Plasmonics is a field focused on the interaction between light and free electrons in metallic structures, leading to the excitation of collective electron oscillations known as surface plasmonic resonance.1
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Unlike traditional optical systems, which are limited by the diffraction limit to scales of several hundred nanometers, plasmonics enables subwavelength optics. By using plasmons, light can be manipulated and concentrated at scales smaller than its wavelength, facilitating advancements in nanotechnology and enabling new applications.2
Surface Plasmons
Surface plasmons are collective oscillations of free electrons at the conductor-dielectric interface, driven by an external electromagnetic field. These waves, known as surface plasmon waves (SPWs), propagate along the boundary and require TM-polarized fields with additional momentum for excitation.2
Optical fiber-based SPR sensors use evanescent fields to interact with plasmonic surfaces, achieving resonance when the frequency of incident photons matches the natural frequency of free electrons. This resonance is highly sensitive to refractive index changes, enabling these compact and cost-effective sensors to be used for applications such as temperature, pressure, environmental monitoring, food safety, and biological detection.1
Plasmonic Materials
Plasmonic materials, including silver (Ag), gold (Au), copper (Cu), and emerging alternatives, are important in surface plasmon resonance (SPR)-based applications due to their optical and electrical properties.1 These metals support strong plasmonic resonances, making them suitable for various applications.
Ag provides narrower resonance curves and higher signal-to-noise ratios (SNRs) for precise detection but requires protective coatings due to chemical instability. Au is chemically stable and enables larger resonance shifts but is affected by surface roughness. Bimetallic Ag/Au layers combine Ag’s sharp resonance with Au’s stability, improving SNR and sensitivity for chemical and biological sensors.1
Cu has optical properties similar to Au but is susceptible to oxidation, which can be mitigated with graphene coatings to enhance durability and performance. Emerging materials like niobium, known for its mechanical strength and chemical resistivity, and indium tin oxide (ITO), with low optical damping, are gaining attention for their unique properties.3
Localized Surface Plasmon Resonance (LSPR)
Localized surface plasmon resonances (LSPRs) occur when light interacts with metallic nanoparticles, leading to collective oscillations of free electrons localized at the nanoparticle’s surface. These resonances are highly dependent on the particle’s size, shape, material, and surrounding environment.4
By tuning these parameters, LSPRs can be manipulated to absorb and scatter light across a wide range of wavelengths, from ultraviolet to infrared. Advanced nanofabrication techniques enable the creation of diverse particle geometries, including spheres, rods, stars, and toroidal shapes, as well as core-shell and inhomogeneous structures.4 These designs enhance electromagnetic field localization, making LSPRs critical for applications in sensing, imaging, and nanophotonics.
An introduction to surface plasmon resonance
Applications of Plasmonics
Sensing and Biosensing
Plasmonics is used in sensing and biosensing to detect changes in the surrounding dielectric environment caused by chemical or biological interactions. These changes shift the resonance peak or intensity of the plasmonic signal, enabling sensitive detection. Metrics such as refractive index sensitivity (S) and figure of merit (FOM) are used to evaluate sensor performance.5
Recent advancements include sensors based on metal nanoparticle arrays, metamaterials, and hybrid plasmonic–photonic designs, which offer improved sensitivity and spectral resolution. For instance, Liu et al. (2019) designed sensors with hybrid plasmonic-photonic modes that demonstrate atomic-layer sensitivity and narrow resonance linewidths.6 Such designs are applicable to detecting gas adsorption, biomolecules, molecular vibrations, and explosives.
Chen et al. developed a plasmonic waveguide system with a metal nanowire-on-mirror configuration to achieve subpicometer resolution. This surpasses the theoretical vertical resolution limits of scanning probe microscopes and showcases potential for ultrasensitive sensing applications.7
Plasmonic nanostructures have also been designed as signal amplifiers and transducers for optical sensing, using various modes to achieve narrower plasmonic resonance linewidths.5
Energy Harvesting
Plasmonics offers innovative solutions for improving solar energy harvesting by utilizing the unique properties of plasmonic nanoparticles. Plasmonic nanoparticles such as Au and Ag enhance solar cell efficiency through light trapping and scattering, increasing the photon path length and boosting absorption.2 They are particularly valuable in thin-film solar cells, where they localize and concentrate light in the active layer.
Additionally, plasmonic nanoparticles can generate high-energy “hot carriers” when interacting with photons, which can be harnessed for electricity generation or chemical reactions. They also enable up-conversion and down-conversion processes to broaden the spectral range of solar cells, improving sunlight utilization.3
Despite challenges such as optimizing designs and ensuring long-term stability, plasmonics holds great promise for advancing solar energy technologies.
