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Electrical response of a columnar liquid crystal applied in a diode structure.

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Apresentação do trabalho que ganhou o Prêmio Bernhard Gross ao melhor oral do XIII Encontro da SBPMat.

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Electrical response of a columnar liquid crystal applied in a diode structure.

  1. 1. Electrical response of a columnar liquid crystal applied in a diode structure Juliana Eccher1, Gregório C. Faria2, Harald Bock3, Heinz von Seggern4, Wojciech Pisula5, Wojciech Zajaczkowski5, Ivan H. Bechtold1. UNIVERSIDADE FEDERAL DE SANTA CATARINA XIII Brazilian Materials Research Society Meeting 1Universidade Federal de Santa Catarina, Departamento de Física, SC, Brasil. 2Universidade de São Paulo, Instituto de Física de São Carlos, SP, Brasil. 3University of Bordeaux, Centre de Recherche Paul-Pascal, CNRS , France. 4 Technical University of Darmstadt, Department of Electronic Materials, Germany. 5Max-Planck-Institut for Polymer Research, Mainz, Germany. João Pessoa, September, 2014. Laboratório de Optoeletrônica Orgânica e Sistemas Anisotrópicos e-mail: juh_19@yahoo.com.br
  2. 2. Liquid Crystals (LCs)  molecular order + fluidity (charge transport) (easy processability)  anisometric organic molecules  rod-shape  disk-shape Crystal Smetic A Smetic C Nematic Isotropic Liquid Temperature Liquid-crystalline mesophases 2
  3. 3. Discotic Liquid Crystals  Hexagonal columnar mesophase (Colh):  Synthesis: Dr. Harald Bock, CRPP, France.  Colh at room temperature.  n-type semiconductor.  μ > 1 cm2/Vs.  Material: benzo[ghi]perylene-diimidodiester 3 Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935-11943 (2013).
  4. 4. 4 Orientation of the Columnar LCs  Edge-on Orientation (Planar Alignment)  Face-on Orientation (Homeotropic Alignment)  Transistor  Diode Advantage:  Modify the molecular orientation to control and improve the electro- optical properties of the devices (thermal annealing, surface treatments, electric and magnetic fields); The mobility (μ) is highly dependent on the intracolunar alignment.
  5. 5. Results: -60 -30 0 30 60 90 120 150 180 H = 9.1 kJ/mol H = 8.8 kJ/mol 148.2 0C Colh Iso Iso heating Colh Heat Flow Temperature (oC) cooling 153.4 0C 120 ºC 25 ºC  Polarizing optical microscopy cooling: Iso 148.2ºC Colh 5  DSC (Differential Scanning Calorimetry) Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935-11943 (2013).
  6. 6. 6  Spin-coating thin film:  Thermal annealing: device at 120 ºC  Polarizing optical microscopy:  Homeotropic alignment: face-on (c) (d) (a) (b) (e) (f) face-on 3h 0h 0h 1h 3h 1h (c) Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935-11943 (2013).
  7. 7. Charge Carrier Mobility from J-V Curves 7   : Poole-Frenkel coefficient  Boundary condition: E (0) = 0 Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935-11943 (2013).
  8. 8. 8 J-V and Luminance-Voltage Characteristics spin-coating film Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935-11943 (2013).
  9. 9. 9 Charge Carrier Mobility from J-V Curves Parameter Before During After μ0 (cm2/Vs) 9.86 × 10-10 9.12 × 10-10 9.03 × 10-10 (cm/V) 1/2 0.44 × 10-2 1.98 × 10-2 2.11 × 10-2 μ at +15 V (cm2/Vs) 8.8 × 10-8 4.5 × 10-4 8.5 × 10-3 Mobility 5 orders of magnitude higher after alignment. 0 10 20 30 40 50 60 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 Applied Voltage (V) After During Before Mobility (cm 2 /Vs) Published in: J. Eccher et al. ACS Appl. Mater. Interfaces, 5, 11935- 11943 (2013).
  10. 10. CONCLUSIONS 10  Spin-coating film: The annealing process resulted in the homeotropic alignment. A gain of 4 orders of magnitude in current and 5 orders of magnitude in charge carrier mobility was surprisingly obtained. The electroluminescence was also improved dramatically.  Evaporated film: Homeotropic alignment was not observed. A high rectification degree was obtained even before annealing, indicating that the molecular packing in the evaporated film is more ordered and compact than in the spin-coated film before annealing.
  11. 11. 10th Ibero-American Workshop on Complex Fluids FLORIANÓPOLIS - SANTA CATARINA - BRAZIL 25-29 October 2015 11 Chairman: Prof. Ivan H. Bechtold Prof. Hugo Gallardo Website: http://10ibero.paginas.ufsc.br/
  12. 12. 12 Thanks for attention!!! Financial Supports: Acknowledgments:

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