Free residual DC voltage for nematic liquid crystals on solution-derived lanthanum tin oxide film

We present the liquid crystal (LC) alignment properties of solution-derived lanthanum tin oxide (LaSnO) films cured at various temperatures and exposed to ion-beam (IB) irradiation. Using a solution process, LaSnO films were deposited on the indium-tin-oxide glass substrates and IB irradiation was used as an alignment method. Homogeneous and uniform LC alignment was achieved and observed by cross-polarised optical microscopy. Pre-tilt angle results with low standard deviation supported the notion of uniform LC alignment. The LaSnO film cured at 300°C showed nearly zero capacitance–voltage hysteresis. The change of the surface morphology of the LaSnO film due to IB irradiation was observed by atomic force microscopy. The effects of IB irradiation on the LC alignment layer were further demonstrated by X-ray photoelectron spectroscopy. The strong IB irradiation broke the metal–oxide bonds present, which in turn induced an increased number of oxygen vacancies on the whole surface. Uniform LC alignment was attributed to surface reformation and van der Waals forces.     

Liquid crystal aligning capabilities on surface-reformed indium-doped zinc oxide films via ion-beam exposure

We investigated the characteristics of a solution-processed indium-doped zinc oxide (In:ZnO) film formed via ion-beam (IB) irradiation as a liquid crystal (LC) alignment layer. The In:ZnO film was deposited using solution processing and cured at various temperatures. Uniform LC alignment was observed at all curing temperatures in cross-polarised optical microscopy images. A regular pre-tilt angle supported these results and showed homogeneous LC alignment. Several surface analyses were conducted to evaluate the effect of IB irradiation on the In:ZnO film surface. X-ray diffraction analysis showed an amorphous structure both before and after IB irradiation, and physical surface reformation was observed using atomic force microscopy. Root mean square surface roughness was reduced and a smooth surface was achieved after IB irradiation. X-ray photoelectron spectroscopy was used to detect chemical surface reformation. It was found that the IB irradiation broke the metal-oxide bonds and increased the occurrence of oxygen vacancies, which affected the van der Waals forces between the LC molecules and the In:ZnO film surface. Electrical performance was observed to identify the possibility of using the In:ZnO film in LC applications. Enhanced electro-optical performance was measured and zero residual DC voltage which was verified using a capacitance-voltage curve was achieved.     

Homogeneous alignment of liquid crystals on low-temperature solution-derived gallium oxide films via IB irradiation method

In this paper, solution-derived gallium oxide (GaO) films are fabricated for the homogeneous alignment of liquid crystals (LCs) after an ion-beam (IB) irradiation process. GaO thin films are prepared under a variety of temperatures and different IB irradiation intensities, and the physicochemical performances of the fabricated GaO thin films are analysed using a UV-vis spectrometer, an atomic force microscope, and X-ray photoelectron spectroscopy. A higher transmittance of 85.40% from GaO thin film is obtained compared with that of polyimide (PI) film (83.52%), which indicates the feasibility for a GaO thin layer to substitute for a conventional PI layer as an alignment layer. LCs are found to align on the GaO thin film after pre-baking at 100°C and homogeneous and uniform low-IB intensity irradiation. We also determined the electro-optical (EO) characteristics of the twisted nematic (TN) cells fabricated with GaO thin layers and found them to be similar to those of cells fabricated with PI layers. Overall, GaO films achieved via the IB irradiation method are promising LC alignment layers due to the method’s low-temperature solution-derived process.     

Physicochemical analysis of ion beam-induced surface modifications on polyethylene glycol films for liquid crystal alignment

ABSTRACT

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.     

Homogeneously aligned liquid crystal molecules on unidirectional buckle pattern of polyurethane films

We present the fabrication of an anisotropic structure on a polyurethane (PU) film for aligning liquid crystal (LC) molecules with ion beam (IB) irradiation at an incident angle. The obtained anisotropic structure assembles the LC cells in a layer that aligns LC molecules uniformly. Polarised optical microscopy images of an LC cell fabricated with IB-irradiated PU were captured to confirm the LC alignment state and compared with those fabricated with non-treated PU. To analyse the effects of the IB irradiation, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy were used to investigate the chemical and morphological modifications, respectively. IB irradiation modifies the chemical structure of PU, which indicates that a new skin layer is formed on the PU films. This skin layer generates an in-plane compressive strain, thereby creating buckles on the PU films. Simultaneously, the physical collision of the reactive Ar⁺ ions during IB irradiation induces a directional strain on the surface, thereby forming a unidirectional structure of buckles along the direction of IB irradiation. The PU film annealed at 200°C showed the high average transmittance of 88.9%, which is appropriate as an alignment layer.     

