Schuckman, Amanda Eileen (2011-05). Charge Transport through Organized Organic Assemblies in Confined Geometries. Doctoral Dissertation. Thesis uri icon

abstract

  • Organic molecules such as porphyrins and alkanethiols are currently being investigated for applications such as sensors, light-emitting diodes and single electron transistors. Porphyrins are stable, highly conjugated compounds and the choice of metal ion and substituents bound to the macrocycle as well as other effects such as chemical surrounding and cluster size modulate the electronic and photonic properties of the molecule. Porphyrins and their derivatives are relatively non-toxic and their very rich photo- and electro-chemistry, and small HOMO-LUMO gaps make them outstanding candidates for use in molecularly-enhanced electronic applications. For these studies, self-assembled tri-pyridyl porphyrin thiol derivatives have been fully characterized on Au(111) surfaces. A variety of surface characterization techniques such as Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) have been implemented in order to obtain information regarding the attachment orientation based on the angle and physical height of the molecule, conductivity which is determined based on the apparent height and current-voltage (I-V) measurements of the molecule, conductance switching behavior due to conformational or other effects as well as the stability of the molecular ensembles. Specifically, the transport properties of free base and zinc coordinated tri-pyridyl porphyrin thiol molecular islands inserted into a dodecanethiol matrix on Au(111) were investigated using STM and cross-wire inelastic electron tunneling spectroscopy (IETS). The zinc porphyrin thiol islands observed by STM exhibited reversible bias induced switching at high surface coverage due to the formation of Coulomb islands of ca. 10 nm diameter driven by porphyrin aggregation. Low temperature measurements (~ 4 K) from crossed-wire junctions verified the appearance of a Coulomb staircase and blockade which was not observed for single molecules of this compound or for the analogous free base. Scanning probe lithography via nanografting has been implemented to directly assemble nanoscale patterns of zinc porphyrin thiols and 16-mercapotohexadecanoic acid on Au surfaces. Matrix effects during nanopatterning including solvent and background SAMs have been investigated and ultimately ~ 10 nm islands of zinc porphyrins have been fabricated which is the optimal size for the observed switching effect.
  • Organic molecules such as porphyrins and alkanethiols are currently being

    investigated for applications such as sensors, light-emitting diodes and single electron

    transistors. Porphyrins are stable, highly conjugated compounds and the choice of metal

    ion and substituents bound to the macrocycle as well as other effects such as chemical

    surrounding and cluster size modulate the electronic and photonic properties of the

    molecule. Porphyrins and their derivatives are relatively non-toxic and their very rich

    photo- and electro-chemistry, and small HOMO-LUMO gaps make them outstanding

    candidates for use in molecularly-enhanced electronic applications.

    For these studies, self-assembled tri-pyridyl porphyrin thiol derivatives have

    been fully characterized on Au(111) surfaces. A variety of surface characterization

    techniques such as Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy

    (STM), FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) have been

    implemented in order to obtain information regarding the attachment orientation based

    on the angle and physical height of the molecule, conductivity which is determined

    based on the apparent height and current-voltage (I-V) measurements of the molecule, conductance switching behavior due to conformational or other effects as well as the

    stability of the molecular ensembles. Specifically, the transport properties of free base

    and zinc coordinated tri-pyridyl porphyrin thiol molecular islands inserted into a

    dodecanethiol matrix on Au(111) were investigated using STM and cross-wire inelastic

    electron tunneling spectroscopy (IETS). The zinc porphyrin thiol islands observed by

    STM exhibited reversible bias induced switching at high surface coverage due to the

    formation of Coulomb islands of ca. 10 nm diameter driven by porphyrin aggregation.

    Low temperature measurements (~ 4 K) from crossed-wire junctions verified the

    appearance of a Coulomb staircase and blockade which was not observed for single

    molecules of this compound or for the analogous free base. Scanning probe lithography

    via nanografting has been implemented to directly assemble nanoscale patterns of zinc

    porphyrin thiols and 16-mercapotohexadecanoic acid on Au surfaces. Matrix effects

    during nanopatterning including solvent and background SAMs have been investigated

    and ultimately ~ 10 nm islands of zinc porphyrins have been fabricated which is the

    optimal size for the observed switching effect.

publication date

  • May 2011