Van der Waals force contribution to the vertical alignment of liquid crystal on Al2O3 films using ion-beam method

This study demonstrates liquid crystal (LC) alignment on Al₂O₃ films using the ion-beam (IB) method as well as the optimization of the IB irradiation condition. Uniform LC alignment was achieved at an IB incident energy of 1800 eV with an IB incident angle of 45°, while inferior LC alignments were observed in other tested conditions. The pretilt angles and transmittances of the LC cell were also shown as part of the same trend for the LC alignment states. This result was subject to van der Waals forces which were caused by topographical changes during the IB process.     

Orientational control of liquid crystal molecules by reformed poly(dimethylsiloxane) alignment layer via ion-beam irradiation

We introduce an alternative approach to making a reformed PDMS layer as a pretilt controllable alignment layer, which can be used in the vertical alignment (VA) and twisted nematic (TN) modes, by varying the ion beam (IB) energy. Depending on different the dielectric anisotropy of surfaces, PDMS layers have been demonstrated to align LC molecules homogeneously and homeotropically. The electro-optic characteristics of aligned VA and TN-LCD based on PDMS layer were comparable to those of VA and TN-LCD based on polyimide, showing good potential of PDMS film as an alignment layer.     

Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC–LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena.     

添加剂对聚酰亚胺液晶垂直取向剂性能的影响

研究了添加剂对PI取向性能、耐摩擦性、热稳定性以及透光率的影响。用均苯四甲酸二酐(PM-DA),对苯二胺(PDA),4-已氧基联苯酚-3’,5’-二胺基苯甲酸酯(C6-BBDA),制备了三元共聚型PI取向膜,并采用添加剂(封端剂和交联剂)对PI改性。通过调节添加剂的组成制备了4种PI。利用红外光谱仪(FT-IR)、热失重分析仪(TGA)、紫外分光光度计(UV-Vis)、偏光显微镜(POM)和预倾角测试仪对合成的PI进行了结构表征和性能测试。研究发现LC分子在4种PI膜上都获得了均匀的垂直取向;添加交联剂的PI膜具有良好的耐摩擦性,经摩擦强度为600mm摩擦后,仍对LC分子具有垂直取向的能力;加入添加剂的PI膜具有良好的热稳定性,此外,加入添加剂的PI膜仍具有较高的透光率。     

Use of polydimethylsiloxane thin film as vertical liquid crystal alignment layer

The possibility of the use of polydimethylsiloxane to align liquid crystals is studied. The polydimethylsiloxane thin films coated on glass substrates exhibit a very low surface free energy, and are found to be capable of vertical liquid crystal alignment. Comparing to thin films made using a typical polyimide polydimethylsiloxane films possess a more stable surface energetic state. The pretilt angle of the calamitic liquid crystal molecules sandwiched between the silicon elastomer thin films was virtually 90°, and the molecular tilt can be maintained in a wide temperature range. Liquid crystal sandwiched between the silicon-based polymer thin films can operate in the in-plane-switching mode.     

Nano-engineering of the anchoring of liquid crystals on solid surfaces

The solid surface in the conventional liquid crystal displays, being responsible for the liquid crystal alignment in the absence of external fields, is playing only a passive role in the switching of the liquid crystal layer. Recently, we have shown that the anchoring strength and the easy axis, two important parameters characterizing the liquid crystal alignment, can effectively be controlled by light via photo-induced nano-scale changes of the solid surface properties. We have also introduced two novel concepts of commanded anchoring, the electrically commanded surfaces (for mediating switching of the liquid crystal) and the high performance alignment layers (for facilitating the switching of the liquid crystal) realized practically by means of a proper nano-engineering of the alignment layer. Electrically commanded anchoring concepts are strong candidates for implementation in a new generation of advanced liquid crystal displays and devices.     

