Advancement of electro-optical properties through changes in the physicochemical composition of hybrid thin films by doping reduced graphene oxide into a sol-gel process solution.

A hybrid thin film was fabricated by doping graphene oxide into a sol-gel solution containing a mixture of zirconium, bismuth, and indium oxide. The thin film was fabricated using a brush coating process. The graphene oxide doping ratios used were 0, 5, and 15 wt%. During the thin film fabrication process, the produced sol-gel solution generates a contractile force due to the shear stress of the brush bristles, resulting in a microgroove structure. This structure was confirmed through scanning electron microscopy analysis, which revealed the clear presence of rGO. Comparing the electrical properties of a zirconium bismuth indium oxide thin film without graphene oxide doping and a thin film doped with 15 wt% graphene oxide, the electro-optical properties were significantly improved with graphene oxide doping. In general, the threshold voltage decreased by approximately 0.42 V. In addition, bandgap measurements confirmed the improved conductivity characteristics with graphene oxide doping. Since this improvement in electro-optical properties is associated with the reduction process due to graphene oxide doping, X-ray photoelectron spectroscopy analysis was performed to assess the intensity change of each element. Based on these observations, hybrid thin films doped with graphene oxide emerge as promising candidates for next generation thin film.

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.

Advanced thin films of indium-tin oxide doping with photosensitive polymer via embossing process.

We propose a sol-gel thin film formation process involving nanoimprint lithography. First, indium tin oxide was dissolved in 2-methoxyethanol at a ratio of 5:5 and the mixture were mixed with 10 wt% of a UV-curable. Subsequently, a polydimethylsiloxane sheet prepared by covering a silicon wafer with a polydimethylsiloxane mold was attached to a InSnO thin film to duplicate the nanostructure through UV irradiation exposure. The replicated nanostructured thin films formed about morphological and chemical composition changes on the surface, we progressed to x-ray photoelectron spectroscopy and atomic force microscopy analysis. Furthermore, atomic force microscopy image analysis showed superior patterned grooves for a UV exposure time of 3 min. A suitability test involving the measurement of the transmittance was performed for examining the suitability of the thin film for use in display devices.

High electrical characteristics through graphene oxide doping process on physicochemically reformed inorganic thin films.

This study investigated the improvement of the electro-optical properties of a liquid crystal (LC) cell fabricated through brush coating using graphene oxide (GO) doping. The physical deformation of the surface was analyzed using atomic force microscopy. The size of the groove increased as the GO dopant concentration increased, but the direction of the groove along the brush direction was maintained. X-ray photoelectron spectroscopy analysis confirmed that the number of C-C and O-Sn bonds increased as the GO concentration increased. Since the van der Waals force on the surface increases as the number of O-metal bonds increases, we were able to determine why the anchoring energy of the LC alignment layer increased. This was confirmed by residual DC voltage and anchoring energy measurements that were later performed. As the GO concentration increased, the width of the hysteresis curve decreased, indicating that the residual DC voltage decreased. Additionally, the 15% GO-doped sample exhibited a significant increase in its anchoring energy up to 1.34 × 10-3 J/m2, which is similar to that of rubbed polyimide. It also secured a high level of electro-optical properties and demonstrated potential as a next-generation thin-film display despite being produced via a simple brush-coating process.

Physicochemically Constructed Unidirectional Aluminum Bismuth Gallium Zinc Oxide Film for Enhanced Nematic Liquid Crystal System Using a Brush-Coating Method.

We propose a convenient brush coating method for liquid crystal (LC) alignment. This method enables film deposition and an alignment layer treatment process simultaneously. Aluminum bismuth gallium zinc oxide (AlBiGaZnO) is used as the alignment layer. After the curing process, a unidirectional AlBiGaZnO film is formed; its surface morphology and chemical composition were verified using scanning electron microscopy and X-ray photoelectron spectroscopy. This oriented structure of the surface was produced by shear-stress which originated from brush movement. That structure induced a surface anisotropic characteristic and resulted in a uniform LC alignment. The uniform and homogeneous LC alignment state on the film was confirmed using polarized optical microscopy and pre-tilt angle analysis. The brush coated AlBiGaZnO film exhibited excellent thermal budget for advanced LC system. The film exhibited enhanced electro-optical performance with a low operating voltage. These results demonstrate the potential of LC alignment technology via the brush coating method.

Solution-Driven Imprinting Lithography of Sol-Gel ZnO Thin Films for Liquid Crystal Display.

