Imaging electromechanical phenomena with microwave impedance microscopy

Electromechanics combines processes from electrical and mechanical systems and focuses on their interactions, which lead to wide applications in modern electronics. The observation of microscale and nanoscale electromechanical phenomena is critical for understanding the underlying physics and inspiring scientific and technological innovations. Near-field scanning microscopy is a promising tool that utilizes evanescent waves to detect local physical properties at a length scale much smaller than the far-field resolution limit. This dissertation demonstrates the discoveries of novel electromechanical phenomena revealed by microwave impedance microscopy (MIM) and shows the invention and application of new scanning microwave microscopy technique inspired by the discoveries.

In this dissertation, I first introduce the development of near field scanning probe microscopy. In Chapter 2, I begin by reviewing the basic components and the system design of microwave impedance microscopy (MIM), followed by a description of data analysis and its main application - local conductivity mapping. I then elaborate its other applications in the following chapters, categorized by the different properties probed by the technique. Chapter 3 demonstrates the discovery of a unique phonon mode existing in the ferroelectric domain walls. Chapter 4 shows a novel electromechanical transduction phenomenon in the ferroelectric domains of LiNbO₃. In Chapter 5, I present the invention of a new microwave microscopy technique, transmission-mode MIM (T-MIM), which can be used to visualize the microwave field directly and has achieved great success on mapping surface acoustic wave (SAW). I conclude the thesis in Chapter 6 with a summary of the published discoveries and an outlook of the ongoing projects and future plans in this area.