High Aspect Ratio Plasmonic Nanotrench Structures with Large Active Surface Area for Label-Free Mid-Infrared Molecular Absorption Sensing

Abstract

Mid-infrared spectroscopy offers unique sensing schemes to detect target molecules thanks to the absorption of infrared light at specific wavelengths unique to chemical compositions. Due to the mismatch of the mid-infrared light wavelength on the order of micron and nanometer size molecules, the interaction between them is typically weak, resulting in small signatures of absorption. Plasmonics can play an important role, enhancing photon−matter interactions by localization of light in small volumes or areas. Thus, it enables the increase of light absorption by molecules providing higher sensitivity. Here, we demonstrate the enhancement of infrared absorption in plasmonic trench structures that function as hyperbolic metamaterials. The metamaterial is composed of plasmonic trenches made of aluminum-doped zinc oxide. We use a 5 nm thick silica layer as a model analyte conformally coated around the plasmonic trenches, which absorbs light with wavelengths around 8 μm. The enhanced absorption is achieved by the interaction of bulk plasmon modes propagating in the trenches with the analyte silica layer on the pronounced extended surface area of the trench structure. Such plasmonic nanotrench structures may serve as a highly sensitive bio-and chemo-sensing platform for mid-infrared absorption spectroscopy.

Progress of infrared guided-wave nanophotonic sensors and devices

“…In order to increase the sensing area, a high aspect ratio plasmonic nanotrench structure was proposed. When the sensing area increases by 14.5 times, an over 9% increase in absorption was reported [180]. On top of sensing, low dimensional materials such as graphene have been introduced into the nanoplamonic systems for enhancing plasmonic absorbers [181], enhancing nonlinear optical effects [182], tuning plasmon-phonon coupling [183], and enabling plasmonic modulation [184].…”

Optics with hyperbolic materials [Invited]

“…In case of semiconductors, multilayer HMM can be made of the same semiconductor but with different doping levels: highly doped layers serve as metal and low doped layers serve as dielectric [15]. Apart from these structures, there are other variations of metal-dielectric multilayer HMMs [64], such as, trench and high aspect ration plasmonic grating structures as a vertical version of multilayer HMM [19][20][21], tubular HMMs [64], fishnet structures that function as Magnetic HMM [65].…”

“…Typically, HMMs contain alternating deeply-subwavelength metal and dielectric features. Among basic HMMs configurations there are multilayer stacks with thin films of subwavelength thicknesses [10][11][12][13][14][15][16], shallow [17,18] and deep nanotrenches structures [19][20][21], and arrays of metal nanowires [22][23][24][25][26][27][28] as illustrated in Fig. 1.…”

“…Large wavevectors also enable high localization of fields at the nanoscale. Field localization is of great interest in such optical applications as waveguiding [31], sensing [13,20,23] and sub-diffraction imaging [32].…”

III-V on CaF2: a possible waveguiding platform for mid-IR photonic devices

“…On one hand, in the field of optoelectronics, the control of material deposition at the atomic scale has revolutionized industrial applications, leading for instance to quantum cascade lasers (QCLs, from the mid-IR up to the THz spectral region) and quantum-well infrared photodetectors (QWIPs); on the other hand, by engineering plasmonic nanostructures, the ability to confine light down to the micro-and nano-scales has further boosted technological applications. To cite a few, enhanced optoelectronics [1] and energy-transfer [2], biochemical spectroscopy [3][4][5][6], electrochemical and photochemical catalysis [7], photovoltaics [8], and more. Novel materials have at last differentiated the possible platforms, allowing great manufacturing flexibility and possibilities [6,9,10].…”