Electro-optical Properties Research Articles

Fabrication of Sx/In2O3−x based microsphere for photoexcitation enhancing the NO2 gas detection properties

Development research as a NO2 gas sensor has attracted extensive attention recently. However, how to improve the electrical conductivity of materials, adjust the band structure of materials through photoexcitation and improve the carrier lifetime is still a challenge. In this work, an S-doped In2O3 structure (Sx/In2O3−x) was synthesized by enforcing the simple hydrothermal method. Doping directly controls the distribution of structural defects and oxygen vacancies in the material structure, and the response to NO2 increases by orders of magnitude under photoexcitation. Various structural characterization techniques examined the properties of the Sx/In2O3−x-based material. More specifically, its electro-optical properties and the impact of S doping on its energy band structure were thoroughly analyzed to investigate the origins of the enhanced responsivity.

Generation of vector vortex beams by axially symmetric sheared polymer network liquid crystals.

Liquid crystals have been widely used in optoelectronic devices because of their fast response and excellent electro-optic properties. Featuring a unique ability to manipulate light, they are also proposed as a good candidate in topological photonics for further applications. In this study, an axially symmetric sheared polymer network liquid crystal (ASPNLC) is fabricated to demonstrate vector vortex beams. Linearly and circularly polarized light is used to illuminate the sample, and the output vector vortex beams generated from the ASPNLC indicate that the polarization states of the output beams are dependent on the polarization of the incident light. The measured phenomena are modeled on the bases of phase retardation and Jones calculus to eventually calculate the polarization-resolved intensity profiles accordingly. Hence, our experimental study provides a holistic understanding of the method for generating vector vortex beams by an ASPNLC, which is expected to enhance the knowledge of optical mechanisms for liquid crystal applications.

Optoelectronic Transitions in Gold Spherical Nanoparticles - A Simulation Study

This study examined extinction spectra, electric field intensity, and their variations due to various semiconductor medium, for gold nanoparticles, using Nanosphere Optics Lab Field Simulator which is based on Mie’s theory of scattering by sphere. The peak extinction wavelength and bandwidth are found to get varied with size of the gold nanoparticle, in four different regimes. Asymmetric distributions of electric fields are observed in particles typically larger than 25nm. The significant differences are found in the results due to changes in the embedding medium. The gold nanoparticles' unique tunable electro-optical properties may therefore be useful for medical, health care, industrial catalysts, and other consumer products. The study shows improved results may be obtained in the medium size range i.e. 25-75nm. In addition, the selectivity can be improved linearly as the refractive index of the host material increases.

Synthesis of MgO thin films: How heat treatment affects their structural, electro-optical, and surface properties

In this study, MgO thin films were grown using Chemical Bath Deposition (CBD) and annealed at various temperatures (300, 350, 400, and 450°C). Their structural properties were obtained by X-ray diffraction (XRD), and amorphous MgO structures were observed in the XRD pattern. EDX composition analysis showed that the amount of Mg increased with temperature, and so did oxidation. Surface morphologies and surface roughness were analyzed by FESEM and AFM. The amorphous structures were in the form of a sugar cube at 300°C and turned into a homogeneous nanorod-like structure as the temperature increased to 400-450°C. Current-voltage (I-V) measurements were taken with a Keithley 2400 sourcemeter, and electrical resistivity was calculated using film thickness. The increase in surface roughness created a resistance effect in transmission, reducing the charge storage capacity. The transmittance (T), reflectance (R), refractive index (n), and damping coefficient (k) were determined via a UV-vis spectrophotometer. E g values of MgO thin films tempered at 300, 350, 400, and 450°C were 3.85, 3.98, 3.87, and 4.08eV, respectively.

Resolving the Subsurface Structure and Elastic Modulus of Layered Films via Contact Resonance Atomic Force Microscopy.