We present a simple and economically convenient method to fabricate nanopatterned ZnO films by imprinting lithography and use them for the layer alignment of liquid crystal (LC) displays. First, a one-dimensional nanopattern was obtained by laser interference lithography on a silicon wafer, and the silicon mold replica was transferred onto a flexible polydimethylsiloxane (PDMS) sheet for conformal patterning. The so-obtained PDMS mold was then applied on a ZnO film spin-coated on a glass substrate. During the imprinting process, the temperature was controlled from 100 to 250 °C to observe the transferring morphologies of the ZnO film; the nanopattern was successfully transferred at annealing temperatures of 200 and 250 °C because the ZnO film at the sol state filled the cavities of the PDMS nanopattern and solidified, forming a negative replica of the nanopattern. The direction of the nanopatterned ZnO film served as a guide for aligning the LC molecules on the LC surface at the centimeter scale and, due to their elastic characteristics and group behavior, propagating their directional states in the LC bulk. The resulting LC cell exhibited an enhanced electro-optical performance and high thermal endurance above 180 °C. The geometry of the alignment layer increased the electric field on the ZnO film and showed reduced threshold voltage. In addition, since flexible devices are generally based on polyimide, which imidized at around 200 °C, the relatively low annealing temperatures of our fabricated nanopatterned ZnO film allow it to be mounted on such devices without any deterioration of the underlying thermoplastic substrate. Therefore, nanopatterned ZnO has a considerable potential for advanced LC displays.

Formation of Wrinkle Structures on Styrene-b-isoprene-b-styrene Films Using One-Step Ion-Beam Irradiation.

We investigated the wrinkle formation on ion-beam (IB)-irradiated substrates coated with the thermoplastic elastomer styrene-b-isoprene-b-styrene (SIS) and demonstrate a relation of the wrinkle structure and the newly formed top layer induced by IB. IB irradiation led to polymer cross-linking on the surface, thereby forming a new skin layer, a finding which was supported by an X-ray photoelectron spectroscopy analysis, Young moduli calculated using force-distance curves, and time-of-flight secondary ion mass spectrometry depth profiling. The wrinkle wavelength increased according to the irradiation time, which indicates that the latter mainly increased the thickness of the cross-linking layer. The increase in the wrinkle wavelength varied from 420 to 670 nm by changing the IB irradiation time. In this paper, we present not only the expectation of wrinkle fabrication using our method but also the possibility of choosing diverse materials such as the thermoplastic elastomer SIS for fabrication of wrinkle structures.

One-dimensional surface wrinkling for twisted nematic liquid crystal display based on ultraviolet nanoimprint lithography.

Surface wrinkling method is used to fabricate a 1-dimensional nanostructure. The structure is transferred to an ultraviolet cured polymer which is used as an alignment layer. The anisotropic geometry serves as a guide for aligning liquid crystal molecules uniformly without defects. The TN-LC cell showed a successful LC switching, with a response time of 20.5 ms, and a threshold voltage of 2.00 V. It also exhibited high thermal stability above 180°C. The proposed UV-cured polymers with 1-D nano wrinkle geometry can be a candidate for alternative alignment techniques, for advanced liquid crystal devices with high thermal budgets.

Physicochemical Modification Effect on Homogeneously Aligned Liquid Crystals Based on the Nickel Oxide Thin Film.

We demonstrated homogeneous liquid crystal (LC) alignment on Nickel Oxide (NiO) films subjected to ion beam (IB) irradiation. Uniform LC alignment was achieved at high IB intensity values of 1200 and 1800 eV. To determine the mechanism of LC alignment following IB irradiation, physicochemical analysis was performed using atomic force microscopy and X-ray photoelectron spectroscopy. IB irradiation with high intensity increases uniformity of the surface, and IB irradiation induces the formation of oxygen vacancies and increases the NiO (Ni2+) phase components. Hence, both of the smooth surface and the strong van der Waals interactions between the NiO film and the LC molecules provides the LC molecules with a stable anchor on the surface, leading to uniform LC alignment on NiO films after IB irradiation. IB-irradiated NiO exhibited a high transparency of 85% in the visible light range as compared with the 83% average transmittance of conventional polyimide, which makes the IB-irradiated NiO alignment layer attractive in display devices.

Ion beam fabrication of aluminum-doped zinc oxide layer for high-performance liquid crystals alignment.

In this paper, a 1.8 keV ion beam (IB) sputtered thin layer of aluminum-doped zinc oxide (AZO) with columnar AZO bumps covering the surface working as an alignment layer for the homogeneous alignment of liquid crystals (LC) is investigated. Bumpy AZO alignment layers in twisted nematic (TN) cells generated larger LC pre-tilt angles and thus enabled accelerated switching of LC, and the highly conductive bumpy AZO thin layers allowed super-fast release of accumulated charges, and led to low residual DC performance. These results indicate the promising applications of AZO bumps layer as alignment layer in LC devices.

