Search

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. [ABSTRACT FROM AUTHOR]

Herein, we propose a brush‐coated zirconium‐doped lanthanum oxide (ZrLaO) film as a liquid crystal (LC) alignment layer. The film‐curing temperature was adjusted to 70, 150, and 230°C. Polarized optical microscopy and pre‐tilt angle analysis confirmed that there was uniform and homogeneous LC alignment on the 230°C cured ZrLaO film. Atomic force microscopy revealed that the surface had a nano/microgroove structure, which was caused by the shear stress generated by the brush‐coating process. This structure induced the uniform LC alignment. X‐ray photoelectron spectroscopy verified that the ZrLaO film was well‐formed on a glass substrate. The ZrLaO film displayed hydrophilic characteristics, and its surface energy increased as the film‐curing temperature increased. The ZrLaO alignment layer displayed suitable optical transmittance for LC device applications. The ZrLaO layer‐based twisted‐nematic LC cell exhibited more stable switching properties and better threshold voltage characteristics than conventional polyimide layers. Therefore, we expect that this brush‐coated ZrLaO layer will be a suitable LC alignment layer for LC device applications. [ABSTRACT FROM AUTHOR]

We investigated enhancing the electro-optical properties of thin films by doping them with graphene oxide (GO) following the fabrication of a zirconium strontium tin oxide solution via the sol–gel method. GO was doped into inorganic materials at 0, 5, and 15 wt%, respectively. The characteristics of the resulting thin films were analyzed based on doping ratio. Our study confirmed significant improvements in electrical properties through accelerated reaction speeds via response time vs. transmission measurements and notably enhanced T90 transmittance values in voltage–transmission measurements. X-ray photoelectron spectroscopy was employed to analyze the chemical composition of the thin film surfaces, revealing the impact of graphene's carbon isomer nature and the oxygen environment. Furthermore, changes in surface roughness were assessed using atomic force microscopy, validating the alterations in properties. Finally, the thin film's suitability for display devices was confirmed through transmittance measurements. [ABSTRACT FROM AUTHOR]

We investigated the alignment properties of liquid crystals (LC) on a brush-coated composite film made of graphene oxide and zinc oxide (GO-ZnO). The GO-ZnO composites were prepared using a sol-gel solution process, and the resulting solution was brush-coated onto indium tin oxide (ITO) glass. During the annealing process, an anisotropic roughened surface was created; however, the crystallinity analysis of GO-ZnO indicated that the brushed coating did not affect the crystalline structure significantly. The LC molecules exhibited stable alignment characteristics owing to the aligned surface roughness and hydrophilic properties of GO-ZnO, resulting in a homogeneously aligned structure. Residual DC measurements showed similar levels as the conventional rubbed polyimide cells, and a switching voltage of 1.7 V was observed. Brush coating is a cost-effective and simple deposition/alignment process, making it crucial in terms of cost-efficiency and process simplicity. Highlights: Demonstrate the application of brush-coated graphene oxide and zinc oxide films as alignment layers for LCDs. The sol-gel process, which converts precursor solutions into solid gel-like materials, allows production of homogeneously dispersed zinc oxide with graphene oxide. The functional groups present in graphene oxide offer opportunities for further chemical modifications and functionalization, enabling incorporation of specific properties and functionalities tailored toward specific applications. Combining GO and ZnO in a composite has a potential synergistic effect derived from its unique properties, making it a high-performance material for energy harvesting, photocatalysis and sensing applications. [ABSTRACT FROM AUTHOR]

In this study, a hybrid thin film was manufactured by doping graphene oxide (GO) into a sol–gel solution of aluminum magnesium oxide (AlMgO) using a brush process. The graphene oxide doping ratios used were 0, 5, and 15 wt%. In the process of manufacturing a thin film, the produced sol–gel solution generates a contractile force due to the shear stress of the brush bristles, forming a microgroove structure. This structure was analyzed through atomic force microscopy and transmission electron microscopy, and large particles were generated on the AlMgO-GO surface and roughness increased due to the shrinkage force of the solution. In addition, we investigated changes in the chemical composition of the surface due to the formation of a hybrid thin film through XPS analysis and found that thermal oxidation becomes more active as the oxygen deficiency layer decreases. Lastly, by comparing the change in electro-optical properties of the thin film due to the physical and chemical changes in the surface due to GO doping, it was demonstrated that GO doping greatly improved the electrical properties. Based on these observations, AlMgO-GO thin films can be considered promising candidates for next-generation displays and applications in semiconductors and solar and battery thin films. [ABSTRACT FROM AUTHOR]

Aluminum–nickel oxide and graphene oxide hybrid films are investigated in this study. The films produced via solution processing were doped with GO at three concentrations: 0, 5, and 15 wt%. The optical transmittances of the produced hybrid AlNiO films were examined for liquid crystal device applications, and their chemical properties were assessed via X-ray photoelectron spectroscopy. Atomic force microscopy and line profiling were used to examine the film surfaces. Polarized optical microscopy and pretilt angle analysis were used to confirm the uniform and homogeneous LC alignment on the hybrid AlNiO layer. The anisotropic oriented nano/microgroove structures on the surfaces of the films are believed to be due to the shear stress generated by the brush-coating process. LC cells assembled using the hybrid films showed stabler and faster switching performances with increasing GO doping. GO doping of the pure AlNiO film was also noted to increase the LC polar anchoring energy. [ABSTRACT FROM AUTHOR]

