New Avenues for Anticounterfeiting by Phase Selection and Plasmonic Shifts in Binary Plasmonic Alloy Nanoclusters

Anticounterfeiting decisively relies on tailoring structural colors based on plasmon resonances. The structural color is uniquely determined by the plasmon resonances’ spectral shape and position [1]. For the first time, we are able to directly observe in situ and quantify the onset of different phases and compositional changes in binary alloy plasmon-active silver (Ag)-copper (Cu) nanoclusters due to spinodal decomposition [2]. We are able to tune and establish an advanced Cu-rich core and Ag-rich shell morphology for the alloy clusters in a high-density nanocluster plasmonic multilayer device during sputter deposition of the alloy. In this ground-breaking study we are able to quantify effective diffusion coefficients and to clearly corroborate theoretical assumptions on the phase separation process on the nanoscale in complex alloy self-assembled nanocluster devices: With Cu being the structure-defining component and Ag predominantly in the shell, our findings offer the potential to partially decouple structural (distance) effects and size- and composition-related influences on the plasmon resonance in directly deposited, high-density, organic shell-free cluster layers. With scale effects coming into play, we are thus able to uniquely correlate cluster morphology and composition with the changing optoelectronic properties. Such tunable, plasmon resonance-based structural color paves an unprecedented way for advanced for high-density nanocluster-based anti-counterfeiting.<br/><br/>[1] M. Gensch, M. Schwartzkopf, C. J. Brett, S. J. Schaper, N. Li, W. Chen, S. Liang, J. Drewes, O. Polonskyi, T. Strunskus, F. Faupel, P. Müller-Buschbaum, and S. V. Roth, <i>Correlating Optical Reflectance with the Topology of Aluminum Nanocluster Layers Growing on Partially Conjugated Diblock Copolymer Templates</i>, ACS Appl. Mater. Interfaces <b>13</b>, 56663 (2021).<br/>[2] M. Schwartzkopf, A. Rothkirch, N. Carstens, Q. Chen, T. Strunskus, F. C. Löhrer, S. Xia, C. Rosemann, L. Bießmann, V. Körstgens, S. Ahuja, P. Pandit, J. Rubeck, S. Frenzke, A. Hinz, O. Polonskyi, P. Müller-Buschbaum, F. Faupel, and S. V. Roth, <i>In Situ Monitoring of Scale Effects on Phase Selection and Plasmonic Shifts during the Growth of AgCu Alloy Nanostructures for Anticounterfeiting Applications</i>, ACS Appl. Nano Mater. <b>5</b>, 3832 (2022).