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«ANNUAL REPORT Riga 2012 Annual Report 2011, Institute of Solid State Physics, University of Latvia. Editor: A.Krumins. Composed matter: A.Muratova. ...»

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2) supervision of physics masters work of LU Physics and Mathematics Faculty student K. Bavrins.

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Scientific projects of the Latvian Council of Sciences 09.1548 Physical Processes in Multilayer and Multicomponental Structures (2009-2013) 10.0032 „Development of research and technology potential for elaboration of new and nanostructured materials and related applications.” subproject „Supramolecular nanostructuring of photonic materials – theoretical modeling and experimental investigations” (2010-2013) National Research Program in Materials Science and Information Technologies IMIS (2010-2014) Project No.1, Multifunctional materials for high-tech applications in conversion of radiation energy, information recording, storage, transfer and processing ERAF projects of the activity 2.1.1.1.”Support of science and research” No.2010/0308/2DP/2.1.1.1.0/10/APIA/VIAA/051, “Development of Polymer EO modulator prototype device” No. 2010/0252/2DP/2.1.1.1.0/10/APIA/VIAA/009, “Materials and its tandem structure for solar cells” (2010-2013) No. 2010/0275/2DP/2.1.1.1.0/10/ APIA/VIAA/124, „RTD for fabrication of diffractive optical elements” (2010-2013)

–  –  –

Institute of Chemistry, Academia Sinica, R.O.C., Taiwan

Main equipments:

1. Equipments for preparation of thin films:

the vacuum deposition of organic compounds and metals (Edwards 306A);

the Langmuir-Blodgett technique;

the self-assembled techniques;

the casting and spin-coating techniques (Lite Single Wafer Spin Processor, Laurell technology Corporation).

2. High vacuum setups for measuring of electrical and photoelectrical conductivity between 10 and 400K. The sample is provide by a digitally controlled voltage supply over range up to 5kV and the current is measured in range 1fA to 1mA.

3. Computer controlled corona poling systems.

4. Computer-controlled Kelvin probe setup with the temperature control up to +130ºC and measuring the surface potential in a range between –9.6 and +9.6V with the accuracy ±1mV. The diameter of vibrating gold electrode was 2mm

5. Scanning Kelvin Probe SKP5050

6. Surface Profile Measuring System Dektak 150

7. Computer-controlled SHG setup (λ=1064 nm) allows us to measure SHG (λ=532 nm) intensity as function of the fundamental power, incidence angle, fundamental and SH light polarization as well as sample surface mapping by SHG intensity. The detection threshold of equipment is 1 x 10-6 pm/V

Cooperations

Latvia

1. Institute of Applied Chemistry, Riga Technical University (Prof. V.Kampars, Prof.

V.Kokars).

2. Latvian Institute of Organic Synthesis (Dr. E.Markava).

3. Institute of Chemical Physics, University of Latvia, (Dr. D.Erts).

4. Institute of Physical Energetics (Dr. I.Kaulach).

Lithuania

1. Institute of Physics (Prof. L.Valkunas, Dr. V.Gulbinas).

2. Institute of Material Science and Applied Research, Vilnius University, (Prof. S.Juršenas).

3. Kaunas Technology University (Prof. J.V. Grazulevicius) Germany

1. Lehrstuhl Physik kondensierter Materie, Universität Potsdam, Potsdam (Prof. D.Neher, Dr. B.Stiller).

Taiwan

1. Institute of Chemistry, Academia Sinica, (Prof. Chao-Ping Hsu)

–  –  –

Calculation of chromophore polar order, i.e. polarization, of poled by external field nonlinear optically (NLO) active polymers is challenging. One of possible solutions is to reproduce the orientation polarization of chromophores under external field using Langevin dynamics (LD) molecular modeling.

–  –  –

0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2

–  –  –

-0.6 -0.6

-0.8 -0.8

-1.0 -1.0 DC poling hysteresis loops of model clusters built from 10 D dipoles with dipole density N = 10x1020 mol/cc: a) “Guest/ Host” system; b) and “Grafted” system In spotlight of this investigation we would like to describe NLO polymer as a “coloid” mixture or “ferrofluid” were chromophores (in our case model dipolar molecules) take part in the role of active particles - electrets. According to our simulations of model systems at low dipolar densities such system behaves “paraelectric” like. For dipole densities within a range of practical interest polarization behavior of such “ferrofluid” profoundly depends on translation movement freedom of electrets and their dipole moment. In the model systems where translation movement of “electrets” is prohibited (“Grafted” models) an “antiferroelectric” behavior start to show up with increase of dipole density and moment value. In a case when “electrets” allowed moving freely (“Guest/Host”) model systems behavior is different. Dipolar “chains” and “rings” are formed with dipole density rise in “Guest/Host” model systems. The dipolar “chains” could form “ferroelectric” like structure when oriented parallel or “antiferroelectric” like if in opposite orientation and “rings” definitely behaves “antiferroelectric” like. The shape of obtained polarization hysteresis loops allows us to suggest coexistence of both “antiferroelectric” and “ferroelectric” like structures in densely loaded “Guest/Host” model systems.





