Showing papers on "Conductance published in 2000"
TL;DR: The intrinsic high-field transport properties of metallic single-wall carbon nanotubes are measured using low-resistance electrical contacts and it is shown that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.
Abstract: Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10(9) A/cm(2). As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.
1,415 citations
TL;DR: The observation of a quantized limiting value for the thermal conductance, Gth, in suspended insulating nanostructures at very low temperatures is reported, consistent with predictions for phonon transport in a ballistic, one-dimensional channel.
Abstract: The physics of mesoscopic electronic systems has been explored for more than 15 years. Mesoscopic phenomena in transport processes occur when the wavelength or the coherence length of the carriers becomes comparable to, or larger than, the sample dimensions. One striking result in this domain is the quantization of electrical conduction, observed in a quasi-one-dimensional constriction formed between reservoirs of two-dimensional electron gas. The conductance of this system is determined by the number of participating quantum states or 'channels' within the constriction; in the ideal case, each spin-degenerate channel contributes a quantized unit of 2e^2/h to the electrical conductance. It has been speculated that similar behaviour should be observable for thermal transport in mesoscopic phonon systems. But experiments attempted in this regime have so far yielded inconclusive results. Here we report the observation of a quantized limiting value for the thermal conductance, G_(th), in suspended insulating nanostructures at very low temperatures. The behaviour we observe is consistent with predictions for phonon transport in a ballistic, one-dimensional channel: at low temperatures, G_(th) approaches a maximum value of g_0 = π^2k^2BT/3h, the universal quantum of thermal conductance.
810 citations
TL;DR: The input conductance of cells in the cat primary visual cortex (V1) has been shown recently to grow substantially during visual stimulation, suggesting that the intracortical synaptic inputs to simple cells of cat V1 originate from cells with similar orientation tuning.
Abstract: The input conductance of cells in the cat primary visual cortex (V1) has been shown recently to grow substantially during visual stimulation. Because increasing conductance can have a divisive effect on the synaptic input, theoretical proposals have ascribed to it specific functions. According to the veto model, conductance increases would serve to sharpen orientation tuning by increasing most at off-optimal orientations. According to the normalization model, conductance increases would control the cell's gain, by being independent of stimulus orientation and by growing with stimulus contrast. We set out to test these proposals and to determine the visual properties and possible synaptic origin of the conductance increases. We recorded the membrane potential of cat V1 cells while injecting steady currents and presenting drifting grating patterns of varying contrast and orientation. Input conductance grew with stimulus contrast by 20-300%, generally more in simple cells (40-300%) than in complex cells (20-120%), and in simple cells was strongly modulated in time. Conductance was invariably maximal for stimuli of the preferred orientation. Thus conductance changes contribute to a gain control mechanism, but the strength of this gain control does not depend uniquely on contrast. By assuming that the conductance changes are entirely synaptic, we further derived the excitatory and inhibitory synaptic conductances underlying the visual responses. In simple cells, these conductances were often arranged in push-pull: excitation increased when inhibition decreased and vice versa. Excitation and inhibition had similar preferred orientations and did not appear to differ in tuning width, suggesting that the intracortical synaptic inputs to simple cells of cat V1 originate from cells with similar orientation tuning. This finding is at odds with models where orientation tuning in simple cells is achieved by inhibition at off-optimal orientations or sharpened by inhibition that is more broadly tuned than excitation.
523 citations
TL;DR: The effects of impurities and local structural defects on the conductance of metallic carbon nanotubes are calculated using an ab initio pseudopotential method within the Landauer formalism and shows a much more complex behavior than the prediction from the widely used pi-electron tight-binding model.
Abstract: The effects of impurities and local structural defects on the conductance of metallic carbon nanotubes are calculated using an ab initio pseudopotential method within the Landauer formalism. Substitutionally doped boron or nitrogen produces quasibound impurity states of a definite parity and reduces the conductance by a quantum unit $({2e}^{2}/h)$ via resonant backscattering. These resonant states show strong similarity to acceptor or donor states in semiconductors. The Stone-Wales defect also produces quasibound states and exhibits quantized conductance reduction. In the case of a vacancy, the conductance shows a much more complex behavior than the prediction from the widely used $\ensuremath{\pi}$-electron tight-binding model.
