| 1. |
- Men, Arturo, et al.
(författare)
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Spectroscopic ellipsometry study on the dielectric function of bulk Ti2AlN,Ti2AlC, Nb2AlC, (Ti0.5,Nb0.5)2AlC, and Ti3GeC2 MAX-phases
- 2011
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Ingår i: Journal of Applied Physics. - USA : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109, s. 013530-
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Tidskriftsartikel (refereegranskat)abstract
- The averaged complex dielectric function epsilon=() /3 of polycrystalline Ti2AlN, Ti2AlC,Nb2AlC, (Ti0.5,Nb0.5)2AlC, and Ti3GeC2 was determined by spectroscopic ellipsometry coveringthe mid infrared to the ultraviolet spectral range. The dielectric functions of epsilon correspond to the perpendicular and parallel dielectric tensor components relative to the crystallographic c-axis ofthese hexagonal compounds. The optical response is represented by a dispersion model with Drude–Lorentz and critical point contributions. In the low energy range the electrical resistivity is obtainedfrom the Drude term and ranges from 0.48 microOhm m for Ti3GeC2 to 1.59 mucro Ohm m for (Ti0.5,Nb0.5)2AlC.Furthermore, several compositional dependent interband electronic transitions can be identified. Forthe most important ones, Im(epsilon) shows maxima at: 0.78, 1.23, 2.04, 2.48, and 3.78 eV for Ti2AlN;0.38, 1.8, 2.6, and 3.64 eV for Ti2AlC; 0.3, 0.92, and 2.8 eV in Nb2AlC; 0.45, 0.98, and 2.58 eV in(Ti0.5,Nb0.5)2AlC; and 0.8, 1.85, 2.25, and 3.02 eV in Ti3GeC2.
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| 2. |
- Arwin, Hans, 1950-, et al.
(författare)
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Exploring optics of beetle cuticles with Mueller-matrix ellipsometry
- 2014
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Ingår i: Materials Today: Proceedings. - : Elsevier. - 2214-7853.
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Konferensbidrag (refereegranskat)abstract
- Spectroscopic Mueller-matrix ellipsometry at variable angles of incidence is applied to beetle cuticles using a small (50 -100 μm) spot size. It is demonstrated how ellipticity and degree of polarization of the reflected light can be derived from a Mueller matrix providing a detailed insight into reflection properties. Results from Cetonia aurata, Chrysina argenteola and Cotinis mutabilis are presented. The use of Mueller matrices in regression analysis to extract structural and optical parameters of cuticles is briefly described and applied to cuticle data from Cetonia aurata whereby the pitch of the twisted layered structure in the cuticle is determined as well as the refractive indices of the epicuticle and the exocuticle.
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| 3. |
- Arwin, Hans, 1950-, et al.
(författare)
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Exploring polarization features in light reflection from beetles with structural colors
- 2015
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Ingår i: <em>Proc. SPIE </em>9429, Bioinspiration, Biomimetics, and Bioreplication 2015. - : SPIE - International Society for Optical Engineering. - 9781628415322 ; , s. 942909-1-942909-13
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Konferensbidrag (refereegranskat)abstract
- A Mueller matrix of a sample can be used to determine the polarization of reflected light for incident light with arbitrary polarization. The polarization can be quantified in terms of ellipticity, polarization azimuth and degree of polarization. We apply spectroscopic Mueller-matrix ellipsometry at multiple angles of incidence to study the cuticle of beetles and derive polarization features for incident unpolarized light. In particular we address chiral phenomena in scarab beetles, the origin of their structural colors and the observed high degree of circular polarization is discussed. Results from beetles in the Scarabaeidae subfamilies Cetoniinae and Rutelinae are presented including specimens with broad-band silver- or gold-like colors with metallic shine as well as specimens with narrow-band green or red reflectors. The variation of polarization with angle of incidence and occurrence of both left-handed and right-handed polarization from a single species are presented. We also use Mueller-matrix spectra in electromagnetic modeling and show how to determine structural parameters including cuticle layer thicknesses and optical properties. Interference oscillations in the observed spectra are due to allowed optical modes and we show how to develop a structural model of a cuticle based on this effect. Sum decomposition of Mueller matrices measured on a depolarizing cuticle of a beetle is briefly discussed.
