Current Seminars and Colloquia

PHYSICS Colloquium

September 16 2021, Thursday, 3:30 pm CST

Physical Sciences 110

Dr. Erin Iski  
Chemistry and Biochemistry
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.

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PHYSICS Colloquium

September 23 2021, Thursday, 3:30 pm CST

Physical Sciences 110

 Dr. Francesco (Frank) Narducci

 Naval Postgraduate School

Associate Editor: Physical Review A, Physical Review Letters

Towards a T³ atom interferometer

In this talk, I will discuss a novel atom interferometer being developed at the Naval Postgraduate School. I will begin the talk by reviewing the theory of light pulse atom interferometers, concentrating on how the phase of the interferometer scales with the time between the atom optic pulses, T.  I will discuss the connection between the Lagrangian and Hamiltonian formulations for the calculation of the phase.  Next, I will demonstrate that the T² scaling is due to a symmetry in the problem and that when the symmetry is broken, a T³ scaling appears (and in our geometry, the phase becomes purely dependent on a T³ term with no T² terms). I will then turn to a discussion of an experimental implementation involving interferometry on magnetic transitions. The experiment is quite challenging and, although the signature T³ signal has so far eluded us, has provided many interesting features and physics which I will discuss.

PHYSICS Colloquium

September 30 2021, Thursday, 3:30 pm CST

Physical Sciences 110

 Dr. David Tománek

 Michigan State University

Saving Humankind from Thirst

Whereas water itself is bountiful on Earth, much of it requires treatment to make it suitable for human consumption. Lack of potable water is currently the leading cause of death, ahead of any disease. Recent progress in fabricating nanostructured carbon allotropes may bring a long-awaited paradigm shift in designing membranes that would make efficient desalination of salt water using reverse osmosis and filtration of contaminated water possible. A previously unexplored membrane design [1] based on a unique layered assembly of carbon nanostructures including graphite oxide (GO), buckypaper consisting of carbon nanotubes, and a strong carbon fabric should provide high mechanical strength and thermal stability, resilience to harsh chemical cleaning agents and electrical conductivity, thus addressing major shortcomings of commercial reverse osmosis membranes. Microscopic insight into the critical permeation of water molecules in-between GO layers and across in-layer vacancy defects in graphitic carbon can be obtained using ab initio density functional theory calculations. Results of these computational studies elucidate the reason for selective rejection of solvated Na+ ions in an optimized layered all-carbon membrane.

[1] David Tománek and Andrii Kyrylchuk, Designing an All-Carbon Membrane for Water Desalination, Phys. Rev. Applied 12, 024054 (2019).