455 citations
06 Nov 2000
TL;DR: High resolution transmission electron microscopy predictions of the structure of gold nanowires generated by mechanical stretching show remarkable agreement with conductance measurements from a break junction operating in ultrahigh vacuum, corroborating the derived correlation between nanowire atomic structure and conductance behavior.
Abstract: We have used high resolution transmission electron microscopy to determine the structure of gold nanowires generated by mechanical stretching. Just before rupture, the contacts adopt only three possible atomic configurations, whose occurrence probabilities and quantized conductance were subsequently estimated. These predictions have shown a remarkable agreement with conductance measurements from a break junction operating in ultrahigh vacuum, corroborating the derived correlation between nanowire atomic structure and conductance behavior.
363 citations
TL;DR: In this article, mean canopy stomatal conductance of individual tree crowns (G Si ) was estimated using sap flux measurements in Fagus sylvatica L., and the hypothesis that G Si decreases with tree height was tested.
Abstract: Variation in stomatal conductance is typically explained in relation to environmental conditions. However, tree height may also contribute to the variability in mean stomatal conductance. Mean canopy stomatal conductance of individual tree crowns (G Si ) was estimated using sap flux measurements in Fagus sylvatica L., and the hypothesis that G Si decreases with tree height was tested. Over 13 d of the growing season during which soil moisture was not limiting, G Si decreased linearly with the natural logarithm of vapour pressure deficit (D), and increased exponentially to saturation with photosynthetic photon flux density (Q o ). Under conditions of D = 1 kPa and saturating Q o , G Si decreased by approximately 60% with 30 m increase in tree height. Over the same range in height, sapwood-to-leaf area ratio (A S :A L ) doubled. A simple hydraulic model explained the variation in G Si based on an inverse relationship with height, and a linear relationship with A S :A L . Thus, in F. sylvatica, adjustments in A S :A L partially compensate for the negative effect of increased flow-path length on leaf conductance. Furthermore, because stomata with low conductance are less sensitive to D, gas exchange of tall trees is reduced less by high D. Despite these compensations, decreasing hydraulic conductance with tree height in F. sylvatica reduces carbon uptake through a corresponding decrease in stomatal conductance.
303 citations
TL;DR: In this paper, the pore diameters in alumina tubular membranes were progressively reduced via SiO2 and TiO2 atomic layer deposition (ALD) using sequential surface reactions.
Abstract: The pore diameters in alumina tubular membranes were progressively reduced via SiO2 and TiO2 atomic layer deposition (ALD) using sequential surface reactions. The SiO2 ALD was accomplished using alternating exposures of SiCl4 and H2O. The TiO2 ALD was achieved using alternating exposures of TiCl4 and H2O. The reduction of the pore diameter was observed using in situ N2 conductance measurements. The total conductance, Ct = Q/ΔPt, was measured using a mass flow controller to define a constant gas throughput, Q, and two capacitance manometers to monitor the total pressure drop, ΔPt. These N2 conductance measurements revealed that the SiO2 and TiO2 ALD progressively reduced the pore diameter from an initial diameter of 50 A to molecular diameters. Using an aperture model for the conductance, the pore diameter was found to decrease at a rate of 1.3 ± 0.1 A per SiCl4/H2O AB cycle during SiO2 deposition and 3.1 ± 0.9 A per TiCl4/H2O AB cycle during TiO2 deposition. The N2 conductance measurements were also very ...
186 citations
TL;DR: In this article, the 0.7 (2e^2/h) conductance anomaly is investigated in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as the temperature.
Abstract: The 0.7 (2e^2/h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as a function of temperature. We investigate in detail how, for a given gate voltage, the differential conductance depends on the finite bias voltage and find a so-called self-gating effect, which we correct for. The 0.7 anomaly at zero bias is found to evolve smoothly into a conductance plateau at 0.85 (2e^2/h) at finite bias. Varying the gate voltage the transition between the 1.0 and the 0.85 (2e^2/h) plateaus occurs for definite bias voltages, which defines a gate voltage dependent energy difference $\Delta$. This energy difference is compared with the activation temperature T_a extracted from the experimentally observed activated behavior of the 0.7 anomaly at low bias. We find \Delta = k_B T_a which lends support to the idea that the conductance anomaly is due to transmission through two conduction channels, of which the one with its subband edge \Delta below the chemical potential becomes thermally depopulated as the temperature is increased.
