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Molecular Films for Optical Applications

#G-875


Advanced Molecular Thin Films for Optical Applications: Properties, Structure, Modeling and Technology

Tech Area / Field

  • MAT-ELE/Organic and Electronics Materials/Materials
  • PHY-OPL/Optics and Lasers/Physics

Status
3 Approved without Funding

Registration date
08.04.2002

Leading Institute
Sukhumi Institute of Physics and Technology, Georgia, Tbilisi

Supporting institutes

  • Russian Academy of Sciences / Institute of Crystallography, Russia, Moscow

Collaborators

  • University of Minnesota / School of Physics and Astronomy, USA, MN, Minneapolis\nOsaka University / Graduate School of Engineering, Japan, Osaka\nUniversita della Calabria, Italy, Arcavacata di Rende

Project summary

The proposed project aims at a common effort of the Georgian and Russian scientists involved to create stable ultrathin film assemblies with specific ordering at the supramolecular level. Control of organization at this level can lead to smart materials with unique physical properties. A wide class of low molecular mass and polymer materials will be used, like liquid crystals (LC), side-chain polymers, azo-dye derivatives and hybrid block copolymers. Films of these materials are of fundamental importance in the context of the physics of low-dimensional and self-organising systems. Such highly ordered organic films and multilayer structures are of major interest in areas like information storage, non-linear and integrated optics, display applications. Prepared as thin films these materials may serve as smart command surfaces and anisotropic coatings.

The general objective of the project is to study the structure and properties of such new ordered thin film assemblies and develop technological schemes of their application. Of special interest is the creation of the ultrathin photosensitive organic films where significant optical anisotropy can be induced by polarized light illumination- so called photoinduced optical anisotropy (POA) effect. The POA is very promising for creating of the new types of spatial light modulators and memory media for computer technology. It is important to control the layer sequence and the inpidual parameters of the molecular films such as layer thickness, optical anisotropy and dielectric properties. Appropriate techniques include the Langmuir-Blodgett (LB) method for preparing multilayer films and superlattices, spin-coating of polymer solutions onto a substrate, controlled evaporation of such solutions, and the preparation of free standing LC films, both from monomers and polymers. Advanced x-ray, scanning probe techniques, optical and dielectric spectroscopy will be applied for study of the structure and material properties of such films. Theoretical modeling will be an important component of the project. For this purpose the general approach based on the Catastrophe Theory will be applied for the study of the bulk and surface phase transformations in organized molecular films.

The project will create a scientific basis for extensive applications of advanced molecular thin films by numerous research groups and in the industry (especially in LC display applications and for computer technology). The common expertise of the Georgian-Russian team will be especially important in obtaining a more complete understanding of the structure, stability and material properties of thin film assemblies, which is required to develop the potential for different types of applications.

The particular objectives are:

– Development of new methods and technologies of creation of novel low molecular mass and polymer organized molecular films.

– Experimental study of the structure transformations in thin films of LC polymers and block copolymers. Theoretical description and modeling of these phase transformations in the framework of the Catastrophe Theory.

– Development of methods and technologies for creating novel organized molecular films showing the phenomenon of photoinduced optical anisotropy.

– Characterization and optimization of the films and study of the mechanisms of photoinduced optical anisotropy in different organic systems. Theoretical description of the POA effect on the basis of Catastrophe Theory. Computer modeling of the POA effect.

– Determination of the origin of polar behaviour of the thin film assemblies of LC monomers and polymers.

– Optimization of write/erase processes in the films for applications of the POA effect in optical memory devices, holograms, diffraction gratings, light polarizers, etc.

– Computer simulation and experimental study of novel liquid crystalline materials (bistable cholesterics and ferroelectrics) in combination with photo-anisotropic orienting layers for high-speed spatial light modulators and other optical devices.

Importance of the project:

The proposed research belongs to intensively growing field of the study of basic properties and technology applications of thin film molecular assemblies. These films are currently of great potential for information storage, non-linear and integrated optics, computer technology and display applications. The planned research is complementary to the activity of various European, Japanese and American groups and will help to consolidate knowledge about the mechanisms of self-organization, structure, material properties and technology application of ordered molecular systems. Because of the importance of these systems for the understanding of the basic physics in organized molecular films and particularly because of their great potential effect on computer technology and display applications, the research in this field is on the cutting edge of the present research. Moreover this project is an effort to diminish the information technology gap between Japan and USA on one side and Europe on the other side. All this and the high scientific reputation of all participating groups and Collaborators guarantee the success of the project.

Topicality of the proposed problems is stressed by the fact that there is an obvious need in novel advanced monomer and polymer thin film materials for different optical and computer applications. The scientific teams, participating in the project, have mutually complementary experimental technique and experiences, which is important to achieve the objectives of the project. However, difficult economic situation in the former CIS countries creates the obvious problems in experimental work and technological developments of novel perspective materials. To overcome these problems the funding and other types of support from ISTC are highly desirable.

