Showing papers on "Conductance published in 2012"
12 Aug 2012
TL;DR: This work studies a set of 230 large social, collaboration and information networks where nodes explicitly define group memberships and finds that two of these definitions, Conductance and Triad-participation-ratio, consistently give the best performance in identifying ground-truth communities.
Abstract: Nodes in real-world networks, such as social, information or technological networks, organize into communities where edges appear with high concentration among the members of the community. Identifying communities in networks has proven to be a challenging task mainly due to a plethora of definitions of a community, intractability of algorithms, issues with evaluation and the lack of a reliable gold-standard ground-truth.We study a set of 230 large social, collaboration and information networks where nodes explicitly define group memberships. We use these groups to define the notion of ground-truth communities. We then propose a methodology which allows us to compare and quantitatively evaluate different definitions of network communities on a large scale. We choose 13 commonly used definitions of network communities and examine their quality, sensitivity and robustness. We show that the 13 definitions naturally group into four classes. We find that two of these definitions, Conductance and Triad-participation-ratio, consistently give the best performance in identifying ground-truth communities.
712 citations
TL;DR: It is shown that the conductance properties of a single molecule can be correlated with its electronic states and the importance of the edge states and a planar geometry.
Abstract: The conductance properties of a narrow graphene nanoribbon are correlated with its electronic states over a wide range of bias voltages using a scanning tunnelling microscope
323 citations
TL;DR: The experimental data and simulations suggest a nonresonant tunneling mechanism involving hole transport through the molecular HOMO, with a decay constant β = 3.4 ± 0.1 nm(-1) and a contact resistance R(c) = 40 kΩ per Au-S bond.
Abstract: The charge transport characteristics of 11 tailor-made dithiol-terminated oligo(phenylene-ethynylene) (OPE)-type molecules attached to two gold electrodes were studied at a solid/liquid interface in a combined approach using an STM break junction (STM-BJ) and a mechanically controlled break junction (MCBJ) setup We designed and characterized 11 structurally distinct dithiol-terminated OPE-type molecules with varied length and HOMO/LUMO energy Increase of the molecular length and/or of the HOMO-LUMO gap leads to a decrease of the single-junction conductance of the linearly conjugate acenes The experimental data and simulations suggest a nonresonant tunneling mechanism involving hole transport through the molecular HOMO, with a decay constant β = 34 ± 01 nm(-1) and a contact resistance R(c) = 40 kΩ per Au-S bond The introduction of a cross-conjugated anthraquinone or a dihydroanthracene central unit results in lower conductance values, which are attributed to a destructive quantum interference phenomenon for the former and a broken π-conjugation for the latter The statistical analysis of conductance-distance and current-voltage traces revealed details of evolution and breaking of molecular junctions In particular, we explored the effect of stretching rate and junction stability We compare our experimental results with DFT calculations using the ab initio code SMEAGOL and discuss how the structure of the molecular wires affects the conductance values
277 citations
TL;DR: It is shown that a free-base tetraphenyl-porphyrin molecule, which is anchored to a silver surface, can function as a molecular conductance switch and which could be controllably integrated into the surrounding nanoscale environment.
Abstract: The development of a variety of nanoscale applications requires the fabrication and control of atomic or molecular switches that can be reversibly operated by light, a short-range force, electric current or other external stimuli. For such molecules to be used as electronic components, they should be directly coupled to a metallic support and the switching unit should be easily connected to other molecular species without suppressing switching performance. Here, we show that a free-base tetraphenyl-porphyrin molecule, which is anchored to a silver surface, can function as a molecular conductance switch. The saddle-shaped molecule has two hydrogen atoms in its inner cavity that can be flipped between two states with different local conductance levels using the electron current through the tip of a scanning tunnelling microscope. Moreover, by deliberately removing one of the hydrogens, a four-level conductance switch can be created. The resulting device, which could be controllably integrated into the surrounding nanoscale environment, relies on the transfer of a single proton and therefore contains the smallest possible atomistic switching unit.
