Metal assisted chemical etching of silicon and solution synthesis of Cu$_2$O/Si radial nanowire array heterojunctions

Cu$_2$O/Si radial nanowire (NWs) array heterojunctions were prepared by depositing Cu$_2$O nanoparticles via chemical bath deposition on $n$-Si nanowire arrays that were fabricated by metal-assisted electroless etching. After 20 cycles of deposition, large numbers of Cu$_2$O nanoparticles with form shells that wrap the upper segment of each Si nanowire. This method of etching offers exceptional simplicity, flexibility, environmental friendliness, and scalability for the fabrication of three-dimensional silicon nanostructures with considerable depths, because of replacement of harsh oxidants such as H$_2$O$_2$ and AgNO$_3$.