Showing papers on "Conductance published in 1998"
TL;DR: The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized and Extremely high stable current densities, J > 10(7) amperes per square centimeter, have been attained.
Abstract: The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum G0 5 2e 2 /h 5 (12.9 kilohms) ‐1 . The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities, J . 10 7 amperes per square centimeter, have been attained.
1,992 citations
TL;DR: In this article, the authors measured the conductance of a single strand of gold atoms with an STM and a double strand with an ultrahigh-vacuum electron microscope.
Abstract: As the scale of microelectronic engineering continues to shrink, interest has focused on the nature of electron transport through essentially one-dimensional nanometre-scale channels such as quantum wires1 and carbon nanotubes2,3. Quantum point contacts (QPCs) are structures (generally metallic) in which a ‘neck’ of atoms just a few atomic diameters wide (that is, comparable to the conduction electrons' Fermi wavelength) bridges two electrical contacts. They can be prepared by contacting a metal surface witha scanning tunnelling microscope (STM)4,5,6,7 and by other methods8,9,10,11,12, and typically display a conductance quantized in steps of 2e2/h(∼13 kΩ−1)13,14, where e is the electron charge and h is Planck's constant. Here we report conductance measurements on metal QPCs prepared with an STM that we can simultaneously image using an ultrahigh-vacuum electron microscope, which allows direct observation of the relation between electron transport and structure. We observe strands of gold atoms that are about one nanometre long and one single chain of gold atoms suspended between the electrodes. We can thus verify that the conductance of a single strand of atoms is 2e2/h and that the conductance of a double strand is twice as large, showing that equipartition holds for electron transport in these quantum systems.
1,167 citations
TL;DR: In this article, the authors describe the breaking of atomic-scale gold contacts, which leads to the formation of gold chains one atom thick and at least four atoms long, confirming that the conductance never exceeds 2e2/h, thus indicating that the neck of the contact consists of a single atom.
Abstract: The continuing miniaturization of microelectronics raises the prospect of nanometre-scale devices with mechanical and electrical properties that are qualitatively different from those at larger dimensions. The investigation of these properties, and particularly the increasing influence of quantum effects on electron transport, has therefore attracted much interest. Quantum properties of the conductance can be observed when ‘breaking’ a metallic contact: as two metal electrodes in contact with each other are slowly retracted, the contact area undergoes structural rearrangements until it consists in its final stages of only a few bridging atoms1,2,3. Just before the abrupt transition to tunnelling occurs, the electrical conductance through a monovalent metal contact is always close to a value of 2e2/h (≈12.9 Ω−1), where e is the charge on an electron and h is Planck's constant4,5,6. This value corresponds to one quantum unit of conductance, thus indicating that the ‘neck’ of the contact consists of a single atom7. In contrast to previous observations of only single-atom necks, here we describe the breaking of atomic-scale gold contacts, which leads to the formation of gold chains one atom thick and at least four atoms long. Once we start to pull out a chain, the conductance never exceeds 2e2/h, confirming that it acts as a one-dimensional quantized nanowire. Given their high stability and the ability to support ballistic electron transport, these structures seem well suited for the investigation of atomic-scale electronics.
831 citations
TL;DR: In this paper, the conductance spectrum (dI/dV vs. V) can be understood fairly well in terms of a relatively simple model, provided the spatial profile of the electrostatic potential under bias is properly accounted for.
Abstract: A relatively simple and straightforward procedure for characterizing molecular wires is to measure the conductance spectrum by forming a self-assembled ordered monolayer (SAM) on a metallic surface and using a high scanning-tunneling microscope resolution (STM) tip as the other contact. We find that the conductance spectrum (dI/dV vs. V) can be understood fairly well in terms of a relatively simple model, provided the spatial profile of the electrostatic potential under bias is properly accounted for. The effect of the potential profile is particularly striking and can convert a symmetric conductor into a rectifier and vice versa. The purpose of this paper is to (1) describe the theoretical model in detail, (2) identify the important parameters that influence the spectra and show how these parameters can be deduced directly from the conductance spectrum, and (3) compare the theoretical prediction with experimentally measured conductance spectra for xylyl dithiol and phenyl dithiol.
