Showing papers on "Conductance published in 2002"
TL;DR: In this article, a single-crystalline SnO2 nanobelts were fabricated using the integrity of a single nanobelt with a sensitivity at the level of a few ppb.
Abstract: Gas sensors have been fabricated using the single-crystalline SnO2 nanobelts. Electrical characterization showed that the contacts were ohmic and the nanobelts were sensitive to environmental polluting species like CO and NO2, as well as to ethanol for breath analyzers and food control applications. The sensor response, defined as the relative variation in conductance due to the introduction of the gas, is 4160% for 250 ppm of ethanol and −1550% for 0.5 ppm NO2 at 400 °C. The results demonstrate the potential of fabricating nanosized sensors using the integrity of a single nanobelt with a sensitivity at the level of a few ppb.
1,424 citations
TL;DR: Analysis shows that all the three approaches are able to capture the important electrostatic interactions between ions and the charge distribution of the channel that govern ion permeation and selectivity in OmpF, which suggests that a treatment on the basis of a rigid protein and continuum dielectric solvent is valid in the case of Ompf.
372 citations
TL;DR: Evidence is presented that the disappearance of the 0.7 structure at very low temperature signals the formation of a Kondo-like correlated spin state, including a zero-bias conductance peak that splits in a parallel field, scaling of conductance to a modified Kondo form, and consistency between peak width and the Kondo temperature.
Abstract: Besides the usual conductance plateaus at multiples of 2e(2)/h, quantum point contacts typically show an extra plateau at approximately 0.7(2e(2)/h), believed to arise from electron-electron interactions that prohibit the two spin channels from being simultaneously occupied. We present evidence that the disappearance of the 0.7 structure at very low temperature signals the formation of a Kondo-like correlated spin state. Evidence includes a zero-bias conductance peak that splits in a parallel field, scaling of conductance to a modified Kondo form, and consistency between peak width and the Kondo temperature.
335 citations
TL;DR: Results show that the low-bias conductance of molecules is dominated by resonant tunneling through coupled electronic and vibration levels, approaching the single-molecule limit.
Abstract: A new method of fabricating small metal-molecule-metal junctions is developed, approaching the single-molecule limit. The conductance of different conjugated molecules in a broad temperature, source-drain, and gate voltage regime is reported. At low temperature, all investigated molecules display sharp conductance steps periodic in source-drain voltage. The position of these steps can be controlled by a gate potential. The spacing corresponds to the energy of the lowest molecular vibrations. These results show that the low-bias conductance of molecules is dominated by resonant tunneling through coupled electronic and vibration levels.
293 citations
TL;DR: The differential conductance of individual multiwall carbon nanotubes is measured and a Kondo enhancement of the conductance is observed when the number of electrons on the tube is odd.
Abstract: We have measured the differential conductance of individual multiwall carbon nanotubes. Coulomb blockade and energy level quantization are observed. The electron levels are nearly fourfold degenerate (including spin) and their evolution in magnetic field (Zeeman splitting) agrees with a g factor of 2. In zero magnetic field the sequential filling of states evolves with spin S according to S = 0-->1/2-->0.... A Kondo enhancement of the conductance is observed when the number of electrons on the tube is odd.
168 citations
TL;DR: In this paper, the atomic arrangements and quantum conductance of silver nanowires generated by mechanical elongation were analyzed and the structural properties of Ag nano-structures were analyzed.
Abstract: We have analyzed the atomic arrangements and quantum conductance of silver nanowires generated by mechanical elongation. The surface properties of Ag induce unexpected structural properties, such as, for example, predominance of high aspect-ratio rodlike wires. The structural behavior was used to understand the Ag quantum conductance data and the proposed correlation was confirmed by means of theoretical calculations. These results emphasize that the conductance of metal point contacts is determined by the preferred atomic structures, and that atomistic descriptions are essential to interpret the quantum transport behavior of metal nanostructures.
151 citations
TL;DR: In this paper, a scanned probe technique based on electrostatic force microscopy capable of probing the conductance of samples without requiring attached leads was proposed. But the technique was not suitable for the case of DNA, which is a subject with reported results ranging from metallic to insulating.
Abstract: We have devised a scanned probe technique based on electrostatic force microscopy capable of probing the conductance of samples without requiring attached leads. We demonstrate that, using our technique, conductance can be probed on length scales as small as 0.4 Im. To demonstrate the utility of our technique, we use it to probe the conductance of DNA, a subject that has been the focus of intense debate with reported results ranging from metallic to insulating. In contrast to conducting single-wall carbon nanotubes, used as a control, individual strands of I-DNA, a widely studied sequence, are found to be insulating on the length scale probed.
