Applied Physics Seminar
We present new spectroscopic techniques that enable visualization of nanoparticle phase transitions in reactive environments and light-matter interactions with nanometer-scale resolution. First, we directly monitor hydrogen absorption and desorption in individual palladium nanocrystals. Our approach is based on in-situ electron energy-loss spectroscopy in an environmental transmission electron microscope. By probing hydrogen-induced shifts of the palladium plasmon resonance, we find that hydrogen loading and unloading isotherms are characterized by abrupt phase transitions and macroscopic hysteresis gaps. These results suggest that alpha and beta phases do not coexist in single-crystalline nanoparticles, in striking contrast with ensemble measurements of Pd nanoparticles. Then, we introduce a novel tomographic technique, cathodoluminescence spectroscopic tomography, to probe optical properties in three dimensions with nanometer-scale spatial and spectral resolution. Particular attention is given to reconstructing a 3D metamaterial resonator supporting broadband electric and magnetic resonances at optical frequencies. Our tomograms allow us to locate regions of efficient cathodoluminescence across visible and near-infrared wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. The experimental signal can further be correlated with the radiative local density of optical states in particular regions of the reconstruction. Our results provide a general framework for visualizing chemical reactions and light-matter interactions in plasmonic materials and metamaterials, with nanometer-scale resolution and in three-dimensions.
More about the Speaker: Jennifer Dionne is an assistant professor in the department of Materials Science and Engineering at Stanford University. Jen received B.S. degrees in Physics and Electrical & Systems Engineering from Washington University in St. Louis in 2003, and a Ph.D. degree in Applied Physics from the California Institute of Technology in 2009, under the supervision of Prof. Harry Atwater. She joined Stanford in 2010 following a postdoctoral research fellowship at the University of CA, Berkeley and Lawrence Berkeley National Laboratory, working with Prof. Paul Alivisatos. Jen's research develops new optical materials for applications ranging from high-efficiency solar energy conversion to bioimaging and manipulation. This research has led to demonstration of negative refraction at visible wavelengths, development of a subwavelength silicon electro-optic modulator, development of quantum plasmonic materials, design of new optical tweezers for nano-specimen trapping, and demonstration of a metamaterial fluid. She was recently awarded the Presidential Early Career Award for Scientists and Engineers (2014), the inaugural Kavli Nanoscience Early Career Lectureship (2013), and was also named one of Technology Review's TR35 - 35 international innovators under 35 tackling important problems in transformative ways (2011). Further, her work has been recognized with an NSF CAREER Award (2012), AFOSR Young Investigator Award (2011), Outstanding Young Alum award from Washington University in St. Louis (2012), and the Materials Research Society Gold Award (2008).