[Show abstract][Hide abstract] ABSTRACT: The doping-induced conductivity transitions in molecular layers of polyaniline have been studied by monitoring the correlated optical and spectroscopic changes using spectroscopic and single wavelength extinction ellipsometry, also in total internal reflection mode (TIRE), together with reflection spectrometry. The measurements were performed on deposited multilayers as well as on a Langmuir monolayer at the air-water interface, as a function of acidic doping. We found that the characteristic spectroscopic features of conducting and insulating polyaniline persisted down to the single layer, both in the solid state and at the air-water interface. We also investigated in real time the modulation of conductivity induced by the intercalation of Li ions in the polyaniline film, by a combination of time-resolved ellipsometry and reflectivity spectra measurements. In this case, the enhanced sensitivity provided by the TIRE geometry, combined with the relatively fast time scale accessible by the single wavelength ellipsometry, allowed us to follow in detail in real time the doping/dedoping process.
[Show abstract][Hide abstract] ABSTRACT: We report detailed structural investigations, by synchrotron X-ray reflectivity (XRR), grazing incidence diffraction (GID), and space-resolved grazing incidence X-ray-induced fluorescence (GIXF), on the structure of molecular layers of polyaniline (PANI) that can be converted from insulating to conducting state simply by doping. We first address the simpler, but more intriguing, system, i.e., a floating monolayer of PANI on different subphases, for which we found a typical thickness of 28(1) A, not much affected by the doping process. For the doped film we also found an internal lateral structure, with in-plane spacing of 3.5 A-albeit with a small coherence of 3-4 repeat units only-compatible with face-to-face interchain stacking of phenyl rings, in agreement with the literature. By GIXF we could confirm the crucial role of Cl(-) intercalation in the doping process of the PANI film: under doping conditions (0.1 M HCl subphase) the Cl(-) intake is 8 times larger than in nondoping conditions (0.1 M KCl subphase). Multilayers transferred onto solid substrate were studied also as a function of the applied voltage, as this system constitutes the core of an electrochemically controlled device whose strongly nonlinear characteristic make it useful for applications to adaptive networks for complex information processing. By the application of an electrostatic field of 140 V/m, Cl ionic migration was observed confined to the polymeric film surface.
[Show abstract][Hide abstract] ABSTRACT: Polymeric electrochemical elements of adaptive networks are considered. The main features of these elements are compared with
the elements of the nervous system of the snail Lymnaea stagnalis. In particular, synthetic analogues of neurons and synapses are fabricated. The capability of the system for learning is
demonstrated with a model of the simplest network composed of eight electrochemical elements. An alternative approach based
on the formation of fiber networks is proposed. This approach will make it possible to fabricate more complex systems with
a random distribution of mutual contacts between elements.
[Show abstract][Hide abstract] ABSTRACT: We present the use of Reflectance Anisotropy Spectroscopy (RAS) as a
probe to study the deposition of organics We started the study of
ordered layers deposited onto disordered substrates by Langmuir-Blodgett
(LB) and Langmuir-Schaefer (LS) techniques, nevertheless we believe that
the goal is the application of RAS to OMBE (Organic Molecular Beam
Epitaxy), to monitor the growth process in real time and in situ,
similarly to the deposition of inorganic semiconductors. After a short
introduction, we discuss an example testing the RAS sensitivity to the
structure of the growing layers: in particular, we report recent data
about the polarization dependence of the optical reflectivity for LS
PdC10OAP porphyrin layers. Deposition has been carried out at
two values of the surface pressure (Π1=30 mN/m;
Π2=10 mN/m), corresponding to different layer structures.
The RAS spectra measured in two cases are successfully explained in
terms of the particular morphological characteristics of the layer.