氧分压对动态离子束辅助沉积合成的氧化钛膜的影响

采用离子束增强沉积的方法,改变氧分压,在硅基体表面制备出了不同组分及不同取向的 氧化钛薄膜。采用 XRD,掠角衍射以及 XPS分析方法对薄膜的成分、结构和取向进行了分析,并 通过 RBS分析计算出了薄膜的 O/Ti比。实验结果发现,所制备的氧化钛薄膜为具有一定择优取 向的多晶膜,薄膜内 TiO、 Ti2O3和 TiO2共同存在。当氧分压低于 8.4× 10-4 Pa时,氧化钛薄膜的 成分以 TiO为主,且 TiO的取向随氧分压的增加从（ 220）向（ 031）转变,氧分压对薄膜取向的影响 较大。当氧分压高于 8.6× 10-4 Pa时,氧化钛薄膜的成分以具有（ 100）择优取向的金红石型 TiO2 为主,含有少量其他结构的 TiO2和低价 Ti,其成分及取向相对较为稳定,对氧分压的变化不敏感。     

Homogeneously aligned liquid crystal display on silicon oxynitride thin film using ion beam bombardment

This paper introduces the homogeneously aligned liquid crystal (LC) display using ion beam (IB) bombardment of a new silicon oxynitride (SiON) alignment layer for the first time. The pretilt angle was shown to be a function of the IB incident energy, and possible mechanisms of LC alignment were investigated with physical and chemical methods. An X-ray photoelectron spectroscopy analysis showed that the LC alignment on the IB-bombarded SiON inorganic surface was due to the reformation of Si–O bonds as a major factor. The electro-optical characteristics were comparable to those of rubbed polyimide films.     

Spectrographic ellipsometry study of a liquid crystal display substrate consisting of thin films of SiO2, polyimide and indium tin oxide on glass

Variable angle spectrometric ellipsometry at room temperature is used to determine thin film parameters of substrates used in liquid crystal displays. These substrates consist of sequential thin films of polyimide (PI), on indium tin oxide (ITO),on SiO₂ deposited on a glass backing approximately 1.1 mm thick. These films were studied by sequentially examining more complex systems of films (SiO₂, SiO₂-ITO, SiO₂-ITO-PI). The SiO₂ layer appears to be optically uniform and flat. The ITO film is difficult to characterize. When this surface film's lower surface is SiO₂ and upper surface is an air-ITO-interface it is found that including surface roughness and variation of the optical properties with ITO thickness in the model improved the fit; suggesting that both phenomena exist in the ITO films. However, the surface roughness and graded nature of optical properties could be not determinable by ellipsometry when the ITO is coated with a polyimide film. The PI films are ellipsometrically flat and over the wavelength range from 500 to 1400 nm the real refractive index of polyimide films varying in thickness between 25 and 80 nm is well modeled by a two-term Cauchy model with no absorption. The ellipsometric thickness of the ITO layer is the same as the profilometric thickness; however, the ellipsometric thickness of the polyimide layers is roughly 10 nm larger than that obtained from the profilometer. These final observations are consistent with the literature.     

Development of Ga-doped ZnO transparent electrodes for liquid crystal display panels

Liquid crystal displays (LCDs) with Ga-doped ZnO (GZO) transparent electrodes on RGB color filters were fabricated to demonstrate the feasibility of using this new material as an alternative to indium tin oxide (ITO) electrodes. The process flow for fabricating LCDs with GZO electrodes was entirely compatible with that for commercially available LCDs using ITO electrodes. Concurrently, photolithography processing and wet-chemical etching techniques for the formation of GZO transparent electrodes on thin film transistor (TFT) arrays in LCD panels was developed. Fine-patterns of GZO with 2-μm line widths were successfully formed using lithography and wet -etching technology with a weakly acidic etchant of pH 5.5-6.8.     

High-temperature-dependent optical properties of ZnO film on sapphire substrate

In order to fabricate fiber-optic temperature sensors based on ZnO film, it is important to study the temperature-dependent optical properties of this material. In this work, we deposited ZnO films on c-plane (0001) sapphire substrate at 250 °C. Atomic force microscope and X-ray diffraction measurements show the smooth surface and high orientation along [0001] of ZnO film, respectively. The high-temperature-dependent optical properties of ZnO film were measured by ultraviolet-visible transmission with temperatures ranging from room-temperature to 300 °C and analyzed by theoretically fitting the optical absorption edge curve. It is observed that the band gap energy red shifts nonlinearly from 3.345 to 3.153 eV with increasing temperature. The sharp absorption edge of ZnO films after annealing at 300 °C is almost consistent with that of the as-deposited sample, indicating an excellent thermal stability and the potential application in fiber-optic temperature sensors.     

