Showing papers on "Conductance published in 2013"
TL;DR: The results demonstrate the major role of anatomy in constraining mesophyll diffusion conductance and, consequently, in determining the variability in photosynthetic capacity among species.
Abstract: Abbreviations: α, leaf absorptance; β, fraction of absorbed light that reaches photosystem II; Γ*, CO2 compensation point in the absence of mitochondrial respiration; ФPSII, effective quantum efficiency of the PSII photochemistry; Δ Lias, effective diffusion path length in the gas phase; ϵPSII, fraction of electrons absorbed by PSII; ς, diffusion path tortuosity; Amass, photosynthetic capacity per dry mass; AN, net CO2 assimilation rate; Ca, atmospheric CO2 concentration; Cc, chloroplastic CO2 concentration; Ci, substomatal CO2 concentration; Ci-Cc, CO2 drawdown from intercellular airspace to chloroplasts; Da, diffusion coefficient for CO 2 in the gas phase; DL, leaf density; Dw, aqueous phase diffusion coefficient for CO 2; fias, volume fraction of intercellular air spaces; Fm’, maximum fluorescence in lightadapted state; Fs, steady-state fluorescence emission; g cel, partial liquid phase conductance for different portions along cell walls; gcyt, cytosol conductance; genv, chloroplast envelope conductance; gias, intercellular air space conductance to CO2 (gas phase conductance); gliq, sum of liquid and lipid phase conductances; gm, mesophyll diffusion conductance; gpl, plasma membrane conductance; gs, stomatal conductance to CO2; gtot, total conductance to CO2 from ambient air to chloroplasts; H/(RTk), dimensionless form of Henry’s law constant; JF, linear electron transport rate from chlorophyll fluorescence; J max, maximum photosynthetic electron transport rate; Kc, Michaelis–Menten constant for the carboxylation activity of Rubisco; Ko, Michaelis–Menten constant for the oxygenation activity of Rubisco; lb, biochemical limitation; Lchl, length of chloroplasts exposed to intercellular air spaces; Lcyt, diffusion pathway length in the cytoplasm; lias, gas-phase limitation; lm, mesophyll limitation; ls, stomatal limitation; MA, leaf mass per area; O, leaf internal oxygen concentration; pi, effective porosity in the given part of the diffusion pathway; Q, incident quantum flux density; R, gas constant; R d, leaf respiration in the dark; rf,i, proportional reduction of Dw in the cytosol and in the stroma compared with free diffusion in water; RL, leaf respiration in the light; SC/O, Rubisco specificity factor; S c/S, chloroplast surface area exposed to intercellular air spaces per unit of leaf area; Sc/Sm, ratio of exposed chloroplasts to mesophyll surface areas; Sm/S, mesophyll surface area exposed to intercellular air spaces per unit of leaf area; Ss, cross-sectional area of mesophyll cells in micrograph; SE, standard error; Tchl, chloroplast thickness; Tcw, cell wall thickness; Tcyt, cytoplasm thickness; Tk, absolute temperature; TL, leaf thickness; tmes, mesophyll thickness; Vcmax, maximum rates for the carboxylation activity of Rubisco; W, width of the leaf anatomical section.
346 citations
TL;DR: BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoyne studied and, moreover, are higher than other conjugated molecular wires of similar length.
Abstract: We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with n = 1, 2, and 4 triple bonds and the anchor dihydrobenzo[b]thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH2), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar len...
274 citations
TL;DR: In this article, molar conductance data are exploited to ascertain electrolytic and non-electrolytic nature of metal complexes, which can provide brief insights into their nature and composition.
Abstract: Molar conductance studies of electrolytic solutions have always been exciting for chemists. The studies of electrolytic behavior of metal complex solutions provide brief insights into their nature and composition. These studies provide a clue of the number of ions present in a particular solution responsible for the conduction of electric current and, thereby, quite significant structural information can be obtained. Molar conductance data are exploited to ascertain electrolytic and non-electrolytic nature of metal complexes. Attempts have been made to summarize molar conductance ranges of metal complexes in various solvents, which might prove useful to researchers and academia. Besides, molar conductance data have been applied to predict geometries of metal complexes. Moreover, efforts have been made to discuss the applications of conductance data for the estimation of the size of structurally relevant complexes. In addition, molar conductance has been applied to determine metal-ligand stoichiometry. Fin...
