05 M. Then, the solution was stirred at 60°C for 5 min to yield a clear and homogeneous solution. Next, a clean Si substrate was dipped into the solution, lifted at 1 mm/s, and GW2580 dried in the air. Finally, the as-coated substrate was sintered at 250°C for 10 min to achieve ZnO seed layers [1, 17]. Hydrothermal growth of ZnO nanorods To grow ZnO nanostructures, the Si check details substrates coated with the ZnO seed layers were fixed upside down in the reaction vessel containing 40 ml of aqueous solution of Zn(NO3)2 ⋅ 6H2O (99.5% purity, Sigma-Aldrich Corporation, St. Louis, MO, USA) and hexamethylenetetramine

(99.5% purity, Sigma-Aldrich) with the identical concentration. Then, the reaction vessel was sealed

and kept at a constant temperature for a certain time. Finally, the sample was taken out, rinsed in deionized water, and dried in air for characterization [18]. Characterization Surface morphologies of the seed layers and ZnO nanostructures were characterized by atomic force microscopy (AFM; Solver P47, NT-MDT, MGCD0103 supplier Moscow, Russia) and field-emission scanning electron microscopy (SEM; FE-S4800, Hitachi, Tokyo, Japan), respectively. The crystal structure identification of the ZnO nanostructures was performed by XRD in a normal θ-2θ configuration using a Rigaku (Tokyo, Japan) Dmax 2500 diffractometer with a Cu Kα X-ray source. The PL spectra were acquired by excitation with a 325-nm He-Cd laser with

a power of 30 mW at room temperature. Results and discussion For hydrothermal growth of ZnO nanostructures on lattice-mismatched substrates, such as the Si substrate, the ZnO seed layer is essential [19, 20], which will influence the morphology and orientation of resulting ZnO nanostructures. Thus, we investigate the effect of deposition method and thickness of the seed layer on the ZnO nanostructures in the following. The typical AFM images of the ZnO seed layers prepared by RF magnetron sputtering and dip coating are shown in Figure 1a,b, respectively, to distinguish typical surface features previous to the hydrothermal process. It is obvious that the size and roughness of the seed layers by different methods Molecular motor vary widely. Both ZnO seed layers present a high density of ZnO seeds, which act as nucleation sites during the growth step, and will decide the density of resulting ZnO nanostructures [21]. In addition, the size and roughness of the seed layer also have a significant effect on the growth mode and morphology of the ZnO nanostructures [22]. The diameter and root-mean-square (rms) roughness of seed layers can be derived from the AFM data corresponding to the AFM images shown in Figure 1a,b. For seed layers deposited by RF magnetron sputtering and dip coating methods, the corresponding diameter of seeds is 25 to 35 nm and 40 to 90 nm, and the rms roughness is 1.17 and 4.28 nm, respectively.