Two Phases of Monolayer Tantalum Sulfide on Au(111).

We prepared monolayers of tantalum sulfide on Au(111) by evaporation of Ta in a reactive background of HS. Under sulfur-rich conditions, monolayers of 2H-TaS formed, whereas under sulfur-poor conditions TaS with 0 ≤ ≤ 1 were found. We identified this phase as TaS, a structure that can be derived from 2H-TaS by removal of the bottom S layer.

Resonance Raman Spectrum of Doped Epitaxial Graphene at the Lifshitz Transition.

We employ ultra-high vacuum (UHV) Raman spectroscopy in tandem with angle-resolved photoemission (ARPES) to investigate the doping-dependent Raman spectrum of epitaxial graphene on Ir(111). The evolution of Raman spectra from pristine to heavily Cs doped graphene up to a carrier concentration of 4.4 × 10 cm is investigated.

Suppression of Quasiparticle Scattering Signals in Bilayer Graphene Due to Layer Polarization and Destructive Interference.

We study chemically gated bilayer graphene using scanning tunneling microscopy and spectroscopy complemented by tight-binding calculations. Gating is achieved by intercalating Cs between bilayer graphene and Ir(111), thereby shifting the conduction band minima below the chemical potential. Scattering between electronic states (both intraband and interband) is detected via quasiparticle interference.

Energy-Dependent Chirality Effects in Quasifree-Standing Graphene.

We present direct experimental evidence of broken chirality in graphene by analyzing electron scattering processes at energies ranging from the linear (Dirac-like) to the strongly trigonally warped region. Furthermore, we are able to measure the energy of the van Hove singularity at the M point of the conduction band. Our data show a very good agreement with theoretical calculations for free-standing graphene.

Structure and Growth of Hexagonal Boron Nitride on Ir(111).

Using the X-ray standing wave method, scanning tunneling microscopy, low energy electron diffraction, and density functional theory, we precisely determine the lateral and vertical structure of hexagonal boron nitride on Ir(111). The moiré superstructure leads to a periodic arrangement of strongly chemisorbed valleys in an otherwise rather flat, weakly physisorbed plane. The best commensurate approximation of the moiré unit cell is (12 × 12) boron nitride cells resting on (11 × 11) substrate cells, which is at variance with several earlier studies.