Template-assisted synthesis vapor deposition

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 exist a variety of methods to synthesize quasi-one-dimensional nanostructured materials, which include but not limited to vapor phase growth, template-assisted synthesis, sol-gel deposition, surfactant-assisted growth, sonochemical method, hydrothermal method, and electrochemical deposition [21], Among the various methods, the electrochemical anodization method is one of the simplest and cheapest methods to synthesize ordered quasi-one-dimensional nanostructure. 

Over the past few years, a large number of experimental approaches have been successfully used as routes to synthesize nanorods or nanowires based on titania, such as combining sol-gel processing with electrophoretic deposition,152 spin-on process,153 sol-gel template method,154-157 metalorganic chemical vapor deposition,158-159 anodic oxidative hydrolysis,160 sonochemical synthesis,161 inverse microemulsion method,162 molten salt-assisted and pyrolysis routes163 and hydrothermal synthesis.163-171 We will discuss more in detail the latter preparation, because the advantage of this technique is that nanorods can be obtained in relatively large amounts. 

The so-called dry gel method [20-22] is another alternative for membrane synthesis where vapors containing templates (i.e., amines) and water are employed to crystallize silica or silica-alumina layers previously deposited onto the support (vapor-phase transport method) or where steam is used to crystallize silica and template or sUica-alumina and template dry layers previously deposited onto the support (steam-assisted crystallization). Using this approach, the reactant consumption is clearly diminished, an important issue for scale-up purposes on the other hand, synthesis time is delayed due to transport-controlled phenomena. 

Vertically aligned MWCNTs and SWCNTs can be produced through template synthesis methods by chemical vapor deposition (CVD) of a gaseous hydrocarbon (e.g., acetylene or ethylene) precursor on metal-coated surfaces " or within porous membranes " or through covalent, electrostatic, or metal-assisted assembly on surfaces. - " Electrodes composed of vertically aligned CNTs offer signal enhancement and improved electron-transfer kinetics compared to many types of electrodes modified with randomly oriented CNTs. - - - For example, carbon-fiber microdisks modified with vertically aligned SWCNTs (often called SWCNT forests ) exhibited over 30 times... 

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