In this study, we describe the characterization and applicability of the liquid crystal (LC) system of brush-coated indium strontium oxide (InSrO) film. To achieve this aim, the film curing temperature was adjusted and the surface morphology was examined using atomic force microscopy and corresponding line profile data. In particular, we revealed a nano/microgroove anisotropic surface structure on the film after curing at 230°C, which was derived from the shear stress generated during movement of the wet brush hairs and subsequent active thermal oxidation of InSrO. In addition, x-ray photoelectron spectroscopy confirmed the presence of a well-formed InSrO film on the substrate. The film also exhibited hydrophilic properties at higher curing temperatures along with an amorphous structure. The InSrO film represented high optical transmittance to the LC system, and we confirmed the uniform and homogeneous LC alignment state using polarized optical microscopy and pre-tilt angle analyses. The oriented anisotropic film structure induced the alignment of LCs on the surface through geometric constraints. The InSrO film also exhibited advanced electro-optical performance with a fast response time and low operating voltage compared to the polyimide layer conventionally used in LC systems. From these results, we expect that brush-coated InSrO film will be a good alternative in advanced LC systems. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs) are an active area of interest for electro-optical devices, and the alignment of LCs has emerged as an extremely essential issue for LC devices. Evidence suggests that the surface topology of alignment layers plays a key role in both tuning the tilt angles and modulating the switching of LCs. Herein, nanotips are constructed by self-assembly of two different two-dimensional (2D) nanoflakes in PI hybrid alignment layers to modulate the switching of LCs. Both MoS2 nanotips and Ti3C2Tx MXene nanotips were observed on hybrid thin layers, but MoS2 nanotips are much thinner and taller. The hybrid thin layers are highly transparent, and the nanotips penetrating the hybrid layers roughened the surface but moderately declined the surface energy. LCs are strongly anchored on hybrid alignment layers, and the nanotips were found to topologically hinder the in-plane switching of LCs and hence accelerate the rewriting speed of optical data. Besides the accelerated optical rewriting speed, the surface plasmon–polariton (SPP) of nanoflakes also substantially boosted the external electric field to switch LCs and hence remarkably diminished the operating voltage and likewise sufficiently shortened the response time. In particular, the optical rewriting time of LCs that homogeneously aligned on hybrid alignment layers with 0.5% MoS2 nanoflakes doping has been deduced to as short as 43.36 s, which is a decrease of 37.81% compared to that of PI alignment layers cell; LCs can be electrically driven to switch optical data at 2.51 V and return to their original alignment state within 24.142 ms. These results signify the promising applications of hybrid thin layers for both traditional LC devices and optical rewritable LC devices. [ABSTRACT FROM AUTHOR]

Liquid crystal (LC) orientation films are one of the key technologies in display devices. Currently, the commonly used polyimide rubbing method exposes problems such as micro‐defects and static electricity. In this paper, a thin film was prepared from a mixture of UV‐curable polymer and NiO solution using the UV‐NIL method. At room temperature, all three temperatures showed good liquid crystal alignment properties. However, in terms of thermal stability, it was more thermally stable in the 1‐min sample. This means that the formation of patterns has a significant impact on orientation properties, and the change in van der Waals force due to chemical changes also affects the orientation properties to some extent. In addition, excellent electro‐optical properties were also confirmed. [ABSTRACT FROM AUTHOR]

A nanostructured composite of ultraviolet (UV)-curable polymer and TaO was fabricated by UV imprinting and confirmed by physical and chemical analysis using atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). Increasing the content of UV-curable polymers in the composite can successfully network with TaO and allow transfer. It was confirmed that nanostructured composite films could be successfully deposited on glass substrates depending on the UV-curable polymer content. AFM images with cross-sectional line profiles of 20 wt% composite films demonstrate that nanostructures can be successfully transferred. A uniform alignment was achieved with a stable pretilt angle on the transferred nanostructures. In addition, remarkably high-thermal budgets were observed due to the heat resistance of the films and nanostructures. Also, better C-V characteristics were observed compared to the rubbed polyimide liquid crystal (LC) cell. Therefore, nanostructured composites containing metal oxides and UV-curable polymers have great potential for LC devices considering their flexibility and sensitivity to heat such as rolling capability. This film can be used as an LC alignment layer with strong potential for high-quality LC applications. [ABSTRACT FROM AUTHOR]

This study investigated the modification effects of ion-beam exposure on polyacrylamide films according to molecular concentrations. Surface morphological examination using scanning electron microscopy showed increasing polyacrylamide particle size and film thicknesses with increasing concentrations. X-ray photoelectron spectroscopy and contact angle analysis were used to confirm the surface chemical reconstruction and increased surface energy after ion-beam exposure. As the molecular concentration increased, the changes were also observed to increase. The anisotropic ion-beam exposure induced strong van der Waals interactions with the liquid-crystals, leading to their uniform alignment. The uniform and homogeneous liquid-crystal alignment state was confirmed by polarized optical microscopy and pretilt angle analysis. Electro-optical performance evaluations showed the high potential of the ion-beam-exposed polyacrylamide film for use in liquid-crystal devices. Therefore, the correlation between the film molecular concentration and the IB process is successfully verified, and its applicability to liquid-crystal devices is confirmed. [ABSTRACT FROM AUTHOR]

