Using nonequilibrium Green's function formalism combined first-principles density functional theory, we analyze the transport properties of a 4,4-dimethyl-6-(4-nitrophenyl)-2-phenyl-3,5-diaza-bicyclo[3.1.0]hex-2-en...Using nonequilibrium Green's function formalism combined first-principles density functional theory, we analyze the transport properties of a 4,4-dimethyl-6-(4-nitrophenyl)-2-phenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene molecular optical switch. The title molecule can convert between closed and open forms by visible or ultraviolet irradiation. The I-V characteristics, differential conductance, on-off ratio, electronic transmission coefficients, spatial distribution of molecular projected self-consistent Hamiltonian orbitals, HOMO-LUMO gaps, effect of electrode materials Y(111)(Y =Au, Ag and Pt) on electronic transport and different molecular geometries corresponding to the closed and open forms through the molecular device are discussed in detail. Based on the results, as soon as possible the open form translates to the closed form, and there is a switch from the ON state to the OFF state(low resistance switches to high resistance). Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.展开更多
Exploring the charge transport properties and electronic functions of molecules is of primary interest in the area of molecular electronics.Conjugated polymers(CPs) represent an attractive class of molecular candida...Exploring the charge transport properties and electronic functions of molecules is of primary interest in the area of molecular electronics.Conjugated polymers(CPs) represent an attractive class of molecular candidates,benefiting from their outstanding optoelectronic properties.However,they have been less studied compared with the small-molecule family,mainly due to the difficulties in incorporating CPs into molecular junctions.In this review,we present a summary on how to fabricate CP-based singlechain and monolayered junctions,then discuss the transport behaviors of CPs in different junction architectures and finally introduce the potential applications of CPs in molecular-scale electronic devices.Although the research on CP-based molecular electronics is still at the initial stage,it is widely accepted that(1) CP chains are able to mediate long-range charge transport if their molecular electronic structures are properly designed,which makes them potential molecular wires,and(2) the intrinsic optoelectronic properties of CPs and the possibility of incorporating desirable functionalities by synthetic strategies imply the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.展开更多
The elastic scattering Green function method has been developed to describe the I-V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface ...The elastic scattering Green function method has been developed to describe the I-V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. An ab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.展开更多
Based on the nonequilibrium Green function method and density functional theory calculations, we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular...Based on the nonequilibrium Green function method and density functional theory calculations, we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular switch. The molecule comprises the switch which can exhibit different chiralities, that is, cis-form and trans-form by ultraviolet or visible irradiation. The results clearly reveal that the switching behaviors can be realized when the molecule converts between cis-form and trans-form. ~urthermore, the on-off ratio can be modulated by the chirality of the carbon nanotube electrodes. The maximum on-off ratio can reach 109 at 0.4 V for the armchair junction, suggesting potential applications of this type of junctions in future design of functional molecular devices.展开更多
Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challen...Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challenge.Here,we experimentally and theoretically investigated the charge transport characteristics of isoindigo(ISO)-molecules at the single-molecule level using the scanning tunneling microscope break junction technique.We find that the single-molecule junctions of ISO-molecules display bias voltage-driven switching characteristics.These switches are realtime,reversible,and nondestructive under low-bias voltages.Experimental results show that the mechanism of the switch is not the transition from nonresonant charge transport to resonant charge transport,but it is the shift of the frontier orbital energy levels of ISO-molecules and the change of the interfacial electronic coupling with bias voltage.Our results will advance the design of high-performance bias voltage-driven molecular switches.展开更多
The influence of InAs deposition thickness on the structural and optical properties of InAs/InA1As quantum wires (QWR) superlattices (SLS) was studied. The transmission electron microscopy (TEM) results show tha...The influence of InAs deposition thickness on the structural and optical properties of InAs/InA1As quantum wires (QWR) superlattices (SLS) was studied. The transmission electron microscopy (TEM) results show that with increasing the InAs deposited thickness, the size uniformity and spatial ordering of InAs QWR SLS was greatly improved, but threading dislocations initiated from InAs nanowires for the sample with 6 monolayers (MLs) InAs deposition. In addition, the zig-zag features along the extending direc- tion and lateral interlink of InAs nanowires were also observed. The InAs nanowires, especially for the first period, were laterally compact. These structural features may result in easy tunneling and coupling of charge carders between InAs nanowires and will hamper their device applications to some extent. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs, and for suppressing the formation of the threading dislocations in InAs QWR SLS.展开更多
