Semiconductor particulate films

Cf are the resistance and capacitance due to the particulate semiconductor film R m and are the resistance and capacitance of the parts of the BLM which remained unaltered by the incorporation of the semiconductor particles Rsc and Csc are the space charge resistance and capacitance at the semiconductor particle-BLM interface and Rss and Css are the resistance and capacitance due to surface-state on the semiconductor particles in the BLM. Electrolytes short circuit the porous semiconductor particles (Rf = Rsol = 1.4 kO) such that their contribution, along with that due to the Helmholtz layer, can be neglected. This allows the simplification of the equivalent circuit to that shown in Fig. 108c. As seen, the working electrode is connected (via ions) to the semiconductor particulate film. 

Methodologies developed for the in situ formation of semiconductor particulate films on BLMs have been applied to monolayer systems [638-641]. There are several advantages to the use of monolayer matrices for semiconductor particle generation. Monolayers are considerably more stable than BLMs and they also possess surface areas and charges which are two-dimensionally controllable. They may also, in association with the semiconductor paniculate films grown in their matrices, by conveniently transferred to solid supports. 

The experimental set-up used in the generation and in situ monitoring of semiconductor particulate films is identical to that used for nanosized, metallic, particulate films. Evolution of a nanocrystalline particulate film, illustrated by the formation of sulfide semiconductor particulate films (Fig. 110), has been discussed in terms of the following steps [639] ... 

To date, cadmium sulfide, zinc sulfide, lead sulfide, cadmium selenide, and lead selenide semiconductor particulate films have been grown, in situ, under... 

Electrical and photoelectrical measurements were carried out on CdS particulate films deposited on glass substrates or teflon sheets [640]. The resistivity (p) of a semiconductor particulate film, measured between two parallel copper electrodes, is given by... 

The thin semiconductor particulate film prepared by immobilizing semiconductor nanoclusters on a conducting glass surface acts as a photosensitive electrode in an electrochemical cell. An externally applied anodic bias not only improves the efficiency of charge separation by driving the photogenerated electrons via the external circuit to the counter electrode compartment but also provides a means to carry out selective oxidation and reduction in two separate compartments. This technique has been shown to be veiy effective for the degradation of 4-chlorophenol [116,117], formic acid [149], and surfactants [150] and textile azo dyes [264,265]. 

Zhao, X.K. and Fendler, J.H. (1991) Semiconductor particulate films on solid supports. Chem. Mater., 3, 168-174. 

Nanocrystalline particulate films, which exhibit pronounced quantum size effects in three dimensions, are of great interest due to applications in solar cell (108-112) and sensor (57, 113-115) applications. They exhibit novel properties due to not only the SQE manifested by individual nanoparticles but also the total surface area. Unlike MBE and MOCVD methods used to prepare quantum well electrodes, these electrodes can be prepared by conventional chemical routes described in Section 9.5.2.2. For example, II-VI semiconductor particulate films were prepared by using low concentrations of precursors and by controlling the temperature of the deposition bath. Nodes demonstrated the SQE for CdSe thin films deposited by an electroless method (98). The blue shift in the spectra of CdSe films has been demonstrated to be a function of bath temperature. As described in Section 9.5.2.1, electrodeposition of semiconductors in non-aqueous solvents leads to the formation of size-quantized semiconductor particles. On a single-crystal substrate, electrodeposition methods result in epitaxial growth (116, 117), and danonstrate quantum well properties. 

Available results on the preparation, characterization, and utilization of metallic and catalytic particles (Sect. 3), semiconductor particles and particulate films (Sect. 4), conductors and superconductors (Sect. 5), magnetism and magnetic particles and particulate films (Sect. 6), and advanced ceramic materials (Sect. 7) will constitute the main body of the monograph. An attempt will be made to cover these materials exhaustively. 

Semiconductor Particles and Particulate Films in Membrane-Mimetic Compartments... 

Membrane-mimetic compartments are being increasingly utilized as hosts for semiconductor particles and particulate films. Available information is summarized in Table 7 [611-709]. 

Table 7. Semiconductor particles and particulate films in membrane-mimetic compartments...

CdS, ZnS, PbS, CuS, and In2S3 System A = single composition of particulate semiconductor on one side of the BLM System B = two different compositions of particulate films on the same side of the BLM System C = two different compositions of particulate films on opposite sides of the BLM... 

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