A review is given of our present general classification of the liquid crystals. The liquid crystal structures are divided into two main groups: nematic phases with parallel ordering of the long molecular axes and smectic phases having additional layered structure. An interesting phenomenon is that the liquid crystal phases when formed by optical active molecules develop chiral modifications: chiral nematics and chiral smectics. There are four fundamental smectic phases: A, B, L, and E having skewed analogues: C for smectic A and F, G, H, (with long molecular axes tilted to the side of the hexagon) and I, J, K (tilted to the apex of the hexagon) for smectics B, L, and E, respectively. Chiral nematics N and chiral modifications of smectics with weak interlayer correlation (C, I, and F) form long-range helicoidal structures. We also briefly discuss the main topological defects in liquid crystal structures: dislocations in layered (smectic) or pseudolayered (chiral nematic) phases and disclinations (including focal domains) that are fundamental defects of structures with continuous symmetries.

An overview of preparation methods, physical principles, main properties, present and possible applications of polymer dispersed liquid crystals is presented. Special attention is paid to polymer dispersed chiral smectic liquid crystals.

The term `semiconductor superlattice' is usually used to refer to a periodic structure of thin layers of two semiconductors along one dimension. The period in thickness lies typically in the range from several to tens of nanometers, which is shorter than the electron mean free path in semiconductors but longer than the crystal lattice constant. This periodic, or superlattice potential, modifies significantly the band structure of the host semiconductors, creating minizones in wave-vector space and subbands in energy. In this regard the superlattice can be considered as a new synthesized semiconductor not present in nature, which exhibits unusual electronic and optical properties. The paper presents the fundamentals of the physics of semiconductor superlattices, as well as the crystallization methods and the most interesting application areas of these man-made structures.

The emergence of HgCdTe as the most important intrinsic semiconductor alloy system for IR detectors is well established. The future of this material continues to be uncertain because of difficulties associated with its growth and processing. This paper is to devoted technology and performance of IR detectors manufactured from alternative to HgCdTe, new ternary alloy systems, such as InAsSb, HgZnTe, HgMnTe; and III-V superlattices, such as AlGaAs/GaAs superlattice multiple quantum wells.

Some physical effects and properties of quantum wells (QWs) and superlattices (SLs) for IR optoelectronics are discussed. Recently published results are reviewed.

The influence of blocking contacts on IR MCT photoconductor parameters is studied. The photoelectric gain, current responsivity and detectivity are investigated by numerical approach. It is shown that the best performance should be expected in n+v devices.

Non-traditional materials for solid-state electronics such as porous silicon, perovskites, electrides, conducting polymers whose structure imperfections and peculiar features of the structure are responsible for their unusual properties, are considered in this paper. Their distinctive characteristics, features of the structure, methods of fabrication have been presented. An outline of their properties and possible applications in micro- and optoelectronics are reported. The fundamental character of the cluster structure is emphasized, as an example, quasicrystals and fullerens are used.

Results of dc and ac small signal electronic transport study of ZnTe/ZnSe heterostructures grown by molecular beam epitaxy are presented. The small signal admittance characteristics of these heterostructures show certain distinct features which are located at a bias point dependent on the interfaces. From the bias location of these features, the interfaces barrier height in ZnTe/ZnSe heterostructures is found to be 0.6 +/- 0.1 eV for electrons injected into ZnSe.

Oxygen atoms contained in Czochralski-grown silicon single crystal (Cz-Si) precipitate at higher temperatures and produce strain at the oxygen agglomerate/Si matrix boundary. The strain is manifested by the changes of lattice constant and x-ray anomalous transmission values and ought to be taken into account for Si used as the reference standard. Hydrostatic pressure treatment applied to the Cz-Si single crystals makes it possible to obtain better understanding of the strain related to oxygen agglomeration.

Potassium titanyl phosphate is actually the best non-linear optical material. Also it's very good electro-optic coefficients, low dielectric constants and large figure of merit make it attractive for practical use. Crystals can be grown by both hydro-thermal and flux methods.

The SrLaAlO₄ single crystals are used as a substrate for high temperature superconductor epitaxial layers with uniform physical properties. Good quality of epitaxial layers requires both crystallographic perfection and appropriate physical properties of substrate material. In this paper we investigated the crystallographic perfection of SrLaAlO₄ crystals by means of x-ray diffraction topography. The samples were cut-out perpendicular to [100] direction. In some of the samples the present investigations revealed thin lamellar volume defects. It was stated at different interplanar spacing in the defect region.

The thermally stimulated absorption was found for some photochromic sillenite (BGO:Mo). The effect is explained in terms of the non-equilibrium processes between some trap centers and the photochromic (polaron) one.