The project participants are internationally recognized experts in their scientific fields. The results of their investigations have been documented in numerous reports made in the framework of Academy of Sciences and State Committee on Science and Technology of the USSR, in hundreds of papers published in the former Soviet Union, Georgia, Russia and worldwide. Many of participants have author's certificates and are the authors of a number of methodical documents and recommendations of highest normative level. Some general publications of the participants of the project are listed below:

1. L.M. Blinov, Electro – and Magnetooptics of Liquid Crystals, Nauka, Moscow, 1978.

2. B.I. Ostrovskii, X-ray diffraction study of nematic, smectic A and C liquid crystals, Sov. Sci. Rev. Ser. A Phys., 12, part 2, Harwood Academic publishers, 85-146 (1989).

3. N. Zoidze, Application of Catastrophe Theory to the Theory of Phase Transformations in Multicomponent Systems. Izvestija Academy of Sciences of Georgia, Serie of Chemestry, V. 18, №3 Mezniereba, Tbilisi, 1992.

4. L. M. Blinov, V.G. Chigrinov, Electrooptic effects in Liquid Crystal materials. Springer Verlag, 1993.

5. S.P. Palto, G. Durand, Friction Model Of Photoinduced Reorientation Of Optical Axis In Photooriented Langmuir-Blodgett Films. J.Phys. II France, 5, 963-978 (1995).

6. L.M. Blinov, Photoinduced molecular reorientation in polymers, liquid crystals and Langmuir-Blodgett films, J.Nonlinear Opt. Phys. and Materials 5, 165-187 (1996).

7. B.I. Ostrovskii, X-ray studies of new types of ordering in liquid crystals, Problems of Modern Crystallography, Nauka, Moscow, pp. 377-406, 1996.

8. B.I. Ostrovskii B, Packing and molecular conformation, and their relationship with LC phase behaviour, Liquid Crystals I, Vol. 94, D.M.P. Mingos (ed.) pp. 199-240, Springer, Berlin-Geidelberg, 1999.

9. S.P. Palto, G.N. Andreev, N.N. Petukhova, S.G. Yudin and L.M.Blinov, Measurements of Landau Coefficients in Ferroelectrics, Journal of Experimental and Theoretical Physics, Vol. 90, No.5, 872- 880 (2000).

10. A. Chanishvili, D. Sikharulidze, G.Chilaya and G. Petriashvili, Electrooptics of “amorphous” cholesteric structures with intermediate chirality, Mol. Materials, 1997, Vol. 8, pp. 295-299.

11. D. Sikharulidze, A. Chanishvili, G. Petriashvili, N. Scaramuzza, R. Barberi, and R.Bartolino, Polarity sensitive bistable color effect in cholesteric liquid crystals with an asymmetric polymer network, Applied Physics Letters, volume 75, number 7, 16 august 1999.

The project is attributed to applied research in the course of which the following activity is planned:

– development of new methods and technologies of creation of ultrathin, stable monomer and polymer photosensitive films, showing effect of photoinduced optical anisotropy.


– development of the methods of structural studies of such films with the application of X-ray diffraction, atomic force microscopy, optical spectroscopy and dielectric relaxation spectroscopy.
– development of new molecular media for optical memory devices.
– development of new methods for theoretical and computer modeling of the structure transformations in thin films of liquid crystals and polymers.
– the using of optically controlled command surfaces of polymers and LB films for planar orientation of nematic liquid crystals for display applications.
– development of the write/erase processes for applications of the POA effect in optical memory devices, holograms, diffraction gratings and light polarizers.
– development of electrically controlled photoinduced optical anisotropy and polarity providing optimum anchoring conditions for liquid crystals.
– development of the liquid crystal cells with bistable cholesteric and smectic (ferroelectric) materials and light controlled interfaces for high switching rate spatial light modulators.

The sphere of application of the research results:

The thin molecular films with the optically controlled anisotropy can be used as command surfaces for display applications, as a media for non-violate optical memory devices for computers, hologram recordings, light polarizers, diffraction gratings and other systems. Of special importance for RAM memory devices is the study of erasing/writing processes of the induced anisotropy. The photo-induced reorientation in the presence of electric field can result in induction of a polar axis in the film. The detailed study of this phenomenon in ultrathin organic films can lead to novel polar systems which are of potential interest for the computer technology and display applications.

Realization of the ISTC's objectives:

The project will give opportunity to its performers, the Georgian and Russian scientists having worked before on optical devices and theoretical modeling for military applications to employ their qualification, knowledge and experience in the peaceful activity - in the field of development of advance computer technology for conventional, civil techniques. Additionally the project will allow them to reestablish and stabilize cooperation with scientists and specialists of the world scientific community by means of joint investigations with collaborators, exchanging experience and scientific information, participating in international scientific forums, publishing common papers and reports.

