Abstract
We report a simple and scalable method for the fabrication of spiral-type chiral plasmonic oligomers based on the stepwise colloid sphere lithography technology. Through carefully adjusting the azimuthal angle Φ of polystyrene (PS) sphere array monolayer and the deposition thickness kn, the chiral plasmonic oligomers composed of four achiral particles can be successfully fabricated on a desired substrate. And their chiral sign, i.e., left-hand or right-hand, is dependent on the anticlockwise or clockwise deposition sequence of the achiral particles. The measured results show a large chiroptical resonance in the visible region, and this resonance can be easily adjusted by using different sizes of PS spheres. Our in-depth theoretical and experimental researches further reveal that the obtained chiral plasmonic oligomers are indeed a kind of quasi-three-dimensional chiral nanostructures, which own a three-dimensional geometrical morphology, but with nonreciprocity chiroptical effect. The ease and scalability (>1 cm2) of the fabrication method make chiral plasmonic oligomers promising candidates for many applications, such as chiral biosensor and catalysis.
Highlights
According to Lord Kelvin, any geometrical figure or group of points is defined as chiral if its mirror image cannot be made to coincide with itself [1]
The Nikon Eclipse Ti-U atomic force microscopy (AFM) has been used to verify the 3D geometric morphology of the quasi-3D chiral plasmonic oligomers (CPO), and the obtained AFM images are shown in Fig. 4c, d, where the 3D geometric morphology is well presented
In this paper, we have demonstrated that a kind of quasi-3D CPO can be achieved through the stepwise colloid sphere lithography technology
Summary
According to Lord Kelvin, any geometrical figure or group of points is defined as chiral if its mirror image cannot be made to coincide with itself [1]. Almost all of the important biomolecules, such as proteins, amino acids, and DNA, own the same chirality, i.e., left-hand (LH) and right-hand (RH). The cross coupling between the electric and magnetic dipoles in the chiral medium can break the degeneracy between the helicity eigenmodes of light (i.e., LCP and RCP), leading to an absorption difference (i.e., circular dichroism, CD) or a phase retardation difference (i.e., circular birefringence, CB) for the LCP and RCP.
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