Catalyst-free synthesis of single crystalline ZnO nanonails with ultra-thin caps
Abstract
Arrays of single-crystalline ZnO nanonails with tapering diameters and ultra-thin caps have been successfully synthesized on a silicon substrate via a simple 0> in the cap. Remarkably, the ultra-thin cap shows a diameter-to-thickness ratio of over 20 : 1, which is much higher in magnitude than those reported in previous works. Based on the systematic morphological characterization and structural analysis, a self-catalyzed vapor–liquid–solid (VLS) mechanism followed by a vapor–solid (VS) process is proposed to explain the growth of the nanonails. Optical properties are also investigated with Raman and photoluminescence (PL) techniques, which show good crystal quality of the synthesized nanonails.