157 citations
TL;DR: In this paper, the authors suggest that the reset occurs in two phases: a progressive narrowing of the conducting filament to the limit of a quantum wire (QW) followed by the opening of a spatial gap that exponentially reduces the CF transmission.
Abstract: Discrete changes of conductance of the order of G0 = 2e2/h reported during the unipolar reset transitions of Pt/HfO2/Pt structures are interpreted as the signature of atomic-size variations of the conducting filament (CF) nanostructure. Our results suggest that the reset occurs in two phases: a progressive narrowing of the CF to the limit of a quantum wire (QW) followed by the opening of a spatial gap that exponentially reduces the CF transmission. First principles calculations show that oxygen vacancy paths in HfO2 with single- to few-atom diameters behave as QWs and are capable of carrying current with G0 conductance.
154 citations
TL;DR: Results show conductance quantization in InSb nanowires at nonzero magnetic fields as a function of source-drain bias and magnetic field, enabling extraction of the Landé g factor and the subband spacing.
Abstract: Ballistic one-dimensional transport in semiconductor nanowires plays a central role in creating topological and helical states. The hallmark of such one-dimensional transport is conductance quantization. Here we show conductance quantization in InSb nanowires at nonzero magnetic fields. Conductance plateaus are studied as a function of source-drain bias and magnetic field, enabling extraction of the Lande g factor and the subband spacing.
154 citations
TL;DR: A tight-binding model that explicitly includes the gateway states and the molecular backbone states accurately captures the experimentally measured conductance and thermopower trends is reported.
Abstract: We report the simultaneous measurement of conductance and thermopower of highly conducting single-molecule junctions using a scanning tunneling microscope-based break-junction setup. We start with molecular backbones (alkanes and oligophenyls) terminated with trimethyltin end groups that cleave off in situ to create junctions where terminal carbons are covalently bonded to the Au electrodes. We apply a thermal gradient across these junctions and measure their conductance and thermopower. Because of the electronic properties of the highly conducting Au-C links, the thermoelectric properties and power factor are very high. Our results show that the molecular thermopower increases nonlinearly with the molecular length while conductance decreases exponentially with increasing molecular length. Density functional theory calculations show that a gateway state representing the Au-C covalent bond plays a key role in the conductance. With this as input, we analyze a series of simplified models and show that a tight-binding model that explicitly includes the gateway states and the molecular backbone states accurately captures the experimentally measured conductance and thermopower trends.
153 citations
TL;DR: These studies simulate sodium channel conductance based on an experimentally determined structure of a sodium channel pore that has a completely open transmembrane pathway and activation gate, and calculated single-channel conductance and selectivity ratio correspond closely with the electrophysiology measurements of the NavMs channel expressed in HEK 293 cells.
Abstract: The crystal structure of the open conformation of a bacterial voltage-gated sodium channel pore from Magnetococcus sp. (NaVMs) has provided the basis for a molecular dynamics study defining the channel’s full ion translocation pathway and conductance process, selectivity, electrophysiological characteristics, and ion-binding sites. Microsecond molecular dynamics simulations permitted a complete time-course characterization of the protein in a membrane system, capturing the plethora of conductance events and revealing a complex mixture of single and multi-ion phenomena with decoupled rapid bidirectional water transport. The simulations suggest specific localization sites for the sodium ions, which correspond with experimentally determined electron density found in the selectivity filter of the crystal structure. These studies have also allowed us to identify the ion conductance mechanism and its relation to water movement for the NavMs channel pore and to make realistic predictions of its conductance properties. The calculated single-channel conductance and selectivity ratio correspond closely with the electrophysiology measurements of the NavMs channel expressed in HEK 293 cells. The ion translocation process seen in this voltage-gated sodium channel is clearly different from that exhibited by members of the closely related family of voltage-gated potassium channels and also differs considerably from existing proposals for the conductance process in sodium channels. These studies simulate sodium channel conductance based on an experimentally determined structure of a sodium channel pore that has a completely open transmembrane pathway and activation gate.
148 citations
TL;DR: It is demonstrated that the reversible structure changes induced by isomerization of a single bispyridine-substituted DHP molecule are correlated with a large drop of the conductance value and an excellent reversibility of conductance switching.