151 citations
TL;DR: In this article, self-assembled monolayers of 4-ferrocenylbenzyl alcohol attached to silicon provided the basis for electrolyte-molecule-silicon capacitors.
Abstract: Self-assembled monolayers of 4-ferrocenylbenzyl alcohol attached to silicon provided the basis for electrolyte-molecule-silicon capacitors. Characterization by conventional capacitance and conductance techniques showed very high capacitance and conductance peaks near ∼0.6 V associated with charging and discharging of electrons into and from discrete levels in the monolayer owing to the presence of the redox-active ferrocenes. The reversible charge trapping of these molecules suggest their potential application in memory devices. Due to the molecular scalability and low-power operation, molecular-silicon hybrid devices may be strong candidates for next-generation electronic devices.
105 citations
TL;DR: In this paper, a novel molecular junction based on a monolayer between carbon and mercury contacts was investigated by examining current/voltage behavior as a function of temperature and monolayers thickness.
Abstract: A novel molecular junction based on a monolayer between carbon and mercury “contacts” was investigated by examining current/voltage behavior as a function of temperature and monolayer thickness. Monolayers of phenyl, biphenyl, and terphenyl were covalently bonded to flat, graphitic carbon, then a top contact was formed with a suspended mercury drop. Similar molecular junctions were formed from multilayer nitroazobenzene (NAB) films of 30 A and 47 A thickness, and junctions were examined over the temperature range of +80 °C to −50 °C. Junction resistances were a strong function of molecular length and structure, with mean resistances for 0.78 mm2 junctions of 34.4 Ω, 13.8 KΩ, and 41.0 KΩ for phenyl, biphenyl, and terphenyl junctions. The i/V characteristics of biphenyl and phenyl junctions were nearly independent of temperature, while those of terphenyl and NAB junctions were temperature independent below 0 °C but thermally activated above 10 °C. The results are consistent with a tunneling process at low t...
100 citations
TL;DR: In this article, a molecular junction formed by a 10-15 A organic monolayer between carbon and mercury contacts exhibited conductance switching for several polygonal structures, including a terphenyl junction and a planar quinoid structure.
Abstract: A molecular junction formed by a 10-15 A organic monolayer between carbon and mercury contacts exhibited conductance switching for several monolayer structures. When the carbon potential was scanned to a sufficiently negative voltage relative to the mercury, the junction resistance suddenly decreased by at least an order of magnitude, and high resistance could be restored by a positive voltage scan. The high and low conductance states were persistent, and conductance switching was repeatable at least 100 cycles for the case of a terphenyl junction. The switching behavior is consistent with phenyl ring rotation and formation of a planar, quinoid structure as a consequence of electron injection into the monolayer. A unique feature of the junction structure is the strong electronic coupling between the monolayer p system and the graphitic carbon through a quinoid double bond. Not only does this interaction lead to high conductivity and possible practical applications as a molecular switch, it also combines the electronic properties of the conjugated monolayer with those of the graphitic substrate. The switching mechanism reported here is an example of ‘‘dry electrochemistry’’ in which a redox process appears to occur under the influence of a high electric field in the absence of solvent or electrolyte. © 2002 The Electrochemical Society. @DOI: 10.1149/1.1490716#
100 citations
TL;DR: In this article, the authors investigated the temperature dependence of the conductance of Au nanoparticles linked by alkane dithiol molecules in the temperature range between 5 and 300 K and found that the observed temperature dependence is non-Arrhenius-like and can be described in terms of a percolation theory which takes account of disorder in the system.
Abstract: We have investigated theoretically and experimentally the temperature dependence of the conductance of films of Au nanoparticles linked by alkane dithiol molecules in the temperature range between 5 and 300 K. Conduction in these films is due to tunneling of single electrons between neighboring metal nanoparticles via the linker molecules. During tunneling an electron has to overcome the Coulomb charging energy. We find that the observed temperature dependence of the conductance is non-Arrhenius-like and can be described in terms of a percolation theory which takes account of disorder in the system. Disorder in our nanoparticle films is caused by variations in the nanoparticle size, fluctuations in the separation gaps between adjacent nanoparticles and by offset charges. To explain in detail our experimental data, a wide distribution of separation gaps and charging energies has to be assumed. We find that a wide Coulomb charging energy distribution can arise from random offset charges even if the nanoparticle size distribution is narrow.
