Position-controlled hydrothermal growth of ZnO nanorods on arbitrary substrates with a patterned seed layer viaultraviolet-assisted nanoimprint lithography

A novel technique for the position-controlled growth of ZnO nanorods is established, by combining ultraviolet-assisted nanoimprint lithography (UV-NIL) and hydrothermal growth. Various ZnO nanorod arrays were obtained on silicon substrates, by UV-NIL of ZnO seed patterns with lines of 200 nm wide at a pitch of 1000 nm from a photosensitive ZnO precursor, followed by a position-controlled hydrothermal growth step with varied growth times. It was found that the aspect ratio of ZnO nanorods increased from 2.7 to 11.8 as the growth time was increased from 2 to 6 h. Selected area electron diffraction (SAED) analysis indicates that the root of studied ZnO nanorods consists of both amorphous and polycrystalline phases whereas the stem shows a single-crystalline nature with a preferred (002) growth. ZnO nanorod arrays were also routinely obtained on transparent glass and flexible polyethylene terephthalate (PET). In all cases, ZnO nanorods were observed on both the sidewalls and top surfaces of the ZnO seed patterns with a nanoflower-like structure regardless of substrate substances. This technique offers an alternative method for integrating ZnO nanorods at low temperatures and free of high vacuum, potentially useful in applications such as nanophotonics, photovoltaics and flexible nanoelectronics.