Assembly, Chirality, and Polymorphism of Large Molecules on Metal Surfaces.
Iski, Erin.
2011
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Abstract: The invention of the Scanning Tunneling Microscope (STM) by Binnig
and Rohrer at IBM in 1981 revolutionized the field of surface chemistry. This instrument
operates by scanning a very sharp metal tip over a surface, ultimately generating an image
of the sample. Unlike conventional microscopes, STM does not rely on using visible light to
image the sample, but rather electrical current; ... read moretherefore its resolution is not limited by
the wavelength of light and can be much higher than optical microscopes. STM is a powerful
technique used to map out both the topography and the electronic structure of metal
surfaces and adsorbates on those surfaces. Atomic and molecular resolution is routinely
achieved under ambient, in situ, electrochemical, and ultrahigh vacuum conditions. This
dissertation examines four main topics: the formation and study of an ultra-stable layer
via electrochemical STM (EC-STM), the potential use of surfaces to control the polymorphism
of a pharmaceutical compound, the analysis and transmission of chirality of a
technologically important acene across a metal surface, and finally, how STM can be used to
further chemical education. Using the ability of STM to interrogate the atomic structure of
a surface combined with the electrochemical capabilities of EC-STM, like under potential
deposition (UPD) and cyclic voltammetry, an ultra-stable AgClx layer on Au(111) was
discovered which was stable on the surface up to temperatures as high as 1,000 K (Chapter
3). Ambient STM, low-temperature STM, ex situ Xray photoelectron spectroscopy (XPS), and
density functional theory (DFT) were also employed to show how the presence of chloride on
the Ag adlayer greatly affected both the structure and properties of the AgClx film in very
unexpected ways. The high resolution capabilities of low-temperature STM were exploited to
examine the packing of a pharmaceutical compound, Carbamazepine (CBZ), on Au(111) and
Cu(111) single crystals, which resulted in the formation of complex chiral molecular
architectures that were previously unreported (Chapter 4). The identity of the metal
surface altered the way in which the molecules packed both in density and in chirality,
indicating that different metallic surfaces could be used as templates to control the
molecular packing density or polymorphism of pharmaceutical compounds. Furthermore, we were
able to examine how the packing of CBZ changed as a result of an increase in surface
coverage and how second layer growth began to replicate a predicted, but previously not
observed experimentally, structure for the bulk crystal (Chapter 5). The study of chiral
surface chemistry was extended to include the spontaneous transmission of chirality through
multiple length scales for a simple, robust polyaromatic hydrocarbon, Naphtho[2,3-a]Pyrene
(NP), on a Cu(111) surface (Chapter 6). Additionally, the interaction of that
technologically important molecule with a Au(111) surface was examined in an effort to
understand the changes in the organic-metal interface as a function of various annealing
treatments (Chapter 7). The final chapters of this thesis are devoted to the use of STM in
undergraduate classrooms as a visual method to incorporate nanotechnology and fundamental
physical chemistry concepts into the curriculum of college students. In Chapter 8, the use
of STM in the undergraduate classroom is examined in a general sense in which the
addressable areas of physical chemistry and amenable systems to study are explored. In the
final chapter of the thesis, we describe a novel undergraduate laboratory experiment in
which STM is used to interrogate and identify the different lengths of alkyl chains in a
two-component self-assembled monolayer (SAM) on Au(111). Through this exercise, students
are given the chance to learn about scanning probes, molecular packing structures, SAMs,
electron tunneling, and molecular conductance (Chapter 9).
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Chemistry.
Advisor: E. Charles Sykes.
Committee: Elena Rybak-Akimova, Arthur Utz, and Jim Whitten.
Keyword: Physical Chemistry.read less - ID:
- d217r206g
- Component ID:
- tufts:20886
- To Cite:
- TARC Citation Guide EndNote
