<p>Investigation of laser-matter interaction has been an important research topic which is closely related to applications in various fields including industry, military, electronics, photonics, etc. With the advent of ultrafast transmission electron microscope (UTEM), in situ investigation of the interaction between pulsed laser and nanostructured materials becomes accessible, with unprecedented spatial and temporal resolution. Here, we studied two categories of materials with the help of UTEM, namely, energetic materials and plasmonic nanostructures. The results demonstrate that UTEM provides a novel and convenient way for the investigation the structural and morphological change of energetic materials under external stimuli at nanoscale. Also, UTEM makes it possible to visualize the light-induced welding between plasmonic nanostructures at real time, which helps to reveal more details about the mechanisms involved. Furthermore, we studied the formation of some novel structures by combing different gold and silver nanostructure.</p>

The objective of this research was to develop a novel technique for mechanical treatment to manipulate the microstructure of Nickel-Manganese-Gallium Hesuler alloys to increase anisotropy, which can lead to higher magnetocaloric properties. Ni2+xMn1-xGa intermetallics have the potential to be employed in magnetic refrigeration devices including residential refrigerators, heat pumps, and air conditioning. Solid-state magnetic refrigeration systems are smaller, quieter, and reduce energy consumption by 20% compared to existing conventional vapor-cycle refrigeration devices which rely on harmful hydro-fluorocarbon gases and pump millions of tons of greenhouse gases into the atmosphere. The magnetic refrigeration market is predicted to reach US$ 315.7 Million by 2022. Magnetic refrigeration systems can also be used in electronic systems and the space industry. The current state-of-the-art magnetic refrigeration systems use expensive rare earth elements including Gadolinuim (Gd). The need to replace Gd and other rare earth elements with cheaper and more available elements led to other alloys including Ni-Mn-Ga. By understanding the processing-microstructure-property relationship of Ni-Mn-Ga alloy, it is possible to manipulate the microstructure in order to obtain higher refrigeration capacity. It is a promising alternative to rare earth elements and improves national security by minimizing foreign dependence on the import of rare earth metals. This novel in situ study establishes that twin boundaries can be manipulated in a polycrystalline Ni-Mn-Ga alloy. This results in a change in magnetocrsytalline anisotropy, which leads to a higher magnetic cooling power. Mechanical loading in a preferred direction, traditionally referred to as a training process, was able to move the twin boundaries, and the combination of focused ion beam imaging linked specific movement with mechanical loading. This technique, in situ monitoring process, can be utilized to devise training procedures for future iterations of magnetocaloric and shape memory alloys.