A preview of the papers appearing in the July 2006 issue of the Journal of the SID. To obtain access to these articles on-line, please go to www.sid.org

Edited by Aris Silzars

Optoelectronic applications of lanthanide-doped sol-gel products and porous anodic alumina

G. K. Maliarevich
I. S. Molchan
N. V. Gaponenko
A. V. Mudryi
S. V. Gaponenko
A. A. Lutich
G. E. Thompson

Belarusian State University of Informationand Radioelectronics, Belarus

Abstract — Recent studies on structures, comprising lanthanide-doped xerogels embedded in porous anodic alumina, are presented. It is shown that a terbium and europium co-doped sol-gel film embedded in porous anodic alumina allows a change in the color of the photoluminescence, from red to green, with a change in the excitation wavelength. The possibility of strong erbium-related 1.53-μm emission from yttrium–aluminium garnets in porous anodic alumina is also demonstrated. Visually, it is revealed that the blue alumina-related emission is predominant over the red europium-related emission from the xerogel/porous anodic alumina structure. Finally, the birefringence effect of a porous anodic alumina membrane is discussed.

Figure 7 demonstrates luminescence from the specimen consisting of porous anodic alumina and non-anodized aluminum regions, covered with a Eu–TiO2 xerogel film. The Eu-related emission is red from the non-anodized region, whereas the same xerogel generates a blue emission when deposited on the anodized region. It is known that porous anodic alumina is capable of blue photoluminescence, suggested to result from the presence of oxygen vacancies and species derived from the electrolyte. The spectra, recorded for the anodized region, reveal both blue and red emission; however, visually, the blue emission is predominant.


FIGURE 7 — Photoluminescence from a specimen revealing a nonanodized aluminium region and an anodized region covered with a Eu–TiO2 xerogel film. Blue emission is evident from the anodized region and red emission is revealed from anodized region.

Photoinduced ferroelectric parameter changes in liquid-crystal systems containing chiral α,β-unsaturated ketones

Ekaterina V. Popova
Aleksandr P. Fedoryako
Nikolay S. Pivnenko
Lidiya A. Kutulya

Institute for Single Crystals, NASU, Ukraine

Abstract — Photoinduced changes that were revealed for ferroelectric liquid-crystalline systems with helical supra-molecular structures induced with chiral α,β-unsaturated ketones have been summarized. Photoinduced inversion of the spontaneous polarization sign and a concomitant increase in its absolute value and other ferroelectric parameters were observed. The EZphotoisomerization of the chiral compounds was determined to be responsible for the discovered effects.

Photoinduced changes in FLC are of great interest. Two main types of photoinduced variations in such systems are known, vis, the inversion of the spontaneous polarization (Ps) sign provoked with phototransformation of a chiral compound (CC) and changes in ferroelectric parameters associated with a photoisomerization of host phase molecules at a photostabile CC. The aim of this work is to investigate the influence of UV irradiation on the properties of FLC systems containing photosensitive CCs 1. Such an investigation is stipulated with results concerning the ferroelectric parameters for systems, including separately obtained isomers of CC 1c. In this connection, the dynamics of the FLC parameter changes during the irradiation is of great interest.

SCHEME — E–Z photoisomerisation of (+)-isomenthone 2-arylidene derivatives.

Polarization and phase of light transmitted through polymer-dispersed liquid-crystal film

Valery A. Loiko
Alexander V. Konkolovich
Polina G. Maksimenko

Stepanov Institute of Physics, NASB, Belarus

Abstract — A method for calculating the transmission coefficient, phase shift, and characteristics of the polarization state of light, transmitted through a PDLC film with nanosized nematic droplets, is considered. Functional dependences of these values on the morphological characteristics of a film are obtained and graphically illustrated. Good agreement between the theoretical and available experimental data is established.

Polymer-dispersed liquid-crystal (PDLC) films consist of liquid-crystal (LC) droplets, embedded in a polymer matrix and placed between two thin transparent plates covered with transparent electrodes. These films are widely used as electro-optical modulators. Molecules of liquid crystal in the PDLC film change their orientation under an external electric or magnetic field. As a result, the optical characteristics of films are changed. The azimuth and ellipticity of transmitted light depend on the orientation of the LC droplets. Therefore, by changing the external field, it is possible to control the polarization state of light transmitted through a PDLC film with fine LC droplets.


FIGURE 2 —Schematic representation of light scattering on a PDLC film. Notations are in text.