546 citations
IBM1
TL;DR: In this paper, the conductance of carbon-atom chains is found to vary in an oscillatory manner as the number of carbon atoms is increased, with odd numbered chains having a lower resistance than even-numbered chains.
Abstract: The conductance of carbon-atom chains is found from first-principles calculations to vary in an oscillatory manner as the number of carbon atoms is increased, with odd-numbered chains having a lower resistance than even-numbered chains. This finding is explained in terms of the electronic structure of the free chains and its modification by interaction with the metal electrodes: the critical factor is the density of states at the Fermi level of the combined electrode\char21{}atomic-wire system. Stronger electrode\char21{}atomic-wire coupling, i.e., shorter metal-carbon distance, does not necessarily imply a higher conductance.
263 citations
TL;DR: A miniaturized conductance-manometer system was developed to study detailed systolic and diastolic left ventricular chamber mechanics in mice in vivo, further supporting comparable chamber mechanics between species.
Abstract: The mouse is the species of choice for creating genetically engineered models of human disease. To study detailed systolic and diastolic left ventricular (LV) chamber mechanics in mice in vivo, we ...
257 citations
TL;DR: In this article, a screen printed thick-film H2, CO and CH4 gas sensors were fabricated on an alumina substrate by mixing ZnO with lead borosilicate glass frits as a binder and Sb as a catalyst.
227 citations
TL;DR: In this article, a universal heat conductance expression that depends on the properties of the conducting pathway only through the mode cutoff frequencies is derived, and corrections due to reflections at the junction between the thermal body and the conducting bridge are found to be small except at very low temperatures where only the lowest few bridge modes are excited.
138 citations
TL;DR: In this paper, the conductance of carbon nanotube wires in the presence of disorder, in the limit of phase-coherent transport, was studied and a simple numerical procedure was developed to compute transmission through nanotubes and related structures.
Abstract: We study the conductance of carbon nanotube wires in the presence of disorder, in the limit of phase-coherent transport. For this purpose, we have developed a simple numerical procedure to compute transmission through carbon nanotubes and related structures. Two models of disorder are considered, weak uniform disorder and isolated strong scatterers. In the case of weak uniform disorder, our simulations show that the conductance is not significantly affected by disorder when the Fermi energy is close to the band center. Further, the transmission around the band center depends on the diameter of these zero band-gap wires. We also find that the calculated small bias conductance as a function of the Fermi energy exhibits a dip when the Fermi energy is close to the second subband minima. In the presence of strong isolated disorder, our calculations show a transmission gap at the band center, and the corresponding conductance is very small.
134 citations
TL;DR: Brownian dynamics simulations have been carried out to study ionic currents flowing across a model membrane channel under various conditions, finding that the conductance first increases linearly with concentration and then begins to rise at a slower rate with higher ionic concentration.
126 citations
TL;DR: Observations indicate that fluorination does not change the rotameric conformation of the side chain, and Eadie-Hofstee plot slopes suggest similar destabilization of K+ binding in both lipids.
TL;DR: In this article, the authors describe quantum wires and point contacts fabricated in GaAs/AlxGa1−xAs heterostructures that are free of the disorder introduced by modulation doping and in which the electron density and the confining potential are separately adjustable by lithographically defined gates.
Abstract: We describe quantum wires and point contacts fabricated in GaAs/AlxGa1−xAs heterostructures that are free of the disorder introduced by modulation doping and in which the electron density and the confining potential are separately adjustable by lithographically defined gates. We observe conductance plateaus quantized near even multiples of e2/h in 2 μm wires and up to 15 conductance steps in 5 μm wires at temperatures below 1 K. Near the conductance threshold the quantum point contact and the 2 μm wire both show additional structure below 2e2/h.
TL;DR: It is shown that the effects of lipid charge titration on channel conductance are masked 1) by conductance saturation with Cs+ ions in the neutral pH range and 2) by increased proton concentration when the bathing solution pH is less than 3.0.
TL;DR: In this article, the interaction constant governing the long-range electron-electron interaction in a quantum wire coupled to two reservoirs and capacitively coupled to a gate can be determined by a low-frequency measurement.
