Electro-optical Properties Research Articles

The regulation of electro-optical properties and polymer morphology of polymer-dispersed liquid crystal films with silicon nanostructure

ABSTRACT In this work, the thiol modified silica nanostructures (SiO2-SH) were doped into polymer-dispersed liquid crystal (PDLC) films. The SEM was used to observe the morphology of the polymer microstructure. The electro-optical (E-O) property test was determined by a liquid crystal parameter tester. The SEM images suggested that the SiO2-SH nanoparticles can react with acrylate groups to form the polymer matrix. The saturation voltage decreased by half in the sample when the dosage of the SiO2-SH nanoparticles was 7.5 wt%, which may be due to the reduced anchoring strength of the polymer matrix incorporated with silicon nanoparticles resulting from the lower surface energy and the enhanced steric repulsions of LC droplets and polymer matrix. In addition, the preparation conditions like polymerisation temperatures and UV light intensity also effectively regulated the E-O properties and polymer microstructure of the PDLC film with silica nanostructure. Thus, the results showed that the E-O properties and the polymer morphology of PDLC films with silicon nanostructures can be effectively regulated by doping SiO2-SH nanoparticles and regulating the preparation conditions such as the polymerisation temperature and UV light intensity. This work can provide practical guidance for modulating the properties of PDLC films.

Electro-optical properties of a graphene device on a tip-enhanced Raman spectroscopy system.

This paper investigates the impact of graphene on tip-enhanced Raman spectroscopy (TERS) by developing an electromagnetic characterization of the TERS-graphene device system. The study focuses on the interaction between the tip, the gate voltage, and the sample, specifically examining the electromagnetic effects in the system. Employing a finite element method (FEM)-based simulation model, we meticulously dissect the electric field distribution and the Raman amplification when graphene is introduced into the system. Our findings reveal that including graphene results in a marginal reduction in Raman amplification and a negligible variation in the induced charges within the system. To reinforce our simulations, we employ a simplified capacitor model, which corroborates our results, showcasing negligible induced charges and validating the obtained capacitance values. In this manuscript, we also explore the influence of the setup on the electro-optical properties of graphene, revealing a slight variation in conductivity despite strong changes in chemical potential. Overall, this work contributes to understanding TERS's electromagnetic aspects in the presence of graphene.

Improvement of rewriting time of optically driven liquid crystal display by azo-dye doping

ABSTRACT Optically driving liquid crystal display (ODLCD) uses polarized light field to control the orientation of the liquid crystal, and the display content can be maintained without external electric field, with extremely low power consumption. However, it has a long rewriting time, which is difficult to achieve industrialization. In order to improve the rewriting performance, the influence of the rotational viscosity of the mixed system of azo-dyes (SD1, MR) and nematic liquid crystal (5CB) on the rewriting speed is investigated. The experimental results show that the electro-optical properties of SD1-5CB and MR-5CB have great changes after irradiation by polarized light, among which the SD1-5CB is the best to improve the performance. With the increase of SD1 concentration, the rotational viscosity of SD1-5CB decreases significantly due to the change of cis-trans isomerization of azo-dye, and the optimal doping concentration is 0.5 wt%. In this case, the rewriting time is shortened from 45 s to 11 s, which has the potential to broaden the application of ODLCD.

Integrated self-injection-locked narrow linewidth laser based on thin-film lithium niobate.

Narrow linewidth lasers have a wide range of applications in the fields of coherent optical communications, atomic clocks, and measurement. Lithium niobate material possesses excellent electro-optic and thermo-optic properties, making it an ideal photonic integration platform for a new generation. The light source is a crucial element in large-scale photonic integration. Therefore, it is essential to develop integrated narrow linewidth lasers based on low-loss LNOI. This study is based on the multimode race-track type add-drop microring resonator with multimode interferometric coupler (MMRA-MRR) of the DFB laser self-injection-locked, to achieve the narrowing of linewidth to the laser. The microring external cavity was used to narrow the linewidth of the laser to 2.5 kHz. The output power of the laser is 3.18 mW, and the side-mode suppression ratio is 60 dB. This paper presents an integrated low-noise, narrow-linewidth laser based on thin-film lithium niobate material for the communication band. This is significant for achieving all-optical device on-chip integration of lithium niobate material in the future. It has great potential for use in high-speed coherent optical communication.

