This thesis deals with the development of a versatile technique to measure spin polarization with atomic resolution. A microscopy technique that can measure electronic spin polarization is relevant for characterization of magnetic nanostructures and spintronic devices. Scanning tunneling microscopy (STM) can achieve atomic spatial resolution and it can probe the electronic structure of the sample, but so far STM-based techniques with spin sensitivity do not offer a reliable measure of sample spin polarization. We pursue in this work the goal of designing and implementing an STMbased technique to study magnetic surfaces with practical and quantitative analysis of spin polarization near the Fermi level. Our new technique, spin-filter scanning tunneling microscopy (SF-STM), is based on spin-polarized tunneling and subsequent analysis of the spin polarization in a multi-terminal semiconductor/ferromagnet probe tip. The spin analysis in the probe relies on the spin-dependent transmission of hot electrons through thin ferromagnetic layers and on the energyfiltering capabilities of semiconductor/metal Schottky barriers. An independent electrical contact to the SF-STM probe offers an information channel decoupled from the tunneling signal, providing a proper separation of magnetic information from topographic or non-spin-polarized electronic contributions. We describe the design of SF-STM probes and develop a microfabrication process based on anisotropic wet etching and local oxidation of silicon. The probes are fabricated in the form of silicon double pyramids terminated with micrometer-sized Schottky diodes, serving as the active elements for tunneling and spin filtering. We demonstrate the use of SF-STM probes to image magnetic surfaces and evaluate the spin-dependent transmission properties of ballistic electrons within the probes. This work satisfies the basic requirements for using the probes for quantitative imaging of spin polarization. Initial imaging results are an indication of the successful implementation of SF-STM. This new and complementary technique shows the promise of contributing to the development of new systems for spintronics and magnetic data storage.
|Award date||20 May 2010|
|Place of Publication||Zutphen|
|Publication status||Published - 20 May 2010|