Yohannes Abate, PhD, California State University
MAIN RESEARCH ACCOMPLISHMENTS AND THEIR SIGNIFICANCE
The main research is focused on plasmonic high-resolution near-field imaging of several noble metal and metamaterials and their interaction with organic molecular films (Pc family) and thin silica (SiO2) films. We have succeeded in characterizing and understanding many fundamental plasmonic properties in the near field, which resulted in 3 publications and one under preparation. Our research on quantifying the effect of local plasmons on photovoltaic is directly in line with the original proposed goal. We believe we have exceeded the original plan proposed and performed very well during this grant period. Our research resulted not only in several publications but also in a major grant (discussed below) from Department of Defense, Army Research Office (DoD, ARO) as a result of seed money we acquired from ACS PRF. Several students have benefited from the training, so far 2 graduate students defended their MS thesis, one of already in the PhD physics program (discussed in more detail). One other Ms student is in the pipeline towards finishing his MS thesis.
We have been focused on imaging plasmonics on metal bare nanoparticles/nanostructures and buried plasmonic nanostructures under polymers and organic thin films in real-space according to the proposed outline funded by ACS PRF. We have also recently imaged plasmonic hotspots located in the nanogaps of infrared optical antennas in the near-field. The enhanced evanescent field resonance is shown to depend strongly on excitation wavelength, the excitation and detection laser polarization, and gap size. In addition, we demonstrate that in nanogap hotspot imaging using scattering probes, the probe tip can be considered as a load in the gap of the antenna, and the impedance of the load can then be tuned from inductive to capacitive or vice versa by changing the dielectric value of the tip load. Experimental results are in agreement with finite-difference time-domain simulations .
We have imaged the polarization states of symmetric and antisymmetric bowties. Graduate student Sarah Grefe has done theoretical simulations using the Finite Domain Model and the dipole model to understand the enhancement and modification of near-field plasmonics on these nanostructures. Undergraduate student Stefan Mastel and Daan Leiva have performed the experiments and are preparing the manuscript for this work together with Sarah. Stefan Mastel who has been paid from ACS PRF grant has gone back to Germany to complete his MS degree soon be graduating with MS in physics and greatly acknowledges ACS PRF.
STUDENT PARTICIPATION (Since last report)
Sarah Grefe: Sarah joined our group in the Spring of 2011 and has been a key member of the group since then. She is responsible for most of the FDTD (lumerical co.) calculations and have been training undergraduate students Matthew Acosta and Daan Leiva on FDTD. Sarah, together with undergraduate studrents in the group, did most of the work on the IR plasmonic antenna studies with and without the thin organic coatings. She is preparing one paper to be submitted to Optics Express. Sarah is also a coauthor (second author) of the paper we just published on Applied Physics Letters.
Brando Hessler. Brandon is one of the most active undergraduate student in the group. He has done most of the preparation of the samples for both the visible and mid IR frequency experiments. Brandon also performed most of the work on organic coated plasmonic structures. Brandon Hessler have presented our research results at various meeting around campus and California Sections of APS.
Codi Bonney. Codi is a very talented programmer. He has done theoretical calculations to support and improve our experiments. He write a fantastic program that can simulate the experiments we conduct using MATLAB. The program he wrote will remain a very important part of our research lab that could be used for many other experiments to come. He recently got hired at start-up company iViu Technologies, Inc. as a iOS Software Developer.
Ralph Demato. Ralph joined the group in Fall of 2011 and is already making significant progress in his research. Ralph is completing the work on plasmonics on metallic nanoparticles near-field studies and is writing his thesis. Recently he got hired by Kaiser as an assistant Medical physicist.
Terry Dunlap. Terry is who started out as an undergraduate student in our group has now stayed in the group as a graduate student. He has been responsible for various programing related issues in the group including design of our new website. His research is in organic covered plasmonic structure near-field imaging.
Matthew Acosta and Daan Leiva. Undergraduate students Matthew and Daan joined our group in the Fall of 2012 they have been significant in FDTD calculations working together with Sarah. They are both learning to prepare samples and to perform AFM imaging.
Group Student awards (since last report):
several awards including Who's Who in America Award (2012), Florence and Richard Scalettar Physics Award, Spyros-Pathos Chemistry Award and AAPM Physics Fellowship at UCSF. 2010-Present, President's List, 2010-President's Scholar Recipient, 2011 NASA Internship at Dryden Flight Research Center, 2011-Phi Beta Kappa Honor's Society.