Ahmad Nurul Fariha, Yasui Kanji, Hashim Abdul Manaf
Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia.
Department of Electrical Engineering, Nagaoka University of Technology, Kamitomioka-machi, Nagaoka, Niigata 940-2137 Japan.
Nanoscale Res Lett. 2015 Jan 22;10:10. doi: 10.1186/s11671-014-0716-z. eCollection 2015.
A seed/catalyst-free growth of ZnO on graphene by thermal evaporation of Zn in the presence of O2 gas was further studied. The effects of substrate positions and graphene thicknesses on the morphological, structural, and optical properties were found to be very pronounced. By setting the substrate to be inclined at 90°, the growth of ZnO nanostructures, namely, nanoclusters and nanorods, on single-layer (SL) graphene was successfully realized at temperatures of 600°C and 800°C, respectively. For the growth on multilayer (ML) graphene at 600°C with an inclination angle of 90°, the grown structures show extremely thick and continuous cluster structures as compared to the growth with substrate's inclination angle of 45°. Moreover, the base of nanorod structures grown at 800°C with an inclination angle of 90° also become thicker as compared to 45°, even though their densities and aspect ratios were almost unchanged. Photoluminescence (PL) spectra of the grown ZnO structures were composed of the UV emission (378-386 nm) and the visible emission (517-550 nm), and the intensity ratio of the former emission (I UV) to the latter emission (I VIS) changed, depending on the temperature. The structures grown at a low temperature of 600°C show the highest value of I UV/I VIS of 16.2, which is almost two times higher than the structures grown on SL graphene, indicating fewer structural defects. The possible growth mechanism was proposed and described which considered both the nucleation and oxidation processes. From the results obtained, it can be concluded that temperature below 800°C, substrate position inclined at 90° towards the gas flow, and ML graphene seems to be preferable parameters for the growth of ZnO structures by thermal evaporation because these factors can be used to overcome the problem of graphene's oxidation that takes place during the growth.
进一步研究了在氧气存在下通过锌的热蒸发在石墨烯上无籽晶/催化剂生长氧化锌的方法。发现衬底位置和石墨烯厚度对形态、结构和光学性质的影响非常显著。通过将衬底倾斜90°，分别在600°C和800°C的温度下成功实现了单层（SL）石墨烯上氧化锌纳米结构（即纳米团簇和纳米棒）的生长。对于在600°C、倾斜角为90°的多层（ML）石墨烯上的生长，与衬底倾斜角为45°时的生长相比，生长的结构呈现出极其厚实且连续的团簇结构。此外，与45°倾斜角相比，在800°C、倾斜角为90°时生长的纳米棒结构的基部也变厚了，尽管它们的密度和纵横比几乎没有变化。生长的氧化锌结构的光致发光（PL）光谱由紫外发射（378 - 386 nm）和可见发射（517 - 550 nm）组成，并且前一种发射（I UV）与后一种发射（I VIS）的强度比随温度而变化。在600°C的低温下生长的结构显示出I UV/I VIS的最高值为16.2，几乎是在SL石墨烯上生长的结构的两倍，表明结构缺陷更少。提出并描述了可能的生长机制，该机制同时考虑了成核和氧化过程。从获得的结果可以得出结论，低于800°C的温度、衬底向气流倾斜90°以及ML石墨烯似乎是通过热蒸发生长氧化锌结构的优选参数，因为这些因素可用于克服生长过程中发生的石墨烯氧化问题。
