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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.

Langmuir-Blodgett films of mesomorphic side-chain poly(methacrylates) are investigated from the point of view of their phase change versus temperature via X-ray and neutron reflectivity together with atomic force microscopy measurements. Upon heating, «thick» films undergo an irreversible transition toward the wellknown smectic Ar lamellar phase. In contrast, a bilayer deposited onto a solid substrate appears to be very stable upon annealing. Such a behavior is believed to induce an epitaxial mechanism when cooling «thick» films from the isotropic melt phase

Langmuir-Blodgett films of mesomorphic side-chain polymethacrylates are investigated from the point of view of their phase change versus temperature via X-ray and neutron reflectivity. Upon heating, “thick” films undergo an irreversible transition towards the well known smectic Al lamellar phase. In contrast a bilayer deposited onto a solid substrate appears to be very stable upon annealing. Such a behaviour is believed to induce an epitaxial mechanism when cooling “thick” Rims from the isotropic melt phase.

The “in-plane anisotropy” of a triphenylene derivative in Langmuir-Blodgett (L.B.) films has been investigated. Upon heating, L.B. films exhibit a reversible phase transition appearing as an abrupt increase from a low to a high “in-plane anisotropy” corresponding to the formation of the same hexagonal liquid crystal phase observed in the bulk material at almost the same temperature, with the columnar axis aligned along the dipping direction.

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.

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.

This work presents two new amphiphilic molecules derived from the tetrathiafulvalene (TTF) cycle. The purpose of this work is to realize a controlled in-plane molecular architecture. In order to obtain well organized macrocycles at the air-water interface we have added to the TTF cycle four long alkyl chains, each with an acid (or ester) group. Compound I has been designed to form a regular paving in the polar plane whereas for compound II an identical arrangement in the hydrophobic plane is predicted. The synthesis and thermodynamic stability of the monolayers are investigated for both molecules. The results show that these macrocycles are lying flat on the water surface: this is the first step in two-dimensional molecular engineering.

We report recent work developed in Saclay. BEDT derivatives possessing two aliphatic chains both grafted at the same end of the electroactive nucleus have been used. Hence in the resulting films, the conjugated systems stand on edge with their long axis perpendicular to the support. After a controlled oxidation by iodine vapour, films are obtained as conducting sheets, the DC conductivity of which is close to 0.2 S cm−1 at room temperature. Such a structure is especially designed to mimic the sheet-like molecular array of classical (BEDT)2I3 highly conducting or even superconducting bulk crystals. In addition, the stoichoimetries are found to be basically the same. The DC conductivity abruptly decreases as the number of superimposed monolayers decreases and a bilayer thick film is found to be an insulator. Such a behaviour is understood in terms of superimposed conducting domains separated by more or less insulating boundaries. Basically different properties are currently obtained by the use of homodoped TCNQ containing films. The homodoping strategy consists of mixing in the same monolayer neutral amphiphilic octadecyl TCNQ (OD-TCNQ) together with the anion radical semi-amphiphilic TCNQ salts, for example octadecylsulfonium+ TCNQ−. Hybrid stacks are obtained in that way. The everage electronic charge of TCNQ (and hence the conductivity) can be accurately adjusted by properly choosing the molecular ratio of the individual components.

BEDT-TFF derivatives, labeled 1a and 1b are used to build Langmuir-Blodgett films. — In the first step, oxidation by iodine vapor leads, in both cases, to the formation of radical cation dimers: (1a·+)2 and (1b·+)2. However, the subsequent behavior of films strongly depends on the way the aliphatic substituents are grafted onto the electroactive nucleus. Built-up films of 1b go back reversibly to their initial insulating state, and those of 1a undergo a solid state reorganization leading to a permanent conducting phase. These differences are explained in terms of steric hindrance. Spectroscopic arguments are used to derive the stoichiometry of the conducting films of 1a, which is likely to be that of conducting bulk crystals of (BEDT-TFF)2I3.

A new strategy for building conducting LB films is presented. The conducting behaviour is obtained by mixing in the same layer amphiphilic and semi-amphiphilic TCNQ derivatives. The optimum conductivity (6.9*10-3 S cm-1) is obtained for hybrid stacks of TCNQ in which the average electronic charge is -0.33.

