Ruslan Kravchuk

Plasma beam alignment for the large-area substrates: Equipment and process

— We have developed an effective method for liquid-crystal alignment of the large-area substrates. This method is based on the oblique treatment of the alignment substrates with a “sheet” of accelerated plasma generated by the anode layer source of the “race track” geometry. During this treatment, the substrate or source is cyclically translated in the direction perpendicular to the plasma “sheet.” This method provides planar, tilted, and vertical liquid-crystal alignment with excellent uniformity and reproducibility and easy axis control in the azimuthal and polar planes.

Second wind of the oblique deposition method of liquid‐crystal alignment: Ion‐beam sputtering technique

Abstract— Liquid-crystal (LC) alignment on SiOx films produced by ion-beam sputtering deposition was comprehensively studied. The conditions for planar, tilted planar, homeotropic, and tilted homeotropic LC alignment of high uniformity were determined. The alignment photostability and aging issue are discussed. An original sputtering system based on the anode-layer source excelling in high reliability and quality of sputtered coatings were used. Because this system can be easily scaled up, the alignment treatment of the large-area alignment substrates, including those used in modern LCD manufacturing, can be realized. The advantages of the sputtering LC alignment technique, in comparison with its vapor-deposition predecessor, are described.

Liquid-crystal anchoring transitions on aligning substrates processed by a plasma beam

We have studied a sequence of anchoring transitions observed in nematic liquid crystals (NLCs) sandwiched between hydrophobic polyimide substrates treated with a plasma beam. There is a pronounced continuous transition from a homeotropic to a slightly tilted (nearly planar) alignment with the easy axis parallel to the incidence plane of the plasma beam (the zenithal transition) which takes place as the exposure dose increases. In NLCs with positive dielectric anisotropy, a further increase in the exposure dose results in in-plane reorientation of the easy axis by 90 degrees (the azimuthal transition). This transition occurs through the twofold degenerate alignment characteristic of second-order anchoring transitions. In contrast to the critical behavior of anchoring, the contact angle of the NLC and water on the treated substrates declines monotonically with increasing exposure dose. It follows that the surface concentration of hydrophobic chains decreases continuously. The anchoring transitions under consideration are qualitatively interpreted by using a simple phenomenological model of competing easy axes which is studied by analyzing anchoring diagrams of generalized polar and nonpolar anchoring models.

Plasma-beam alignment technique for ferroelectric liquid crystals

The plasma-beam alignment procedure earlier developed for the alignment of nematic liquid crystals is successfully extended to ferroelectric liquid crystals (FLC). The highly uniform alignment of the “chevron” structure (before electrical treatment of FLC cells) and “quasi bookshelf” structure (after the electrical treatment) are realized. The contrast of bistable switching larger than 350:1 is achieved. This makes the non-contact plasma-beam alignment procedure especially attractive for high-contrast bistable LCDs on an LCOS base, particularly used in PDA and e-books. Fast switching and realization of gray scale in the plasma-beam aligned FLC cellsmakes this technique also promising for full-color displays including color LCD TV.

Aging of Liquid Crystal Alignment on Plasma Beam Treated Substrates: Choice of Alignment Materials and Liquid Crystals

We studied temporal degradation (aging) of liquid crystal (LC) alignment on plasma beam processed substrates using LC pretilt angle as a measure of this process. It was shown that aging may manifest itself either in pretilt angle decay or pretilt angle growth depending on LC and alignment material. The alteration of electro-optic curves due to alignment aging was revealed. The weakest aging effect was observed for inorganic alignment layers obtained by PECVD method. An important reason of aging is chain scission and generation of low molecular weight reactive species disturbing surface anisotropy of atomic bonds and anisotropy of surface topology.

The Multimode LC Alignment on the Substrates Obliquely Treated with a Plasma Flux