Insulating ZnO film on silicon for MIS application

High resistive zinc oxide thin film (∼ 0·5 μm) was deposited on single crystalp-silicon (100) wafers by an inexpensive spray-CVD method and was characterized both optically and electrically. Al/ZnO/Si (MIS) device structure was subsequently fabricated and bothI − V andC − V characteristics were studied. The semiconductor-insulator interface charge density (D _it) was calculated by Terman method and was found to be 3·85 × 10¹¹ cm⁻²eV⁻¹.     

纳米氧化锌掺杂液晶/聚合物膜的阻抗谱特性

本文研究了采用纳米氧化锌棒掺杂的聚合物分散液晶(PDLC)的电阻抗谱特性及其传感应用。利用聚合物分散液晶薄膜具有稳固结构、能抵御机械冲击、容易制备等特点,在材料中掺杂纳米氧化锌棒,通过电阻抗谱性质分析,实现对极性分子如乙醇气体的传感功能。通过对比实验,研究分析了薄膜在遇到乙醇分子时的复阻抗谱的变化,并建立了电化学等效电路,发现该薄膜能有效地实现对乙醇分子的传感功能。并进一步分析研究了该检测传感的灵敏度和响应时间等特性。结果表明,以纳米氧化锌棒掺杂PDLC薄膜有望作为检测乙醇等极性的气体传感器,具有高灵敏度、结构稳定、重复性高、易于制造等优点。     

Anisotropy and Raman absorption of the polyimide surface irradiated by the ion beam for liquid crystal alignment

In this paper, polyimide surfaces irradiated by an ion-beam for liquid crystal alignment are investigated by using atomic force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. A liquid crystal cell aligned homogeneously through the ion-beam exposure exhibits electro-optic switching behavior similar to that of a rubbing-aligned liquid crystal cell. However, we found that the surface morphology and bonding molecules of ion-beam-treated polyimide surfaces show properties very different from mechanically-rubbed ones. Experimental results show that optical anisotropy of ion-beam-treated polyimide surfaces results in the formation of hydrogenated amorphous carbon-like structure with a short main-chain, while mechanical rubbing has little effect on structural and compositional variations of polyimide layers.     

Langmuir Blodgett films of arachidic acid and a nematic liquid crystal: Characterization and use in homeotropic alignment

We study the behavior of a mixed Langmuir monolayer consisting of a fatty acid and a nematic liquid crystal. We demonstrate that the mixed monolayer successfully transfers as a Langmuir-Blodgett film and characterize the transferred film using UV spectroscopy. An important application of Langmuir-Blodgett films is in the alignment of liquid crystals for electro-optical applications, such as displays. We show that including the liquid crystal in the Langmuir-Blodgett film produces homeotropic alignment for a system which fails to align by other standard techniques.     

Intrinsic high thermal conductive liquid crystal epoxy film simultaneously combining with excellent intrinsic self-healing performance

One kind of side chain liquid crystal epoxy(S-LCE) based on biphenyl mesomorphic unit is synthesized from 2,2-bis(hydroxymethyl)propionic acid,4-phenyl phenol,and epichlorohydrin.And the intrinsic thermal conductive liquid crystal epoxy film(LCEF) simultaneously combining with intrinsic self-healing performance is then prepared via thiol-epoxide nucleophilic ring-opening reaction and coating method.1 H NMR and FTIR show that S-LCE and LCEF have been successfully prepared.S-LCE presents nematic liquid crystal from room temperature to 160℃.LCEF maintains nematic liquid crystal performance and shows highly intrinsic thermal conductivity & excellent self-healing performance.Thermal conductivity coefficient(λ)values in vertical direction(λ⊥)and parallel direction(λ‖)of LCEF are 0.33 and 1.25 W/mK,re spectively,much higher than that of general bisphenol A epoxy resin(E-51,λ⊥ of 0.19 W/mK and λ‖ of0.65 W/mK).Tensile strength of LCEF is 10.6 MPa,which can maintain at 90.6 % and 61.3 % after one and four cycles of self-healing behavior,respectively.In addition,LCEF presents a wide service temperature range(-9.8-251℃) and good thermal stability(THRI of 148.5℃).Simultaneously,LCEF has good transparency,flexibility,and tailorability,expected to be utilized in the fields of flexible electronic devices and intelligent structures.     

