Semiconducting Langmuir-Blodgett films of Phthalocyanine analogues 1 and 2 have been prepared. These compounds orient vertically on the Langmuir and Langmuir-Blodgett layers. Six layer LB films show a conductivity around 10−4 Ω−1 cm−1. Resistance temperature dependence experiments have been performed. The resistance behaviour of the samples is rational with a semiconductor.

This paper presents a new method for the calculation of the tunnel current through a metal/multilayer of conjugated molecules/metal sandwich structure under low and moderate electric field. The electron transfer from one electrode to the other through the cascaded molecules is treated step by step by considering hopping integrals between neighbouring molecules. A rather simple computer calculation gives access to the tunnel current. This method has been applied to a practical system : Langmuir-Blodgett films made of a two-dimensional porphyrin polymer. The LUMO level in tetrapyridinoporphyrin bromide, which is the monomeric unit of the polymer, has been calculated and found to lie 2.8 eV below the vacuum level. From this value, and literature values for the other parameters, the tunnel current densities vs. voltage have been calculated for various film thickness (2 to 5 monomolecular layers). The tetrapyridinoporphyrin polymeric Langmuir-Blodgett film is suggested to check the model experimentally.

This document deals with the terminology in relation to the preparation and characterization of liquid and solid thin films and layers, It is not comprehensive, in that no consideration is given to certain types of layers such as ferromagnetic, ferroelectric, He or liquid metal films, Topics covered include: general terminology and characterization methods applicable to both solid and liquid films; terminology and characterization methods applicable specifically to either liquid or solid films, layers and multilayers. Comprehensive indexes of terms and methodologies (preparation and characterization) are given.

This paper presents the detection performances of low-conducting Langmuir-Blodgett (LB) films, based on tetracyanoquinodimethane (TCNQ) and tetrathiofulvalene (TTF) derivatives, towards nitrogen dioxide (NO2). TTF-based LB films appear to be more sensitive than TCNQ ones, and well adapted to the detection of low concentrations. The detection mechanism is clearly established for TCNQ LB films, but is still unclear for LB films based on TTF.

This paper presents the results of X-ray photoelectron spectroscopy and secondary ion mass spectrometry experiments performed to obtain information about the sensing mechanism involved in the detection of phosphine by conducting Langmuir-Blodgett (LB) films based on TCNQ and EDT-TTF derivatives. In contrast to the EDT-TTF based LB films, it is shown that with the TCNQ derivative the action of phosphine (PH3) results in the insertion of phosphine subproducts in the LB film. This information is correlated with the general behaviour of each film towards phosphine detection.

The static SIMS studies of two different phosphine gas sensors based on ODP-TCNQ (N-octadecylpyridinium-tetra-cyanoquinodimethane) and EDTCS18)2 (Bis(-octadecylthio) ethylenedithiotetrathiofulvalene) conducting Langmuir-Blodgett films are presented. This characterization method is well adapted to precise the detection mechanisms of phosphine. In the case of ODP-TCNQ sensor the presence of phosphate ions shows that phosphine interacts with water molecules embedded in the film. For EDT(SC18)2 sensors, phosphine destroys the I−3 chain responsible for the conductivity.

Field effect transistors have been made, the channels of which consist of conducting, iodine-doped Langmuir-Blodgett (LB) films. In the chosen configuration, the modulation effect is shown to arise mostly from the source-channel contact, which behaves as a reverse-biased Schottky diode. The gate voltage modulates the height of the diode barrier by controlling the surface charge density of the oxide-LB film interface states. This model explains qualitatively and quantitatively the behaviour of the transistor and gives rise to remarkably good fits with the experimental transistor characteristics. The model is also supported by a counterexperiment in which the source and drain contacts are ohmic, as expected this leads to almost no drain current modulation.

Experimental IR properties of conducting (ODS-TCNQ)0,33(TCNQC18)0,66.LB films are presented and discussed within the frame of the electron-vibration coupling model of Rice, extended to take into account the modifications induced by grafting an alkyl chain to TCNQ molecule. Quite good theoretical fit of experimental spectra (including unusual fine structure of agν5 vibronic band) indicates that, inside the layer, an energy transfer takes place between the electroactive part and the alkyl chain via a two step coupling process.

