The schematic cross-section of the ODT-coated control MA with dielectric film (c) and MA with dielectric nano pedestal (d) for the plane depicted in (a) and (b). The SEM images of the top view of the control MA array (a) and the tilted view of the MA with.
Introduction
Overview
Outline
In particular, here we use the TCMT analysis to monitor the polaritonic phase response and take into account the experimental results of beam diffraction and beam steering. The electrical dynamic modulation ability of the metasurface was verified via the optical signal of the beam steering response at 10 kHz.
Theoretical Background
- Surface Plasmon Polaritons
- Localized Surface Plasmon Polaritons
- Temporal Coupled Mode Theory
- Intersubband Transition in Quantized Electron Energy State from Quantum Well
- Dielectric Function from Intersubband Transition
- Surface Enhanced Infrared Absorption Spectroscopy
Conceptual schematic of a localized surface plasmon in metal nanoparticles.2 An oscillating electric field induces a coherent collective oscillation of the electron cloud, resulting in an enhancement of the near-electric field near the nanoparticles. The structures of metamaterial absorbers can be well explained by a single-coupled resonator model by TCMT analysis, as schematically shown in Figure 2.3.1 (c).3 TCMT analysis considers a single resonator coupled to input and output electromagnetic (EM) waves. through a single opening, and its energy conservation can be expressed by the following dynamic equations.3, 24.
Plasmon-enhanced Infrared Spectroscopy Based on Metamaterial Absorbers with Dielectric
Introduction
Design of Plasmonic Metamaterial Absorbers with Nanopedestals
The geometrical parameters of the cross-shaped nanoantenna of both structures are available in the caption of Figure 3.2.1. To excite the plasmonic resonance near the absorption wavelengths of the infrared fingerprints of ODT molecules, the upper cross nanoantenna MA with a nanostand requires a longer antenna length than the control MA with a dielectric film due to the lower effective refractive index of the partially removed SiO2 spacer. The longer antenna length required for the nanopod MA provides an effective detection range, which is essential for SEIRA applications.
Schematics for the unit structures for controlling MA with dielectric film (a) and MA with dielectric nanopedestals (b).
Simulation and Calculation of Optical Responses
According to the calculation results shown in Table 3.3.1, the MA structure with nanopedestal can provide a sensing area 2 times larger and integrated near-field intensities 3.2 times larger than that of the MA with dielectric film due to the larger geometric dimensions of the cross antennas . This arises from the additional near-field area confined at the top surface of the Au bottom metal backplane and the bottom surface of. The plasmonic resonances of the control MAs and MA structures with nanopedestals are excited near 3400 nm and 3500 nm, respectively.
Calculated sensing area and integrated near-field intensity for unit structure of the control-MA, and nanopedestal-MA, respectively, with lateral undercut depth 80 nm, respectively.
Device Fabrication
Scanning electron microscope (SEM) images for the fabricated control MA with dielectric foil and MA with arrays of dielectric nanostands are shown in Figure 3.4.2. For the MA with nano-frame structures, the SiO2 spacer was spatially etched by 80 nm along the lateral all directions and 50 nm along the vertical direction from the SEM images. Comparison of numerically simulated and measured absorption spectra for MA with arrays of nanopods with different undercut depths or isotropic dry etching times, shown in Figure 3.4.3.
Simulated (a) and experimental (b) absorption spectral shifts of MA with nanopedestal array under different isotropic etching depths and scaling times, respectively.
Experimental Results
The top-to-peak values of the absorbance difference of MA with nanopedestals at two IR fingerprint wavelengths were 4.2 and 3.7 times higher than those of the control structure at 3427 nm, 3509 nm, respectively. Conceptual schematic of the TCMT-based coupling states between the vibrational states of ODT molecules and the plasmonic MAs as the single-gate resonator system. 3.4) Where γa and γb are the absorption loss rate and radiation loss rate of the ODT-coated plasmonic MA, respectively, γ1 and γ2 are the absorption loss rates of asymmetric and symmetric vibrations of the ODT, respectively.
Extracted two coupling rates between the two infrared vibrations of the ODT monolayer and the plasmon resonance of the MA structure through TCMT analysis.
Conclusion
Introduction
The schematic of the proposed SEIRA vertical nanogap MA sensor platform and its unit structure are illustrated in Figure 4.2.1 (a-b). Therefore, the vertical nanogap of MA can be indirectly verified through the blue-shifted reflectance spectrum. Finally, a plasma shear with appropriate conditions was used to form the vertical MA nanogap.
The simulated far-field profiles as a function of polar angle for beam diffraction (a) and selective beam steering (b). The schematic of the coupled oscillator model between the plasmonic nanocavity and the intersubband transition. We experimentally demonstrate the multifunctional capabilities of the electric beam diffraction and the beam steering through the polaritonic phase tuning.
Design of Plasmonic Metamaterial Absorbers with Vertical Nanogap
Simulation and Calculation of Optical Responses
This tendency can be more clearly identified by taking the ratio of the two loss rates (γrad / γabs) as the etching depth changes, as shown in Figure 4.3.1(d). As the depth of the undercut etch continues to increase, the ratio between the two loss rates increases, and consequently the absorption of the three MAs can rise to 0.87 or more according to Equation (4.1). The three MAs have similar absorption levels, but as the spacer thickness decreases, a higher integrated near-field intensity is induced, which also increases linearly with increasing undercut etch depth.