Strain effects of stability, transport, and electro-optical properties of novel Ga2TeS monolayer

Strain effects of stability, transport, and electro-optical properties of novel Ga2TeS monolayer

Impact of porous nanoparticles on the electro-optical and dielectric parameters of nematic liquid crystals for display applications: Cost effective approach

In this study, several vital electro-optical and dielectric properties of nematic liquid crystal (NLC) dispersed with porous carbon nanoparticles (PCNP) with three different concentrations were measured. NLCs are birefringent materials. Increased birefringence was observed for NLC-PCNP composites. Dielectric study was also performed for NLC dispersed with PCNPs. Dielectric anisotropy was found to be increased for PCNP dispersed NLC system. Contrast ratio was also measured for NLC dispersed with PCNP, and it is found to be enhanced. Decreased threshold voltage was observed after dispersing PCNP into NLC. High birefringence reduces the cell gap so this work may be applicable in the making of flat panel displays (FPDs).

Modulation of two donors at different sites of the thiophene conjugate bridge for enhancing the electro-optical properties of dual-donor chromophores

We successfully synthesized and systematically investigated novel chromophores Y1, Y2, and Y3 with a dual-donor structure. By adjusting the electron-donating groups at different positions (C3 and C4) of thiophene, we optimized the electro-optical properties of the chromophores. We have optimized thenonlinear optical properties of the chromophores Y1 and Y2, which work with the common FTC hosts, incorporated additional electron-donating groups (DEA) at positions 3 and 4 of thiophene, respectively. At a doping concentration of 20 %, the r33 values for FTC/APC Y1/APC and Y2/APC were 21 p.m. V−1, 56.2 p.m. V−1, and 5.8 p.m. V−1. This indicates that introducing the donor group at positions 2 and 3 of thiophene is more favorable than positions 3 and 4 (Y1 > Y2). And we successfully synthesized Y3 by replacing DEA with a julolidine moiety. At a doping concentration of 30 %, Y3/APC had the greatest r33 of all values at 153.3 p.m. V−1. This demonstrates that introducing DEA at the 3 positions of thiophene in FTC effectively enhances the electron-donating ability, and the additional donor moiety acts as an isolated group, effectively reducing intermolecular dipole-dipole interactions. Furthermore, Y3, with julolidine as the donor group, exhibits stronger electron-donating ability, ultimately leading to enhanced macro EO activity. These findings highlight the potential application of these novel chromophores for potential applications in optoelectronic devices.

Fluorinated liquid crystals and their mixtures giving polar phases with enhanced low-temperature stability

ABSTRACT The fluid ferroelectrics, called ferroelectric nematics (NF), have recently become available by incorporating strong polarity into rod-shaped liquid crystal molecules. Its unprecedented electro-optic properties have created significant excitement in soft matter research. The further progression from the NF phase to the antiferroelectric smectic Z (SmZA) phase, and ultimately to the ferroelectric Smectic A (SmAF) phase, represents a remarkable journey in emerging polar liquid crystal states. Nevertheless, the limitation of NF liquid crystal materials remains one of the prominent obstacles to physical property optimization and optoelectronic device development. In this work, we synthesized a series of fluorinated liquid crystal molecules with large dipole moments and systematically investigated their phase behavior. We designed them with a similar fluorinated aromatic skeleton and varied the structures of the terminal group and bridging bond. We found that the dipole moment density and shape anisotropy significantly affect the phase behavior. Notably, diverse polar liquid crystal phases, including NF, SmZA, and SmAF were observed. Through a multi-component mixing strategy, we successfully achieved a much-expanded temperature window and improved low-temperature stability not only in the NF phase but also in the SmZA and SmAF phases.

