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Magnetic properties of Ni/Si(111) and Co/Si(111) with nanoscale Ag buffer layers
Throughout my doctoral research, the main topic will be surrounded by magnetic surface alloys including two main kinds which are magnetic materials on surface alloy and surface alloys formed by magnetic material and semiconductor substrates. Combined with Auger electron spectroscopy (AES), surface magneto-optic Kerr effect (SMOKE), scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), the structure, composition and magnetic properties can clearly investigated. Because magnetic metal/silicide interface is claimedto have great potential on quantum computing, spintronic devices and nanoscale Ag buffer layer is commonly used to influence the magnetic properties of ferromagnetic materials, we focus on the some novel methods of producing magnetic surface alloys and the influence of Ag buffer layers on the magnetic properties of ultrathin magnetic thin films. Nowadays, Ni silicides show great potential on new functionalities. In this dissertation, we first explore the Ni/Si(111) system with Ag buffer layers. When Ni is deposited on Si(111), Ni silicides form at room temperature and the stoichiometrics of Ni silicide show the formation of NiSi compounds. The formation of Ag-Si particles provide a viable strategy for enhancing silicide formation via a specific interaction transfer mechanism even at room temperature, and provides insights into strategies for producing ultrathin silicides at a buried interface. Furthermore, in our previous reports, we find out that the silver reconstruction layer is a flat surface and influence the silicide formations. So we try to compare the effect of the reconstruction layer on Co and Ni ultrathin films, respectively. We propose a molecular-incident reaction effect (MoRE) to explain the phenomena after depositing Co and Ni on -Ag/Si(111). The comparable of crystalline energy with the space groups can be used to make sure that the species of the dominant formation type as CoSi2 and NiSi, respectively. Ag buffer can significantly influence the magnetic properties of magnetic ultrathin films because of the effective magnetic anisotropy change. After capping 1 ML Ag on top, we observe a slight and significant enhancement of coercive force for as-deposited and annealed series, respectively. A further enhancement of coercive force can be observed for both as-deposited and annealed series after annealing to above 450 K. This observation results from the interdiffusion of Ni atoms towards the upper Ag buffer layers to have larger contact area between Ni and Ag interfaces. Because my major is in the field of magnetic surface alloys and Ag buffer layers, the research results show great potential on the industrial applications. In the future, I would like to investigate different magnetic surface alloys and even surface alloys which can induce some ferromagnetic properties. Furthermore, I should find more buffer layers which can significantly influence the magnetic properties and may produce different magnetic properties in one sample after the interaction between buffer and magnetic layers. In order to find more direct evidence supporting our theoretical calculations, x-ray photoelectron spectroscopy mapping and synchrotron radiation can be utilized to investigate the surface morphology and compositions of our sample. Combined these fields of research, we can offer a more expansive range of applications on industry.
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