Uniform and homogeneous liquid crystal (LC) alignment on a poly(ethylene‐co‐vinyl acetate) (EVA) layer subject to plasma ion‐beam (IB) treatment is confirmed. The layer molecular concentrations are controlled to 2, 4, and 6 wt%. Scanning electron microscopy exhibits a wrinkle pattern on the EVA surface that hinders LC alignment after IB treatment. However, X‐ray photoelectron spectroscopy shows chemical reconstruction on the surface; this induces strong van der Waals interactions with the LCs, which contribute to uniform LC alignment. The layer with higher molecular concentration is more heavily modified by IB treatment than that with low concentration, thereby achieving uniform LC alignment and overcoming topological disturbance. Contact angle analysis is used to verify that the surface energy increases via IB treatment; the uniform and homogeneous LC alignment is also confirmed by polarized optical microscopy and pretilt angle analysis. The EVA layer shows good optical transmittance and fine electro‐optical performances in terms of the switching and operating properties. Therefore, the plasma IB treatment is an effective method of deriving the surface characteristics of various polymeric materials for LC alignment, and the IB‐treated EVA layer has potential for application to LC systems. [ABSTRACT FROM AUTHOR]

This study compressed the conventional two-step process of brush coating and orientation for liquid crystal (LC) alignment layer manufacturing into a one-step process. Surface modification and LC alignment were performed by brush coating with a tin oxide solution prepared via the solgel process at different curing temperatures. The effect of the curing temperature on atomic bonds was analyzed through x-ray photoelectron spectroscopy, the physical morphology of the film surface was characterized by scanning electron microscopy and atomic force microscopy, and the LC alignment of the brush-coated tin oxide film was verified via polarized optical microscopy and pretilt angle measurements. The shear stress generated during the brush coating process formed a partial groove structure; the resulting anisotropy aligned the LC molecules homogeneously. The brush-coated film showed excellent LC orientation properties, confirming the potential of the proposed and efficient fabrication process as a new orientation technology. [ABSTRACT FROM AUTHOR]

This study uses imprint lithography to produce an anisotropic unidirectional indium gallium oxide (IGO) film for the uniform liquid crystal (LC) alignment layer. The curing temperature was controlled to 110, 180, and 250 °C during the process, and the 250 °C cured film presented a distinct one‐dimensional pattern transferred from the polydimethylsiloxane (PDMS) mold during scanning electron microscopy (SEM). X‐ray photoelectron spectroscopy (XPS) confirmed an active thermal oxidation effect at a high curing temperature, contributing to the formation of a unidirectional structure. This unidirectional IGO structure functioned as a guide for LCs and induced a uniform alignment state, verified by polarized optical microscopy (POM) and a pre‐tilt angle analysis. The IGO film also revealed improved thermal endurance to the LC alignment state and optical transmittance compared with the conventional rubbed polyimide (PI) layer. Given this performance, the one‐dimensional pattern‐imprinted IGO film can be a promising LC alignment layer for an advanced LC system. [ABSTRACT FROM AUTHOR]

In this study, a bismuth – lanthanum–tin oxide film was fabricated via brush coating to obtain a process-efficient liquid crystal (LC) alignment layer. The brush-coating solution was prepared through a sol – gel process, applied onto an indium tin oxide glass, and cured at various temperatures. The shearing stress caused by the brush coating process formed a micro-/nanogroove structure, as confirmed via atomic force microscopy and line profile analyses. The chemical composition of the surface was analysed through X-ray photoelectron spectroscopy, and the optical transmittance of the film was measured. As regards the LC alignment, polarised optical microscopy observations, thermal stability tests, and pretilt angle measurements were performed, confirming a stable alignment; the grooves generated during the shearing and hardening phases were most clearly formed after curing at 180°C, which led to stable LC orientation. [ABSTRACT FROM AUTHOR]