275 citations
TL;DR: The first concurrent determination of conductance (G) and thermopower (S) of single-molecule junctions via direct measurement of electrical and thermoelectric currents using a scanning tunneling microscope-based break-junction technique was reported in this paper.
Abstract: We report the first concurrent determination of conductance (G) and thermopower (S) of single-molecule junctions via direct measurement of electrical and thermoelectric currents using a scanning tunneling microscope-based break-junction technique. We explore several amine-Au and pyridine-Au linked molecules that are predicted to conduct through either the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO), respectively. We find that the Seebeck coefficient is negative for pyridine-Au linked LUMO-conducting junctions and positive for amine-Au linked HOMO-conducting junctions. Within the accessible temperature gradients (<30 K), we do not observe a strong dependence of the junction Seebeck coefficient on temperature. From histograms of thousands of junctions, we use the most probable Seebeck coefficient to determine a power factor, GS(2), for each junction studied, and find that GS(2) increases with G. Finally, we find that conductance and Seebeck coefficient values are in good quantitative agreement with our self-energy corrected density functional theory calculations.
249 citations
TL;DR: Estimates of mesophyll conductance are influenced by the amount of respiratory and photorespiratory CO(2) from the mitochondria diffusing towards the chloroplasts and can affect the estimates of ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) kinetic constants in vivo.
Abstract: The CO(2) concentration at the site of carboxylation inside the chloroplast stroma depends not only on the stomatal conductance, but also on the conductance of CO(2) between substomatal cavities and the site of CO(2) fixation. This conductance, commonly termed mesophyll conductance (g(m) ), significantly constrains the rate of photosynthesis. Here we show that estimates of g(m) are influenced by the amount of respiratory and photorespiratory CO(2) from the mitochondria diffusing towards the chloroplasts. This results in an apparent CO(2) and oxygen sensitivity of g(m) that does not imply a change in intrinsic diffusion properties of the mesophyll, but depends on the ratio of mitochondrial CO(2) release to chloroplast CO(2) uptake. We show that this effect (1) can bias the estimation of the CO(2) photocompensation point and non-photorespiratory respiration in the light; (2) can affect the estimates of ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) kinetic constants in vivo; and (3) results in an apparent obligatory correlation between stomatal conductance and g(m) . We further show that the amount of photo(respiratory) CO(2) that is refixed by Rubisco can be directly estimated through measurements of g(m) .
196 citations
TL;DR: It is shown that the dc current can be predicted for a fixed probe by solving the Nernst-Planck equation and that the ac response can be derived from this response, and both responses are shown to agree well with experiment.
Abstract: Scanning electrochemical cell microscopy (SECCM) is a high resolution electrochemical scanning probe technique that employs a dual-barrel theta pipet probe containing electrolyte solution and quasi-reference counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochemical cell. The substrate can be an electrical conductor, semiconductor, or insulator. The main focus here is on the general case where the substrate is a working electrode, and both ion-conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice, a small perpendicular oscillation of the probe with respect to the substrate is employed, so that an alternating conductance current (ac) develops, due to the change in the dimensions of the electrolyte contact (and hence resistance), as well as the direct conductance current (dc). It is shown that the dc current can be predicted for a fixed probe by solving the Nernst-Planck equation and that the ac response can also be derived from this response. Both responses are shown to agree well with experiment. It is found that the pipet geometry plays an important role in controlling the dc conductance current and that this is easily measured by microscopy. A key feature of SECCM is that mass transport to the substrate surface is by diffusion and, for charged analytes, ion migration which can be controlled and varied quantifiably via the bias between the two QRCEs. For a working electrode substrate this means that charged redox-active analytes can be transported to the electrode/solution interface in a well-defined and controllable manner and that relatively fast heterogeneous electron transfer kinetics can be studied. The factors controlling the voltammetric response are determined by both simulation and experiment. Experiments demonstrate the realization of simultaneous quantitative voltammetric and ion conductance measurements and also identify a general rule of thumb that the surface contacted by electrolyte is of the order of the pipet probe dimensions.
