It is known that metals such as gold and silver have high 'absorptive' and 'radiative' loss when they interact with light, compromising their use in optics and photonics research, particularly in industrial applications. Structured surfaces, also known as metasurfaces, that are made of metal nanoparticles have unique benefits over non-metallic nanoparticles. As described by Md Saad Bin Alam, doctoral student with CRPuO member Ksenia Dolgaleva, “light does not confine or trap inside the metal nanoparticles but concentrates close to their surface. This phenomenon is scientifically called 'localized surface plasmon resonances (LSPRs)'. This feature gives a great superiority to the metal nanoparticles compared to their dielectric counterparts, because one could exploit such surface resonances to detect bio-organisms or molecules in medicine or chemistry. Also, such surface resonances could be used as the feedback mechanism necessary for laser gain. In such a way, one can realize a nanoscale tiny laser gain medium or nanolaser that can be adopted in many future nanophotonic applications, like light detection and ranging (LiDAR) for the far-field object detection.” (Media, University of Ottawa, 2021)
Due to the high radiative and absorptive loss in metal nanoparticles, what is known as the LSPRs Q-factors are very low (5 - 10). The efficiency of the applications for metal nanoparticles depends on the resonant Q-factors. Although previous research has found ways to mitigate these losses through 'surface lattice' manipulation, a new 'surface lattice resonance (SLR)', the maximum Q-factors for the SLRs were only around 100 - 300. “Although such early reported SLRs were relatively better than the Low-Q LSPRs, they were still not very impressive for the efficient applications. It led to create the myth that 'metal is not useful for practical applications'” explains Dr. Orad Reshef, a postdoctoral fellow of CRPuO members Robert W. Boyd (Media, University of Ottawa, 2021)
Recently, CRPuO members Ksenia Dolgaleva, Canada Research Chair in Integrated Photonics and Assistant Professor with the School of Electrical Engineering and Computer Science, cross-appointed to the Department of Physics, and Robert W. Boyd, Canada Excellence Research Chair in Quantum Nonlinear Optics and Professor with the Department of Physics, cross-appointed to the School of Electrical Engineering and Computer Science, in collaboration with Jean-Michel Ménard, Assistant Professor, Department of Physics, and with the help of their research groups, have debunked this myth to prove that metal (plasmonic) nanostructures can be suitable for real-life optical applications through proper engineering of the nanostructure and carefully conducting an experiment. Through a combination of techniques rather than a single approach, a metal nanoparticle array (metasurface) with a record-high Q factor was demonstrated. As described by Prof. Dolgaleva, “[w]e broke the record for the resonance quality factor (Q-factor) of a periodic array of metal nanoparticles by one order of magnitude compared to previous reports. These resonances can be used for efficient light manipulating and enhanced light-matter interaction.” (Media, University of Ottawa, 2021).
The ground breaking research was primarily conducted by Md Saad Bin Alam and Dr. Orad Reshef. Md Saad Bin Alam designed the metasurface structure and conducted the experiment, while Dr. Reshef fabricated the metasurface sample in the CRPuO’s NanoFab facility. Yaryna Mamchur and Dr. Mikko Huttunen supported the experiment and numerical modelling, respectively. Prof. Dolgaleva and Prof. Boyd jointly supervised the research in collaboration with Prof. Ménard and Iridian Spectral Technologies. Other co-authors, Dr. Zahirul Alam and Dr. Jeremy Upham, took part in preparing the manuscript.
This significant breakthrough was recently published in the paper “Ultra-high-Q resonances in plasmonic metasurfaces” in the prestigious journal Nature Communications.
uOttawa Media published a story about this breakthrough as well.
Congratulations to all involved on this momentous discovery and for continuing to progress the field of photonics research!
Media, University of Ottawa (2021, March 19). Light It Up: uOttawa Researchers Demonstrate Practical Metal Nanostructures. https://media.uottawa.ca/news/light-it-uottawa-researchers-demonstrate-practical-metal-nanostructures