We present the influence of the free carrier concentration on the elastic properties of n-ZnSe single crystals using Brillouin light scattering method. For this purpose the Brillouin polarized spectra of n-ZnSe single crystals with different free carrier concentration were measured at room temperature. It has been shown that the value of the velocity of the elastic waves propagating in n-ZnSe single crystals strongly depends on the free carriers concentration. The large effect of the annealing of n-ZnSe single crystals on their elastic properties is also discussed.

In the paper we consider the sense of making crystal growth from solution experiments on board space laboratories. Based on our experimental data and experiences connected with preparing a facility for a space laboratory we analyze the possibility of replacing space experiments by cheaper ground-based studies and some technical problems appearing during the preparation of the apparatus for space experiments. In the end we present construction and experimental capabilities of the crystal growth from a solution facility for microgravity conditions research which is built in the Institute of Physics, Technical University of Lodz.

The BCF differential diffusion equation is solved and the growth units concentration at the surface is found. The analysis of the growth units concentration distribution gives information regarding the transport processes and adsorption phenomena as well as it indicates that the BCF expression for the growth rate is strongly limited to low values of supersaturation.

In the paper copper acetate doped single crystal production technology is presented. Temperature runs of (epsilon) ', tg(sigma) , Ps, and Ec have been established. The Curie temperature and Curie-Weiss constant have also been determined.

The reduced second-order self-consistent phonon approximation is applied to the calculations of the effect of pressure on the instability temperature and relative displacement of atoms. As the model of nearest-neighbors central force interaction is used the Lennard-Jones (n,m) self- consistent potential. The results of calculations are compared with experimental and other theoretical data for the anharmonic rare gas solids.

In the paper the results of experiments on single crystal growth of CaNdAlO₄ (CNA) are reported. CaNdAlO₄ is a very promising material for use as a substrate for high temperature superconducting (HTSC) epitaxial layers. The method of preparation of charge material as well as the conditions of single crystal growth by the Czochralski method are given. The equipment type MSR-2 with induction heating made by Metals Research Ltd., England and the thermal system with iridium crucible and afterheater were used. The quality of obtained single crystals was examined by polarizing methods. Optical transmission in the range 200 - 2000 nm was also measured. Using a newly developed ESR spin-probing methodology, magnetic properties of this material were investigated. It should be pointed out that because of neodymium presence the material exhibits high paramagnetic susceptibility.

The results of experimental investigations on single crystal growth of lithium niobate for optical purposes are reported. The crystals were grown by the Czochralski method with the use of induction heated equipment type CGS-2 made by Spexon. The thermal system consisted of platinum crucible and active platinum afterheater. To determine the homogeneity and optical quality of single crystals the distribution of birefringence and of refractive indices n_o and n_e were measured. Samples of active elements were prepared and their conoscopic images were checked. On the basis of these elements the electro-optic modulators were made for which extinction ratio and V_(lambda /2) were measured. Optoelectronic structures with `cut-off' effect on lithium niobate substrates were also prepared for straight and Y waveguides. The waveguides were obtained by Ti in-diffusion.

In this paper we propose the optimal growth conditions for acenaphthene crystals by Bridgman method.

The p⁺-n homojunctions were formed by arsenic diffusion in the HgCdTe monocrystals and epilayers. Photodiode performance was established by measuring the current-voltage and spectral response characteristics. LWIR photodiodes are background limited at 77 K. MWIR photodiodes effectively operate at elevated temperature around 200 K and exhibit near BLIP performance when optical immersion is used.

The results of investigations on dosimetric properties of activated bismuth germanate single crystals in mixed radiation fields have been reported. The usefulness of bismuth germanate single crystals for registration of mixed radiation (gamma + fast neutrons) has been shown.

This paper describes preliminary investigations of Li₂B₄O₇ thermoluminescent phosphors as candidates for gamma radiation dosimetry materials. Single crystals, glasses, and polycrystals of lithium tetraborate activated with different dopants have been investigated.

The temperature dependences of the electron concentration and electron mobility in the AgInS₂ chalcopyrite crystals have been determined, in the temperature range 180 divided by 400 K, from the Hall effect study by using the van der Pauv method. The ionization energies and the densities of donors have been determined.

Electron paramagnetic (EPR) spectrum in undoped strontium lanthanum aluminate (SrLaAlO₄) single crystals was observed.

The paper is devoted to a two dimensional x-ray diffraction study of non ideal (GaAs_{(1 - c})P_c)/(GaAs) superlattice showing the broadening of satellite reflections which lie on a line making a small constant angle with the [00L] reciprocal lattice rod containing the nodal reflection. This additional broadening is due to nonzero lateral gradient of the phosphorus concentration -- dc/dy -- which implies dividing crystal volume into coherent scattering domains (CSDs). A model of coherently diffracting domains with rectangular composition modulation waves that have a different amplitude and wavelength in each domain is presented.