Role of collaborators:

Consistent with the scope of activities of the proposed project, the role of foreign collaborators is highly important and may be specified as follows:

– discussions on the problems of common interests;


– information exchange in the course of project implementation and organization;
– carrying out joint seminars, discussions, workshops and conferences;
– comments on the technical reports and recommendations;
– cross-checks of results obtained in the course of project implementation and assessment of proposed methods;
– participation in testing and evaluation of project activities performed by ISTC staff, supporting ISTC staff in participation in international scientific meetings.

Common investigations of photochromic liquid crystal polymers will be carried out in Osaka University, Japan (photochromism, photo-dielectric effect and X-ray structural changes under UV excitation). Common AFM studies of ultrathin photo-anisotropic films and properties of diffraction gratings based on the latter will be carried out in collaboration with Calabria University (Italy).

Methodology.

The Georgian and Russian scientists participating in the project have a long time experience in investigation of the physical properties of soft condensed media. The Georgian scientists from the Institute of Nuclear Physics are experts in theoretical description and modeling of the phase transformations in condensed media based on the Catastrophe Theory. This approach utilizes the complete analysis of thermodynamic potential (Gibbs potential – GP) in the multidimensional space of the thermodynamic variables. The Georgian scientists participating in the project has developed the general algorithm based on the Catastrophe Theory theorems which allows reconstruct the topology of the thermodynamic potential of the system. They were the first who recognized that GP of the multicomponent systems contains generally all of the canonical forms of catastrophes and have demonstrated the equivalence of some of them with the known thermodynamic models of the liquid and solid solutions. The physicists from the Institute of Nuclear Physics has derived the algorithm to estimate the critical parameters of the phase transitions (critical temperature, critical composition, critical exponents etc.) for the multicomponent systems. The potentials used for the description of the phase equilibrium in three-dimensional systems can be used to calculate their material parameters of the type of viscosity and surface tension. In the later case the properties of two-dimensional systems are effectively involved into consideration. This allows to model the phase transformations in the surface layers of the bulk materials and thin films. The Catastrophe Theory theorems can be used also to specify the features of phase transformations in liquid crystals, polymers and other soft matter materials.

The liquid crystal laboratory in the Institute of Crystallography has more than 30 years experience in the liquid crystal field. Investigations on the electrohydrodynamic and electrooptic effects, physical phenomena at the liquid crystal-solid surface boundary and other studies were carried out. In the laboratory the first polymer ferroelectric liquid crystal was studied, and first observation of antiferroelectric properties in low molecular LC have been made. The distorted helix ferroelectric (DHF) effect based on the field-induced deformation of a planar helical ferroelectric layer was discovered and joint patent on the DHF liquid crystal displays with La Roche company (Switzerland) is available. The laboratory is well equipped to make liquid crystal display prototypes and perform investigations of the most important liquid crystal properties (optic, electric, electrooptic, photooptic, etc). The structure of the thin films is studied using X-ray diffraction and reflectivity. For this purpose X-ray diffractometers with linear and area detectors and triple-axis x-ray spectrometer is used. Complementary information about surface ordering is obtained by exploring the possibilities of atomic force microscopy (AFM).

The laboratory of liquid crystals has a long time experience in investigation of physical properties of organized molecular films (20 years). The phenomenon of POA in Langmuir-Blodgett films was discovered by this team. In addition, here the first ferroelectric Langmuir-Blodgett films were prepared and investigated. In order to understand the fundamental properties of the effect of Photoinduced Optical Anisotropy and optimize the novel optical devices based on different molecular films, the computer simulation and theoretical modeling of the phenomena based on the Catastrophe Theory will be done. The new methodological approaches will be developed with respect to measurements of birefringence and electrooptical properties of the ultrathin films.

Existing in the group technologies for preparation of polymer, Langmuir-Blodgett and freely suspended films will be developed and adapted according to the tasks of the project. The preparation of Langmuir-Blodgett films have to be controlled by computer, and special software will be designed for the film preparation. Collection and processing of numerical data about technological conditions (temperature, surface pressure, phase state of monomolecular layer on a water surface) during film preparation will allow make further correlation of these data with structure and optical properties of the films. The study of orientation of liquid crystals on substrates covered with anisotropic polymer films are of vital importance for display applications. For these purposes the measurements of light induced birefringence and UV and IR spectral measurements are used. Another interests are related with the investigations of the polar properties of materials with the lack of inversion symmetry and the development of new advanced polar materials. The experimental facilities include the set-ups to measure pyroelectric, dielectric and electrooptic responses of polar materials. We plan to create a new computer-controlled experimental set-up to measure optical retardation, optical spectra and electrooptical response in ultra-thin organic films. The use of virtual devices developed in the group will help to make a detailed study of all the fundamental properties of the new thin film assemblies.

Analysis and systematization of data will be realized on the basis of experience and knowledge of the project participants, and conceptual approaches, methods, theoretical models worked out by the participants, and modified accordingly to the project tasks.


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