The effect of substrate topography on the local electronic structure of WS2 nanotubes

We explore the possibility of controlling electronic properties along an inorganic nanotube (INT) through the influence of nanometer-scale features in the underlying substrate. We examined single multi-walled WS2 INTs using scanning tunneling microscopy (STM) in high vacuum. As long as the INTs lie flat on MoS2 (0 0 0 1) or graphite (0 0 0 1) surfaces, they appear semimetallic. However, when the INT is suspended above the surface due to crossing steps or other nanotubes, a band gap opens up. We discuss this observation in terms of either a potential drop under the INT, or a change in its electronic properties due to its distortion when it lies flat on a surface.