Anchoring and gliding of easy axis of 5CB on photoaligning PVCN-F surface

O. Buluy
A. Iljin
E. Ouskova
Yu. Reznikov
C. Blanc
M. Nobili
K. Antonova

Institute of Physics, NASU, Ukraine

Abstract — The photoaligning properties of the popular photoaligning material polyvinyl-4(fluoro-cinnamate) (PVCN-F) are presented. The aligning quality and azimuthal and zenithal anchoring energy were measured and the drift of the easy orientation axis (gliding effect) on the PVCN-F surface, depending on UV exposure, was studied. Special attention is paid to unraveling the contribution of the adsorption liquid-crystal molecules onto the aligning surface to the anchoring properties of PVCN-F and measuring the drift of the easy orientation axis over the PVCN-F surface. It is shown that a relatively weak azimuthal anchoring energy (Waz » 10–7 – 10–5 J/m2) leads to strong drift of the easy axis in the azimuthal plane that was observed in a moderate (~0.1–0.3 T) magnetic field. A much stronger polar anchoring (Wzen » 10–4 J/m2) allowed us to observe the essential gliding of the easy axis in the zenithal plane in a rather strong electric field (~5 V/μm).

Despite advantages in photoalignment technology, some specific features of photoaligning materials (weak anchoring energy, strong sticking effect, etc.) prevent wide application of photoalignment in the LCD industry, and photoalignment has been used up until now in academic research. Wide application of this technology requires a deep understanding of the interaction of LC with photosensitive polymers and detailed characterization of the anchoring properties of the existing photoaligning materials.


FIGURE 4 — Dependences of the reorientation angle φsurf and anchoring energy Wazad on exposure time texp.

An LCOS IC layout verification method that uses a computational model for lithography manufacturing

S. N. Koukharenko
S. V. Volk
A. M. Zayats
A. G. Smirnov

Belarusian State University of Informaticsand Radioelectronics, Belarus

Abstract — An advanced approach to LCOS IC layout verification is presented. It is based on incorporating the results of optical lithography computational models into the verification process. The first section describes an algorithm for the numerical modeling of optical lithography that uses a source integration method for computation of an aerial image. The second section dwells on an application of this algorithm for layout physical verification. A proposed physical verification method uses modeled contours of the manufactured elements to check whether a given layout will be manufacturable. The proposed verification method also considers deviations of manufactured contours from their modeled shapes due to variation of manufacturing parameters to further improve verification quality. At the same time, the method is conservative in terms of the use of a time-consuming lithographical modeling.

The main factor causing distortions in a subwavelength lithography is the impact of optical discrepancies, produced by an optical system due to the finite size of the pupil of a projection optical system and, as a consequence, limited resolution of an optical system as a whole. The impact on the optical factors is a good first-order approximation of a lithography manufacturing process.


FIGURE 1 — Schematic of the optical system.

Influence of the preparation and excitation conditions of ZnS:Er,F TFELS on the radiative characteristics in the visible and near-infrared spectral regions

N. A. Vlasenko
L. I. Veligura
Z. L. Denisova
M. A. Mukhlyo
Yu. A.Tsyrkunov
V. F. Zinchenko

Institute of Semiconductor Physics, NASU, Ukraine

Abstract — The voltage (V) dependences of the luminance and transferred charge of ZnS:Er,F TFELS prepared by varying the annealing temperature (Tann) are given at different frequencies (f). The change in the relative intensity of the green band (523 nm) and the near-infrared bands (983 and 1530 nm) in the emission spectrum when V, f, and Tann are varied is also considered. The influence of the annealing temperature on the energy spectrum of defects in ZnS:Er,F film was studied by photodepolarization spectroscopy. The revealed effect of the above excitation and preparation conditions on the radiative characteristics is discussed.

TFELS under study consisted of an electroluminescent (EL) ZnS:ErF3 film, two electrodes (ITO and Al films), and two insulator layers (Al2O3/Y2O3 films), which separate the EL film from the electrodes. The ITO electrode deposited by magnetron sputtering was rather thin (~80 nm) to increase its optical transmission in the NIR region. The insulator layers and the ZnS film were deposited by electron-beam evaporation at a substrate temperature of 170°C. Doping of the ZnS film was performed by the thermal co-evaporation of ErF3.


FIGURE 1 — Typical emission spectrum of ZnS:Er,F TFELS in the range 900–1600 nm.

Interactive display technologies

Yuri Trofimov
Valery Posedko
Vladimir Sivenkov
Sergey Lishik
Vitalii Tsvirko
Alla Posedko
Alexander Pautino

Institute of Electronics, NASB, Belarus

Abstract — The current state of the art of interactive displays, the main principles of their operation, and their functional characteristics are reviewed. Special attention is given to interactive displays with contactless control; in particular, to photosensitive displays. A number of photosensitive display cell designs are considered, as well as the problems related to the production of such cells. The results of the authors' research in this field are presented.