186 citations
TL;DR: The results, which are in agreement with the predictions of theoretical models, also clarify the origins of the long-standing discrepancy between the calculated and measured conductance values of 1,4'-benzenedithiol, which often differ by orders of magnitude.
Abstract: The conductance of a single molecule of 1,4'-benzenedithiol bridged between two gold electrodes increases as it is stretched because the energy of the highest occupied molecular orbital is shifted towards the Fermi energy of the electrodes, leading to a resonant enhancement of the conductance.
181 citations
TL;DR: The low-temperature conductance of a weakly interacting one-dimensional helical liquid without axial spin symmetry allows for inelastic backscattering of a single electron, accompanied by forward scattering of another, resulting in a temperature-dependent deviation from the quantized conductance.
Abstract: We evaluate the low-temperature conductance of a weakly interacting one-dimensional helical liquid without axial spin symmetry. The lack of that symmetry allows for inelastic backscattering of a single electron, accompanied by forward scattering of another. This joint effect of weak interactions and potential scattering off impurities results in a temperature-dependent deviation from the quantized conductance, delta G proportional to T-4. In addition, delta G is sensitive to the position of the Fermi level. We determine numerically the parameters entering our generic model for the Bernevig-Hughes-Zhang Hamiltonian of a HgTe/CdTe quantum well in the presence of Rashba spin-orbit coupling.
174 citations
TL;DR: In this article, a method to enhance and tune thermal interface conductance at vibrationally mismatched solid-solid interfaces is presented. But the authors do not consider the effects of altering the interfacial film thickness, vibrational spectrum, and temperature of the system.
Abstract: The thermal conductance of interfaces plays a major role in defining the thermal properties of nanostructured materials in which heat transfer is predominantly phonon mediated. Ongoing research has improved the understanding of factors that govern interfacial phonon transport as well as the ability to predict thermal interface conductance. However, despite this progress, the ability to control interface conductance remains a major challenge. In this manuscript, we present a method to enhance and tune thermal interface conductance at vibrationally mismatched solid-solid interfaces. Enhancement is achieved through the insertion of an interfacial film with mediating vibrational properties, such that the vibrational mismatch at the interface is bridged, and consequently, the total interface conductance is enhanced. This phenomena is explored using nonequilibrium molecular dynamics simulations, where the effects of altering the interfacial film thickness, vibrational spectrum, and the temperature of the system are investigated. A systematic study of these pertinent design parameters explores the ability to enhance and tune phonon transport at both ideal (sharp) and nonideal (compositionally disordered) interfaces. Results show that interface conductance can be broadly enhanced by up to 53% in comparison to the vibrationally mismatched baseline interface. Additionally, we find that compositional disorder at an interface does not imply a deterministic change in interface conductance, but instead, that the influence of compositional disorder depends on the characteristics of the disordered region itself. These results, in contrast to macroscopic thermal transport theory, imply that it is possible to increase thermal conductance associated with interface scattering by adding more material along the direction of heat flux.
157 citations
TL;DR: Attempts to modulate this transition in single-crystal VO(2) nanowires via electrochemical gating using ionic liquids are reported, suggesting that significant field-effect modulation of the metal-insulator transition is not possible, at least along the crystallographic directions relevant in thesenanowires.
Abstract: Vanadium dioxide (VO2) is a strongly correlated transition metal oxide with a dramatic metal–insulator transition at 67 °C. Researchers have long been interested in manipulating this transition via the field effect. Here we report attempts to modulate this transition in single-crystal VO2 nanowires via electrochemical gating using ionic liquids. Stray water contamination in the ionic liquid leads to large, slow, hysteretic conductance responses to changes in the gate potential, allowing tuning of the activation energy of the conductance in the insulating state. We suggest that these changes are the result of electrochemical doping via hydrogen. In the absence of this chemical effect, gate response is minimal, suggesting that significant field-effect modulation of the metal–insulator transition is not possible, at least along the crystallographic directions relevant in these nanowires.
