Abstract
The implementation of metasurface absorbers for advanced sensing applications in the infrared spectral range is gaining prominence. Nevertheless, scale-up is challenging because their subwavelength features require complex fabrication techniques. Here, we present centimeter-sized nanostructured metasurface absorbers, prepared using the nanoporous anodic aluminum oxide template method, which exhibit a high and polarization-insensitive absorptivity at near-infrared wavelengths. Their sensing potential as surface-enhanced Raman spectroscopy substrates is demonstrated by analyzing Raman spectra of methyl parathion pesticides at concentrations as low as 100 ppb. Our results offer a stable, cost-effective, scalable, and uniform solution for metasurface-based molecular detection applications with a high sensitivity.
Highlights
We present near-infrared optical metal-dielectricmetal metasurface absorber (MSA) obtained by a cost-effective, scalable, and highly uniform fabrication method based on nanoporous anodic aluminum oxide (AAO) templates
A slight broadening observed for the experimental absorption peak at d = 95 nm could be attributed to the lower homogeneity of the disk diameter
The Raman peak is still pronounced at a concentration of 0.1 ppm, which is the value recommended by the Collaborative International Pesticides Analytical Council (CIPAC) as the limit of detection for methyl parathion in pesticides
Summary
There is an increased interest in metasurfaces that exhibit a near-unity absorption in a specific electromagnetic spectral range from radio waves to visible light. The first metasurface absorber (MSA) was introduced in 2008 by Landy and co-workers, utilizing a metal-dielectric-metal design and showing an absorptivity of 88% at 11.48 GHz. Since the operational frequency of MSAs has been extended to millimeter waves, terahertz, infrared, and visible spectral ranges. In addition to the particular interest of higher working frequencies, there have been many efforts to explore the functional limits of MSAs by manipulating their absorption band, incident angle and polarization dependence, and frequency tunability. With the richness of their unique fundamental electromagnetic properties, MSAs offer either a wide variety of promising applications in the optical range, such as thermal detectors, surface-enhanced sensing, photocatalysis, and energy harvesting, or possibilities of integrating them into existing devices for performance boosting.. Within the size range of infrared and visible metasurface resonators, whose dimensions are on the order of tens to hundreds of nanometers, electron-beam lithography has been widely applied as the most effective fabrication method.. The standard photolithography in combination with e-beam evaporation has been used to fabricate wafer-scale (2 in.) MSAs, but their operation frequency is limited to the far-infrared regime due to micrometer-sized metasurface units. We present near-infrared optical metal-dielectricmetal MSAs obtained by a cost-effective, scalable, and highly uniform fabrication method based on nanoporous anodic aluminum oxide (AAO) templates. By utilizing this scheme, gold nanodisks could be formed periodically on top of a 4 × 4 cm Al2O3/Al thin film, which functions as a perfect absorber. We demonstrate that this MSA has a high potential to be used as a surface-enhanced Raman spectroscopy (SERS) substrate for probing molecules
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