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.

International audience; Phthalocyanines substituted by paraffinic chains are known to form liquid crystals with the macrocycle stacked in columns. The Langmuir-Blodgett (LB) technique is used to prepare thin films of three types of tetrasubstituted phthalocyanines that differ by the nature of the substituent. The LB films are investigated by linear dichroism in the infrared range, which reveals a moderate in-plane anisotropy that strongly improves upon annealing a few hours at 100 C or higher. The highest in-plane anisotropy is obtained when using an aliphatic substituent (C6) linked to the macrocycle through an ester link. This substituent seems to be a good compromise between a purely aromatic one and an aliphatic-rich one (with two C8 chains), which ensures fluid Langmuir films and allows the high in-plane anisotropy after transfer. The texture of these high in-plane anisotropic films is further investigated by atomic force microscopy in tapping mode. We find that the films are lamellar and have defects one monolayer or a few monolayers deep. It is shown that the variations of the texture of the film can be explained assuming a transfer ratio slightly below 1. Investigations of the film after annealing reveal that the number and size of the defects of the layers are greatly reduced. Their shape becomes elongated, and they become aligned with the dipping direction

Since the discovery, in 1984, of a strategy leading to conducting films one or a few molecules thick[l,2], many electronic conducting Langmuir-Blodgett (LB) films have been fabricated[3–12], mainly based on tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF), di-mercapto-dithiol-thione (dmit) and their derivatives. A great deal of interest for potential applications, especially for molecular electronics, has arisen from some of their unique features: thin, Angstrom thick conducting plane; self insulation and decoupling of each conducting plane from the next one; optically quasi-transparent electrode; very well defined interelectrode spacing.

Using a phenomenological lattice-dynamical theory in the quasiharmonic approximation, we present a comprehensive study to understand the effects of pressure on the vibrational properties of Ga-In pnictides that exhibit a sphalerite crystal structure. The existing pressure-induced Raman scattering data for phonon frequencies, the ultrasonic measurements of elastic and lattice constants, are used as constraints to stringently test the reliability of our rigid-ion model. The effects of high pressure on phonon dispersion curves are shown to lead to a softening in the transverse acoustic modes. At low temperatures this provides a possible driving mechanism for the decrease in the Debye temperature and the occurrence of a negative Gr\"uneisen constant and thermal-expansion coefficient in semiconductors. With a few exceptions (InP, GaAs, and GaSb), our calculated values for several elemental and compound semiconductors have qualitatively satisfied the empirical linear relationship between the Gr\"uneisen parameter ${\ensuremath{\gamma}}_{\mathrm{T}\mathrm{A}(\mathit{X})}$ and the transition pressure ${\mathit{P}}_{\mathit{t}}$. Numerical results for the lattice dynamics, one-phonon and two-phonon density of states, Debye temperature, Gr\"uneisen constant, and linear thermal-expansion coefficient are all shown to be in reasonably good agreement with the existing experimental data.

Advantages of the Langmuir-Blodgett (LB) method in building conducting films are pointed out, together with the main results obtained in this field by the use of charge-transfer (CT) systems.

International audience; 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.

Preliminary resonance Raman spectroscopy experiments on Langmuir-Blodgett (LB) films made of a small number of porphyrin layers are reported. It is shown that the angular molecular distributions inside LB films can be obtained from these data.

Recently, Ruaudel and al. 1 demonstrated that reasonably low resistivity organic conductors could be obtained after an “in situ” chemical reaction in a Langmuir-Blodgett film. In the present paper, we summerize the results and point out some questions arising from this work.

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...

We describe the properties of pristine and iodine-doped Langmuir-Blodgett films built up from a new semi-amphiphilic tetracyanoquinodimethane (TCNQ) salt, namely trimethyloctadecylphosphonium TCNQ. The films are transferred from a water subphase to a solid substrate. After exposure to diluted iodine vapour, the films become conducting. This behaviour is checked by the IR absorption spectrum. The conductivity estimated from the energy of the maximum of the charge transfer absorption band is about 20–50 Ω-1 cm-1.