A hafnium strontium oxide (HfSrO) liquid crystal (LC) alignment film was efficiently created through brush coating, and its ability to change the LC alignment direction was confirmed. A brush was applied to HfSrO sol coated on an indium-tin oxide substrate, after which the coating was solidified at various curing temperatures. It was confirmed that a directional micro/nanostructure was formed above 280°C due to the shear stresses caused by the movement of the brush hairs. Surface chemical changes were analyzed by using X-ray photoelectron spectroscopy and contact angle measurements. As the curing temperature increased, the prevalence of oxygen bonds increased and the contact angle decreased, thereby increasing the surface energy. The anisotropic boundary of the microgrooves and the van der Waals forces due to an increase in surface energy changed the alignment direction of LC molecules from vertical to horizontal, as verified through polarized optical microscopy and pretilt angle measurements. Thus, the efficiency of the brush-coating method, which dramatically simplifies the LC alignment film process, was confirmed. The homeotropic/homogeneous LC alignment property of the HfSrO film produced through brush coating depending on the curing temperature provides an innovative approach for LC alignment. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) nanoimprint lithography (NIL) was performed using a hybrid solution of ZnO and UV-curable polymer. The concentration of the UV-curable polymer was varied as 5, 10, and 15 wt.%, and the surface was analyzed for each film. Physical modification of the surface morphology was analyzed by atomic force microscopy, and the clearest pattern was confirmed at 15 wt.%. Through X-ray photoelectron spectroscopy analysis, it was confirmed that the difference in the concentration of the UV-curable polymer caused a difference in the atomic and bonding composition on the film surface. Through optical transmittance measurements, it was observed that all of the patterned ZnO hybrid films exhibited sufficient transmittance. To investigate liquid crystal (LC) alignment, each of these films was assembled into an antiparallel structure to fabricate LC cells. Using polarized optical microscopy and thermal stability tests, it was confirmed that the LC cells fabricated with the 15 wt.% solution showed the most stable LC alignment. Moreover, pretilt angle measurements showed that the most stable transmittance curve was obtained with the 15 wt.% LC cell. The relationship between the height of the groove pattern and alignment of the LC molecules was analyzed using Berreman's model. Highlights: Nanoimprint lithography was performed by coating a hybrid solution of zinc oxide and UV-curable-polymer. Surface modification was analyzed through AFM, TEM, XRD, and XPS. It showed good LC alignment performance when cured for 15wt%. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We propose an efficient alignment method for liquid crystals (LCs). A brush-coating method handles film deposition and LC alignment treatment simultaneously herein, meaning a reduction in the conventional alignment layer treatment process steps. A lanthanum yttrium strontium oxide (LaYSrO) film prepared by the sol–gel process was used for the alignment layer. Topographical details of the brush-coated LaYSrO films (compared with spin-coated films) were investigated by atomic force microscopy. Spin-coated LaYSrO meant that the film formation alone without orientation treatment represented an isotropic surface. On the other hand, the 270 °C-cured brush-coated LaYSrO showed nano/microstructure with directionality. It indicates that brush-hair sweeping induced shearing stress on the sol state of the LaYSrO, which results in surface anisotropy for LC alignment. The uniform LC alignment state was confirmed by polarized optical microscopy and pretilt analysis. The brush-coated LaYSrO shows fine optical transparency compared to plain and indium-tin-oxide coated glasses, and thermal stability up to 150 °C for LC alignment. Competitive electro-optical performances of the brush-coated LaYSrO were verified in a twisted-nematic LC system compared to those of the conventionally used polyimide layer. Consequently, we expect that the brush-coating process can be an innovative technology for LC alignment. [ABSTRACT FROM AUTHOR]

A strontium-aluminum-lanthanum oxide (SrAlLaO) solution was prepared using the sol–gel method and brush-coated on ITO glass. The shear stress generated by brush coating aligns the SrAlLaO in one direction and creates a groove-shaped nanostructure. To confirm this, film surface analysis was conducted. The morphology of the surface was analyzed using atomic force microscopy, and the molecular composition of the surface was confirmed using x-ray photoelectron spectroscopy. By measuring the optical transmittance, the applicability to optical devices was confirmed. Additionally, it was analyzed whether the SrAlLaO film in which the nanostructure occurred functions as an LC alignment layer. For analysis, polarized optical microscopy and pretilt angle measurement were used. The groove structure and LC alignment were confirmed in the SrAlLaO film cured at 280 °C. [ABSTRACT FROM AUTHOR]

The surface modifications and liquid crystal (LC) alignment properties of polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene‐graft‐maleic anhydride (SEBS‐g‐MA) films induced by ion‐beam (IB) irradiation are reported herein. Changes to the surfaces of the SEBS‐g‐MA films from IB irradiation at various incidence angles and changes in the LC orientations upon LC cell fabrication were analyzed. The physical surface modifications due to IB irradiation were observed via atomic force microscopy. Additionally, changes in the molecular composition of the surface were observed through X‐ray photoelectron spectroscopy analysis. Polarized optical microscopy analysis shows that excellent LC alignment properties could be obtained after IB irradiation at angles exceeding 45°. Further, the anisotropy caused by IB irradiation was more responsible for uniform LC alignment than the corrugated pattern. [ABSTRACT FROM AUTHOR]

In this study, the surface modification and liquid crystal alignment characteristics of polystyrene-block-poly(ethylene-ran-butylene)-block- polystyrene (SEBS) coated glass substrates were analysed by varying the ion beam irradiation time. For the determination of the liquid crystal alignment characteristics, polarised optical microscopy was observed, and transmittance and pretilt angle were also measured. For the ascertainment of changes on the film surface, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analysis were conducted. AFM analysis showed changes in peaks on the film surface and the formation of wrinkled structures, and XPS analysis showed that the element ratio of the surface and the bonding structure changed, leading to strong dipole-dipole interaction that enhanced liquid crystal alignment characteristics. Notably, ion beam irradiation rendered the surface anisotropic, resulting in the liquid crystal molecules being aligned in one direction, and the orientation was stronger than the effect of the wrinkled structures. [ABSTRACT FROM AUTHOR]

In this study, a well‐ordered unidirectional nanostructure was successfully imprinted on a UV curable polymer/indium oxide hybrid film using UV nanoimprint lithography (NIL). The surface morphologies of the hybrid films were analyzed by atomic force microscopy (AFM), and the uniform nanostructure with a period of 820 nm and height of 30 nm was observed on a 6 min UV‐irradiated film by line profile from AFM. The chemical modification of the films according to UV irradiation time was analyzed by X‐ray photoelectron spectroscopy. The nanopatterned hybrid film was applied to the liquid crystal (LC) alignment layer and the polarized optical microscopy and pretilt angle analysis demonstrated the highly uniform and homogeneous LC alignment state. The unidirectional nanostructure guided the LCs orientation and the aligned surface anisotropy which induces the uniform LC alignment. The hybrid film chemical affinity was analyzed by contact angle measurement, and the increased surface energy after UV irradiation contributed to the homogeneous LC alignment. Therefore, various organic/inorganic hybrid films can be used for nanostructure construction via UV NIL, and it has a high potential for application in diverse LC systems. [ABSTRACT FROM AUTHOR]