The relaxed multilayer structure is characterized by means of a tilt angle, C-factor, and the lateral coherency length. All these parameters were evaluated for the GaAs_(0.7)P_(0.3)/GaAs multilayer structure grown on a miscut GaAs(001) substrate. The determination of SL structural parameters was performed using the simulation program developed for two dimensional calculations important for multilayer structure grown on miscut substrates.

The x-ray diffraction investigations of the terraced structure in GaAs(P)/GaAs superlattice were performed, assuming that there appears scattering of the terrace widths. It was shown that in this case the satellite profiles are significantly affected by interference.

The detailed knowledge of strain and misfit dislocations profiles are important for the production and application of thin epilayer. It is shown that Raman scattering spectroscopy is needed to investigate these problems satisfactorily. In this paper we present Raman scattering measurements of the ZnSe epilayers with different thickness grown on GaAs substrate. The dependence of the frequency shift and the halfwidth of LO mode vs thickness of ZnSe epilayer is presented.

Luminescence in ZnSe single crystals doped with isoelectronic Mg has been studied. It has been shown that Mg easily enters substitutionally on a Zn site forming Mg_xZn_{1 - x}Se mixed crystals with band-gap energy considerably larger than that of `pure' ZnSe. The photoluminescence spectrum of such crystals is dominated by blue and violet emission, the efficiency of which is higher than the efficiency of blue luminescence in `pure' ZnSe. Low voltage blue-violet electroluminescence with maximum emission at 2.98 eV at T equals 45 K and 2.875 eV at room temperature in Mg_xZn_{1 - x}Se mixed crystals has been demonstrated. What makes this material very promising for future application in constructing blue and violet light emitting diodes is discussed.

The thermally stimulated currents (TSC) in a previously photoexcited insulating crystal with different initial trap occupancy are analyzed. Various characteristics of the TSC (trap occupancy, fractional recombination probability, thermally stimulated free electron density, free electron lifetime) are calculated as functions of the temperature and the initial occupancy of active traps. The results show that the TSC curves calculated for different values of the trap parameters and the initial trap occupancies can have similar shape. This suggests that there is no unique information about the recombination model of high-resistivity crystal that can be obtained from the shape of the TSC curve.

We demonstrate, that performing series of simultaneous TL/TSC (thermoluminescence/thermally stimulated conductivity) experiments it is possible to estimate the relative density of deep (thermally disconnected) traps in semiconducting crystals and other high-resistivity materials. The method is based on new, recently derived analytical formula for TSC. It is assumed that the crystal under study has an arbitrary number of discrete trap levels and one kind of recombination centers. The method is verified by means of numerical calculations.

Spatial correlation of traps and recombination centers may significantly change the kinetics of charge carriers' trapping in semiconductors and insulators. This phenomenon can be observed in thermally stimulated relaxation measurements, especially in the experiment of thermally stimulated conductivity (TSC). To study the kinetics we applied the Monte Carlo method. The calculations were performed for various spatial correlations and various retrapping coefficients r. The results for weakly correlated systems were compared to classical solutions obtained by solving the set of nonlinear equations by using the Gear method.

On the basis of the reduced second-order self-consistent phonon theory the dynamic functions of rare gas solids are computed and compared with experimental and other theoretical data in the low temperature limit. The system of self-consistent equations is solved for the Singh and Neb model of interatomic interaction.

The paper presents the derivation of expression enabling the determination of the concentration level of dopands introduced in the solid state materials by thermodiffusion (grad T > O). It enables us to estimate the possibilities of exceeding the limit of solubility achieved during the diffusion processes (grad T equals O). The analysis of the effect is given as well as its significance in modification of physico-chemical properties of substances in the solid state. The definition of thermodiffusive drift of the mass is introduced, as a consequence of action and changes resulting from temperature gradient. The expressions enabling calculation of drift quantity of migrating mass are given. It is the relation between the solubility level and the factors influencing the character and drifting mass intensity.

We attempt to define the influence of solution volume on nucleation and crystal growth of naphthalene from 1,2-dichloroethane (1,2-dCHLE).

We attempt to calculate the interfacial surface tension (gamma) for growth systems of naphthalene in 1.2-dichloroethane (1.2-dCHLE) and pyrene in chloroform (CHL) and trichloroethylene (tCHLE) based on the experimental data of metastable zone widths ((Delta) T_MET), induction periods ((Tau) ) and solubility.

Let us list the main directions of P—G dr Gennes' research. Most Nobel prizes are awarded for a well-defined discovery. This Nobel prize honours the overall achievement of Professor de Gennes in the field of liquid crystals and polymers. The Swedish Royal Academy of Sciences stated: "that methods developed for studying order phenomena in single systems can be generalized to more complex of matter, in particular to liquid crystals and polymers", for which the term soft matter is now used. The problem of phase transitions in what is now called soft matter can be discussed from the point of view of Landau concepts. Liquid crystals are natural materials with order parameters. Formal analogies with superconductivity and superfluidity exist. All that belongs to the so-called Landau - de Gennes theory.

