Structure and quantum-size effects in a surface carbide:W(110)∕C−R(15×3)

Abstract

Results of the combined investigation of atomic and electronic structure of the $\mathrm{W}(110)∕\mathrm{C}\text{\ensuremath{-}}R(15\ifmmode\times\else\texttimes\fi{}3)$ surface carbide are reported. A variety of experimental techniques has been involved such as scanning tunneling microscopy (STM), low-energy electron diffraction, x-ray photoelectron spectroscopy, and angle-resolved photoemission (ARPES). Distance-dependent STM measurements show a nontrivial geometrical behavior in the topography data, demonstrating five different patterns representing the superstructure at different values of the tip-surface separation. Atomic resolution was achieved at lower tunneling gap resistance. An unexpected spatial asymmetry in the distribution of the local density of states across the surface unit cell has been observed as well. Photoelectron spectroscopy of $\mathrm{C}1s$ and $\mathrm{W}4f$ core levels clarifies the nature of the chemical bonding in the system. The band mapping with ARPES provides information on the wave-vector dependence of the electronic states. Notable quantum size and superlattice effects were discovered in the dispersion of the valence-band states. The experimental data suggests an apparent one-dimensional character of the electronic structure. Lateral quantization and umklapp scattering are proposed as explanation. Finally, based on photoemission and STM measurements, an improved crystallographic model of the tungsten surface carbide is introduced.