Abstract: The conductance properties of a photoswitchable dimethyldihydropyrene (DHP) derivative have been investigated for the first time in single-molecule junctions using the mechanically controllable break junction technique. We demonstrate that the reversible structure changes induced by isomerization of a single bispyridine-substituted DHP molecule are correlated with a large drop of the conductance value. We found a very high ON/OFF ratio (>104) and an excellent reversibility of conductance switching.
132 citations
TL;DR: In this paper, a platinum (Pt)/yttrium iron garnet (YIG) bilayer system with a well-controlled interface has been developed; spin mixing conductance at the Pt/YIG interface was studied.
Abstract: A platinum (Pt)/yttrium iron garnet (YIG) bilayer system with a well-controlled interface has been developed; spin mixing conductance at the Pt/YIG interface has been studied. A clear interface with good crystal perfection is experimentally demonstrated to be one of the important factors for an ultimate spin mixing conductance. The spin mixing conductance is obtained to be 1.3 × 1018 m–2 at the well-controlled Pt/YIG interface, which is close to a theoretical prediction.
123 citations
TL;DR: Reflectance and conductance transitions were interpreted as critical junctures corresponding to a surface coverage that exceeded the percolation threshold of the Au NP films at the [heptane + 1,2-dichloroethane]/water interface.
Abstract: Gold nanoparticle (Au NP) mirrors, which exhibit both high reflectance and electrical conductance, were self-assembled at a [heptane + 1,2-dichloroethane]/water liquid/liquid interface. The highest reflectance, as observed experimentally and confirmed by finite difference time domain calculations, occurred for Au NP films consisting of 60 nm diameter NPs and approximate monolayer surface coverage. Scanning electrochemical microscopy approach curves over the interfacial metallic NP films revealed a transition from an insulating to a conducting electrical material on reaching a surface coverage at least equivalent to the formation of a single monolayer. Reflectance and conductance transitions were interpreted as critical junctures corresponding to a surface coverage that exceeded the percolation threshold of the Au NP films at the [heptane + 1,2-dichloroethane]/water interface.
117 citations
TL;DR: This finding provides the first experimental evidence of the possibility of mechanical exfoliation of Bi bilayers, the existence of the QSH phase in a two-dimensional crystal, and, most importantly, the observation of theQSH phase at room temperature.
Abstract: We report electrical conductance measurements of Bi nanocontacts created by repeated tip-surface indentation using a scanning tunneling microscope at temperatures of 4 and 300 K. As a function of the elongation of the nanocontact, we measure robust, tens of nanometers long plateaus of conductance G0 = 2e2/h at room temperature. This observation can be accounted for by the mechanical exfoliation of a Bi(111) bilayer, a predicted quantum spin Hall (QSH) insulator, in the retracing process following a tip-surface contact. The formation of the bilayer is further supported by the additional observation of conductance steps below G0 before breakup at both temperatures. Our finding provides the first experimental evidence of the possibility of mechanical exfoliation of Bi bilayers, the existence of the QSH phase in a two-dimensional crystal, and, most importantly, the observation of the QSH phase at room temperature.
01 Jun 2013
TL;DR: In this paper, the spectral partitioning algorithm is shown to be a constant factor approximation algorithm for finding a sparse cut if lk is a constant for some constant k. This bound is improved to O(k) l2/√lk by Cheeger's inequality.
Abstract: Let φ(G) be the minimum conductance of an undirected graph G, and let 0=λ1 ≤ λ2 ≤ ... ≤ λn ≤ 2 be the eigenvalues of the normalized Laplacian matrix of G. We prove that for any graph G and any k ≥ 2, [φ(G) = O(k) l2/√lk,] and this performance guarantee is achieved by the spectral partitioning algorithm. This improves Cheeger's inequality, and the bound is optimal up to a constant factor for any $k$. Our result shows that the spectral partitioning algorithm is a constant factor approximation algorithm for finding a sparse cut if lk is a constant for some constant k. This provides some theoretical justification to its empirical performance in image segmentation and clustering problems. We extend the analysis to spectral algorithms for other graph partitioning problems, including multi-way partition, balanced separator, and maximum cut.
TL;DR: This work compares the conductance of a series of amine-terminated oligophenyl and alkane molecular junctions formed with Ag and Au electrodes using the scanning tunneling microscope based break-junction technique and explains the trends observed in the single molecule junction conductance.
