Growth of Single Crystalline ZnO Nanotubes and Nanosquids
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1057-II13-02
Growth of Single Crystalline ZnO Nanotubes and Nanosquids Abhishek Prasad, Samuel Mensah, Jiesheng Wang, Archana Pandey, and Yoke Khin Yap Department of Physics, Michigan Technological University, 118 Fisher Hall, 1400 Townsend Drive, Houghton, MI, 49931 ABSTRACT The growth of ZnO nanotubes and nanosquids is obtained by conventional thermal chemical vapor deposition (CVD) without the use of catalysts or templates. Characterization of these ZnO nanostructures was conducted by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), Raman spectroscopy, and photoluminescence (PL). Results indicate that these ZnO nanostructures maintain the crystalline structures of the bulk wurtzite ZnO crystals. Our results show that rapid cooling can be used to induce the formation of ZnO nanotubes and ZnO nanosquids. The self-assembly of these novel ZnO nanostructures are guided by the theory of nucleation and the vapor-solid crystal growth mechanism. INTRODUCTION ZnO is a useful direct band gap (3.37 eV) semiconductor for short-wavelength optoelectronic devices such as laser diodes and light emitting diodes. ZnO has a high exciton binding energy (60 meV) which makes it useful for room temperature optoelectronic devices. ZnO is also a piezoelectric material due to it non-centrosymmetric structure. ZnO nanostructures have been synthesized in various morphologies such as nanowires [1], nanorods [2], nanobelts [3], nanocombs [4], nanonails [5], nanocastles [6], etc. Various kinds of ZnO nanostructures have been used in different electronic [7, 8], optics [2], mechanical [9], and piezoelectric [10] devices. In this proceeding, we will discuss about the growth of ZnO Nanotubes (ZnO NTs) [11] and Nanosquids (ZnO NSqs) by using thermal chemical vapor deposition (CVD). ZnO Nanosquids are a new type of ZnO nanostructures. These novel nanostructures contain multiple ZnO nanowires branching out from a ZnO nanotube or a ZnO Nanorod. From the structure of these ZnO Nanosquids, we speculate that they can be useful for future multiplexing devices. EXPERIMENT The synthesis of ZnO nanotubes and Nanosquids was conducted in a double quartz tube horizontal furnace. This furnace has one large quartz tube which acts as the vacuum chamber. Another smaller quartz tube is closed at one end, 60 cm long and 2 cm in diameter. The precursor materials for the growth of ZnO nanotubes and ZnO nanosquids were place in a boron nitride boat and inserted to the closed-end of the small quartz tube. These precursors are a mixture of ZnO (0.2 g) and graphite (0.1 g) powders. A series of oxidized silicon substrates (1 to 4) were then placed downstream from the mixture in the small quartz tube as shown in Figure 1. The smaller quartz tube is inserted into the vacuum chamber such that the closed end is at the center of the vacuum chamber. When furnace temperature is around 350 oC, oxygen gas was introduced into the chamber at a flow rate of 40 sccm. The temperature of the vacuum chamber was held constant at 1100 oC for 30 minutes fo
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