ABSTRACT We describe a variety of liquid crystal (LC) alignment modes on the aligning substrates obliquely treated with a flux of accelerated plasma from the anode layer thruster (ALT). The discharge area has a form of race track so that the generated flux contained two sheets of plasma corresponding to linear parts of the discharge. Within each “sheet” the intensity of flow (ion current density) is uniform in the direction parallel to the linear part of discharge. Across the “sheet”, the intensity of flow has the Gaussian distribution. The alignment of LC with positive and negative dielectric anisotropy, Δϵ, was tested on the substrates of organic (polymers) and inorganic (glass and DLC) origin treated in static and dynamic regime (unidirectional translation perpendicularly to plasma “sheet”). In the dynamic regime of irradiation, with the substrate moving with respect to the plasma beam, for LC with Δϵ > 0 we observed two aligning modes, with the easy axis confined to the plane of plasma incidence (mode 1) or perpendicular to this plane (mode 2). In the 1st aligning mode the LC pretilt angle is non-zero and can be varied with the incidence angle of plasma beam and the irradiation dose. With the increase of irradiation dose, the alignment transition from the 1st to the 2nd mode occurs. For LC with Δϵ < 0 only the 1st alignment mode uniform over all substrate was observed. In the static regime of irradiation, characterized by smooth distribution of the particles flow across the sheet, two modes are clearly observed simultaneously; 2nd mode alignment occurs in central, most intensive part of flow, while the periphery part shows the 1st mode. The areas of the 1st and the 2nd mode are separated with the narrow transition area showing multidomain (two-fold degenerate) LC alignment. The easy axis in these domains is turned by about ±45° with respect to the alignment direction in the 1st mode area. This sequence of the alignment transitions is observed in both LC with Δϵ > 0 and Δϵ < 0. We also describe a high-tilt alignment (87°–90°) in the 1st mode realized on the hydrophobic polymers at the extremely low doses of plasma irradiation. The origin of the observed alignment effects is discussed.

Plasma‐beam alignment of passive liquid crystals (Invited Paper)

— A plasma-beam process, developed for the alignment of liquid crystals (LC) in electro-optic applications, has been successfully applied to align “non-standard” LC, such as crystalline materials with LC phases at elevated temperatures and reactive mesogenes. In addition to the high alignment quality of the materials, there is no need for an intermediate layer between the substrate and the LC layer. Furthermore, the construction of our source simplifies the alignment procedure of large-area rigid substrates and the roll-to-roll processing of flexible films. This method opens new horizons for optical retarders and polarizers, as well as anisotropic semiconducting films for organic electronics.

P-130: Plasma Beam Alignment of Reactive Mesogenes

We demonstrate that plasma beam processing of the alignment substrates, earlier recognized as an effective tool of liquid crystal alignment, provides excellent alignment of reactive mesogenes (RMs). for this processing we utilized anode layers source generating two sheet-like beams of accelerated plasma allowing to treat large-area substrates by sample movement across the plasma “sheets”. The oblique treatment by plasma beam results in planar or oblique alignment of planar RMs (p-RMs) and homeotropic alignment of homeotropic RMs (h-RMs). The homeotropic alignment of h-RMs can also be achieved by normal processing with plasma beam or processing by diffuse (non-directed) plasma. Good alignment effect is observed for a big variety of organic and inorganic materials. The widely used in LCD technology glass, silicon and plastic substrates processed by plasma beam also demonstrate excellent RM alignment that excludes necessity to use additional alignment layers. Besides, in the case of flexible plastic substrates, roll-to-roll alignment treatment can be realized. Thus the developed method is an advance in technology of optical films based on RMs.

Surface electrical potential of the aligning polymer substrates and dielectric properties of LC layers

UV light influence on the surface potential φs of poly(vinylcinnamate) (PVCN) layers widely used for liquid crystal (LC) photoalignment is investigated. In case when PVCN film is spin coated on the ITO electrodes the surface potential changes under irradiation in both PVCN aligning film and ITO coating. The measured increment of the surface potential changes under irradiation in both PVCN aligning film and ITO coating. The measured increment of the surface potential Δφs=400 mV is mainly cuased by the photoconductivity of ITO electrodes, whereas the part caused by PVCN substrate is at least one order of magnitude lower. The relaxation time of Δφs for the ITO-PVCN coatings was estimated to be about 1 h. The induced potential may substantially modify dielectric properties of the aligned LC layers and its anchoring characteristics when the freshly irradiated substrates are used. On the contrary, this influence is weak when the substrates are irradiated several hours before the use for LC alignment.

Atmospheric Pressure Planar Radio Frequency Discharge With Isolated Electrodes: Glow Features and Application Prospects

Operation characteristics of RF planar barrier discharge in atmospheric pressure argon appropriate for obtaining the discharge extension outside the electrodes in a form of planar plasma jet are determined experimentally. The plasma jet images and spatial distributions of its light emission intensity are presented, and their features are discussed. The prospects of studied jet discharge for creation of liquid crystal alignment and etching polymer materials are demonstrated.