Photochemical deposition

The advantages of this method are that the extent of gold deposition is almost quantitative, and thermal treatment is unnecessary because gold is already reduced by the UV irradiation. The gold particles can be very small, but the method has not been used very much, although it has been applied to preparing bimetallic catalysts (see Section 4.6.2.4). 

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Deposition of Thin Films. Laser photochemical deposition has been extensively studied, especially with respect to fabrication of microelectronic stmctures (see Integrated circuits). This procedure could be used in integrated circuit fabrication for the direct generation of patterns. Laser-aided chemical vapor deposition, which can be used to deposit layers of semiconductors, metals, and insulators, could define the circuit features. The deposits can have dimensions in the micrometer regime and they can be produced in specific patterns. Laser chemical vapor deposition can use either of two approaches. 

Despite extensive studies, laser photochemical deposition has not yet replaced the conventional processes for fabrication of integrated circuits, except in selected appHcations such as making and breaking of selected links for customization of circuits and in the repair of defects. The reason is that laser processing of an entire wafer has remained more expensive than the conventional processes. 

Vigil E, Gonzalez B, Zumeta I, Domingo C, Domenech X, Ayllon JA (2005) Preparation of photoelectrode with spectral response in the visible without applied bias based on photochemically deposited copper oxide inside a porous titanium dioxide thin film. Thin Solid Films 14 489 50-55... 

Marrs, J.M. Ultraviolet Light for Photochemical Deposition, Chem. Eng. Progress, 31-34 (January 1986). 

Fig. 14. AFM images of polycrystalline rutile surfaces before (a,c,e) and after (b,d,f) the photochemical deposition of silver (white contrast).

Laser surface chemistry has been used as a basis for many new methods in surface processing, for example, photochemical deposition of metals and photochemical etching of solid substrates, which are potentially useful techniques for the microelectronics industry (1-3). However, molecular dynamical studies of UV photodissociation of adsorbates on solid surfaces have been very scarce (4-7). We have studied UV laser photodissociation of small molecules on solid surfaces using photofragment spectroscopy. 

Since the late 1980s several innovative syntheses of polypyrroles have been discovered. The photosensitized polymerization of pyrrole in aqueous solution and in polymer matrices using tris(2,2 -bipyridine)ruthenium(II) as a photosensitizer has been reported <89CC132>, and PPy can be photochemically deposited on to any type of surface under visible light irradiation conditions <89CC657, 90CC387). The preparation and potential applications of surface-functionalized polypyrrole-silica nanocomposite particles have been discussed <94PP217>. 

More recently, Nocera s catalyst was electrodeposited onto mesostructured hematite (a-Fe203) [61], and photochemically deposited, as 10-30 nm nanoparticles, on a semiconductor photoanode of ZnO [62], leading to performance and fabrication improvements. The resulting photoanodes show >0.35 V and 0.23 V reduction, respectively, of the bias voltage required for promoting water oxidation, with respect to bare oxides [63]. 

Steinmiller EMP, Choi KS (2009) Photochemical deposition of cobalt-based oxygen evolving catalyst on a semiconductor photoanode for solar oxygen production. Proc Natl Acad Sci USA 106 20633-20636... 

One of the major applications of organometallic photochemistry to materials chemistry is in the photochemical deposition of thin fdms. In the photochemical film-deposition process, a thin metal fdm is deposited on a substrate surface by using light to dissociate the ligands from an organometallic complex. During the irradiation, the organometallic molecule can either be adsorbed to the substrate surface (Equation (37)) or it can be in the gas phase above the substrate (Equation (38)). 

Typically lithographic processes require two steps. The first is the formation of a mask using a polymer while the second is the deposition of the material of interest. Our work has concentrated on the direct photochemical deposition of inorganic materials. This process has the advantage that it is inherently photolithographic in nature. In this paper we outline the process for the deposition of a range of ferroelectric materials. 

Photochemical deposition is based on the principle that metal cations with appropriate redox potentials can be reduced by photoelectrons created by bandgap illumination of semiconductors used as supports. Titania support was used, either as colloids [117, 118] or powder [26] or nanofibers [119]. UV irradiation of deaerated solutions containing HAuCLj and titania led to both the deposition of gold and its reduction. As a matter of fact, experimental conditions were such that at least part of [AuCLj] or [AuChOH]" could adsorb... 

Carrillo I, Rangel E, Magana LF (2009) Photochemical deposition of Ag nanoparticles on multiwalled carbon nanotubes. Carbon 47 2752-2760... 

J. M. Kern, J. P. Sauvage, Photochemical deposition of electrically conducting polypyrrole, Chemical Communications 1989, 10, 657. 

A few methods for the photochemical deposition of pigments have been reported. Harima et al. reported the photochemical deposition of pigments onto a Ti02 substrate [26]. Photogenerated holes from the valence band edge oxidize the FPEG. Mizuno et al. reported... 

Photochemical deposition (PD) is nowadays gaining importance as an alternative method for preparing heterogeneous catalysts. It allows metal deposition over semiconductor materials, with simultaneous reduction of metal ions by the electrons of the conduction band. This process can be enhanced by addition of sacrificial electron donors (such as formaldehyde, methanol or 2-propanol) that can supply an almost unlimited amount of electrons. PD takes place at, or near, the photoexcited sites, leading to an enhanced dispersion. 

Wang Y, Wang Y, Xu R (2013) Photochemical deposition of Pt on CdS for H-2 evolution fiom water markedly enhanced activity by controlling Pt reduction environment. J Phys ChemC 117 783-790... 

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