X-ray photoelectron spectroscopy (XPS) is used to characterize copper sulphides inserted into Langmuir-Blodgett (LB) films of behenic acid. Comparisons are made between samples exhibiting very different electrical conductivity but synthesized by the same method. Sulphur atoms with two different environments are found: divalent sulphur S2- and dimer sulphur (S2)2-, higher concentrations of dimer sulphur (S2)2- being present in insulating samples. Chemical bonding of copper in LB films is compared with CuS and Cu2S powders. The copper to sulphur ratio and the divalent to dimer sulphur ratio are obtained from various samples and lead to the formula: Cu2S, xS2 with x ranging from 0.5 to 0.8.

The present paper deals with the use of semi-insulating and conducting LB films as conductimetric sensors. The response of such sensors consists in conductivity changes induced by gas exposure. Examples collected in the literature are presented and show that the LB technique is very convenient for making continuous ultrathin organic materials exhibiting detection properties towards toxic gases (NO2, PH3,…). Very interesting results have been obtained using mixed LB films even if the conducting properties of the resulting material and the detection mechanism are not well understood. Some multifunctional materials are required exhibiting conduction properties for transduction and ‘recognition properties’ for selective detection. With that goal, the LB technique associated with organic chemistry provides undeniable advantages.

Experimental IR properties of conducting (ODS-TCNQ)ξ(TCNQC18)1−ξ Langmuir–Blodgett (LB) films are presented and discussed within the frame of the electron-vibration coupling model of Rice, extended to take into account the modifications induced by grafting an alkyl chain to the TCNQ molecule. The quite good theoretical fit of experimental spectra (including unusual fine structure of agν5 vibronic band) indicates that (i) optical as well as electrical properties of the films can be accounted for by the existence of dimers the type of which depends on ξ; and (ii) inside the layer, an energy transfer takes place between the electroactive part and the alkyl chain via a two step coupling process.

Langmuir-Blodgett films built of a mesomorphic side chain polymethacrylate are investigated from the point of view of their phase changes against temperature. With heating, a strong 'out of plane' molecular reorganization towards a smectic phase takes place giving rise to an increase of the order parameter.

A new type of solid polymer electrolyte (SPE) PH3 electrochemical sensor is reported. The oxidation of PH3 on the SPE–Pt electrode is studied by electrochemical and XPS methods. At the same time, the linearity, the stability and response time of the sensor is investigated and discussed. The results obtained indicate the SPE-based PH3 sensor possesses a number of attractive properties.

We show by X-ray induced photoelectron spectroscopy (XPS) that the amphiphilic tetrapyridinoporphyrazinium CuS18 undergoes different redox modifications when in the amorphous phase or in LB films. In the case of the LB films, CuS18 appears in a two-electron reduced state, but the XPS spectrum is surprisingly dominated by a copper(II) signal. On the contrary, amorPhous CuS18 is spontaneously reduced on the copper atom when exposed to various X-ray irradiations. Semi-empirical calculations show that the extra electrons can be added either on the macrocycle (LB films) or on the metallic ion (amorphous phase), probably depending on a slight geometric distortion around the cupric ion within the LB films.

Conducting Langmuir-Blodgett (LB) films based on tetracyanoquinodimethane (TCNQ) and ethylenedithio-tetrathiafulvalene (EDT-TTF) appear to be very promising candidates for phosphine sensors. Gas diffusion through the LB structure is an important factor which must be controlled. The study of a molecular assembly of silver behenate underlayers (the reaction of which towards PH3 is followed by infrared spectroscopy) on top of which the conducting film is transferred shows that phosphine penetration in these conducting films limits the response time of the sensor. The two types of conducting films lead to two different sensors.

We describe optical and electrical porperties of semi-conducting copper sulfide layers inserted in the polar planes of a LB matrix. The most current resistivity values are around 103 ωcm. The samples are also photoconducting. In some cases, under vacuum, uncontrolled doping drops the resistivity down below 1 ω cm. The temperature behaviour of these samples proves the continuity of the semi-conducting film. Micrometer scale resistivity measurements show two sorts of samples: thin, continuous semi-conducting layers and insulated aggregates.

In this paper we report on the second harmonic generation properties of non-centrosymmetrical Langmuir-Blodgett films built from mixtures of push-pull carotenoids with ω-tricosenoic acid or amphiphilic cyclodextrin. The effects of the carotenoid as well as of the diluent on the orientational order have been studied both in monolayers and alternate active-passive multilayers.

Designed supermolecular assemblies can be built up by the Langmuir-Blodgett technique, through the vectorial control of chemical interactions occurring at the air/water interface between adjacent amphiphilic molecules.

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.