Laser-material interaction: From applications of pulsed laser deposition to the fundamental heat affected zone

A universal goal of the engineering community is the ability to alter the macroscopic properties of a material through microscopic alterations. The fabrication of structures with atomic scale precision is the means to reach this goal. Great interest exists in increasing the strength of materials, altering the thermal characteristics, controlling the magnetic properties, as well as a host of other features through nanostructuring. Exploiting the fundamentally different behavior between nanoscale and bulk material is the key to many future breakthroughs in the science of nano structuring. There have been successes in nanostructuring, such as in the thin metal films for random access memory; and there is hope for future successes in just about every high tech field, such as engineering hydrogen storage materials. This dissertation provides an in depth study of magnesium based hydrogen storage materials deposited by pulsed laser deposition (PLD). The advantages and requirements of nanostructured metal hydrides are discussed. A series of experiments are performed to investigate the properties and characteristics of the laser deposited materials, and improvement in hydrogen sorption capacity is realized over the original target material. Possible advantages of PLD performed with ultrafast femtosecond pulses rather than traditional nanosecond pulses are discussed. A fundamental investigation is conducted to inspect the laser-material interaction which begins the PLD process for both the femtosecond and nanosecond pulse duration cases. A significantly smaller heat affected zone is determined to exist for the femtosecond case compared to that of the nanosecond pulse duration. Lastly, a material phase change phenomenon in which an anomalously large heat affected zone occurs by explosive crystallization is investigated. A phase change induced by a laser pulse is observed to become self sustaining under appropriate material conditions. A series of experiments are completed to investigate this phenomenon as it occurs from a laser pulse below the threshold for ablation, but above that for melting; resulting in the transformation of metastable amorphous germanium to the more stable polycrystalline phase. The conditions, characteristics, and stability of this laser induced phase change phenomenon are experimentally determined and discussed. The goal of this dissertation is to help illuminate some of the mechanisms and controls in laser-material interactions, while concentrating on practical and research based applications.