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Lydie Valade

An approach to the origin of transport properties in a series of molecular conductors, based on XPS and spectroscopic studies. Lydie Valade. Pont-Neuf. Toulouse. Place du Capitole. CNRS - Laboratoire de Chimie de Coordination 205 route de Narbonne - 31077 Toulouse Cedex 5 France.

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Lydie Valade

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  1. An approach to the origin of transport properties in a series of molecular conductors, based on XPS and spectroscopic studies Lydie Valade Pont-Neuf Toulouse Place du Capitole CNRS - Laboratoire de Chimie de Coordination 205 route de Narbonne - 31077 Toulouse Cedex 5 France valade@lcc-toulouse.fr www.lcc-toulouse.fr

  2. Molecular materials as thin films Crystals vs. films • Single crystal morphology is not appropriate for device applications • Film or nanowire morphology is more appropriate • Use of knowledge from materials science • Application to molecular materials

  3. Processing films of molecular materials Chemical Vapor Deposition (CVD) High Vacuum Deposition Dip-coating (DC) Langmuir-Blodgett Polymeric casting … Electrodeposition (ED)

  4. Problematic • Identification of the chemical nature of the product • EDS  nature of atoms • XPS  nature of atoms and stoichiometry • Incidence of the process on the chemical nature of the material • Comparison of the deposit properties vs. single crystal ones when known • Raman spectroscopy  charge of building blocks • Incidence of morphology on physical properties • SEM, AFM morphology • Conductivity measurements

  5. TTF Ni(dmit)2 BEDT-TTF or ET M(dcbdt)2 M = Ni, Co TMTSF Selected materials • FOSC and p-DA conductors • Building blocks

  6. TTF[Ni(dmit)2]2 Recall of properties sb (300 K) = 300 S cm-1 (TC = 1,62 K, 7 kbar) C.R. Acad. Sci. Paris, 1986 Synthetic procedure Cell: H-type cell Substrate: Si (0.5×1 mm) Temperature: 25 °C Prec.: TTF and NBu4[Ni(dmit)2] Solvent: CH3CN

  7. 20 µm 5 µm TTF[Ni(dmit)2]2 on Si by electrodeposition Morphology vs. conditions j = 1.5 mA cm-2 [Ni] : 1 mMol.L-1 TTF : 3,2 mMol.L-1 j = 6.25 µA.cm-2 [Ni] : 1.2 mMol.L-1 TTF : 4.5 mMol.L-1 Adv. Mater. 2004, 835

  8. TTF[Ni(dmit)2]2 on Si Stoichiometry by XPS 3 S2p contributions A: 161.8 eV: C-S-Ni (8) B: 163.5 eV: C-S-C (12) C: 161.8 eV: C=S (4) Intensity ratios B/A = 1.4 (vs. 1.5 if 1:2) Ni2p3/2/S2p = 0.3 in both film and a compressed pellet B A C 1:2 stoichiometry confirmed J. Fraxedas Adv. Mater. 2004, 835

  9. TTF[Ni(dmit)2]2 on Si Charge transfer nC=C (TTF) TTF0=1518 cm-1 TTF+=1420 cm-1 Needle-like deposit Grain-like deposit R. Bozio, C. Pecile, 1980 nC=C (TTF) 1430-1436 cm-1 Charge transfer: 0.86-0.82(calc 0.8)

  10. TTF[Ni(dmit)2]2 on Si Conductivity 4 probe method • (300 K) = 15 S.cm-1 • (12 K) = 50 S.cm-1 Metallic behavior despite of grain-like morphology 1st example by ED Grain-like deposit C. Faulmann Now studied at LPS Orsay: superconductive ? Adv. Mater. 2004, 835

  11. [NBu4]2[Ni(dcbdt)2]5 by ED on Si 20 mm j = 0.5 mA cm-2 Si (1 cm2), 25°C NBu4[Ni(dcbdt)2] in CH2Cl2 Morphology, stoichiometry and conductivity X-ray powder diffraction: in agreement with crystal data (M. Almeida); c-oriented growth Conductivity of the film: s(25°C) = 1.2×10-2 S cm-1 semiconductive behavior as single crystal 2:5 stoichiometry confirmed J. Mater. Chem. 2004, 14, 2801

