Optical Characterization of Ultra-Thin Films of Azo-Dye-Doped Polymers Using Ellipsometry and Surface Plasmon Resonance Spectroscopy

Andam, Najat; Refki, Siham; Ishitobi, Hidekazu; Inouye, Yasushi; Sekkat, Zouheir

doi:10.3390/photonics8020041

Cited by 14 publications

(11 citation statements)

References 63 publications

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“…Note that the slope p = 178 of the slow rate k 2 = 0.35 k vs X ′ yields ϕ tc 633.8 nm = 0.11 ± 0.01, confirming that the double exponential with the rates k 1,2 is appropriate for describing PIB dynamics and measuring reaction parameters, such as ϕ , ε trans 632.8 nm = 4.46 × 10 3 L mol –1 cm –1 (σ trans 632.8 nm = 1.7 × 10 –17 cm 2 molecule –1 ) …”

Section: Introductionmentioning

confidence: 64%

Efficient Surface Structuring of Photomechanical Solid Polymers by Near-Zero Light Absorption

2023

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Mechanics enabled by photon absorption generates work from materials and is perhaps one of the most important applications of light-active matter, which mediates an intensity-tostress transduction and moves in intensity gradients. Photomechanics can be put at work in surface structuring of materials, which has applications in several areas of science and engineering including photonics and biology and medicine. We demonstrate that photosensitive materials can be unexpectedly micro-and nanotextured by single-step irradiation with weakly absorbed lowpower red light. We report highly efficient surface structuring induced by interference patterns of two coherent nonresonant red (wavelength of 632.8 nm), less than 5 mW, laser beams operating in the near-zero absorption tail of azo-polymer films with optical densities in the 0.02−0.09 range, i.e., 80 − 95% light transmission. The heights of the observed structures are comparable to those obtained by resonant absorption, a feature that is counterintuitive and thus never reported to date. Low-and high-energy n − π* and π − π* excitations of the azo dye are equally efficient in inducing isomerization and mass motion of polymers. Our work is of central importance to photomechanics, and to surface texturing in particular, since it demonstrates that efficient material motion can be driven by weekly absorbed, i.e., low-energy excitation, low-power red light, in solid films of polymers well below the glass transition temperature, pointing to possible biological and cost-effective industrial applications.

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Section: Introductionmentioning

confidence: 64%

Efficient Surface Structuring of Photomechanical Solid Polymers by Near-Zero Light Absorption

2023

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“…The pump beam was in diameter and it was centered on the probe beam and irradiated the plasmonic structure from the back perpendicularly to the plane of the structure. The pump wavelength is close to the absorption maximum of the SL and efficiently induces photoisomerization of DR1 10 , 27 , 28 .…”

Section: Methodsmentioning

confidence: 99%

“…Indeed, SPs are highly sensitive to any change of the metal/dielectric interface, i.e. boundary, such as the adsorption of molecules to the conducting surface 8 , 9 , thereby allowing for thin film sensing and characterization 10 , and SPs waves penetrate to different extents, i.e. penetration depths, into metals and dielectrics, allowing for sensing of changes in the refractive index of media thicker than the SPs penetration depths 11 – 15 .…”

Section: Introductionmentioning

confidence: 99%

Plasmonic mode coupling and thin film sensing in metal–insulator–metal structures

Andam

Refki

Hayashi

et al. 2021

Sci Rep

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Optical sensors based on surface plasmon resonance (SPR) in the attenuated total reflection (ATR) configuration in layered media have attracted considerable attention over the past decades owing to their ability of label free sensing in biomolecular interaction analysis, and highly sensitive detection of changes in refractive index and thickness, i.e. the optical thickness, of thin film adsorbates (thin film sensing). Furthermore, SPR is highly sensitive to the refractive index of the medium adjacent to the bare metal, and it allows for bulk sensing as well. When deposited at the metal/air interface, an adsorbed layer disturbs the highly localized, i.e. bound, wave at this interface and changes the plasmon resonance to allow for sensing in angular or wavelength interrogation and intensity measurement modes. A high degree of sensitivity is required for precise and efficient sensing, especially for biomolecular interaction analysis for early stage diagnostics; and besides conventional SPR (CSPR), several other configurations have been developed in recent years targeting sensitivity, including long-range SPR (LRSPR) and waveguide-coupled SPR (WGSPR) observed in MIM structures, referred here to by MIM modes, resulting from the coupling of SPRs at I/M interfaces, and Fano-type resonances occurring from broad and sharp modes coupling in layered structures. In our previous research, we demonstrated that MIM is better than CSPR for bulk sensing, and in this paper, we show that CSPR is better than MIM for thin film sensing for thicknesses of the sensing layer (SL) larger than 10 nm. We discuss and compare the sensitivity of CSPR and MIM for thin film sensing by using both experiments and theoretical calculations based on rigorous electromagnetic (EM) theory. We discuss in detail MIM modes coupling and anti-crossing, and we show that when a thin film adsorbate, i.e. a SL), is deposited on top of the outermost-layer of an optimized MIM structure, it modifies the characteristics of the coupled modes of the structure, and it reduces the electric field, both inside the SL and at the SL/air interface, and as a result, it decreases the sensitivity of the MIM versus the CSPR sensor. Our work is of critical importance to plasmonic mode coupling using MIM configurations, as well as to optical bio- and chemical-sensing.

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“…The Lorentz oscillator model satisfies the Kramer-Kronig (KK) causality relations. Some authors [8,9] have used Lorentz oscillator models for dispersion relations for azo-dyes. The Lorentz oscillator model can produce realistic absorption frequencies and amplitudes.…”

Section: Introductionmentioning

confidence: 99%

“…The Lorentz oscillator model can produce realistic absorption frequencies and amplitudes. However, as the Lorentz oscillator model tends to predict tails with slower decays, the fitting to the absorption data is poor away from the absorbance peaks [9,10].…”

Section: Introductionmentioning

confidence: 99%

Optical characterization of dyed liquid crystal cells

Addai1¹,

Xiao²,

Zheng³

et al. 2022

Preprint

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The guest-host liquid crystal display, first proposed in 1968, relies on controlling the orientation of dichroic dyes dissolved in a nematic liquid crystal host. Controlling the orientation of the liquid crystal and of the dissolved dye with an electric field allows control of the transmittance of the cell. Knowing the dielectric properties at optical frequencies of the dye and liquid crystal mixtures is crucial for the optimal design of guest-host liquid crystal devices. In this work, the dielectric functions of various layers in liquid crystal cells are described by models obeying the Kramers-Kronig relations: the Sellmeier equation for transparent layers and causal Gaussian oscillator model for absorbing layers. We propose a systematic way to accurately model the dielectric response of each layer by minimizing the sum of squared differences between the measured transmittance spectrum of a guest-host cell in the near-UV/vis range and the prediction of the transmittance of the modeled multilayer structure. By measuring the transmittance for incident light polarized parallel and perpendicular to the nematic director allows us to separately characterize the two principal dielectric functions of the uniaxial sample. Our results show that the causal Gaussian oscillator model can accurately characterize the dielectric functions of dyes in liquid crystals.

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Optical Characterization of Ultra-Thin Films of Azo-Dye-Doped Polymers Using Ellipsometry and Surface Plasmon Resonance Spectroscopy

Cited by 14 publications

References 63 publications

Efficient Surface Structuring of Photomechanical Solid Polymers by Near-Zero Light Absorption

Efficient Surface Structuring of Photomechanical Solid Polymers by Near-Zero Light Absorption

Plasmonic mode coupling and thin film sensing in metal–insulator–metal structures

Optical characterization of dyed liquid crystal cells

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