Abstract: We compare the conductance of a series of amine-terminated oligophenyl and alkane molecular junctions formed with Ag and Au electrodes using the scanning tunneling microscope based break-junction technique. For these molecules that conduct through the highest occupied molecular orbital, junctions formed with Au electrodes are more conductive than those formed with Ag electrodes, consistent with the lower work function for Ag. The measured conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same for Ag and Au electrodes. However, the formation and evolution of molecular junctions upon elongation are very different for these two metals. Specifically, junctions formed with Ag electrodes sustain significantly longer elongation when compared with Au due to a difference in the initial gap opened up when the metal point-contact is broken. Using this observation and density functional theory calculations of junction structure and conductance we explain the trends observed in the single molecule junction conductance. Our work thus opens a new path to the conductance measurements of a single molecule junction in Ag electrodes.
TL;DR: The thermopower has little correlation with the conductance, but it decreases with the transition voltage, which is consistent with a theory based on Landauer's formula and shows that the thermopOWER provides valuable information about the relative alignment between the molecular energy levels and the electrodes' Fermi energy level.
Abstract: We have measured the thermopower as well as other important charge transport quantities, including conductance, current–voltage characteristics, and transition voltage of single molecules. The thermopower has little correlation with the conductance, but it decreases with the transition voltage, which is consistent with a theory based on Landauer’s formula. Since the transition voltage reflects the molecular energy level alignment, our finding also shows that the thermopower provides valuable information about the relative alignment between the molecular energy levels and the electrodes’ Fermi energy level.
TL;DR: In this paper, the authors used nonequilibrium molecular dynamics to study heat transfer across structures consisting of a few layers of graphene sandwiched between silicon crystals, and they found that the integrated contribution of the phonons to the interfacial thermal conductance is essentially independent of the number of layers.
Abstract: We use nonequilibrium molecular dynamics to study heat transfer across structures consisting of a few layers of graphene sandwiched between silicon crystals. We find that when heat transfers from a silicon lead on one side across the graphene layers to a silicon lead on the other side, the interfacial conductance is essentially independent of the number of layers, in agreement with recent experimental findings. By contrast, wave-packet simulations show that the transmission coefficient of individual vibrational modes depends strongly on frequency and the number of graphene layers, indicating significant interference effects. This apparent contradiction is resolved by a theoretical calculation, which shows that the integrated contribution of the phonons to the interfacial thermal conductance is essentially independent of the number of layers. When one atomic layer of graphene is heated directly, the effective interfacial conductance associated with heat dissipation to the silicon substrate is much smaller. We attribute this to the resistance associated with heat transfer between high and low frequency modes within heated graphene.
TL;DR: Conjugated molecules containing a trimethylsilylethynyl terminus, -C≡CSiMe(3) give exclusively a single conductance value in I(s) measurements on gold substrates, the value of which is similar to that observed for the same molecular backbone with thiol and amine based contacting groups when bound to under-coordinated surface sites.
Abstract: Conductance across a metal|molecule|metal junction is strongly influenced by the molecule–substrate contacts, and for a given molecular structure, multiple conductance values are frequently observed and ascribed to distinct binding modes of the contact at each of the molecular termini. Conjugated molecules containing a trimethylsilylethynyl terminus, –CCSiMe3 give exclusively a single conductance value in I(s) measurements on gold substrates, the value of which is similar to that observed for the same molecular backbone with thiol and amine based contacting groups when bound to under-coordinated surface sites.
TL;DR: An approach is presented to calculate thermal boundary resistance in molecules, which occurs, for example, at the interfaces between moieties held at fixed temperatures and a molecular bridge that connects them, in terms of the low-order anharmonic interactions between a moiety and a Molecular bridge.
Abstract: An approach is presented to calculate thermal boundary resistance in molecules, which occurs, for example, at the interfaces between moieties held at fixed temperatures and a molecular bridge that connects them. If the vibrational frequencies of each moiety lie outside of the band of heat-carrying modes of the bridge, anharmonic interactions mediate thermal conduction at the boundaries. We have expressed thermal boundary conductance in terms of the low-order anharmonic interactions between a moiety and a molecular bridge. Differences in the temperature-dependent boundary conductance at each end of the bridge can be exploited in the design of a molecular thermal diode. The approach is illustrated with the calculation of thermal boundary conductance and thermal rectification in azulene-(CH2)N-anthracene.
