Structural and optical properties of ZnO whiskers grown on ZnO-coated silicon substrates by non-catalytic thermal evaporation process

Well-crystallized with excellent optical properties, tetrapod-like and multipod-like ZnO whiskers were successfully synthesized by two steps: pulsed laser deposition (PLD) and catalyst-free thermal evaporation method. Firstly, the ZnO films were pre-deposited on Si(1 1 1) substrates by PLD. The ZnO whiskers grew on ZnO-coated Si(1 1 1) substrates by the simple thermal evaporation of the metallic zinc powder at 800 °C in the air without any catalysts or additives. The pre-deposited ZnO films by PLD on the substrates can provide growing sites for the ZnO whiskers. Also it can further advance the growth of the ZnO whiskers accordingly. The as-synthesized ZnO whiskers were characterized by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Fourier transform infrared spectrum. The results showed that the legs of the ZnO whiskers were highly crystalline with the wurtzite hexagonal structure phase, grown along the [0 0 0 1] in the c-axis direction. Room-temperature photoluminescence spectrum of the as-synthesized whiskers showed UV (390 nm) and green (517 nm) emission, respectively. In addition, the possible growth mechanism of ZnO whiskers is also discussed based on the experimental results.