|Author||Iski, Erin V.|
|Thesis Title||Assembly, Chirality, and Polymorphism of Large Molecules on Metal Surfaces.|
|Advisor||E. Charles H. Sykes|
|Abstract||Summary: 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; therefore 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 X-ray 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 AgCl x 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).