Super fast switching and low operating of liquid crystals sandwiched between ion beam-spurted ITO thin layers

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.     

Homogeneous liquid crystal orientation on ion beam exposure TiO2 surfaces depending on an anisotropic dipole field

We studied homogeneous liquid crystal (LC) alignment properties on ion-beam (IB) irradiated TiO₂ films deposited by the electron beam evaporation method. Stable homogeneous LC alignment on a TiO₂ surface resulted from IB irradiation energy over 1800 eV. X-ray photoelectron spectroscopy analyses showed that Ti⁴⁺ 2p_3/2 and Ti⁴⁺ 2p_1/2 peaks were increased with increasing IB energy. Assuming that the increased peaks produced anisotropy dipole fields in the direction of the IB exposure process, we confirmed that the increasing IB energy induced strengthened the surface energy for entirely clear and stable LC molecule orientation. The voltage-transmittance characteristics of the twisted-nematic cell on the TiO₂ surface indicate that the TiO₂ film has potential for use as the LC alignment layer.     

Twisted nematic LC mode with high electro-optical performance and high thermal endurance formed using IB-irradiated poly(methyl methacrylate) as an alignment layer

We obtained homogeneously aligned liquid crystals (LCs) on ion beam (IB) irradiated poly(methyl methacrylate) (PMMA) by controlling the IB energy. We then examined the LC alignment state using polarized optical microscopy and conducted thermal stability testing. We obtained homogeneous LC alignment at IB energies above 1,400 eV, indicating that strong IB energy facilitates the alignment of LCs on the PMMA surface. This surface was analyzed by atomic force microscopy, and the contact angles (CAs) were measured to elucidate the mechanism of LC alignment. The increased surface energy strengthened the van der Waals interaction between the surface and LCs, thereby inducing stable, homogeneous LC alignment. Electro-optical (EO) characteristics were measured using twisted nematic (TN) LC mode. Compared to LC cells with conventionally used rubbed polyimide (PI), the LC cells with IB-irradiated PMMA exhibited higher thermal budgets and good electro-optical characteristics. These new LC cells have promising potential for advanced LC displays.     

Liquid crystal alignment on ion-beam irradiated bismuth-doped tin oxide films and their application to liquid crystal displays

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.     

Alignment of liquid crystals on solution-processed HfZnO films via ion beam irradiation

Liquid crystal (LC) alignment layers were prepared by fabricating solution-processed HfZnO films, annealing them, and treating them with ion beam (IB) irradiation, and the effect of annealing temperature upon the resulting film properties was studied. Homogeneous LC alignment was achieved on IB-irradiated HfZnO films. Topographical changes were observed from field-emission scanning electron microscopy as annealing temperature increased. X-ray photoelectron spectroscopy analysis showed that IB irradiation resulted in oxidation of HfZnO surfaces, which caused the LCs to be oriented more uniformly. The best electro-optical characteristics observed corresponded to the annealing temperature of 200°C. The low optimal annealing temperature for fabricating the HfZnO films suggested that this material has remarkable potential for LCD applications.     

The effects of oxygen concentration on ultraviolet luminescence of ZnO films by sol–gel technology and annealing

ZnO thin films were successfully deposited on SiO₂/Si substrate using the sol–gel technique and annealed in various annealing atmospheres at 900 °C by rapid thermal annealing (RTA). X-ray diffraction revealed the (002) texture of ZnO thin films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the grains of the ZnO thin film were enlarged and its surface was smoothed upon annealing in oxygen. PL measurement revealed two ultraviolet (UV) luminescence bands at 375 and 380 nm. The intensity of the emission peak at 380 nm became stronger as the concentration of oxygen in the annealing atmosphere increased. The X-ray photoelectron spectrum (XPS) demonstrated that a more stoichiometric ZnO thin film was obtained upon annealing in oxygen and more excitons were generated from the radiative recombination carriers consistently. Additionally, the UV intensity increased with the thickness of ZnO thin film.     