In contrast to the static operations of conventional semiconductor devices,the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as...In contrast to the static operations of conventional semiconductor devices,the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as a molecular conformational switch or for molecular data storage.Bistable molecules such as those having two stable cis and trans isomeric confi gurations could provide,once clamped between two electrodes,a switching phenomenon in the non-equilibrium current response.Here,we model molecular switch junctions formed at silicon contacts and demonstrate the potential of such tunable molecular switches in electrode/molecule/electrode confi gurations.Using the non-equilibrium Green function(NEGF)approach implemented with the density-functional-based tight-binding(DFTB)theory,a series of properties such as electron transmissions,current voltage characteristics in the different isomer conformations,and potential energy surfaces(PESs)as a function of the reaction coordinates along the trans to cis transition were calculated for two azobenzene-based model compounds.Furthermore,in order to investigate the stability of molecular switches under ambient conditions,molecular dynamics(MD)simulations at room temperature were performed and time-dependent fl uctuations of the conductance along the MD pathways were calculated.Our numerical results show that the transmission spectra of the cis isomers are more conductive than trans counterparts inside the bias window for both model compounds.The currentvoltage characteristics consequently show the same trends.Additionally,calculations of the time-dependent transmission fluctuations along the MD pathways have shown that the transmission in the cis isomers is always signifi cantly larger than that in their trans counterparts,showing that molecular switches can be expected to work as robust molecular switching components.展开更多
By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Th...By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Three kinds of adsorption sites including the hollow, bridge and top sites are studied. The two forms of this molecule, namely the open form and the closed form, can reversibly switch from each other upon photoexcitation. Their transmission spectra are remarkably distinctive. Theoretical results show that the current of the closed form is always significantly larger than that of the open form for all three adsorption sites, which promises this system as possibly one of the good candidates for optical switches due to its unique advantage, and which may have some potential applications in the future molecular circuit.展开更多
基金Supported by the Damghan University,the Ferdowsi University of Mashhad and the Islamic Azad University of Shahrood
文摘Using nonequilibrium Green's function formalism combined first-principles density functional theory, we analyze the transport properties of a 4,4-dimethyl-6-(4-nitrophenyl)-2-phenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene molecular optical switch. The title molecule can convert between closed and open forms by visible or ultraviolet irradiation. The I-V characteristics, differential conductance, on-off ratio, electronic transmission coefficients, spatial distribution of molecular projected self-consistent Hamiltonian orbitals, HOMO-LUMO gaps, effect of electrode materials Y(111)(Y =Au, Ag and Pt) on electronic transport and different molecular geometries corresponding to the closed and open forms through the molecular device are discussed in detail. Based on the results, as soon as possible the open form translates to the closed form, and there is a switch from the ON state to the OFF state(low resistance switches to high resistance). Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.
基金the financial support from 985/211 Project(No.WF220411002)Shanghai Jiao Tong University and the national "1000-talent Plan(Youth)"
文摘Exploring the charge transport properties and electronic functions of molecules is of primary interest in the area of molecular electronics.Conjugated polymers(CPs) represent an attractive class of molecular candidates,benefiting from their outstanding optoelectronic properties.However,they have been less studied compared with the small-molecule family,mainly due to the difficulties in incorporating CPs into molecular junctions.In this review,we present a summary on how to fabricate CP-based singlechain and monolayered junctions,then discuss the transport behaviors of CPs in different junction architectures and finally introduce the potential applications of CPs in molecular-scale electronic devices.Although the research on CP-based molecular electronics is still at the initial stage,it is widely accepted that(1) CP chains are able to mediate long-range charge transport if their molecular electronic structures are properly designed,which makes them potential molecular wires,and(2) the intrinsic optoelectronic properties of CPs and the possibility of incorporating desirable functionalities by synthetic strategies imply the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.
基金the National Natural Science Foundation of China(Grant No.10274044)Shandong Science Foundation(Grant No.Y2000A03)the Foundation for Outstanding Teachers of the Education Ministry of China.
文摘The elastic scattering Green function method has been developed to describe the I-V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. An ab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.
基金Supported by the National Natural Science Foundation of China under Grant No 11004156the Natural Science Foundation of Shaanxi Province under Grant No 2014JM1025+2 种基金the Science and Technology Star Project of Shaanxi Province under Grant No2016KJXX-38the Special Foundation of Key Academic Subjects Development of Shaanxi Province under Grant No 2008-169the Xi'an Polytechnic University Young Scholar Supporting Plan under Grant No 2013-06
文摘Based on the nonequilibrium Green function method and density functional theory calculations, we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular switch. The molecule comprises the switch which can exhibit different chiralities, that is, cis-form and trans-form by ultraviolet or visible irradiation. The results clearly reveal that the switching behaviors can be realized when the molecule converts between cis-form and trans-form. ~urthermore, the on-off ratio can be modulated by the chirality of the carbon nanotube electrodes. The maximum on-off ratio can reach 109 at 0.4 V for the armchair junction, suggesting potential applications of this type of junctions in future design of functional molecular devices.
