Postdoctoral Candidate Seminar with Omur Dagdeviren

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 show that a recently developed scanning probe microscopy
method referred to as tuned-oscillator atomic force microscopy (TO-AFM) can be used
for advanced material characterization. The main breakthrough introduced by TO-AFM
is the ease of its application for high-resolution characterization compared to existing
modulation techniques. TO-AFM enables robust, high-resolution material
characterization with picometer and pico-Newton resolution with only one control loop,
whilst alternative modulation techniques require at least two and most commonly three
interacting control loops. To establish its usefulness, its imaging and spectroscopy
performance will be illustrated with layered materials, ionic crystals, and metal oxides as
model systems. Besides, I will demonstrate an analysis of the contrast mechanism of
high-resolution scanning probe microscopy images with simultaneous TO-AFM and
scanning tunneling microscopy measurements.

In the last part of my talk, applications of the developed methodologies and instrumentation
to exotic materials will be given. For example, I will demonstrate an ability to probe and modify
the charge carrier densities of perovskites with a scanned probe, which may advance the epitaxial
growth of high-temperature superconducting thin films by fine-tuning the local charge carriers
during the growth. More prominently, I will present the results of my investigations into the growth
and characterization of epitaxial topological crystalline insulators employing scanning probe
microscopy and spectroscopy experiments and discuss them in the light of complementary ab
initio density functional theory calculations. Thereby, the effect of local symmetry on topological
surface states of topological crystalline insulators will be highlighted in particular, ultimately providing
a gateway for the tuning of the surface states with the scanned-probe by tailoring the
surface topography. This effect of broken local symmetry on topological surface states
opens new horizons for spin-orbit based electronic devices, which span transistors,
quantum dots, and microwave circuits.