Alloying: A Platform for Metallic Materials with On-Demand Optical Response

Abstract

CONSPECTUS: Metallic materials with engineered optical properties have the potential to enhance the performance of energy harvesting and storage devices operating at the macroand nanoscale, such as solar cells, photocatalysts, water splitting, and hydrogen storage systems. For both thin films and subwavelength nanostructures, upon illumination, the coherent oscillation of charge carriers at the interface with a dielectric material gives rise to resonances named surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR), respectively. These resonances result in unique light absorption, scattering, and transmission responses over the electromagnetic spectrum, which, in turn, can be exploited to tailor the behavior of active metallic components in optoelectronic devices containing Ag, Au, Cu, Al, Mg, among other metals. The wavelength in which the resonances occur primarily depends on the metal itself (i.e., the dielectric function or permittivity), the dielectric medium surrounding the metals, and the size, geometry, and periodicity of the metallic nanostructures. Nevertheless, the aforementioned parameters allow a limited modulation of both SPP and LSPR over a narrow window of frequencies. To overcome this constraint, we have proposed and realized the alloying of metals via physical deposition methods as a paradigm to almost arbitrarily tuning their optical behavior in the UV-NIR, which leads to permittivity values currently not available. Our approach offers an additional knob, chemical composition, to engineer light-matter interactions in metallic materials. This Account highlights recent progress in using alloying as a pathway to control the optical behavior of metallic thin films and nanostructures for energy harvesting and storage applications, including (photo)catalysis, photovoltaics, superabsorbers, hydrogen storage, among other systems. We choose to primarily focus on the optical properties of the metallic mixtures and in their near-to far-field responses in the UV-NIR range of the spectrum as they represent key parameters for materials' selection for the devices above. By alloying, it is possible to obtain metallic materials with LSPR not available for pure metals, which can enable the further control of the electromagnetic spectrum. First, we discuss how the permittivity of binary mixtures of coinage metals (Au, Ag, and Cu) can be tailored based on the chemical composition of their pure counterparts. Second, we present how novel metallic materials can be designed through band structure engineering through density functional theory (DFT), a paradigm that could benefit from artificial intelligence methods. Concerning alloyed thin films, we discuss the promise of earthabundant metals and provide an example of the superior performance of AlCu in superabsorbers. In the realm of nanostructures, we focus the discussion on physical deposition methods, where we provide a detailed analysis of how chemical composition can affect the far-and near-field responses of metallic building blocks. Fina...

In Situ Optical and Stress Characterization of Alloyed PdxAu1–x Hydrides

“…Instead, both the Pd 0.52 Au 0.48 and the Pd 0.73 Au 0.27 alloys have a higher n than pure Pd across the entire wavelength range investigated. The nonlinearity of the optical properties with composition is not unique to the Pd x Au 1– x system but is also present in the properties of other noble-metal alloys . The addition of Pd to PdAu results in a nonmonotonic and dramatic increase of the valence band at the Γ point .…”

“…The alloying of different metals to finely tune optical and material properties has allowed for great advancements in a wide variety of applications from plasmonic sensors to catalysts. − Alloying creates opportunities to improve the material characteristics beyond that of the pure metal components. Furthermore, one can combine the desirable optical and structural properties from different metals into a single alloy.…”

Anisotropic optical response of gold-silver alloys

“…Likewise, for the valence band, we observe a band split of order of 10 −3 eV with no significant impact on the optical properties. 33 The optical response of the bimetallic systems are direct dependent on their chemical composition 10,21,36 . For instance, in energy-dependent reflectance measurements one can clear see an 4/17 abrupt reduction of the spectra transitioning from the ultra-violet around 3.5 eV (Ag) to the visible around 2 eV (Au) 23 .…”

“…In the last decade, the rapid progress of the plasmonic field occurred due to the advance of new techniques of fabrication and characterization of pure metallic structures 4,8 . More recently, a change of paradigm driven by the maturing of nanofabrication methods and the systematic analysis of alloyed nanostructured systems [9][10][11] resulted in the rise of applications of this novel system as plasmonic tweezers 12 , hydrogen sensors 13 , photocatalystis 14 , and bio-sensors 15 .…”

“…The complex permittivity of materials is directly related to their optical properties. The control of the permittivity through alloying allowed the engineering of surface plasmon polariton (SPP) resonances, diversifying and increasing the efficiency of devices such as sensors, nanoscale lasers, and solar cells 10,16,17 .…”