Preparation of Progressive Driving Bilayer Polymer-Dispersed Liquid Crystals Possessing a PDLC-PVA-PDLC Structure.

In this paper, the bilayer polymer-dispersed liquid crystals possessing a PDLC-PVA-PDLC structure were prepared by integrating two monolayer PDLCs. The effect of the polymer mesh size on the electro-optical properties of a bilayer PDLC was investigated by comparing the micro-morphology and electro-optical curves under different polymerization conditions. In addition, the impact of doping MoO2 nanoparticles with surface modification on the comprehensive performance of the bilayer PDLC was further researched. The contrast ratio of the bilayer PDLC prepared under the optimal conditions was improved by more than 90% and still maintained excellent progressive driving performance. Therefore, the development of a bilayer PDLC with optimal electro-optical properties will significantly enhance the technological prospects for the application of PDLC-based devices in smart windows, displays, and flexible devices.

Enhanced Electrical and Optical Properties of Bismuth Tantalum Oxide Thin Films through Graphene Oxide Doping.

In this study, a hybrid thin film was fabricated by doping graphene oxide in a bismuth tantalum oxide solution in the sol-gel state. The thin film was produced by a brush-coating process. The graphene oxide doping ratios used were 0, 5, and 15 wt %. In the process of producing the thin film, the prepared sol-gel solution generates contraction forces, owing to the shear stress from the bristles of the brush, forming a microgroove structure. This structure was confirmed through atomic force microscopy, transmission electron microscopy, and energy-dispersive spectroscopy analyses. As a result of line profile analysis in atomic force microscopy, the groove heights of the thin film surface at 0, 5, and 15 wt % doping were 110, 130, and 160 nm, respectively, and the width of all grooves was 1 μm. The width of all thin films was approximately 1 μm, and microgrooves were confirmed. Moreover, the hybrid thin-film formation was confirmed by X-ray photoelectron spectroscopy. By comparing the electrical properties of the bismuth tantalum oxide thin film without graphene oxide doping and the thin film doped with 15 wt % graphene oxide, it was demonstrated that the electro-optical properties increased excellently with graphene oxide doping. Typically, the threshold voltage was reduced by approximately 0.26 V. Based on these observations, graphene oxide doped bismuth tantalum oxide hybrid thin films can be considered as promising candidates for thin-film applications in next-generation displays.

Nematic liquid crystal dispersed with two-dimensional functionalised graphene oxide (fGO): insights on improving the nematic ordering and reducing electro-optic response time

ABSTRACT Doping a nematic liquid crystal (NLC) with nanoparticles (NPs) of varied dimensions and properties to form LC-NP nanocomposites with improved electro-optic and dielectric properties has recently been a much-explored field of work. But still, NLC nanocomposites based on two-dimensional (2D) NPs have not been studied vividly because of the high tendency of 2D NPs to aggregate together. In the present work, we have studied the effect of incorporating hexadecanethiol functionalised graphene oxide (fGO), a 2D NP, in a conventional NLC medium under varying doping concentrations. We found that at a lower doping concentration (⁓10−4 wt.%), the NLC nanocomposite showed a substantial increase in dielectric anisotropy (Δε) and birefringence (Δµ) values as compared to pure NLC sample. A significant decrease (⁓50%) in ionic conductivity as well as reduced electro-optic response time (⁓75%) was also observed in this NLC nanocomposite. As the fGO doping concentration was increased (⁓10−2 wt.%), a reverse trend was observed for Δε, Δµ and response time values, which declined sharply with increasing doping concentration. Hence, the present work highlights two different working mechanisms at low- and high-doping concentrations of 2D NPs.