[Show abstract][Hide abstract] ABSTRACT: By means of microgravimetry, UV-Vis spectroscopy and optic microscopy, sorption of pyridine, primary aliphatic amines and benzylamine by the Langmuir-Blodgett (LB) films of tetra-4-tert-butyl- and tetra-(3-nitro-5-tert-butyl)-substituted cobalt phthalocyanines (CoPc' and CoPc*, respectively) was studied over a broad concentration range. In general, sorption occurs as stepwise intercalation of the sorbate molecules into the supramolecular 3D structure of the phthalocyanine assembly followed by formation of the donor-acceptor complexes. Both intercalation depth and stoichiometry of the complexes are determined by the molecular structure of amines. The supramolecular factor allows discrimination between amines in air but not in aqueous solutions because of concurrent intercalation of water.
Biosensors and Bioelectronics 01/2004; 20(6):1177-84. · 5.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of the present work is to develop a method for the patterning
of the nanocapsule arrays immobilized on solid surfaces applying
electron beam treatment to the formed layers of nanoparticles with
magnetic materials in the cavity or in the shell. The successful
patterning was demonstrated by optical microscopy, while morphology and
structure of the formed system were analyzed by atomic force
microscopy. (C) 2003 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials 01/2004; 272-276(Part 2 Sp. Iss. SI):1353-1354. · 1.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, polycyanoacrilate as ultrathin electron resist layer, testing its sensitivity and employing it as a mask for etching of metal layers were proposed.
Microprocesses and Nanotechnology Conference, 2003. Digest of Papers. 2003 International; 11/2003 · 1.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present work, monolayer engineering was used to fabricate biocatalytic nanostructured thin films based on the enzyme penicillin G acylase. The biocatalytic films with enhanced characteristics were produced by the deposition of alternate-layer assemblies with a predetermined structure using a combination of Langmuir–Blodgett and adsorption techniques. The value of enzyme activity and the level of protein detachment were measured in dependence on the variation of film composition and on the sequence of layer alternation. As a result, highly active and stable structures were found, which could be promising candidates for practical applications. The method of modification of the deposition method to provide continuous film formation on large-area supports is discussed.
[Show abstract][Hide abstract] ABSTRACT: The myelin basic protein (MBP) is the second most abundant protein in the myelin sheath of the central nervous system and is believed to be important for the compactness and integrity of the membrane. We investigated the mechanism of the interaction of lipid-free MBP with phospholipid monolayers at the air/water interface; in particular, we studied the process of MBP adsorption onto monolayers made up either of neutral dipalmitoylphosphatidylcholine (DPPC) or of negatively charged dipalmitoylphosphatidylserine (DPPS) monolayers. They are natural constituents of the myelin membrane, and sharing an identical hydrophobic chain, they differ only in headgroup, composition. The MBP-lipid interaction is investigated for the first time by means of nullellipsometric measurements, monitoring in real time the effect of adsorbed molecules in the insoluble monolayer at different monolayer conditions, such as surface pressure and molecular area. The different behavior of monolayer thickness and surface pressure confirmed the hypothesis of a different interaction mechanism of MBP with the two kind of lipids. While in the presence of neutral DPPC the protein seems to penetrate among the lipid domains, in the case of negatively charged DPPS the electrostatic interaction appears to be the driving force, because protein intimately associates with the headgroups and binds to the Langmuir layer as a specific lipid-protein complex. Results with DPPS were confirmed by FTIR spectroscopy measurements, performed after transferring phospholipid multilayers onto a solid substrate by the Langmuir-Schaefer method.
[Show abstract][Hide abstract] ABSTRACT: In this paper we summarize our recent results on the self organized motion of a photosensitive polymeric liquid crystal. We studied the quality of pristine Langmuir-Blodgett molecular layers and their photoinduced dewetting. In particular, we have found that the dewetting proceeds in very different ways depending on the initial film thickness: above a certain threshold a long range molecular flow is obtained, with mass transport over macroscopic distances. The resulting morphology comprises of a wide distribution of polymeric droplets, very polydispersed in size. On the contrary, below the threshold, the self-organized dewetting motion is quasi-local, resulting in a dense and uniform distribution of droplets of similar size. Finally, we discuss the quality of the molecular layers as a function of substrate pre-treatment, and of layercomposition when a fraction of monomers is introduced. We discuss these results- relevant for the confinement of glass formers in monodispersed nanoparticles- also in the framework of thickness dependent melting phenomena, trying to elucidate the eventual role of the polymer mesogenicity in determining the observed phenomenology.