TL;DR: The results demonstrate that atomic point contacts can be realized in an oxide-based MIM structure that functions as a nanogap-based atomic switch and shows that the oxide- based atomic switch has potential for use as an essential building block of neural computing systems.
Abstract: Quantized conductance was observed in a cation-migration-based resistive switching memory cell with a simple metal-insulator-metal (MIM) structure using a thin Ta(2)O(5) layer. The observed conductance changes are attributed to the formation and dissolution of a metal filament with an atomic point contact of different integer multiples in the Ta(2)O(5) layer. The results demonstrate that atomic point contacts can be realized in an oxide-based MIM structure that functions as a nanogap-based atomic switch (Terabe et al 2005 Nature 433 47). By applying consecutive voltage pulses at periodic intervals of different times, we also observed an effect analogous to the long-term potentiation of biological synapses, which shows that the oxide-based atomic switch has potential for use as an essential building block of neural computing systems.
TL;DR: The combination of M4PP and THz-TDS conductance measurements reveals that the film is electrically continuous on the nanoscopic scale with microscopic defects likely originating from the transfer process, dominating the microscale conductance of the investigated graphene film.
Abstract: We demonstrate a combination of micro four-point probe (M4PP) and non-contact terahertz time-domain spectroscopy (THz-TDS) measurements for centimeter scale quantitative mapping of the sheet conductance of large area chemical vapor deposited graphene films. Dual configuration M4PP measurements, demonstrated on graphene for the first time, provide valuable statistical insight into the influence of microscale defects on the conductance, while THz-TDS has potential as a fast, non-contact metrology method for mapping of the spatially averaged nanoscopic conductance on wafer-scale graphene with scan times of less than a minute for a 4-in. wafer. The combination of M4PP and THz-TDS conductance measurements, supported by micro Raman spectroscopy and optical imaging, reveals that the film is electrically continuous on the nanoscopic scale with microscopic defects likely originating from the transfer process, dominating the microscale conductance of the investigated graphene film.
TL;DR: Microcrossbar structured electrochemical metallization cells based on silver iodide (AgI) solid electrolyte were fabricated and analyzed in terms of the resistive switching effect to imply the existence of quantized conductance higher than 78 µS.
Abstract: Microcrossbar structured electrochemical metallization (ECM) cells based on silver iodide (AgI) solid electrolyte were fabricated and analyzed in terms of the resistive switching effect. The switching behavior implies the existence of quantized conductance higher than 78 µS which can be identified as a multiple of the single atomic point contact conductivity. The nonlinearity of the switching kinetics has been analyzed in detail. Fast switching in at least 50 ns was observed for short pulse measurements.
TL;DR: In this article, the authors provide a derivation allowing the calculation of thermal conductance at interfaces by equilibrium molecular dynamics simulations and illustrate their approach by studying thermal conduction mechanisms in Si/Ge superlattices.
Abstract: We provide a derivation allowing the calculation of thermal conductance at interfaces by equilibrium molecular dynamics simulations and illustrate our approach by studying thermal conduction mechanisms in Si/Ge superlattices. Thermal conductance calculations of superlattices with period thicknesses ranging from 0.5 to 60 nm are presented as well as the temperature dependence. Results have been compared to complementary Green-Kubo thermal conductivity calculations demonstrating that thermal conductivity of perfect superlattices can be directly deduced from interfacial conductance in the investigated period range. This confirms the predominant role of interfaces in materials with large phonon mean free paths.
