Showing papers on "Conductance published in 1999"
TL;DR: In this paper, the effect of modifying the molecule−electrode binding interface of an α,α,α-xylyl-dithiol molecular wire was investigated and it was shown that except for the length of the surface bond, the conductance is not affected by variations of surface geometry.
Abstract: We report on the effect of modifying the molecule−electrode binding interface of an α,α‘-xylyl-dithiol molecular wire. We find that except for the length of the surface bond, the conductance is not affected by variations of the surface geometry. We also compare the conductance of different terminal atom−electrode metal combinations and find that the conductance is substantially larger when the wire is terminated by selenium rather than sulfur or oxygen. We also find that gold makes a better electrode than silver.
333 citations
246 citations
TL;DR: The physical mechanisms underlying the transport of ions across a model potassium channel, which corresponds closely to that deduced from crystallography, and the conductance exhibits the saturation property observed experimentally are described.
210 citations
TL;DR: In this paper, the conductance through two quantum dots in series is studied using general qualitative arguments and quantitative slave-boson mean-field theory, and it is demonstrated that measurements of conductance can explore the phase diagram of the two-impurity Anderson model.
Abstract: The conductance through two quantum dots in series is studied using general qualitative arguments and quantitative slave-boson mean-field theory. It is demonstrated that measurements of the conductance can explore the phase diagram of the two-impurity Anderson model. Competition between the Kondo effect and the interdot magnetic exchange leads to a two-plateau structure in the conductance as a function to the gate voltage and a two or three peak structure in the conductance versus interdot tunneling. [S0031-9007(99)09017-1]
178 citations
TL;DR: In this article, measurements on the Kondo effect in a small quantum dot connected strongly to one lead and weakly to the other have been performed, showing that the conductance of the dot reveals an offset of the kondo resonance at zero magnetic field.
Abstract: We present measurements on the Kondo effect in a small quantum dot connected strongly to one lead and weakly to the other. The conductance of the dot reveals an offset of the Kondo resonance at zero magnetic field. While the resonance persists in the negative bias regime, it is suppressed in the opposite direction. This demonstrates the pinning of the Kondo resonance to the Fermi levels of the leads.
176 citations
Patent•
04 Jun 1999
TL;DR: In this paper, a vapor supply apparatus, for use in a semiconductor device manufacturing process, provides high flow conductance and high thermal conductance showerhead plate for supplying various precursors to a reaction chamber.
Abstract: A vapor supply apparatus, for use in a semiconductor device manufacturing process, provides high flow conductance and high thermal conductance showerhead plate for supplying various precursors to a reaction chamber. The high flow conductance and high thermal conductance showerhead plate comprises a thick plate for high thermal conductance and variable size delivery hole for high flow conductance. A variation of the high flow conductance and high thermal conductance showerhead plate having the delivery holes tilted outward can be used as a baffle to diffuse the precursor to a large area. A showerhead system using high flow conductance and high thermal conductance showerhead plates is well suitable for delivering liquid precursors.
147 citations
01 May 1999
TL;DR: It is shown that in a convex body in IR, with diameter D, random walk with steps in a ball with radius δ mixes in O(nD/δ) time (if idle steps at the boundary are not counted).
Abstract: The notion of conductance introduced by Jerrum and Sinclair [JS] has been widely used to prove rapid mixing of Markov chains. Here we introduce a variant of this instead of measuring the conductance of the worst subset of states, we show that it is enough to bound a certain weighted average conductance (where the average is taken over subsets of states with different sizes.) In the case of convex bodies, we show that this average conductance is better than the known bounds for the worst case; this helps us save a factor of O(n) which is incurred in all proofs as a “penalty” for a “bad start” (i.e., because the starting distribution may be arbitrary). We show that in a convex body in IR, with diameter D, random walk with steps in a ball with radius δ mixes in O(nD/δ) time (if idle steps at the boundary are not counted). This gives an O(n) sampling algorithm after appropriate preprocessing, improving the previous bound of O(n).
