University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
Understanding the fundamental physics of nanomaterials is critical for the advancement and rational design of new nanotechnologies. On the nanoscale, differences between individual structures, and even variations between different spatial locations within the same structure, can have a significant impact on the functional properties of nanomaterials and the electronic performance of nanodevices; yet much of our knowledge of nanostructure function is inferred from measurements that average over entire structures or integrate over long times. The existence of multiple conformations or structures within an ensemble, which often exhibit different dynamical behaviors, shroud the underlying dynamics, making it difficult to reach meaningful and quantitative conclusions. These limitations are overcome with the development and implementation of an ultrafast pump-probe microscopy technique. With combined spatial and temporal resolution, the microscope is capable of collecting data from individual nanostructures at various spatially distinct locations with a high throughput. Additionally, the microscope’s ability to excite an object in one location and probe it in another, allows the direct visualization of charge carrier motion and acoustic lattice motion on the nanoscale without the need for physical contact or active electrical connection. In this work, the microscope has been used to image electron diffusion in intrinsically doped silicon nanowires as well as image a combination of electron diffusion and drift in silicon nanowire devices with built-in electric fields. Additionally, to demonstrate the versatility of the microscope, it has been employed to study the insulator to metal transition and coherent acoustic phonon mode propagation in vanadium (IV) oxide (VO2) nanowires in a contactless imaging mode.Doctor of Philosoph
