Semiconducting nanostructure, fabrication

This chapter deals with the fabrication of semiconducting nanostructures, electrochemistry at these nanostructures, and their apphcations. We will... 

The demonstration of nano fabrication on semiconductive electrodes was reported as early as in 1990 by Nagahara et aL These anthors fabricated nanostmctnres on Si(lOO) and GaAs(lOO) surfaces via local etching by maintaining a tip-surface bias and tunneling current. They observed nanostructures 20-nm wide and 1.5-nmdeep. 

Figure 10.8 Polymer line fabricated at 10 nm s 48% humidity, -12 V. Polymer line width 30 nm scale bar 250 nm. (Reprinted with permission from Journal of the American Chemical Society, Direct-Writing of Polymer Nanostructures Polyftbiopbene) Nanowires on Semiconducting and Insulating Surfaces by Benjamin W. Maynor et a ., 124, 4. Copyright (2002) American Chemical Society)...

An efficient one-pot synthesis of core/shell TiO /PANI-NPs from meth-acrylic acid-functionalized TiO -NPs by self-catalyzed hydroamination and oxidative polymerization of aniline was demonstrated by Bae et al. [118]. Core/shell-structured TiO /PANI nanocomposite was also fabricated by grafting aniline on aminobenzoate monolayer that is chemically adsorbed on the TiO nanocrystal surface [119]. Ferromagnetic semiconducting PANI/TiO nanocomposites [96], PANI/TiO nanocomposite photocatalysts [97], as well as composites of self-assembled PANI nanostructures with TiO -NPs [88] or TiO nanotubes [98] were synthesized by... 

Semiconducting nanowires, nanorods, nanodots, nanocones, nanopins, etc. are interesting due to their broad range of applications. Electrochemically, the most easily fabricated semiconductors are Il-Vl semiconductors, for example, CdS, CdSe. There are three approaches for electrodeposition of semiconductors. The first method [131] is deposition of metal in alumina nanopores, followed by etching of alumina surface by phosphoric/chromic acid to access metallic surface for sulphur or arsenic vapour to attain metal sulphide or arsenide nanostructures. The second method deals with electrolysis of sulphuric acid, causing the sulphide atoms to be deposited in pores. 

The first part of this section focuses on the main characteristics and fabrication techniques used for obtaining templating membranes and depositing metal nanostructures by suitable electroless and elecuochemical procedures. Methods such as sol-gel (10-12) or chemical vapor deposition (10, 13), which have been used primarily for the template deposition of carbon, oxides, or semiconducting-based materials, will not be considered here in detail. The second part of the section focuses on the electrochemical properties of the fabricated nanomaterials with emphasis on the characteristics and applications of nanoelectrode ensembles (NEEs). 

Nanostructured materials fabricated by the aforementioned methods are usually amorphous, thus offering relatively poor properties. In order to improve, e.g., electrical properties in the case of semiconducting oxides, thermal crystallization at elevated temperatures has to be implemented, typically resulting in polycrystalline materials. 

In order to carry out electrochemistry, nanostructures need to be back contacted to form an electrode. Electrodes are fabricated by various routes that coat an electronically conducting substrate with a thin layer of the semiconducting material. This thin layer formation is either based on deposition of the already synthesized nanostructured materials (often in a random arrangement such as sintered nanoparticle layers), or it is based on growth of nanostructured layers directly on a conducting substrate. The methods can generally be classified into non-electrochemical or electrochemical techniques, which are briefly discussed below. 

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