Current-voltage curves measurement

Fig. 53. Current-voltage curves measured in vacuum at RT on M-DNA (open circles) and B-DNA (closed circles). The former indicates semiconductor-like behavior and the latter metal-like. Reproduced with permission from Ref. (178). Copyright 2001, American Physics Society.

This scanned mercury electrode technique is not a conventional measurement approach. We have compared Hg as a top electrode to other thin-film counterelectrodes, particularly platinum and aluminum, using known dielectric materials including a-SiOx, a-TaO and a-Al203 thin films. Current-voltage curves measured using mercury top electrodes are comparable to those measured using Pt or A1 top electrodes. 

Implicit in the above is the notation that current-voltage curves measured at macroelectrodes for all but fast voltage scan rates are characterized by a mass transport limited current plateau rather than a current peak as in linear sweep voltammetry at a planar electrode of larger than micro dimensions. 

Fig. 32 Diagrams showing current-voltage curves measured at a microdisc electrode at scan rates corresponding to the limits of (a) convergent diffusion and (b) planar...

Figure 5.37 Current—voltage curves measured at 4.2 l< (open squares) and at 295 K (solid squares). The solid curves denote fits of the Korotkov-Nazarov model, as described in Ref. [51]. Fitting parameters for these curves are Vc = 55mV, Ro=fl x lO Q, qo = 0.15e...

Grain-Boundary Conductivity, Fig. 4 A log-log plot of the current-voltage curve measured for a single grain boundary in 2 mol% Y-doped BaZrOs at 350 °C [15]... 

Determine the half-wave potential from the current-voltage curve as described in Section 16.6 the value in 1M potassium chloride should be about — 0.60 vs S.C.E. Measure the maximum height of the diffusion wave after correction has been made for the residual current this is the diffusion current Id, and is proportional to the total concentration of cadmium ions in the solution. 

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-... 

Another measurement that follows the line of the Porath et al. [14] experiment was performed by Yoo et al. [75]. In this experiment, long poly(dG)-poly(dC) and poly(dA)-poly(dT) molecules were electrostatically trapped between two planar metal electrodes that were 20 nm apart (see Fig. 11) on a Si02 surface, such that they formed a bundle that was -10 nm wide. A planar gate electrode added another dimension to this measurement. The current-voltage curves showed a clear current flow through the bundle and both temperature and gate dependencies. The resistivity for the poly(dG)-poly(dC) was calculated to be 0.025 flcm. 

Measurements on a different type of DNA-based material were reported by Rinaldi et al. [68] (see Fig. 13). In this experiment they deposited a few layers of deoxyguanosine ribbons in the gap between two planar metal electrodes, -100 nm apart. The current-voltage curves showed a gap followed by rise of the current beyond a threshold of a few volts. The curves depended strongly on the concentration of the deoxyguanosine in the solution. 

The photoconductive gain G as measured from saturated current-voltage curves is of the order of unity in several dyes 3,50,51) .g. in malachite green G =0.2, pinacyanol G=0.37 and merocyanine A 10 7 G=0.6. 

In the early 1950 s it first became possible to determine the photoelectric sensitivity of dyes of different classes (phthalocyanines, cyanines, etc.) by measuring barrier-layer photopotentials in cases where barriers were strongly affected by carriers trapped in the surface states of adsorbed gases 54-56>. Jn agreement with the theory of inorganic surface-barrier rectifiers, asymmetric current-voltage curves were also observed. 

The voltammogram, which is a current-voltage curve, / = f( ), corresponds to a voltage scan over a range that induces oxidation or reduction of the analytes. This plot allows the identification and measurement of the concentration of each species. Several metals can be determined by this method. 

Figure 4 compares the current voltage curves of anodic chlorine evolution measured at graphite and Ru02 anodes in brine solution of a concentration, which is typical for chloralkali electrolysis (300 g NaCl/dm3) (22). 

For either of these two methods, in which the measurement of the current is restricted to one selected potential, it is necessary to carry out a preliminary recording of the i — E curves in the reaction mixture at chosen time intervals. This makes it possible to choose the correct applied potential corresponding to the limiting current of the wave studiet. It is also advisable to record one complete i — E curve at the end of each kinetic run, in order to confirm that the applied voltage chosen really corresponded to the limiting current of interest. Such a current-voltage curve also allows unexpected reactions to be detected, if new waves appear. 

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