TL;DR: The single-molecular conductance of a redox active molecular bridge has been studied in an electrochemical single- molecule transistor configuration in a room-temperature ionic liquid (RTIL) and this molecular conductance vs electrochemical potential relation could be modeled well as a sequential two-step charge transfer process with full or partial vibrational relaxation.
Abstract: The single-molecular conductance of a redox active molecular bridge has been studied in an electrochemical single-molecule transistor configuration in a room-temperature ionic liquid (RTIL). The redox active pyrrolo-tetrathiafulvalene (pTTF) moiety was attached to gold contacts at both ends through −(CH2)6S– groups, and gating of the redox state was achieved with the electrochemical potential. The water-free, room-temperature, ionic liquid environment enabled both the monocationic and the previously inaccessible dicationic redox states of the pTTF moiety to be studied in the in situ scanning tunneling microscopy (STM) molecular break junction configuration. As the electrode potential is swept to positive potentials through both redox transitions, an ideal switching behavior is observed in which the conductance increases and then decreases as the first redox wave is passed, and then increases and decreases again as the second redox process is passed. This is described as an “off–on–off–on–off” conductance ...
TL;DR: Despite the strong Au-S bond and the evidence for disruption of the Au structure, the experiments show that on average these junctions also rupture at a smaller force than that measured for pristine single-atom gold contacts.
Abstract: We use a modified conducting atomic force microscope to simultaneously probe the conductance of a single-molecule junction and the force required to rupture the junction formed by alkanes terminated with four different chemical link groups which vary in binding strength and mechanism to the gold electrodes. Molecular junctions with amine, methylsulfide, and diphenylphosphine terminated molecules show clear conductance signatures and rupture at a force that is significantly smaller than the measured 1.4 nN force required to rupture the single-atomic gold contact. In contrast, measurements with a thiol terminated alkane which can bind covalently to the gold electrode show conductance and force features unlike those of the other molecules studied. Specifically, the strong Au-S bond can cause structural rearrangements in the electrodes, which are accompanied by substantial conductance changes. Despite the strong Au-S bond and the evidence for disruption of the Au structure, the experiments show that on average these junctions also rupture at a smaller force than that measured for pristine single-atom gold contacts.
TL;DR: In this article, a detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements was performed to extract the information about the interface trap states, and the discrepancy between the high barrier height values obtained from the I-V and the C-V measurements was also analyzed.
Abstract: Schottky diodes with Au/ZnO nanorod (NR)/n-SiC configurations have been fabricated and their interface traps and electrical properties have been investigated by current-voltage (I-V), capacitance-voltage (C-V), capacitance-frequency (C-f), and conductance-frequency (Gp/ω-ω) measurements. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements was performed to extract the information about the interface trap states. The discrepancy between the high barrier height values obtained from the I-V and the C-V measurements was also analyzed. The higher capacitance at low frequencies was attributed to excess capacitance as a result of interface states in equilibrium in the ZnO that can follow the alternating current signal. The energy of the interface states (Ess) with respect to the valence band at the ZnO NR surface was also calculated. The densities of interface states obtained from the conductance and capacitance methods agreed well with each other and this confirm that the observed capacitance and conductance are caused by the same physical processes, i.e., recombination-generation in the interface states.
TL;DR: The results suggest that designs combining metal with single graphene layers provide the best thermal properties, and that both cases show a strong performance dependence on the number of graphene layers between metal phases.