127 citations
TL;DR: In this article, the spin-polarized quasiparticle transport in ferromagnet-$d$-wave-superconductor junctions with the same interface was studied.
Abstract: Within a scattering framework, a theoretical study is presented for the spin-polarized quasiparticle transport in ferromagnet--$d$-wave-superconductor junctions with ${110}$ interface. We find that the subgap conductance behaviors are qualitatively different from a nonmagnetic case, due to the modification of Andreev reflection by the exchange field in the ferromagnet, and can also be significantly different from those of a ferromagnet--$s$-wave junction because of the sign change of the d-wave order parameter along the ${110}$ direction of the crystal. For a ballistic ferromagnet--$d$-wave-superconductor junction, a zero-bias conductance minimum is achieved. In addition, a conductance maximum at finite bias can also be evolved by interfacial scattering. For a normal-metal--ferromagnet--$d$-wave-superconductor junction, conductance resonances are predicted.
113 citations
TL;DR: In this paper, the second moment of the distribution of the Tn's was measured by measuring the voltage dependence of the conductance s √GyV 2 IyV 2 d d and showed that the fluctuation pattern changes randomly between contact configurations and that the amplitude of the fluctuations is suppressed for conductance values near G0.
Abstract: Metallic contacts consisting of only a few atoms can be obtained using scanning tunneling microscopy or mechanically controllable break junction [1] techniques. The electrical conductance through such contacts is described in terms of electronic wave modes by the Landauer-Buttiker formalism [2]. Each of the N modes forms a channel for the conductance, with a transmission probability Tn between 0 and 1. The total conductance is given by the sum over these channels G › P N›1 TnG0, where G0 › 2e 2 yh is the quantum of conductance. By recording histograms of conductance values [3] for contacts of simple metals (Na, Au), a statistical preference was observed for conductances near integer values. This statistical preference was interpreted as an indication that transmitted modes in the most probable contacts are completely opened (Tn › 1, i.e., saturation of channel transmission), in analogy with the conductance quantization observed in 2D electron gas devices [4]. Here, we test this interpretation by performing a new type of measurement giving access to the second moment of the distribution of the Tn’s. The atomic contacts are formed by breaking a gold wire at low temperatures, and then finely adjusting the size of the contact between the fresh fracture surfaces using a piezoelectric element [1]. Figure 1 shows the differential conductance, ›Iy›V measured as a function of bias voltage for three atomic-size contacts with different conductance values, using a modulation voltage eV ? kBu (with u the temperature). For each contact, both of the curves for increasing and decreasing bias voltage are given. Measurements such as those of Fig. 1 suggest that the fluctuation pattern changes randomly between contact configurations and that the amplitude of the fluctuations is suppressed for conductance values near G0. In order to establish such a relation, it is necessary to statistically average over a large number of contacts. We do this by measuring the voltage dependence of the conductance s›Gy›V › › 2 Iy›V 2 d and
112 citations
TL;DR: In this paper, the authors demonstrate the electrical conductance quantization in a Ni nanowire formed in a break junction between a ferromagnetic Ni wire and a Ni plate in applied magnetic fields.
Abstract: We demonstrate the electrical conductance quantization in a Ni nanowire formed in a break junction between a ferromagnetic Ni wire and a Ni plate in applied magnetic fields. The conductance of the nanowire is clearly quantized in units of 2e2/h in a zero magnetic field, but it is switched to e2/h by applying magnetic fields above 60 Oe. This switching behavior seems closely related to a ferromagnetic domain formation in the vicinity of a nanowire, suggesting that nanoscale magnetic domain walls play an important role in determining nanoscale spin-dependent transport. The effect offers the possibility of a new device, a nanoscale colossal magnetoresistive sensor.
108 citations
TL;DR: In this paper, the thermopower and conductance of atomic-size metallic contacts have been simultaneously measured using a mechanically controllable break junction and an expression that describes these results in terms of quantum interference of electrons backscattered in the banks was derived.
