SURFACE VALENCE CHARGE-DISTRIBUTIONS AND SCANNING TUNNELING MICROSCOPY OF WTE2

We have studied the surface electronic structures of the van der Waals surfaces of tungsten ditelluride (WTe2) with first principles calculations of the spatial distribution of the surface valence charge densities and compared the results to images obtained with the scanning tunneling microscope (STM). The energy- and z(distance from the surface)-dependent calculations show that the valence charge density distribution above the Te surface could be derived from the surface Te layer, as we previously calculated, but the charge density distribution close to but below the Fermi energy has a distortion that coincidentally makes it appear to have a symmetry close to the paired, zig-zag and buckled rows of the W layer. These results dramatically illustrate that in highly covalent compounds, the surface valence charge density distribution does not necessarily follow the surface atomic positions even on ideal, unreconstructed surfaces. An alternative interpretation of the STM images of this surface is proposed in light of this new surface electronic structure. Our calculated and experimental results are also discussed with reference to recent STM results on other transition metal dichalcogenides. © 1990.