The death (in April this year) of professor Marian Misowicz, a great physicist and a great man saddened all those who knew him. He offered me his friendship many years ago and although twenty years my senior he always treated me like his equal. I admired and respected him. As it is generally known ca. 60 years ago he discovered the phenomenon of viscosity anisotropy in liquid crystals. Then he turned to another field and became a high energy physicist. But his passion for the old subject of interest was strong enough to encourage me to undertake the study of liquid crystals when I was young. I am grateful to him for this. Below you will find some very personal memories from the years of our friendship.

The paper presents the formulation of the theory of ferroelectric liquid crystals (smectic C^*). In this formulation the formalism of bundle space has been applied. The used bundle space has a form of a Cartesian product of the three-dimensional Euclidean space E³ (the base space) and a differentiable manifold M_s with a conical structure. The presentation contains: the formulation of the kinematics of the continuous micropolar model, the local form of the conservation laws (the equations of the evolution of the medium), and the constitutive relations for chiral smectic C^*. The kinematic of the medium is described by two vector fields: the director, d, and the normal to the smectic layers, k. The vector d rotates around the vector k, the axis of instantaneous rotation. From the integral principle of the energy conservation law the equations of evolution of the mass, momentum and angular momentum densities are derived. The set of the constitutive arguments is established and the integrity base or the set of invariants of the group of material symmetry is obtained. The constitutive relations for stresses and internal forces are presented.

Freedericksz' transition in twisted nematics layer, in which all characteristic properties of nematic liquid crystal manifest, is one of the most important phenomena observed in these media. It may be understood as a transition (forward and backward) between two stationary states, one of them induced by boundary conditions on layer surfaces and the other induced by those boundary conditions and constant external field (either magnetic or electric) applied to the layer. In this paper the study of stationary states in twisted nematics layer is presented. The considerations are based on Ericksen's and Leslie's macroscopic theory of incompressible nematics, which seems to enable obtaining sufficiently exact and relatively simple description of the phenomenon. The full system of equations of motion of nematics layer (in one- dimensional approximation) has been derived from the Leslie's equations. The stability of stationary states in electric field has been investigated. New stability condition for stationary states has been deduced from a linearized version of these equations; it implies the existence of two types of stationary states in the layer, induced by the boundary conditions: with nematics molecules parallel or nonparallel to the surfaces. The threshold magnitudes of the total twist angle of the layer and of the constant voltage applied to the layer have been estimated. The usefulness of the formulae for threshold magnitudes has been confirmed by the results of computations of stationary states in quasi-MBBA (MBBA of assumed positive dielectric anisotropy), which are presented in the paper.

An influence of material constants such as elastic constants, electric permittivity constants, refractive indices, viscosity and concentration of optical dopants on the performance of STN displays are discussed. It is shown that mixtures containing as main components isothiocyanato and borodioxane compounds are speedily operating liquid crystalline materials and a high multiplexing level in this mode is obtained.

Studies of complexes: [R-C₆H₄-CO(CH)₂N-Alk]₂Cu, (I), [Alk-CO(CH)₂N-C₆H₄-R]₂Cu, (II), and [R¹-C₆H₄-CO(CH)₂N-C₆H₄-R²]₂Cu, (III), for various terminal substituents R, R¹, R², are presented. For alkyl substituents R, complexes are low- melting and low-clearing nematics [group (I)] and smectics A [group (II)]. Mesophases are monotropic for pure compounds, enantiotropic for mixtures. Elongation of molecular core by introduction trans-cyclohexyl rings into R substituents leads to enantiotropic paramagnetic mesogens. Complexes of the group (III) are high-melting and high-clearing mesogens which usually undergo decomposition in the isotropic phase.

Binary mixtures composed of 80BCAB with polar nTPCHB and nonpolar nMPCHB as well as with nonpolar A-n compounds have been investigated. It is shown that dimerization of 80BCAB compound takes place only in polar matrix. It is shown that generation of smectic A_d is due to the application a matrix with a long aliphatic chain and not to the lowering of its polarity.

Dielectric measurements of liquid crystalline polyester were made using a Du Pont Dielectric Analyser over the frequency 0.03 to 100,000 Hz and over temperature -100 to 160 degree(s)C ranging from (gamma) transition region up to isotropic fluid, upon heating. Dielectric relaxation process (gamma) , (beta) , (alpha) and (delta) were observed and analyzed. Apparent activation energies of the processes were calculated.

A short review of liquid crystals x-ray and microscopy investigation on freely suspended films and x-ray surface reflectivity are presented.

In the introduction the aims of high pressure (h.p.) studies of molecular systems are discussed. Then some experimental results of h.p. studies of liquid crystals are presented. Special attention is paid to the results of dielectric studies of pentyl-cyanobiphenyl (5CB) as a function of temperature and pressure. The obtained results are analyzed in terms of Maier-Saupe theory of the nematic state. Some conclusions concerning the form of the interaction potential in liquid crystals are presented.