Abstract: Graphene has excellent mechanical, electrical and thermal properties. Recently, graphene-metal composites have been proposed as a means to combine the properties of metals with those of graphene, leading to mechanically, electrically and thermally functional materials. The understanding of metal-graphene nanocomposites is of critical importance in developing next-generation electrical, thermal and energy devices, but we currently lack a fundamental understanding of how their geometry and composition control their thermal properties. Here we report a series of atomistic simulations, aimed at assessing the geometry and temperature effects of the thermal interface conductance for copper- and nickel-graphene nanocomposites. We find that copper-graphene and nickel-graphene nanocomposites have similar thermal interface conductances, but that both cases show a strong performance dependence on the number of graphene layers between metal phases. Single-graphene-layer nanocomposites have the highest thermal interface conductance, approaching ~500 MW m(-2) K(-1). The thermal interface conductance reduces to half this value in metal-bilayer graphene nanocomposites, and for more than three layers of graphene the thermal interface conductances further reduces to ~100 MW m(-2) K(-1) and becomes independent with respect to the number of layers of graphene. This dependence is attributed to the relatively stronger bonding between the metal and graphene layer, and relatively weaker bonding between graphene layers. Our results suggest that designs combining metal with single graphene layers provide the best thermal properties.
TL;DR: In this paper, the authors compare the results of nonequilibrium (NEMD) and equilibrium molecular dynamics methods to compute the thermal conductance at the interface between solids.
Abstract: In this article, we compare the results of nonequilibrium (NEMD) and equilibrium (EMD) molecular dynamics methods to compute the thermal conductance at the interface between solids. We propose to probe the thermal conductance using equilibrium simulations measuring the decay of the thermally induced energy fluctuations of each solid. We also show that NEMD and EMD give generally speaking inconsistent results for the thermal conductance: Green-Kubo simulations probe the Landauer conductance between two solids which assumes phonons on both sides of the interface to be at equilibrium. On the other hand, we show that NEMD give access to the out-of-equilibrium interfacial conductance consistent with the interfacial flux describing phonon transport in each solid. The difference may be large and reaches typically a factor 5 for interfaces between usual semiconductors. We analyze finite size effects for the two determinations of the interfacial thermal conductance, and show that the equilibrium simulations suffer from severe size effects as compared to NEMD. We also compare the predictions of the two above-mentioned methods---EMD and NEMD---regarding the interfacial conductance of a series of mass mismatched Lennard-Jones solids. We show that the Kapitza conductance obtained with EMD can be well described using the classical diffuse mismatch model (DMM). On the other hand, NEMD simulation results are consistent with an out-of-equilibrium generalization of the acoustic mismatch model (AMM). These considerations are important in rationalizing previous results obtained using molecular dynamics, and help in pinpointing the physical scattering mechanisms taking place at atomically perfect interfaces between solids, which is a prerequisite to understand interfacial heat transfer across real interfaces.
TL;DR: Experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se microflakes is reported and the electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior.
Abstract: The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se microflakes. The solely-B⊥-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such survived UCFs of the surface states result from the limited dephasing length of the bulk carriers in ternary crystals. The electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior.
TL;DR: Ag/GeS2/W conductive-bridge random access memory (CBRAM) cells are shown to program at room temperature to conductance levels near multiples of the fundamental conductance G0 = 2e2/h.
Abstract: Ag/GeS2/W conductive-bridge random access memory (CBRAM) cells are shown to program at room temperature to conductance levels near multiples of the fundamental conductance G0 = 2e2/h. This behavior is not accounted for in the traditional view that the conductance of a CBRAM cell is a continuous variable proportional to the maximum current allowed to flow during programming. For on -state resistances on the order of 1/G0 = 12.9 kΩ or less, quantization implies that the Ag “conductive bridge” typically contains a constriction, or even an extended chain, that can be as narrow as a single atom. Implications for device modeling and commercial applications are discussed.
TL;DR: It is found that the spacing between average values of lnτ(n) is constant and it is demonstrated that when surface interactions are taken into account it is equal to the inverse of the bare conductance.
