ELSEVIER Synthetic Metals 94 (1998) 157-159 SYlITilETII[ RITRLS Conductivity and magnetoconductivity below 1 K in films of poly(3,4-ethylenedioxythiophene) doped with CF3SO 3 A.N. Aleshin a, l, R. Kiebooms a, H. Yu u, M. Levin b,., I. Shlimak b ~ lnstituteJbr Polymers and Organic Solids, Universi~' of California at Santa Barbara, Santa Barbara, CA 93106, USA hJack and Pearl Resnick Institute of Advanced Technology Department of Physics, Bar-llan Universi~_,,Ramat-Gan 52900, Israel Received 26 January 1998; accepted 28 January 1998 Abstract The temperature dependence of the electrical conductivity tr(T) and the magnetoconductivity o'(B,T) of poly (3,4-ethylenedioxythiophene) (PEDOT) films heavily doped with CF3SO3 has been measured down to T= 150 mK in magnetic fields up to B = 9 T. It is shown that, below 1 K, o-(T) at In T and tr(B,T) depends significantly on the orientation of B parallel or perpendicular to the film surface. These facts are interpreted as a manifestation of two-dimensional character of electron transport in highly doped PEDOT films because of the possible formation of strongly graphitized layers with plane structure of polymer chains or fibrils. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Polythiopheneand derivatives; Conductivity;Magnetotransport I. Introduction Electrical conductivity in conducting polymers in the metallic state has been the subject of intensive study over the last few years [ l ]. Measurements of low-temperature charge transport in heavily doped conjugated polymers, such as poly- yacetylene (PA) [2-4], polyaniline (PANI) and polypyr- role (PPy) [ 5-7 ], have demonstrated properties which are similar to a 3D metal close to a disorder-induced metal- insulator transition [ 8 ]. Particularly, the temperature depend- ence of the conductivity o-(T) for potassium-doped PA sat- isfies Atr(T) - tr(T) - tr(0) = CT I/2, which is characteristic of a disordered 3D metal with strong electron-electron cor- relations. The T ~/2 term appears from electron diffusion in states near the Fermi level, reduced by the electron-electron interaction. However, it has been observed in a number of polymers, such as AsFs-doped PA [9], I-doped PA [ 10], PF6-doped PPy [ 10,11] and ion-implanted PANI [ 12], that the low- temperature conductivity satisfies Art(T)ctln T, which is characteristic of 2D metallic conductivity when quantum cor- * Corresponding author. Tel.: +972 3 531 8433; fax: +972 3 535 3298; e-mail: levin@ physnet.ph.biu.ac.il Present address: A.F.Ioffe Physico-Technical Institute, RussianAcademy of Sciences, St. Petersburg 19402 l, Russia. 0379-6779/98/$19.00 © 1998Elsevier Science S,A. All rights reserved. PIIS0379-6779(98)00021-6 rections to the zero-temperature conductivity tr(0) are deter- mined by the effect of weak localization [ 13,14]. On the one hand, the assumption of 2D character of the conductivity is not reasonable because of the macroscopic thickness of the investigated polymer films. On the other hand, the possibility of low dimensionality of electron trans- port in conducting polymers should also be taken into account. It is now well established that electron transport in these materials consists of motion along the conjugated poly- mer chain and hopping between chains and fibrils. The weak interchain bonding leads to quasi-lD character of electron transport along the backbone structure. The interchain hop- ping may have 3D or 2D character depending on the space organization of the polymer chains and fibrils. The problem of possible 2D character of the metallic conductivity in poly- mer films is far from understood and needs further experi- mental data. We present here the results of measurements of the low- temperature d.c. conductivity o-(T) and magnetoconductivity (MC) o'(B,T) in films ofpoly(3,4-ethylenedioxythiophene) (PEDOT) heavily doped with CF3SO 3. PEDOT is a conju- gated polymer with a maximum optical absorption in the middle of the visible spectrum and with room-temperature electrical conductivity up to 300 S/cm after doping. This material is promising for practical applications as a transpar- ent conductor and as elements of polymer microelectronic