Electronic, optical, and thermoelectric characteristics of (Ae)xFBiS2 (Ae=Sr, Ba, and x=1.7) layered materials useful in optical modulator devices

The recent discovery of superconductivity behavior in the mother BiS2-layered compounds has captivated the attention of several physicists. The crystal structure of superconductors with alternate layers of BiS2 is homologous to that of cuprates and Fe-based superconductors. The full-potential linearized augmented plane-wave (FP-LAPW) technique was utilized to investigate the electronic structures and density of states in the vicinity of the Fermi energy of SrFBiS2 and BaFBiS2 compounds under the electron carriers doping. The introduction of electron doping (carries doping) reveals that the host compounds SrFBiS2 and BaFBiS2 exhibit features indicative of superconductivity. This carrier doping of SrFBiS2 and BaFBiS2 compounds (electron-doped) has a significant impact on the lowest conduction states near the Fermi level for the emergence of the superconducting aspect. The electron doping modifies and induces changes in the electronic structures with superconducting behavior in (Ae)1.7FBiS2(Ae=Sr,Ba) compounds. A Fermi surface nesting occurred under the modification of electrons (carriers) doping in the host compounds SrFBiS2 and BaFBiS2. Furthermore, the optical characteristics of the carrier-doped SrFBiS2 and BaFBiS2 compounds are simulated. Due to the anisotropic behavior, the optical properties of these materials based on BiS2 demonstrate a pronounced polarization dependency. The starting point at zero photon energy in the infrared region is elucidated by considering the Drude features in the optical conductivity spectra of SrFBiS2 and BaFBiS2 compounds, when the electron carriers doping is applied. It was clearly noticed that the spin-orbit coupling (SOC) influences the electronic band structures, density of states, Femi surface, and optical features because of the heavy Bismuth atom, which may disclose fascinating aspects. Further, we conducted simulations to assess the thermoelectric properties of these mother compounds. The two BiS2-layered compounds could be suitable for practical thermoelectric purposes and are highlighted through assessment of electrical conductivity, thermal conductivity, Seebeck coefficient, and power factor. As a result, we propose that the mechanisms of superconducting behavior in BiS2 family may pave new avenues for investigating the field of unconventional superconductivity. It may also provide new insights into the origin of high-Tc superconductivity nature.

Combining rigid and deformable groups to construct a robust birefringent crystal for compact polarization components

There is a pressing demand for the development of novel birefringent crystals tailored for compact optical components, especially for crystals exhibiting large birefringence across a range of temperatures. This has commonly been achieved by introducing various deformable groups with high polarizability anisotropy. In this study, we combined both rigid and deformable groups to synthesise a new birefringent crystal, Al2Te2MoO10, which demonstrates an exceptional birefringence value of 0.29@550 nm at room temperature. Not only is this higher birefringence than that of commercial crystals, but Al2Te2MoO10 exhibits excellent birefringence stability over a wide temperature range, from 123 to 503 K. In addition, the first-principles theory calculations and structural analyses suggest that although the rigid AlO6 groups do not make much contribution to the prominent birefringence, they nonetheless played a role in maintaining the structural anisotropy at elevated temperatures. Based on these findings, this paper proposes a novel structural design strategy to complement conventional approaches for developing optimal birefringent crystals under various environmental conditions.

High dielectric transparent polymer composite with well-organized carboxymethyl cellulose microfibers in silicon elastomer fabricated under direct current electric field

The combination of transparency, high dielectric permittivity, biocompatibility and flexibility is highly desired in the embedded capacitors. Herein, we show that assembling biodegradable sodium carboxymethyl cellulose (CMC) microfibers in biocompatible silicon elastomer (PDMS) under direct current (DC) electric field enables the production of high dielectric constant composite film with above desired properties. This process leads to the formation of columns of CMC microfibers spanning across the thickness direction, thus generating microfiber depleted regions in between fibers and polymer matrix. The as-prepared composite film with CMC (15 wt%) aligned exhibits a remarkable and an almost sevenfold higher dielectric permittivity as compared to that of the film with CMC randomly dispersed (72 vs 11.4, at 100 Hz). This high CMC loading does not compromise the flexibility and optical transmittance. Interestingly, the compression modulus along the thickness direction increases by >20 times from 16.4 MPa (CMC unaligned) to 339.9 MPa (CMC aligned). We demonstrate a facile strategy of fabricating high dielectric materials combining transparency, biocompatibility, flexibility and compression resistant, making the dielectric materials more versatile. This work shows that biomass derived CMC is a promising filler for high dielectric constant polymer composites benefiting from electric field driven construction of ordered micromorphology.

