Spin-Polarized Transport and Spin Filtering in Organic Nanostructures

• Author / Creator

  Alam, Kazi, MM

• Electrons, the fundamental charge carriers in solid-state devices, possess three intrinsic
  properties: mass, charge and spin. Spin is a quantum mechanical property, but can be loosely
  visualized as a tiny “intrinsic” magnetic dipole moment attached to an electron. In conventional
  electron devices, spin magnetic moments point along random directions in space and play no
  significant role in device operation. In the emerging field of “spintronics” the central theme is to
  harness the spin degree of freedom of charge carriers to realize novel data storage and
  information processing technologies. Spintronic devices are already ubiquitous in state-of-the-art
  hard disks with large storage densities. A concerted global effort is underway to explore various
  spin-based information processing concepts, which can potentially be more energy-efficient than
  traditional charge-based electronics.
  In recent years, substantial research has been devoted to understanding carrier spin dynamics in
  metallic multilayers, tunnel junctions and inorganic semiconductors such as silicon, germanium
  and various III-V compounds. On the other hand, π-conjugated organic semiconductors that play
  a crucial role in organic electronics and displays are relatively new materials in the area of
  spintronics. Organic semiconductors offer several advantages (such as mechanical flexibility,
  chemical tunability of physical properties, low-cost and low-temperature processing) compared
  to their inorganic counterparts. The ability to control carrier spin dynamics in organic materials
  will open up possibility of new devices such as flexible non-volatile memories, spin-based
  organic light emitting diodes and spin filters.
  iii
  In this work, we have explored two key spin related phenomena in organic semiconductor
  nanostructures: (a) spin-polarized transport and (b) spin filtering. In the first sub-project, we
  explore spin transport in “nanowire” geometry instead of commonly studied thin film devices.
  Such experiments shed light on the spin relaxation mechanisms in organics and indicate ways to
  minimize such effects. Fabrication of organic nanowires with well-controlled geometry in the
  sub-100 nm range is a non-trivial task, and in this subproject we have developed a novel
  technique for this purpose. Spin transport in rubrene nanowires has been studied, which indicates
  significant suppression of spin relaxation in nanowire geometry compared to rubrene thin films.
  Our experimental data indicates that spin-orbit coupling is the dominant spin relaxation
  mechanism in rubrene nanowires. In the second sub-project, we explore spin filtering
  (transmission of one particular type of spin) through an organic nanostructure in which single
  wall carbon nanotubes (SWCNT) are wrapped with single stranded DNA (ssDNA) molecules.
  Efficient spin filtering has been observed in this system, which may enable magnetless spintronic
  devices in the future.

• Subjects / Keywords

  • Spin Transport
  • Anodization
  • Rubrene
  • Magnetotransport
  • Organic Nanowire
  • Self-assembly
  • Spin Valve
  • Carbon nanotubes
  • DNA
  • Organic Semiconductor
  • Spin Filter

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3T96P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.