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

Abstract

Free-standing exfoliated monolayer graphene is an ultrathin 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 band-structure measurements can be extracted. Our measurements rely on our development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. Our angle-resolved photoemission spectroscopy 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 ${E}_{F}$. Further, we show that suspended graphene behaves as a marginal Fermi liquid, with a quasiparticle lifetime that scales as ${(E\ensuremath{-}{E}_{F})}^{\ensuremath{-}1}$; comparison with other graphene and graphite data is discussed.