Conducting LB Films Research Articles

The homodoping strategy towards Langmuir-Blodgett conducting films: mixture of amphiphilic octadecyl-tetracyanoquinodimethane with various semi-amphiphilic tetracyanoquinodimethane salts

The homodoping strategy, which consists of mixing within the same layer two derivatives of the same electroactive nucleus (TCNQ here), the first one being neutral and amphiphilic, the second one being charged and semi-amphiphilic, is used to build up conducting LB films. The results obtained when varying the cation of the semi-amphiphilic compound are reported, and some general features of these films are presented.

Electronic transport in Langmuir-Blodgett films of metal-(dmit) 2

Thermoelectric power in highly conductive Langmuir-Blodgett films of tridecylmethylammonium-Au(dmit) 2 ( σ RT 30−50 S cm ) was examined. The metallic nature of this material is suggested from the results of the thermoelectric power. The resistivity increased with aging, however the thermoelectric power was invariant. These results suggest that the metallic nature of the film is preserved after aging. The newly developed conductive LB films of didecyldimethylammonium-Pd(dmit) 2 showed a high conductivity of 5.1 S cm at room temperature. From the temperature dependence of the conductivity, semiconductor-like transport was suggested.

Conducting Langmuir-Blodgett films of new tetrathiafulvalene derivatives

Conducting LB films of hexadecylethylenedithiopropylenedithiotetrathiafulvalene and hexadecylethylenedithiooxapropylenedithiotetrathiafulvalene are obtained. The properties of monolayers at the air-water interface and multilayers on the solid substrates are compared with those of hexadecylbis(ethylenedithio)tetrathiafulvalene. The influence of surfactant acceptor additions into the donor matrix on the film quality is studied. The dependences of conductance on the dose of irradiation by electrons are measured. The patterns consisting of insulating lines are drawn in the conducting films with an electron beam.

Evaluation of conducting LB films based on ethylenedithio-tetrathiafulvalene (EDT-TTF) derivatives for phosphine sensing

We report the preliminary results obtained with new conducting LB films based on EDT-TTF derivatives used as sensing heads in conductivity phosphine sensors. This second generation of conducting materials for gas sensors derived from the phosphine sensing properties of the previous heads based on TCNQ derivatives: like TCNQ derivative films, EDT-TTF derivative films exhibit a stable and well-controlled conducting behaviour after iodine vapour exposure and large conductivity variations under phosphine exposure. The mean features of the new sensing head are a short response time (30 s) and a ppm range sensitivity, which is achieved without the need of cycling at high concentrations of gas.

Conducting LB films based on metal complexes of sulphur donor ligands

AbstractPreliminary studies are reported on the film forming characteristics of compounds such as dialkyldimethylammonium‐M (dmit)2 and dialkyldimethylammonium‐M (mnt)2 where M = Ni, Pt or Pd. All materials investigated show good monolayer behaviour and deposit readily onto evaporated aluminium or gold films. This is confirmed by surface potential and FTIR measurements. The lateral conductivity of deposited films increases by many orders of magnitude when exposed to bromine vapour.

The influence of structure change on electrical properties of conducting LB films produced from hexadecyl‐TCNQ and heptadecyldimethyl‐TTF mixture

AbstractConducting Langmuir‐Blodgett films of hexadecyl‐TCNQ and heptadecyl dimethyl‐TTF mixture in the ratios from 1:1 to 1:2.5 are studied. Temperature dependence of film conductivity possesses some specific features. Strong increase of conductivity and decrease of activation energy take place after annealing at 307–315 K. On the other hand, the film loses conductance after heating above 315 K. To explain this behaviour the investigations of conducting multilayers by means of electron diffraction, electron microscopy, and X‐ray small‐angle scattering were carried out. Some relations between changes of electrical properties and structural transformations are ascertained.

“Homodoping” strategy for building conducting Langmuir‐Blodgett films

AbstractA strategy leading to the formation of conducting LB films without any doping treatment is investigated. The method consists of mixing, within the same layer, semi‐amphiphilic and amphiphilic derivatives of the same electroactive nucleus (here Tetracyanoquinodimethane (TCNQ)). LB films obtained in this way with the sulphonium TCNQ salt as the semi‐amphiphilic molecule and the octadecyl TCNQ as the amphiphilic one in the molecular ratio 1 to 2, are of high optical quality. Such films show a d.c. conductivity which is almost constant with variation in the number of layers, down to one bilayer. Preliminary results obtained by changing the nature of the counterion in the semi‐amphiphilic molecule are in good agreement with those of the sulphonium TCNQ‐octadecyl TCNQ0.

ESR and ENDOR Studies of Functional LB Films

Abstract Role of ESR and ENDOR spectroscopies in the characterization of functional LB films is discussed. Two illustrative examples are shown. In the first case, the detailed study of in-plane molecular orientation is discussed from the analysis of the ESR and ENDOR spectra of the stable radicals detected in LB films of a merocyanine dye. By identifying a nitrogen hyperfine structure, computer simulation of the ESR spectra yields a characteristic orientation of radicals with respect to the dipping direction of the substrate. The results strongly suggest a flow orientation of J-aggregates from which radicals may originate. The observed orientation is well described by the recent theory of flow orientation. In the second case, study of the temperature dependence of ESR signal, in particular the spin susceptibility, is shown to provide the microscopic evidence for the development of columnar structures in conducting LB films composed of amphiphilic charge-transfer complexes.

General Trends for Obtaining Conducting TCNQ Langmuir-Blodgett Films

Abstract Some structure-property relationships for conducting LB films based on semiamphiphilic TCNQ salts with closed shell cations are worked out. Formation of a 3-D ordered structure containing (TCNQ−)2 dimers on the water subphase followed by a remarkable structural rearrangement of deposited films upon iodination is found to be a necessary requirement for conductivity. Among the studied salts, these processes occur only for those with similar cations.

ESR study on LB films of TMTTF-octadecylTCNQ

An ESR investigation has been made on the first intrinsically conducting LB films consisting of the charge transfer complex, TMTTF-octadecylTCNQ. The occurrence of a single line without structures and observed g value indicate that there is a strong coupling between TMTTF radical spins and TCNQ radical spins as in the TTF-TCNQ crystal. The temperature dependence of the spin susceptibility of the system implies the presence of spin species due to conduction electrons, which is consistent with the conductivity measurements.

Novel Conducting LB Films

A layered anisotropic conducting structure is described. The LB technique is used for an amphiphilic TCNQ salt.