Growth of Ultralong ZnS/SiO₂ Core−Shell Nanowires by Volume and Surface Diffusion VLS Process

Nanowires of up to 1 cm in length and approximately 30 nm in diameter were synthesized through a simple chemical vapor deposition process. Scanning electron microscopy (SEM) data showed that these nanowires were well-aligned and grew in the direction along the flow of the carrier gas. Through transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis, the nanowires were found to be composed of a single-crystalline ZnS core and amorphous SiO2 shell. Gold catalyst particles were found at the tips of the nanowires and completely encased by a silica shell. Photoluminescence (PL) measurements were performed on nanowire samples in which the synthesis time was systematically varied to provide information regarding growth dynamics. After a systematic study on the structure, we propose that the core−shell nanowires were formed via a distinct volume and surface diffusion process occurring simultaneously for different chemical species in and on the gold catalyst particle.