Controlled doping rates of graphene oxide in aluminum for high electrical performance and oxygen reduction reaction

The brush coating method allows the advantage of being able to produce thin films simply and quickly. This study introduces a method for thin-film production by brushing a solution containing graphene doped in Al2O3 using the sol–gel method. Graphene oxide (GO) is suitable for semiconductors with bandgap values of about 1.7 eV at room temperature, and the characteristics of the thin films were analyzed according to the doping ratio. First, X-ray photoelectron spectroscopy measurements were obtained to analyze the chemical composition of the thin-film surface. Since graphene is a carbon isomer, the characteristic of oxygen vacancies was confirmed by the increasing C–C bond intensity with increasing GO doping concentration. In addition, Raman analysis was performed to analyze the concentration of molecular groups of compounds for defects in graphene. Thereafter, through atomic force microscopy measurements, as the graphene doping ratio increased, the average roughness increased from 1.785 to 33.67, the residual DC voltage also increased by about 48.42 %, and the polar anchoring energy also increased by about 16.33 %. In addition, response-time–transmittance measurements were performed to measure the electro-optical properties of the thin film, and excellent Vth and stable response speed were obtained. Additionally, the validity of the results was supported through bandgap analysis. Finally, the degree of alignment of liquid–crystal molecules on the film surface was confirmed by polarized optical microscopy and pretilt angle measurements, and the suitability of the thin film for display devices was shown via transmittance measurements. As a result, GO:Al2O3 hybrid thin film is an excellent candidate for use as an alignment film for solar energy, secondary batteries, and next-generation liquid crystal displays.

Low driving voltage reverse-mode polymer-stabilised cholesteric liquid crystal devices using small phenylacetylene molecule

ABSTRACT Polymer-stabilised liquid crystal devices have found widespread use in intelligent displays and dimming glass applications, but their high driving voltage induces high power consumption and needs to be reduced. In this paper, we use several small phenylacetylene molecule materials with linear structures to reduce the driving voltage and obtain a high contrast ratio in reverse-mode polymer-stabilised cholesteric liquid crystals (RPSCLC). In particular, the drive voltage of the 8-micron-thick sample was reduced by nearly 40%, and the 20-micron-thick sample was reduced by nearly 45%. Additionally, we explore the physical mechanism through which various small phenylacetylene molecule materials improve the electro-optical properties, based on polymer network morphology effects. The results will be of great value for enhancing the use of RPSCLC devices.

Electrical tuning of branched flow of light

Branched flows occur ubiquitously in various wave systems, when the propagating waves encounter weak correlated scattering potentials. Here we report the experimental realization of electrical tuning of the branched flow of light using a nematic liquid crystal (NLC) system. We create the physical realization of the weakly correlated disordered potentials of light via the inhomogeneous orientations of the NLC. We demonstrate that the branched flow of light can be switched on and off as well as tuned continuously through the electro-optical properties of NLC film. We further show that the branched flow can be manipulated by the polarization of the incident light due to the optical anisotropy of the NLC film. The nature of the branched flow of light is revealed via the unconventional intensity statistics and the rapid fidelity decay along the light propagation. Our study unveils an excellent platform for the tuning of the branched flow of light which creates a testbed for fundamental physics and offers a new way for steering light.

Fine-tuning of organic optical double-donor NLO chromophores with DA-supported functional groups.

New strategic chromophores with updated fine-tuning of previously reported BLD1 and BLD3 chromophores were designed. BLD1 and BLD3 have silicon functional groups on the donor unit, and the bridge has a good chance of self-assembling, so in the present study we fine-tuned the isolating groups to the bulky cyclic alkene to improve their dipole moment and organic electro-optic (OEO) properties as well. To demonstrate the impact of cyclic alkenes on the electron-donating groups in sensible NLO chromophore designs, a thorough analysis and comparison of the chromophore synthesis, UV-Vis calculations, solvatochromic behavior of the chromophore, DFT quantum mechanical calculations, thermal stabilities, and much lower dipole moments was conducted.