  12. 50 mm (ET)[Ni(dcbdt)2]by ED on Si Morphology and stoichiometry H-type cell - Si (1cm2) – 25°C ET + NBu4[Ni(dcbdt)2] in CH2Cl2 A: j = 1 mA cm-2 B: j = 3.3 mA cm-2 A New compound associating BEDT-TTF and Ni(dcbdt)2 B XRD analysis on a single crystal removed from the Si surface 1:1 phase (C. Faulmann) J. Mater. Chem. 2004, 14, 2801

  13. [NBu4]2[Ni(dcbdt)2]5 and (ET)[Ni(dcbdt)2] XPS studies (NBu4)2[Ni]5 N1s CN 398.7 NBu4: 401.7 Ref: (NBu4)(BF4) Stoichiometry of ET[Ni] N1s CN 398.7 ET[Ni] XPS intensity ratio: S2p(total)/N1s lines = 3.2 to be compared to S/N = 12/4 = 3 if1:1 phase 1:1 stoichiometry confirmed J. Mater. Chem. 2004, 14, 2801

  14. ET (C=C) central Ni(dcbdt)2 (ET)[Ni(dcbdt)2]on Si nC=C arCharge of Ni(dcbdt)2 1557 cm-1 [Ni]-0.4(2:5 phase) 1550 cm-1 ET[Ni] close to 1 1546 cm-1[Ni]-(1:1 phase) Charge of ET nC=C ET = 1420, 1450 cm-1 H.H. Wang et al., Chem. Commun. 1994 d = 1 Conductivity: 3×10-6 S cm-1 at RT measured on powder collected from the substrate J. Mater. Chem. 2004, 14, 2801

  15. 10 m (TMTSF)x[Co(dcbdt)2]y by ED on Si Morphology and stoichiometry H-type cell, Si (1 cm2), j = 3.3 A.cm-2 TMTSF : 5 mMol.L-1 (n-Bu)4N[Co(dcbdt)2] :6 mMol.L-1 Solvent: CH2Cl2 Comparison of S2s and Se2s XPS lines (ref. BETS, S/Se = 1) Intensity ratio: IS2s/ISe2s = 1.4 ± 0.1 2 possible stoichiometriesx:y = 4:3 or 3:2

  16. 1560 TMTSF 1540 1520 (TMTSF)0.5+ 1500 1480 Frequency 1460 TMTSF+ 1440 1420 (TMTSF)x[Co(dcbdt)2]y 1400 1380 0 0,2 0,4 0,6 0,8 1 Charge of TMTSF (TMTSF)x[Co(dcbdt)2]y by ED on Si Charge transfer Central C=C C=C ar Charge of TMTSF = +0.8 s(300K) = 2 S/cm Ea = 46 meV Bozio, Pecile Mol. Cryst. Liq. Cryst. 1985

  17. Conclusions • 4 molecular conductors as films on Si • From XPS: stoichiometry of the grown phases • Confirmed for TTF[Ni(dmit)2]2 and ET[Ni(dcbdt)2] • Evaluated for TMTSFx[Co(dcbdt)2]y x/y = 1.4 • From Raman: charge of the donor component • Confirmed for TTF[Ni(dmit)2]2 • In agreement with conductive properties for TTF[Ni(dmit)2]2, ET[Ni(dcbdt)2], andTMTSFx[Co(dcbdt)2]y

  18. "Molecules and Materials"  team andJ. Fraxedas M. Almeida Support : CNRS ATUPS, FSE grants COST D14-003 Films and nanowires processing CVD, dip-coating, electrodeposition Integration into devices, morphology vs properties Multi-property materials Conductivity, magnetism, photochromism Addition or synergy between properties Poster Session 1 C. Faulmann MAGMOL Wednesday 2:20 & Poster Session 1

  19. (TMTSF)2ClO4 on Si Thank you

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