Abstract: We show that the interaction constant governing the long-range electron-electron interaction in a quantum wire coupled to two reservoirs and capacitively coupled to a gate can be determined by a low-frequency measurement. We present a self-consistent, charge and current conserving, theory of the full conductance matrix. The collective excitation spectrum consists of plasma modes with a relaxation rate which increases with the interaction strength and is inversely proportional to the length of the wire.
TL;DR: In this article, full distributions of conductance through quantum dots with single-mode leads are reported for both broken and unbroken time-reversal symmetry, and they agree well with random matrix theory calculations that account for a finite dephasing time, once broadening due to finite temperature.
Abstract: Full distributions of conductance through quantum dots with single-mode leads are reported for both broken and unbroken time-reversal symmetry. Distributions are nongaussian and agree well with random matrix theory calculations that account for a finite dephasing time, $\tau_\phi$, once broadening due to finite temperature $T$ is also included. Full distributions of the derivatives of conductance with respect to gate voltage $P(dg/dV_g)$ are also investigated.
TL;DR: In this paper, the tunneling conductance is calculated as a function of the gate voltage in wide temperature range for the single quantum dot systems with Coulomb interaction, where two orbitals are active for tunneling process.
Abstract: The tunneling conductance is calculated as a function of the gate voltage in wide temperature range for the single quantum dot systems with Coulomb interaction. We assume that two orbitals are active for the tunneling process. We show that the Kondo temperature for each orbital channel can be largely different. The tunneling through the Kondo resonance almost fully develops in the region \(T \lesssim 0.1 T_{\rm K}^{*} \sim 0.2 T_{\rm K}^{*}\), where T K * is the lowest Kondo temperature when the gate voltage is varied. At high temperatures the conductance changes to the usual Coulomb oscillations type. In the intermediate temperature region, the degree of the coherency of each orbital channel is different, so strange behaviors of the conductance can appear. For example, the conductance once increases and then decreases with temperature decreasing when it is suppressed at T =0 by the interference cancellation between different channels. The interaction effects in the quantum dot systems lead the sensitivit...
TL;DR: It was found that heteromers have a threefold larger conductance compared to homomeric channels in symmetrical high-K+ solutions, which explains in part their larger macroscopic conductance in heterologous expression systems.
Abstract: Gating of the delayed rectifier K+ channel KvLQT1 is drastically slowed by the association with the small membrane protein minK and it is thought that the KvLQT1/minK complex underlies the slow delayed rectifier K+ current of cardiac cells. There is controversy about the effects of the association between KvLQT1 and minK on the single-channel conductance. Here, nonstationary fluctuation analysis was applied to inward K+ tail currents recorded with a high-time resolution (5 kHz bandwidth) from macropatches of homomeric KvLQT1 and heteromeric KvLQT1/minK channels expressed in Xenopus oocytes to estimate their single-channel conductance. It was found that heteromers have a threefold larger conductance (5.8 pS) compared to homomeric channels (1.8 pS) in symmetrical high-K+ solutions. The larger conductance of heteromers explains in part their larger macroscopic conductance in heterologous expression systems. The molecular mechanism underlying the conductance increase remains to be identified.
TL;DR: In this paper, tunneling conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically as triplet paring states and several types of symmetries that are promising candidates for the superconducting states in UPt 3 and in Sr 2 RuO 4 are selected.
Abstract: Tunneling conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically As triplet paring states we select several types of symmetries that are promising candidates for the superconducting states in UPt 3 and in Sr 2 RuO 4 The calculated conductance spectra are sensitive to the orientation of the junction which reflects the anisotropy of the pairing states They show either zero-bias conductance peaks or gap-like structures depending on the orientation of the junctions The existence of a residual density of states, peculiar to nonunitary states, is shown to have a significant influence on the properties of the conductance spectra Present results serve as a guide for the experimental determination of the symmetry of the pair potentials in UPt 3 and Sr 2 RuO 4
TL;DR: In this paper, the electrical properties of shallow etched GaAs/GaAlAs quantum point contacts (QPCs) of various shapes have been studied as a function of temperature above 0.3 K.
Abstract: The electrical characteristics of shallow etched GaAs/GaAlAs quantum point contacts (QPCs) of various shapes have been studied as a function of temperature above 0.3 K. Quantized conductance was observed up to 36 K, and from the temperature dependence of the conductance staircase we find energy separations between the lowest one-dimensional subbands up to 20 meV. This value exceeds the highest values so far reported for laterel QPC constrictions in GaAs/GaAlAs heterostructures. In addition, very well behaved quantized conductance plateaus were observed at the lowest temperatures.
