Wang et al. Nanoscale Research Letters 2012, 7:246 http://www.nanoscalereslett.com/content/7/1/246 Page 3 of 7 Figure 2 The SEM image of ZnO dot area and nanorod arrays. (a) The SEM image of ZnO dot area with 200 × 200 nm; (c) dot area is 500 × 500 nm; and (e) dot area is 1 × 1 μm. (b) The SEM image of ZnO nanorod arrays with 1-h hydrothermal reaction process on 200 × 200 nm seed areas; (d) on 500 × 500 nm seed areas; and (f) on 1 × 1 μm seed areas. patterns after peeling the PMMA layer from the Si sub- strate (a). The dot area is 200 × 200 nm, and the distance between each dot is 1 μm (c). The dot area is 500 × 500 nm, distance is 2 μm (e). The dot area is 1 × 1 μm, distance is 4 μm. Different dot areas with dif- ferent spacing distances are obtained through EBL and subsequent magnetron sputtering techniques. Figure 2b, d,f is the nanorod arrays after hydrothermal process on the patterned ZnO seed areas at 80°C for 1-h reaction time. The results indicate that ZnO nanorod arrays are successfully obtained which confined to the ZnO seed areas. The length of the nanorod is about 1 μm with a diameter less than 100 nm. For the 200 × 200 nm ZnO seed areas with 1 μm spacing distance, the bundles of the nanorods are connected with each other without the edge confinement just like flowers on the Si substrate as shown in Figure 2b. While for the larger ZnO seed areas (500 × 500 nm) and longer spacing distance (2 μm), the nanorod patterns are separated with each other on the Si substrate, and the larger ZnO seed areas include more nanorods when compare with that of 200 × 200 nm areas. For the 1 × 1 μm ZnO seed areas, there are no nanorods that appear in the middle of the dot areas due to the short reaction time which is in accordance with the literature reports [19]. Since the growth time in the hydrothermal process is the main factor which can be used to control the morph- ology and density of ZnO nanorod patterns; therefore, the density variations of ZnO nanorod arrays are investi- gated for the different reaction times during the hydro- thermal process. Figure 3a,b,c is the SEM images of ZnO nanorods with a 1.5-h reaction time on the same