Tip-versterkte optische spectroscopie van WS2 voor elektronische toepassingen

Two-dimensional (2D) transition metal dichalcogenides (TMDCs), such as tungsten disulfide (WS2), are among the emerging channel materials for next-generation opto- and nanoelectronics. The capability to achieve high carrier mobility, strong excitonic effects, and ultimate body thickness are among the main characteristics that promise device miniaturization while improving transport properties. Thus far, the realized performance of TMDC channels remains noticeably below the levels their intrinsic material properties predict, especially in the case of epitaxially grown layers. This discrepancy has motivated extensive efforts to identify its underlying causes that are limiting device performance. One primary reason is that the layer properties are strongly modulated and limited by nanoscale inhomogeneities including strain, defects, and disorder. To bridge the gap between theory and experiment, the implications of these inhomogeneities on the excitonic and electronic properties of the layer must be explored. This includes the inherent intrinsic properties of as-deposited layers and extrinsic process-related disorders. However, detection and characterization of these inhomogeneities is far from trivial; most are sensitive to demanding sample preparation procedures that are prerequisite to many atomic- or nanoscale metrology techniques or lie beyond the reach of diffraction‑limited spectroscopy that does not require these procedures. Furthermore, several alternative characterization techniques either lack sensitivity, only operate under restrictive environments, or provide structural information without direct correlation to local electronic or excitonic behavior. There is therefore a critical need for a technique that can facilitate simultaneous characterization of structural, electronic, and excitonic properties at the nanometer scale under ambient conditions and without specialized sample preparation. Tip‑enhanced optical spectroscopy (TEOS) fulfills these requirements and is thus employed to address this metrology need. This thesis is dedicated to the different aspects of design, execution, and interpretation of advanced characterization procedures with TEOS serving as the central metrology technique. The goal is to elucidate structure - property - performance correlations in monolayer WS2. The focus is on the detection of intra-layer inhomogeneities and their implications on electronic properties such as conductivity, carrier density, and mobility. This is mainly achieved through correlated colocalized procedures with other well-established metrology techniques. As a result, the capabilities of TEOS in defect characterization systematically examined and further expanded through these studies.