Since its discovery, atomic force microscopy (AFM) has become widely used for surface characterization, evolving from a tool for probing surface topography to a versatile method for characterizing mechanical, electrical, chemical, magnetic, and electro-optical properties of surfaces at the nanoscale. Developments of several AFM-based techniques have enabled even subsurface imaging, which is routinely being carried out at the qualitative level of feature detection for localized subsurface inhomogeneities. We surmise, however, that a quantitative three-dimensional (3D) subsurface characterization can emerge from the AFM mechanical response of flat buried interfaces, and present here a methodology for determining the depth of a film and its mechanical properties. Using load-dependent contact resonance atomic force microscopy (CR-AFM) and accurate modeling of the contact between the AFM tip and a layered sample, we determine the relationship between the measured resonance frequency of the AFM probe and the contact stiffness. Our subsequent statistical analysis reveals an intrinsic and sample-specific interdependence between the depth and modulus sensitivities of CR-AFM. This interdependence prevents the simultaneous accurate determination of both depth and modulus from measurements on a single-layered sample. If the elastic moduli of the sample components are predetermined from separate investigations of bulk samples (or otherwise known), then this methodology accurately yields the location of the interface between the layers of the sample; as such, it can serve as a nondestructive and robust technique for probing layer thickness, subsurface features, and elastic properties of materials used in semiconductor electronics, additive manufacturing, or biomaterials.

Enhancement of birefringence for liquid crystal with the doping of ferric oxide nanoparticles

Electro-optical (E-O) property of nematic liquid crystalline (NLC) materials is the key parameter of display and non-display applications. Optical anisotropy (i.e., birefringence) is one of the critical parameters of these LCs via which E-O properties are governed. In this article, we have investigated the effect of ferric oxide nanoparticles (Fe2O3 NPs) on the birefringence and the order parameter of a NLC when doped into different weight percentages (wt%). The birefringence of the NLC has been examined via the phase modulation optical transmittance technique. It is noticed that the value of birefringence increases with the concentration of NPs in the LC matrix which is analogous to an improved order parameter of NLC after the addition of NPs. The improved ordering of LC molecules has been verified using polarized optical microscopy. This study helps in understanding the guest-host interactions for improved optical applications of LC materials.

Functionalized and non-functionalized multi walled carbon nanotubes in the anisotropic media of liquid crystalline material

We report the effect of dispersion of functionalized and non-functionalized multi walled carbon nanotubes on the thermodynamic, dielectric, optical and electro-optical properties of a nematic host 4′-octyl-4-cyanobiphenyl. Increase of transition temperature and associated enthalpy is observed in thermodynamic study. Dielectric anisotropy has increased in the both dispersed nano-composites as compared to the pure sample. Conductivity of non-functionalized multi walled carbon nanotubes has increased by 2 orders of magnitude than for the pure sample. Ultraviolet–visible spectroscopy study shows the decrease of the optical band gap in both of the dispersed nanocomposites. Electro-optical parameters such as threshold voltage, splay elastic constant, and rotational viscosity are decreased for functionalized multi walled carbon nanotubes dispersed nanocomposite, whereas for non-functionalized multi walled carbon nanotubes dispersed nanocomposite the threshold voltage is decreased while splay elastic constant and rotational viscosity are increased marginally.

Tunable dielectric and memory features of ferroelectric layered perovskite Bi4Ti3O12 nanoparticles doped nematic liquid crystal composite

Herein, we report the synthesis of ferroelectric layered perovskite Bi4Ti3O12 (BT4) nanoparticles (NPs) and the temperature-dependent dielectric and electro-optical (especially memory effect) properties of 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal (NLC) doped with 1 wt% BT4 NPs (i.e. 5CB-BT4 composite) using polarising optical microscopy and frequency-dependent dielectric spectroscopy techniques. BT4 NPs were synthesised via a microwave-assisted chemical method and characterised using various instrumental techniques, which confirmed the formation of a non-stoichiometric and oxygen-deficient orthorhombic crystal phase. The agglomeration-free and uniform dispersion of BT4 NPs in the 5CB matrix was confirmed by optical textures. The optical memory studied by bias voltage-dependent (ON-OFF) optical textures is decreased by ∼ 2.6 times in the 5CB-BT4 composite compared with 5CB. Moreover, dielectric parameters such as dielectric permittivity, dielectric loss, loss tangent, conductivity, and activation energy of 5CB and composite (5CB-BT4) are estimated using dielectric spectroscopy. The dielectric anisotropy is decreased, whereas no shift in the clearing temperature is observed in the 5CB-BT4 composite compared to the 5CB sample. Also, the DC conductivity of 5CB-BT4 composite is found to be increased by approximately four times compared to the 5CB. Our studies clearly demonstrate the tunability of the dielectric and optical memory features of NLC (5CB) matrix by dopant BT4 NPs, without significantly affecting the molecular alignment of the NLC molecules. Such composites would certainly be useful in the fabrication of NLC based tunable devices such as optical memory and conductivity switches.