Abstract: We measure the field transmission matrix t for microwave radiation propagating through random waveguides in the crossover to Anderson localization. From these measurements, we determine the dimensionless conductance g and the individual eigenvaluesn of the transmission matrix tt y whose sum equals g. In diffusive samples, the highest eigenvalue, � 1, is close to unity corresponding to a transmission of nearly 100%, while for localized waves, the average of � 1, is nearly equal to g. We find that the spacing between average values of lnn is constant and demonstrate that when surface interactions are taken into More than 50 years ago, Anderson (1) showed that beyond a certain threshold in disorder the electron wave function within a material becomes exponentially peaked and diffusion ceases. In the intervening years, localization and its precursors in diffusive samples of enhanced fluctu- ations and suppressed transmission have been shown to affect every aspect of transport (2-4). Relating transmis- sion in disordered systems to random matrices (5-12) has provided a powerful approach to calculating the scaling and fluctuations of conductance. In this approach, the flow of electrical current through a disordered conductor is assumed to proceed via a set of orthogonal channels on the input and output sides of the sample which are coupled via the field transmission matrix t. Each channel is a superposition of the N orthogonal transverse momentum channels supported by the sample leads. Alternatively, t gives the coupling of the field between different points on opposite surfaces of the sample. The focus of random matrix theory has been the calculation of the dimensionless conductance, g, which is the conductance in units of
TL;DR: The analysis of the molecular projected self-consistent Hamiltonian and the evolution of the frontier molecular orbitals (MOs) as well as transmission coefficients under various external voltage biases gives an inside view of the observed results, which suggests that the dual conductance behavior and rectifying performance are due to the asymmetry distribution of the Frontier MOs.
Abstract: We investigate the electronic transport properties for a molecular device model constructed by a phenylene ethynylene oligomer molecular with different side groups embedding in a carbon chain between two graphene electrodes. Using the first-principles method, the unusual dual conductance, negative differential resistance (NDR) behavior with large peak to valley ratio, and obvious rectifying performance are numerically observed in such proposed molecular device. The analysis of the molecular projected self-consistent Hamiltonian and the evolution of the frontier molecular orbitals (MOs) as well as transmission coefficients under various external voltage biases gives an inside view of the observed results, which suggests that the dual conductance behavior and rectifying performance are due to the asymmetry distribution of the frontier MOs as well as the corresponding coupling between the molecule and electrodes. But the NDR behavior comes from the conduction orbital being suppressed at certain bias. Interestingly, the conduction properties can be tuned by introducing side groups to the molecule and the rectification as well as the NDR behavior (peak to valley ratio) can be improved by adding different side groups in the device model.
TL;DR: In this paper, the authors investigated the conductance spectra of Sn-Bi2Se3 interface junctions down to 250mK and in different magnetic fields and found that a number of conductance anomalies were observed below the superconducting transition temperature of Sn, including a small gap that is different from that of Sn and a zero-bias conductance peak that increases at lower temperatures.
Abstract: We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions down to 250mK and in different magnetic fields. A number of conductance anomalies were observed below the superconducting transition temperature of Sn, including a small gap that is different from that of Sn, and a zero-bias conductance peak that increases at lower temperatures. We discussed the possible origins of the smaller gap and the zero-bias conductance peak. These phenomena support the idea that a proximity-effect-induced chiral superconducting phase is formed at the interface between the superconducting Sn and the strong spin-orbit coupling material Bi2Se3.
TL;DR: In this article, non-equilibrium molecular dynamics simulations were employed to study the Kapitza conductance of symmetric tilt grain boundaries in the monolayer graphene sheet, and both armchair and zig-zag oriented bicrystal graphene were investigated.
Abstract: Non-equilibrium molecular dynamics simulations were employed to study the Kapitza conductance of symmetric tilt grain boundaries in the monolayer graphene sheet. Both armchair and zig-zag oriented bicrystal graphene were investigated. The Kapitza conductance of the interface shows length dependence up to 300 nm, which arises from the fact that long-wavelength phonons allowed in large-size graphene are able to transmit through the interface contributing to the Kapitza conductance. The Kapitza conductance exhibits monotonic increase with temperature, opposite to the trend of thermal conductivity of bulk graphene above room temperature. We found that the Kapitza conductance is inversely proportional to the number of dislocations per length of grain boundaries. The facts that the phonon density of states (DOS) shows no difference between the two crystals separated by the grain boundary and the vibrational DOS of grain boundary region atoms deviates from that of bulk atoms reveal that the interfacial thermal r...