Smart windows that both reversibly occlude visible light and modulate the penetration of near‐infrared (NIR) light save a great deal of energy. Here, a simple, super‐fast, electrically switchable smart window that initially reflects NIR light and then scatters it in response to thermal stimuli is designed and fabricated. Transparent polymer‐stabilized cholesteric liquid crystals (PSCLCs) are prepared by photo‐polymerizing RM 257 monomers in which the planar CLCs fully reflected NIR light (1050–1550 nm). Next, an ultra‐thin, thermotropic, W0.003V0.997O2‐doped polyvinylpyrrolidone hybrid thin layer that modulates NIR light penetration over a very broad temperature range is overlaid on the PSCLCs, and the final WVO‐PSCLCs smart window features four NIR modulation modes. Specifically, when a model wood house with three 1.5‐ × 2‐cm WVO‐PSCLCs smart windows is thermally irradiated by a 250‐W infrared light for 10 min, the internal temperature is 4.8 °C less than that of a house lacking smart windows. Flexible smart windows fabricated from polyethylene terephthalate (PET) could be bent through a radius of 15 mm without any noticeable damage, and are very resistant to external vertical pressure. The flexible WVO‐PSCLCs smart windows are versatile, and afford outstanding transparency management and modulation of NIR light penetration. [ABSTRACT FROM AUTHOR]

Tunable liquid crystal (LC) alignment with twisted nematic (TN) and vertical alignment (VA) driving modes is achieved by a convenient brush‐coating method. The brush‐coating process combines film deposition and alignment treatment processes, and lanthanum aluminum zirconium zinc oxide (LaAlZrZnO) is used for the LC alignment layer. X‐ray photoelectron spectroscopy results confirm LaAlZrZnO film formation with fine optical transparency. Atomic force microscopy and line profile data indicate nano/micro surface structure with dense or directional morphologies induced by shear stresses according to film curing temperature. Low‐temperature‐cured films exhibit hydrophobic properties with low surface energy, whereas high‐temperature‐cured films show hydrophilicity with high surface energy. The geometric constraints and chemical affinities of the films induce homeotropic and homogeneous LC alignments on the surface according to the film curing temperature, respectively. The LC alignment state is verified by polarized optical microscopy and pretilt angle analysis. The brush‐coated LaAlZrZnO film demonstrates high thermal budget for advanced LC systems. The VA‐mode and TN‐mode LC cells based on the LaAlZrZnO film enable high electro‐optical performances and low power consumption. Therefore, the brush‐coating method is expected to be adoptable for next‐generation LC device applications. [ABSTRACT FROM AUTHOR]

A uniform unidirectional nanostructure composed of aluminum tin oxide and ultraviolet (UV)-curable polymer is introduced herein. The nanostructure was produced by UV-nanoimprint lithography (UV-NIL), and the fabricated hybrid film was used as a uniform liquid crystal (LC) alignment layer. Atomic force microscopy and line profile analysis were performed to confirm a well-ordered nanostructure with 760 nm periodicity and 30 nm height. X-ray photoelectron spectroscopy analysis was also conducted to examine the chemical modifications to the hybrid film surface during UV exposure. Optical transmittance investigation of the nanopatterned hybrid film revealed its compatibility for LC device application. Stable, uniform, and homogeneous LC alignment on the hybrid film was confirmed by polarized optical microscopy observance and analysis of LC pretilt angle. The unidirectional structure on the film surface enabled uniform LC orientation along with surface anisotropy property. Hence, we expect that the proposed UV-NIL process can be applied to fabricate high-resolution unidirectional nanostructures with various inorganic/organic hybrid materials and that these nanostructures have high potential for next-generation LC systems. [ABSTRACT FROM AUTHOR]

We present a convenient liquid crystal (LC) alignment method using brush hairs. An yttrium strontium tin oxide (YSrSnO) solution was prepared using a sol–gel process, and the one-step brush-coating process integrated film deposition and alignment. X-ray photoelectron spectroscopy confirmed a well-formed YSrSnO film via thermal oxidation. Atomic force microscopy showed oriented micro/nanostructures of the brush-coated film, attributed to shearing stress from brush-hair movements on the coating surface; the directionality was identical to that of the brushed coating, which caused physical surface anisotropy and uniform LC alignment on the YSrSnO layer. Uniform and homogeneous LC alignment was confirmed by polarized optical microscopy and pretilt angle measurements. Thermal stability tests of the LCs showed a suitable thermal budget, and the YSrSnO film showed fine optical transparency. Excellent electro-optical properties were observed in twisted-nematic LC system with remarkable low operating voltage. Thus, we expect brush coating to be a viable next-generation technology for LC systems. [ABSTRACT FROM AUTHOR]

We investigated ion‐beam (IB)‐treated polyacrylamide (PAM) film as a liquid crystal (LC) alignment layer. Polarized optical microscopy and pretilt angle analysis show the uniform LC alignment status. Atomic force microscopy shows the IB etching effect, and X‐ray photoelectron spectroscopy indicates the formation of carbon–oxygen bonds on the surface, which ensured the uniform alignment of LC molecules via van der Waals forces interaction. The reformed PAM films also had good thermal budgets and optical transparency for the LC system. The IB‐treated PAM films demonstrated stable electro‐optical performances in a twisted nematic LC system. Hence, IB treatment can be an effective method to apply several polymer materials to the LC alignment layer, and IB‐irradiated PAM films have remarkable potential for use in the LC system. [ABSTRACT FROM AUTHOR]

