Morphology-Dependent Spectroelectrochemical Behavior of PbS Nanoparticulate Films Grown Under Surfactant Monolayers
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Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
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WAVELENGTH, nm Figure 1. Absorption spectra of PbS-I (a), PbS-Il (b) and PbS-III (c).
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WAVELENGTH, nm Figure 2A. Absorption spectra of PbS-I at different applied potentials. The insert shows the absorbances at 384 nm as functions of the applied potential.
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WAVELENGTH, nm Figure 2B. Absorption spectra of PbS-Il at different applied potentials. The inserts show the absorbances at 750 nm and at 386 nm as functions of the applied potential.
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WAVELENGTH, um Figure 2C. Absorption spectra of PbS-ill at different applied potentials. The insert shows the absorbances at 380 run as functions of the applied potential.
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Increase of this absorption results from the accumulation of trapped conduction-band electrons at negative bias potentials in PbS-I and PbS-II. Indeed, absorbances for PbS-II at 750 nm were found to decrease with increasing applied positive potential linearly to -0.6 V, after which they remained unaltered (see insert in Figure 2B). The point of inflection, -0.50±0.05 V, may be taken to correspond to the flat-band potential, Vfo, of the PbS-II nanoparticulate film.8 Interestingly, non-epitaxially grown PbS nanoparticulate films (PbS-HI) do not show electron accumulation under identical conditions. The effect of applied potential on absorbance at the absorption maxima of the PbS nanoparticulate films is more complicated. The absorbances for PbS-I at 384 um were found to increase upon a decrease of the applied potential from 0 V to -0.4 V, after which they decreased rapidly in the -1.6 to -2.0 V range (See insert in Figure 2A). Applying a negative potential, from o V to -0.4 V, increased the absorbance of PbS-TI at 386 nm; the absorbance then decreased in the -0.4 V to -1.2 V range, increased in the -1.3 V to -1.8 V range, and decreased again at bias voltages more negative than -1.8 V (see insert in Figure 2B). In contrast, the absorbance at 380 nm decreased linearly in the 0 V to -1.7 V range, after which it dropped precipitously upon biassing PbS-ITT (insert in Figure 2C). The absorption spectra vs. applied potential plots (Figures 2A-C) have been reproduced for a number of films which were deposited with significant procedure variations (washing, drying time, density of film, preliminary irradiation, etc.). Minimal deviation from the presented behavior has been observed. The absorption spectra, corrected for reflectivity and scattering in the 700-800 nm region, were found to be indistinguishable from the uncorrected spectra. Cyclic voltammograms of PbS-I, PbS-II, and PbS-III indicated no ch
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