FIGURE 1 — Classification of the sensor technologies used in interactive displays.


FIGURE 2 — An ID used in an architectural design.


Spectral-polarizing properties and light stability of film polarizers with azodyes

V. Agabekov
N. Ariko
L. Filippovich

Institute of Chemistry of New Materials,NASB, Belarus

Abstract — Results of the investigation of film polarizers on a base of polyvinyl alcohol and azoben-zeneazonaphtalene dyes are presented. The dependence of the light stability of these polarizers on the structure and concentration of a dye, the stretching and conditions of the chemical treatment of films, as well as the physical state of the polymer matrix have been studied. Based on obtained results, a method for improving the light stability has been proposed.

A polarizer must have good light stability. But it is well known that most organic dyes are sensitive to light, especially to UV irradiation that causes photodestruction and reduces the polarizing efficiency of a colored film. Experimental investigations indicate that the speed of the photoreaction depends on different factors such as the dye and polymer structure, presence of admixtures, and film-production conditions.

TABLE 2 — Influence of UV irradiation on the quantity of transformed dye.

Passively addressed FLC display possessing an inherent gray scale and memory

E. P. Pozhidaev, V. G. Chigrinov,
Yu. P. Bobilev, V. M. Shoshin,
A. A. Zhukov, A. L. Andreev,
I. N. Kompanets, Li Xihua,
E. E. Gukasjan, P. S. Komarov,
O. A. Shadura, H. S. Kwok

P.N. Lebedev Physical Instituteof the RAS, Russia

Abstract — A passively addressed 64 x 64 ferroelectric liquid-crystal display (FLCD) has been developed. The display matrix has a 33 x 33 mm2 aperture, and the FLC layer thickness is 5.2 ± 0.2 μm. The display device operates with a frame frequency of 30 Hz (at Vrow = ±18 V, Vcol = ±9 V, T = 23°C), generating a continuous gray scale which can be memorized for more than 10 days after the driving voltage is switched off. A new approach for multiplex electronic addressing of the FLCD gray scale is proposed. The conditions of the hysteresis-free gray-scale generation for multiplex addressing and the gray-scale memorization after the voltage is switched off, as well as the time steadiness of memorized images, are considered.

The inherent physical gray scale of passively addressed FLCDs can be obtained only if the FLC possesses high spontaneous polarizationPs > 50 nC/cm2. Then, ferroelectric domains exist, being one of several possible reasons for gray scale. Generally, any type of spatial nonuniformity of helix-free FLCs coupled with minimization of the FLC free energy can be considered principally as a base for the gray scale. On the contrary, at high Ps, depolarizing fields appear in FLC cells, suppressing the bistability if the aligning layers are thick enough. Therefore, extremely thin aligning layers are necessary for the development of a passively addressed FLCD having gray scale.



FIGURE 16 — Photographs of images memorized by a 64 x 64 FLC display matrix: (a)–(c), (f) – binary images, (d) and (g) – images with gray-scale levels.

Dynamic parameters of electrically controlled light scattering in helix FLC cells

Alexander L. Andreev
Yury P. Bobylev
Tatiyana B. Fedosenkova
Ildar B. Yambaev
Igor N. Kompanets
Eugene P. Pozhidaev
Vadim M. Shoshin
Yuliya P. Shumkina

P.N. Lebedev Physical Institute, Russia

Abstract — The light-scattering structures in monomeric FLCs have been considered and a mechanism for the scattering on transient domains in the helix layers has been proposed. An optical response with a bistable characteristic of light scattering and transmission was realized at a defined electrical pulse regime and boundary conditions in electro-optical FLC cells. The total time of the scattering switching on and switching off is less than 400 μsec at ±36 V. They are quite fast, and FLC cells are quite transparent to be used in a stack of 30–100 light-scattering shutters for a volumetric screen of a 3-D display.

The transient scattering appears during the reorientation of the FLC director just after changing the sign of the electric field, and scattering disappears when the formation of the homogeneous layer structure is completed at some high level of the electric field. Transient domains in helix FLCs are the boundaries of spontaneous ordered regions generated in the process of nonlinear helix deformation via the electric field. They result in the appearance of refraction-index gradients along the helix axis, and this process is accompanied with light scattering of a FLC cell.


FIGURE 1 — Helix FLC in the electro-optical cell: 1) glass substrates, 2) transparent conducting coatings, 3) smectic layers, 4) electric voltage generator, P) polarizer, β) an angle between the light polarization plane and helix axis, D) light-beam aperture, Ps) spontaneous polarization vector.

