Abstract
Tailoring of plasmon resonances is essential for applications in anticounterfeiting. This is readily achieved by tuning the composition of alloyed metal clusters; in the simplest case, binary alloys are used. Yet, one challenge is the correlation of cluster morphology and composition with the changing optoelectronic properties. Hitherto, the early stages of metal alloy nanocluster formation in immiscible binary systems such as silver and copper have been accessible by molecular dynamics (MD) simulations and transmission electron microscopy (TEM). Here, we investigate in real time the formation of supported silver, copper, and silver–copper-alloy nanoclusters during sputter deposition on poly(methyl methacrylate) by combining in situ surface-sensitive X-ray scattering with optical spectroscopy. While following the transient growth morphologies, we quantify the early stages of phase separation at the nanoscale, follow the shifts of surface plasmon resonances, and quantify the growth kinetics of the nanogranular layers at different thresholds. We are able to extract the influence of scaling effects on the nucleation and phase selection. The internal structure of the alloy cluster shows a copper-rich core/silver-rich shell structure because the copper core yields a lower mobility and higher crystallization tendency than the silver fraction. We compare our results to MD simulation and TEM data. This demonstrates a route to tailor accurately the plasmon resonances of nanosized, polymer-supported clusters which is a crucial prerequisite for anticounterfeiting.
Highlights
The tuning of plasmon resonances has important applications in biosensor devices[1−5] and photovoltaics[6,7] because the plasmon resonance strongly depends on the cluster size, arrangement, the materials used, and their composition.[8]
We present a combined in situ study using grazingincidence small- and wide-angle X-ray scattering (GISAXS/ GIWAXS) and UV−vis spectroscopy during sputter deposition to observe in real-time and quantitatively the alloy cluster formation and phase separation of the immiscible Ag−Cu binary system during growth on poly(methyl methacrylate) (PMMA) thin films
We present here the results of the combined time-resolved GISAXS/GIWAXS and in situ sputter deposition experiments on the three investigated systems on PMMA: Ag, Cu, and Ag42Cu58
Summary
The tuning of plasmon resonances has important applications in biosensor devices[1−5] and photovoltaics[6,7] because the plasmon resonance strongly depends on the cluster size, arrangement, the materials used, and their composition.[8]. We present a combined in situ study using grazingincidence small- and wide-angle X-ray scattering (GISAXS/ GIWAXS) and UV−vis spectroscopy during sputter deposition to observe in real-time and quantitatively the alloy cluster formation and phase separation of the immiscible Ag−Cu binary system during growth on poly(methyl methacrylate) (PMMA) thin films. Scheme 1 illustrates the bottom-up multilayer system and fabrication from a material perspective (spin coating of PMMA from toluene and subsequent sputter deposition of Cu, Ag, and the alloy). This functional stack consisting of metal alloy clusters/PMMA. This is advantageous for experiments involving Cu and CuAg in particular because Cu is prone to oxidation (especially for nanoscale clusters due to their high surface/volume ratio)
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