Si-target power dependence on the microstructure, mechanical behavior, and electro-optical characteristics of magnetron sputtered Six(TiZrHf)1-xN coatings

Si-doped (TiZrHf)N was cosputtered from TiZrHf and Si targets on Si substrates in N2/Ar atmosphere. The effect of Si-target power on crystal, microstructural, mechanical, and electro-optical characteristics was examined. The Si content raised to 8.74 at.% significantly with increased Si target power to 70 W. The Si-free coatings had a V-shaped columnar structure with voided boundaries and a (111)-preferred direction. With increased Si-target power, the grain size and residual compressive stress initially increased and then decreased. The microstructure of the coatings obviously became compact and eventually transformed into a nanofibrous structure with (200) preferred orientation. When the Si-target power rised up to 50 W, the Si content reached 2.60 at.% and the coating demonstrated a maximum hardness of 34.8 GPa. The electro-optical properties of coatings greatly deteriorated with Si content regardless of structural evolution. The electrical resistivity of the coatings increased from 52 μΩ cm to 6250 μΩ cm, and their light reflectivity at 0.62 eV dropped from 83.5% to 33.6%.

Investigation of magneto-electronic and optical properties of rare earth Ag and Co co-doped CdS

CdS is a potential candidate for material in optoelectronic applications. The magnetic, electronic and optical properties of Ag- doped and Co -codoped CdS were calculated using full potential linear augmented plane wave (FP-LAPW) based on popular density – functional theory (DFT). The band gap and density of states for Ag -doped and Cocodoped CdS have been determined by using Tran Blaha modified Becke-Johnson (TBmBJ) potential. The optical and electronic properties of Ag-doped and Co-codoped CdS such as absorption coefficient, energy loss function, reflectivity, refractive index, electrical conductivity and extinction coefficient are presented. The results indicate that the magnetic and electro-optical properties are improved by this doping.

New series of fluorinated hydrogen-bonded liquid crystals with SmB and nematic phases

ABSTRACT A new series of hydrogen-bonded liquid crystals was prepared by mixing 4-n-alkoxy-2.3-difluorobenzoic acid and 4-pentyl-4-biphenylcarbonitrile (5CB). Thermal and liquid crystal behaviour was established using differential scanning calorimetry and polarizing optical microscopy. The influence of terminal acid donors on mesogenic behaviour was discussed in detail. It was found that all complexes with a (1:1) molar ratio exhibit the smectic B phase. In addition, the binary phase diagram that has been established revealed that the mixtures with lower concentration exhibit a nematic phase at room temperature with large stability. Dielectric, electro-optic and viscoelastic properties of 5CB/9OBAFF with molar fraction x = 0.1 were discussed.

Improvement in the electro-optical and electronic properties of the reduced graphene oxide dispersed in a liquid crystalline material 4’-octyl-4-cyano-biphenyl

ABSTRACT Herein, a small concentration (0.05 wt %) of reduced graphene oxide is dispersed in the liquid crystalline media. Thermodynamic study shows the reduction of the transition temperature, enthalpy and entropy of the reduced graphene oxide dispersed nanocomposite. Optical study suggests the decrease of the optical bandgap of the dispersed nanocomposite as compared to that of the pure sample. Dielectric spectroscopic measurement is done for measuring the permittivity and conductivity of the pure and the dispersed samples. The value of dielectric anisotropy has decreased for the dispersed nanocomposite whereas the value of ionic (DC) conductivity of the dispersed nanocomposite has increased by 3 orders of the magnitude as compared to that of the pristine sample. The activation energy for DC conductivity has reduced in the dispersed nanocomposite which is responsible for the increment in DC conductivity of the system. The cut-off region of DC conductivity has increased in the dispersed nanocomposite. Electro-optical studies suggest the reduction of the threshold voltage for the Freedericksz transition, splay elastic constant and rotational viscosity for the dispersed nanocomposite.

