Robust High-Resolution Imaging and Applications to Materials and Systems
Ömür E. Dağdeviren
Abstract: Interactions of atoms with their environment govern many physical phenomena, and heterogeneous chemical reactions producing either desirable or non-desirable products occur often at surfaces and interfaces. Despite the tremendous progress in surface science achieved during the last decades, a deeper, more complete understanding of the fundamental mechanisms of atomic-scale surface interactions remains a major scientific challenge. One tool that is well suited to address some of the related challenges is scanning probe microscopy, as it allows to reveal the physical, chemical, biological, and optical properties of surfaces in real space with high resolution.
In this seminar, I will briefly introduce scanning probe microscopy and its recent developments which confront advanced material characterization. Following the introduction of this novel microscopy technique, I will present some of the selected applications. First, I will discuss the ergodic and nonergodic dynamics of lattice defects and their collective interaction with each other and their surroundings. Fundamentally, lattice defects determine the electronic, optoelectronic, and chemical properties of materials. For this reason, the physics underlying defect interactions, migration, and exchange is not only important for our basic understanding of material properties, but it also underpins a wide spectrum of technologies, including solid oxide fuel cells, oxygen separation membranes, energy conversion, computing devices, and high-temperature superconductors. Within these applications, perovskites are widely utilized either as a primary component or as a substrate in which the dynamics of charged defects play an important role. Current knowledge regarding the dynamics of vacancy mobility in perovskites is solely based upon volume and/or time-averaged measurements. The underlying nanoscale phenomena are thus averaged over scales orders of magnitude larger than the governing spatial and temporal lattice dimensions. This impedes our understanding of the basic physical principles governing defect migration in inorganic materials. Here I present the ergodic and nonergodic dynamics of vacancy migration at the relevant spatial and temporal scales using time-resolved atomic force microscopy techniques. Our findings demonstrate that the time constant associated with vacancy migration is a local property and can change drastically on the short length and time scales, such that nonergodic states lead to a dramatic increase in the migration barrier (:cell PQA(PSS(1):). This correlated spatial and temporal variation in vacancy dynamics can extend hundreds of nanometers across the surface in perovskites. In the last part of this seminar, I will demonstrate the effect of photo-induced surface oxygen vacancies on the charge carrier dynamics in metal-oxide semiconducting films (:cell PQA(PSS(2):).
1. Dagdeviren, O. E. et al., Nano Letters 20, 7530-7535, (2020).