The authors recently succeeded in growing two-dimensional ZnO nanowalls on sapphire substrates using high-pressure pulsed laser deposition (PLD) without any catalysts. Depending on the PLD growth conditions and the composition of the target, ZnO nanowalls with thickness of tens of nanometers and dimension of several micrometers were synthesized reproducibly. Most of the nanowalls were vertically epitaxial on the c-cut sapphire substrates with a preferred c-axis orientation as confirmed with X-ray diffraction and transmission electron microscopy. The room temperature photoluminescence spectrum of such a ZnO nanowall exhibited a strong intrinsic UV emission and a week defect-related visible emission. It was found that the ZnO nanowalls showed stable field emission properties with low threshold field and a big field enhancement factor. Photocurrent measurements also indicated that these ZnO nanowall films showed a high sensitivity to UV light, which can be used as a UV photodetector.
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