On the nature of AFM tip metal-MoS2 contact; effect of single layer character and tip force

Abstract

In the present study, the nature of metal-MoS2 contacts has been investigated using conductive atomic force microscopy. The point I-V characteristics have been acquired as a function of loading force (53 nN–252 nN) for an interface formed between the atomic force microscopy (AFM) tip (Pt and Co coated) and MoS2 domains (single and multilayer). The metal-MoS2 junctions for both Co and Pt tips exhibit a rectifying nature with higher forward current for the Co tip as compared to the Pt tip for both single and multilayer samples. An interesting behavior of decreasing junction current and rectification ratio with increasing tip loading force is observed in the case of single layer MoS2. In comparison, negligible or very small change in the forward junction current is observed in the case of multilayer samples. The single layer MoS2 undergoes charge polarization in the presence of uniaxial strain exerted in the form of AFM tip loading force, resulting in current in a direction opposite to the forward current due to the migration of majority electron carriers away from the tip-MoS2 interface. Therefore, the net current which is a sum of the forward junction current and the force induced current reduces with loading force for single layer MoS2. This study emphasizes the influence of the single layer nature of MoS2 on the electrical properties of metal-MoS2 contacts, an understanding of which is important from the perspective of basic physics and its applications.