Engineering Optical Absorption in Late Transition-Metal Nanoparticles by Alloying

Abstract

Alloying is an increasingly important handle to engineer the optical properties of metal nanoparticles that find applications in, for example, optical metamaterials, nanosensors, and plasmon-enhanced catalysis. One advantage of alloying over traditionally used particle size and shape engineering is that it, in principle, enables tuning of optical properties without a spectral shift of the localized surface plasmon resonance, which is important for applications where a specific spectral band is targeted. A second advantage is that alloying simultaneously enables adjustment of nanoparticle electronic, chemical, mechanical, and light absorption properties. However, a systematic survey of the impact of alloying on light absorption in metal nanoparticles does not exist, despite its key role in applications that include photothermal therapy, plasmonic heat generation, and plasmon catalysis. Therefore, we present here the systematic screening of the light absorption properties of binary late transition-metal alloys composed of Au, Ag, Cu, Pd, and Pt in the visible spectral range, based on a combination of experiments and finite-difference time-domain simulations, and discuss in detail the underlying physics. By studying these 10 alloy systems for 14 different nanoparticle sizes, we find that most nanoparticles experience a maximal absorption efficiency at around 80 nm particle diameter, and that most alloy systems outperform their neat constituents, with integrated absorption enhancement factors of up to 200%. This highlights the untapped potential of alloying for the engineering of light absorption in nanoparticles, and the presented material screening constitutes a resource for the rational selection of alloy systems with tailored absorption properties.

Interconnected Dimers with Sub-10 nm Nanogaps by Atomic Layer Deposition for Plasmonic Nanojunctions

“…Figure 4 includes FDTD data for a model with a Cu0.6Pd0.4 alloy using dielectric constants taken from recent studies. 37,42 Compared to the pre-ALD FDTD model, the alloy shows a small blue shift from 815 to 810 nm, which is more consistent with experiments. Both simulation peak shapes are skewed by the diffraction edge and in its absence the agreement with the experiment would likely be better.…”

“…The increased extinction is due to Cu layers coating the Pd surface layers, which are both modeled using bulk optical constants. However, alloying of CuPdAu layers is expected during growth due to the high temperatures. , Figure includes a plot replacing the top CuPd layers with a CuPd binary alloy using optical constants for binary alloys of Cu, Pd, and Au available in the literature. , We are not aware of data for ternary systems that could be used to fully model post-ALD nanostructures (CuPdAu), but replacing the top CuPd layers with a Cu0.6Pd0.4 alloy shows a significant reduction of peak height to a value closer to the pre-ALD level. The simulations suggest that intermixing attenuates extinction peaks and that more pure Cu layers may significantly enhance the plasmonic properties of the dimers.…”

A Microshutter for the Nanofabrication of Plasmonic Metal Alloys with Single Nanoparticle Composition Control

“…The general foundation of our approach is the subsequent PVD of thin metal films of different metallic elements through a supported, prefabricated nanolithography mask (Figure a), which after lift-off and thermal annealing of the nanofabricated surface above the recrystallization temperature of the system at hand generates arrays of homogeneously alloyed nanoparticles on the surface, as we earlier have demonstrated using hole-mask colloidal lithography , and have applied widely in the context of plasmonic hydrogen sensors. ,,,,,− The particle dimensions are determined by the mask and their composition by the amount of evaporated alloy constituents, which can be accurately controlled by the thickness of the subsequently evaporated layers (Figure a–g). ,, Here we note that it is important to consider the order of alloy constituent evaporation due to the continuous buildup of material around the rim of the holes in the mask, which results in a continuous shrinking of the diameter of the hole, and thus of the growing nanostructure, where the rate of shrinking depends on the evaporated material …”

Probing Oxidation Mechanisms in Plasmonic Catalysis: Unraveling the Role of Reactive Oxygen Species

“…It should be noted that though the SERS data at 532 nm laser for Au was provided, it holds limited relevance to the discussions because the interband transition between 5d and 6sp leads to a poor SERS sensitivity (Figure S13). − …”