The effect of substrate topography on the local electronic structure of WS 2 nanotubes

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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 WS 2 INTs using scanning tunneling microscopy (STM) in high vacuum. As long as the INTs lie flat on MoS 2 (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.