Bent-core liquid crystal-functionalised flexible polymer substrates for liquid crystal alignment

ABSTRACT

A transparent flexible polymer film is chemically functionalised with a bent-core liquid crystal (BCLC) compound for effective alignment of the bulk BCLC sample at the substrate–LC interface. The surface attachment was achieved via a simple procedure which involved pre-treatment of the polymer film (commercial name: over head projector film) using piranha solution followed by chemically attaching the BCLC compound through silane condensation reaction. Surface characterisation of the unmodified and BC-modified flexible films was carried out through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, contact angle (CA) and atomic force microscopy (AFM) techniques. The BC-modified flexible substrates are analysed for their efficiency to orient the bulk LC sample. Remarkably, the chemically modified polymer substrates are highly efficient in vertically aligning both the BC and rod-like LC samples at the substrate–LC interface, in comparison to their unmodified counterparts. The described method is simple, reproducible, surface modified substrates are highly stable and more importantly reusable. The demonstrated method for the alignment of BCLCs advances a step forward towards the realisation of applications proposed for these fascinating compounds.     

Morphological Investigation of Poly[methyl(H)silane-co-diphenylsilane] Irradiated by XeCl Excimer Laser

The morphological properties of poly[methyl(H)silane-co-diphenylsilane] copolymer (PSH) under XeCl (308 nm) laser irradiation were investigated. For this purpose, PSH films were exposed to XeCl excimer laser, 308 nm, at various UV doses (122 and 366 mJ/cm²), with 11 and 33 mJ/pulse and 1 Hz pulse repetition rate. The morphology of the PSH film surface was investigated by the atomic force microscopy (AFM) technique. AFM identifies that the films of the copolymer form a wormlike morphology before irradiation and conical defects are created on the polymer surface and grow with the laser irradiation.     

Vertical alignment of liquid crystal on tocopherol-substituted polystyrene films

We synthesised a series of vitamin-based and renewable tocopherol-substituted polystyrene (PTOC#, # = 20, 40, 60, 80 and 100), where # is the molar content of tocopherol moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of tocopherol side group showed vertical LC alignment behaviour. The vertical alignment (VA) behaviour was well correlated with the surface energy value of these polymer films. For example, VA was observed when the surface energy values of the polymer were smaller than about 35.22 mJ/m² generated by the nonpolar tocopherol moiety having long and bulky carbon groups. Good electro-optical characteristics, such as voltage holding ratio and residual DC voltage, and aligning stabilities at 200°C and ultraviolet irradiation of 10 J/cm² were observed for the LC cells fabricated using PTOC100 as a LC alignment layer. Therefore, it was first found that the renewable tocopherol-based materials can produce an eco-friendly vertical LC alignment system.     

Fabrication and electrical characterization of transparent NiO/ZnO p–n junction by the sol–gel spin coating method

Sol–gel spin technique was used to fabricate transparent p–n junction between NiO and ZnO semiconductors. Atomic force microscopy studies indicated that ZnO film had a fibrous structure, while NiO film showed very smooth surface morphology. The optical transmittance of these films was about 75 %. The optical band gaps of ZnO and NiO films were obtained to be 3.25 and 3.89 eV, respectively. The current–voltage characteristics of NiO/ZnO junction showed a good rectifying behavior. The junction parameters such as ideality factor and barrier height were calculated using thermionic emission model. The barrier height and ideality factor values of the diode were obtained to be 0.48 and 2.91 eV, respectively. The variation of photocurrent with wavelength indicates that this device had high efficiency in wavelength range of 450–475 nm.     

Multi-technique surface characterization of bio-based films from sisal cellulose and its esters: a FE-SEM, μ-XPS and ToF-SIMS approach

Bio-based films were prepared from LiCl/DMAc solutions containing sisal cellulose esters (acetates, butyrates and hexanoates) with different degrees of substitution (DS 0.7–1.8) and solutions prepared with the cellulose esters and 20 wt% sisal cellulose. A novel approach for characterizing the surface morphology utilized field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle analysis. XPS and ToF-SIMS were a powerful combination while investigating both the ester group distribution on the surface and effects of cellulose content on the film. The surface coverage by ester aliphatic chains was estimated using XPS measurements. Fibrous structures were observed in the FE-SEM images of the cellulose and bio-based films, most likely because the sisal cellulose chains aggregated during dissolution in LiCl/DMAc. Therefore, the cellulose aggregates remained after the formation of the films and removal of the solvent. The XPS results indicated that the cellulose loading on the longer chain cellulose esters films (DS 1.8) increased the surface coverage by ester aliphatic chains (8.2 % for butyrate and 45 % for hexanoate). However, for the shortest ester chains, the surface coverage decreased (acetate, 42 %). The ToF-SIMS analyses of cellulose acetate and cellulose hexanoate films (DS 1.8) revealed that the cellulose ester groups were evenly distributed across the surface of the films.     

