Disorder and screening in decoupled graphene on a metallic substrate

International audienceWe report the coexistence of charge puddles and topographic ripples in graphene decoupled from the Ir(111) substrate it was grown on. We show the topographic and the charge disorder to be locally correlated as a result of the intercalation of molecular species. From the analysis of quasiparticle scattering interferences, we find a linear dispersion relation, demonstrating that graphene on a metal can recover its intrinsic electronic properties. The measured Fermi velocity v F = 0.9 ± 0.04×10 6 m/s is lower than in graphene on dielectric substrates, pointing to a strong screening of electron-electron interactions in graphene by the nearby metallic substrate. PACS number(s): 61.48.Gh, 68.37.Ef, 73.22.Pr The study of electron-hole puddles in graphene [1,2] has so far largely focused on graphene sheets isolated by mechanical exfoliation of graphite on dielectric substrates such as SiO 2. The origin of these has been subject to debate, as different studies have pointed to either charged impurities between graphene and SiO 2 [2,3], others invoking in addition the mixing of the π and σ orbitals due to local curvature [4–9]. In this context, the limited knowledge about the graphene/SiO 2 interface and the ensuing low graphene mobility calls for the use of other substrates. Experiments based on different dielectric environments, that is, different strengths of charged impurities' screening, have been performed. They, however, showed no significant influence of the substrate dielectric constant on the graphene electronic properties, thereby questioning the role of charged impurities for the puddle formation [10,11]. On metallic supports, the origin of charge disorder might be very different. Periodic ripples, arising from the lattice parameter mismatch between graphene and most transition-metal surfaces, were, for instance, correlated to local density of states (LDOS) variations [12] in graphene on Ru(0001). It, however, turned out that charge carriers in this system do not exhibit Dirac fermionlike properties, due to a strong hybridization between the 4d Ru and p z C orbitals [13,14]. Even in less strongly coupled systems, interaction between graphene's conduc-tion/valence bands with surface states of the metal [15,16] cannot be excluded. A linear dispersion relation in the electronic band structure at the Brillouin zone corners was recovered in graphene on Ru(0001) intercalated with an atomic layer of oxygen below the graphene [17]. This layer unfortunately suppresses the graphene ripples, which prevents one from addressing the possible relationship between puddles and topography. In this work, we report on a scanning tunneling mi-croscopy/scanning tunneling spectroscopy (STM/STS) study of corrugated graphene lying on an Ir metallic substrate, after exposure to ambient air conditions. The analysis of the quasiparticle interference pattern reveals the linear dispersion relation of the graphene band structure, and demonstrates the absence of hybridization with the Ir substrate. Despite the immediate proximity of the metal that acts as an electrostatic screening plate, we observe electron-hole puddles close to the * clemens.winkelmann@grenoble.cnrs.f