A new method for building up conducting Langmuir-Blodgett (LB) films is described. The film is initially formed and compressed on a glycerol subphase from a semi-amphiphilic mixed-valence conducting tetracyanoquinodimethane (TCNQ) salt, namely octadecylpyridinium+ ∮(TCNQ1,45)−. We show that the conducting properties are retained on this subphase for surface pressures up to 18 mN m−1, which corresponds to the elasticity limit of the film. The film is then shifted onto a water subphase, contained in a dipping compartment, which has been previously incorporated in the main Langmuir trough, the water level being set identical to that of the glycerol. The shift onto the water allows the transfer onto a solid substrate with the classical dipping-withdrawing method. The propertie films are investigated by analysing their UV-visible and IR spectra and their linear dichroism. The IR and UV-visible spectra are reminiscent of those of mixed-valence TCNQ complexes with only a poor conductivity. This behaviour is verified bya d.c. conductivity measurement at room temperature, which provides a stable value of 10−4μ−1 cm−1. Furthermore, the high degree of order in the film is evidenced by its strong dichroic behaviour. It turns out that TCNQ molecules stand edge on with their molecular planes roughly perpendicular to the plane of the substrate and their long axis close to being perpendicular to it. In addition, the influence of the subphase in the fibrication of LB conducting films is pointed out.

A theoretical study of impurity modes in mixed cuprous halides ($\mathrm{Cu}{A}_{1\ensuremath{-}x}{B}_{x}$ with $A,B=\mathrm{C}\mathrm{l},\phantom{\rule{0ex}{0ex}}\mathrm{B}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{I}$) in the low-concentration limit ($x\ensuremath{\ll}1$) is reported using the Green's-function technique. The perturbation caused by the halogen impurity $B$ on the phonon spectra of $\mathrm{Cu}A$ is accounted for in terms of mass change at the impurity site as well as the change in the nearest-neighbor impurity-lattice interaction. The involved lattice Green's functions have been computed by incorporating the phonons generated by an 11-parameter rigid-ion-model fit to the recent neutron data. We find that different substitutional impurities in cuprous halides may give rise to well defined symmetry vibrations both in and outside the band-mode region. The possibility is pointed out for some of the important cases to be observed by (ir or Raman) experimental techniques. In the cases of known experimental data, we have determined the force perturbation describing the impurity-host bonding in terms of our one-parameter model. The calculated force-constant changes, in particular for $\mathrm{Cu}Cl:\mathrm{Br}$ and $\mathrm{Cu}Cl:\mathrm{I}$ systems, are similar to some extent to the behavior noticed in alkali halides rather than in II-VI and III-V compounds. In view of the insufficient experimental data, the possibility of the size effect cannot be ruled out. However, more experimental data on isoelectronic substituents in cuprous halides are very much needed to arrive at a general conclusion regarding the trend of force-constant change with the size of the impurity atom.

Scanning electron microscopy (SEM) performed on ultrathin in-plane conducting Langmuir-Blodgett (LB) films with a transverse electric field applied across the sample (voltage-induced contrast) shows electrically active defects selectively. Scratches or cracks which cut off conduction can be sorted out from others which do not, whereas standard SEM or optical microscopy does not distinguish between the two sorts of defects. Grain boundaries in LB conducting films of several semiamphiphilic compounds of tetracyanoquinodimethane (TCNQ) were easily observed, but were completely invisible by other methods. Grain boundaries are shown to be more resistive than the insides of grains, but the situation is shown to be less drastic than in thin films of conventional molecular conductors, owing to the alignment in molecular conducting planes in LB films.

Infrared absorption measurements of localized vibrational modes (LVM) due to Al in ZnSe performed under high‐resolution conditions reveal additional features as compared to previous data. The cluster of bands near 340 cm− 1 is resolved into at least six and possibly eight individual absorptions. A Green’s function calculation over various pertinent models best explains most of these LVM as probably arising from a (2 AlZn‐ZnSe) antisite complex (or at least an AlZn pair) with other complexes less likely. The linewidth of individual features can be explained in terms of nearest‐neighbor Se host lattice isotopes. Finally, features perturbed from the isolated AlZn case are considered as well as the remaining LVM of unknown origin.

