Novel hierarchical heterostructures made of Si core microwires covered by dense, aligned SiO2 nanowires that form multiple junctions to the cores, have been synthesized on a large scale (see Figure). The Si wires are single crystals with a diameter of similar to 1-3 mu m, whereas the SiO2 nanowires are amorphous with a diameter of similar to 30-80 nm. The materials are envisaged as becoming important for optical fibers, low-dimensional waveguides, scanning near-field optical microscopes, and high-bandwidth optical signal processing devices.