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We investigate electronic band-structure images in reciprocal space of few-layer graphene epitaxially grown on SiC(000-1). In addition to the observation of commensurate rotation angles of the graphene layers, the k-space images recorded near the Fermi edge highlight structures originating from diffraction of the Dirac cones due to the relative rotation of adjacent layers. The 21.9° and 27° rotation angles between two sheets of graphene are responsible for a periodic pattern that can be described with a superlattice unit cells. The superlattice generates replicas of Dirac cones with smaller wave vectors, because of a Brillouin zone folding. Copyright © 2014 John Wiley & Sons, Ltd.

Micron scale ferroelectric (FE) domains have been written into a 20-nm-thick epitaxial thin film of BaTiO3 (001) [BTO(001)] on a Nb-doped SrTiO3 substrate using a piezoforce microscope (PFM). The domain-dependent electronic structure has been studied using fully energy-filtered photoemission electron microscopy (PEEM) and synchrotron radiation. Shifts, induced by FE polarization, of up to 300 meV were observed in the work function of the sample. The surface is Ba-O terminated. Polarization-induced distortion of the electronic structure was observed in the valence band and on the Ba 3d, Ti 2p and O 1s core levels of BTO. Polarization-dependent surface adsorption was observed. A simple electrostatic model based on net surface charge is not sufficient to explain the observed modifications in the electronic levels. Copyright © 2010 John Wiley & Sons, Ltd.