UC Merced

A great number of chemical and mechanical phenomena, ranging from catalysis tofriction, are dictated by the atomic-scale structure and properties of material surfaces. Despite such enormous significance, the principal tools utilized to characterize surfaces at the atomic level rely heavily on strict environmental conditions such as ultrahigh vacuum and low temperature. Results obtained under such well-controlled, pristine conditions bear limited relevance to the great majority of processes and applications that often occur under ambient conditions. In this thesis, we report true atomic- resolution surface imaging via conductive atomic force microscopy (C-AFM) under ambient conditions, performed at high scanning speeds. We hypothesize that atomic resolution can be enabled by either (i) a confined, electrically conductive pathway at the tip–sample contact, or (ii) tunneling through a confined water layer accumulated on the sample surface under ambient conditions. Our approach delivers atomic- resolution maps on a variety of material surfaces that comprise defects including single atomic vacancies. Using our method, we also report the capability of in situ charge state manipulation of defects on MoS 2 . Finally, we employ the high-speed C- AFM methodology to study a thin transition metal carbide crystal (i.e., an MXene), α–Mo 2 C. Along with a variety of atomically-resolved defect structures, we observe an exotic electronic effect: room-temperature charge ordering. Our findings demonstrate that C-AFM can be utilized as a powerful tool for atomic-resolution imaging and manipulation of surface structure and electronics under ambient conditions, with wide-ranging applicability.