In recent years, nanoparticle plasmonics has emerged as an exciting field of research, promising applications in photovoltaics, biological and chemical sensing, and more recently in photocatalysis. The promise of plasmonics emerges from control over manipulation of light on a subwavelength scale, a regime in which nature operates. Currently, most efforts focused on developing plasmonic applications employ the well-studied nanoparticles of silver and gold. Not only are these materials expensive, they are also prone to oxidation over time.

Theory suggests that magnesium is a suitable metal for plasmonic applications. A few reports on the synthesis of magnesium nanoparticles do exist; however, there are no reports on the fundamental understanding of their plasmonic properties until now. Reporting in a recent issue of Nano Letters, the research team of John Biggins, Sadegh Yazdi, and Emilie Ringe has united theory and experiment to synthesize and characterize the plasmonic properties of magnesium nanoparticles.

“It is really exciting that we are able to add a new metal in the plasmonics toolbox. And, much to everyone’s surprise, it is a really viable option as it is remarkably stable in air owing to a self-limiting oxide layer,” says Ringe, a lecturer in the Department of Materials Science and Metallurgy and the Department of Earth Sciences at the University of Cambridge. The formation of a thin, yet complete, oxide layer—as evidenced by chemical composition mapping—renders the nanoparticle solutions stable for many months.

Although aluminum has emerged as another cost-effective metal for plasmonics, it is not suitable for broad-spectrum applications. “[It] is intrinsically lossy in the visible range, and does not sustain high-quality plasmons in the near-IR, limiting its ability to trap light and sunlight. What we show in this paper is that magnesium is a good plasmonic material across the UV, Vis, and NIR,” Ringe says.

“[Magnesium] exhibits strong metallic response in the UV wavelength range and shows the ability for reversible hydrogenation. These features make magnesium an attractive constituent material for plasmonic sensing and encryption device designs,” says Alexandra Boltasseva, professor of electrical and computer engineering at Purdue University, who was not involved in this study. “The novelty of this work reporting on realization of magnesium nanoparticles is in the synthesis of the hexagonal Mg nanoparticles that support strong localized surface plasmon resonances across a broad, UV-Vis-NIR spectral range. The proposed large-scale synthesis approach combined with non-toxicity of Mg could make these nanoparticles a promising platform for bio-plasmonics, document security, and dynamic, switchable plasmonic colors,” she says.

The researchers were able to use transmission electron microscopy to characterize the size distribution of the synthesized nanoparticles, while chemical composition mapping on cross-sections of the nanoparticles allowed the team to characterize the oxide growth. Simulations based on the measured dimensions resulted in scattering spectra which closely resembled experimentally collected single particle dark-field scattering spectra. Moreover, electron energy loss measurements allowed for mapping of different localized surface plasmon modes that also matched theoretical results (see figure).

Now that the material has been characterized for its plasmonic properties, Ringe and her team want to integrate this material into various applications. “This is only the start of this effort in my group,” Ringe says; “now that we have made this exciting discovery, we will be developing this technology, from the synthesis all the way to the utilization in sensing and photocatalysis.”

Read the abstract in Nano Letters.