On the time-resolved atomic force microscopy

Abstract

Understanding charge carrier dynamics and defect-mediated processes at the nanoscale is essential for advancing the performance and reliability of functional metal oxide materials. In systems such as titanium dioxide (TiO2), electronic behavior is governed by a complex interplay between charge transport, oxygen vacancy defects, surface energetics, and external stimuli including illumination, temperature, and electrical excitation. Many of these processes are spatially heterogeneous and strongly time dependent, yet conventional characterization techniques often provide only spatially or temporally averaged information, limiting insight into the mechanisms that control macroscopic material behavior. This thesis employs advanced atomic force microscopy (AFM)–based techniques to directly probe nanoscale charge carrier dynamics and electrostatic phenomena across multiple timescales. By combining electrostatic force microscopy, Kelvin probe force microscopy (KPFM), and time-resolved AFM approaches, this work investigates how local defect landscapes and excitation conditions govern electronic behavior in TiO2 under nonequilibrium conditions. Time-resolved AFM measurements are used to quantify charge carrier relaxation dynamics over millisecond-to-second timescales, revealing spatially heterogeneous kinetics associated with defect-mediated transport and cooperative charge motion. Temperature-dependent measurements enable extraction of effective migration barriers, providing insight into the role of oxygen vacancies in governing transport dynamics. To access faster electronic processes, sub-microsecond time-resolved AFM is implemented through real-time cantilever signal analysis, allowing investigation of rapid charge redistribution dynamics that complement slower defect-driven processes. In parallel, KPFM is employed to probe local surface potential and energetic evolution under controlled ultraviolet illumination. By varying photon energy, irradiation geometry, and interfacial conditions, the thesis elucidates how photoinduced surface oxygen vacancies and metal–oxide interfaces modulate Fermi-level shifts and charge carrier kinetics. Collectively, the results demonstrate that nanoscale charge carrier dynamics in TiO2 are highly sensitive to defect distribution, excitation history, and measurement timescale. By integrating electrostatic and time-resolved AFM techniques, this thesis provides a unified framework for correlating local energetics with dynamic transport behavior, advancing the understanding of defect-driven processes in metal oxides and establishing time-resolved AFM as a powerful tool for nanoscale characterization of functional materials.

Date	16 Jun 2026
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Omur Dagdeviren (Supervisor)