We report uniform liquid crystal (LC) alignment on a polyacrylamide (PAM) film via ion beam (IB) treatment. The IB incidence angle is adjusted from 15° to 75°. Physicochemical modifications caused by the IB process are investigated by atomic force microscopy and x-ray photoelectron spectroscopy. Low IB incidence results in biased and bumpy surfaces, whereas high IB incidence forms isotropic and smooth surfaces; both of these are unsuitable for uniform LC alignment. The 45° IB incidence induces anisotropic surface chemical reformations, and these modifications induce van der Waals forces between the LCs and modified PAM, thereby leading to uniform LC alignment. The LC alignment state is verified by polarized optical microscopy and pretilt angle. The electro-optical characteristic of the modified PAM showed excellent switching performance in twisted-nematic LC system. Thus, the IB-treated PAM film is a good candidate for LC alignment layers and suitable for LC device applications. [ABSTRACT FROM AUTHOR]

Nanoimprint lithography is a very convenient and cost-effective method, and when combined with a sol–gel process, can be used to simply accomplish the nanopatterning of a bismuth tin oxide (BTO) film. We achieved the transfer of a nanostructure to a solution-driven BTO film by using nanoimprint lithography for utilization as a liquid crystal (LC) alignment layer. A curing temperature of 250 ℃ was ideal for the transfer of the nanopattern from polydimethylsiloxane to a BTO film, as confirmed by using atomic force microscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy. The nanopattern led to the uniform alignment of LC molecules, as confirmed via polarized optical microscopy and pretilt angle analysis. In addition, the nanopattern-imprinted BTO film showed great potential for LC applications due to its high thermal stability and optical transmittance, along with super-fast switching and low voltage operating electro-optical characteristics. Sol–gel nanopatterning of metal oxides is a convenient process to create LC-alignment films for application in diverse electro-optical devices. [ABSTRACT FROM AUTHOR]

A liquid crystal (LC) alignment layer was created using the nanoimprint lithography method and ultraviolet (UV) curing. A hybrid film of a solution of gallium oxide (GaO) and a UV-curing polymer was coated on a substrate and cured by UV irradiation. After that, an LC cell was manufactured by assembling two films by an antiparallel method. The LC orientation characteristics and the surface were analyzed by varying the curing time. The molecular composition of the coated film surface was confirmed via X-ray photoelectron spectroscopy, and nanopattern formation was observed through atomic force microscopy. The LC alignment characteristics were analyzed by polarized optical microscopy and pretilt angle measurements, and thermal stability tests were performed. It was confirmed that the refractive index anisotropy and van der Waals forces based on the nanopattern formation enabled a homogeneous and uniform alignment of the LC molecules; further, it was found that the GaO hybrid film was suitable for use as an LC alignment layer. [ABSTRACT FROM AUTHOR]

The characteristics of a poly(ethylene-co-vinyl acetate) (PEVA) film formed by spin coating process and ion beam (IB) irradiation was investigated with irradiation times. A physicochemical analysis was used to analyse the suitability of the PEVA film as a uniform liquid crystal (LC) alignment layer. Atomic force microscopy (AFM) revealed an increased surface roughness after IB irradiation. X-ray photoelectron spectroscopy (XPS) analysis showed IB irradiation broke the polymer branches and increased the oxygen concentration and bonding on the surface. These derived the strong Van der Waals forces and dipole-dipole interactions between the PEVA surface and LCs. The IB irradiation generated surface anisotropy on the PEVA film and unidirectional LC alignment was achieved. Polarised optical microscopy (POM) and pre-tilt angle measurements were carried out to show the uniform LC alignment. The transmittance curve exhibited a high optical performance. These results show the promising capabilities of IB irradiated PEVA film as an alignment layer in LC displays. [ABSTRACT FROM AUTHOR]

Behavior of liquid crystal (LC) is a result of interaction between the geometrical shape restrictions of the adjacent surface and molecular forces among LCs or adjacent surface. For years, continuous efforts have been made to control LC orientation and anchoring with pretilt angle for modulating the electro‐optical characteristics. For now, diverse driving modes have been developed including twisted nematic, optically compensated bend, electrically controlled birefringence, and vertical alignment. However, it has the limitation that different fabrication process should be adopted in different driving mode such as materials of alignment layer and techniques for aligning the LCs. Herein, selective LC modes are achieved by controlling the LC pretilt angle using nanopatterned organic/inorganic hybrid thin films composed of polyimide (PI) and tin oxide (SnO). It is possible to control the surface wettability according to the composition ratio between PI and SnO, thereby adjusting the pretilt angle of the LCs. Fabrication of SnO combined with PI applied via embossing allows for the large‐scale replication for LC alignment and based on consumer demand, devices can be manufactured in various modes through simple configuration changes. Therefore, an inorganic compound combined with an organic one permits designing addressable LC driving modes. [ABSTRACT FROM AUTHOR]