The outcome of these chromophore poling simulations of model systems by Langevin Dynamics convinced us, that method could be applicable for modeling of real chromophore/polymer composites. Results obtained within an investigated model systems give us some inspirations for practical NLO polymer design. First of all our model simulations confirm that at low (typically used for NLO polymers) poling fields high dipole moment chromophores are preferable and should yield a higher load factor and therefore better NLO efficiency. In a case when one could achieve a higher poling field values low dipole moment chromophores should perform better and higher NLO efficiency achieved.

Increased (above typically used nowadays) poling fields could be a key for breakthrough in EO polymer design. Possibility to achieve same (or even higher) NLO efficiency by using low μ with high Ep scheme in contradiction to high μ with low Ep could be recommended also due to eventually better PO stability.

This research was granted by Latvian National Research Program in Materials Science, Project No.3 “Materials for photonics and nanoelectronics based on novel functional low molecular organic compounds and polymers” and Latvian Council of Science collaboration project 10.0032 „ Development of research and technology potential for elaboration of new and nanostructured materials and related applications.” subproject 10.0032.14 “Supramolecular nanostructuring of photonic materials – theoretical modeling and experimental investigations”.

–  –  –

Study of charge carrier transport in organic electroluminescent devices, organic photovoltaic devices, and organic field-effect transistors is one of the most important points. In order to realize comparable electron and hole transport in thin organic films with electrodes the energy structure of such devices are of great importance. In this work, we have studied electrical properties and energy structure of two carbazole derivatives.

–  –  –

The energy gap of two carbazole derivatives 1 and 2 in thin film is obtained. The energy gap characterisized by threshold energy of photoconductivity quantum efficiency is 2.90 eV and optical energy gap following from optical absorption spectrum is 3.3 eV for compound 1 in thin films. The values of the surface potential characterisizing ionization potential in solid state (hole conducting energy level) are 5.17 eV for compound 1 and 5.19 eV for compound

2. The values of work function of ITO, Au, Cu and Pd electrodes are energetically close to conductivity level of holes (Eh) and holes injection dominates from electrodes. In these thin films local trapping states of holes are situated at holes conducting level. When electrode is Al layer the local shallow trapping states for electrons at Et = 0.10 eV for compound 1 and at Et = 0.18 eV for compound 2 are determined This work is supported by ERAF Project Nr. 2DP/2.1.1.2.0/10/APIA/VIAA/010 and LatvianLithuanian-Taiwan joint project „Design, Synthesis and Studies of New Effective Materials for Organic Optoelectronics”

PYRANYLIDENE INDENE-1,3-DIONE DERIVATIVES AS AN AMORPHOUS RED

ELECTROLUMINESCENCE MATERIAL

–  –  –

The organic light emitting diode (OLED) has a promising applications in flat panel displays and novel light sources. So far the OLED structures have mostly been made by thermal evaporation in vacuum. An alternative approach is to use small molecules which form amorphous (glassy) structure from solutions. Such compounds can be used in the ink-jet printing technologies and result in reducing the OLED prices. In this paper, we present an original red fluorescent organic compound 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6methyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK1) and it derivative 2-(2,6-bis(4bis(2-(trityloxy)ethyl) amino)styryl)-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK2) where methyl group replaced with 4-substituted-styryl group. This change could improve the formation of glassy structure.

–  –  –

Electroluminescence spectrum of ZWK1 (line) and ZWK2 (doted line) The thickness of the electroluminescent layer in the device was optimized to the higher power efficiency and obtained: ITO/PEDOT:PSS(40nm)/ZWK1(95nm) /LiF(1nm)/Al(100nm) and ITO/PEDOT:PSS(40nm)/ZWK2(85nm)/LiF(1nm)/Al(100nm). The maximum of electroluminescence spectra for the device with ZWK1 compound was 667 nm wich correspond to the CIE coordinates x=0.65 and y=0.34. The power and luminance efficiency at the luminance of 100 cd/m2 is 0.63 lm/W and 1.78 cd/A, respectively. Adding additional 4substituted-styryl group to ZWK1 molecule shifted maximum of EL spectra to red region (705 nm) and decreased the efficiencies by one order.

