Ohmic behavior

When particles are arranged in an FCC structure, as shown in Figure 3, the I V) curve shows a linear ohmic behavior (Fig. 9C). The detected current, above the site point, markedly increases compared to data obtained with a monolayer made of nanocrystals (Fig. 9C). Of course, the dIldV(Y) curve is flat (inset Fig. 9C). This shows a metallic character without Coulomb blockade or staircases. There is an ohmic connection through multilayers of nanoparticles. This effect cannot be attributed to coalescence of nanocrystals on the gold substrate, for the following reasons ... 

The electron transport properties described earlier markedly differ when the particles are organized on the substrate. When particles are isolated on the substrate, the well-known Coulomb blockade behavior is observed. When particles are arranged in a close-packed hexagonal network, the electron tunneling transport between two adjacent particles competes with that of particle-substrate. This is enhanced when the number of layers made of particles increases and they form a FCC structure. Then ohmic behavior dominates, with the number of neighbor particles increasing. In the FCC structure, a direct electron tunneling process from the tip to the substrate occurs via an electrical percolation process. Hence a micro-crystal made of nanoparticles acts as a metal. 

Here g, go, Tu, e, and h are respectively the conductance, the quantum of conductance equal to 77.48 microsiemens, the transmission through channel i, the electronic charge, and Planck s constant. The idea that conductance can be quantized is a remarkably new one compared with ohmic behavior - Fig. 6 shows experiments that directly demonstrate quantization of transport in atomic gold wires. 

In parallel, Kasumov et al. [60] reported ohmic behavior of the resistance of A-DNA molecules deposited on a mica surface and stretched between rhenium-carbon electrodes (see Fig. 6). This behavior was measured at temperatures ranging from room temperature down to 1 K. Below 1 K a particularly unexpected result was observed proximity-induced superconductivity. The resistance was measured directly with a lock-in technique and no current-voltage curves were presented. This surprising proximity-induced supercon-... 

Fig. 9 a Schematic illustration of the measurement with a conducting-probe AFM. b Relationship between resistance and DNA length for poly(G)-poly(C) (dark marks) for poly(A)-poly(T) (empty marks). The exponential fitting plots of the data are also shown, c Typical I-V curves of poly(dG)-poly(dC), the linear ohmic behaviors on I lOO nm at the repeat measurement of five samples, d Rectifying curves of poly(dG)-poly(dC) at L=100 nm (from [68], with permission Copyright 2000 by the American Institute of Physics)... 

The form of the I vs. V relation (7.317) for a cell, which has just been derived, depends upon the assumption that the activation overpotentials Tij and ti2 at the two interfaces have pushed the i vs. T) curves into the exponential region. If, instead, the two interfaces are showing ohmic behavior, then one has from Eq. (7.308) and linear i vs. T) relations (7.25) ... 

Figure 2.16 Ohmic behavior of heterogeneous electron transfer at low overpotentials.

Transport of electrons along conducting wires surrounded by insulators have been studied for several decades mechanisms of the transport phenomena involved are nowadays well understood (see [1, 2, 3] for review). In the ballistic regime where the mean free path is much longer than the wire lengths, l 3> d, the conductance is given by the Sharvin expression, G = (e2/-jrh)N, where N (kpa)2 is the number of transverse modes, a, is the wire radius, a Fermi wave vector. For a shorter mean free path diffusion controlled transport is obtained with the ohmic behavior of the conductance, G (e2/ph)N /d, neglecting the weak localization interference between scattered electronic waves. With a further decrease in the ratio /d, the ohmic behavior breaks down due to the localization effects when /d < N-1 the conductance appears to decay exponentially [4]. 

Additional information with respect to the mechanism of the grain boundary resistance can be obtained from temperature- and voltage-dependent impedance measurements. The grain boundary semicircle varies, for example, considerably with the applied dc bias (Fig. 39a). The current-voltage relations calculated from such bias-dependent impedance measurements are thus non-linear. In the logarithmic plot (Fig. 39b) it can be seen that the low bias regime exhibits a non-linearity factor a (= d og(I/A)/d og(U/ V)) of almost one (ohmic behavior), while at a bias value of about 0.35 V this factor changes to a x 2. 

At low electrical field, Eq. (8) can be linearized, and thus an ohmic behavior is obtained ... 

Figure 5. The complex a -(EDT-TTF)[Pd(dmit)2]. Pressure-dependence of the resistivity a, ambient pressure b, 2 c, 5 d, 10 kbar) and (insert) non-ohmic behavior at ambient pressure for an injected current of 150 pA ( ) and 1.5 mA (—). [Adapted From (97).]...

The origin of these effects is not at all clear. The bias effects and the room temperature persistent photoconductivity have similar annealing properties. There is also an obvious similarity between the annealing curves and those for the frozen-in excess conductivity of bulk doped a-Si H (e.g. Fig. 6.3). It is therefore probable that carrier-induced defect creation is the origin of the changes in conductivity and that annealing to the equilibration temperature restores the initial state. However there is as yet no complete explanation for the non-ohmic behavior and why it depends on the applied bias. 

The slope of the IV profile of ohmic ion channels and pores gives their conductance g (Fig. 11.4, 8c, dotted). Non-ohmic ion channels are ion channels that violate Eq. (11.4) (Fig. 11.8c, solid). Because of importance in biology and materials science, the creation of non-ohmic ion channels and pore has attracted considerable interest in supramolecular chemistry [2, 9]. The key parameter characterizing non-ohmic behavior is the gating charge Zg [5, 9]. 

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