High-resolution Observation of Nucleation and Growth Behavior of Nanomaterials on Graphene

Abstract

Studying nucleation and growth has been one of the major goals in materials science. Fundamental understanding of initial growth is essential for fabrication of nanomaterials with desired physical properties. Consequently, atomic level investigation on as-grown nuclei and local atomic arrangements around defects is required. Such high-resolution study along with crystallographic analysis could be performed using transmission electron microscopy (TEM). Here, we report on atomic-resolution observation of initial growth behavior using TEM by growing nanomaterials directly on graphene. Graphene exhibiting excellent electron beam transparency and high mechanical strength is an ideal supporting layer for TEM measurements by minimizing the background signal from the underlying membrane. In addition to merely sustaining nanomaterials as a support, graphene can be further used as a substrate for nanomaterials growth. The crystalline nature of graphene along with its electron beam transparency ultimately enables direct imaging of nanomaterials and allows us to systematically investigate the initial growth mechanisms. Using direct growth and imaging method, we could clearly observe the initial states of Zinc oxide (ZnO) nanomaterials. This enabled the observation of the transition in crystal structure of ZnO nuclei along with their orientational relationship with graphene. Furthermore, formation of various defects during nanomaterial growth could be clearly visualized with atomic-resolution. More generally, we believe that this simple technique may be readily expanded to investigate the growth mechanisms of many other nanomaterials on various two-dimensional layered substrates.