We report progress in the field of characterization of Langmuir-Blodgett films. Special attention is paid to intermolecular distance determination, film texture and visualization of defects, surface investigation and orientational order of molecules. Some aspects of the characterization of conducting films are also presented.

Resume Un modele d'ions rigides a 11 parametres comprenant les interactions generales entre premiers voisins, seconds voisins et les forces de Coulomb, est utilise pour expliquer a la fois les resultats experimentaux de diffusion de neutrons et les resultats d'absorption IR dans InP. Un modele mathematique qui utilise la technique des fonctions de Green est ensuite employe pour prevoir les frequences de vibration des impuretes substitutionnelles pour ce materiau dans l'approximation du defaut de masse et du defaut de constante de force entre premiers voisins. La frequence des modes localises, de gap et de bande est calculee pour diverses impuretes substitutionnelles en fonction du defaut de constante de force pris comme parametre. Le meme calcul est donne pour deux autres composes ayant egalement la structure de la blende et un grand gap de phonons: GaP et ZnS. Une comparaison est donnee avec les resultats experimentaux disponibles.

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.

An absorption spectrum with a resolved fine structure starting at 130 meV is measured on p -type CdTe. With the help of photoluminescence data, this spectrum is associated to a complex acceptor involving at least one group III donor and one cadmium vacancy.

Raman spectroscopy is an attractive method for the characterization of Langmuir-Blodgett (LB) films which has been shown to be workable. This communication reports on theoretical calculations as well as experimental studies developed with the aim of determining the orientations of the macrocycles of porphyrins in LB films. An experimental method, together with the procedure for the analysis of the results, is proposed through an example. After characterization of the molecule and its vibration modes from spectra of solutions we show that the porphyrin rings in the layers are oriented parallel to the film plane.

The results of reflection spectra at 300 °K in the far‐infrared region (100–400 cm−1) are reported due to low concentration of Hg atoms in the Cd‐rich CdHgTe mixed crystals. A gap mode is observed at 131 cm−1 due to isolated Hg occupying Cd in CdTe. The experimental results are analyzed theoretically using the well‐know Green’s function technique. The perturbation caused by low concentration of Cd(Hg) is described by the mass change at the impurity site as well as local variation of impurity‐host interactions. In the nearest neighbor approximation, all the involved Green’s function matrix elements have been computed numerically by incorporating the lattice phonons from an eleven parameter rigid‐ion model fitted to recent neutron data of HgTe and CdTe. We find that different substitutional defects in Hg‐Cd tellurides can give rise to well‐defined symmetry vibrations both within the gap and outside the maximum phonon frequency regions. Our calculations suggest that a gap mode of Hg substituted to Te is like...

In monolayers the planar array of highly polarizable and adjoining dye molecules is favourable to singlet energy transfer. We give some evidences of energy transfer between sensitizers and acceptors in the plane of the layers. The radius of the excitonic cross section of the acceptor is about 60 A.

An investigation is made of the lattice dynamics of low concentration of Hg atoms (x < 0.3) in Cd-rich Cd1−xHgxTe mixed system. The vibrational mode frequency for the isolated Hg replacing Cd atoms in CdTe is observed at 131 cm−1. The impurity is described by a perturbation model that accounts for the change of mass at the impurity site as well as the local variation of nearest-neighbour forces. A calculation based on the Green's function theory suggests stiffening in nearest-neighbour forces (Δf/f = +0.25) due to isolated Hg in CdTe system. On etudie la dynamique de reseau des alliages Cd1−xHgxTe du cǒte riche en cadmium (x < 0,3). La frequence du mode vibrationnel du mercure en substitution isolee sur site Cd est trouvee egale a 131 cm−1. Ce cas est discute en connexion avec la variation locale des forces introduites par la presence du defaut. Un calcul base sur une technique de fonctions de Green revele que l'introduction du mercure isole (x = 0) conduit a un net renforcement des forces entre l'impurete et ses premiers voisins (Δf/f ≈ +0,25).

