Advanced Real-Space Measurements with STM: Application to Molecular Monolayers, Monolayer Defects, and Surface Chemistry

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professors Bumm and Huang and their students at University of Oklahoma are investigating ways to improve measurements of the arrangement and motion of molecules on surfaces to understand how these details affect the chemical and physical properties of the molecules. The ultimate goal is to understand how the properties of molecules, and therefore the surface on which they reside, depend on how molecules pack together. Understanding this relationship is crucial for design of unique surfaces of better bio compatibility and the coatings for corrosion protection and lubrication. The goal of this work is to develop improved tools for measurement and analysis with high precision. This interdisciplinary team combines the research groups of Bumm (experimental physical chemistry) and Huang (theoretical chemical engineering) which provides a unique training ground for graduate and undergraduate students working on the project. University of Oklahoma is a consortial member of the Louis Stokes-Oklahoma Alliance for Minority Participation (LS-OKAMP) in addition to operating the Multicultural Engineering Program (MEP). Both Professors Bumm and Huang are working on actively recruiting students from underrepresented minority groups to their programs, including Native Americans students. The scanning tunneling microscope (STM) can image surfaces with sub-nanometer resolution, revealing the arrangement of atoms and molecules on the surface. Despite the remarkable resolution, accurate measurements are complicated by the image distortion inherent in the STM. Recent advances in image post-processing by the Bumm group can remove this distortion to a level where accurate real-space measurements to be achieved. This project builds on that success and develops new advanced image analysis methods to characterize motion of molecules in sequences of images. The project develops and tests these methods on self-assembled monolayers (SAMs)--a 2D crystalline organic film, one molecule thick. SAMs are widely used in many areas of science and technology. Although they are well studied, many fundamental questions remain concerning their structure and properties. The analysis methods being developed can measure the position of each molecule in the image to better than 30 pm. Analysis methods to study point defects introduced into SAMs are to be developed and applied to fundamental characteristics of SAMs difficult to perform in other ways. The Huang group provide expertise in molecular dynamics and DFT modeling which is a critical component to bridge the observed STM images with the underlying molecular structure.