Modifications on Surface Electronic and Magnetic Properties via Metal and Organic Molecule Deposition
| Autor: | Yu-Hsun Chu, 朱宇軒 |
|---|---|
| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 During development of electronics and spintronics, modifications on the surface electronic and magnetic properties have drawn broad interest. One of the most sophisticated surface-sensitive instrument, scanning tunneling microscopy (STM), has largely expanded the horizon of fundamental physics as well as nanotechnology, from observations of crystalline structures and electronic states to control of individual adatoms for artificial and novel constructions. In this dissertation, deposition of metals and organic molecules and the consequent effects on exotic surfaces are revealed by STM and spin-polarized STM (SP-STM). From morphology in topography to variance of electronic and magnetic structures in space and energy, the studies function as the cornerstone of surface engineering of heterostructure and its applications. On single ferromagnetic domains from Co nanoisland on Cu(111), investigations of manganese-phthalocyanine(MnPc)-Co and pentacene(PEN)-Co hybrid systems are achieved using STM, SP-STM, and first-principle calculations. While MnPc follows the Co spin-polarization near the Fermi level, PEN exhibits an opposite one. We conclude that different orbitals hybridizing with Co and different exchange mechanism result in the inverse spin polarization between MnPc and PEN. In addition, symmetry reduction of PEN, which clarifies the Co stacking methods, is found recovered in SP-STM spin-dependently, which brings out the significance of bonding and antibonding states in organic-ferromagnetic interfaces for designs of spin-distribution. On the other hand, spatial variations of electron and spin-polarization distributions induced by quasiparticle interference in Co islands are revealed by SP-STM. Tip manipulations allow us to compare interference patterns with and without spin information, which correspond to each other closely and are described by the particle-in-a-box model. Quasiparticle interference also reveals spin-dependent scattering processes in the Rashba spin-split surface states. STM measurements on the strong bulk Rashba crystal BiTeI resolve both the morphology of different surface terminations as well as scattering events from an interference dispersion. To put BiTeI in practical use, submonolayer Fe is deposited on it to unveil influences from magnetic impurities on Rashba spin-split states and electron scattering. Without appearance of new scattering channels and distortions in the intrinsic interference dispersion, Fe induces band shift which can be attributed to creations of Fe-substitution Bi defects. Organic molecules PTCDA (perylene-3,4,9,10-tetracarboxylic dianhydride) and PEN are also deposited and termination-selected growths are observed. Intramolecular dipoles in PTCDA induce molecule self-assembly as well as possible preference to the Te-termination. The dissertation covers issues in surface science from measurements of electronic and magnetic properties using STM to state modifications and creations via deposition of metals and organic materials. The combination of in-situ sample fabrications and delicate STM measurements with first-principles calculations resolves the complicated interactions among different elements and systems. Each of them contributes to development of spintronics from different angles, and in total, they depict a vision of future devices based on organic molecules and emergent crystals with all kinds of versatility. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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