Characterization of Individual Straight and Kinked Boron Carbide Nanowires
Boron carbides represent a class of ceramic materials with p-type semiconductor natures, complex structures and a wide homogeneous range of carbon compositions. Bulk boron carbides have long been projected as promising high temperature thermoelectric materials, but with limited performance. Bringing the bulk boron carbides to low dimensions (e.g., nanowires) is believed to be an option to enhance their thermoelectric performance because of the quantum size effects. However, the fundamental studies on the microstructure-thermal property relation of boron carbide nanowires are lack. In this dissertation work, systematic structural characterization and thermal conductivity measurement of individual straight and kinked boron carbide nanowires were carried out to establish the true structure-thermal transport relation. Depending on the stacking faults orientations (transverse (TF), axial (AF), and inclined (IF)) in the two arms of the kink, kinked boron carbide nanowires were categorized into TF-TF, AF-TF, AF-AF, TF-IF and AF-IF kinks. With knowing the structural details (i.e., carbon contents, diameters, stacking faults densities/orientations and kinks) of boron carbide nanowires, the effect of each parameter on phonon transport was explored. The most interesting finding is the significant reduction of thermal conductivity in kinked boron carbide nanowires due to phonon mode conversion and scattering at the kink site. Last but not least, micro-Raman spectroscopy study on individual boron carbide nanowires was conducted. The results indicate that stacking fault orientations have no effect on the Raman scattering, but stacking fault densities and carbon concentrations do affect the Raman bands (i.e., width and position).
Sponsoring Chair: Dr. Terry Xu
Committee: Dr. Qiuming Wei, Dr. Thomas Schmedake, Dr. Haitao Zhang, Dr. Wesley Williams
Read Zhiguang's thesis here.