Optimization of the Selenization Temperature on the Mn-Substituted Cu2ZnSn(S,Se)4 Thin Films and Its Impact on the Performance of Solar Cells.

Cu2ZnSn(S,Se)4 (CZTSSe) films are considered to be promising materials in the advancement of thin-film solar cells. In such films, the amounts of S and Se control the bandgap. Therefore, it is crucial to control the concentration of S/Se to improve efficiency. In this study, Cu2MnxZn1-xSnS4 (CMZTS) films were fabricated using the sol-gel method and treated in a Se environment. The films were post-annealed in a Se atmosphere at various temperature ranges from 300 °C to 550 °C at intervals of 200 °C for 15 min to obtain Cu2MnxZn1-xSn(S,Se)4 (CMZTSSe). The elemental properties, surface morphology, and electro-optical properties of the CMZTSSe films were investigated in detail. The bandgap of the CMZTSSe films was adjustable in the scope of 1.11-1.22 eV. The structural propeties and phase purity of the CMZTSSe films were analyzed by X-ray diffraction and Raman analysis. High-quality CMZTSSe films with large grains could be acquired by suitably changing the selenization temperature. Under the optimized selenization conditions, the efficiency of the fabricated CMZTSSe device reached 3.08%.

Insight of the role of F-impurity on the structural, electro-optical properties of ZnO: DFT and experiment

A comprehensive study is performed to investigate the consequence of F doping on the structural, electronic, optoelectrical, and photoluminescence properties of ZnO. In the theoretical part, the density functional theory (DFT) is used to study the electronic and optical properties of F-doped ZnO. Whereas, the role of F on the structural, morphological, and optoelectrical characteristics of spray deposited ZnO thin films are studied by experimental means. Electronic band structures, density of states, and optical properties indicated that F is an efficient donor and broadened the direct band gap of F:ZnO system because of the well-known Burstein-Moss effect which matches the experimental data. Shifting of the Fermi level into conduction band (CB) fallouts the improvement of electrical conductivity and carrier concentrations of the doped system. The lattice constants of ZnO are increased due to F doping which is in accord with our experimental results. The existence of F1s in the films is confirmed by X-ray photoelectron spectroscopy (XPS) inspection. Surface morphology reveals the formation of nano-wall structures with different aspect ratios. Photoluminescence spectra show PL emissions for un-doped and 5% F-doped samples at 3.38 eV assigned to the near band edge (NBE) emission and weak peaks at 2.74 and 2.63 eV are attributed to emission from defect states. The optical band gap value first decreased up to 1% F content and then started to increase with increasing F concentration, which is well supported by the theoretical results. The findings from this study will be helpful for further investigation and selecting suitable areas of applications.

Effects of nematic liquid crystal doped with multi-walled carbon nanotube on electro-optic properties and electrostatic discharge immunity of liquid crystal display device

ABSTRACT Electrostatic discharge is a vexing problem in liquid crystal display device, which can cause abnormal display. Conventional solutions for liquid crystal doped with antistatic agent usually introduce additional impurity ions and increases the power consumption of liquid crystal display device. In this study, multi-walled carbon nanotube doped liquid crystal cells without obvious clusters are successfully fabricated. Comparing the electro-optic properties of undoped and doped cells, it is verified that doping does not negatively affect the liquid crystal cells with E7 host by measuring basic parameters such as relative permittivity, threshold voltage and response time. The liquid crystal cells are then tested using an electrostatic discharge generator to simulate the human-machine air discharge that occurs during actual operation. The immunity of the doped versus undoped cells is quantitatively compared in terms of the duration of so-called image sticking, it is found that the electrostatic discharge immunity of cell has a significant relationship with electrical conductivity. In addition, the relationship between the conductivity and relaxation time of image sticking is obtained by theory. It is determined that doping carbon nanotubes into E7 can effectively improve the electrostatic discharge immunity of liquid crystal display device without negatively affecting practical application.