More than 80 strong near-field gains are induced at the corner edges of the top nanoantenna in the three MAs.
Device Fabrication
Measured reflectance spectra for the MA with 30 nm vertical nanogap for different undercut etch times up to 4 min with 1 min step. To fabricate the MAs, the patterned array on the Si master was transferred onto a polyurethane acrylate (PUA) mold film. For the pattern transfer using NIL, the LOR1A pull-down resist (MicroChem) and LV400 resist (UV-curable Si-based resist, Chemoptics) were coated on the deposited metal layers on Si wafer.
Atomic force microscope (AFM) images of MA with a 30 nm vertical nanoslit pattern are shown in Figure 4.4.3. a) AFM can produce a 3D image of MA with a 30 nm vertical nanoslit structure.
Experimental Results
The largest SEIRA signal was identified for MA with 10 nm thick vertical nanogap sample, and the SEIRA sensing signal was observed in the electromagnetically induced transparency (EIT) type at the two wavelengths of ODT molecule fingerprints. We note that the maximum signal of the SEIRA sensor can be observed when the absorption peak of the ODT-coated MA structure coincides with the absorption peaks of the ODT vibration as shown in Figure 4.5.2. For a quantitative analysis of the measured SEIRA sensing signals, physical parameter extraction and spectral fitting were performed from the experimentally measured reflectance spectra of the vertical nanogap ODT-coated MA from the TCMT reflectance model derived from a system coupled to which two vibrational modes of ODT molecules are related to the plasmonic resonance of MAs with vertical nanostep (μ1 ≠ μ2 ≠ 0, cf.
The μi is the coupling rate that reflects the direct optical energy change rate between the plasmonic resonance of the MA and two vibrational modes of an ODT monolayer.
Conclusion
Outlook
Electrically Tunable Beam Manipulation from Intersubband Polaritonic Metasurfaces
Introduction
After patterning the mesa with a size of 400 μm × 400 μm to protect the mesa from a photoresist (PR) mask (AZ5214E, MicroChem.), the background Au and MQW layers were removed by ICP dry etching and wet chemical etching (BOE), respectively. From the measured absorbance, as shown in Figure 5.9 (b), the absorption coefficient αIST was extracted using the following equation.110. 5.4) Where Lmpl = 0.6 μm is the effective multipath pass length through the pattern of the MQW piece. The absorption coefficient (red) spectrum was calculated taking into account the effective multipaths in the MQW from the measured absorbance. c) Real (black) and imaginary (red) parts of the z-component of the dielectric constant for the measured MQWs.
Experimental results and physical analysis of the phase lattice metasurface. a) SEM image of the fabricated one-dimensional lattice metasurface for electric beam diffraction. The red dotted lines represent the position of the polaritonic reflection peaks under linear TM polarized light with change of DC voltages from -3 V to +6 V (V2a = V2b). e) The solid black and red dashed lines indicate reflectance spectra and TCMT fitting curves for phase lattice metasurfaces for 3 conditions of (V2a = V2b = -3 V, 0 V and +6 V), respectively. f) Extracted phase responses of the reflected waves from the metasurface by TCMT analysis. Inset: zoomed-in view of the bottom edge of one superlattice (Γg), where no strain is applied to the left background. Metal insulated 4 grids (orange shading) and 4 grid elements (blue and green shading) are contacted to the left (V3a) and right (V3b) contact surfaces respectively.
Designs of MQWs and Metasurfaces
Simulation and Calculation of Optical Responses
The distance between the red dots indicates the phase difference of 180 degrees for the state V2a = -2 V and V2b = +2 V or vice versa, and the red dashed line indicates an operating wavelength of the beam diffraction. For the condition of V3a = -1 V and V3b = +1 V or vice versa, the distance between the points of the blue dots indicates the phase difference of ±120 degrees from the phase to zero bias, and the dashed blue line indicates an operating wavelength of the beam direction . For beam diffraction simulation, the metasurface is applied to an electrical bias condition of V2a = -2 V and V2b = +2 V.
To simulate the selective beam steering, the metasurface is applied to the electrical bias condition V3a = -1 V and V3b = +1 V (top panel), which achieves a phase difference of ±120 degrees at the operating wavelength of 6.37 μm, effectively supporting the light beam steering response almost on the left side.
Device Fabrication
From left, one-dimensional lattice array, mesa engraved pattern, SixNy. group gap divider and final step with two upper contact pads for the application of various voltage biases.
Experimental Results
It leads to the effective spectral shifts from the negative to positive voltages near the anti-pass region at 6.90 μm being achieved for the condition of V2a = V2b = 0. The |S+⟩ and |S-⟩ are the amplitudes of the incoming and outgoing electromagnetic waves in a single-port system. The total loss rate of a nanocavity can be considered as the sum of the absorption loss rate (γca) and the radiation loss rate (γcr).
Experimental results of selective beam steering by the electrical biases. a) SEM image of the tunable phase gradient metasurface with two metal contact surfaces for applying differential electrical bias.
Conclusion
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H.; Morita, A.; Mawatari, K.; Kitamori, T.; Tanaka, T., Metamaterials-enhanced infrared spectroscopic investigation of nanoconfined molecules by plasmonics-nanofluidics hydride device.