TL;DR: In this article, the electrochemical gating of a single anthraquinone-based molecule bridged between two gold electrodes using the STM break-junction technique was reported.
Abstract: Herein we report the electrochemical gating of a single anthraquinone-based molecule bridged between two gold electrodes using the STM break-junction technique. Once a molecule is trapped between the STM gold tip and the gold substrate, the potential is swept in order to alternate between the oxidized anthraquinone (AQ) and the reduced hydroanthraquinone (H2AQ) forms. It is shown that the conductance increases about an order of magnitude with a net conversion from the oxidized AQ form to the reduced H2AQ form. The results obtained from sweeping the potential (dynamic approach) on a single molecule are compared to those obtained from measuring the conductance at several fixed potentials (static approach). By comparing the static and dynamic approach, qualitative information about the kinetics of the redox conversion was achieved. The threshold potential of the conductance enhancement was found to shift to more negative potentials when the potential is swept at a single molecule. This shift is attributed to...
TL;DR: In this article, a microscopic derivation of the two-particle inelastic backscattering process in the presence of a time-reversal invariant Rashba impurity potential is presented.
Abstract: The occurrence of two-particle inelastic backscattering has been conjectured in helical edge states of topological insulators and is expected to alter transport. Here, by using a renormalization group approach, we provide a microscopic derivation of this process, in the presence of a time-reversal invariant Rashba impurity potential. We are able to prove that such an effect only occurs in the presence of electron-electron interactions. Furthermore, we find that the linear conductance as a function of temperature exhibits a crossover between two scaling behaviors, ${T}^{4K}$ for $Kg1/2$ and ${T}^{8K\ensuremath{-}2}$ for $Kl1/2$, with $K$ the Luttinger parameter.
TL;DR: It is found that covering a single π-conjugated wire with an α-cyclodextrin molecule is a promising technique for suppressing conductance fluctuations in conventional molecular junctions.
Abstract: An electronic conductance with small fluctuations, which is stipulated in single-molecule junctions, is necessary for the precise control of single-molecule devices. However, the suppression of conductance fluctuations in conventional molecular junctions is intrinsically difficult because the fluctuations are related to the contact fluctuations and molecular motion. In the present study involving experimental and theoretical investigations, it is found that covering a single π-conjugated wire with an α-cyclodextrin molecule is a promising technique for suppressing conductance fluctuations. The conductance histogram of the covered molecular junction measured with the scanning tunneling microscope break-junction technique shows that the conductance peak for the covered junction is sharper than that of the uncovered junction. The covering technique thus has two prominent effects: the suppression of intramolecular motion, and the elimination of intermolecular interactions. Theoretical calculations of electronic conductance clearly support these experimental observations.
TL;DR: Pc molecular junction has high spin-filter efficiency as well as negative differential resistance (NDR) and predictions indicate that FePc junction holds great promise in molecular electronics and spintronics applications.
Abstract: We investigate the spin transport properties of iron-phthalocyanine (FePc) molecule sandwiched between two N-doped graphene nanoribbons (GNRs) based on the density functional theory and nonequilibrium Green's function methods. Our calculated results clearly reveal that the FePc molecular junction has high spin-filter efficiency as well as negative differential resistance (NDR). The zero-bias conductance through FePc molecule is dominated by the spin-down electrons, and the observed NDR originates from the bias-dependent effective coupling between the FePc molecular orbitals and the narrow density of states of electrodes. The remarkable high spin-filter efficiency and NDR are robust regardless of the edge shape and the width of GNRs, and the N-doping site in GNRs. These predictions indicate that FePc junction holds great promise in molecular electronics and spintronics applications.