Recent developments in single-crystal inorganic nanotubes synthesised from removable templates

Since Sumio lijima identified the hollow Carbon Nanotubes (CNTs) in the early 1990s, there have been significant research efforts to synthesise inorganic nanotubes of various solids. Generally, the formation of tubular nanostructures requires layered, anisotropic, or pseudo-layered crystal structures. Inorganic nanotubes, which typically do not possess such structures, are usually synthesised using template-based methods. However, these nanotubes are either amorphous, polycrystalline or exist only in ultrahigh vacuum. Recently, an 'epitaxial casting' method using removable ZnO nanowires as templates has been developed to synthesise single-crystal GaN nanotubes. This opens up an exciting field of research on the synthesis of single-crystal nanotubes with non-layered or non-anisotropic structures. In this paper, we review recent research activities on single-crystal inorganic nanotubes synthesised using removable templates via vapour phase methods based on similar 'epitaxial casting' concepts. The applications and nanodevices that have been built using these novel inorganic nanotubes are also presented.