Synthesis and characterization of novel boron-based nanostructures and composites

A number of nanomaterials have been synthesized by using a method that has been previously utilized to make pure boron nanostructures through the addition of different reactant gases to the process. This method was pioneered by Iqbal-Liu and will be referred to as the IL method in this dissertation. The IL method successfully created boron nanowires, boron nanoflakes, and boron nanotubes. In this dissertation, by adding methane, hydrogen sulfide, and ammonia to the process, an entire family of nanomaterials is prepared. These include nanowires, nano-heterostructures, and thin nanoplatelets of a variety of elemental compositions. These materials can be integrated with other known nanostructures to form a number of novel electronic nanodevices and nanosensors. A method to create nanocomposites by the chemical vapor infiltration (CVI) of nanomaterials into a metal matrix has been developed further. This work builds on past efforts which successfully developed carbon nanotube (CNT)-infiltrated metal composites which demonstrated enhanced mechanical strength. The nanocomposite method is successfully performed with boron nitride nanotubes in a nano-iron matrix. A graphene composite with iron is also synthesized but, unlike composites with CNTs, there was no strength enhancement. This could be attributed to the two-dimensional morphology of graphene. To put the dissertation in perspective, a review of several characterization techniques utilized is presented, including Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Additionally, a summary of possible novel growth mechanisms is required to explain the formation mechanism of the materials synthesized in this work. Nearly all of the materials synthesized in this work were grown with a vapor-liquid-growth mechanism. Background information on nanowires, nanotubes, and nanocomposites has also been included to clarify the significance of the research conducted. In conclusion, future experiments and some difficult to explain results are discussed