Probing Atomic-Scale Properties of Magnetic and Optoelectronic Nanostructures
- Author(s): Zhang, Xiaowei
- Advisor(s): Crommie, Michael F.
- et al.
This dissertation presents scanning tunneling microscopy and spectroscopy studies of individual molecules and graphene nanoribbons (GNRs) bound to a substrate. Understanding the local electronic properties of these systems is importance from a fundamental physics viewpoint and for advancing potential technological applications in nanoelectronics. Two molecular systems, tetracyanoethylene (TCNE), and bithiophene naphthalene diimide (BND), were investigated. The basic questions addressed are (1) how do molecules respond to a condensed matter environment (i.e. a metal or semiconducting surface), (2) how do spins behave in molecule-scale structures, and (3) how do the intrinsic electronic properties of molecules affect their self-assembly behavior. We find that TCNE molecules display variable surface coupling and enable tunable magnetic exchange coupling between covalently bonded spin centers in Vx(TCNE)y complexes. We also were able to determine the TCNE adsorption site within a molecular monolayer on Ag(100) through a combination of inelastic electron tunneling spectroscopy and density functional theory calculations. We find that BND molecules exhibit type-II heterojunction energy level alignment. The interplay between the bipolar electronic nature of the molecule and the substrate results in different self-assembly patterns on a Au(111) surface. In GNRs we have demonstrated the presence of magnetic edge states for chiral nanoribbons with atomically smooth edges. We have further controlled GNR edges via hydrogen plasma etching, and have determined their exact edge termination.