Characterization of Plasma-Polymerized 4-vinyl Pyridine with Silver Nanoparticles on Poly(ethylene terephthalate) Film for Anti-Microbial Properties

4-vinyl pyridine was polymerized on poly(ethylene terephthalate) (PET) film by using lower energy pulsed AC plasma under low pressure in Ar atmosphere. The plasma polymerized coating was characterized by ATR Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Different thicknesses of poly(4-vinyl pyridine) coating under different plasma polymerization conditions were studied. Silver nanoparticles with diameter around 50nm deposit were precipitated on the poly(4-vinyl pyridine) coating by UV irradiation in Silver nitride water solution, in order to enhance the anti-microbial properties. Different kinds of modified PET films were tested for anti-microbial properties against yeast (Debaryomyces hansenii) by using microbiological analyser µ-4200 and direct microscopic count method.     

Homogeneous liquid crystal alignment on poly(vinylidene fluoride-trifluoroethylene) films subjected to ion-beam irradiation

We demonstrate homogeneous and uniform liquid crystal (LC) alignment on poly(vinylidene fluoride-trifluoroethylene) [PVDF-TrFE] films using ion-beam (IB) irradiation and a performance improvement of twisted nematic (TN) cells using IB-irradiated PVDF-TrFE films. Spontaneous ferroelectricity of the PVDF-TrFE films was modified by IB irradiation, which affected the LC alignment properties. The variation in the pre-tilt angles of the LC molecules on the IB-irradiated PVDF films is attributed to surface reformation, including defluorination and oxidation because the pre-tilt angles of LC molecules can be controlled by adjusting the fluorine content. The results of contact angle measurements supported this phenomenon. A 58% reduction in the switching voltage was observed for TN cells, indicating that the IB-irradiated PVDF-TrFE films are a promising candidate for use as an alignment layer.     

Quantitative analysis of an organic thin film by XPS,AFM and FT‐IR

We report the characterization of Firpic (iridium(III)bis[4,6‐di‐fluorophenyl]‐pyridinato‐N,C²,]picolinate) organic thin film prepared by vacuum deposition to provide a systematic route to organic film quantification. To analyze the characteristics of thin Firpic films on a Si substrate, various techniques such as XPS, Fourier transform infra‐red (FT‐IR) spectrometer, and atomic force microscopy (AFM) are utilized. The Firpic films remain stable without surface morphological or compositional change during deposition and after exposure to X‐ray irradiation or atmospheric environment, for which qualities these films are believed to be an ideal platform as a pure organic thin film. The monotonic increases in FT‐IR and XPS intensities with film thickness are matching well with each other. In particular, from the XPS intensity analysis, the relative atomic sensitivity factors of the present system, electron attenuation length, and molecular density in the organic thin film can be evaluated. Copyright © 2011 John Wiley & Sons, Ltd.     

铝合金表面原位自组装超疏水膜层的制备及耐蚀性能

采用阳极氧化法在铝合金表面原位构造粗糙结构, 经表面自组装硅氧烷后得到超疏水自清洁表面, 与水滴的接触角最大可达157.5°±2.0°, 接触角滞后小于3°. 通过傅立叶变换红外(FT-IR)光谱分析仪、场发射扫描电子显微镜(FE-SEM)、能谱仪(EDS)、原子力显微镜(AFM)和接触角测试对阳极氧化电流密度、硅氧烷溶液中水的含量和自组装时间等参数进行了分析, 并得到制备超疏水自清洁表面的最优工艺参数. FE-SEM及AFM的测试结果表明, 由自组装硅氧烷膜层的无序性形成的纳米结构和阳极氧化构造的微米级粗糙结构与硅氧烷膜层的低表面能的协同作用构成了稳定的超疏水表面. 电化学测试(动电位极化)的结果表明, 原位自组装超疏水膜层极大地提高了铝合金的耐蚀性.