Endoscopic imaging of white matter fiber tracts using polarization-sensitive optical coherence tomography

Polarization sensitive optical coherence tomography (PSOCT) has been shown to image and delineate white matter fibers in a label-free manner by revealing optical birefringence within the myelin sheath using a microscope setup. In this proof-of-concept study, we adapt recent advancements in endoscopic PSOCT to perform depth-resolved imaging of white matter structures deep inside intact porcine brain tissue ex-vivo, through a small, rotational fiber probe. The probe geometry is comparable to microelectrodes currently used in neurosurgical interventions. The presented imaging system is mobile, robust, and uses biologically safe levels of optical radiation making it well suited for clinical translation. In neurosurgery, where accuracy is imperative, endoscopic PSOCT through a narrow-gauge fiber probe could provide intra-operative feedback on the location of critical white matter structures.

LIF spectroscopy of epithelial tissues: Assay of structural changeover due to the cancer progression

Most of the human cancers occur in epithelial tissues containing basic cells with different shapes, and not only do the spectral properties of the tissue pigments alter due to cancer, but the cellular architecture also change. However, in optical diagnosis of the cancerous tissues, attention has been paid to the spectral changeover of native chromophores as bio-markers. Here, we have attempted to assay the structural alterations of the epithelial tissues during the cancer progression utilizing Laser induced fluorescence (LIF) spectroscopy as a fast, sensitive and easy-to-use method. In this regard, angular dependence of the LIF spectral features of the healthy and cancerous epithelial tissues (soaked in Rhodamine 6G solution) from three different human organs i. e. uterus, colon and kidney with distinct microstructures have been examined. In general, both wavelength and intensity at the peak of the LIF spectra depend on the tissue orientation and the angle of detection respect to the laser beam direction. Those optical parameters also demonstrate distinctive alterations in different tissues that is explicated based on the morphological alteration of the epithelial cells in each carcinoma type provided by pathology data.

Anisotropic cellulose nanocrystal hydrogel with multi-stimuli response to temperature and mechanical stress

Conventional hydrogels with isotropic polymer networks usually lack selective response to external stimuli and that limits their applications in intelligent devices. Herein, hydrogels with distinctive anisotropic optical characteristics combined with thermosensitivity were prepared through in situ photopolymerization. Self-assembled cellulose nanocrystals (CNCs) with chiral nematic ordered structure were embedded in polyethylene glycol derivatives/polyacrylamide polymer networks. The arrangement of CNCs showed a strong dependence on the self-assembly angle and standing time, enabling the fabrication of hydrogels with customizable CNCs arrangements. Increasing the self-assembly angle from 0° to 90° changed the CNCs arrangement from chiral nematic to symmetrical nematic order which, together with CNCs dynamic arrangement from isotropic to annealed chiral nematic phase at longer standing time, provided versatile ways to produce CNCs hydrogels with tunable anisotropic properties. In addition, the obtained hydrogel displayed reversible temperature and compression response, showing excellent promise to be used as soft mechanical stress and temperature sensors or novel anti-counterfeiting materials.

Quasiphonon polaritons

Mid-infrared reflection spectra of c- and m-plane bulk AlN show a reststrahlen band related to the formation of phonon polaritons. However, it is worth noting that there are additional hump- and spike-shaped peaks in the spectra, which cannot be explained by the phonon-polaritons model applicable to optically isotropic crystals. Here, considering the existence of quasiphonons in wurtzite crystals, we suppose that the extra peaks result from the generation of quasiphonon polaritons (QPPs) induced by the coupling between photon and quasi-transverse optical phonon. On the basis of this point, a QPPs model applicable to optically anisotropic wurtzite crystals is developed, which successfully explains the reststrahlen band of bulk AlN. Besides, on the ground of our model, a series of reststrahlen band of bulk AlN under various configurations is also predicted and presented.