TL;DR: Low resistance states with desired quantized conductance values are successfully achieved, thus showing the potential for ultrahigh density memory applications and extrapolated retention properties over ten years are demonstrated.
Abstract: Resistive switching and conductance quantization are systematically studied in a Ag/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester/indium?tin oxide sandwich structure. The observed bipolar switching behavior can be attributed to the formation and dissolution of Ag filaments during positive and negative voltage sweeps, respectively. More importantly, conductance quantization with both integer and half integer multiples of single atomic point contact can be realized by slowing down the voltage sweep speed as well as by pulse measurement. The former may reflect the formed Ag filaments with different atomic point contacts, while the latter probably originates from the interaction between the Ag filaments and the elemental hydrogen provided by the organic storage medium. With appropriate current compliances, low resistance states with desired quantized conductance values are successfully achieved, thus showing the potential for ultrahigh density memory applications. Besides, 100 successive switching cycles with densely distributed resistance values of each resistance state and extrapolated retention properties over ten years are also demonstrated.
TL;DR: In this paper, single-molecule conductance of three sulphur-functionalized organometallic wires with two ruthenium(II) centers spaced by 1,3-butadiyne was investigated using an electrochemically assisted-mechanically controllable break junction (EC-MCBJ) approach.
Abstract: Single-molecule conductance of three sulphur-functionalized organometallic wires with two ruthenium(II) centres spaced by 1,3-butadiyne was firstly investigated using an electrochemically assisted-mechanically controllable break junction (EC-MCBJ) approach. It is demonstrated that single-molecular conductance of these diruthenium(II) incorporated systems is significantly higher than oligo(phenylene-ethynylene) (OPE) having comparable lengths and exhibits weaker length dependence. The conductance improvement in these diruthenium(II) molecules is ascribable to the better energy match of the Fermi level of gold electrodes with the HOMO that is mainly resident on the Ru–CC–CC–Ru backbone. Furthermore, modulation of molecular conductance is achieved by changing the length and π-conjugated system of the chelating 2,2′:6′,2′′-terpyridyl ligand.
TL;DR: A temperature analysis of the conductance curves revealed that electron-phonon coupling is the principal decoherence mechanism causing large conductance oscillations at low temperature.
Abstract: Quantum interference in cross-conjugated molecules embedded in solid-state devices was investigated by direct current-voltage and differential conductance transport measurements of anthraquinone (AQ)-based large area planar junctions. A thin film of AQ was grafted covalently on the junction base electrode by diazonium electroreduction, while the counter electrode was directly evaporated on top of the molecular layer. Our technique provides direct evidence of a large quantum interference effect in multiple CMOS compatible planar junctions. The quantum interference is manifested by a pronounced dip in the differential conductance close to zero voltage bias. The experimental signature is well developed at low temperature (4 K), showing a large amplitude dip with a minimum >2 orders of magnitude lower than the conductance at higher bias and is still clearly evident at room temperature. A temperature analysis of the conductance curves revealed that electron-phonon coupling is the principal decoherence mechanism causing large conductance oscillations at low temperature.
TL;DR: In this paper, conductance quantization in an anion-migration-based resistive switching memory cell with the structure of (Ti, Ta, W)/Ta2O5/Pt.
Abstract: Quantized conductance was observed in an anion-migration-based resistive switching memory cell with the structure of (Ti, Ta, W)/Ta2O5/Pt. The conductance of the cell varies stepwise in units of single atomic conductance (77.5 μS), which is responsible for the formation and annihilation of atomic scale filament built from oxygen vacancies in Ta2O5 film. The quantized conductance behavior can be modulated by voltage pulses as fast as 100 ns. The demonstration of conductance quantization in Ta2O5 based memory device would open the door for quantized multi-bit data storage of anion-migration-based resistive switching nonvolatile memories.
TL;DR: This work demonstrates that the conductance of bithiophene displays a strong dependence on the conformational fluctuations accessible within a given junction configuration, and that the symmetry of such small molecules can significantly influence their conductance behaviors.
