Abstract
Abstract Nanostructures composed of dielectric, metallic or metalo-dielectric structures are receiving significant attention due to their unique capabilities to manipulate light for a wide range of functions such as spectral colors, anti-reflection and enhanced light-matter interaction. The optical properties of such nanostructures are determined not only by the shape and dimensions of the structures but also by their spatial arrangement. Here, we demonstrate the generation of vivid colors from nanostructures composed of spatially disordered metalo-dielectric (In/InP) nanopillar arrays. The nanopillars are formed by a single-step, ion-sputtering-assisted, self-assembly process that is inherently scalable and avoids complex patterning and deposition procedures. The In/InP nanopillar dimensions can be changed in a controlled manner by varying the sputter duration, resulting in reflective colors from pale blue to dark red. The fast Fourier transform (FFT) analysis of the distribution of the formed nanopillars shows that they are spatially disordered. The electromagnetic simulations combined with the optical measurements show that the reflectance spectra are strongly influenced by the pillar dimensions. While the specular and diffuse reflectance components are appreciable in all the nanopillar samples, the specular part dominates for the shorter nanopillars, thereby leading to a glossy effect. The simulation results show that the characteristic features in the observed specular and diffused reflectance spectra are determined by the modal and light-scattering properties of single pillars. While the work focuses on the In/InP system, the findings are relevant in a wider context of structural color generation from other types of metalo-dielectric nanopillar arrays.
Highlights
The refractive indices for the In and InP substrates were taken from Palik [44] and that for the amorphous InP (a-InP) substrate came from the Adachi database [45]
Changing the period from 250 to 400 nm does not have a dramatic effect on the position of the reflectance dip, while the overall reflectance is influenced to a certain extent (Supplementary material, Figure S3)
We have demonstrated structural colors in reflection from metalo-dielectric (In/InP) disordered nanopillar arrays (DNPA)
Summary
Dyes and pigments are vulnerable to photo bleaching and they can degrade over time In this regard, structural colors are advantageous as their optical properties are mostly governed by the physical and material parameters of the structured media [4,5,6,7,8]. Precise control over the way by which the incident light interacts with nanostructures is necessary to obtain the desired spectral characteristics over the entire visible wavelength range. This can be achieved through specific choices of the material properties (e.g. refractive index, absorption) and geometrical designs for the nanostructures (e.g. dimensions, shape and spatial arrangement).
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