005)the China Postdoctoral Science Foundation(no.2017M622060).
文摘Electronic coupling between individual building blocks plays an essential role in charge transport through molecular materials and devices.However,the investigation of the transmission mechanism in charge transport via intramolecular coupling remains challenging.Herein,we demonstrate the transition of the intramolecular through-bond and through-space coupling in a single-molecule junction with a family of diketopyrrolopyrrole(DPP)derivative by varying intramolecular donor–acceptor(D–A)interactions.The transition is accomplished by regulating D–A interactions by inserting different aromatic rings inside,leading to two orders of magnitude difference of the single-molecule conductance.The flicker noise analysis demonstrates that the conductance difference arises from the control of the contribution between through-bond and through-space coupling.These findings are further supported by the calculation that the intramolecular coupling among molecular building blocks correlates with the D–A interaction,providing a promising way to regulate the contribution between through-bond and through-space coupling in the charge transport through molecular materials and devices.
基金supported by the Fundamental Research Funds for the Central Universities in China (Xiamen University: 20720170035)the National Natural Science Foundation of China (21503179, 61573295, 21722305)the Nation Key R&D Program of China (2017YFA0204902)
文摘State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level.Experimentally, molecular electronics face two primary challenges. One challenge is the reliable construction of single-molecule junctions, and the second challenge is the arbitrary modulation of electron transport through these junctions. Over the past decades, electrochemistry has been widely adopted to meet these challenges, leading to a wealth of novel findings. This review starts from the application of electrochemical methods to the fabrication of nanogaps, which is an essential platform for the construction of single-molecule junctions. The utilization of electrochemistry for the modification of molecular junctions,including terminal groups and structural backbones, is introduced, and finally, recent progress in the electrochemical modulation of single-molecule electron transport is reviewed.
基金the support from the National Natural Science Foundation of China(Nos.21973079 and 22032004)the National Key R&D Program of China(No.2017YFA0204902)the Fundamental Research Funds for the Central Universities(Xiamen University:No.20720190002).
文摘Recent years have witnessed the fabrication of various non-covalent interaction-based molecular electronic devices.In the noncovalent interaction-based molecular devices,the strength of the interfacial coupling between molecule and electrode is weakened compared to that of the covalent interaction-based molecular devices,which provides wide applications in fabricating versatile molecular devices.In this review,we start with the methods capable of fabricating graphene-based nanogaps,and the following routes to construct non-covalent interaction-based molecular junctions with graphene electrodes.Then we give an introduction to the reported non-covalent interaction-based molecular devices with graphene electrodes equipped with different electrical functions.Moreover,we summarize the recent progress in the design and fabrication of new-type molecular devices based on graphene and graphene-like two-dimensional(2D)materials.The review ends with a prospect on the challenges and opportunities of non-covalent interaction-based molecular electronics in the near future.
