DFT-Based Approach Enables Deliberate Tuning of Alloy Nanostructure Plasmonic Properties

Abstract

Alloying of noble metals is lately being explored as a way to tune the optical and plasmonic properties of metal nanostructures. In order to rationally modulate properties by alloying, there is a need to fundamentally understand how the composition affects them. This work demonstrates that deep insights, useful for tailoring of noble alloy plasmonic and optical properties, can be gained by a low-cost approach based on density functional theory (DFT). We show in this work that the PBE functional, commonly used for calculation of alloy optical properties, can largely underestimate and in some cases even fail to predict a plasmonic response of an alloy. We propose the use of the GLLB-SC functional as a same-cost alternative and demonstrate it has an overall better performance than PBE for alloyed nanoparticles, thin films, and bulk alloys. The evolution of optical properties with composition range in the UV/Vis region is explained by connecting the alloy composition, band structure, and the resulting dielectric function. Additionally, an emergent property of alloying in the form of strong optical losses due to interband transitions in the IR region is identified and its origin is elucidated.

Recent Developments in Plasmonic Alloy Nanoparticles: Synthesis, Modelling, Properties and Applications

“…[112,113] Recently, Bubas and Parramon proposed an approach based on the GLLB-SC functionals to calculate the OCs of AuÀ Ag, AuÀ Cu, AgÀ Cu and PdÀ Au systems, which represent a satisfactory compromise between computational cost, efficiency and accuracy. [114] They used the GPAW package, based on the projector augmented wave (PAW) method, and chose the GBLL-SC functional because of its computational efficiency and the better treatment of d-band electrons compared to other GGA functionals. They computed the OCs of bulk alloy (AuÀ Ag, AuÀ Cu, AgÀ Cu, PdÀ Au) systems and monometallic equivalents within the independent-particle approximation (IPA) and compared the results obtained with LDA, PBE (and its revisions), vdW-DF and GLLB-SC to the experimental reference.…”

“…Recently, Bubas and Parramon proposed an approach based on the GLLB‐SC functionals to calculate the OCs of Au−Ag, Au−Cu, Ag−Cu and Pd−Au systems, which represent a satisfactory compromise between computational cost, efficiency and accuracy [114] . They used the GPAW package, based on the projector augmented wave (PAW) method, and chose the GBLL‐SC functional because of its computational efficiency and the better treatment of d‐band electrons compared to other GGA functionals.…”

Hot Carrier Distribution Engineering by Alloying: Picking Elements for the Desired Purposes

“…Upon folding, states of different energies in a single band end up at the same k -point (vertically above one another), which allows direct transitions between them. Besides that, band degeneracy is broken due to the hybridization with the orbitals of two different elements, which causes “band splitting”loss of degeneracy resulting in several closely spaced and often near-parallel bands. , …”

“…Besides that, band degeneracy is broken due to the hybridization with the orbitals of two different elements, which causes "band splitting"�loss of degeneracy resulting in several closely spaced and often nearparallel bands. 21,32 Since electronic structures of noble metals commonly used in plasmonics such as Ag, Au, and Cu are relatively similar (low-lying d-bands, far below the Fermi level, sp-bands at similar positions), their alloying does not change the DOS a lot (an example shown in Figure 1). However, hot carrier generation is still modulated in different ways, through band splitting and folding, which leads to the generation of hot electrons even at very low energies (IR range) and to a continuous distribution of electrons and holes with energies up to the photon energy above and below the Fermi level.…”

Plasmon-Induced Hot Carriers: An Atomistic Perspective of the First Tens of Femtoseconds

“…An interesting idea is to harness metal alloys. , Recently, in ref , based on theoretical and experimental results, a library of transition metal alloy dielectric functions has been released. The dielectric functions and the electronic structure simulations presented in this reference suggest that tuning the chemical composition of NPs can pave the way to a significant improvement of the HC generation and photocatalytic yields.…”