185 citations
TL;DR: In this paper, the authors studied molecular adsorption onto stable metallic nanowires fabricated with an electrochemical method and found that the quantized conductance decreases, typically to a fractional value, which may be attributed to the scattering of the conduction electrons by the adsorbates.
Abstract: We have studied molecular adsorption onto stable metallic nanowires fabricated with an electrochemical method. Upon the adsorption, the quantized conductance decreases, typically, to a fractional value, which may be attributed to the scattering of the conduction electrons by the adsorbates. The further conductance change occurs when the nanowire is exposed to another molecule that has stronger adsorption strength. Because the quantized conductance is determined by a few atoms at the narrowest portion of each nanowire, adsorption of a molecule onto the portion is enough to change the conductance, which may be used for chemical sensors.
181 citations
TL;DR: In this paper, four families of conjugated molecules, containing between one and three phenyl rings and having both thiol (SH) and isocyanide (NC) end groups, have been synthesized and assembled as monolayers on flat Au(111) substrates.
161 citations
TL;DR: Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, the ballistic quantum conductance of multiwall carbon nanotubes is calculated.
Abstract: Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)].
TL;DR: In this article, it has been observed that the conductance fluctuations of atomic-size gold contacts are suppressed when conductance is equal to an integer multiple of a conductance quantum, and the fact that these contacts tend to consist exclusively of fully open or closed modes has been argued to be the origin for this suppression.
Abstract: Recently it has been observed that the conductance fluctuations of atomic-size gold contacts are suppressed when the conductance is equal to an integer multiple of the conductance quantum. The fact that these contacts tend to consist exclusively of fully open or closed modes has been argued to be the origin for this suppression. Here the experiments have been extended to a wide range of metallic elements with different chemical valences, and they provide information about the relation between the mode composition and statistically preferred conductance values observed in conductance histograms.
TL;DR: In this article, the limiting molar conductance (Λ0) and molal ion association constant (KA(m)) of dilute (10-5 to 10-3 mol kg-1) aqueous LiOH, NaOH, and KOH solutions were determined by a flow-through conductance.
Abstract: The limiting molar conductance (Λ0) and molal ion association constant (KA(m)) of dilute (10-5 to 10-3 mol kg-1) aqueous LiOH, NaOH, and KOH solutions were determined by a flow-through conductance ...
TL;DR: The experimental data are discussed in terms of electrochemical-potential-induced defect scattering and Fermi energy shift, but a complete theory of the phenomenon is yet to be developed.
Abstract: We study the electrical conductance of gold nanoconstrictions by controlling the electrochemical potential. At positive potentials, the conductance is quantized near integer multiples of ${G}_{0}({2e}^{2}/h)$ as shown by well-defined peaks in the conductance histogram. Below a certain potential, however, additional peaks near ${0.5G}_{0}$ and ${1.5G}_{0}$ appear in the histogram. The fractional conductance steps are as stable and well defined as the integer steps. The experimental data are discussed in terms of electrochemical-potential-induced defect scattering and Fermi energy shift, but a complete theory of the phenomenon is yet to be developed.
TL;DR: In this article, the conduction channels of monatomic Al and Na atom wires bridged between metallic jellium electrodes were investigated using the first-principles recursion-transfer matrix method.
Abstract: We present first-principles calculations of electron transport, in particular, the conduction channels of monatomic Al and Na atom wires bridged between metallic jellium electrodes. The electronic structures are calculated by the first-principles recursion-transfer matrix method, and the conduction channels are investigated using the eigenchannel decomposition (ECD) of the conductance, the local density of states (LDOS), and the current density. The ECD is different from the conventional decomposition of atomic orbitals, and the study of decomposed electronic structures is shown to be effective in clarifying the details of transport through atomic wires. We show channel transmissions, channel resolved LDOS, and channel resolved current density, and elucidate the number of conduction channels, the relation between atomic orbitals and the channels, and their dependency on the geometry of the atomic wire. We demonstrate that stretching of the bent wire can explain the mechanism of the increase of conductance of Al during the elongation of the contacts. The behavior of our calculated conductance and channel transmissions during the stretching process is in good agreement with the experimental data.