Abstract: The thermopower and conductance of atomic-size metallic contacts have been simultaneously measured using a mechanically controllable break junction. For contacts approaching atomic dimensions, abrupt steps in the thermopower are observed which coincide with jumps in the conductance. The measured thermopower for a large number of atomic-size contacts is randomly distributed around the value for large contacts and can be either positive or negative in sign. However, it is suppressed at the quantum value of the conductance ${G}_{0}{=2e}^{2}/h$. We derive an expression that describes these results in terms of quantum interference of electrons backscattered in the banks.
TL;DR: In this article, the electric conductivity of organic molecules was estimated with molecular resolution using self-assembled techniques and scanning tunneling microscopy (STM), and the authors assumed that the molecules are connected to each other with resistors for estimating the effect of intermolecular interaction on the conductance.
Abstract: Electric conductivity of organic molecules was estimated with molecular resolution using self-assembled techniques and scanning tunneling microscopy (STM). Conjugated molecules of [1,1‘:4‘,1‘ ‘-terphenyl]-4-methanethiol (TP) were embedded in self-assembled monolayers of insulative n-alkanethiols, and when observed by STM, TP molecules appeared as protruding domains. The apparent height of the TP domains increases as the lateral size of the domains grows from 1 to 10 nm, reflecting the increase in the vertical conductance of the domains due to the lateral, intermolecular interaction. We assumed that the molecules are connected to each other with resistors for estimating the effect of intermolecular interaction on the conductance and calculated the height of conducting disks with various radii, which should roughly reproduce the size-dependent height of the TP domains observed by STM. The estimated resistance of the single TP molecule was less than 40 GΩ, and the effective lateral conductivity corresponding...
TL;DR: In this paper, field effect conductance measurements were made on individual microscopic crystals of the organic semiconductor sexithiophene (6T) and the resulting wire/6T/wire structures were used in a transistor configuration to probe the in-plane conductance of the crystals as a function of transverse electric field.
Abstract: Field effect conductance measurements were made on individual microscopic crystals of the organic semiconductor sexithiophene (6T). These crystals, ranging from 1 to 6 molecules (2−14 nm) in thickness and from 1 to 2 μm in diameter, were deposited by thermal evaporation onto SiO2 substrates previously patterned with closely spaced (∼400 nm) pairs of Au wires. Atomic force microscopy (AFM) of these substrates demonstrated the growth of individual 6T crystals between the wires. The resulting wire/6T/wire structures were used in a transistor configuration to probe the in-plane conductance of the crystals as a function of transverse electric field (i.e., perpendicular to the substrate). These measurements showed (1) no discernible dependence of the carrier mobility on thicknesseven down to crystals as thin as a monolayersuggesting that much of the current is carried by the first monolayer next to the SiO2, (2) activated transport (EA = 25 meV) at temperatures above 100 K but nearly temperature-independent tra...
TL;DR: In this article, the conductance of carbon nanotubes with a vacancy was studied in a tight-binding model, and the Fermi energy dependence of conductance was examined.
Abstract: The conductance of carbon nanotubes with a vacancy is studied in a tight-binding model. We examine the Fermi energy e dependence of the conductance and show it is quantized into zero, one, and two times the conductance quantum \(e^{2}/\pi\hbar\) depending on the type of vacancy in the half-filled case, i.e., e= 0. In the presence of a magnetic field, the conductance is scaled by the component of the magnetic field in the direction of the vacancy.
TL;DR: In this paper, the authors developed a new theoretical formulation to study ion conductance in electrolyte solutions, based on a mode coupling theory treatment of the electrolyte friction that acts on a moving ion.