基金supported by the National Natural Science Foundation of China(grant nos.21875279,22075080,and 52273176)the Shanghai Municipal Science and Technology Major Project(grant no.2018SHZDZX03)the Fundamental Research Funds for the Central Universities,and East China University of Science and Technology.
文摘Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challenge.Here,we experimentally and theoretically investigated the charge transport characteristics of isoindigo(ISO)-molecules at the single-molecule level using the scanning tunneling microscope break junction technique.We find that the single-molecule junctions of ISO-molecules display bias voltage-driven switching characteristics.These switches are realtime,reversible,and nondestructive under low-bias voltages.Experimental results show that the mechanism of the switch is not the transition from nonresonant charge transport to resonant charge transport,but it is the shift of the frontier orbital energy levels of ISO-molecules and the change of the interfacial electronic coupling with bias voltage.Our results will advance the design of high-performance bias voltage-driven molecular switches.
基金Special Funds for Major State Basic Research Project of China (No.G2000068303)Na-tional Natural Science Foundation of China (No.60390074, 60390071, 90101004)National High-Tech Research and Develop-ment Program of China (No.2002AA311070).
文摘The influence of InAs deposition thickness on the structural and optical properties of InAs/InA1As quantum wires (QWR) superlattices (SLS) was studied. The transmission electron microscopy (TEM) results show that with increasing the InAs deposited thickness, the size uniformity and spatial ordering of InAs QWR SLS was greatly improved, but threading dislocations initiated from InAs nanowires for the sample with 6 monolayers (MLs) InAs deposition. In addition, the zig-zag features along the extending direc- tion and lateral interlink of InAs nanowires were also observed. The InAs nanowires, especially for the first period, were laterally compact. These structural features may result in easy tunneling and coupling of charge carders between InAs nanowires and will hamper their device applications to some extent. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs, and for suppressing the formation of the threading dislocations in InAs QWR SLS.
基金by the Volkswagen Foundation by the Deutsche Forshuhgsgemeinschaft(DFG)under Contracts No.CU 44/5-2,CU 44/8-1,and CU 44/3-3by the WCU(World Class University)program through the Korea Science and Engineering Foundation funded by the Ministry of Education,Science and Technology(Project No.R31-2008-000-10100-0).
文摘In contrast to the static operations of conventional semiconductor devices,the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as a molecular conformational switch or for molecular data storage.Bistable molecules such as those having two stable cis and trans isomeric confi gurations could provide,once clamped between two electrodes,a switching phenomenon in the non-equilibrium current response.Here,we model molecular switch junctions formed at silicon contacts and demonstrate the potential of such tunable molecular switches in electrode/molecule/electrode confi gurations.Using the non-equilibrium Green function(NEGF)approach implemented with the density-functional-based tight-binding(DFTB)theory,a series of properties such as electron transmissions,current voltage characteristics in the different isomer conformations,and potential energy surfaces(PESs)as a function of the reaction coordinates along the trans to cis transition were calculated for two azobenzene-based model compounds.Furthermore,in order to investigate the stability of molecular switches under ambient conditions,molecular dynamics(MD)simulations at room temperature were performed and time-dependent fl uctuations of the conductance along the MD pathways were calculated.Our numerical results show that the transmission spectra of the cis isomers are more conductive than trans counterparts inside the bias window for both model compounds.The currentvoltage characteristics consequently show the same trends.Additionally,calculations of the time-dependent transmission fluctuations along the MD pathways have shown that the transmission in the cis isomers is always signifi cantly larger than that in their trans counterparts,showing that molecular switches can be expected to work as robust molecular switching components.
基金supported by the National Natural Science Foundation of China (Grant No. 11004156)the National Basic Research Program of China (Grant No. 2009CB929204)+1 种基金the Education Department Foundation of Shaanxi Province, China (Grant No. 09JK461)the Fundament Research of Xi’an Polytechnic University (Grant No. 09XG09)
文摘By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Three kinds of adsorption sites including the hollow, bridge and top sites are studied. The two forms of this molecule, namely the open form and the closed form, can reversibly switch from each other upon photoexcitation. Their transmission spectra are remarkably distinctive. Theoretical results show that the current of the closed form is always significantly larger than that of the open form for all three adsorption sites, which promises this system as possibly one of the good candidates for optical switches due to its unique advantage, and which may have some potential applications in the future molecular circuit.