Electron-phonon coupling effect on the optical absorption of gated β12-borophene.

This study addresses the effect of electron-phonon coupling (EPC) on the electro-optical properties of gated β12-borophene. The focus is on how EPC influences the orbital hybridization of boron atoms, particularly within the Bariśic-Labbe-Friedel-Su-Schrieffer-Heeger framework, and considers the role of gate electrodes in this process. The results reveal a redshift in the optical spectrum only when there is positive feedback from one electrode on EPC. In other configurations, except for the y-direction, a blueshift spectrum is observed. The study emphasizes the importance of tuning these spectral shifts for maximizing the performance of solar cells in converting sunlight into usable energy.

Electro-optical properties of a strain-induced borocarbonitride monolayer from many-body perturbation theory

Electro-optical properties of a borocarbonitride monolayer under tensile strains.

Tailoring the structural and electro-optical properties of avisible-light emitting BaZrO3 photocatalyst: integrating DFT and comprehensive experimental analysis.

In the present work, the synthesis of BaZrO3 nano-ceramics is explored through flash combustion utilizing glycine as a fuel. The resulting nanoparticles exhibit a cubic Pm3̄m space group and a spherical morphology with an average size of 45.31 nm. XRD and EDAX verify the integrity of the phase. FTIR and Raman spectroscopy is used to analyze the molecular bonds and their vibrations, while XPS reveals surface compositions and oxidation states. The electro-optical properties of BaZrO3 are explored through UV-Vis spectroscopy and electronic band structure analysis. The Tauc plot displays a pair of band gaps, with values of 3.08 eV and 3.84 eV, corresponding to indirect and direct characteristics. BaZrO3 demonstrates photocatalytic potential with a degradation efficiency of approximately 36.41% for rhodamine B under visible light. Electronic band structure analysis reveals an indirect band gap of 3.05 eV in BaZrO3. The Bader analysis emphasizes the pronounced covalent characteristics present in the Zr-O bond. Photoluminescence spectra exhibit electronic transitions with a peak observed at 420.57 nm (∼2.94 eV), suggesting activity within the violet light spectrum. The CIE chromaticity coordinates imply prospective uses in the manufacture of violet-blue LEDs. These findings underscore the tailored properties of BaZrO3 nano-ceramics, showcasing their versatility for various applications, notably in advanced optoelectronic devices.

Unveiling the role of electrode polarization in modulating dielectric and electro-optical properties of SnSe dispersed nematic liquid crystal

This study explores the impact of electrode polarization on SnSe nanosheets blended with liquid crystal cells and investigates how impurity ions influence the performance of the liquid crystal.

Functionalized hexagonal boron nitride bilayers: desirable electro-optical properties for optoelectronic applications.

Structural, electronic, and optical properties of functionalized hexagonal boron nitride (h-BN) bilayer were deeply explored by carrying out the PBE + G0W0 + BSE calculations. Hydrogenation/hydrofluorination/fluorination can cause the planar h-BN bilayer to form a novel diamane-like monolayer by interfacial sp3 atom bonding. These functionalized h-BN bilayers are estimated to be stable dynamically due to their phonon dispersions. The functionalization on h-BN bilayer can induce its electronic nature to be transformed from an indirect wide-gap insulator to direct narrow-gap semiconductor, which is desirable for its application in optoelectronics. In particular, hydrogenated and hydrofluorinated h-BN bilayers have strong absorbance coefficients for the near-infrared and visible part of the incident sunlight (larger than 105 cm-1). More interestingly, the binding energy of the observed first bright exciton can achieve a value beyond 1 eV, which can effectively reduce the recombination of photogenerated electron-hole pairs. These results are potentially important for extending the applications of the h-BN bilayer in optoelectronic devices.