TL;DR: In this article, the quantized conductance in point contacts of macroscopic nickel wires under varying external parameters, the temperature (above and below Tc) and the applied magnetic field was observed.
Abstract: We have observed systematic change of the quantized conductance in point contacts of macroscopic nickel wires under varying external parameters, the temperature (above and below Tc) and the applied magnetic field. The observed quantized conductance can be explained by the number of the channels for electronic transport through the point contact and the spin-dependent transmission coefficient.
TL;DR: In this article, the conductance through two quantum dots connected in series is studied below the Kondo temperature, based on the slave boson formalism of the Anderson model, and the transport properties are characterized by the ratio of the magnitude of the tunneling coupling between two dots to the width of the level broadening.
Abstract: The conductance through two quantum dots connected in series is studied below the Kondo temperature, based on the slave boson formalism of the Anderson model. The transport properties are characterized by the ratio of the magnitude of the tunneling coupling between two dots to the width of the level broadening. When the ratio is less than unity, the Kondo resonant states are formed between each dot and an external lead, and the conductance is determined by the hopping between the two resonant states. When the ratio is larger than unity, these Kondo resonances are split into the bonding and antibonding peaks, which are located below and above the Fermi level in the leads, respectively, for low gate voltages. As a result, the conductance is suppressed. The conductance has a maximum of 2e 2 /h when the bonding peak is matched with the Fermi level by controlling the gate voltage.
TL;DR: In this article, the results of a numerical calculation on the quantum transport properties in junctions of a two-dimensional electron gas and a superconductor in the presence of a perpendicular magnetic field were presented.
Abstract: We present the results of a numerical calculation on the quantum transport properties in junctions of a two-dimensional electron gas and a superconductor in the presence of a perpendicular magnetic field. The low-field conductance drops in a steplike manner, whenever the Landau levels are depopulated, provided that quasiparticle excitations are almost perfectly Andreev reflected from the interface. If the normal reflection is enhanced, the conductance exhibits a sinusoidal oscillation. In contrast to the behavior in conventional conductors, the maxima of the oscillation take place at the depopulation thresholds. In high magnetic fields, a periodic transmission resonance with a complete disappearance of the conductance is found, irrespective of the Andreev-reflection probability. The current distribution indicates that this high-field oscillation is ascribed to the skipping orbit along the interface. We show that the plateau value in the Hall resistance remains unchanged when one of the leads is replaced by the superconductor. Using the selective edge-state detection technique, the distribution of Andreev-reflected quasiparticles among the edge states can be evaluated.
TL;DR: Yannouleas et al. as mentioned in this paper investigated the energy and quantized conductance of jellium-modeled nanowires using the localdensity-functional-based shell correction method.
Abstract: Energetics and quantized conductance in jellium-modeled nanowires are investigated using the localdensity-functional-based shell correction method, extending our previous study of uniform-in-shape wires @C. Yannouleas and U. Landman, J. Phys. Chem. B 101, 5780 ~1997!# to wires containing a variable-shaped constricted region. The energetics of the wire ~sodium! as a function of the length of the volume-conserving, adiabatically shaped constriction, or equivalently its minimum width, leads to the formation of self-selecting magic wire configurations, i.e., a discrete configurational sequence of enhanced stability, originating from quantization of the electronic spectrum, namely, formation of transverse subbands due to the reduced lateral dimensions of the wire. These subbands are the analogs of shells in finite-size, zero-dimensional fermionic systems, such as metal clusters, atomic nuclei, and 3 He clusters, where magic numbers are known to occur. These variations in the energy result in oscillations in the force required to elongate the wire and are directly correlated with the stepwise variations of the conductance of the nanowire in units of 2 e 2 /h. The oscillatory patterns in the energetics and forces, and the correlated stepwise variation in the conductance, are shown, numerically and through a semiclassical analysis, to be dominated by the quantized spectrum of the transverse states at the most narrow part of the constriction in the wire. @S0163-1829~98!01908-0#
TL;DR: In this article, the pore diameter in alumina tubular membranes with an initial diameter of 50 A was systematically reduced using the atomic layer controlled deposition of Al2O3 using sequential exposures of Al(CH3)3 (trimethylaluminum, TMA) and H2O in an ABAB... binary reaction sequence.