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| 4. |
- Arwin, Hans, et al.
(författare)
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Optical Chirality Determined from Mueller Matrices
- 2021
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 11:15
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Tidskriftsartikel (refereegranskat)abstract
- Featured Application The analysis of the transmission of Mueller matrices facilitates studies of optical activity in samples that also exhibit linear anisotropy and depolarization and may have a multilayered structure. Such studies are important for the development of applications in chiroptics. Optical chirality, in terms of circular birefringence and circular dichroism, is described by its electromagnetic and magnetoelectric material tensors, and the corresponding optical activity contributes to the Mueller matrix. Here, spectroscopic ellipsometry in the spectral range 210-1690 nm is used to address chiral phenomena by measuring Mueller matrices in transmission. Three approaches to determine chirality parameters are discussed. In the first approach, applicable in the absence of linear polarization effects, circular birefringence and circular dichroism are evaluated directly from elements of a Mueller matrix. In the second method, differential decomposition is employed, which allows for the unique separation of chirality parameters from linear anisotropic parameters as well as from depolarization provided that the sample is homogeneous along the optical path. Finally, electromagnetic modeling using the Tellegen constitutive relations is presented. The last method also allows structural effects to be included. The three methods to quantify optical chirality are demonstrated for selected materials, including sugar solutions, alpha-quartz, liquid crystals, beetle cuticle, and films of cellulose nanocrystals.
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| 5. |
- del Río, Lía Fernández, 1985-
(författare)
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Optical and Structural Characterization of Natural Nanostructures
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The spectacular biodiversity of our planet is the result of millions of years of evolution. Over this time animals and plants have evolved and adapted to different environments, developing specific behavioral and physical adaptations to increase their chances of survival. During the last centuries human's curiosity has pushed us to study and understand the phenomena and mechanisms of the nature that surrounds us. This understanding has even led to the fields of biomimetics where we seek solutions to human challenges by emulating nature.Scarab beetles (from the insect family Scarabaeidae) have fascinated humans for centuries due to the brilliant metallic shine of their chitin-rich exoskeletons and more recently for their ability to polarize reflected light. This doctoral thesis focuses on the optical characterization of the polarized reflected light from beetles in the Chrysina genus, although beetles from other genera also have been investigated. All the Chrysina beetles studied here share one characteristic, they all reflect left-handed near-circular polarized light. In some cases we also detect right-handed polarized light.We have observed two different main behaviors among the studied Chrysina beetles. Those which are green-colored scatter the reflected polarized light, whereas those with metallic appearance are broadband specular reflectors. We present a detailed analysis of the optical properties with Mueller-matrix spectroscopic ellipsometry combined with optical- and electron-microscopy studies of the exoskeletons. This allow us to create a model that reproduces the optical properties of these structures. The model consists of a chiral (helicoidal) multilayer structure with a gradual change of the pitch and a constant rotation of the optic axis of the layers.Beetles are not alone to have polarizing structures in nature and it is known that many birds and insects have the ability to detect linearly polarized light. This raises the question of whether the polarization properties of the beetles are the direct or indirect results of evolution or just pure coincidence. In order to get a better understanding of the possible reasons of this particular ability, we present a simulation study of different possible scenarios in nature where incoming light could be polarized or unpolarized, and where we consider detectors (eyes) sensitive to different states of polarized light. If the beetles are able to use this characteristic for camouflage, to confuse predators or for intraspecific communication is,however, still unknown and requires further investigation.My research results provide deeper understanding of the properties of light reflected on the beetle's exoskeleton and the nanostructures responsible for the polarization of the reflected light. The developed model could be used as bioinspiration for the fabrication of novel nano-optical devices. My results can also complement biological behavioral experiments aiming to understand the purposes of this specific optical characteristics in nature.