IBM1
TL;DR: In this article, the effects of lateral interactions on the conductance of two atomic wires connected in parallel are investigated using density-functional theory, and large variations of low-bias conductance as a function of the separation of the two wires on the atomic scale are predicted.
Abstract: The effects of lateral interactions on the conductance of two atomic wires connected in parallel are investigated using density-functional theory. Carbon-atom wires with a cumulene structure end bonded to two metal electrodes are used as the model system. Large variations of the low-bias conductance of the system as a function of the separation of the two wires on the atomic scale are predicted. This variation results from two types of interactions: (a) a direct bonding interaction between the atomic wires, and (b) an indirect interaction associated with the presence of the metal electrodes. The electrodes transfer an amount of charge to the carbon wires that varies with the separation d between the wires by as much as a factor of 2. The conductance changes, as a function of d, follow closely the variation of the density-of-states of the system at the Fermi level.
TL;DR: In this article, structural transformations, electronic spectra, and ballistic transport in pulled gold nanowires are investigated with ab initio simulations, and correlated with recent measurements, and the conductance of the initial double-stranded contact is close to 2(2e2/h) ≡ 2g0, and it drops sharply to 1g0 during the transformation to a single chain, exhibiting subsequently a ∼1g0 plateau extending over an elongation well above typical Au−Au distances.
Abstract: Structural transformations, electronic spectra, and ballistic transport in pulled gold nanowires are investigated with ab initio simulations, and correlated with recent measurements. Strain-induced yield of an initial double-strand wire results first in formation of a bent chain which transforms upon further elongation to a linear atomic chain exhibiting dimerized atomic configurations. These structures are stabilized by directional local bonding with spd hybridization. The conductance of the initial double-stranded contact is close to 2(2e2/h) ≡ 2g0, and it drops sharply to 1g0 during the transformation to a single chain, exhibiting subsequently a ∼1g0 plateau extending over an elongation well above typical Au−Au distances.
TL;DR: It is proposed that the P-region and the COOH terminus contribute independently to the conductance and selectivity properties of the pore.
Abstract: The structural domains contributing to ion permeation and selectivity in K channels were examined in inward-rectifier K+ channels ROMK2 (Kir1.1b), IRK1 (Kir2.1), and their chimeras using heterologous expression in Xenopus oocytes. Patch-clamp recordings of single channels were obtained in the cell-attached mode with different permeant cations in the pipette. For inward K+ conduction, replacing the extracellular loop of ROMK2 with that of IRK1 increased single-channel conductance by 25 pS (from 39 to 63 pS), whereas replacing the COOH terminus of ROMK2 with that of IRK1 decreased conductance by 16 pS (from 39 to 22 pS). These effects were additive and independent of the origin of the NH2 terminus or transmembrane domains, suggesting that the two domains form two resistors in series. The larger conductance of the extracellular loop of IRK1 was attributable to a single amino acid difference (Thr versus Val) at the 3P position, three residues in front of the GYG motif. Permeability sequences for the conducted ions were similar for the two channels: Tl+ > K+ > Rb+ > NH4+. The ion selectivity sequence for ROMK2 based on conductance ratios was NH4+ (1.6) > K+ (1) > Tl+ (0.5) > Rb+ (0.4). For IRK1, the sequence was K+ (1) > Tl+ (0.8) > NH4+ (0.6) >> Rb+ (0.1). The difference in the NH4+/ K+ conductance (1.6) and permeability (0.09) ratios can be explained if NH4+ binds with lower affinity than K+ to sites within the pore. The relatively low conductances of NH4+ and Rb+ through IRK1 were again attributable to the 3P position within the P region. Site-directed mutagenesis showed that the IRK1 selectivity pattern required either Thr or Ser at this position. In contrast, the COOH-terminal domain conferred the relatively high Tl+ conductance in IRK1. We propose that the P-region and the COOH terminus contribute independently to the conductance and selectivity properties of the pore.
