Influence of the State of the Tungsten Tip on STM Topographic Images of SnSe Surfaces

Tin selenide (SnSe) has recently attracted significant attention because of its excellent thermoelectric properties with a figure of merit (ZT) of 2.6. Previous scanning tunneling microscopy (STM) studies of SnSe surfaces showed that only Sn atoms are resolved in topographic images due to the dominant contribution of the Sn 5p (z) states in tunneling. However, when the state of the tungsten (W) tip changes from a typical four-lobe d state such as d (xy) or to a two-lobe state, the atomic features observed on the SnSe surface in STM topography can be dramatically altered. In this report, we present the results of a systematic study on the influence of the W tip's states on the STM images of SnSe surfaces. Sn atoms are observed with much stronger corrugation amplitude and smaller apparent radius when the tip is in a state. In addition, the atomic features of the Se atoms become visible because of the sharply focused shape of the W state. We expect our results to provide important information for establishing a better understanding of the microscopic nature of SnSe surfaces.