Growth and electronic structure of topological insulator Bi$_{2}$Se$_{3}$ thin films on graphene/SiC(0001) substrate*

We report on the growth of atomically smooth and stoichiometric Bi$_{2}$Se$_{3}$ thin films on bilayer graphene prepared on SiC(0001) substrate using molecular beam epitaxy. It is found that the position of the Dirac point changes with film thickness, and that the Dirac transport regime appears in Bi$_{2}$Se$_{3}$ film as thin as 10 quintuple layers. By mapping the step edge-induced interference patterns with scanning tunneling microscopy, a linear Dirac surface state band is obtained. By manipulating the charge states of subsurface Fe acceptors, we demonstrate the presence of a bulk bandgap in the Bi$_{2}$Se$_{3}$ films. The high quality films pave a way for fundamental research of topological insulators, and are important for potential spintronic and quantum-computing applications at room temperature.