Structural, mechanical, and electro-optical properties of hydrogenated graphene/h-BN heterobilayer

Structural, mechanical, and electro-optical properties of hydrogenated graphene/h-BN heterobilayer

Anisotropic Surface Formation Based on Brush-Coated Nickel-Doped Yttrium Oxide Film for Enhanced Electro-Optical Characteristics in Liquid Crystal Systems

This paper introduces anisotropic nickel yttrium oxide (NYO) film formed by the brush coating technique. X-ray photoelectron spectroscopy confirmed well-formed NYO film after the curing process, and the morphology of the surface was investigated using atomic force microscopy. The shear stress driven from brush hair movements caused the nano/micro-grooved anisotropic surface structure of NYO. This anisotropic surface induced uniform liquid crystal (LC) alignment on the surface, which was confirmed by pre-tilt angle analysis and polarized optical microscopy. The contact angle measurements revealed an increase in hydrophilicity at higher temperature curing, which contributed to homogenous LC alignment. The NYO film achieved good optical transmittance and thermal stability as an LC alignment layer. In addition, the film demonstrated good electro-optical properties, stable switching, and significantly enhanced operating voltage performance in a twisted-nematic LC system. Therefore, we expect that this brush coating method can be applied to various inorganic materials to achieve an advanced LC alignment layer.

Effect of Curing Temperature on the Properties of Electrically Controlled Dimming Film with Wide Working Temperature Range

In this paper, a polymer dispersed liquid crystal (PDLC) film with good electro-optical properties and wide working temperature range was prepared by the UV-polymerization induced phase separation (PIPS) method by optimizing the curing temperature using a LC with wide temperature range. The investigation found that when the polymerization temperature was at the clearing point of the prepolymer/LC mixture, the film had better electro-optical properties and a high contrast ratio of 51 at 90 °C, and the rise time and decay time were respectively as fast as 241.5 ms and 1750 ms at −20 °C. This study provides further methodological guidance for the curing process of PDLC film, and promotes its application in outdoor smart windows.

Impact of terminal group of organic dopant on liquid crystal-based electro-optic device

In this study, the influences of terminal group of organic dopant in nematic liquid crystals (LCs) are investigated. A novel organic molecule, N-(4-Fluoro-2-methylphenyl)benzenemethanamine (BFM) with fluorine terminal group and a similar one, N-benzyl-2-methyl-4-nitroaniline (BNA) with nitro terminal group are doped into the nematic LCs, separately. The electro-optical characteristics of the BFM-doped and BNA-doped LC cells are demonstrated. The LC cells with organic dopings have the lower threshold and operation voltages than the pristine LC cell, due to the enhanced electrical torque of LCs. The fluorine terminal atoms in the BFM-doped LC cell prevents the drastic absorbance at short visible wavelengths and suppresses the free-ions in the BNA-doped LC cell significantly. BFM-doped and BNA-doped LC cells have the fall times that are 5.79X and 5.05X faster than pristine LC cell, respectively, owing to decreased viscosity and threshold voltage and increased local electric field. Furthermore, density functional theory calculation confirms that organic dopant enhances the dipole moment, polarizability, polarizability anisotropy and hence the dielectric anisotropy of LC mixture. The competition between the dipole moment and free-ions of organic molecule-LC composite has a crucial influence on the electro-optical properties of LC cell. BFM doping not only prevents the color shift but also improves the operation voltage and response time of LC cell significantly.

Electro-Optical Characteristics of Polymer Dispersed Liquid Crystal Doped with MgO Nanoparticles.

In this paper, inorganic oxide MgO nanoparticles-doped polymer dispersed liquid crystal (PDLC) films were made from a mixture of the prepolymer, SLC1717 liquid crystal, and MgO nanoparticles by the polymerization induced phase separation (PIPS) process. To observe the effect of MgO concentration, PDLC was dispersed with 0.2, 0.4, 0.6, and 0.8 wt.% MgO. Electro-optical properties of the films have been investigated using LCD parameter meter and Scanning Electron Microscope (SEM) at room temperature. It is established that MgO nanoparticles affect the microstructure of PDLC films significantly because of the formed agglomerates of MgO nanoparticles. Results show an improvement in the electro-optical properties and a decrease in the driving voltage for doped systems with MgO nanoparticles. When the doping amount of MgO is 0.8 wt.%, the threshold voltage (Vth) is reduced to about 7.5 V. Therefore, MgO-doped PDLC is expected to become an excellent choice in the field of energy-saving.