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Prior to the synthesis of ZnO nanorods, substrates made of glass are cleaned with acetone, ethylene glycol, and ethanol by ultrasonication sequentially. The substrates are then wetted with a small quantity (e.g. a drop) of zinc acetate ethanol solution (5.0 mM) and dried under a flow of nitrogen. This step is repeated for three to five times in order to provide layer of sufficient zinc acetate uniformly covering the substrates. The substrates are then heated at 350° C. in air for about 20 mins. to form a layer of ZnO seeds. The seeded substrates are held by a holder (e.g. rubber holder) and placed vertically into a Teflon-lined stainless steel autoclave filled with zinc nitrate hydrate (25.0 mM), hexamethylenetetramine (25.0 mM), and polyethylenimine (5.0 mM) aqueous solution, and kept at 90° C. for 6-12 hours. Finally, the samples are taken out from the solution, washed with deionized water and ethanol, and then dried in air. FIG. 2 is a photographic image showing the SEM morphology of samples procuded according these procedures. b) Chemical Vapour Deposition (CVD): To grow ZnO nanorod arrays by CVD, quartz/sapphire substrates are first coated with a thin layer of PR (AZ5206E) by spin coating at a speed of 8000 rpm for 60 s and then treated by hard-baking at 100° C. for 10 min. At this stage the RR layer is converted to amorphous carbon, which serves as catalyst for the CVD growth of ZnO nanorods. The synthesis of ZnO nanorod arrays is carried out in a traditional three-temperature zone CVD system. For example, an alumina boat containing 3 g of ZnO powder is placed in the center of a tube furnace. The substrate is placed downstream for the nucleation and growth of ZnO NWs. Argon is used as carrier gas at a flow rate of 50 sccm with additional 0.5 sccm oxygen flow to facilitate the reaction. The furnace is heated to 1100-1300° C. and kept for half an hour under vacuum conditions (10−2 Torr). ZnO NWs are found to grow on the substrates when the temperature was about 600-800° C.

1. customPrior to the synthesis of ZnO nanorods, substrates
2. customdried under a flow of nitrogen