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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2011-05-9055 |
| Date | 2011 May 1900 |
| Creators | Schuckman, Amanda Eileen |
| Contributors | Batteas, James D. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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