Tailoring the Orientation and Periodicity of Wrinkles Using Ion-Beam Bombardment.

The present study demonstrates that surface reformation in polydimethylsiloxane can be controlled using ion-beam (IB) irradiation. This can be done by simply varying the IB incidence angle and requires no change in the energy source. By controlling the incidence angle of IB irradiation, we were able to continuously control the pattern of the wrinkle structure, that is, a randomly formed pattern or an anisotropic one. Moreover, the directional characteristics of the wrinkle pattern control the alignment of liquid crystal molecules. This control is a function of the incidence angle of the IB. These simple methods can provide considerable flexibility in the fabrication of wrinkle structures.

Liquid Crystal Alignment on Solution Derived Zinc Oxide Films via Ion Beam Irradiation.

A 75-nm-thick ZnO film was deposited by a sol-gel method on indium-tin oxide (ITO)-coated glass. This film served as a liquid crystal (LC) alignment layer. We report the fabrication and characteristics of this film after ion-beam (IB) irradiation. Uniform LC alignment was achieved at an IB incident energy above 2400 eV. The IB-treated ZnO surface was analyzed by X-ray photoelectron spectroscopy (XPS), monitoring the intensity of the Zn 2p and O 1s peaks as a function of IB-irradiation energy density. The electro-optical (EO) characteristics of a twisted nematic-liquid crystal display (TN-LCD) were comparable to rubbed polyimide.

Homogeneous liquid crystal alignment characteristics on solution-derived HfYGaO films treated with IB irradiation.

Solution-derived HfYGaO films have been treated by ion beam (IB) irradiation and used as liquid crystal (LC) alignment layers. Solution processing was adopted due to its simplicity, high throughput, and facile composition modification. Homogeneous and uniform LC alignment was achieved on the IB-irradiated HfYGaO films, and when these films were adopted in twisted nematic (TN) cells, electro-optical performance comparable to that of TN cells with conventional polyimide layers was achieved, with almost no capacitance-voltage hysteresis. Moreover, LC cells based on IB-irradiated HfYGaO films had a high thermal budget. The proposed IB-irradiated solution-derived HfYGaO films have considerable potential for use in advanced LC applications.

Electro-optical switching of liquid crystals sandwiched between ion-beam-spurted graphene quantum dots-doped PEDOT:PSS composite layers.

Graphene quantum dots (GQDs)-doped PEDOT: PSS composite layers were utilized to align liquid crystals (LCs) via an ion-beam (IB)-spurting pre-treatment process. LCs were homogeneously aligned between sandwiched GQDs/ PEDOT: PSS composite thin layers, and the alignment of LCs was found to be affected by both the quantity of doped GQDs and IB-spurting intensity. Competitive electro-optical switching properties and non-residual DC performance of the cell equipped with GQDs/ PEDOT: PSS composite alignment layers were obtained because of the enhanced field effect and charge transport induced by doped GQDs. Notably, using IB-spurted GQDs/ PEDOT: PSS layers as alignment layers for next generation high-performance liquid crystal display (LCD) is promising.

Nickel Oxide Nanoparticles Doped Liquid Crystal System for Superior Electro-Optical Properties.

We examined the properties of nematic liquid crystal (N-LC) systems with dispersed nickel oxide nanoparticles (NPs). Uniform LC alignments with regular pretilt angles were achieved on rubbed polymer surface regardless of NiO nanoparticles concentration. We confirmed the electro-optical characteristics of twisted nematic (TN) cells containing NiO nanoparticles on rubbed polymer surface, which exhibited lower threshold voltages and faster response times with less capacitance hysteresis than pure LC cells. It is clear that the response time of TN cells on rubbed polymer surfaces decreases with increasing the NiO nanoparticles concentration. These results demonstrate the relationship between NP doping concentration and trapping of impurity ions, and were confirmed by a software simulation of electric flux and field density. NiO nanoparticles in the LC cells focused the electric field flux and strengthened the electric field. Further, NiO nanoparticles in LC medium trapped charged ionic impurities and suppressed the screen effect, leading to a stronger electric field and the van der Waals interactions between LC molecules and the alignment layers.

High performance twisted nematic liquid crystal display with solution-derived YZO surface modification via ion-beam irradiation.