Abstract: We develop a new theoretical formulation to study ion conductance in electrolyte solutions, based on a mode coupling theory treatment of the electrolyte friction. The new theory provides expressions for both the ion atmosphere relaxation and electrophoretic contributions to the total electrolyte friction that acts on a moving ion. While the ion atmosphere relaxation term arises from the time-dependent microscopic interaction of the moving ion with the surrounding ions in the solution, the electrophoretic term originates from the coupling of the ion's velocity to the collective current mode of the ion atmosphere. Mode coupling theory, combined with time-dependent density functional theory of ion atmosphere fluctuations, leads to self-consistent expressions for these two terms which also include the effects of self-motion of the ion under consideration. These expressions have been solved for the concentration dependence of electrolyte friction and ion conductance. It is shown that in the limit of very low ion concentration, the present theory correctly reduces to the well-known Debye-Huckel-Onsager limiting law which predicts a linear dependence of conductance on the square root of ion concentration (c). At moderate and high concentrations, the present theory predicts a significant nonlinear and weaker dependence on root c which is in very good agreement with experimental results. The present theory is self-contained and does not involve any adjustable parameter.
TL;DR: It might turn out that the logarithmic relationships between the stimuli of some modalities and the perception of the stimulus intensity have a cellular basis in the involvement of SK conductances in the processing of these stimuli.
TL;DR: Current was measured from single open channels of the calcium release channel of cardiac sarcoplasmic reticulum in pure and mixed solutions of the alkali metal ions Li+, K+, Na+, Rb+, Cs+, ranging in concentration from 25 mM to 2 M.
TL;DR: In this paper, the conductance properties of a wire formed at the junction between two macroscopic metallic electrodes are investigated and the effect of tunneling and quantum-size effects are treated exactly using the scattering matrix formalism.
Abstract: The conducting and mechanical properties of a metallic nanowire formed at the junction between two macroscopic metallic electrodes are investigated. Both two- and three-dimensional wires with a wide-narrow-wide geometry are modeled in the free-electron approximation with hard-wall boundary conditions. Tunneling and quantum-size effects are treated exactly using the scattering matrix formalism. Oscillations of order ${E}_{F}/{\ensuremath{\lambda}}_{F}$ in the tensile force are found when the wire is stretched to the breaking point, which are synchronized with quantized jumps in the conductance. The force and conductance are shown to be essentially independent of the width of the wide sections (electrodes). The exact results are compared with an adiabatic approximation; the latter is found to overestimate the effects of tunneling, but still gives qualitatively reasonable results for nanowires of length $L\ensuremath{\gg}{\ensuremath{\lambda}}_{F},$ even for this abrupt geometry. In addition to the force and conductance, the net charge of the nanowire is calculated and the effects of screening are included within linear response theory. Mesoscopic charge fluctuations of order e are predicted that are strongly correlated with the mesoscopic force fluctuations. The local density of states at the Fermi energy exhibits nontrivial behavior that is correlated with fine structure in the force and conductance, showing the importance of treating the whole wire as a mesoscopic system rather than treating only the narrow part.
TL;DR: Recording conditions sufficient for evaluation of the intrinsic gating characteristics of human Cx43-derived gap junction channels have been used and indicate that despite their greater frequency, the duration of subconductance events is so short relative to the main state duration as to render them physiologically insignificant.
Abstract: Subconductance states are a commonly observed feature of gap junction channels Their overt frequency and consistent appearance in both single and multichannel records have led to speculation that they might be of physiological importance in terms of altering the rate of small solute transfer from cell to cell Among the connexin gene family, connexin43 (Cx43) is the most ubiquitous connexin that has been shown to generate subconductive states Therefore, it was the explicit aim of this investigation to more fully evaluate the potential contribution of human Cx43-derived subconducting states to intercellular communication in cultured human corporal vascular smooth muscle cells To determine the weight of subconductive states in our records, we analyzed amplitude histograms of multichannel and single-channel data during the application of transjunctional voltages larger than expected for physiological conditions but still smaller than transjunctional voltages known to induce lower conductive states (Vo>Vj) The data clearly indicated that the subconducting states occupy only a small fraction of the total channel open time This was reflected by the fact that the average open probability for the subconductive state(s) determined from the 9 records analyzed was approximately 2% Closer inspection of the data revealed that the frequency of subconductive states was actually higher than the frequency of the main state conductance In summary, recording conditions sufficient for evaluation of the intrinsic gating characteristics of human Cx43-derived gap junction channels have been used Under these conditions, our data clearly indicate that despite their greater frequency, the duration of subconductance events is so short relative to the main state duration as to render them physiologically insignificant
TL;DR: In this article, the results of electron-transport measurements in V-groove GaAs/AlxGa12xAs quantum wires are reported, showing that a poor coupling between the 1D states of the wire and the 2D states outside the gated region is responsible for the conductance suppression for strong lateral confinement.