Abstract: We have measured the single-molecule conductance of a family of bithiophene derivatives terminated with methyl sulfide gold-binding linkers using a scanning tunneling microscope based break-junction technique. We find a broad distribution in the single-molecule conductance of bithiophene compared with that of a methyl sulfide terminated biphenyl. Using a combination of experiments and calculations, we show that this increased breadth in the conductance distribution is explained by the difference in 5-fold symmetry of thiophene rings as compared to the 6-fold symmetry of benzene rings. The reduced symmetry of thiophene rings results in a restriction on the torsion angle space available to these molecules when bound between two metal electrodes in a junction, causing each molecular junction to sample a different set of conformers in the conductance measurements. In contrast, the rotations of biphenyl are essentially unimpeded by junction binding, allowing each molecular junction to sample similar conformers...
TL;DR: This work model the zero-bias conductance for the four different DNA strands that were used in conductance measurement experiment and finds that the coherent electrical conductance is tremendously smaller than what the experiments measure.
Abstract: In this work, we model the zero-bias conductance for the four different DNA strands that were used in conductance measurement experiment [A. K. Mahapatro, K. J. Jeong, G. U. Lee, and D. B. Janes, Nanotechnology 18, 195202 (2007)]. Our approach consists of three elements: (i) ab initio calculations of DNA, (ii) Green's function approach for transport calculations, and (iii) the use of two parameters to determine the decoherence rates. We first study the role of the backbone. We find that the backbone can alter the coherent transmission significantly at some energy points by interacting with the bases, though the overall shape of the transmission stays similar for the two cases. More importantly, we find that the coherent electrical conductance is tremendously smaller than what the experiments measure. We consider DNA strands under a variety of different experimental conditions and show that even in the most ideal cases, the calculated coherent conductance is much smaller than the experimental conductance. To understand the reasons for this, we carefully look at the effect of decoherence. By including decoherence, we show that our model can rationalize the measured conductance of the four strands, both qualitatively and quantitatively. We find that the effect of decoherence on $G:C$ base pairs is crucial in getting agreement with the experiments. However, the decoherence on $G:C$ base pairs alone does not explain the experimental conductance in strands containing a number of $A:T$ base pairs. Including decoherence on $A:T$ base pairs is also essential. By fitting the experimental trends and magnitudes in the conductance of the four different DNA molecules, we estimate for the first time that the deocherence rate is 6 meV for $G:C$ and 1.5 meV for $A:T$ base pairs.
TL;DR: In this article, the authors studied photoinduced electron injection efficiencies from modular assemblies of a Zn-porphyrin dye and a series of linker molecules which are axially bound to the Znporphryin complex and covalently bound to TiO2 nanoparticles.
Abstract: High performance dye-sensitized solar cells (DSSCs) rely upon molecular linkers that allow efficient electron transport from the photoexcited dye into the conduction band of the semiconductor host substrate. We have studied photoinduced electron injection efficiencies from modular assemblies of a Zn-porphyrin dye and a series of linker molecules which are axially bound to the Zn-porphyrin complex and covalently bound to TiO2 nanoparticles. Experimental measurements based on terahertz spectroscopy are compared to the calculated molecular conductance of the linker molecules. We find a linear relationship between measured electron injection efficiency and calculated single-molecule conductance of the linker employed. Since the same chromophore is used in all cases, variations in the absorptivities of the adsorbate complexes are quite small and cannot account for the large variations in observed injection efficiencies. These results suggest that the linker single-molecule conductance is a key factor that shou...
TL;DR: In this article, the authors used an admittance spectroscopy technique to study the electrical properties of the samples La 0.67 Ba 0.33 Mn 1− x Fe x O 3, and found that the material evolves from metallic to semi-insulating behavior when increasing Fe content.
TL;DR: In this article, the effect of surface plasmons on the conductance of single-molecule junctions was studied using a squeezable break junction setup, and the plasmon induced oscillating field within the nanoscale metal gap was calculated to be ∼1000.
Abstract: The effect of surface plasmons on the conductance of single-molecule junctions is studied using a squeezable break junction setup. We show that the conductance of 2,7-diaminofluorene single-molecule junctions can be enhanced upon laser irradiation. Our experimental approach enables us to show that this enhancement is due to the plasmon-induced oscillating field within the nanoscale metal gap of the junctions. The effective plasmon field enhancement within the gap is calculated to be ∼1000. The experimental procedure presented in this work, which enables one to explore the coupling between plasmons and molecular excitations via transport measurements, could potentially become a valuable tool in the field of plexcitonics.
