Preparation, Characterization And Properties Of Oriented And Ga-doped ZnO Nanorod Arrays

In the past few years, there has been an increasing interest in ZnO nanowires/ nanorods because of their unique optoelectronic properties and potential applications in UV electronic devices, gas and biological sensors, and solar cells etc. However, most of these proposed applications will require an aligned and oriented ZnO nanowires/nanorods as well as an effectively p-type doping. In this paper, we mainly demonstrate the preparation of oriented and doped-Ga ZnO nanomaterials and their properties in wettability, optical absorption and luminescence. A so-called two-step chemical reaction in solution is improved for preparing aligned ZnO nanorods with different diameters and orientations including a-axis and c-axis as well as doped-Ga ZnO nanorods.Contact angle measurements show that the surface wettability of ZnO nanorod arrays is related with the diameter and order of aligned nanorods. The water contact angle becomes larger as the diameter of ZnO nanorod increases, showing a decreasing hydrophilicity. When the order of aligned ZnO nanorod is of low quality, the corresponding contact angle decreases, giving an increasing hydrophilicity. It is found that in the case of relative large diameter of ZnO nanorod, although the c-axis oriented nanorods remain to be hydrophilicity, the a-axis oriented ones exhibit hydrophobicity. This dissimilarity in wettability may be attributed to a different surface free energy between (100) and (002) crystal face of ZnO. Furthermore, the behaviour that the water contact angle of ZnO nanorod array depends on diameter, orientations and order provides a possibility for controllable wettability of ZnO nanomaterials. In addition, it is noted from optical absorption and photoluminescence measurements that the a-axis oriented nanorods have a slight red-shift of absorption band edge and lower intensity of luminescence compared with those of the c-axis oriented ones, suggesting that there exists a different energy band structure between them.We have also developed a simple and cost-effective method for preparing Ga-doped ZnO nanorods based on the two-step chemical reaction in solution. In the method, Ga3+ is doped into ZnO nanorods through a co-crystallization of ZnO and Ga2O3 from their salt solution. A further annealing the Ga-doped ZnO nanorods in NH3 atmosphere may result in a co-doping of Ga-N in the ZnO nanorods, which is very helpful for fabricating p-ZnO nanorods. The corresponding absorption spectrum presents a very sharp peak (about 361 nm) of Ga-N band, indicating the formation of Ga-N in the ZnO crystal lattice.