ZnO/Ge core-shell nanowires and Ge nanotubes fabricated by chemical vapor deposition and wet etching.

One-dimensional germanium (Ge)-related nanostructures including core-shell nanowires and nanotubes with high specific surface area show enhanced performance in energy storage and electronic devices, and their structural control is important for further improving their performance and stability. In this work, we fabricated vertically formed ZnO/Ge core-shell nanowires with different shell thicknesses. The dependence of morphology, crystallinity, and internal stress of the nanowires on the shell growth time and temperature was investigated. By applying the wet-etching method to the ZnO/Ge core-shell heterojunction nanowires, we demonstrated the Ge nanotube fabrication and stress relaxation in Ge after ZnO core removal.

Defect control and Si/Ge core-shell heterojunction formation on silicon nanowire surfaces formed using the top-down method.

Control of surface defects and impurity doping are important keys to realizing devices that use semiconductor nanowires (NWs). As a structure capable of suppressing impurity scattering, p-Si/i (intrinsic)-Ge core-shell NWs with radial heterojunctions inside the NWs were formed. When forming NWs using a top-down method, the positions of the NWs can be controlled, but their surface is damaged. When heat treatment for repairing surface damage is performed, the surface roughness of the NWs closely depends on the kind of atmospheric gas. Oxidation and chemical etching prior to shell formation removes the surface damaged layer on p-SiNWs and simultaneously achieves a reduction in the diameter of the NWs. Finally, hole gas accumulation, which is important for suppressing impurity scattering, can be observed in the i-Ge layers of p-Si/i-Ge core-shell NWs.

Au-Sn Catalyzed Growth of Ge1-xSnx Nanowires: Growth Direction, Crystallinity, and Sn Incorporation.

Ge1-xSnx nanowires (NWs) have been a focus of research attention for their potential in realizing next-generation Si-compatible electronic and optoelectronic devices. To control the growth of NWs and increase their Sn content, the growth mechanism needs to be understood. The use of Au-Sn alloy catalysts instead of Au catalysts allows an easier understanding of Ge1-xSnx NW growth, and the effects of Sn at different concentrations in catalysts on growth direction, Sn incorporation, and crystallinity of Ge1-xSnx NWs can be clarified. High Sn content in Au-Sn alloy catalysts favors ⟨110⟩-oriented NW growth and high Sn incorporation in NWs. The higher Sn content in Au-Sn alloy catalysts also improves the crystallinity of NWs.

Silicon Nanotubes Fabricated by Wet Chemical Etching of ZnO/Si Core-Shell Nanowires.

Silicon nanotubes (SiNTs) have garnered a great deal of interest for both their synthesis and their potential for application to high-capacity energy storage, biosensors, and selective transport. In this study, we report a convenient and low-cost route to the fabrication of vertically aligned SiNTs via a wet-etching process that enables the control of the wall thickness of SiNTs by varying the gas flux and growth temperature. Transmission electron microscopy (TEM) characterization showed the resultant SiNTs to have an amorphous nature and a hexagonal hollow core. These SiNTs can be crystallized by thermal annealing.