TL;DR: In this paper, both the classical and the improved slope-intercept techniques have been applied to streaming potential data measured with slit glass channels, ranging in height from 3 µm to 66 µm, for several aqueous electrolyte solutions.
TL;DR: Water conductance of the cuticular membrane of mature sweet cherry fruit was investigated by monitoring water loss from segments of the outer pericarp excised from the cheek of the fruit, finding a positive relationship between conductance and stomatal density.
Abstract: Water conductance of the cuticular membrane (CM) of mature sweet cherry fruit (Prunus avium L. cv. Sam) was investigated by monitoring water loss from segments of the outer pericarp excised from the cheek of the fruit. Segments consisted of epidermis, hypodermis and several cell layers of the mesocarp. Segments were mounted in stainless-steel diffusion cells with the mesocarp surface in contact with water, while the outer cuticular surface was exposed to dry silica (22 +/- 1 degrees C). Conductance was calculated by dividing the amount of water transpired per unit area and time by the difference in water vapour concentration across the segment. Conductance values had a log normal distribution with a median of 1.15 x 10(-4) m s(-1) (n=357). Transpiration increased linearly with time. Conductance remained constant and was not affected by metabolic inhibitors (1 mM NaN3 or 0.1 mM carbonylcyanide m-chlorophenylhydrazone) or thickness of segments (range 0.8-2.8 mm). Storing fruit (up to 42 d, 1 degrees C) used as a source of segments had no consistent effect on conductance. Conductance of the CM increased from cheek (1.16 +/- 0.10 x 10(-4) m s(-1)) to ventral suture (1.32 +/- 0.07 x 10(-4) m s(-1)) and to stylar end (2.53 +/- 0.17 x 10(-4) m s(-1)). There was a positive relationship (r2=0.066**; n=108) between conductance and stomatal density. From this relationship the cuticular conductance of a hypothetical astomatous CM was estimated to be 0.97 +/- 0.09 x 10(-4) m s(-1). Removal of epicuticular wax by stripping with cellulose acetate or extracting epicuticular plus cuticular wax by dipping in CHCl3/methanol increased conductance 3.6- and 48.6-fold, respectively. Water fluxes increased with increasing temperature (range 10-39 degrees C) and energies of activation, calculated for the temperature range from 10 to 30 degrees C, were 64.8 +/- 5.8 and 22.2 +/- 5.0 kJ mol(-1) for flux and vapour-concentration-based conductance, respectively.
TL;DR: In this article, the authors show that the total conductance changes nonmonotonically with the magnetic field strength for different magnetic configurations, due to the precession of the spin accumulation in the normal metal.
Abstract: conductance of the system in the presence of a magnetic field can be asymmetric with respect to time reversal. The total conductance changes nonmonotonically with the magnetic field strength for different magnetic configurations. This modulation of the conductance is due to the precession of the spin accumulation in the normal metal. The difference between the conductance of the parallel and antiparallel configurations can be either positive or negative as a function of the applied magnetic field. This effect should be best observable on Al single crystals attached to ferromagnetic electrodes by means of tunnel junctions or metallic contacts.
TL;DR: The dual-frequency method and independent flow signal can be used to provide absolute volumes in mice and the dominant source of V(p) in mice was found to be the left ventricular wall itself, since surrounding the heart in the chest with physiological saline or markedly varying right ventricular volumes had a minimal effect on the left vents signal.
Abstract: The conductance catheter method has substantially enhanced the characterization of in vivo cardiovascular function in mice. Absolute volume determination requires assessment of parallel conductance...
TL;DR: In this paper, the electrical properties evolution of a series of SnO2 thin films doped with small amounts of Pd or Pt under pure air and air with 300 ppm CO is presented.