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| 6. |
- Juarez-Rivera, Olga Rubi, et al.
(författare)
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Quantification of Optical Chirality in Cellulose Nanocrystal Films Prepared by Shear-Coating
- 2021
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 11:13
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Tidskriftsartikel (refereegranskat)abstract
- Featured Application Chiral films are susceptible to changes in humidity enabling humidity detectors. They can also be used in optical devices due to their interesting polarization properties. Evaporation-induced-self-assembly is widely used to produce chiral cellulose nanocrystal (CNC) free-standing films reflecting left-handed polarized light. Research on supported chiral CNC films is rather scarce. The reflection and/or transmission of unpolarized light are the most common optical techniques used to characterize the selective reflection of CNC films whereas the use of techniques to quantify chiral properties is limited. Here, the fabrication of chiral CNC films supported on glass substrates by a shear-coating method, as well as a full characterization of their polarization properties, are reported. Optical chirality is evidenced in films, showing a brilliant blue structural color when viewed through a left-handed polarizer and darkness through a right-handed polarizer. Mueller-matrix data in the reflection and transmission modes are used to quantitatively characterize the structural origin of color in the films. The quantification of the linear and circular birefringence, as well as circular dichroism, is performed by analytical inversion of the Mueller matrix data in the transmission mode and regression analysis using Tellegen constitutive equations. The equivalence of the two methods to quantify the structural chirality in CNC films is demonstrated. The swelling of films in water and kinetics during drying is studied by reflection spectroscopy.
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| 7. |
- Juárez-Rivera, Olga R., et al.
(författare)
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Shear-Coated Linear Birefringent and Chiral Cellulose Nanocrystal Films Prepared from Non-Sonicated Suspensions with Different Storage Time
- 2021
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 11:9
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Tidskriftsartikel (refereegranskat)abstract
- Nanocelluloses are very attractive materials for creating structured films with unique optical properties using different preparation techniques. Evaporation-induced self-assembly of cellulose nanocrystals (CNC) aqueous suspensions produces iridescent films with selective circular Bragg reflection. Blade coating of sonicated CNC suspensions leads to birefringent CNC films. In this work, fabrication of both birefringent and chiral films from non-sonicated CNC suspensions using a shear-coating method is studied. Polarization optical microscopy and steady-state viscosity profiles show that non-sonicated CNC suspensions (concentration of 6.5 wt%) evolve with storage time from a gel-like shear-thinning fluid to a mixture of isotropic and chiral nematic liquid crystalline phases. Shear-coated films prepared from non-sonicated fresh CNC suspensions are birefringent, whereas films prepared from suspensions stored several weeks show reflection of left-handed polarized light. Quantification of linear and circular birefringence as well circular dichroism in the films is achieved by using a Mueller matrix formalism.
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| 8. |
- Mendoza-Galvan, Arturo, et al.
(författare)
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Modular Optical Diodes for Circular Polarization Based on Glass-Supported Cellulose Nanocrystal/Polyethylene Glycol Composite Films
- 2023
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Ingår i: ADVANCED PHOTONICS RESEARCH. - : WILEY. - 2699-9293.
