January 23, Vivian Ferry, University of California, Berkeley
Designing Absorption with Nanophotonics: from Photovoltaics to Plasmon Rulers
Abstract: Subwavelength nanostructures enable the manipulation and molding of light in nanoscale dimensions. By controlling and designing the complex dielectric function and nanoscale geometry we can tune macroscale properties such as reflection, transmission, and absorption. I will discuss two applications of plasmonic nanostructures: enhanced absorption in nanoscale photovoltaics, and the design of DNA-mediated chiral assemblies of nanoparticles.
Most solar cell systems face a tradeoff with decreasing semiconductor thickness: reducing the semiconductor volume increases open circuit voltages, but also decreases the absorption and thus the photocurrent. Light trapping is particularly critical for thin film amorphous Si (a-Si:H) solar cells, which must be made less than optically thick to enable complete carrier collection. Here plasmonic nanostructures are used to couple incident sunlight into localized resonant modes and propagating waveguide modes of an ultrathin semiconductor for enhanced solar-to-electricity conversion. By enhancing absorption in a given semiconductor volume, high efficiency devices utilizing less than 100 nm of active material can be realized.
The second part of the talk will discuss the design and implementation of three-dimensional chiral assemblies of colloidal metal nanoparticles assembled using DNA. Plasmonic nanoparticles possess high resonant scattering and absorption cross sections, are non-blinking, and exhibit strongly distance-dependent optical spectra, making these nanoparticles ideal for integration into metamaterials and biological sensors. The chiral assemblies I will discuss exhibit circular dichroism, which arises from the three-dimensional coupling between the dipole moments of the plasmonic nanoparticles. By changing the distance between the nanoparticles in response to external stimuli, properties such as the intensity and color of the spectrum may be tuned.
Biography: Dr. Vivian Ferry received her Bachelor’s of Science degree in Chemistry from the University of Chicago in 2006, working with Prof. Michael Hopkins on optical properties of molecular wires. She completed her PhD in 2011 from the California Institute of Technology under the direction of Prof. Harry A. Atwater. She is currently a postdoctoral fellow at the University of California Berkeley and Lawrence Berkeley National Laboratories in the research group of Prof. A. Paul Alivisatos. Her research interests include nanophotonic design of light trapping in solar cells, silicon and quantum dot photovoltaics, self-assembly of plasmonic structures, and plasmon rulers. Dr. Ferry has published in journals such as Nano Letters, Advanced Materials, and Nature Communications, and has received a number of academic awards including the Demetriades-Tsafska-Kokkalis award for her thesis research.
Faculty Host: Theodore Moustakas
Student Host: Adam Moldawer