Abstract: An analysis of the electrical properties evolution of a series of SnO2 thin films doped with small amounts of Pd or Pt under pure air and air with 300 ppm CO is presented. As several types of chemical reactions are clearly involved in the solid–gas interactions at the film surface, it has been necessary to simplify the system by favouring interactions in absence of oxygen. Films were consequently also put in contact with N2 or Ar mixed with small amounts of H2, CO, H2S to favour behaviours in absence of oxygen gas. As under air+CO at 300°C, important features of Pd/Pt-doped film conductance closely resemble CO2 production rates of CO oxidation at the surface of Pd aggregates reported in the literature, an attempt of interpretation of the conductance evolution has been made along this line. Under CO and H2 mixed with neutral gas, dynamic (kinetic) electrical conductance measurements show that the dispersions of metallic elements induce a two-step time dependent behaviour. The first step is associated with a reduction of the oxygen molecules adsorbed at the SnO2 grain surface and an increase of electron density in the SnO2 depletion zone. The second step with a sharp conductance increase implies a reduction of the metallic aggregates and an electron transfer from the aggregates to the SnO2 grain conduction band. For H2S the conductance increases smoothly.
TL;DR: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability.
Abstract: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability. Addition of hexagonal boron nitride particles up to 16.0 vol. percent further increases the conductance of sodium silicate, due to the higher thermal conductivity of BN. However, addition beyond 16.0 vol. percent BN causes the conductance to decrease, due to the decrease in fluidity. At 16.0 vol. percent BN, the conductance is up to 63 percent higher than those given by silicone based pastes and is almost as high as that given by solder. Water is almost as effective as sodium silicate without filler, but the thermal contact conductance decreases with time due to the evaporation of water. Mineral oil and silicone without filler are much less effective than water or sodium silicate without filler. @S1043-7398~00!00402-3#
TL;DR: In this paper, the sensitivity of the four probe electrical conductance of compressed bismuth iron molybdate (Bi3FeO4(MoO4)2) powder to humid air was measured under conditions of varying degrees of chemical reduction at 24°C, 40°C and 60°C.
Abstract: The sensitivity of the four probe electrical conductance of compressed bismuth iron molybdate (Bi3FeO4(MoO4)2) powder to humid air was measured under conditions of varying degrees of chemical reduction at 24°C, 40°C and 60°C. It is expected that the oxygen vacancies created will alter the water adsorption sites and have a big effect on a conductance dominated by proton hopping, hydronium ion diffusion, or vacancy donor traps releasing electrons into the conduction band. The data was analyzed as the logarithm of the conductance change due to humid air vs. the logarithm of the humidity. Slopes were calculated as limiting values at the two ends of the graphs and were interpreted in terms of the Fleming model of surface conductance, where they represent the average number of physisorbed molecules per cation site. This analysis implies that a Grotthuss chain reaction through multi-layers of surface water is the correct mechanism for the oxidized surface at both low and high humidity. A maximum slope of four argues against significant micropore condensation and a minimum slope of one argues against electronic effects. But for the chemically reduced surfaces, electronic conduction in the semiconductor is increasingly important at low humidity, as seen by slopes less than one. If this is the case, chemical reduction may increase the material's sensitivity to fermi level shifts due to adsorbed water emptying vacancy surface traps, as has been claimed for other materials.
TL;DR: In this paper, the effect of the proximity of a bulk conductor on hopping transport is studied, and it is shown that putting a metal plane close to the dot layer causes a crossover from Efros-Shklovskii variable-range hopping conductance to two-dimensional Mott behavior as the temperature is reduced.
Abstract: An array of $3\ifmmode\times\else\texttimes\fi{}{10}^{7}$ Ge self-assembled quantum dots is embedded into the active channel of a Si metal-oxide-field-effect transistor. Conductance oscillations with a gate voltage resulting from a successive loading of holes into the dots are observed. Based on measurements of the temperature dependence of the conductance maxima, the charge-transfer mechanism in the channel is identified as being due to variable-range hopping between the dots, with the typical hopping energy determined by interdot Coulomb interaction. The characteristic spatial dimension of the hole wave functions as well as the charging energies of the dots are determined from the conductance data. The effect of the proximity of a bulk conductor on hopping transport is studied. We find that putting a metal plane close to the dot layer causes a crossover from Efros-Shklovskii variable-range hopping conductance to two-dimensional Mott behavior as the temperature is reduced. At the crossover temperature the hopping activation energy is observed to fall off. The metal plane is shown not to affect the conductance of samples which show Mott hopping. In the Efros-Shklovskii hopping regime, the conductance prefactor was found to be $\ensuremath{\simeq}{e}^{2}/h,$ and the conductance to scale with the temperature. In the fully screened limit, the universal behavior of the prefactor is destroyed, and it begins to depend on the localization length. The experimental results are explained by a screening of long-range Coulomb potentials, and provide evidence for strong electron-electron interaction between dots in the absence of screening.