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Tidskriftsartikel (refereegranskat)abstract
- Depending on processing methods and conditions, cellulose nanocrystal (CNC) films exhibit linear birefringence or selective Bragg reflection. The latter means reflection of light with left-handed circular polarization (LCP) due to CNC in a helicoidal microstructure of the same handedness. Herein, glass-supported CNC/polyethylene glycol (CNC/PEG) composite films with PEG concentrations in the range of 0-30% w/w with selective Bragg reflection at wavelengths from 440 to 550 nm are prepared. A modular device comprised of a dip-coated birefringent CNC-glass sample sandwiched between two CNC/PEG-glass samples shows different responses to light with LCP and to light with right-handed circular polarization (RCP). The device suppresses selective Bragg reflection from the rear (front) CNC/PEG sample for incident light with LCP (RCP), even when the birefringent film does not meet the condition for a halfwave plate. This behavior resembles the performance of optical diodes for circular polarization. Polarization properties of composite films and optical diodes in terms of degree of polarization and ellipticity are discussed within the Stokes-Mueller formalism. Electromagnetic simulations of Mueller matrices reveal the equivalence of modular and in-tandem film approaches of optical diodes. The handedness of circular polarization of light is reversed by a modular device comprised of a dip-coated birefringent cellulose nanocrystal (CNC) film sandwiched by two CNC/polyethylene glycol composite films. Asymmetric forward and backward propagation of circular propagation resembles an optical diode at wavelengths of selective Bragg reflection.image (c) 2023 WILEY-VCH GmbH
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| 9. |
- Mendoza-Galvan, Arturo, et al.
(författare)
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Mueller matrix spectroscopic ellipsometry study of chiral nanocrystalline cellulose films
- 2018
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Ingår i: Journal of Optics. - : IOP PUBLISHING LTD. - 2040-8978 .- 2040-8986. ; 20:2
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Tidskriftsartikel (refereegranskat)abstract
- Chiral nanocrystalline cellulose (NCC) free-standing films were prepared through slow evaporation of aqueous suspensions of cellulose nanocrystals in a nematic chiral liquid crystal phase. Mueller matrix (MM) spectroscopic ellipsometry is used to study the polarization and depolarization properties of the chiral films. In the reflection mode, the MM is similar to the matrices reported for the cuticle of some beetles reflecting near circular left-handed polarized light in the visible range. The polarization properties of light transmitted at normal incidence for different polarization states of incident light are discussed. By using a differential decomposition of the MM, the structural circular birefringence and dichroism of a NCC chiral film are evaluated.
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| 10. |
- Mendoza-Galván, Arturo, et al.
(författare)
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Mueller matrix spectroscopic ellipsometry study of nanocrystalline cellulose free-standing chiral films
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The astonishing colors exhibited by many birds, insects and other creatures have inspired the development of materials and structures for optical biomimetics. Particularly, aqueous suspensions of cellulose nanocrystals self-assembly in a chiral nematic liquid crystalline phase producing nanocrystalline cellulose (NCC) chiral films after slow evaporation [1] that mimic the left-handed helicoidal arrangement of chitin-protein fibrils found in some beetle cuticles. Owing to the helical structure, left-handed polarized light is selectively reflected from beetle cuticles and NCC chiral films at normal incidence in a spectral band centered at wavelength l0=nL where n is the in-plane average refractive index and L the helix pitch.In this work we report the normalized Mueller matrix (M) of NCC free-standing chiral films measured with a dual rotating compensator ellipsometer (J. A. Woollam Co., Inc.) in the wavelength (l) range 250-1000 nm. Measurements performed on NCC films in reflection at angles of incidence (q) between 20 and 75° are shown in the contour map in Fig. 1 and display the same structure as those found in M of beetle cuticles [2]. At q=20° the band of selective reflection of left-handed polarized light (m41=m14<0) is centered at 520 nm. However, NCC chiral films are characterized by a mosaic-like texture as can be observed in the optical microscopy image inserted on the right panel of Fig. 1. The multidomain texture indicates both random helix direction and pitch distribution. Therefore, measurements in different places show selective reflection bands with different spectral characteristics. On the other hand, the transmission of right-handed polarized light (m41=m14>0) is confirmed from measurements at normal incidence, as observed in the right panel of Fig. 1. Other properties of the transmitted light like degree of polarization, ellipticity, and azimuth are determined for incident unpolarized as well as for different polarizations of incident light. Also, circular dichroism and optical rotation of NCC chiral films are evaluated.References[1] J. A. Kelly et al, Acc. Chem. Res. 47 (2014) 1088−1096.[2] E. Muñoz-Pineda et al, Thin Solid Films (2014) http://dx.doi.org/10.1016/j.tsf.2013.11.144
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