TL;DR: These data provide the first evidence of AQP6 channel gating at a single-channel level and suggest that each monomer contains the pore region for ions based on the number of Hg2+-binding sites and the kinetics of H g2-activation of the channel.
TL;DR: The classical Smoluchowski formula for streaming potential is shown to be not applicable to the channels (pores) with conducting walls, and measurements of streaming current instead of streaming potential are clearly beneficial in this case.
Abstract: The classical Smoluchowski formula for streaming potential is shown to be not applicable to the channels (pores) with conducting walls. The classical procedure of accounting for surface conductivity may also be ineffective in some cases. Measurements of streaming current instead of streaming potential are clearly beneficial in this case. Variation of channel height may also be used to extrapolate to true values of ζ-potential not complicated by the wall conductivity.
TL;DR: Three experiments that quantify the amount of selectivity exhibited by a biological ion channel are examined with Poisson-Nernst-Planck (PNP) theory and the results show that the conductance ratio measures the ratio of the diffusion coefficients of the ions inside the channel and the permeability ratio measures both diffusion coefficients and excess chemical potentials.
Abstract: Three experiments that quantify the amount of selectivity exhibited by a biological ion channel are examined with Poisson-Nernst-Planck (PNP) theory. Conductance ratios and the conductance mole fraction experiments are examined by considering a simple model ion channel for which an approximate solution to the PNP equations with Donnan boundary conditions is derived. A more general result is derived for the Goldman-Hodgkin-Katz permeability ratio. The results show that (1) the conductance ratio measures the ratio of the diffusion coefficients of the ions inside the channel, (2) the mole fraction experiment measures the difference of the excess chemical potentials of the ions inside the channel, and (3) the permeability ratio measures both diffusion coefficients and excess chemical potentials. The results are used to divide selectivity into two components: partitioning, an equilibrium measure of how well the ions enter the channel, and diffusion, a nonequilibrium measure of how well the ions move through the channel.
TL;DR: The validity of the tetraphenylarsonium-tetraphenyborate hypothesis that the magnitude of the hydration energies of the anions and cations are equal (i.e., charge independent), so that their different rates of transport across the membrane are solely due to differential interactions with the membrane phase is investigated.
TL;DR: In this article, an analysis on the conductance of multiwall carbon nanotubes (MWNTs) is presented, and it is shown that tunneling current between states on different walls of a defect-free, infinitely long MWNT is vanishingly small in general, which leads to the quantization of the MWNT's.
Abstract: An analysis on the conductance of multiwall carbon nanotubes (MWNT's) is presented. Recent experiment indicated that MWNT's are good quantum conductors. Our theory shows that tunneling current between states on different walls of a defect-free, infinitely long MWNT is vanishingly small in general, which leads to the quantization of the conductance of the MWNT's. With a reasonable simple model, we explicitly show that the conductance of a capped MWNT can be determined by the outermost wall for an infinitely long nanotube. We apply the theory to finite MWNT's and estimate the generic interwall conductance to be negligible compared to the intrawall ballistic conductance.
TL;DR: Using oxygen adsorption experiments on poly (dG)-poly (dC) DNA molecules, the authors found that their conductance can be easily controlled by several orders of magnitudes using oxygen hole doping, which is a characteristic behavior of a p-type semiconductor.
Abstract: Using oxygen adsorption experiments on poly (dG)-poly (dC) DNA molecules, we found that their conductance can be easily controlled by several orders of magnitudes using oxygen hole doping, which is a characteristic behavior of a p-type semiconductor. It also suggests that the conductance of the DNA under doping results from charge carrier transport, not from an ionic conduction. On the other hand, we will also show that the poly (dA)-poly (dT) DNA molecules behave as an n-type semiconductor. This letter demonstrates that the concentration and the type of carriers in the DNA molecules could be controlled using proper doping methods.
TL;DR: In this article, a generalized conductance formula for the multiband tight-binding model based on the formula by Caroli is presented, and the transmission coefficients for Bloch states can be calculated using the expression for the self-energies of the leads in terms of the eigenstates of the secular matrix.
Abstract: We present a generalized conductance formula for the multiband tight-binding model based on the formula by Caroli. We show that the transmission coefficients for Bloch states can be calculated using the expression for theself-energies of the leads in terms of the eigenstates of the secular matrix. We also show that evanescent states cannot be neglected in the calculation as is usually done. Although they do not explicitly contribute to the total conductance, they are needed to obtain the correct Green's function and the self-energies. This formula allows for an alternative to the usual iterative method for calculating the conductance of a molecule connected to two semi-infinite leads, and can give the contributions to the conductance decomposed by conduction channel.