A comprehensive phenomenological calculation is reported to understand the temperature- and pressure-dependent phonon properties in ZnS, ZnSe, and ZnTe. Using the pressure dependence of optical data established recently by Weinstein, we have constructed an 11-parameter rigid-ion model, which in the pressure $p\ensuremath{\rightarrow}0$ limit goes over to the fitting of neutron scattering results of phonon dispersions. Model calculations for the lattice dynamics, frequency spectrum, mode gammas, Gr\"uneisen constant, and the linear thermal-expansion coefficient are shown to be in good agreement with the experiments. The present results not only compare well with the low-temperature experimental data, but also predict accurately the temperature region for which the Gr\"uneisen constant [$\overline{\ensuremath{\gamma}}(T)$] and the linear thermal-expansion coefficient [$\ensuremath{\alpha}(T)$] will be negative. We believe that the variation of ${\ensuremath{\alpha}}_{min}$ and ${\ensuremath{\gamma}}_{\mathrm{TO}}$ is not simply related to the ionicity but also to the physical fact that ionicity is affected by the bond charge and the bond length in zinc-blende-type crystals.

The infrared absorption of lithium doped CdTe shows sharp lines in the energy range 30–80 meV which are attributed to electronic transitions from the ground state to the excited states in the lithium acceptor and LO phonon assisted transitions. This excitation spectrum is analyzed using the theory of Baldereschi and Lipari what leads to a determination of the Luttinger valence band parameters.

On calcule pour la diffusion Raman les activites observables pour un systeme oriente uniaxialement, dans des conditions geometriques generales jamais examinees jusqu'ici. Le tenseur de polarisabilite Raman est arbitraire, la direction de l'axe directeur par rapport a un repere lie a l'echantillon est egalement arbitraire et le faisceau d'excitation arrive sur l'echantillon avec une incidence quelconque. Les resultats trouves mettent en evidence des symetries fondamentales ou les parametres d'ordre sont simplement multiplies par d'autres polynomes de Legendre Pk dont l'argument reflete les conditions geometriques. Certaines situations particulieres sont discutees.

From the recent information on the neutron scattering data of phonon dispersions, we have established an eleven parameter rigid‐ion model to understand the vibrational properties of both perfect and imperfect HgSe. Model calculations for the lattice dynamics, frequency spectrum, and the temperature dependence of the specific heat are shown to be in very good agreement with the recent experimental measurements. Our Green’s function calculations suggests that the possibility of a gap mode (due to Hg in HgSe) for the observed anomalous structure in infrared reflectivity experiments near ∼110 cm−1 cannot be completely ruled out. More optical (infrared and Raman) experiments regarding the influence of uniaxial compression are very much needed to help at least in assigning the symmetry of the defect center involved in the observed behavior.

We have obtained very stable Langmuir films from a (1:1) mixture of a tetrathiafulvalene (TTF) derivative (ethylenedithiodioctadecylthio TTF) with ω-tricosenoic acid, compressed on a pure water subphase at surface pressures up to about 35 mN/m. These films can be transferred by the classical Langmuir-Blodgett method with a constant transfer efficiency close to unity, and films more than 100 layers thick can be built up in this way. After exposure to iodine vapor and subsequent moderate heating at about 40°C, these films become conducting, and their in-plane direct current conductivity reaches a value of about 2 × 10−1 Ω −1 · cm−1 at room temperature. A preliminary interpretation of this behavior is proposed and strong arguments are brought out in favor of an electronic conduction mechanism arising from a mixed valence state in the TTF derivative array.

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

Green's-function theory has been reported for studying the vibrations of impurity complexes with a maximum of three defect centers in zinc-blende-type crystals. By incorporating appropriate perturbation models and lattice phonons from an eleven-parameter rigid-ion model we have made numerical calculations for the localized vibrational modes of almost all the existing cases of pair defects with ${C}_{s}$ and ${C}_{3v}$ pointgroup symmetries. The results of force perturbation for isolated charged defects have assisted us to reasonably fit the various optical experiments and tentatively assign the movements of "donor-acceptor," "acceptor-donor," "donor-host-acceptor," and "donor-host-vacancy" complexes. The force perturbation correlation with bond ionicity noticed for isolated donor or acceptor impurities has also proved to be an important factor for studying the pair vibrations in elemental and compound semiconductors.