The dipole-dipole association of nematogen molecules with comparison to non-nematogen molecules has been discussed on the basis of the results of static dielectric polarization studies. A dielectric method for investigation of the kinetics of dipolar aggregation process has been described.

We have measured the dielectric constants of 6CHBT. The results of the studies for different alignment and thicknesses under different electric measuring fields and magnetic fields are presented. We discuss how dielectric properties depend on boundary condition, thicknesses of the samples, and magnitudes of electric and magnetic fields. The obtained experimental results and the discussion in the terms of continuum theory make it possible to compute the diamagnetic anisotropy ((Delta) _(Chi)), splay and bend elastic constants (K₁₁, K₃₃) of 6CHBT.

Static electric permittivities of the homologous series of p-cyano-p'- alkylphenylcyclohexanes (PCH) have been measured as a function of temperature in isotropic and nematic phases. The mean square effective dipole moment components along the principal directions of a liquid crystal have been determined. The Kirkwood correlation factors g_(i), obtained from Maier and Meier equations, exhibit the odd-even alteration within the studied series. The g-factors values have been interpreted in terms of an anti-parallel association.

Low frequency dielectric properties of selected liquid crystalline materials have been measured in time as well as frequency domain. The results have been compared with those related to liquid crystalline polymer. It is worth noting that in this case different behavior of the sample is observed in respect to current i vs time t as well as conductivity (sigma) vs frequency f dependencies. The behavior of polymer samples is like the behavior of solidified liquid crystals. The phenomena were interpreted and a possible explanation is proposed.

A simple and experimentally convenient method for determination of the twist elastic constants of the c-director in tilted smectic phases is proposed. The method consists in measurement of changes in electrical permittivity at high frequencies (about 1 MHz) caused by a dc electric field applied in the direction parallel to the smectic layers. The computer controlled apparatus performing the whole experiment has been described. The results of measurement of an effective elastic constant in a ferroelectric liquid crystal are presented.

The polarized absorption spectra of the naphthalene bicarboxylic acid derivatives dissolved in nematic liquid crystal mixture ZLI 1695 have been studied in the ultraviolet and visible spectral region. On the basis of these spectra the degree of anisotropy and the order parameters S and D have been determined as a function of temperature. The experimental data have been compared with theoretical calculations predicted by the mean field theory.

The acoustic waves on the interface surface between elastic medium and liquid crystal (LC) were examined. When the elastic body is Bi₁₂SiO₂₀ and liquid crystal is smectic A (DEADB) then Rayleigh type and leaky waves are present in the considered case. For leaky waves final results are similar to those reported for Langmuir-Blodget films. Calculations were made in the case without dispersion of elasticity in liquid crystal medium.

Passive liquid crystal elements such as wave plates, linear and circular polarizers and active, based on electro-optical effects, are currently promising candidates for numerous applications. The principles of operation, materials and fabrication of these types of devices are discussed.

In this work, the electro-optic response of 6CB liquid crystal is studied using a sensitive differential technique. The liquid crystal layer is held at a temperature just above the nematic to isotropic (N-I) phase transition. Transverse magnetic (p) polarized light incident on the cell is coupled to guided modes in the liquid crystal layer using either grating or prism coupling. In both cases the modes manifest themselves as sharp resonances in the reflectivity as the angle of incidence is scanned. When a low frequency sinusoidal voltage is applied to the cell the resonance shapes and positions are altered at a frequency which is twice that of the applied field, resulting in a modulation of the reflectivity for a given angle of incidence. By carefully observing the modulated signal, and comparing the data with modelling generated from multilayer optics theory, two effects are quantified. The first of these is an induced birefringence, (delta) n, varying quadratically with applied voltage, which is well understood and can be expressed in terms of Landau De Gennes theory. The second is a field induced perturbation in the imaginary part of the optical permittivity, (delta) (epsilon) _i, which implies a modification of the light scattering properties of the liquid crystal. The measurement of the latter effect is, as far as we know, a novel one, being only made possible by the remarkable sensitivity of the synchronous differential technique.

The guest-host effect permits us to eliminate at least one polarizer. This effect we apply to black and white displays. Our black and white mixtures were prepared with antraquinoe and azo-dyes and isothiocyanate LC. The optimization investigations of mixtures containing dyes admixtures were performed. The black and white displays for negative mode with the wide range of temperature (-30 divided by 85 degree(s)C) were constructed.

In this paper we give an overview of the effects of ionic impurities present in LCDs. First we discuss the case of active matrix addressed nematic LCDs (AMLCD) as these are at this moment the most interesting candidates for high performance flat display panels with multi- color possibilities. As a second type we consider the surface stabilized ferroelectric LCDs (SSFLCD).