Abstract: values of the conductance steps are suppressed. Our results suggest that a poor coupling between the 1D states of the wire and the 2D states of the reservoirs outside the gated region is responsible for the conductance suppression for strong lateral confinement. @S0163-1829~99!50516-X# In this paper we report the results of electron-transport measurements in V-groove GaAs/AlxGa12xAs quantum wires ~QWR's!. With these structures, it is possible to con- trol the strength of the lateral quantum confinement, thus allowing the comparison between nearly adiabatic and more abrupt transitions between the wire and the reservoir regions. In the ballistic transport regime, obtained for wires shorter than ;1.5 mm, we observe a systematic increase in the de- viation of the conductance steps from G 0 as the strength of the lateral confinement increases. Our data support recent models 7,9 assigning these deviations to electron scattering at
TL;DR: A comparison between both types of theoretical results in a wide range of particle sizes demonstrates that Stern layer conductance always increases the magnitude of the low-frequency dielectric constant of suspensions, but its effect is less important the smaller the particle size and the larger the zeta potential for fixed ionic conditions in the dispersion medium.
TL;DR: In this paper, a scattering approach for correlated one-dimensional systems is developed, where the perfect contact to charge reservoirs is encoded in time-dependent boundary conditions, and the conductance matrix for an arbitrary gated wire, respecting charge conservation, is expressed through a dynamic scattering matrix.
Abstract: A scattering approach for correlated one-dimensional systems is developed. The perfect contact to charge reservoirs is encoded in time-dependent boundary conditions. The conductance matrix for an arbitrary gated wire, respecting charge conservation, is expressed through a dynamic scattering matrix. Two applications are developed. First, it is shown that the dc conductance is equal to e2/h for any model with conserved total left- and right-moving charges. Second, the ac conductance matrix is explicitly computated for the Tomonaga-Luttinger model (TLL).
TL;DR: Results appear to be the first direct evidence that new pore induction in HEM is a significant flux enhancing mechanism under moderate voltage conditions.
TL;DR: In this article, the transport properties of multiwalled carbon nanotubes were analyzed based on a scattering-theoretic approach that takes into account scattering within each tube, between tubes, and at the metal contacts.
Abstract: We report calculations of the transport properties of multiwalled carbon nanotubes based on a scattering-theoretic approach that takes into account scattering within each tube, between tubes, and at the metal contacts. We find that only the outer tube contributes to the conductance, as has been implied by experiments. Referring to experiments performed with liquid-metal contacts, we also explain why the measured conductance is close to an integer number of conductance quanta, when the tubes are immersed in the liquid metal for several hundreds of nanometers and is not an integer when they are immersed for only a few nanometers. Finally, we propose that the observed conductance of only one quantum (instead of the expected two quanta) is due to intertube interactions.
TL;DR: In this paper, the authors used the kubo formula to get the DC conductance of a statistical ensemble of two-dimensional clusters of the square lattice in the presence of standard diagonal disorder, a uniform magnetic field and random magnetic fluxes.
TL;DR: In this paper, the effects of impurities with a strong and short-range potential on carbon nanotubes within a k · p scheme were studied and the calculated conductance approaches those obtained for carbon nanotsubes with a lattice vacancy when the strength of the potential is sufficiently large.
