Molecular-Scale Properties of Functional Materials and Molecules:
Advanced materials have led to new and improved
technologies. My work in Paul Weiss's group investigated some fundamental
structural and electronic properties of molecular surface coatings. The
structures formed by alkaneselenolate molecules were observed to pack in two
distinctly different surface morphologies in comparison to structures commonly
formed by alkanethiolate molecules. Structural and electronic differences
between these molecules were determined to originate specifically from the
headgroup linking the molecule to the surface. The electronic contact
resistances of these linkers (-S-Au and Se-Au) that connect molecules to Au were
measured using a combination of scanning tunneling microscopy and apparent
tunneling barrier height microscopy. Using the same methods, the conductance of
selected individual molecules was measured and contrasted.
Advanced inorganic materials were also investigated. Hydrothermally-grown PbTiO3
crystals were probed using scanning surface potential and piezoresponse
microscopy. The piezoelectric hysteresis characteristics observed for PbTiO3
crystals were observed to be dependent on the material thickness, as no
piezoelectric properties were observed for platelets thinner than 12 nm. Using
similar techniques, the ferromagnetic properties of 10 nm g-Fe2O3
nanoparticles were ascertained. Magnetic force microscopy data revealed
that defects (including domain boundaries and second layers) have larger effects
on the magnetic force observed than individual nanoparticles. Further, the
second layer was observed to have stronger magnetic properties than the initial
layer.
These results demonstrate that changes which are perceived to be minute are
actually very important and cause significant differences at the molecular
scale. For devices to be manufactured at the molecular scale, these changes are
crucial to understand and exploit.
Comments or questions?
Email:
jmonnell@engr.pitt.edu
This page was last updated on 09/07/05.
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