Electrical resistance and conductance

About: Electrical resistance and conductance is a research topic. Over the lifetime, 10619 publications have been published within this topic receiving 205313 citations.

Electric Field Effect in Atomically Thin Carbon Films

Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.

Carbon nanotube quantum resistors

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.

Formation of Bimolecular Membranes from Lipid Monolayers and a Study of Their Electrical Properties

Abstract: Bimolecular membranes are formed from two lipid monolayers at an air-water interface by the apposition of their hydrocarbon chains when an aperture in a Teflon partition separating two aqueous phases is lowered through the interface. Formation of the membrane is monitored by an increase of the electrical capacity, as measured with a voltage clamp. Electrical resistance of the unmodified membrane is analogous to that of conventional planar bilayers (black lipid membranes) prepared in the presence of a hydrocarbon solvent, i.e., 106-108 ohm cm2; the resistance can be lowered to values of 103 ohm cm2 by gramicidin, an antibiotic that modifies the conductance only when the membranes are of biomolecular thickness. In contrast to the resistance, there is a significant difference between the capacity of bilayers made from mono-layers and that of hydrocarbon-containing bilayers made by phase transition; the average values are 0.9 and 0.45 μF cm-2, respectively. The value of 0.9 μF cm-2 approximates that of biological membranes. Assuming a dielectric constant of 2.1 for the hydrocarbon region, the dielectric thickness, as calculated from a capacity of 0.9 μF cm-2, is 22 A. This value is 6-10 A smaller than the actual thickness of the hydrocarbon region of bilayers and cell membranes, as determined by x-ray diffraction. The difference may be due to a limited penetration of water into the hydrocarbon region near the ester groups that would lower the electrical resistance of this region and reduce the dielectric thickness. Asymmetric membranes have been formed by adjoining two lipid monolayers of different chemical composition.

Direct measurement of electrical transport through DNA molecules

Abstract: Attempts to infer DNA electron transfer from fluorescence quenching measurements1,2,3,4,5,6,7,8,9 on DNA strands doped with donor and acceptor molecules have spurred intense debate10,11 over the question of whether or not this important biomolecule is able to conduct electrical charges. More recently, first electrical transport measurements on micrometre-long DNA ‘ropes’12, and also on large numbers of DNA molecules in films13, have indicated that DNA behaves as a good linear conductor. Here we present measurements of electrical transport through individual 10.4-nm-long, double-stranded poly(G)-poly(C) DNA molecules connected to two metal nanoelectrodes, that indicate, by contrast, large-bandgap semiconducting behaviour. We obtain nonlinear current–voltage curves that exhibit a voltage gap at low applied bias. This is observed in air as well as in vacuum down to cryogenic temperatures. The voltage dependence of the differential conductance exhibits a peak structure, which is suggestive of the charge carrier transport being mediated by the molecular energy bands of DNA.

Thermal conductivity of single-walled carbon nanotubes

Abstract: We have measured the temperature-dependent thermal conductivity $\ensuremath{\kappa}(T)$ of crystalline ropes of single-walled carbon nanotubes from 350 K to 8 K. $\ensuremath{\kappa}(T)$ decreases smoothly with decreasing temperature, and displays linear temperature dependence below 30 K. Comparison with electrical conductivity experiments indicates that the room-temperature thermal conductivity of a single nanotube may be comparable to that of diamond or in-plane graphite, while the ratio of thermal to electrical conductance for a given sample indicates that the thermal conductivity is dominated by phonons at all temperatures. Below 30 K, the linear temperature dependence and estimated magnitude of $\ensuremath{\kappa}(T)$ imply an energy-independent phonon mean free path of \ensuremath{\sim}0.5--1.5 \ensuremath{\mu}m.