Green's function calculations of force variation due to charged impurities in elemental and compound semiconductors are analysed on the basis of simple physical arguments. It is strongly suggested that the trends of force variation may not be related with the long range Coulomb interactions, however, the important criteria should be the effect of electric field of charged impurity on its nearest neighbour bonds that mainly affects the short range couplings. Some new experimental results by i.r. method due to Si and Cl impurities in CdTe are also included that lend additional justification to the arguments. Rechnungen mittels Greenscher Funktion fur die Kraftanderung infolge geladener Storstellen in Element- und Verbindungshalbleitern werden auf der Grundlage von einfachen physikalischen Argumenten analysiert. Es wird angenommen, das die Trends der Kraftanderungen nicht mit langreichweitigen Coulombwechselwirkungen verknupft zu sein brauchen, das jedoch das wesentliche Kriterium der Einflus des elektrischen Feldes der geladenen Storstelle auf die Bindung seiner nachsten Nachbarn sein sollte, der hauptsachlich die kurzreichweitige Kopplung beeinflust. Einige neue experimentelle Ergebnisse durch IR-Methoden von Si- und Cl-Storstellen in CdTe werden ebenfalls angegeben, die eine zusatzliche Rechtfertigung fur die Argumente liefern.

The Langmuir-Blodgett technique enables the production of ultrathin organic films. These layers are known for their high quality and well-organized structure. However, defects are present in them. In the present paper a review is given of the different types of defects together with their electrical characterization and their visualization by optical or electron microscopy. Several examples of decoration techniques and the importance of the defects for various applications are also presented.

A Green's-function technique and a rigid-ion model including general forces between nearest neighbors, next-nearest neighbors, and Coulomb forces were used to calculate the frequency of vibrational modes against the relative variation of forces between nearest neighbors $\frac{\ensuremath{\Delta}f}{f}$ for some isolated atomic substitutions in nine compounds possessing the zinc-blende structure: GaP, GaAs, GaSb, InSb, InAs, ZnSe, ZnTe, ZnS, CdTe. By comparison of these results with existing experimental data it was possible to determine $\frac{\ensuremath{\Delta}f}{f}$ for each particular case. For isoelectronic substitutions this quantity can be far from zero and reaches -53% in the case of B on Ga in GaP, still higher values being obtained for nonisoelectronic substitutions (for example, -87% for beryllium substituted on gallium in GaP). These values are found to depend largely on the force model adopted for the perfect crystal and especially on the way in which the forces between next-nearest neighbors are taken into account. No general correlation was observed between the size of the impurity compared with the atom it replaces and the $\frac{\ensuremath{\Delta}f}{f}$ values, which however are clearly related to the donor or acceptor situation of this impurity: for GaAs, where a term of comparison exists, our results agree quite well with those given by a recent model accounting for local charge and polarizability changes consistent with this situation.

Composite layers of behenic acid and tetraphenyl porphyrins made amphiphilic by aliphatic chain grafting were transferred onto solid substrates by the Langmuir method. The orientation of the macrocycles was studied by three independent methods: UV-visible linear dichroism, infrared linear dichroism, and electron spin resonance with paramagnetic markers. The first part of this paper is devoted to the theory relating to each of those methods, with the conditions of validity of formulas. The second part of the paper exposes the experimental results obtained not only by these three methods, but also by specific molecular area measurements and by observations on film crystallinity and stiffness. Results are discussed. All the observations converge to show that the macrocycles are excluded from the behenic film and that they organize aside this film according to order-generating ring-ring, and disorder-generating porphyrin chains-behenic chains, interactions.

For industrial work, an automatic, fast and above all continuous method of film production is needed. This can be achieved with a new generation of troughts, the operation of which is based on the following property; a rotating roller partially immersed in water transfers molecules from one side of the roller to the other. The trough is therefore divided into compartments separated by rotating rollers (patent). In the first compartment the film is continuously spread from the solution and the solvent is allowed to evaporate; a first “hydrophilic” roller provides a pressure of a few dynes per centimetre in the second compartment which supplies molecules to a “hydrophobic” roller feeding the last compartment (where the film is used). The servomechanisms and feedbacks necessary for operating all these cascaded stages are described. The trough is fully automatic and permits the covering of discrete classical samples as well as that of continuous strips such as those used in capacitors. The film fabrication is 10 times faster than with classical Langmuir troughs.