Atomic-Scale Characterization of Nanometer-Sized Graphene

89 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008.We have developed a method for depositing atomically clean, nanometer-sized graphene monolayers with 2-30 nm lateral dimensions and we probe the local electronic properties of the graphene using the ultrahigh-vacuum scanning tunneling microscope (UHV-STM). By using tunneling spectroscopy, we measure a size-dependent energy gap for graphene quantum dots (QDs) (aspect ratio ≈1) and determine the energy gap (Eg)---size ( L) relation. Our Eg (eV) = 1.53 +/- 0.41 eV·nm/L1.01 +/- 0.23 least-squares fit quantitatively agrees with the simple model Eg (eV) = 1.68 eV·nm/L resulting from quantum confinement and the linear dispersion of graphene. Predominantly zigzag-edge QDs with 7-8 nm average dimensions are metallic and diverge from the Eg-L scaling law due to the presence of zigzag edge states which spatially decay into the graphene interior with a 1.0-1.2 nm decay length. In addition to graphene QDs, we study the electronic structure of graphene nanoribbons (GNRs) with 2-3 nm widths and 20-30 nm lengths. GNRs with a higher fraction of zigzag edges exhibit a smaller energy gap than a predominantly armchair-edge ribbon of similar width and the magnitude of the measured GNR energy gaps agree with recent theoretical calculations.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD