2013 Theses Doctoral

Chemical Vapor Deposition Grown Pristine and Chemically Doped Monolayer Graphene

Zhao, Liuyan

Chemical vapor deposition growth has been a popular technique to produce large-area, high-quality monolayer graphene on Cu substrates ever since its first demonstration in 2009. Pristine graphene grown in such a way owns the natures of zero charge carriers and zero band gap. As an analogy to semi-conductor studies, substitutional doping with foreign atoms is a powerful way to tailor the electronic properties of this host materials.

Within such a context, this thesis focuses on growing and characterizing both pristine and chemically-doped CVD grown monolayer graphene films at microscopic scales. We first synthesized pristine graphene on Cu single crystals in ultra-high-vacuum and subsequently characterized their properties by scanning tunneling microscopy/spectroscopy (STM/S), to learn the effects of Cu substrate crystallinity on the quality of graphene growth and understand the interactions between graphene films and Cu substrates. I

n the subsequent chapters, we chemically doped graphene with nitrogen (N) and boron (B) atoms, and characterized their topographic and electronic structures via STM/S. We found that both N and B dopants substitionally dope graphene films, and contribute electron and hole carriers, respectively, into graphene at a rate of approximately 0.5 carrier/dopant. Apart from this, we have made comparisons between N- and B-doped graphene films in aspects of topographic features, dopant distribution and electronic perturbations. In the last part of this thesis, we used Raman spectroscopy mapping to investigate the N dopant distribution within and across structural grains. Future experiments are also brief discussed at the end of the thesis.