Abstract: The pore diameter in alumina tubular membranes with an initial diameter of 50 A was systematically reduced using the atomic layer controlled deposition of Al2O3. The Al2O3 was deposited using sequential exposures of Al(CH3)3 (trimethylaluminum, TMA) and H2O in an ABAB... binary reaction sequence. The pore diameter reduction was monitored using in situ N2 and Ar conductance measurements. The conductance, C = Q/ΔP, was measured using a mass flow controller to define a constant gas throughput, Q, and a pair of capacitance manometers to monitor the transmembrane pressure drop, ΔP. Conductance measurements were periodically obtained at 298 K as a function of AB binary reaction cycles. These conductance measurements were consistent with a pore diameter reduction from 50 A to ∼5−10 A at a rate of ∼2.5 A for each AB cycle. Conductance measurements were also performed during the Al2O3 deposition at 500 K after each half-reaction in the binary reaction sequence. The TMA half-reaction leaves the pore surface covered...
TL;DR: In this paper, the complex ac-response of a quasi-one dimensional electron system in the one-band approximation with an interaction potential of finite range is investigated, and it is shown that linear response is exact for this model.
Abstract: The complex ac-response of a quasi-one dimensional electron system in the one-band approximation with an interaction potential of finite range is investigated. It is shown that linear response is exact for this model. The influence of the screening of the electric field is discussed. The complex absorptive conductance is analyzed in terms of resistive, capacitive and inductive behaviors.
TL;DR: It is demonstrated that correction for both membrane and series resistance reduces the error in measured junctional conductance to near zero, even when membrane resistances on both sides of the gap junction are as low as 20 MΩ and the (true) junctional Conductance is as high as 100 nS.
Abstract: The dual whole-cell voltage-clamp technique is used widely for determination of kinetics and conductance of gap junctions. The use of this technique may, however, occasion to considerable errors. We have analysed the errors in steady state junctional conductance measurements under different experimental conditions. The errors in measured junctional conductance induced by series resistance alone, and by series resistance in combination with membrane resistance, were quantified both theoretically and experimentally, on equivalent resistive circuits with known resistance values in a dual voltage-clamp setup. We present and analyse a method that accounts for series resistance and membrane resistance in the determination of true junctional conductance. This method requires that series resistance is determined during the experiment, and involves some calculations to determine membrane resistance. We demonstrate that correction for both membrane and series resistance reduces the error in measured junctional conductance to near zero, even when membrane resistances on both sides of the gap junction are as low as 20 MOmega and the (true) junctional conductance is as high as 100 nS.
TL;DR: In this article, molecular dynamics calculations of the ionic mobility and limiting conductance of NaCl in supercritical water as a function of density along an isotherm 5% above the critical temperature were performed.
TL;DR: In this article, the influence of electron-electron interactions on the conductance of two-dimensional disordered spinless electrons was investigated using an efficient numerical method which is based on exact diagonalization in a truncated basis of Hartree-Fock states.
Abstract: We investigate the influence of electron-electron interactions on the conductance of two-dimensional disordered spinless electrons. By using an efficient numerical method which is based on exact diagonalization in a truncated basis of Hartree-Fock states we are able to determine the exact low-energy properties of comparatively large systems in the diffusive as well as in the localized regimes. We find that weak interactions increase the d.c. conductance in the localized regime while they decrease the d.c. conductance in the diffusive regime. Strong interactions always decrease the conductance. We also study the localization of single-particle excitations close to the Fermi energy which turns out to be only weakly influenced by the interactions.
TL;DR: In this article, the properties of a large number of individual steps in the conductance of atom-size contacts as a function of cross-section have been investigated, and the results confirm that the steps are the result of atomic structural rearrangements.
Abstract: The properties of a large number of individual steps in the conductance of atom-size contacts as a function of cross-section have been investigated. The results confirm that the steps are the result of atomic structural rearrangements, without exception for all individual steps in the survey. Furthermore, we report the first direct observation of the transformation of a hysteresis cycle around a conductance step in a two-level fluctuation.