The paper discusses application of high-birefringence (HB) fibers as interconnections in liquid crystal logic systems. Since HB fibers can transmit linearly polarized light for a long distance, they are suitable for optical systems which operate only with polarized light. This paper also addresses problems of HB fibers -- liquid crystal combinations used in optical logic as modulators, polarization converters, and logic gates.

Principles of construction and functioning of the liquid crystal displays designed for visualization of the graphic information are proposed. The thermo-optic effect in the LC is the base of the information recording process. By means of a laser beam, controlled by two interperpendicular deflectors, the graphic image is formed on the LC cell. The given image is enlarged by means of the optic system and then is projected on the screen. The study of thermo-optic characteristics for low and highmolecular LC is carried out.

Resonant optical nonlinearity caused by absorption saturation of dye-stuffs in the selective reflection spectra region of chiral liquid crystals (CLC) was for the first time used for dynamic holography grating recording. Such a type of nonlinearity was accompanied with low recording times (about 10 picoseconds) and a rather high diffractive efficiency of 10 - 20%.

Thermally induced phase separation of liquid crystal and polymer is one of the promising methods of polymer dispersed liquid crystal (PDLC) preparation. In this contribution general rules of choosing the proper polymer which fulfill all requirements are presented.

This lecture provides an introduction to flat panel display technologies and gives their status in development. The main flat panel technologies which found PC application, presented in the lecture, are the emissive display technologies of plasma, and electroluminescence, and the non-emissive technologies of passive liquid-crystal and active liquid-crystal. A status of the development achievements, trends, and prospects for each of the technologies is presented. The various technologies are described as to their fundamental electro-optic effect, unique addressing attributes, extendibility limitations, and relative ultimate costs.

Flat active displays designed for large boards emitting public information are discussed. Mainly AC-PDPs, VFDs, and ELDs especially designed for such applications are presented. These displays characterized by flatness, electronic driving, high brightness, good contrast, and relatively large pixels can easily be arranged as modules in rows and columns to construct a large informative board. The boards are installed on railway stations, airport terminals, and in trade and financial centers. Other types of displays are used in informative boards i.e., LEDs and ECDs besides those specified already. Brief information about these displays and about some OBREP results concerning AC-PDPs and VFDs application for informative boards also are given.

The bistable or `memory' mode of operation of an ac plasma display panel is presented. The difference between dc and ac plasma panel operation from the point of view of memory function is discussed. The graphic ac plasma display with thin film Cr-Cu-Cr electrodes was developed in OBREP and its basic parameters are described. It consists of 36 X 59 picture elements, its outer dimensions are: 76 X 52 mm² and the screen size is: 49 X 30 mm². The different dielectric glass materials were applied as dielectric layers and the influence of the properties of these materials on display parameters and memory function was investigated.

The strong increase of applications of liquid crystal displays in various areas (measuring, medical equipment, automotive, telecommunication, office, etc.) has forced the demand for the adequate specification of the LCDs performances. The optical, electro-optical and spectral properties of LCDs are strongly dependent on viewing direction, electrical driving conditions, illumination and temperature. All these quantities have to be precisely controlled, when one of them is varied, the resulting optical response of the object is recorded. In this paper we present measuring methods proposed for LCD panels and the computer controlled measuring system (DMS) for their evaluation.

Liquid crystalline properties of 4-halogenobenzylidene-4'-alkoxy-anilines have been investigated. Among these compounds nematic, smectic A, and smectic B mesophases were found. These phase situations are compared with the isomeric families with the reversed -N equals CH- central group.

The homologous series of 4-isothiocyanatophenyl 4-(trans-4-alkylcyclohexyl) benzoates containing members with alkyl chain ethyl to dodecyl were synthesized and their phase transition temperatures, smectic layer spacing, and dielectric permittivity were measured. It was observed that smectic A₁ layer spacing is expanding from d/1 on the order of magnitude 1 to d/1 on the order of magnitude 1.1 when alkyl is increasing from butyl to dodecyl. This behavior is accompanied by the great change in (epsilon) (perpendicular) which is strongly increasing from pentyl to octyl and then from nonyl begins to decrease. It was proposed to term smectic A₁ with d/1 > 1 enhanced smectic A₁ (A_1c).

Multicomponent nematic mixtures formed from smectic components were described. Their physicochemical and electro-optical parameters (viscosity, threshold voltage, response times) were measured at different temperatures and discussed.

Homologous series of 4'-nitro- and 4'-cyano-derivatives of 1-(4'-alkoxyphenylamino)- 3-phenyl-1-propen-3-ones and a structurally similar series of 1-(4'- alkoxyphenylamino)-3-(4'-pyridyl-N-oxide)-1-propen-3-ones were synthesized and studied by DSC and optical methods. The compounds behave typically for strongly polar mesogens: the smectic A_d phase exists above a critical chain length and the re-entrant nematic phase is observed in the vicinity of the critical double point. For pyridyl N-oxides, a second-order SmA_d - SmC_d phase transition line is observed.

