Doping, LB films

Advantage has been taken of organometallie complexes with long-chain alkyl-ammonium or pyridinium salts to increase the dimensionality and, hence, the lateral conductance [746, 747]. Indeed, the highest reported room temperature conductivity to date (25 Scm ) was measured in bromine-doped LB films prepared from tridecylmethyl-ammonium Au-(dmit)2 [741, 742],... 

Potassium-doped LB film prepared from 50 layers of fullerene (C60) and deposited on a polyethylene terephtphalate substrate Microwave absorption or low-field signal Superconductivity was observed at or below 8.1 K 121... 

Conjugated polymers doped with C60 become p-type semiconductors [305,306] some LB films of two polyalkylthiophenes mixed with arachidic acid and doped with C60 have been prepared [307]. The films of polyalkylthiophene + arachidic acid -l- C60 (spread from mixtures of 1.0 0.33 0.1 ratio) on ITO glass had a well-defined layer structure, as confirmed by x-ray diffraction. The bilayer distance obtained from the Bragg equation was 5.6 nm, the same as for arachidic acid LB films. Since the films were spread on subphases containing... 

In Fig. 29 the crucial elements are the p-doped Si layer, which can be replaced by any thin semiconducting layer, and the very thin insulator below the gate electrode. FET behavior was observed for polymeric LB films three decades ago [138], and by... 

Cgo doped with K T < 8.1 K) [322] and Rb T < 23 K) [323] exhibit superconductivity on LB films, which was detected by the AC complex magnetic susceptibility or low magnetic field microwave absorption measurements. However, both the stmctural disorder inherent to the LB films and the low-dimensional nature of the thin-layer structure severely prohibit the observation of superconductivity by resistivity measurements. 

Construction of LB films having lateral d.c. conductivities is a burgeoning activity. Results of published work are summarized in Table 9 [726-772]. The first formation of a conducting LB film was reported by French workers in 1985 [726]. Non-conducting LB films were formed from N-docosylpyridinium TCNQ. Subsequent exposure to iodine vapor resulted, however, in the lateral conductivities in the order of 0.1 S cm-1 [726]. The initially formed LB film was shown to consist of (TCNQ. )2 dimers whose molecular planes were almost parallel to the substrate. Iodination resulted in the development of a brown-purple color, the partial oxidization erf the radical anions to TCNQ° and, most importantly, a dramatic rearrangement of the LB film. In iodine-doped films, the TCNQ molecules have been shown to assume a position almost perpendicular to the substrate [721, 773],... 

LB films prepared from N-docosylpyridinium (TCNQ)2 and transferred to substrates Absorption and infrared spectra Lateral d.c. conductivity was determined to be 10"2 Scm"1, even without iodine doping 739, 740... 

LB films prepared from poly(p-phenylene vinylene), transferred to substrates, and doped with S03... 

Method of doping (exposure of LB film 763 to iodine vapor, immersion of LB films in aqueous KI3 solution, or anodic oxidation of LB films deposited on indium tin oxide glass) determined properties of the films. Lateral [Pg.165]

LB films prepared from poly(thiophene-3-acetic acid)-stearylamine and from sulfonatedpolyaniline-stearylaminepolyion complexes, transferred to substrates, and doped by acid FTIR, X-ray diffraction, and conductivity measurements Lateral d.c. conductivities of acid-doped films as high as 0.05 S cm"1 were obtained 768, 769... 

K-doped LB multilayer films of Cgo superconduct below 8 K, that is, about 10 K lower than the bulk crystal K3C6o [107] co-evaporated thin films of K and C60 show the same effect. 

The first conductive LB film, consisting of C PyfTCNQ) doped with iodine (Fig. 3) belongs to the class of anion-radical salts [20]. The insulating C PyCTCNQ) LB film was rendered conductive by iodine doping, and the bulk conductivity was about 0.01 S/cm. The nominal charge of TCNQ of... 

Figure 4 Structure of C22Py(TCNQ) LB film doped with iodine. (From Ref. 33.)...

Another conductive LB film was reported using ClgPy(TCNQ) without a doping process [54]. The conductivity is 0.02 S/cm, with an activation energy of 0.13 eV. This compound should be a Mott insulator, and oxidation of the film should have occurred during or after film preparation. 

The LB films of charge-transfer complexes of C TET-TTF, long-chain derivatives of BEDT-TTF, with F4TCNQ were fabricated to try to obtain high conductivities [67-69]. The iodine doping of the LB film yields a conductivity on the order of 10 2 S/cm, which is considered to be due to reduction of the donor. The LB films of a series of 3,4,5-(alkylthio)-l,2-dithiolium and TCNQ were also fabricated [70,71]. The binary mixed LB films were investigated for amphiphilic donors, TTF and BEDT-TTF derivatives, amphiphilic acceptors, TCNQ, and anthraquinodimethane derivatives [72]. There is an LB film based on a charge-transfer complex with... 

The LB films of TTF [73,74] and BEDT-TTF [75-81] derivatives were investigated and secondary treatments, such as iodine or ICI doping, rendered the films conductive. The structure of the LB film of C18TET-TTF doped with iodine is investigated by UV/visible and IR spectroscopies [76— 79]. The initial stage of the chemical reaction involves formation of the cation radical of the donor, which is converted spontaneously into a dimeric form. At this step the film is insulating. Gradual evaporation of I2 from the film takes place afterward and the conductivity of the film reaches a maximum of about 0.1 S/cm. (See the footnote in Section II.A. 1.)... 

Propagation of the polymerization is seen by a change in color of the LB film from the semitransparent white of the precursor LB film to the blackish green or reddish brown of the conductive film. Several other methods were demonstrated to obtain conductive polypyrrole LB films [86,87]. The conductive LB films of polyaniline [85,87] and poly thiophene [85,88—93] were also reported. For the latter LB films, a maximum conductivity of 5 S/cm was obtained by NOPF6 doping [91]. 

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