Strain Engineering on the Electronic and Optical Properties of WSSe Bilayer

Controllable optical properties are important for optoelectronic applications. Based on the unique properties and potential applications of two-dimensional Janus WSSe, we systematically investigate the strain-modulated electronic and optical properties of WSSe bilayer through the first-principle calculations. The preferred stacking configurations and chalcogen orders are determined by the binding energies. The bandgap of all the stable structures are found sensitive to the external stress and could be tailored from semiconductor to metallicity under appropriate compressive strains. Atomic orbital projected energy bands reveal a positive correlation between the degeneracy and the structural symmetry, which explains the bandgap evolutions. Dipole transition preference is tuned by the biaxial strain. A controllable transformation between anisotropic and isotropic optical properties is achieved under an around - 6%~- 4% critical strain. The strain controllable electronic and optical properties of the WSSe bilayer may open up an important path for exploring next-generation optoelectronic applications.

Large Optical Anisotropy in Two-Dimensional Perovskite [CH(NH2)2][C(NH2)3]PbI4 with Corrugated Inorganic Layers

Optical anisotropy plays an indispensable role in a variety of optical components. Organic halide perovskites often rely on artificially oriented nanostructures to enhance optical anisotropy due to their in-plane isotropic crystal structure, which results in unnecessary optical losses and fabrication difficulties. Here, we report the large optical anisotropy in two-dimensional perovskite [CH(NH₂)₂][C(NH₂)₃]PbI₄ crystals. Without specially designing their morphology, we achieved a large photoresponse linear dichroic ratio of 2 and a photoluminescence linear dichroic ratio of 4.7. Furthermore, we identified that the polarization orientation is parallel to the corrugated inorganic layers on every crystal plane by density functional theory calculations. The anisotropy of the ab-plane and ac-plane changes in opposite trend with temperature, suggesting that the perovskite can selectively generate polarized light or unpolarized light from different crystal planes by tuning the temperature. Our studies provide a new platform toward two-dimensional perovskite-based optical polarization devices.

Differential Mueller matrix imaging of partially depolarizing optically anisotropic biological tissues

Since recently, a number of innovative polarization-based optical imaging modalities have been introduced and extensively used in various biomedical applications, with an ultimate aim to attain the practical tool for the optical biopsy and functional characterization of biological tissues. The techniques utilize polarization properties of light and Mueller matrix mapping of microscopic images of histological sections of biological tissues or polycrystalline films of biological fluids. The main drawback of currently developed laser polarimetry approaches and Mueller matrix mapping techniques is poor reproducibility of experimental data. This is due to azimuthal dependence of polarization and ellipticity values of most matrix elements to sample orientation in respect to incidence light polarization. Current study aims to generalize the methods of laser polarimetry for diagnosis of partially depolarizing optically anisotropic biological tissues. A method of differential Mueller matrix mapping for reconstruction of linear and circular birefringence and dichroism parameter distributions of partially depolarizing layers of biological tissues of different morphological structure is introduced and practically implemented. The coordinate distributions of the value of the first-order differential matrix elements of histological sections of brain tissue with spatially structured, optically anisotropic fibrillar network, as well as of parenchymatous tissue of the rectum wall with an “islet” polycrystalline structure are determined. Within the statistical analysis of polarization reproduced distributions of the averaged parameters of phase and amplitude anisotropy, the significant sensitivity of the statistical moments of the third and fourth orders to changes in the polycrystalline structure of partially depolarizing layers of biological tissue is observed. The differentiation of female reproductive sphere connective tissue is realized with excellent accuracy. The differential Mueller matrix mapping method for reconstruction of distributions of linear and circular birefringence and dichroism parameters of partially depolarizing layers of biological tissues of different morphological structures is proposed and substantiated. Differential diagnostics of changes in the phase (good balanced accuracy) and amplitude (excellent balanced accuracy) of the anisotropy of the partially depolarizing layers of the vagina wall tissue with prolapse of the genitals is realized. The maximum diagnostic efficiency of the first-order differential matrix method was demonstrated in comparison with the traditional methods of polarization and Mueller matrix mapping of histological sections of light-scattering biological tissues.

Toluidine blue staining for cell and tissue biology applications

Toluidine blue (TB) staining either alone or in association with other methodologies has the potential to answer a variety of biological questions regarding the human, animal and plant tissues or cells. In this brief review, we not only report the primary use of TB to detect the anionic substrates and availability of their binding sites, but also unveil the resulting applications of TB staining in biological research. Among these applications, the uses of TB staining to identify the changes in chromatin DNA-protein complexes, nucleolus location, and extracellular matrix proteoglycan complexes associated with different physiological and pathological events are described. The usefulness of TB staining to monitor the effects elicited by environmental insults on chromatin and intercalation of drugs into the DNA is also included.