TL;DR: The observation of quantum interference effects occurring at room temperature in single-molecule junctions based on oligo(3)-phenylenevinylene (OPV3) derivatives, in which the central benzene ring is coupled to either para- or meta-positions, finds that the conductance for a single meta-opV3 molecule wired between gold electrodes is one order of magnitude smaller than that of a para-OPV2 molecule.
Abstract: Interference effects on charge transport through an individual molecule can lead to a notable modulation and suppression on its conductance. In this letter, we report the observation of quantum interference effects occurring at room temperature in single-molecule junctions based on oligo(3)-phenylenevinylene (OPV3) derivatives, in which the central benzene ring is coupled to either para- or meta-positions. Using the break-junction technique, we find that the conductance for a single meta-OPV3 molecule wired between gold electrodes is one order of magnitude smaller than that of a para-OPV3 molecule. Theoretical calculations confirm the occurrence of constructive and destructive interference in the para- and meta-OPV3 molecules respectively, which arises from the phase difference of the transmission coefficients through the molecular orbitals.
TL;DR: In this paper, the authors measured simultaneously force and conductance of Ag metal point-contacts under ambient conditions at room temperature and found that the conductance features at ∼ 0.4 G0 and ∼ 1.3 G0 can be attributed to a single-atom contact with an oxygen atom in parallel.
Abstract: We measure simultaneously force and conductance of Ag metal point-contacts under ambient conditions at room temperature. We observe the formation of contacts with a conductance close to 1 G0, the quantum of conductance, which can be attributed to a single-atom contact, similar to those formed by Au. We also find two additional conductance features at ∼0.4 G0 and ∼1.3 G0, which have been previously ascribed to contacts with oxygen contaminations. Here, using a conductance cross-correlation technique, we distinguish three different atomic-scale structural motifs and analyze their rupture forces and stiffness. Our results allow us to assign the ∼0.4 G0 conductance feature to an Ag–O–Ag contact and the ∼1.3 G0 feature to an Ag–Ag single-atom contact with an oxygen atom in parallel. Utilizing complementary information from force and conductance, we thus demonstrate the correlation of conductance with the structural evolution at the atomic scale.
01 Jan 2013
TL;DR: The correlation of conductance with the structural evolution at the atomic scale is demonstrated by using a conductance cross-correlation technique to distinguish three different atomic-scale structural motifs and analyze their rupture forces and stiffness.
Abstract: We measure simultaneously force and conductance of Ag metal point-contacts under ambient conditions at room temperature. We observe the formation of contacts with a con- ductance close to 1 G0, the quantum of conductance, which can be attributed to a single-atom contact, similar to those formed by Au. We also find two additional conductance features at ∼0.4 G0 and ∼1.3 G0, which have been previously ascribed to contacts with oxygen contaminations. Here, using a conductance cross-correlation technique, we distinguish three different atomic-scale structural motifs and analyze their rupture forces and stiffness. Our results allow us to assign the ∼0.4 G0 conductance feature to an AgOAg contact and the ∼1.3 G0 feature to an AgAg single-atom contact with an oxygen atominparallel.Utilizingcomplementaryinformationfromforceandconductance,wethusdemonstratethecorrelationofconductancewiththestructural evolution at the atomic scale.
TL;DR: In this article, the authors measured electric conductance and surface enhanced Raman scattering (SERS) spectra for the benzenedithiol molecules bridging between Au nano gap electrodes at room temperature to investigate the electric and optical properties of the molecular junction.
Abstract: We have measured electric conductance and surface enhanced Raman scattering (SERS) spectra for the benzenedithiol molecules bridging between Au nano gap electrodes at room temperature to investigate the electric and optical properties of the molecular junction. The current–voltage characteristic of the molecular junction was investigated based on the single level tunneling model considering that the Fermi distribution function got smeared out for finite temperature, which provided the information on the number of molecules bridging metal electrodes, energy difference between conduction orbital and Fermi level, strength of the molecule-metal coupling. The conductance measurements confirmed the interaction between molecule and Au electrodes. Due to the interaction between molecule and metal electrodes, we could observe the SERS spectra characteristic of the molecular junction. The SERS measurement showed the disappearance of the SH modes and red shift of some internal vibration modes, which confirmed the mo...