ABSTRACT
Liang Li,a Xiaosheng Fang,a,b Tianyou Zhai,a Yoshio Bando,a and Dmitri Golberga a International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan b Department of Materials Science, Fudan University, Shanghai 200433, People’s Republic of China Li.Liang@nims.go.jp, li.liang1979@yahoo.ca (Li), xshfang@yahoo.cn (Fang), and Zhai.Tianyou@nims.go.jp (Zhai)
which provide precise control of size, periodicity, and shape. However, these techniques are costly and time consuming and have a low throughput; thus, they are impractical in large-scale industrial applications. Recently, template-assisted methods have widely been investigated with respect to fabrication of nanostructured arrays in which the physical and chemical properties can be tailored by adjusting the structural parameters of templates [16-20]. Among these templates, a monolayer colloidal crystal has proved to be a highly effective material [21-23]. Pulsed laser deposition (PLD) has become a popular technique for producing high-quality thin films and nanostructures. PLD has several technological advantages: First, a high-energy laser beam can be delivered to a target and evaporate materials at their melting or sublimation temperatures (above those peculiar to traditional physical vapor deposition systems). Second, the evaporated species form a plasma plume with high kinetic energies that strikes the substrate and promotes crystallization of films at room temperature. Third, PLD can easily transfer the stoichiometry of target materials to substrates. For example, we presented continuous control of the cobalt oxide morphologies, from two-dimensional (2D) thin films to 1D nanorod arrays and zero-dimensional (0D) nanoparticles by tuning the tilting angles of the substrate and the oxygen pressures in a PLD reaction chamber. This provided flexibility in a study of the effects of nanoscale structures on physical properties and was nicely demonstrated by the performance optimization of optical CO gas sensors [24]. In this chapter, we introduce a combined technique that utilizes PLD and monolayer polystyrene (PS) colloidal sphere templates to fabricate vertically ordered and aligned hierarchical nanocolumnar arrays. Some attractive attributes of the present method are (a) the availability of the hierarchical structures in nanocolumns; (b) the presence of uniform, vertically ordered, and aligned arrangement on the substrates; (c) room temperature growth; (d) lack of toxic organic precursors; (e) relatively short growth times; (f) no catalyst use; and (g) transferability onto any type of substrates. Precise control on the morphology of nanocolumnar arrays enables us to systematically investigate their unique properties and applications. Here, as typical examples, we demonstrate the potential applications of these hierarchical nanocolumnar arrays in field emission, photocatalysis, and surface-wetting fields.