Solution-derived YZO films were investigated as liquid crystal (LC) alignment layers modified by ion beam (IB) irradiation. Solution processing was adopted in place of the sputtering method for the deposition of YZO films as LC alignment layers. Uniform and homogeneous LC alignment was achieved to produce a high performance LC system. X-ray photoelectron spectroscopy analysis showed that surface reformation of YZO films by annealing and IB irradiation affects the uniformity of the LC alignment. Superior electro-optical characteristics of twisted nematic LC cells constructed from IB-irradiated YZO films were observed, which indicates that the proposed solution-derived YZO films have strong potential for use in the production of advanced LC displays.

Polarized UV cured reactive mesogens for fast switching and low voltage driving liquid crystal device.

Uniaxial alignment of liquid crystals (LCs) is prerequisite for a vast number of LC applications. To accomplish stable and uniform LC orientation, an alignment process to orient the LCs is required. Herein, we demonstrate a simple strategy for fabricating novel LC alignment layers that ensures well aligned LC, superior switching without any capacitance hysteresis, low transmittance loss, and high thermal stability with sufficient anchoring action. Thin films of reactive mesogens (RMs) were transferred onto conventional homeotropic polyimides from a UV-cured RM stamp via contact printing. LC displays using defect free RM/PI polymeric stacks exhibited superior electro-optic (EO) properties to those containing rubbed PI layers. This approach allows for the fabrication of various-mode LC displays such as twisted nematic (TN), in-plane switching (IPS), and optically compensated bend (OCB) mode LCDs by changing the combinations of RMs, base PIs and LCs.

Enhancement of electro-optic properties in liquid crystal devices via titanium nanoparticle doping.

We investigated the properties of nematic liquid crystal device (NLC) doped with titanium (Ti) nanoparticle (~100nm). The electro-optic (EO) properties of LCs changed according to Ti nanoparticle doping concentration. Ti nanoparticles in the NLC cells focused the electric field flux and strengthened the electric field. Further, Ti nanoparticles in NLC molecules may trap charged ionic impurities and suppress the screen effect, leading to a stronger electric field and the van der Waals dispersion interactions between NLC molecules and the alignment layers. We also simulated the boundary conditions of the Ti nanoparticles in the electric field using Ansoft Maxwell software. Our experimental results agreed with the phenomenon predicted by software simulation based on general physical theory. Synthetically, at a 1.0 wt. % Ti nanoparticle doping concentration, the NLC cells showed the best EO properties, such as a low threshold voltage (1.25V), fast response time (13.2ms), and low pretilt angle (3.90°).

Electro-optical characteristics of ZrO2 nanoparticle doped liquid crystal on ion-beam irradiated polyimide layer.

It is well known that doping liquid crystals (LCs) with nanoparticles can readily change the physical and electro-optical properties of LC mixture. In this paper, we report on how the electro-optical properties and thermal stability of an LC system were enhanced by dispersing zirconia (ZrO2) nanoparticles in nematic LCs on ion-beam irradiated polyimide layers. Homogeneous LC alignment was achieved and ZrO2/LC mixture was applied in twisted-nematic (TN) mode. The addition of ZrO2 nanoparticles contributed to improvement of electro-optical properties in the TN LC cell by lowering voltage operation and decreasing response time. The TN LC cells with a ZrO2 nanoparticle concentration of 2.0 wt% showed the lowest threshold voltage of 2.0 V and the fastest response time of 15.3 ms. This enhanced electro-optical performance was likely due to van-der waals interactions and the screening effect of the ZrO2 nanoparticles in the LC medium. The thermal stability of the ZrO2/LC mixture was also improved compared to a pristine LC system.

Characteristics of Al-doped ZnO films grown by atomic layer deposition for silicon nanowire photovoltaic device.

We report the structural, electrical, and optical characteristics of Al-doped ZnO (ZnO:Al) films deposited on glass by atomic layer deposition (ALD) with various Al2O3 film contents for use as transparent electrodes. Unlike films fabricated by a sputtering method, the diffraction peak position of the films deposited by ALD progressively moved to a higher angle with increasing Al2O3 film content. This indicates that Zn sites were effectively replaced by Al, due to layer-by-layer growth mechanism of ALD process which is based on alternate self-limiting surface chemical reactions. By adjusting the Al2O3 film content, a ZnO:Al film with low electrical resistivity (9.84 x 10(-4) Omega cm) was obtained at an Al2O3 film content of 3.17%, where the Al concentration, carrier mobility, optical transmittance, and bandgap energy were 2.8 wt%, 11.20 cm2 V(-1) s(-1), 94.23%, and 3.6 eV, respectively. Moreover, the estimated figure of merit value of our best sample was 8.2 m7Omega(-1). These results suggest that ZnO:Al films deposited by ALD could be useful for electronic devices in which especially require 3-dimensional conformal deposition of the transparent electrode and surface passivation.