Growth of SnO 2 -In 2 O 3 Hetero Nanostructures
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1058-JJ03-32
Growth of SnO2-In2O3 Hetero Nanostructures S. Joon Kwon, In-Sung Hwang, Dong-Wan Kim, Young-Jin Choi, and Jae-Gwan Park Nano Science and Technology Division, Korea Institute of Science and Technology, Hawolkok-Dong, Seongbuk-Gu, Seoul, 130-650, Korea, Republic of ABSTRACT We present the formation of SnO2-In2O3 hetero nanostructures. Kinetically, SnO2 nanowires form prior to the heterostructure. In2O3 shell was regularly distributed on the SnO2 nanowire surface, and form sheath subsequently. We theoretically explained the morphological evolution of an anisotropic heterostructure such as core-sheath structure. INTRODUCTION Hetero nanostructures have diverse characteristics in that the physical properties such as the structural, optical, electrical properties. There exists a distinctive line between the physical properties of the heterogeneous materials and those of the alloy. For instance, band gap energy of the alloy nanostructure is a complex function of the composition while that of the heterogeneous materials exhibits no variation but shows intensity variation of each band gap energy given by the molar fraction of each component. Here, we present and elucidate the formation of SnO2-In2O3 hetero nanostructures. EXPERIMENTAL DETAILS Thermal evaporation was employed to synthesize SnO2-In2O3 hetero nanostructures onto 3 nm gold coated Si substrates. Mixed Metal Sn and In powders were used as the coevaporation sources. The source was placed on an alumina boat which was loaded in the middle of quartz tube in a horizontal furnace. Temperature at the center of the tube was 750oC under vacuum and then O2 flow was maintained at a rate of 10 sccm for 20 min. Synthesized nanostructures were characterized by XRD, FESEM, and high resolution TEM. DISCUSSION Formation of SnO2 core nanowire followed by thin (In2O3)x(SnO2)1-x alloy layer Prior to the formation of the SnO2-In2O3 heterostructures SnO2 nanowires form as is apparent from FESEM and TEM images in Figure 1(a). These inner nanowires form after 1
min of reaction and provide a site for the growth of subsequent nanostructures as indicated in Figure 2. Two different materials can form alloy structure or heterostructure. Heterogeneity in the crystalline structure kinetically takes precedence over the alloy. In the case of the vapor-solid-liquid growth mechanism of nanowires comprised by two different precursors, the priority of the inner part of the wire is determined by the body diffusion time of each precursor into the catalytic metal nucleus, tbi (i = 1, 2, x, where the subscripts 1, 2, and x indicate SnO2, In2O3, and (In2O3)x(SnO2)1-x, respectively). The body diffusion time of In2O3 into Au matrix (tb2) is about 2-3 times longer than that of SnO2 (tb1) [1]. Moreover, the surface diffusion time of each precursor on the catalytic metal nucleus, tsi, is much longer than tbi in the event of the nanowire accompanied by sub 100 nm radius [2]. Therefore the formation SnO2 for the inner part of the nanowire takes precedence over In2O3 or (In2O3)x(SnO2)1-x alloy, and
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