A super‐fast optically rewritable liquid crystal display (ORLCD) has been developed using a MoS2 nano‐flakes doped polyimide (PI) hybrid thin layer in this paper. The MoS2 hybrid thin layer was prepared by directly doped MoS2 nano‐flakes in PI solution, and is of high transparency over 85% in the visible range of 480 to 780 nm including a substrate. Liquid crystals (LCs) were antiparallelly aligned between rubbed MoS2 hybrid thin layer and optically oriented SD1 thin layer, and subsequently were realigned by polarized blue laser irritation in multi‐domains. The realignment of LCs generates visible optical changes under polarized optical microscope (POM) and makes the written information readable. The rewriting time in which LCs are optically switched to achieve the highest contrast was also found remarkably reduced by MoS2 nano‐flakes. In specific, by using a 1% MoS2 nano‐flakes doped PI hybrid thin layer, the rewriting time has been reduced to 37.36s, which is about 46.41% decrease compared with pure PI cell. The accelerated rewriting time here is believed mainly caused by strengthened anchoring of LCs on bumpy hybrid thin layer due to MoS2 nano‐flakes agglomeration, which super‐fast actualizes the high optical contrast in domains. These findings will significantly contribute to a wide range of research and applications of ORLCD. [ABSTRACT FROM AUTHOR]

In this paper, we reported a highly thermal stable YP‐11 polymer stabilized cholesteric liquid crystal (YP‐11 PSCT) for smart windows that can be electrically switched from transparent to opaque. The polymerization between photo‐sensitive monomers (RM 257) has been characterized using a polarized optical microscope (POM), which has been found to become much firmer and denser by raising the doping concentration. The 3D polymer matrices remarkably affect the electro‐optical performances of YP‐11 PSCT, and the cholesteric liquid crystals (Ch LCs) within polymer matrices were found merely able to be reversibly switched until the doping concentration of RM 257 was raised up to 3%. Specifically, the threshold voltage, raising time and decaying time of a 3% YP‐11 PSCT cell were determined as 22.908 V, 85.442 ms and 18.617 ms, respectively. The critical thermal‐stable temperature of the 3% YP‐11 PSCT was further evaluated using a hot stage and was confirmed as high as up to 100 °C. These findings in this paper will significantly contribute to the development of smart windows. [ABSTRACT FROM AUTHOR]

This paper introduces the characteristics of the zinc oxide (ZnO) inorganic film deposited by radio-frequency magnetron sputtering as an alternative alignment layer for liquid crystal display (LCD) applications. The crystalline structure related to the texture formation of ZnO [formula] was observed with a tilt angle of approximately 28.1° to the ZnO (0001) plane, leading to a smooth surface and high-density structure. Ion beam (IB) bombardment at various incident angles was used to induce liquid crystal (LC) alignment and cause the measured pretilt angle on ZnO films to assume a triangular contour. The orientation order of liquid crystal molecules was due to the van der Waals force for the vertical alignment of LCs with selective breaking of O–Zn bonds by IB bombardment. The contact angle contour as a function of the IB incident angle resembled the behavior of the pretilt angle. The pretilt angle is controllable by adjusting the surface features on ZnO films with IB bombardment. The electro-optic characteristics of vertically aligned (VA)-LCD based on ZnO film were comparable to those of VA-LCD based on polyimide, showing good potential of ZnO film as a LC alignment layer. [ABSTRACT FROM AUTHOR]

This paper introduces the vertically aligned twisted nematic in-plane switching (VPS) structure, and compares the electro-optical (EO) characteristics of VPS liquid crystal displays (LCDs) and in-plane switching (IPS) LCDs. Various VPS-LCD pretilt angles were induced, and ion beam (IB) irradiation was used to enhance the EO properties. An x-ray photoelectron spectroscopic analysis of the IB-irradiated polymer surface confirmed that the intensity of C=O bonding as a function of exposure time traced the pretilt angles. The pretilt angle effect on optical properties was first analyzed in the experimental results. While multidomain vertical alignment LCDs and IPS-LCDs only resolve one difficulty, the VPS-LCDs described here overcome several viewing angle and transmittance curve problems. [ABSTRACT FROM AUTHOR]

We investigated the effects of ion beam (IB) irradiation and rubbing on the directional behavior and alignment mechanism of liquid crystals (LCs) on polyimide (PI) surfaces. We found that the LC direction follows the IB irradiation alignment direction on the PI surface regardless of whether the irradiation occurs before or after rubbing. We assumed that the LC direction depends strongly on the C–O bonds created from C=O bonds on the PI surface broken by IB irradiation and conducted an investigation of the chemical bonding state of the PI surface by x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

The surface modification characteristics of liquid crystal (LC) alignment layers irradiated with various argon (Ar) ion beam (IB) energies were investigated as a substitute for rubbing technology. Various pretilt angles were created on the IB-irradiated polyimide (PI) surfaces after IB irradiation, but the Ar ions did not alter the morphology on the PI surface, indicating that the pretilt angle was not due to microgrooves. The chemical bonding states of the IB-irradiated PI surfaces were analyzed in detail by x-ray photoelectron spectroscopy to verify the compositional behavior for the LC alignment. Chemical structure analysis showed that the alignment ability of LCs was due to the preferential reorientation of the carbon network due to the breaking of C=O double bonds in the imide ring parallel to the incident IB direction. The potential of applying nonrubbing technology to display devices was further supported by the superior electro-optical characteristics compared to rubbed PI. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the generation of high pretilt angles in nematic liquid crystal (LC) on a rubbed surface of polyimide (PI) containing trifluoromethyl moieties. Importance of the alignment of LC; Methodology used; Pretilt angle generated; Results and discussion.

