Kevin Knox

Spectromicroscopy of single and multilayer graphene supported by a weakly interacting substrate

We report measurements of the electronic structure and surface morphology of exfoliated graphene on an insulating substrate using angle-resolved photoemission and low-energy electron diffraction. Our results show that, although exfoliated graphene is microscopically corrugated, the valence band retains a massless fermionic dispersion with a Fermi velocity of

Corrugation in Exfoliated Graphene: An Electron Microscopy and Diffraction Study

\ensuremath{\sim}{10}^{6}\text{ }\text{m}/\text{s}

Making angle-resolved photoemission measurements on corrugated monolayer crystals: Suspended exfoliated single-crystal graphene

. We observe a close relationship between the morphology and electronic structure, which suggests that controlling the interaction between graphene and the supporting substrate is essential for graphene device applications.

Trapping surface electrons on graphene layers and islands

Low-energy electron microscopy and microprobe diffraction are used to image and characterize corrugation in SiO(2)-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short-range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction line shape. The effects of both intrinsic and extrinsic corrugation factors are discussed.

Surface states on vicinal Cu(775): STM and photoemission study

Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane, which exhibits out of plane deformation or corrugation. In this paper, a technique is described to measure the band structure of such free-standing graphene by angle-resolved photoemission. Our results show that photoelectron coherence is limited by the crystal corrugation. However, by combining surface morphology measurements of the graphene roughness with angle-resolved photoemission, energy dependent quasiparticle lifetime and bandstructure measurements can be extracted. Our measurements rely on our development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. Our ARPES measurements show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; we measure the Dirac point to be within 25 meV of

Photoemission band mapping with a tunable femtosecond source using nonequilibrium absorption resonances

E_F

Local Symmetry Breaking in the High Temperature Regime of SnTe

. Further, we show that suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle lifetime which scales as

Nanoscale phase coexistence at the metal-insulator transition in Cu(Ir1–xCrx)2S4

(E - E_F)^{-1}

Two-photon photoemission can map femtosecond-lived unoccupied bulk states

; comparison with other graphene and graphite data is discussed.

Occupied and Unoccupied States of Clean Stepped Cu(775) Surfaces

(Received 9 September 2011; revised manuscript received 26 January 2012; published 13 February 2012)We report the use of time- and angle-resolved two-photon photoemission to map the bound, unoccupiedelectronic structure of the weakly coupled graphene/Ir(111) system. The energy, dispersion, and lifetime of thelowest three image-potential states are measured. In addition, the weak interaction between Ir and graphenepermits observation of resonant transitions from an unquenched Shockley-type surface state of the Ir substrateto graphene/Ir image-potential states. The image-potential-state lifetimes are comparable to those of midgapclean metal surfaces. Evidence of localization of the excited electrons on single-atom-layer graphene islands isprovided by coverage-dependent measurements.DOI: 10.1103/PhysRevB.85.081402 PACS number(s): 73