Cellulose derivatives have been shown to form liquid crystalline solutions at high polymer concentration in a wide range of organic solvents. This paper describes the liquid crystalline behavior of the cellulose derivatives suspended in UV-curable polyester resin. The diffusion phenomena of the acetic acid and methanol to cellulose domain suspended in UV-curable liquid polyester resin was used for obtaining crystalline phase. The samples were investigated by thermo-optical, light and x-ray scattering methods.

Results concerning synthesis and properties of polymers belonging to two classes of organosilicon systems are presented. Synthetic routes leading to polycarbosilane type polymers and cyclic polysiloxanes are described. Preliminary studies of properties of each polymer group members, bearing the same 4'-methoxyphenyl 4-octyloxybenzoate mesogenic side group, by means of polarized optical microscopy, differential scanning calorimetry, and x-ray diffraction are reported.

Results of preliminary studies of thermo- and photostability of 6CHBT and Demus' esters, based on the measurement of the current passing through the sample, are presented. Different purification techniques for 6CHBT are compared. It was found that the best technique of additional purification is adsorption on neutral silica gel. Good results were also obtained when a combined method was used (zinc dust + carbon + silica gel). 6CHBT is resistant to high temperature only when placed in a vacuum but is rather photostable in vacuum and in air. Demus' esters are thermally stable both in the air and in vacuum but they are not resistant to UV-radiation.

Two homologue series of mesogenic enantiomers with chiral semiflexible joint, - C^*H(CH₃)CH₂COO-, are examined. High twist power and presence of blue phases with short lattice period are found for eleven examined compounds. Some effects of chirality in the re-entrant system are discussed. On the phase diagram of enantiomers the SmA_d phase area is shifted toward longer homologues as compared to racemates. In result, an island of the SmA_d phase in the cholesteric sea exists on binary phase diagrams of R- and S- enantiomers.

Two methods of determination of surface tension anisotropy in nematic liquid crystals are presented. Both methods give similar values of surface tension for corresponding orientations on the free surface.

Dielectric relaxation in the isotropic phase of 1-[3-n-alkyl-biphenyl]-2-[4- isothiocyanatophenyl]ethane, C_nH_2n+1-(Phi) -(Phi) -CH₂CH₂- (Phi) -NCS (n-TPEB), for n equals 7, 8, 9 has been measured. Two bands of the dielectric absorption have been interpreted as corresponding to the rotation around the short and long molecular axis.

New results are presented of nonlinear dielectric effect (NDE) measurements in the isotropic phase close to T^C for HCPB, 5CB, and 8CB. With a measurement field frequency of about 6 MHz deviations from the Landau-de Gennes model were observed. This is interpreted as due to the influence of the orientation mechanism of individual molecules which becomes a dominating influence in the range of sufficiently high frequencies.

The ferroelectric spontaneous polarization P and the coercive voltage Vc and their frequency dependences have been measured in frequency range 10 Hz - 10 kHz. The exponents of power law P varies direct as f^-b and Vc varies direct as f^c have been found and confronted with theoretical predictions. The coefficient of rotational viscosity (gamma) has been computed.

A cholesteric liquid crystal (CLC) is considered in a cell with planar boundary conditions, in which long-lived metastable states of molecules with the conformation different from that of initial molecules are formed under the action of light. The phenomenon of molecular phototransformation was suggested to be used for varying the cholesteric twisting ability and, thus for controlling the CLC pitch. The dependence of the pitch on both the molecular twisting ability and the anchoring energy of director with oriented cell planes was investigated. The expression is derived for the anchoring energy which makes it possible to determine its value through the experimentally measured data. It is shown that with discontinuous change of a pitch there may occur a jump of mean values of components of the CLC dielectric susceptibility tensor. The preliminary experiment is discussed.

Measurements of complex electric permittivity have been taken on aligned samples of room- temperature ferroelectric liquid crystals mixtures. The spontaneous polarization, the tilt angle, and pitch in those mixtures have been measured. By fitting to the experimental points of electric permittivity the Cole-Cole modification of the Debye equation dielectric strength, the relaxation frequency, and distribution parameter for the Goldstone mode have been computed. The dielectrically observed Goldstone mode in our mixtures is a function of the concentration of chiral dopant and of measuring field magnitude.

We have measured the critical values of electric E_c and magnetic H_c fields in different types of Freedericksz transitions for 4-trans-n-hexyl-cyclohexyl-isothiocyanatobenzene (6CHBT). Capacitive and optical methods have been employed to detect these transitions. In the case of twist-type deformation we have proposed a new interference method for threshold fields determination. On the basis of these measurements diamagnetic anisotropy (Delta) _(Chi) splay K₁₁, twist K₂₂ and bend K₃₃ elastic constants have been calculated for cells of various thickness, coated with different polyimides.