TL;DR: In this paper, conductance switching of single phenylene ethynylene oligomers embedded in matrices of alkanethiolates is analyzed using scanning tunneling microscopy, and the authors conclude that the molecular switching is a result of motions of the molecules or bundles, rather than electrostatic effects of charge transfer.
Abstract: We have analyzed the conductance switching of single phenylene ethynylene oligomers embedded in matrices of alkanethiolates. When the molecules are studied using scanning tunneling microscopy, they switch reversibly between discrete states that differ in their apparent height by ~ 3 A. The persistence times for molecules in either state ranges from seconds to tens of hours. We demonstrate several methods to control the defect density and quality of the host alkanethiolate matrix, which in turn affects the rate at which the inserted molecules switch. A vapor annealing procedure is described that increases order in the matrix film and reduces the switching rate. Decreased matrix deposition time results in a less-ordered film that increases the switching rate. Because the molecular switching depends on matrix order, we conclude that the switching is a result of motions of the molecules or bundles, rather than electrostatic effects of charge transfer.
TL;DR: In this article, the effects of relative humidity on the conductance of the assembly of poly(dG)-poly(dC) and poly(DA)-poly (dT) DNA molecules were studied.
TL;DR: In this article, the electric conductance of the graphite ribbon with locally applied gate voltage has been studied in terms of the Landauer approach, and it has been shown that it is possible to fabricate a nano-graphite-based switching device by the application of weak gate voltage bias.
Abstract: The electric conductance of the graphite ribbon with locally applied gate voltage has been studied in terms of the Landauer approach. In the low-energy region, nano-graphite ribbon with zigzag boundaries exhibits the single electronic transport channel due to the edge states. The chemical potential dependence of the electric conductance shows qualitatively different behavior, depending on whether the magnitude of the potential barrier (gate voltage bias) Vg is larger than the energy gap Δ of the single channel region of the zigzag ribbon. For positive Vg with Vg Vg. This step-function-like behavior of the conductance shows that it is possible to fabricate a nano-graphite-based switching device by the application of weak gate voltage bias.
TL;DR: The results of this study could be tentatively accounted for by an assumption that one of the rate-limiting steps of proton conduction through gramicidin channels represents, in fact, movement of negatively charged species (negative ionic defects) across a membrane.
TL;DR: In this paper, an antiresonance scattering can occur when an extra defect level is introduced into a conduction band and the conductance of a one-dimensional wire disappears, in good agreement with ab initio calculations.
Abstract: For the ballistic quantum transport, the conductance of each channel is quantized to a value of ${2e}^{2}/h.$ In the presence of defects, electrons will be scattered such that the conductance will deviate from the values of the quantized conductance. We show that an antiresonance scattering can occur when an extra defect level is introduced into a conduction band. At the antiresonance scattering, exactly one quantum conductance of a one-dimensional wire disappears, in good agreement with ab initio calculations. The conductance takes a nonzero value when the Fermi energy is away from the antiresonance scattering.
TL;DR: In this paper, the quantum transport properties of the ultrathin silver nanowires are investigated, and three conduction channels are found, corresponding to three $s$ bands crossing the Fermi level.
Abstract: The quantum transport properties of the ultrathin silver nanowires are investigated. For a perfect crystalline nanowire with four atoms per unit cell, three conduction channels are found, corresponding to three $s$ bands crossing the Fermi level. One conductance channel is disrupted by a single-atom defect, either adding or removing one atom. Quantum interference effect leads to oscillation of conductance versus the inter-defect distance. In the presence of multiple-atom defect, one conduction channel remains robust at Fermi level regardless the details of defect configuration. The histogram of conductance calculated for a finite nanowire (seven atoms per cross section) with a large number of random defect configurations agrees well with recent experiment.
TL;DR: In this article, the interface trap density of low-to-mid 10 11 eV -1 cm -2 was obtained from temperature conductance-voltage measurements, and a slightly lower number was obtained as compared to the conductance method.