Plasmonic Nanocircuits
Plasmonic devices are being developed for high-speed, compact, and energy-efficient data transmission and processing, which are critical for next-generation communication systems. Current research focuses on improving performance through designs such as plasmonic waveguides integrated with phase-change materials for electro-optic switches.2
The integration of photonics, plasmonics, and electronics on a single platform provides a framework for logic operations. Work by Ghosh and Dhawan (2021) includes non-volatile hybrid electro-optic plasmonic switches for combinational and sequential logic circuits, demonstrating the potential of plasmonic devices in telecommunication applications.8
Advancements in Plasmonics
Plasmonics in Quantum Computing
Plasmonics significantly enhances quantum computing by boosting single-photon sources, which are vital for quantum information processing. Plasmonic nanostructures improve the Purcell effect, increasing spontaneous emission rates and enabling efficient photon generation.5
Innovations include coupling quantum emitters with plasmonic structures like nanowires, nanoparticle chains, and metal–insulator–metal (MIM) waveguides, achieving high brightness and directional photon emission.9
Recent designs using materials like Aluminium (Al) and Ag in nanostructures or integrating emitters with plasmonic cavities have achieved Purcell factors exceeding 10,000 and improved quantum efficiencies.10
Plasmonic Metamaterials
Plasmonic metamaterials are engineered materials with optical properties determined by their geometry, exceeding the limitations of their individual components. These materials can exhibit effects such as negative refractive indices, achieved through structures like split-ring resonators and metallic wires, enabling phenomena like the reversal of Snell’s law.2
Shelby et al. demonstrated this effect in the microwave regime by showing a reversal of Snell’s law.11 Efforts to achieve similar effects at visible frequencies are limited by increased metal absorption, leading to research into alternative resonator designs, including H-shaped resonators, chiral structures, and metallic cavity configurations.
Plasmonic metamaterials are also used in imaging applications to overcome the diffraction limit by utilizing surface plasmons to transfer evanescent fields from source to image. This method, demonstrated by Fang et al., allows resolution beyond conventional optical limits but is hindered by absorption losses in metals, highlighting the need for materials with reduced losses.12
Challenges in Plasmonics
A major limitation in plasmonics is material losses due to electron scattering within metals. High optical losses in traditional plasmonic materials like Au and Ag, caused by resistive heating and intrinsic damping, reduce device efficiency, especially in applications requiring long propagation lengths.13
Integrating plasmonics with photonic and electronic systems is further complicated by mismatched fabrication processes and scales, making the development of hybrid devices challenging. Addressing these challenges involves exploring alternative materials such as graphene and transparent conductive oxides to reduce losses and developing scalable fabrication techniques compatible with existing technologies.13
Harnessing the Power of AI and Plasmonics for Early Cancer Detection
References and Further Reading
1. Butt, M.; Khonina, S.; Kazanskiy, N. (2021). Plasmonics: A Necessity in the Field of Sensing-a Review. Fiber and Integrated Optics. https://www.tandfonline.com/doi/full/10.1080/01468030.2021.1902590
2. Butt, MA. (2024). Insight into Plasmonics: Resurrection of Modern-Day Science. Компьютерная оптика. https://computeroptics.ru/KO/Annot/KO48-1/480101.html
3. Tharwat, MM.; Almalki, A.; Mahros, AM. (2021). Plasmon-Enhanced Sunlight Harvesting in Thin-Film Solar Cell by Randomly Distributed Nanoparticle Array. Materials. https://www.mdpi.com/1996-1944/14/6/1380
4. Fang, Z.; Zhu, X. (2013). Plasmonics in Nanostructures. Advanced Materials. https://pubmed.ncbi.nlm.nih.gov/23813594/
5. Wang, B.; Yu, P.; Wang, W.; Zhang, X.; Kuo, H. C.; Xu, H.; Wang, ZM. (2021). High‐Q Plasmonic Resonances: Fundamentals and Applications. Advanced Optical Materials. https://scholar.nycu.edu.tw/en/publications/high-q-plasmonic-resonances-fundamentals-and-applications
6. Liu, Z.; Liu, G.; Liu, X.; Fu, G. (2019). Plasmonic Sensors with an Ultra-High Figure of Merit. Nanotechnology. https://pubmed.ncbi.nlm.nih.gov/31751986/
7. Chen, W.; Zhang, S.; Deng, Q.; Xu, H. (2018). Probing of Sub-Picometer Vertical Differential Resolutions Using Cavity Plasmons. Nature communications. https://www.nature.com/articles/s41467-018-03227-7
8. Ghosh, RR.; Dhawan, A. (2021). Integrated Non-Volatile Plasmonic Switches Based on Phase-Change-Materials and Their Application to Plasmonic Logic Circuits. Scientific reports. https://www.nature.com/articles/s41598-021-98418-6
9. Zhang, G.; Jia, S.; Gu, Y.; Chen, J. (2019). Brightening and Guiding Single‐Photon Emission by Plasmonic Waveguide–Slit Structures on a Metallic Substrate. Laser & Photonics Reviews. https://onlinelibrary.wiley.com/doi/abs/10.1002/lpor.201900025
10. Ng, C.; Wesemann, L.; Panchenko, E.; Song, J.; Davis, T. J.; Roberts, A.; Gómez, D. E. (2019). Plasmonic near‐Complete Optical Absorption and Its Applications. Advanced Optical Materials. https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201801660
11. Shelby, RA.; Smith, DR.; Schultz, S. (2001). Experimental Verification of a Negative Index of Refraction. Science. https://www.science.org/doi/10.1126/science.1058847
12. Fang, N.; Lee, H.; Sun, C.; Zhang, X. (2005). Sub-Diffraction-Limited Optical Imaging with a Silver Superlens. Science. https://pubmed.ncbi.nlm.nih.gov/15845849/
13. Duan, H.; Wang, T.; Su, Z.; Pang, H.; Chen, C. (2022). Recent Progress and Challenges in Plasmonic Nanomaterials. Nanotechnology Reviews. https://www.degruyter.com/document/doi/10.1515/ntrev-2022-0039/html?lang=en&srsltid=AfmBOopjN_M2f7dYAPFUNO8UWf3XwMxhm7d6cq0FDJtWCdUS3rT2lEHT
