Wafer-scale Elliptical Nanohole Arrays

Moxtek has leveraged existing capabilities in wafer-scale patterning of sub-wavelength wire grid polarizers into the fabrication of 1D and 2D periodic plasmonic structures. This work will discuss recent results in the 200 mm diameter wafer-scale fabrication of nanohole arrays (NHAs) on a glass substrate. Potential markets include medical diagnostics, forensic testing, environmental monitoring, and food safety.

Specifically, a system composed of elliptical aluminum nanoholes in a hexagonal array is presented (Fig. 1). Such a system is found to exhibit four distinct plasmonic resonance bands, two at the aluminum air interface and two at the glass aluminum interface, which are redshifted with respect to the first two. One resonance at each interface corresponds to an incident polarization along the elongated hole diameter, while the other corresponds to an incident polarization along the shorter hole diameter (Fig. 2), i.e. orthogonal with respect to the former. The general position of these resonances is tuned via the periodicity/hole-to-hole separation.

By varying the aspect ratio of the long and short elliptical hole diameters, one can also tailor the spectral separation of the two orthogonal resonances. This is very useful in surface enhanced fluorescence sensing (SEFS), as it allows for tuning of the resonances such that one overlaps with the excitation band of a fluorophore, while the other overlaps with its emission band. Additionally, the spectral distance between the two bands can be further increased in order to obtain simultaneous SEFS of dyes such as Cy3 and Cy5. Given that nanohole arrays have been shown to offer highly enhanced fluorescence capabilities in commercial microarray platforms¹, such elliptical NHAs can have great implications for dual laser microarray readers, such as those offered by companies such as Agilent, Affymetrix, and Molecular Devices.

[1] S. Attavar, et al., Lab on a Chip, Jan 2011, 11, 841-844.

mgeorge@moxtek.com