We demonstrated uniform LC alignment on IB-irradiated aluminium tin oxide (AlSnO) by controlling the annealing temperature. Physico-chemical analyses were carried out to determine the surface modification and uniform LC alignment mechanism as a function of the annealing temperature. IB irradiation induced the breakdown of the chemical bonds of AlSnO, preserving its anisotropic characteristics along the direction of IB irradiation, allowing for uniform alignment of the LC molecules on the reformed surface. However, at annealing temperatures under the boiling point of the solvent, residual solvent remained on the surface, thereby prohibiting uniform LC alignment. Moreover, we obtained good optical transmittance in the visual region and good electro-optical performance. Therefore, the IB-irradiated AlSnO film annealed above 200°C exhibited good potential as an alternative candidate for LC display applications. [ABSTRACT FROM AUTHOR]

In this article, we demonstrate the liquid crystal (LC) alignment characteristics of solution‐derived nickel oxide (NiO) film modified with ion‐beam (IB) irradiation. Cross‐polarized optical microscopy and pretilt angle measurements verified that uniform LC alignment was achieved using the NiO film as an alignment layer regardless of IB incidence angle. Contact angle measurements revealed that all of the NiO films had a deionized water contact angle below 90°, which indicates that they had hydrophilic surfaces that had an effect on the homogeneous LC alignment. Atomic force microscopy was conducted to determine the physical surface modification due to the IB irradiation, which showed that it reduced the size of the surface grains with agglomerations depending on the surface tilt from the IB incidence angle. Furthermore, microgroove structures strongly related to uniform LC alignment were observed after IB irradiation. Chemical surface modification was investigated via an X‐ray photoelectron spectroscopy analysis which revealed that IB irradiation modified the chemical bonds in the NiO film, and this affected the LC alignment state. Thus, these results indicate that using NiO film exposed to IB irradiation as an alignment layer is a suitable method for LC applications. [ABSTRACT FROM AUTHOR]

The characteristics of ion beam (IB) irradiated polyethylene glycol (PEG) films were analyzed to determine their potential use as a liquid crystal (LC) alignment layer. The transmittance of the PEG films at various IB intensities was measured to verify the possibility of using it as an alignment layer. Anti-parallel cells with the PEG film were fabricated to examine the LC alignment characteristics. Perfectly dark cross-polarized microscopy images were obtained at an intensity of 700 eV, which indicates uniform LC alignment, and pre-tilt angle measurements supported this finding. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses were conducted to determine the effect of the IB irradiation on the PEG film on the surface modification. After exposure at an IB intensity of 700 eV where uniform LC alignment was achieved, remarkable chemical composition modification of the PEG film, including the reduction of C-O bonds that affected the uniform LC alignment, was observed via the XPS analysis. Furthermore, the AFM analysis revealed that low kurtosis value was obtained at this IB intensity. Therefore, we are convinced that the PEG films irradiated at this low IB intensity show potential as alternative alignment layer in LC applications. [ABSTRACT FROM AUTHOR]

We investigated the surface modification induced by the ion-beam (IB) irradiation of a polyethylene glycol (PEG) film and its liquid crystal (LC) alignment characteristics. The X-ray photoelectron spectroscopy analysis revealed the chemical modification; as the IB incidence angle increased, the number of surface C–O bonds decreased, inducing an anisotropic dipole moment on the PEG film surface. In addition, the physical modification was demonstrated via atomic force microscopy analysis using three-dimensional images as a function of the IB incidence angle. The surface roughness was analyzed; the modification with the smoothest surface was observed for an IB incidence angle of 45°. This modification affected the LC alignment state of the PEG film, as demonstrated by the polarized optical microscopy analysis with pre-tilt angle measurements. Furthermore, for the same IB incidence angle, the residual DC measured using the capacitance–voltage curves was extremely low. Hence, a PEG film irradiated with an IB incidence angle of 45° could be a suitable LC alignment layer. [ABSTRACT FROM AUTHOR]

Ion beam (IB)-spurted indium tin oxide (ITO) thin layers are used to align liquid crystals (LC) with a lower driving voltage. During IB spurting process, the microcrystals transforming to large crystals of ITO is intimated by the change of In (3d), Sn (3d) and O (1s) core level in XPS spectra and the surface topology modifications in SEM and AFM images, and IB-spurted ITO thin layers are comparably transparent and conductive compared with ITO thin layers. The increased interactions between LC and IB-spurted ITO thin layers together with the roughed surface topology of ITO thin layers are the main causes for LC alignment. The fast response and distribution of electrical dipoles to external voltage in LC causes LC's extremely low threshold voltage drive; in addition, LC directly aligned on ITO thin layers free from alignment layers shield effect further decreases LC's threshold voltage. 1.8-keV IB-spurted ITO thin layers are more appropriate to align LC with the threshold voltage of 0.4853 V and the rising time of 0.237 ms. [ABSTRACT FROM AUTHOR]

Uniform and defect-free homogeneous alignment of liquid crystal (LC) molecules on solution-derived bismuth-doped tin oxide (TBO) films has been achieved using ion-beam (IB) irradiation. We performed measurements and physicochemical analysis to verify and establish the cause of the successful LC alignment. In addition, we measured the electro-optical characteristics of twisted-nematic cells with IB-irradiated TBO films to explore the suitability of this material for liquid crystal displays (LCDs). The results indicate that this approach will allow the fabrication of high-performance enhanced LCD devices. [ABSTRACT FROM AUTHOR]