Abstract: Effects of impurities with a strong and short-range potential are studied in carbon nanotubes within a k · p scheme. The calculated conductance approaches those obtained for nanotubes with a lattice vacancy when the strength of the potential is sufficiently large. The conductance at e=0 is analytically shown to be quantized into zero, one, and two times of the conductance quantum \(e^2/\pi\hbar\) depending on the difference in the number of vacancies at A and B sublattices in nanotubes with a sufficiently large diameter.
TL;DR: In this paper, the electronic properties of triangulenes and their use as building blocks in nanotube metallic Y-junctions were investigated using the Landauer formalism.
TL;DR: In this article, the quantum conductance of a metallic carbon nanotube with one end immersed in a jellium metal is studied and it is shown that the incident π-band electrons, having a very high angular momentum with respect to the tube axis, go through the tube without being scattered by the free electrons in surrounding metal and contribute a quantum unit (2e{sup 2}/h) to the conductance.
Abstract: The quantum conductance of a metallic carbon nanotube with one end immersed in a jellium metal is studied. We find that the incident {pi}{sup *}-band electrons, having a very high angular momentum with respect to the tube axis, go through the tube without being scattered by the free electrons in surrounding metal and contribute a quantum unit (2e{sup 2}/h) to the conductance. On the other hand, the incident {pi}-band electrons, with the p{sub z} atomic orbitals in phase along the tube circumference, experience strong resonant back-scattering because the low-angular-momentum states at the Fermi level have a dominantly metallic character in the nanotube-jellium metal coexistence region. These results provide a possible explanation for the experimentally observed conductance of one quantum unit instead of two for nanotubes with one end dipped into liquid metal such as mercury. (c) 1999 The American Physical Society.
01 Oct 1999
TL;DR: In this article, the quantum conductance of a metallic carbon nanotube with one end immersed in a jellium metal is studied and it is shown that the incident π-band electrons, having a very high angular momentum with respect to the tube axis, go through the tube without being scattered by the free electrons in surrounding metal and contribute a quantum unit (2e{sup 2}/h) to the conductance.
Abstract: The quantum conductance of a metallic carbon nanotube with one end immersed in a jellium metal is studied. We find that the incident {pi}{sup *}-band electrons, having a very high angular momentum with respect to the tube axis, go through the tube without being scattered by the free electrons in surrounding metal and contribute a quantum unit (2e{sup 2}/h) to the conductance. On the other hand, the incident {pi}-band electrons, with the p{sub z} atomic orbitals in phase along the tube circumference, experience strong resonant back-scattering because the low-angular-momentum states at the Fermi level have a dominantly metallic character in the nanotube-jellium metal coexistence region. These results provide a possible explanation for the experimentally observed conductance of one quantum unit instead of two for nanotubes with one end dipped into liquid metal such as mercury. (c) 1999 The American Physical Society.
TL;DR: In this article, the effect of increasing oxygen deficiency on the electrical resistivity, tunnelling conductance and thermopower of stoichiometric metal has been investigated in the presence of oxygen deficiency.
Abstract: We report a systematic study of the effect of increasing oxygen deficiency on the electrical resistivity, tunnelling conductance and thermopower of . Stoichiometric behaves like a normal metal with a positive temperature coefficient of resistivity (TCR) and a negative thermopower which is proportional to temperature over the range 5 K-300 K. As the oxygen deficiency increases, the electrical resistivity shows a minimum at low temperature which progressively shifts to higher temperature with increasing . In the low-temperature limit the correction to the electrical conductivity follows a power-law behaviour with an exponent . We also find a cusp-like dip in the tunnelling conductance near zero bias voltage. We attribute both of these behaviours to enhanced interaction between the charge carriers in the system occurring because of the disorder. The thermopower of the oxygen-deficient samples is found to vary systematically with , showing a sign reversal at low temperature.