True Atomic-Resolution Imaging under Ambient Conditions via Conductive Atomic Force Microscopy.

Atomic-scale characteristics of surfaces dictate the principles governing numerous scientific phenomena ranging from catalysis to friction. Despite this fact, our ability to visualize and alter surfaces on the atomic scale is severely hampered by the strict conditions under which the related methods are operated to achieve high spatial resolution. In particular, the two prominent methods utilized to achieve atomic-resolution imaging - scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) - are typically performed under ultrahigh vacuum (UHV) and often at low temperatures. Perhaps more importantly, results obtained under such well-controlled, pristine conditions bear little relevance for the great majority of processes and applications that often occur under ambient conditions. As such, a method that can robustly image surfaces on the atomic scale under ambient conditions has long been thought of as a "holy grail" of surface science. Here, by way of a proof-of-principle measurement on molybdenum disulfide (MoS2), we report that the method of conductive atomic force microscopy (C-AFM) can be utilized to achieve true atomic-resolution imaging under ambient conditions as proven by the imaging of a single atomic vacancy, without any control over the operational environment or elaborate sample preparation. While the physical mechanisms behind this remarkable observation are not elucidated yet, our approach overcomes many of the classical limitations associated with STM and NC-AFM, and the findings herald the potential emergence of C-AFM as a powerful tool for atomic-resolution imaging under ambient conditions.