Perspectives of passive-matrix-LCD improvements

S. A. Studentsov 
V. A. Brezhnev
B. I. Gorfinkel
N. D. Zhukov

Research and Development Institute"Volga," Russia

Abstract — The current status of STN-LCDs is described. The accomplishments and the main problems (low contrast, pure color, and slow response) are discussed. Ways to make improvements (driving methods, retardation film, and memory displays) are considered. The use of memory displays appears to be the most appropriate.

Why have STN-LCDs retreated? 1. Low contrast: 30:1 for STN-LCDs versus 150:1 for AMLCDs. 2. Slow response: 200 msec for STN-LCDs versus 20–30 msec for AMLCDs. 3. Multipex level limitations (with high contrast): 1/240 for STN-LCDs versus 1/768 for AMLCDs. Why STN-LCDs have not gone away? 1. Low cost: $10–15 for STN-LCDs versus $27–35 for AMLCDs. 2. Technology simplicity: these are more than 100 producers of STN-LCDs versus 15–20 for AMLCDs.


FIGURE 2 — Shipment volume and color handset percent. (Toray Industries, Inc., Nov. 2004)

Nonlinear properties of aluminum-doped zinc sulfide under IR excitation

L. V. Grigoryev
V. V. Rychgorskyi
E. V. Komarov
M. M. Sychov
E. V. Sergeev
L. I. Tarasova-Tarosyan
A. I. Kuznetsov

St. Petersburg University, Russia

Abstract — Second-harmonic generation (SHG) in ZnS-based materials is reported. ZnS, ZnS:Cu,Br, and ZnS:Cu,Al,Br samples were studied. Phosphor powders were subjected to 30-mJ pulses from YAG:Nd infrared laser. The wavelength of the generated green emission was 532 nm, exactly one-half that of incident laser light (1064 nm). However, the non-linear dependence of the emission intensity on pump intensity was observed only for the ZnS: Cu,Al,Br powder. It is concluded that aluminum co-doping is crucial for the non-linear properties.

Materials with non-linear properties are very promising for optoelectronics applications. One type of such material is ferroelectrics based on lithium niobate; however, they are difficult to process and deposit onto the substrate. Thus, development of new materials which have non-linear properties and are more suitable for the fabrication and utilization of optoelectronics devices is very important. Recently, there were several reports on second-harmonic generation (SHG) in electron-beam-deposited zinc sulfide thin films and nanometer-sized thin layers of zinc sulfide doped with aluminum, indium, and tin. Therefore, it was interesting to study the non-linear properties of powdered zinc sulfide materials.


TABLE 1 — Characteristics of studied samples.

Light-scattering liquid-crystal composites with reduced off-axis haze

L. O. Dolgov
O. V. Yaroshchuk

Institute of Physics, NASU,Ukraine

Abstract — The majority of liquid-crystal (LC) composites operating in a light-scattering mode suffer from scattering of the obliquely incident light in the field on-state (off-axis haze effect). This is evident in the angularly selective viewing-angle characteristic with a maximal transmittance corresponding to the normally incident light. Methods to control the viewing-angle characteristic of polymer-dispersed LC (PDLC) and filled LC were considered. For PDLC samples, this control is realized by modification of the refractive index of the polymer matrix with highly refractive nanoparticles (NP) having a low rate of aggregation in the polymer. By proper optimization of NP concentration, one can bring the refractive index of the polymer matrix in the range needed to reduce the haze problem. In filled LC, the viewing-angle curve depends on the refractive-index mismatch between the LC and NP. By optimization of this parameter, one can flatten the angular characteristic or obtain selectable viewing angles in the desirable range. These results allow for the construction of optical shutters and a scattering-type LCD with controllable viewing-angle characteristics, particularly with low off-axis haze.

The devices working in the scattering mode are distinguished by high brightness, wide viewing angle, and fast switching. They do not require polarizers, compensation films, alignment layers, and high uniformity of cell gap that greatly simplifies the preparation process. At the same time, samples of this type have several drawbacks, which seriously hinder their wide application. First is the low switching contrast, which cannot compete with the contrast of monodomain samples commonly used in commercial LCDs.


FIGURE 4 —The saturation transmittance Ts vs. incidence angle θ curves for PDLC doped with a different amount of Sb2O5: 1 –φNP = 1 vol.%, 2 – φNP = 3 vol.%. For all cases φLC = 63 vol.%, the rest is polymer content. The lines are just to guide the eyes.