Template-assisted nanostructuring nanowires

The variety of porous solid materials that can be used as templates for nanostructure synthesis has been reviewed by Ozin (1992). In the template-assisted synthesis of nanowires, the pores or voids of the template are filled with the chosen material using a number of approaches. Nanowires have been derived via pressure injection, electrochemical deposition, and vapor deposition, as described in the following sections. 

There are several references reporting on template-assisted approaches for nanofabrication such as Hulteen and Martin. They are regarded as one of the pioneer groups for functional nanowire array fabrication. With the use of a periodic structured template, one-dimensional nanostructures can be prepared thanks to the confinement effect of the porous template. The templates can be prepared easily with anodization. Control of the aspect ratio and the area density of one-dimensional nanostructures can be achieved by changing the diameter and length of the template, and by changing the anodization voltage. 

In this chapter we study the overview of the various naturally and artificially prepared self-assembled nanostructures which are currently very important and in demand in biomedical applications, for example, bone tissues, natural laminated composites present in sea shells, peptide chain arrays and their derivatives and cell membranes are naturally self-assembled materials. And Langmuir—Blodgett films, surfactant-directed nonporous materials, and molecularly directed films, composites, nanombes, nanofibrils, nanowires, spherical vesicles, and template-assisted growth are artificially prepared self-assembled nanostructures. Here we discuss in brief the synthesis of those nanostructures which exist in nature and are prepared artificially to fulfill certain requirements (Figure 2.1). 

Template-assisted route has evolved as a good technique to achieve nanowires and nanodots and various nanostructures, but it has its own limitations. For a given material... 

Fig. 1 Examples of morphologies of semiconductor nanostructures, (a) metal assisted Si etching and formation of Si-NWs. Electrochemical formation of (b) microporous silicon, (c) ZnO nanorods, (d) porous CdSe using porous alumina template, (e) CdTe nanowires using alumina template, (1) CdS nanowires using alumina template, (g) mesoporous Xi02 film using doctor blade method, (h) self-ordered anodic Xi02 nanotubes and (i) cross section image of the same Xi02 nanotubes (reproduced with permission from Ref. 8,27,28,45 8).

There are many experimental techniques for the preparation of nanowires from the liquid phase. A considerable research effort has been expended in developing template-free methods for the deposition of one-dimensional nanostructures in a liquid environment the most important procedures are hydrothermal methods, electrospinning,sonochemical and surfactant assisted. 

A variety of solution methods such as seed-assisted growth, template-based synthesis, polyol method, solvothermal method and oriented attachment have also been developed for the synthesis of one-dimensional nanostructures. Here we will present various examples of the nanowires including metals, oxides, chalcogenides and pnictides with different synthetic methods. 

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