In order to form the hierarchical heterostructured NWs, the interspacing between Si NW cores must be large enough (in other words, the density of Si NWs on the substrate must be low enough) to provide enough space for the lateral growth of ZnO NRs from the Si NWs. In this particular case, chemical vapor deposition method is a better approach to obtain the Si NWs array due to its capability of producing NWs with lower density and larger gaps compared to the metal-assisted etching method [30]. In this work, we present a study on the growth of ZnO nanostructures on Si NWs using an In catalyst. Tapered Si NW arrays were first synthesized

by following a vapor-liquid-solid (VLS) mechanism using In catalyst and a Selleck MLN2238 hot-wire chemical vapor deposition [31]. In seeds were then coated on the as-grown Si NWs using the same system. GS-4997 This was followed by the synthesis of ZnO nanostructures buy GSK2399872A using vapor transport and condensation. The method was carried out by way of a thermal evaporation of graphite-mixed ZnO powder [32]. The ZnO nanostructures formed at different growth time were then studied. Structural, compositional, and optical properties of the as-grown samples were characterized using field emission scanning electron microscopy (FESEM),

high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), and PL spectroscopy methods. Methods Si NWs were synthesized on a p-type Si(111) substrate using a home-built plasma-assisted hot-wire

chemical vapor deposition system [33]. In catalysts with sizes ranging from 40 to 100 nm were coated on the substrate prior to the synthesis of Si NWs. Silane gas diluted in hydrogen (H2) gas in a ratio of 1:20 (5:100 sccm) was used as the Si source for the growth of Si NWs. The details of the deposition process and parameters have been previously described [31, 34–37]. The as-grown Si NWs were first coated with a layer of In seeds using the same system. Next, 1.3 ± 0.1 mg of In wire was hung on a tungsten filament 3 cm above the Si NWs substrate. The In wire was evaporated at filament temperature of approximately Selleck CHIR99021 1,200°C under a hydrogen plasma environment to produce nano-sized In seeds [31]. The H2 flow rate and rf power of the plasma were fixed at 100 sccm and 40 W, respectively. The In seed-coated Si NWs (In/Si NWs) substrate was then transferred into a quartz tube furnace for the ZnO nanostructures deposition. ZnO nanostructures were deposited onto the In/Si NWs via a vapor transport and condensation process. A mixture of ZnO and graphite (1:1) powders with a total weight of approximately 0.2 g was placed at the hot zone center of the quartz tube. One end of the quartz tube was sealed and connected to N2 gas inlet, while the other end remained open. The In/Si NWs substrate was then inserted through the open end and placed at approximately 12 cm from the evaporation source.