Journal Article•
TL;DR: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability as mentioned in this paper.
Abstract: Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability Addition of hexagonal boron nitride particles up to 160 vol percent further increases the conductance of sodium silicate, due to the higher thermal conductivity of BN However, addition beyond 160 vol percent BN causes the conductance to decrease, due to the decrease in fluidity At 160 vol percent BN, the conductance is up to 63 percent higher than those given by silicone based pastes and is almost as high as that given by solder Water is almost as effective as sodium silicate without filler, but the thermal contact conductance decreases with time due to the evaporation of water Mineral oil and silicone without filler are much less effective than water or sodium silicate without filler @S1043-7398~00!00402-3#
TL;DR: In this article, the authors studied the transport propelties of a high quality one-dimensional constriction formed in an undoped GaAs/AlxGa1-xAs heterostructure and therefore largely free of the random potential of ionized donors.
Abstract: We have studied the transport propel-ties of a high quality one-dimensional constriction formed in an undoped GaAs/AlxGa1-xAs heterostructure and therefore largely free of the random potential of ionized donors. We induce an electron gas electrostatically and are able to vary the sheet carrier density (n(2D)) by a factor of at least seven. The constriction shows resonance-free integer conductance plateaus and the additional "0.7 structure," a plateaulike feature, the conductance of which decreases from about 0.80 towards 0.5 x 2e(2)/h at low and high n(2D) This low value is unaffected by a high in-plane magnetic field, supporting previous evidence and theories that the breaking of the spin degeneracy at high fields persists in some form, even at zero field. The height of the feature generally seen at a conductance of about 0.85 x 2 e(2)/h at high de bias also varies, and we show that this is in reasonable agreement with a simple relation linking the conductances of the two features. We use a source-drain bias to study the spin splitting of the lowest one-dimensional subbands, and find a spin gap that is independent of n(2D) for the first subband. We discuss possible reasons for the splitting, and show how various models for the 0.7 structure can be applied in the finite bias regime.
TL;DR: The dynamic conductance of carbon nanotubes was investigated using the nonequilibrium Green's function formalism within the context of a tight-binding model and the important role of photon-assisted transport through nanot tubes is revealed and its implications for experiments discussed.
Abstract: The dynamic conductance of carbon nanotubes was investigated using the nonequilibrium Green's function formalism within the context of a tight-binding model. Specifically, we have studied the ac response of tubes of different helicities, both with and without defects, and an electronic heterojunction. Because of the induced displacement currents, the dynamic conductance of the nanotubes differs significantly from the dc conductance displaying both capacitive and inductive responses. The important role of photon-assisted transport through nanotubes is revealed and its implications for experiments discussed.
TL;DR: In this article, the Bogoliubov-de Gennes equations were solved self-consistently within an extended Hubbard model to find the proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet-$d$-wave superconductor junctions with {110} oriented interface.
Abstract: The proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet--$d$-wave-superconductor junctions with {110}-oriented interface are studied by solving self-consistently the Bogoliubov--de Gennes equations within an extended Hubbard model. It is found that the proximity induced order parameter oscillates in the ferromagnetic region. The modulation period is shortened with the increased exchange field while the oscillation amplitude is depressed by the interfacial scattering. With the determined superconducting energy gap, a transfer matrix method is proposed to compute the subgap conductance within a scattering approach. Many interesting features including the zero-bias conductance dip and splitting are exhibited with appropriate values of the exchange field and interfacial scattering strength. The conductance spectrum can be influenced seriously by the spin-flip interfacial scattering. In addition, a sizable local magnetic moment near the {110}-oriented surface of the d-wave superconductor is discussed.