Ultrafast electron microscope at the Argonnes Centre for Nanoscale Materials. Credit: Argonne National Laboratories.
Anyone who has been to the Grand Canyon knows how strong it is to feel close to nature's edges. Scientists at the U.S. Department of Energy (DOE), Argonne National Laboratory, have found that nanoparticles of the gold behave unusually close to graphene, a 1-atom thick carbon sheet. This discovery could have major implications for the development and use of quantum devices and sensors.
This was possible thanks to a newly constructed ultrafast electron microscope (UEM), which is located at Argonne's Center for Nanoscale Materials, a DOE Office of Science User Facility. The UEM allows for the investigation and visualization of phenomena at the nanoscale in time frames less than one trillionth of a second. This breakthrough could be a major step forward in the rapidly growing field of plasmonics. Plasmonic fields are created when light strikes a surface to trigger waves of electrons.
Scientists have pursued the development of plasmonic devices for a variety of purposes over many years. These include quantum information processing, optoelectronics (which combine electronic and light components), and sensors for medical and biological purposes. They combine two-dimensional materials of atomic-level thickness like graphene with nanosized metal particles to achieve this. Understanding how these materials are combined will help you to understand their plasmonic behavior.
Researchers at Argonne used ultrafast electron microscopy in a recent study to examine the coupling of graphene and gold nanoparticles.
Haihua Liu, an Argonne nanoscientist, said that surface plasmons can be light-induced electron oscillations at the nanoparticle's surface or at its interface with another material. When we shine light on a nanoparticle, it creates an extremely short-lived plasmaonic field. When the two fields overlap, the pulsed electrons of our UEM interact and the electrons gain or lose energy. We then use an energy filter to collect the electrons that gain energy and map the distributions of the plasmonic fields around the nanoparticle.
Liu and his associates discovered an extraordinary phenomenon while studying gold nanoparticles. The plasmonic field formed when the nanoparticle was placed on a graphene sheet. It was symmetric. The plasmonic field was stronger when the nanoparticle was placed close to the graphene edge.
Liu stated that this is a new way to think about charge manipulation in the form a plasmonic and other phenomena using light at nanoscale. "With ultrafast capabilities it's impossible to predict what we might find as we modify different materials and their properties."
The entire experimental process from stimulation of the nanoparticle through to detection of the plasmonic fields takes less than one hundred quadrillionths seconds.
Ilke Arslan, Director of CNM, stated that the CNM has a unique UEM. It is accessible to all users and can take measurements with a sub-picosecond resolution spatially and temporally. "Having the ability take measurements in such a quick time frame opens up the possibility of exploring a wide range of new phenomena in nonequilibrium states that have never been possible before. This capability will be available to international users.
The understanding gained with regard to the coupling mechanism of this nanoparticle-graphene system should be key to the future development of exciting new plasmonic devices.
The June 21 issue of Nano Letters featured a paper that was based on the study: "Visualization plasmonic couplings with ultrafast electron microscopy." Liu and Arslan were not the only authors. Richard Schaller, Thomas Gage, and Stephen Gray are also contributing. Prem Singh and Amit Jaiswal of Indian Institute of Technology contributed, as well as Jau Tang of Wuhan University, and Sang Tae Park of IDES, Inc.
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Haihua Liu and colleagues, Visualization Of Plasmonic Couplings With Ultrafast Electron Microscopy. Nano Letters (2021). Information from the Journal: Nano Letters Haihua Liu et al., Visualization Of Plasmonic Couplings Using Ultrafast Electron Microscopy (2021). DOI: 10.1021/acs.nanolett.1c01824
