André Barraud

Langmuir-Blodgett films of pure porphyrins

Abstract Pure Langmuir-Blodgett films of porphyrins are described. The molecular structure was designed to fulfil the monolayer requirements and the syntheses are described for two porphyrins where the macrocycle is rendered more hydrophilic and this new hydrophilicity is counterbalanced by four aliphatic chains: I, tetra-3- eicosylpyridiniumporphyrin bromide; II, tetra-3- or 4-oxy(2-docosanoic acid) phenylporphyrin. The physical properties of monomolecular layers of pure I, (Zn)I and II on ultrapure water were studied and the pressure-area isotherms are given. The collapse pressures exceed 40 dyn cm−. Visible and IR spectra were recorded in

Polymerized monomolecular layers: A new class of ultrathin resins for microlithography

The potential of photoresists based on monomolecular layers is described. In these organic solid films, polymerization is controlled by the lattice imposed by aliphatic chains, and the low dispersivity of the polymer obtained gives these resists a high contrast (γ = 1.5). Furthermore, owing to this polymerization control and to a suitable design of the molecules, the sensitivity and contrast of these resists can be varied independently. The ultrathin (30–1000 A) films of uniform and controllable thickness obtained by this technique make these resists very suitable for low energy electron beam microlithography. Very high resolutions can be achieved by using these films without the need for high contrast; e.g. a 600 A resolution was obtained on a thick substrate using a monomolecular resist with γ = 0.7.

Solid-state electron-induced polymerization of ω-tricosenoic acid multilayers

Abstract The solid-state, electron-induced two-dimensional polymerization of ω-tricosenoic acid and calcium-ω-tricosenoate multilayers is studied by infrared metallic reflective spectroscopy. The monolayer organization of these ultrathin films (450 A) is maintained during polymerization, although a molecular reorientation occurs. A study of the different factors influencing polymerization (temperature, dose rate, scavengers) yields a number of arguments in favor of an ionic propagation mechanism. The structure combination possibilities offered by monomolecular layers are used to study the effect of molecular environment on polymerization. Finally, the monomer and polymer solubilities are studied. High-quality ultrathin polymerized films are obtained as a result of this work.

Polymerization in Langmuir-Blodgett films and resist applications

Abstract This article is a survey of the main results obtained in microlithography with Langmuir-Blodgett (LB) films as photoresists. Two classes of molecules are reviewed: ω-double-bonded molecules and diynes. In the case of ω-double-bonded molecules, the mechanism giving rise to high contrast with ω-tricosenoic acid is discussed briefly, and typical results are given. The performances of this linear polymer are compared with those of cross-linked molecules, and the reasons for the failure of the latter are given. In the case of diynes, the problem does not lie in polymerization but rather in film homogeneity: rearrangements on transfer often cause local accumulation and depletion of matter which severely degrade resolution and permeability to plasma. From those results, criteria for the choice of a molecule are specified, in respect of film quality, sensitivity, contrast and cross-linking. The field of LB resists is progressing rapidly, but other associated tools such as low voltage electron guns and submicron registration are still needed for very high resolution lithography.

Structural properties of Langmuir–Blodgett films of charge transfer salts: Pristine and iodine doped conducting films of (N‐docosyl‐pyridinium)TCNQ

We have investigated the molecular constitution and ordering of Langmuir–Blodgett films prepared by deposition of N‐docosylpyridinium–TCNQ charge transfer salt onto CaF2 substrates and by their subsequent doping with iodine vapor to yield reasonably good (∼10−1 Ω−1 cm−1) conducting films. Optical and electron scanning microscopy of the precursor film show that it is made up of a mosaic of highly crystalline platelets lying flat on the substrate though with random orientation. Structural information at the molecular level is gained by measuring and analyzing the ESR spectra and their angular and temperature dependence as well as the UV‐visible and infrared spectra and their linear dichroism. A triplet fine structure is observed in the ESR spectra of the precursor films with zero field splitting parameters ‖D‖=7.48×10−3 cm−1 and ‖E‖=1.2×10−3 cm−1 and singlet–triplet activation energy J=0.20 eV, markedly different from those of the N‐docosylpyridinium–TCNQ powder salt. The UV‐visible and infrared spectra sho...

