Shapes, Plasmonic Properties, and Reactivity of Magnesium Nanoparticles

Abstract

Localized surface plasmon resonances have attracted much attention due to their ability to enhance light–matter interactions and manipulate light at the subwavelength level. Recently, alternatives to the rare and expensive noble metals Ag and Au have been sought for more sustainable and large-scale plasmonic utilization. Mg supports plasmon resonances, is one of the most abundant elements in earth’s crust, and is fully biocompatible, making it an attractive framework for plasmonics. This feature article first reports the hexagonal, folded, and kite-like shapes expected theoretically from a modified Wulff construction for single crystal and twinned Mg structures and describes their excellent match with experimental results. Then, the optical response of Mg nanoparticles is overviewed, highlighting Mg’s ability to sustain localized surface plasmon resonances across the ultraviolet, visible, and near-infrared electromagnetic ranges. The various resonant modes of hexagons, leading to the highly localized electric field characteristic of plasmonic behavior, are presented numerically and experimentally. The evolution of these modes and the associated field from hexagons to the lower symmetry folded structures is then probed, again by matching simulations, optical, and electron spectroscopy data. Lastly, results demonstrating the opportunities and challenges related to the high chemical reactivity of Mg are discussed, including surface oxide formation and galvanic replacement as a synthetic tool for bimetallics. This Feature Article concludes with a summary of the next steps, open questions, and future directions in the field of Mg nanoplasmonics.

Plasmonic enhancement of molecular hydrogen dissociation on metallic magnesium nanoclusters

“…With a strong plasmonic response in the UV range, Mg nanoclusters could potentially complement conventional plasmonic materials, which typically absorb in the visible or near UV range. [1][2][3][4]32,35 In order to further characterize the plasmonic behaviour of Mg nanoclusters, we report the homogeneous linewidth (Γ) and lifetime (T 2 ) associated with its plasmonic excitation. The homogeneous linewidth can be calculated by fitting the time-dependent dipole moment response (µ(t)) when the nanostructure is illuminated with a sinusoidal time-dependent electric field as an external perturbation.…”

“…38,40,41,43 This property has been discussed in the literature in the context of hydrogen storage. 32,34,35,39 In the following, we will interpret the predicted optical properties of Mg nanoclusters in the context of plasmonic enhancement of hydrogen dissociative adsorption and associative desorption (hydrogen evolution). In the previous sections, we have shown that LSPR excitation of Mg nanoclusters produces hot electrons with energies of up to 4 eV.…”

“…[1][2][3][4] The plasmonic excitation frequency can be widely tuned by modifying the nanostructure morphology and its chemical environment, [1][2][3][4]8 but is typically limited to wavelengths larger than 400 nm for these specific noble plasmonic metals. In recent years the study of optical and electronic properties of non-standard plasmonic materials such as Al 23,[28][29][30][31] and Mg [32][33][34][35] has gathered increasing interest as they can provide highly cost effective alternatives. Mg nanoclusters emerge as very attractive systems in the context of plasmonics hot-electron effects.…”

“…Mg nanoclusters emerge as very attractive systems in the context of plasmonics hot-electron effects. 32,33,35 Metallic Mg is an earth-abundant element that behaves as a pure plasmonic metal without sp to d interband transitions (like Au and Cu) due to lack of d-electrons in its electronic groundstate band structure.…”

“…36,37 From the point of view of catalysis, metallic Mg exhibits interesting hydrogenation chemistry with high reactivity towards forming hydride compounds (MgH 2 ). 32,35,[38][39][40][41] Mg nanoparticles can switch from a metallic to an insulating state by simple uptake and release of molecular hydrogen. 34,35,39,40 Magnesium can store a large amount of H atoms reaching up to 7.6 % by weight as bulk material representing a promising, efficient and cost-effective alternative to store hydrogen molecules (chemical storage as metal hydride; chemisorption).…”