Abstract
In order to exploit gallium’s (Ga) rich polymorphism in the design of phase-change plasmonic systems, accurate understanding of the dielectric function of the different Ga-phases is crucial. The dielectric dispersion profiles of those phases appearing at atmospheric pressure have been reported in the literature, but there is no information on the dielectric function of the high-pressure Ga-phases. Through first principles calculations we present a comprehensive analysis of the interdependence of the crystal structure, band structure, and dielectric function of two high-pressure Ga phases (Ga(II) and Ga(III)). The plasmonic behavior of these high-pressure Ga-phases is compared to those stable (liquid- and α-Ga) and metastable (β-, γ- and δ-Ga) at atmospherics pressure. This analysis can have important implications in the design of pressure-driven phase-change Ga plasmonic devices and high-pressure SERS substrates.
Highlights
Metallic gallium (Ga) undergoes a solid-liquid phase transition near room temperature, and recent research into its wide polymorphism has identified a variety of applications for controlled Ga phase changes
All the calculations have been performed with the Generalized Gradient Approximation (GGA), using the exchange-correlation potential parametrized by Perdew-Burke-Ernzerhof (PBEsol) method [27], to simulate electronic exchange and correlations
Inspired by the recent use of liquid-Ga hemispheres as SERS substrates [43,44], we analyzed the near-field enhancement produced by Ga(II) and Ga(III) hemispheres on a sapphire substrate to evaluate their applicability to high pressure SERS
Summary
Metallic gallium (Ga) undergoes a solid-liquid phase transition near room temperature, and recent research into its wide polymorphism (see Fig. 1) has identified a variety of applications for controlled Ga phase changes. Ga can exist in six different phases at atmospheric pressure (Fig. 1a), i.e., above 302.7 K Ga is a liquid metal (l-Ga, stable phase), and just below that temperature α-Ga is the solid thermodynamically stable phase [1], at lower temperatures there are the additional Ga-phases: β-Ga with a melting temperature of Tm = 256.8 K [2], γ-Ga (Tm = 237.6 K) [3], -Ga (Tm = 244.6 K) [4], and δ-Ga (Tm = 253.8 K) [5] This polymorphism characteristic of Ga, along with its recently demonstrated plasmonic response from the near-infrared to the UV [6,7] and its low tendency to oxidize [8], has been exploited for phase-change memories [9], reversible light-induced switching [10], phase-change systems for non-linear optics as described by Zheludev et al in Ref.
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