Anomalous voltage dependence of tunnelling microscopy in WSe2

SUMMARY We present scanning tunnelling microscopy (STM) investigations of the layered semiconductor WSe2. The tunnelling experiments were performed in air and under silicone oil with markedly different results. In air, atomic resolution images of the hexagonally structured surface could be obtained for sample‐to‐tip voltages of both negative and positive polarities, from −1·5 to −0·3 V for negative sample and from +0·6 to +1·6 V for positive sample, respectively. Under silicone oil, however, good atomic images could be seen for negative sample biases down to at least −14 V, while for positive sample biases no difference with respect to the tunnelling in air was found.