Benjamen Taber (Apkarian Group) and Chelsea Mueller (Schatz Group) - CaSTL Seminar

Thursday, April 18, 2019 - 13:00
2201 Natural Sciences II - Zoom Meeting Broadcast
Benjamin "Ben" Taber, UC Irvine (Apkarian Group )| Chelsea Mueller (Schatz Group)
Event Title: 
1pm: Seeing What’s Gone: The Impact of a Missing Atom on Cu2N Lattice Vibrations | 1:30pm - Thermodynamic determination of biphasic nanoparticle geometry
CaSTL Center | V. Ara Apkarian, Director and George Schatz


Thursday, April 18, 2019 - Zoom Meeting Broadcast

Benjamen Taber 

UC Irvine, Apkarian Group

Time: 1:00 pm

Title: Seeing What’s Gone: The Impact of a Missing Atom on Cu2N Lattice Vibrations

Abstract: Nitrogen absorbed on Cu(100) can form large-scale superstructures of a simple c(2x2) phase. These Cu2N islands are a model ultrathin dielectric material, with several potential applications including templating nanomaterial growth, memory storage, and interconnects. Here, we probe the missing-Cu atomic defect in the Cu2N c(2x2) phase. Surprisingly, the defect both broadens and blue-shifts the local N-Cu stretch vibrational mode, contrary to the behavior expected in a simple ball-and-spring model. This is indicative of the ionic nature of the lattice, as the neighboring N atoms further repel each other due to the loss of the charge screening provided by Cu. This investigation is enabled by recent advances in picospectroscopy in the atomistic near-field, and we will also discuss some of the techniques and physics behind this nascent field.

Bio: Dr. Taber is a CaSTL Postdoctoral Research Scholar in the group of Ara Apkarian at UC-Irvine, where he combines scanning tunneling microscopy (STM) with optical spectroscopy to interrogate individual molecules and nanomaterials in the atomistic near field. Prior to joining CaSTL, Dr. Taber earned his Ph.D. at the University of Oregon with Prof. Georgy Nazin, where he used STM to investigate organic semiconductors, and as part of his M.S. he spent nine months as a unit process engineer for I.B.M., developing source/drain epitaxy for the 10 nm node.


Northwestern University, Schatz group
Time: 1:30pm

Title: Thermodynamic determination of biphasic nanoparticle geometry

Abstract: Bimetallic nanoparticles are a potential solution to studying the SERS spectra of molecules that do not bind will to traditional SERS substrates without needing a chemical linker.  When the two metals are poorly miscible the resulting biphasic particle can adopt several geometries, including Core-Shell and Janus.  The Janus type particles have great potential as SERS substrates, as one metal can be selected to  bind the target molecule while the other metal provides the plasmonic enhancement.  Some of the challenges of working with these systems are choosing a relative composition of the metals such that the final geometry is the desired Janus type, and determining whether the shape of the Janus particle allows for sufficient field enhancement on the non-plasmonic side.  A  thermodynamics model can be used to predict the geometry of the biphasic particle as a function of composition, and for the Janus type particles can be used to predict the shape of each phase and the interface.

Bio: Chelsea Mueller received her undergraduate degree in Chemistry in 2015 from the University of Wisconsin at Stevens Point.  As a graduate student at Northwestern, she has worked on theory projects involving rotational alignment of open-shell diatomics, TERS imaging with semiempirical methods, and most recently using thermodynamics to predict the geometry of bimetallic nanoparticles in order to study their plasmonic properties. She is currently a fourth year PhD student in the Schatz group.