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Photoexcitation photocurrent

C60 has been used to produce solvent-cast and LB films with interesting photoelec-trochemical behavior. A study of solvent-cast films of C60 on Pt rotating disc electrodes (RDEs) under various illumination conditions was reported [284]. Iodide was used as the solution-phase rednctant. The open-circuit potential shifted by 74 mV per decade of illumination intensity from a continuous wave (cw) argon-ion laser. The photocurrent versus power was measured at -0.26 V under chopped illumination (14-Hz frequency, vs. SCE) up to 30 mW cm and was close to linear. The photoexcitation spectrum (photocurrent versus wavelength) was measured at 0.02 V (vs. SCE) from 400 to 800 mn and found to be... [Pg.110]

Photoirradiation of the modified electrode with nanoclusters of Cj qN alone or the mixture of C oN and MePH afforded anodic photocurrents. The photocurrent action spectrum was in fair agreement with the absorption spectrum of the THF-H2O (2 1) mixed solution containing nanoclusters of the mixture of CfioN and MePH or C oN alone. These results strongly indicate that the photocurrents can be ascribed to photoexcitation of the nanoclusters of C qN. ... [Pg.273]

Photoexcited electrons or holes migrate in a space charge layer towards the electrode interface, where they participate in transfer reactions of cathodic electrons or anodic holes to provide a reaction current as shown in Pig. 10-9. Such a reaction current of photoexcited electrons or holes is called the photoexcited reaction current or simply the photocurrent. [Pg.334]

Fig. 10-9. Photoexcited reaction current (photocurrent) at semicon ductor electrodes (a) photoexcited reaction of cathodic electron transfer (OX + e - RED) at p-type semiconductor electrode, (b) photoexcited reaction of anodic hole transfer (RED - OX + e) at n-type semiconductor electrode, iph = photocurrent. Fig. 10-9. Photoexcited reaction current (photocurrent) at semicon ductor electrodes (a) photoexcited reaction of cathodic electron transfer (OX + e - RED) at p-type semiconductor electrode, (b) photoexcited reaction of anodic hole transfer (RED - OX + e) at n-type semiconductor electrode, iph = photocurrent.
As shown in Fig. 10-9, the photoexcited reaction current occurs only when an appreciable electric field exists in the space chai ge layer. No photocurrent occurs at the flat band potential because no electric field that is required to separate the photoexcited electron-hole pairs is present. The photocurrent occurs at any potentials different from the flat band potential hence, the flat band potential may be regarded as the potential for the onset of the photocurrent. It follows, then, that photoexcited electrode reactions may occur at potentials at which the same electrode reactions are thermodynamically impossible in the dark. [Pg.335]

It follows from Eqn. 10-13 that, if a 6sc is much larger than 1 (a 5sc 1, both a and being great), all the photoexcited minority charge carriers will be consumed in the interfacial reaction (ipb = e Iq ). In such a case, the photocurrent is constant at potentials away from the flat band potential as shown in Fig. 10-11 this figure plots the anodic ciirrent of photoexcited dissolution for a gallium arsenide electrode as a function of electrode potential. [Pg.336]

As shown in Fig. 10-18, the flat band potential that characterizes the onset potential of photocurrent shifts from the dark flat band potential Em to the photoexcited flat band potential Eukpu as photoexdtation continues. [Pg.344]

The study of the dispersion of photoinjected charge-carrier packets in conventional TOP measurements can provide important information about the electronic and ionic charge transport mechanism in disordered semiconductors [5]. In several materials—among which polysilicon, a-Si H, and amorphous Se films are typical examples—it has been observed that following photoexcitation, the TOP photocurrent reaches the plateau region, within which the photocurrent is constant, and then exhibits considerable spread around the transit time. Because the photocurrent remains constant at times shorter than the transit time and, further, because the drift mobility determined from tt does not depend on the applied electric field, the sample thickness carrier thermalization effects cannot be responsible for the transit time dispersion observed in these experiments. [Pg.48]

Figure 4.9 Semilogarithmic plot of the fractional-recovered photocurrent + )/i(T,) versus interruption time fj at two different locations in the specimen. Interruption locations are indicated on the schematic TOP waveforms in the upper inset. Interruption at location (x/L) = 0.65 when photoexcited on side A corresponds to location (x/L) = 0.35 when... Figure 4.9 Semilogarithmic plot of the fractional-recovered photocurrent + )/i(T,) versus interruption time fj at two different locations in the specimen. Interruption locations are indicated on the schematic TOP waveforms in the upper inset. Interruption at location (x/L) = 0.65 when photoexcited on side A corresponds to location (x/L) = 0.35 when...
In the case of a semiconductor electrode, the existence of the energy gap makes a qualitatively different location of energy levels quite probable (Figs. 23b, 23c). One of them, either the ground or excited, is just in front of the energy gap, so that the direct electron transition with this level involved appears to be impossible. This gives rise to an irreversible photoelectro-chemical reaction and, as a consequence, to photocurrent iph. The photoexcited particle injects an electron into the semiconductor conduction band... [Pg.304]

In principle, the same photoexcited reactant, if it is liable both to oxidation and reduction, can inject both electrons (into an -type semiconductor) and holes (into a p-type semiconductor). Such a material is, for example, the crystal-violet dye. Figure 25 shows the spectra of cathodic photocurrent iph at p-type gallium phosphide and anodic photocurrent at n-type zinc oxide both in a solution, which does not absorb light (dashed lines), and in the presence of crystal violet the absorption spectrum of the latter is also shown for comparison. [Pg.306]

In the absence of the dye the photocurrent is observed only in relatively short-wavelength light in the region of intrinsic absorption of semiconductors and is caused by photoexcitation of the electron-hole system of the semiconductor (cf. Part III). For zinc oxide (Eg = 3.2 eV) this region corresponds to wavelengths shorter than 400 nm for gallium phosphide (Eg = 2.2 eV), shorter than 550 nm. [Pg.306]

One interpretation presumes that the photocurrent onset in the absence of sulfide is determined by electron-hole recombination. The sulfide ions on the surface are then supposed to be bound to these surface recombination levels rendering them unavilable for recombination reactions. The charge transfer reactions could then proceed at lower voltages. In this case the corrosion suppression role of the sulfide ions would be to reduce the oxidized corrosion site before a cadmium ion could go into solution. A variation on this theme is to consider the corrosion site to be the recombination state, i.e., the site on the surface that normally leads to corrosion when oxidized by a photoexcited hole can be... [Pg.107]

Regardless of the nature of the surface state it is clear that it can capture an electron from the conduction band producing cathodic current. This cathodic current balances the anodic current produced when the photoexcited holes produced the oxidized surface state. The net result of these two processes is electron-hole recombination leading to no net current. This recombination process is what controls the voltage of photocurrent onset as can be seen in curve 2 of Figure 5. [Pg.112]

The reduction peaks in curve 3 of Figure 7 are presumed to be due to the transfer of an electron from the conduction band to the oxidized compound. After the voltage sweep of curve 3 the current reverts to curve 1 and the 470 nm photocurrent reverts to its original value. The process is repeatable and delays of several minutes between photoexcitation and voltage sweep show little change in curve 3. [Pg.114]


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See also in sourсe #XX -- [ Pg.273 , Pg.274 , Pg.275 , Pg.276 , Pg.277 ]




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Photoexcitation

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