期刊
NANOPHOTONICS
卷 9, 期 2, 页码 533-545出版社
WALTER DE GRUYTER GMBH
DOI: 10.1515/nanoph-2019-0414
关键词
optics; color; surface plasmons; darkfield microscopy
资金
- National Research Foundation (NRF) Competitive Research Programme (CRP) [15-2015-03]
- SUTD Digital Manufacturing and Design (DManD) Centre [RGDM1830303]
We present results on colors of metal disk arrays viewed under a darkfield microscope and show that the darkfield colors can be manipulated independently of the brightfield colors. We investigate the appearance of colors as disks are clustered to form a new array with double the pitch and a basis of four disks. These structures of aluminum disks on aluminum oxide on aluminum have resonances in the visible spectrum, so by arranging them in small tight clusters, a coupled plasmon resonant mode is produced at shorter wavelengths. This feature causes a reflectance minimum and leads to an increase in the gamut of darkfield colors produced. These colors are tuned by changing the size of the disk and the inter-disk gap within the clusters. Interestingly, the intensities of the reflectance peaks also demonstrate good agreement with the Fourier series coefficients for square waves. Polarization-tunable colors are also demonstrated by designing rectangular arrays that have dissimilar periods along the two orthogonal axes of the array, and a four-level security tag is fabricated that encodes images for viewing under brightfield, darkfield (both x and y polarization), and infrared illumination.
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