title: Nanoscale measurements of unoccupied band dispersion in few-layer graphene.
abstract: The properties of any material are fundamentally determined by its electronic band structure. Each band represents a series of allowed states inside a material, relating electron energy and momentum. The occupied bands, that is, the filled electron states below the Fermi level, can be routinely measured. However, it is remarkably difficult to characterize the empty part of the band structure experimentally. Here, we present direct measurements of unoccupied bands of monolayer, bilayer and trilayer graphene. To obtain these, we introduce a technique based on low-energy electron microscopy. It relies on the dependence of the electron reflectivity on incidence angle and energy and has a spatial resolution ∼10 nm. The method can be easily applied to other nanomaterials such as van der Waals structures that are available in small crystals only.
authors.affiliation: Huygens-Kamerlingh Onnes Laboratorium, Leiden Institute of Physics, Leiden University, PO Box 9504, Leiden NL-2300 RA, Netherlands.
authors.forename: Johannes
authors.identifier: http://orcid.org/0000-0002-2422-1209
authors.initials: J
authors.lastname: Jobst
authors.affiliation: Huygens-Kamerlingh Onnes Laboratorium, Leiden Institute of Physics, Leiden University, PO Box 9504, Leiden NL-2300 RA, Netherlands.
authors.forename: Jaap
authors.initials: J
authors.lastname: Kautz
authors.affiliation: Huygens-Kamerlingh Onnes Laboratorium, Leiden Institute of Physics, Leiden University, PO Box 9504, Leiden NL-2300 RA, Netherlands.
authors.forename: Daniël
authors.initials: D
authors.lastname: Geelen
authors.affiliation: Huygens-Kamerlingh Onnes Laboratorium, Leiden Institute of Physics, Leiden University, PO Box 9504, Leiden NL-2300 RA, Netherlands.|IBM T.J. Watson Research Center, 1101 Kitchawan Road, PO Box 218, Yorktown Heights, New York 10598, USA.
authors.forename: Rudolf M
authors.initials: RM
authors.lastname: Tromp
authors.affiliation: Huygens-Kamerlingh Onnes Laboratorium, Leiden Institute of Physics, Leiden University, PO Box 9504, Leiden NL-2300 RA, Netherlands.
authors.forename: Sense Jan
authors.initials: SJ
authors.lastname: van der Molen