  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.
