Observation of Nanosized Cap Structures on 6H–SiC(0001) Substrates by Ultrahigh-Vacuum Scanning Tunneling Microscopy

Abstract

Nanosized cap structures on a thermally treated 6H–SiC(0001) substrate were investigated using atomic-resolution ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). Hexagonal carbon networks, partly composed of pentagons, were clearly observed on the surface of the cap structures for a sample annealed at 1250°C, in which carbon nanotubes (CNTs) had negligibly grow into the SiC substrate. Comparing their sizes and shapes with those annealed at 1350°C, the cap structures were considered to be the initial state of carbon nanotube (CNT) growth which determines the tube diameters of the final grown CNTs.