One serious limitation of these kineticand mechanistic studiesis that they are based on ex situ measurements ofNWs after they have stopped growing, so they onlyprovide indirect information on how the NW geometry evolves during their growth. The growth mechanism of the surface-guidedNWs, however, involves many aspects that the conventional ex situ analysis techniques cannot tackle. Obtaining a comprehensiveunderstanding of the growth mechanism requires observation of thegrowth process in real time. The current work presents a real-timestudy of surface-guided NW growth using in situ scanningelectron microscopy (SEM). In this study, we grow ZnSe NWs along thenanogrooves of a periodically faceted surface (annealed M-plane sapphire,i.e., α-Al2O3 (1010), using a special heating stage inside an SEM, which allows usto directly watch NWs at nanometer-scale resolution as they grow.The recorded movies presented here show in great detail how guidedNWs grow and reveal important aspects of the process that could notbe observed in previous ex situ analyses, such asthe instantaneous elongation velocity, the influence of surface defectson the growth direction, and the reversibility of the growth process.
Despite these numerous real-time studies of NW growth, real-timestudies of surface-guided VLS growth of NWs by an in situ electron microscope have not been reported prior to the presentwork. Neither have movies of growing planar NWs been shown in previousreports. Although NW growth experiments in the electron microscopesare held under different conditions than conventional CVD or PVD growth,they have provided important insights that have broadly changed theunderstanding of NW growth. In situ electron microscopymovies of planar NW growth are thus expected to reveal critical detailsin the mechanism of surface-guided NW growth. 2b1af7f3a8