Abstract: GaN metal oxide semiconductor diodes were demonstrated utilizing MgO as the gate oxide. MgO was grown at 100°C on metal oxide chemical vapor deposition grown n-GaN in a molecular beam epitaxy system using a Mg elemental source and an electron cyclotron resonance oxygen plasma. H 3 PO 4 -based wet-chemical etchant was used to remove MgO to expose the underlying n-GaN for ohmic metal deposition. Electron deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallization, respectively. An interface trap density of low-to-mid-10 11 eV -1 cm -2 was obtained from temperature conductance-voltage measurements. Terman method was also used to estimate the interface trap density, and a slightly lower number was obtained as compared to the conductance method. Results from elevated temperature (up to 300°C) conductance measurements showed an interface state density roughly three times higher (6 × 10 11 eV -1 cm -2 ) than at 25°C.
TL;DR: In this paper, a small quantum dot coupled to two external leads is considered and different signs of dot-lead coupling matrix elements give rise to qualitatively different behavior of physical observables such as the conductance, the phase of the transmission amplitude, and the differential capacitance of the dot.
Abstract: A small quantum dot coupled to two external leads is considered. Different signs of the dot-lead coupling matrix elements give rise to qualitatively different behavior of physical observables such as the conductance, the phase of the transmission amplitude, and the differential capacitance of the dot. For certain relative signs the conductance may vanish at values of the gate potential, where the spectral density is maximal. Zeroes of the conductance are robust against increasing the dot-lead coupling. They are associated with abrupt phase lapses in the transmission phase whose width vanishes as the square of the temperature. We carefully distinguish between phase lapses of $\ensuremath{-}\ensuremath{\pi}$ and phase antilapses of $\ensuremath{\pi}.$
TL;DR: In this paper, first-principles calculations on electron transport through Na nanowires at finite bias voltages are presented, and the mechanism of the occurrence of NDC is also demonstrated based on the finding that a voltage drop locally occurs on the negatively biased end of the nanowire.
Abstract: We present first-principles calculations on electron transport through Na nanowires at finite bias voltages. A nanowire exhibits a nonlinear current-voltage characteristic and negative differential conductance (NDC). NDC is induced by the drastic suppression of the electron-transmission peaks which is attributed to the reduction of the electron conductance through the negatively biased side of the system. The mechanism of the occurrence of NDC is also demonstrated based on the finding that a voltage drop locally occurs on the negatively biased end of the nanowire.
TL;DR: In this paper, the conductance properties of a chain of Na atoms between two metallic leads in the limit of low bias were examined and it was shown that the geometrical shape of the contact leads influences the conductivity by giving rise to additional oscillations as a function of the lead opening angle.
Abstract: We examine the conductance properties of a chain of Na atoms between two metallic leads in the limit of low bias. Resonant states corresponding to the conductance channel and the local charge neutrality condition cause conductance oscillations as a function of the number of atoms in the chain. Moreover, the geometrical shape of the contact leads influences the conductivity by giving rise to additional oscillations as a function of the lead opening angle.
TL;DR: In this article, the lattice vacancy effects on electrical conductance of nanographite ribbon are investigated by means of the Landauer approach using a tight binding model in the low-energy regime.
Abstract: Lattice vacancy effects on electrical conductance of nanographite ribbon are investigated by means of the Landauer approach using a tight binding model In the low-energy regime ribbons with zigzag boundary provide a single conducting channel whose origin is connected with the presence of edge states It is found that the chemical potential dependence of conductance strongly depends on the difference (Δ) of the number of removed A and B sublattice sites The large lattice vacancy with Δ≠0 shows 2Δ zero-conductance dips in the single-channel region, however, the large lattice vacancy with Δ=0 has no dip structure in this region The connection between this conductance rule and the Longuet-Higgins conjecture is also discussed
TL;DR: In this article, Rejec et al. derived the Seebeck thermopower coefficient and linear thermal conductance within the framework of the Landauer-B\"uttiker formalism.
Abstract: Thermoelectric transport coefficients are determined for semiconductor quantum wires with weak thickness fluctuations. Such systems exhibit anomalies in conductance near 1/4 and 3/4 of ${2e}^{2}/h$ on the rising edge to the first conductance plateau, explained by singlet and triplet resonances of conducting electrons with a single weakly bound electron in the wire [T. Rejec, A. Ram\ifmmode \check{s}\else \v{s}\fi{}ak, and J.H. Jefferson, Phys. Rev. B 62, 12 985 (2000)]. We extend this work to study the Seebeck thermopower coefficient and linear thermal conductance within the framework of the Landauer-B\"uttiker formalism, which also exhibit anomalous structures. These features are generic and robust, surviving to temperatures of a few degrees. It is shown quantitatively how at elevated temperatures thermal conductance progressively deviates from the Wiedemann-Franz law.