Polarization-Controlled Directional Multiphoton Photoemission from Hot Spots on Single Au Nanoshells

Author
Abstract
<p>Directional\&nbsp;photoemission\&nbsp;from\&nbsp;single\&nbsp;Au\&nbsp;nanoshells\&nbsp;is demonstrated in the low-intensity,\&nbsp;multiphoton\&nbsp;regime. This\&nbsp;directionality\&nbsp;is shown to be due to the plasmonic excitation of highly photoemissive, nanometer scale surface regions, which are characterized by correlated momentum mapping, scanning electron microscopy (SEM), and laser\&nbsp;polarization-dependence studies. Furthermore, the photoelectron flux from a\&nbsp;single\&nbsp;nanoshell can be systematically rotated by over 90\textdegree in momentum space simply by\&nbsp;polarization-controlled\&nbsp;coupling to different\&nbsp;hotspots. Photoelectron distributions are directly characterized in momentum space via velocity map imaging (VMI) of the two-dimensional transverse (px,\&nbsp;py) momentum components for\&nbsp;singlenanoshells. For the majority of\&nbsp;nanoshells\&nbsp;studied, the\&nbsp;photoemission\&nbsp;is directionally orthogonal to the laser\&nbsp;polarization, which implicates nanoscale crevice-shaped \textquotedbllefthot\&nbsp;spots\textquotedblright clearly observed in the correlated SEM/VMI studies, with the near-field plasmonic nature of these crevices clarified further via finite-element simulations. These results rationalize the large\&nbsp;photoemissionenhancements observed in previous\&nbsp;Au\&nbsp;nanoshell studies, but more importantly provide a novel experimental access to directionally tunable electron emission from nanoscale sources. The ability to control\&nbsp;photoemission/photocurrent angular distributions at the nanoscale with only modest optical fields indicates a new parameter for optimizing nanoplasmonic system performance and suggests new plasmonic applications such as ultrafast,\&nbsp;polarization-controlledphotoelectric/photovoltaic switches.</p>
Year of Publication
2018
Journal
The Journal of Physical Chemistry C
Date Published
2018-06
ISSN Number
1932-7447
URL
http://pubs.acs.org/doi/10.1021/acs.jpcc.8b03402
DOI
10.1021/acs.jpcc.8b03402
JILA PI
Journal Article