The effects of post-annealing on the performance of ZnO thin film transistors

In this study, we investigated the effects of a post-annealing process on the performance and stability of zinc oxide thin film transistors fabricated by atomic layer deposition. After the post-annealing process in ambient air at 250 °C for 2 h, the value of the saturation mobility increased from 1.2 to 1.8 cm/Vs, the subthreshold swing decreased from 0.53 to 0.34 V/decade, and the I_on/I_off ratio increased from 3.1 × 10⁶ to 1.7 × 10⁷. The positive bias stability was also enhanced after post-annealing. These results are related to the formation of another phase in which the difference of enthalpy between the semiconductor material and contact metal electrode causes the carrier concentration at the metal/semiconductor interface to increase, leading to decreased contact resistivity. Additionally, internal modification of the semiconductor/dielectric interface and/or improving the semiconductor structure, which is related to a change in the oxidation state of Zn through the incorporation of oxygen and/or hydroxide, can result in improved device performance.     

The driving force for homeotropic alignment of a triphenylene derivative in a hexagonal columnar mesophase on single substrates

An interesting discotic triphenylene derivative, 2,7-biscarbethoxy-3,6,10,11-tetrapentyloxytriphenylene, can be homeotropically aligned on a large scale as a film on single substrates, i.e. the film with one side on the substrate and the other side freestanding. The alignment is achieved in a controlled condition close to a thermodynamic equilibrium state in a liquid crystal phase when interactions at the substrate surface are limited. Phase changing properties of this material are also a key factor in the alignment processes. The aligned structures are observed with an optical microscope. Within a single domain a hexagonal lattice of a d-spacing 16.3 Å is confirmed by X-ray diffraction measurement.     

Investigation of the liquid crystal alignment layer: effect on electrical properties

Abstract

We investigate the electrical behavior of a symmetric liquid crystal (LC) cell: elecrode-silane-LC-silane-electrode. The silane (chlorodimethyloctadecyl-silane) layer induces a homeotropic orientation of the nematic liquid crystal (NLC) molecules. The wettability technique is used to detect the change of the surface energy of the electrode upon cleaning and silane layer deposition. We report on the dynamic impedance measurements of the nematic liquid crystal cell. It is found that the silane alignment layer has a blocking effect on the liquid crystal (LC) cell. We also study the relaxation behavior of the cell which is later assimilated as an electrical equivalent circuit.     

Effect of Ag doping on the performance of ZnO thin film transistor

Ag-doped zinc oxide (SZO) thin film transistors (TFTs) have been fabricated using a back-gate structure on thermally oxidized and heavily doped p-Si (100) substrate. The SZO thin films were deposited via pulsed laser deposition (PLD) from a 1, 3, and 5 wt.% Ag-doped ZnO (1SZO, 3SZO, and 5SZO, respectively) target using a KrF excimer laser (λ, 248 nm) at oxygen pressure of 350 mTorr. The deposition carried out at both room-temperature (RT) and 200 °C. The SZO thin films had polycrystalline phase with preferred growth direction of (002) as well as a wurtzite hexagonal structure. Compare with ZnO thin films, the SZO thin films were characterized by confirming the shift of (002) peak to investigate the substitution of Ag dopants for Zn sites. The as-grown SZO TFTs deposited at RT and 200 °C showed insulator characteristics. However the SZO TFTs annealed at 500 °C showed good n-type TFT performance because Ag was diffused from Zn lattice site and bound themselves at the high temperature, and it caused generation of electron carriers. The post-annealed 5SZO TFT deposited at 500 °C exhibited a threshold voltage (V_th) of 11.5 V, a subthreshold swing (SS) of 2.59 V/decade, an acceptable mobility (μ_SAT) of 0.874 cm²/V s, and on-to-off current ratios (I_on/off) of 1.44 × 10⁸.