UC San Diego

The first part of this dissertation mainly focus on thin film solid oxide fuel cells. In recent years, solid oxide fuel cells are becoming more popular as a green energy source of electricity due to their high efficiency and low carbon emission. However, high operation temperature and materials costs are the main issues impeding the application of this technique. In this presentation, by applying magnetron sputtering technique to fabricate thin film solid oxide fuel cell, we are able to operate the cells under much lower temperature with superior performance under hydrogen or hydrocarbon fuels. Different composite nano-porous cathodes and anodes are fabricated and characterized, all showing reliable, reproducible and scalable results. The second part of the dissertation focus on fabrication and characterizations of spintronic devices, including Si-doped single crystalline Ni nanowires, spin-triplet spintronic and SOT-MRAM devices. Spintronics has been widely applied in data storage applications such as hard disk drives, STT-MRAMs, and SOT-MRAMs, etc. Recently, development of spintronics theories and experiments has allowed it to expand to broader applications, such as domain wall MRAMs, neuromorphic computing and quantum computing. In this section, we will introduce the growth of Si-doped single crystalline Ni nanowires, the effects from AMR, OMR and domain wall MR at low magnetic fields and electron-magnon interaction at high magnetic fields. We studied superconducting triplet spin valve devices. In general, singlet Cooper pairs generated from superconducting layers cannot survive in magnetic layer. However, if we introduce an inhomogeneous moments between these two layers, triplets Cooper pair appeared and can survive much longer than singlet Cooper pair in ferromagnetic materials. In our study, we fabricated epitaxial Ni and Co superconducting spin-triplet spin valves to study this effect. By rotating the soft NiFe layer to break the linearity of magnetizations, inhomogeneous moments can be generated. Magnetization configurations are characterized by polarized neutron reflectometer. By measuring the change of superconducting critical temperature at different angles of external field, we observed that the behavior of spin valve is highly sensitive to the thickness of the inhomogeneous magnetic layers. Lastly, the SOT-MRAM project during the internship in IBM is presented. SOT-MRAM is a potential second generation MRAM compared to STT-MRAM due to its higher efficiency, stability and lower switching current. We fabricated single SOT-MRAM device using $\beta$-W as spin current source. Ion beam etching process, the most critical fabrication process, has been studied. Shapes and aspect ratio effects on nanopillars are discussed. We also introduced thin Hf interlayers in the heterostructure to further decrease the critical switching current. Simulations proves an enhancement in perpendicular anisotropy will lead to this reduction in critical switching current.