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|Title:||Role of spectral resonance features and surface chemistry in the optical sensitivity of light-confining nanoporous photonic crystals|
|Citation:||ACS Applied Materials and Interfaces, 2021; 13(12):14394-14406|
|Publisher:||American Chemical Society|
|Laura K. Acosta, Cheryl Suwen Law, Siew Yee Lim, Andrew D. Abell, Lluis F. Marsal and Abel Santos|
|Abstract:||Nanoporous anodic alumina optical microcavities (NAA-μQVs) with spectrally tunable resonance band and surface chemistry are used as model light-confining photonic crystal (PC) platforms to elucidate the combined effect of spectral light confinement features and surface chemistry on optical sensitivity. These model nanoporous PCs show well-resolved, spectrally tunable resonance bands (RBs), the central wavelength of which is engineered from ∼400 to 800 nm by the period of the input anodization profile. The optical sensitivity of the as-produced (hydrophilic) and dichlorodimethylsilane-functionalized (hydrophobic) NAA-μQVs is studied by monitoring dynamic spectral shifts of their RB upon infiltration with organic- and aqueous-based analytical solutions of equally varying refractive index, from 1.333 to 1.345 RIU. Our findings demonstrate that hydrophilic NAA-μQVs show ∼81 and 35% superior sensitivity to their hydrophobic counterparts for organic- and aqueous-based analytical solutions, respectively. Interestingly, the sensitivity of hydrophilic NAA-μQVs per unit of spectral shift is more than 3-fold higher in organic than in aqueous matrices upon equal change of refractive index, with values of 0.347 ± 0.002 and 0.109 ± 0.001 (nm RIU<sup>-1</sup>) nm<sup>-1</sup>, respectively. Conversely, hydrophobic NAA-μQVs are found to be slightly more sensitive toward changes of refractive index in aqueous medium, with sensitivities of 0.072 ± 0.002 and 0.066 ± 0.006 (nm RIU<sup>-1</sup>) nm<sup>-1</sup> in water- and organic-based analytical solutions, respectively. Our advances provide insights into critical factors determining optical sensitivity in light-confining nanoporous PC structures, with implications across optical sensing applications, and other photonic technologies.|
|Keywords:||light confinement; nanoporous anodic alumina; optical sensitivity; photonic crystals; surface chemistry|
|Rights:||© 2021 American Chemical Society|
|Appears in Collections:||Chemistry publications|
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