|Description||2020 Spring Physics Colloquium Series|
Erin Iski, Ph.D.
Associate Professor of Chemistry and Biochemistry
The University of Tulsa
Visualizing Nanoscale Surface Chemistry: From
Ultra-High Vacuum to Electrochemical Environments
Scanning tunneling microscopy (STM) is a specialized technique that can be used to examine and study nanoscale surface chemistry due to its extreme resolution. The requirement of pristine molecular resolution of certain systems necessitates the use of low temperature, ultra-high vacuum STM (LT-UHV STM) during the initial characterization of the surfaces. Importantly, it is also possible to study the assembly of molecules and atoms with liquid and electrochemical STM (EC-STM) in an attempt to bridge the temperature and pressure gap of ultra-high vacuum studies and to take measurements under more realistic conditions. The first investigation focuses on the EC-STM study of five simple amino acids (L-Valine, L-threonine, L-Isoleucine, L-Phenylalanine, and L-Tyrosine) as well as two modifications of a single amino acid (L-Isoleucine Ethyl Ester and N-Boc-L-Isoleucine), and the means by which these molecules interact with a Au(111) surface. Using EC-STM under relevant experimental conditions, the amino acids were shown to have a considerable interaction with the underlying surface. In some cases, the amino acids trapped diffusing adatoms to form Au islands and in other cases, they assisted in the formation of magic gold fingers. Importantly, these findings have also been observed under UHV conditions, but this is the first demonstration of the correlation in situ and was controlled via an external applied potential. Additional studies examining the role that surface temperature played in formation of the adatom islands will also be discussed. By analyzing the results gathered via EC-STM at ambient conditions, fundamental insight can be gained into not only the behavior of these amino acids with varied side chains and the underlying surface, but also into the relevance of LT-UHV STM data as it compares to data taken in more realistic scenarios. In the second project, EC-STM was used to study the deposition of Ag on Au(111), which in the presence of chloride, formed an ultra-stable layer that was stable in air and to temperatures as high as 1,000 K. Interestingly, depending on the exact potential used to form the Ag layer, a different type of thermal stability was observed. This atomically thin and ultra-stable layer which was also resistant to oxidation may find applications in a variety of fields and select anti-corrosion applications.
For more information contact: Dr. Zhenrong Zhang, 254-710-2419