Imaging Nanoscale Electronic Inhomogeneity With Microwave Impedance Microscopy

Ability to measure local dielectric constant and conductivity at nanoscale is desir- able for many research disciplines. Traditional transport measurements and many scanning probe techniques require ohmic contacts to the sample, which further com- plicates the sample preparation and is a low throughput process. Techniques based on high-frequency coupling is advantageous over these techniques since the measure- ments rely on the capacitive coupling between the tip and the sample. Among the high-frequency probes, near-field microwave microscopy sits on the sweet spot with the advantages from the high frequency coupling, but still maintains high contrast between metal and insulator. Implementing microwave microscopy technique is no trivial task. The first part of this thesis describes various engineering aspects during the developmental stage of our microwave microscopy, which we call microwave impedance microscope (MIM). We will begin with introduction to the principle of near-field microscopy, and follow by describing various components of MIIM. The second part of the thesis devotes to the study of nanoscale electronic inhomogeneity both at room temperature and low temperature. The room temperature works provide examples of application of MIM for nanoscale electrical characterization in nano graphene and semiconductor devices. The low temperature studies focus on the phase transition in pervoskite manganites and edge states of two-dimensional electron gas. In pervoskite manganites, we provide direct observation of the phase-separation and the glassy behavior of manganites. In the two-dimensional systems, we study the formation edge states during quantum Hall and quantum spin Hall effects. Finally, we concludes the thesis with plans for future developments and scientific problems.