This research was granted by Latvian National Research Program in Materials Science, Project No.3 “Materials for photonics and nanoelectronics based on novel functional low molecular organic compounds and polymers” and by the European Social Fund within the project «Support for Doctoral Studies at University of Latvia»

Scientific publications

1. A.Vembris, M.Porozovs, I.Muzikante, V.Kokars, E.Zarins, Pyranylidene indene-1,3-dione derivatives as an amorphous red electroluminescence material, Journal of Photonics for Energy, 2011, Vol.1, 011001, DOI: 10.1117/1.3524819

2. M.Indrikova, J.Latvels, I.Muzikante, B.Turovska, Photoelectrical Properties and Energetical Structure of Thin Films of Indandione Derivatives, Materials Science, 2011Vol.17, No.2, pp.125-131

3. D.Gustina, E.Markava, E.Laizane, I.Muzikante, Synthesis and investigation of photoisomerization of some new azobenzene carboxylic acids, Latvian J.Chemistry, 2011, No.1/2, pp.129–138, DOI 10.2478/v10161-011-0058-4

4. M. Rutkis, A. Jurgis, Insight in NLO polymer material behavior by Langevin dynamic modeling of chromophore poling, Integrated Ferroelectrics, 123, 2011, pp 53-65, http://dx.doi.org/10.1080/10584587.2011.570635

5. R.Grzibovskis, J.Latvels, I.Muzikante, Photoelectrical properties of thin films of DMABI derivatives, IOP Conf. Series: Materials Science and Engineering, 2011, Vol.23, 012021 doi:10.1088/1757-899X/23/1/012021

6. K.Pudzs, I.Muzikante, E.Fonavs, J.Simokaitiene, S.Grigalevicius, J.V.Grazilevicius, Energy structure of thin films of carbazole derivatives with metal electrodes, IOP Conf.

Series: Materials Science and Engineering, 2011, Vol.23, 012020 doi:10.1088/1757X/23/1/012020

7. K. Traskovskis, I. Mihailovs, A.Tokmakovs, V. Kokars, V. Kampars, M. Rutkis, Synthesis and nonlinear optical properties of novel N,N-dihydroxyethyl based molecular organic glasses using triaryl substitutes as amorphous phase formation enhancers, Proc.

SPIE 8113, 81130Z (2011); doi:10.1117/12.893381

8. A.Sternbergs, I.Muzikante, R.Dobulans, D.Millers, L.Grigorjeva, K.Smits, M.Knite, G.Sakale, Polymer nanomaterials for novel sensing systems, Springer Science and Business Media - NATO Science for Peace and Security Series – B : Physics and Biophysics, 2011

9. O.Vilitis, E.Fonavs, M.Rutkis, Chromophore poling in thin films of organic glasses. 1.

Overview of corona discharge application, Latvian Journal of Physics and Technical Sciences, 2011, No. 6, pp. 53-65; DOI: 10.2478/v10047-011-0038-1

Abstracts

27th Scientific Conference of the Institute of Solid State Physics, University of Latvia, February 14-16, 2011

30. K.Pudžs, A.Vembris, I.Muzikante, J.V.Grazulevicius, Energy structure of thin film with carbazole derivatves determination in light emitting diode structure, Book of Abstracts, p.88

31. A.Vembris, I.Muzikante, R.Karpiz, V.Gulbinas, Red apmlified spontaneous emission in original; organic compounds, Book of Abstracts, p.89

32. M.Rutkis, I.Mihailovs, A.Tokmakovs, A.Ernstsons, Hyper-Rayleigh scattering measrements of molecular hyperpolarizability – comparison of internal and external standard methods, Book of Abstracts, p.90

33. E.Laizāne, D.Gustiņa, I.Muzikante, A.Vembris, Optical study of thin solid films with azobenzene molecules containing carboxyl groups, Book of Abstracts, p.60

34. E.Nitišs, E.Titavs, M.Rutkis, O.Vilītis, Current – voltage characteristics of corona triode setup for NLO polymer poling, Book of Abstracts, p.61

35. E.Nitišs, M.Rutkis, M.Svilans, Application of Abes matrix formalism for determination of thin organic film EO coefficients by Mach – Zehnder interferometer, Book of Abstracts, p.62 54th Scientific conference for young students of physics and natural science „Openreadings 2011”, Vilnius, Lithuania, March 16-19,2011

1. K.Pudzs, A.Vembris, I.Muzikante, J.V.Grazulevicius, Energy structure of thin film determination in light emitting diode, Book of Abstracts,p.100



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