Electrodeposition of Metals and Semiconductors

Section 6.2.1 offers literature data on the electrodeposition of metals and semiconductors from ionic liquids and briefly introduces basic considerations for electrochemical experiments. Section 6.2.2 describes new results from investigations of process at the electrode/ionic liquids interface. This part includes a short introduction to in situ Scanning Tunneling Microscopy. 

In ionic liquids the situation seems to be totally different. It was surprising to us that the electrodeposition of metals and semiconductors in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide delivers nanocrystalline deposits with grain sizes varying from 10 to 200 nm for the different materials, like Si, Al, Cu, Ag and In, investigated to date. It was quite surprising in the case of Al deposition that temperature did not play a tremendous role. Between 25 and 125 °C we always got nanocrystalline Al with similar grain sizes. Similar results were obtained if the deposition was performed in tri-hexyl- tetradecylphos-phonium bis (trifluoromethylsulfonyl) amide. Maybe liquids with saturated nonaromatic cations deliver preferentially nanomaterials this is an aspect which, in our opinion, deserves further fundamental studies. 

Freyland W, Zell CA, Abedin SZE et al (2003) Nanoscale electrodeposition of metals and semiconductors from ionic liquids. Electrochim Acta 48 3053-3058... 

In Section 6.2.1 we will report on the literature on the electrodeposition of metals and semiconductors from ionic liquids and briefly introduce basic considerations... 

Zein El Abedin S, Endres F (2006) Electrodeposition of metals and semiconductors in air- and water-stable ionic liquids. Chem Phys Chem 7 58 Endres F (2002) Ionic liquids solvents for the electrodeposition of metals and semiconductors. Chem Phys Chem 3 144... 

Endres, F. (2002), Ionic Liquids Solvents for the Electrodeposition of Metals and Semiconductors, Chem. Phys. Chem., Vol.3, February 2002, pp.144-154, ISSN 1439-7641... 

Aqueous ionic liquid microemulsions as electrolytes for electrochemical deposition are special and different from traditional aqueous solution and ionic liquids. Electrochemical approaches have been among the first to be used for the fabrication of inorganic nanopartides and nanostructured films in ionic Hquids. The properties of ionic liquids opened the door to the electrodeposition of metals and semiconductors at room temperature, which was ptreviously only possible from high-temperature molten salts. For example, Al, Mg, Ti, Si, Ge and rare-earth-elements related materials can be obtained from ionic hquids. 

In general the potential windows are not as wide as those for the haloaluminates or the discrete anions and they tend to be limited by the deposition of metal at the cathodic limit and the evolution of chlorine at the anodic limit. Since ionic liquids are aprotic solvents, hydrogen evolution and hydrogen embrittlement that often occur in aqueous baths are circumvented in these liquids. Moreover, because of their thermal stability, these ionic liquids make it easier to electrodeposit crystalline metals and semiconductors through direct electrodeposition without subsequent annealing. 

Electrodeposition of metals on semiconductor surfaces has been used by Allongue et al. to form nearly ideal Schottky barriers on GaAs [6.176] and InP [6.177], and to stabilize photoelectrodes with ultrathin and transparent metal films [6.174, 6.178, 6.179]. Selective metal deposition has also been performed to reveal p-n junctions and transistors on silicon chips [6.180]. 

However, it is only recently that the potential benefits of combining sonochemistry with electrochemistry have increasingly been studied. It should be noted that electrochemical methods, mainly electrodeposition, are well established for the preparation of metals and semiconductor nanomaterials (for a review see Mastai et al. [146]). 

This entry focuses on the electrodeposition of binary II-VI and III-V compounds. The electrodeposition of metal oxide semiconductors such as ZnO is covered in another entry. 

The motivation behind the Symposium on Electron Spectroscopy and STM-AFM Analysis of the Solid-Liquid Electrochemical Interface was to assemble in one place some major players in electrochemical surface science. The obvious rationale was that such a gathering would help distill and focus future work to issues deemed most critical to further progress in the area. The processes that were discussed at the symposium included electrodeposition and electrocrystallization, passivation of metals and alloys, anodic dissolution of metals and semiconductors, oxidation of small molecules, assembly of semiconducting layers, hydrogen adsorption, and charge transfer at surface-modified electrodes. 

Electrochemistry provides routes to directly prepare nanostructures both delocalized in a random or organized way and localized at predefined surface sites with adjustable aspect ratios. Purity, monodispersity, ligation, and other chemical properties and treatments are definitely important in most cases. By delocalized electrodeposition it is possible to decorate large areas of metal or semiconductor surfaces with structures of a narrow size distribution stable nuclei-clusters can be... 

In this chapter we present a few selected results on the nanoscale electrodeposition of some important metals and semiconductors, namely, Al, Ta and Si, in air- and water-stable ionic liquids. Here we focus on the investigation of the electrode/electrolyte interface during electrodeposition with the in situ scanning tunneling microscope and we would like to draw attention to the fascinating... 

Electrodeposition of dissolved precursors (especially in aqueous solutions) is a low cost and scalable method which is well suited to the mass production of thin films of metal-oxide semiconductors such as Ti02, Cu20, WO3, and ZnO. Control of temperature, pH and the deposition potential are important because the corresponding electrochemical reactions within the deposition bath mainly depend on these parameters. 

Thin films of nanostructured metals and semiconductors (e.g., Pt, Sn, CdTe) can be prepared by electrodeposition of the metal ions doped into the Hi LLC phase [40,47,48]. Similar to the precipitation of CdS, these films can retain the symmetry of the LLC template during the deposition. These materials allow one to combine well-defined porous nanostructures, high specific surface areas, electrical connectivity, fast electrolyte diffusion, and good mechanical and electrochemical stability. With this approach, hexago-nally structured semiconductor films of uniform thickness can be prepared. Nanostructured thin films of this type are proposed to have relevance in catalysis, batteries, fuel cells, capacitors, and sensors. 

EJ. Taylor, C. Zhou, and J. Sun, Pulse Reverse Electrodeposition for Metallization and Planarization of Semiconductor Substrates , U.S. Patent Pending, filing date 14 October, 1998... 

Local structuring and modification of solid-state surfiices by electrodeposition of metals are of great practical importance. However, the realization of these processes requires an exact knowledge of UPD and OPD of Me at an atomic level. At present, first attempts have been started to develop appropriate polarization routines for a defined nanostructuring or nanomodification of solid-state siufaces (metals, semiconductors, superconductor films) using in-situ STM and AFM. 

We have presented in this section an insight into the electrodeposition of metals, alloys and semiconductors from ionic liquids. As well as environmental... 

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