ABSTRACT

Laterally aligned ZnO nanowire arrays in parallel to a substrate offer the benefit of fabricating integrated nanodevice arrays. Wang and coworkers [10] developed a general method for controlled growth of laterally aligned and patterned ZnO nanowire arrays on any substrate at low temperature (<100°C).The substrate could be any material, inorganic, organic, crystalline, or amorphous, as long as it is flat. The orientation growth was achieved by using different materials to activate or inhibit the growth of nanowires. Two materials were used, ZnO seeds for the growth and a Cr layer for preventing the local growth. The first step was to fabricate a ZnO striped pattern covered with Cr at the top using a lithography process (Fig. 1.2a(1), b). The second step was to put the pattered substrates into the growth solution for NW array growth. The concentrations of Zn(NO3)2 and hexamethylenetetramine (HMTA) were both 0.0025 mol/L. NW arrays were grown only from the ZnO seeds directly exposed to the solution (Fig. 1.2a(2)). One side growth of ZnO nanowire arrays was also induced by evaporating Cr onto the ZnO stripes at an angle, as shown in Fig. 1.2a(3) and (4). Figure 1.2c is the laterally grown ZnO nanowire array on a Si substrate, demonstrating that the ZnO nanowire arrays grew from the lateral sides of the pattern with a good alignment. More than 70% nanowires are parallel to the substrate. ZnO nanowires had diameters of less than 200 nm and lengths of about 4 μm. When the distance between ZnO stripes was small enough, by controlling the growth time, the ZnO nanowire arrays from the adjacent pattern grew toward each other, forming an interdigitated structure (Fig. 1.2d). The ZnO nanowire arrays could grow not only from the straight pattern but also from any shape pattern (Fig. 1.2e). The laterally aligned ZnO nanowire arrays could be employed for various applications, such as gas sensors, field effect transistors, and nanogenerators [10].