Insertion Compounds in L.B. Films

Abstract Solid state chemical reactivity in L. P. films is used to insert inorganic or organic species in a layered organic matrix giving rise to organized insertion compounds with novel physico-chemical properties.

A new family of Langmuir–Blodgett films of tetracyanoquinodimethane charge transfer salts: Pristine and iodine doped conducting films

A new family of semiamphiphilic tetracyanoquinodimethane (TCNQ) ionic salts of nonconjugated cations, namely octadecyl‐dimethylsulfonium, octadecyl‐methyl‐ethyl‐sulfonium, and octadecyl‐trimethylphosphonium labeled a, b, and c, respectively, has been synthetized. Langmuir–Blodgett (LB) films are built up from these three compounds, which are mixed with octadecylurea in a molar ratio 1/1, in order to improve the stability of the film at the water surface. The structural properties of the transferred films are thoroughly investigated by linear dichroism in the IR and UV–visible ranges, together with ESR spectroscopy. In the films of the three compounds, the polar sheets contain (TCNQ− • )2 dimers, which are the largely prevalent species. The molecular planes of these dimers are found to be roughly parallel to the substrate. Moreover, a strong in‐plane orientation of the dimers is found in films of compound c. This phenomenon is thought to be related to an overall flow orientation of rod‐shaped crystallites ...

An automatic trough to make alternate layers

Abstract The Langmuir trough described is specially designed to fabricate alternate multilayers automatically by the Langmuir-Blodgett (LB) technique. Its working principle consists of: (i) making two different films at the surface of a double Langmuir trough; (ii) programming the path of the substrate so that it passes in turn through each film. The apparatus consists principally of a two-compartment Langmuir trough and a system to transfer the substrate from one compartment to the other underneath water. The Langmuir trough contains a single subphase. Its surface is divided into two compartments by a fixed surface barrier located above the central well. Each compartment is equipped with a mobile barrier, so that it can be operated independently for film fabrication and compression. Each compartment is also equipped with an independently programmable dipping arm. Substrate transfer is carried out in the following way: while the two dipping arms are at rest, an auxiliary rotating arm picks up the substrate from one of the arms, transfers it to the other compartment underneath the central barrier and hangs it on the other dipping arm. This sample transferrer is described in detail, together with the way it operates. When the films in the compartments are made of different molecules, this trough builds up alternate LB layers. According to the programme imposed on the substrate transferrer, either centrosymmetric, or non-centrosymmetric, or paired alternate layers can be built. Examples of such alternate layers are given. Their actual structure is discussed: in some cases the films are found to reorganize on or after transfer.

Spin transition in a magnetic Langmuir-Blodgett film☆

Thermal equilibria between electron spin states of different multiplicities are studied in magnetic Langmuir-Blodgett (LB) films of amphiphilic FeII(phen)2 (NCS)2. Three aliphatic chains 18 carbon atoms long are grafted on the phenanthroline moiety and good LB films are obtained on CaF2 and quartz substrates. A temperature-induced spin transition is observed between liquid nitrogen and room temperatures. This transition is characterized in the IR spectral absorption by a 40 cm-1 frequency up shift of the vNCS doublet when changing from high spin to low spin ground state. From these preliminary experiments it appears that the spin transition still takes place in a two-dimensional system as it does in the same non-amphilic complex in three-dimensional single crystal form, as described by Konig.

Conducting Langmuir-Blodgett films☆

Abstract For the first time, conducting Langmuir-Blodgett films with reasonably low resistivity (10–50 Ω cm) have been obtained (N-docosylpyridinium-TCNQ-iodine ternary salts). These two-dimensional polycrystalline films behave as low-resistivity organic semiconductors. The aim of this paper is to determine the intrinsic nature of these films. As far as the electrical characterization is concerned, the Hall effect can hardly be used because of the very high internal resistance of the films. Furthermore, because of the polycrystalline structure, d.c. resistivity measurements are questionable. Optical measurements are especially suitable for an electrodeless evaluation of the resistivity; the IR optical band, located near 3 μm is discussed. More classical methods, including linear IR, dichroism and ESR measurements, are also presented and discussed.