The Frederiks transitions for the n-octyloxycyanobiphenyl (8-OCB) placed in the external magnetic and electric field as a function of the temperature have been studied. On the basis of threshold values B_c and U_c, the elastic constants for splay, bend and twist modes are determined. The magnetic anisotropy of 8-OCB as a function of temperature has been determined. The K₁₁ and K₃₃ elastic constants show the pretransitional nematic- smectic A effect. The values of critical exponents obtained from the temperature dependence of K₁₁ and K₃₃ in the vicinity of N-S_A phase transition are discussed.

A computerized measuring setup based on ultrasonic vibratory viscometer is described. Measurements of temperature dependence of the viscosity in nonoriented samples of nematic liquid crystals are presented as examples of application of the equipment.

We have measured both change in phase differences (delta) between ordinary and extraordinary rays passing through liquid crystal cell and dielectric constants (epsilon) of 4- trans-n-hexyl-cyclohekxyl-isothiocyanatobenzene (6CHBT). The results of the studies for different alignment and thicknesses under various electric measuring and magnetic fields are presented. The obtained experimental results and the discussion on the base of the Oseen and Frank elastic continuum theory of a nematic in the presence of electric and magnetic fields make it possible to calculate the vector field of directors in the LC medium.

The chosen results of investigations of internal and external diffraction maximum, using a transmission beam to freely suspended `thick' and `thin' films of smectic LC, are presented. On the basis of these results the way to the generalization of the Moncton-Pindac method was illustrated. Our generalization of the Moncton-Pindac method can be distinguished from the other methods by study of internal diffraction maximum using reflected (instead of transmission) beam. It is important that the film placed on a heated plate has only one free surface. In commonly used methods, the investigated film has two free surfaces. Some results of diffractometer measurements are presented as examples of studies using the generalized Moncton-Pindac method. Possible experiments using this method, advantages, and inconveniences are discussed.

A possibility of applying poly(vinyl cyclohexanal) to polymer dispersed liquid crystals (PDLC) by thermally induced phase separation is presented. Obtained layers exhibit very good adhesion to glass and satisfactory electro-optical characteristics. The main disadvantage of this material is a complicated preparation of PDLC.

Temperatures of phase transitions in gamma irradiated mesogens decrease with absorbed dose due to the introduction of non-mesogenic products of radiolytic destruction. This effect may be described in terms of lattice model using geometric shapes of mesogen and admixture. The results for cholesterol nonanoate are presented.

The car dashboards we used were original construction. Liquid crystal display works on the twist-nematic effect with color filters. The central element of the dashboard is a digital speedometer. Other displays like tachometer, fuel and temperature gauge are analog. An electronic system assures cooperation with traditional car endowment. Isothiocyanate liquid crystal mixture assures wide range display operation -30 divided by 80 degree(s)C.

A liquid crystal-photoconductor (LC-PC) sandwich system that controls the optical thickness of a liquid crystal layer by means of a ZnS film used as an ultraviolet light sensitive photoconductor has been constructed. The LC-PC devices were investigated using a Mach- Zehnder interferometer and split He-Ne laser beam. The created interference pattern was used to analyze the feature of the image formed on the PC layer by ultraviolet light.

The paper presents the fiber-optic method for measurement of high hydrostatic pressure applied to a sensing element comprising a cholesteric liquid crystal (ChLC) being connected to multimode optical fibers for communication with a light source and a device for measurement of light intensity. The method exploiting the effect of pressure-induced changes in the wavelength of maximum light reflection observed in ChLCs resides in guiding a light beam of predetermined wavelength generated by the light source toward a layer of the ChLC using one of the multimode optical fibers. The light beam reflected by the layer is collected using another of the multimode optical fibers being connected to the device for measurement of light intensity. This method is particularly well adapted for measuring pressure up to 100 MPa with a good linear response and sensitivity for specific ranges of pressure useful in industrial applications. The results obtained indicate that a fiber-optic sensing device based on this method has pressure coefficient two orders of magnitude higher than current high-pressure sensors. The paper also discusses possible approaches towards the temperature desensitization procedure of the fiber-optic method of pressure measurement.

The analysis of a nonlinear directional coupler with two waveguides separated by the liquid crystalline layer is presented. An optimization procedure of the coupler is performed and the results are compared with coupler configurations previously investigated.

Prick tests are commonly used in allergy diagnosis but in some cases obtained results are difficult for objective interpretation. Application of liquid-crystal contact thermography improves this kind of diagnosis especially in the case of colored or sick skin.

The investigations of some anthraquinone dyes in mixture with optical activity were presented. Their twist coefficients were defined. The comparison of electro-optical parameters with typical dichroic anthraquinone dyes were carried.