Morphology and crystallinity control of wet chemically grown ZnO nanorods

The controlled growth of ZnO nanorods on technologically relevant substrates is essential for their practical integration into next generation optoelectronic and piezoelectric devices. In this report, highly ordered and uniform vertical ZnO nanorod arrays were synthesized using a facile, low temperature selective area wet chemical growth process. The nanorods were grown through nucleation windows that were patterned in a PMMA mask using electron beam lithography. At first, the technique was demonstrated on `ideal ZnO single crystal substrates, where the geometrical parameters of the highly uniform and crystallographically coherent nanorods were dictated by the nucleation pattern, the polarity of the substrate, and the growth conditions. The obtained geometry was then compared to 4 further arrays corresponding to different ZnO seed layers deposited on Si and sapphire substrates. Scanning electron microscopy showed that the crystal orientation and the alignment of the nanorods were determined by the underlying seed layer. The piezoresponse force microscopy revealed that the d33 piezoelectric tensor component of the wet chemically grown nanorods was comparable (6-12 pm/V) to that of the highest value measured on ZnO single crystal (12.4 pm/V). The presented nanorod arrays have several potential applications, from nanorod based light emitting devices to CMOS compatible piezoelectric nanoforce sensors.