[Show abstract][Hide abstract] ABSTRACT: We report a detailed study of photoinduced changes in the microscopic structure of monolayers, multilayers, and superlattices of a photosensitive side chain liquid crystalline polymer, deposited by the Langmuir-Schaefer technique. We probe both out-of-plane and in-plane ordering and its changes due to optical pumping of the trans-cis photoisomerization transition of the azobenzene side chain in an azopolyacrylate. Microscopic structure was studied mainly by synchrotron radiation x-ray reflectometry and grazing incidence diffraction; we also used null-ellipsometry and atomic force microscopy. Our results provide a quantitative modeling of the structural changes and corresponding relaxation times taking place as a function of confinement, temperature and optical pumping, and in particular confirm previously reported ellipsometric results on such changes as a function of sample thickness. This allows a quantitative description of the effects of reduced dimensionality on the structural transitions in this glass-forming system.
[Show abstract][Hide abstract] ABSTRACT: We have studied the optical anisotropy of Langmuir–Schaefer layers of PdC10OAP porphyrin, deposited onto gold substrates with thickness in the range 0–16 monolayers (ML). Deposition has been carried out at two values of the surface pressure Π, corresponding to different layer structures. In one case (Π=30 mN/m), molecules are well ordered in stacks oriented edge-on with respect to the substrate. In the other (Π=10 mN/m), a complex reorganization of the system happens several days after deposition, to form a mesoscopic two-dimensional lattice. The spectra measured by reflectance anisotropy spectroscopy (RAS) in two cases are clearly characterized. In the former, the line shape is dominated by a characteristic, large structure appearing in coincidence with the Soret band of the molecule, the development of which from a “peak-like” to a “derivative-like” appearance occurs at a well-defined critical thickness Θc (8 ML). In the latter, the line shape is always “peak-like”. We explain both line shapes in terms of morphological characteristics of the layer, occurring at different thickness values. The present results clearly show the potential of RAS to characterize efficiently the deposition of organic materials, and suggest that in short time it will be used as an in situ and real time spectroscopy, as already done in inorganic growth.
[Show abstract][Hide abstract] ABSTRACT: Conductive polyaniline Langmuir–Blodgett (LB) films are considered to be candidates for numerous applications. However, the quality of their deposition is usually non-satisfactory. In addition, the possibilities of many applications are restricted by the intrinsic low speed of deposition with the LB technique. We have found a solution to these problems and obtained uniform ultra thin polyaniline films using the Langmuir–Schaefer (LS) technique, which allows very fast monolayer transfer onto the substrate. A well known approach of deposition of mixed monolayers was used to obtain uniform films, but in our case the matrix compound was chosen in such a way as to provide a possibility of its selective dissolution from the deposited multilayers without the deterioration of uniformity of remaining polyaniline layer. Finally, we demonstrate an approach to polyaniline film patterning with an electron beam, which is based on the possibility to cross-link the polyaniline molecules without considerable loss of film conductivity and on further dissolution of polyaniline from non-irradiated areas.
[Show abstract][Hide abstract] ABSTRACT: We have studied the optical anisotropy of porphyrin layers with different thicknesses deposited onto gold substrates by the Langmuir-Schaefer technique. In coincidence with the Soret band of the molecule, the optical spectral line shape as determined by reflectance anisotropy spectroscopy exhibits a characteristic, large structure, which changes from a "peaklike" to a "derivative-like" shape at a well-defined thickness (8-10 monolayers). We interpret this result in the framework of electronic effects due to structural changes in the layers, yielding solid-state effects originating from the coupling of the π orbitals of the porphyrin macrocycles.
[Show abstract][Hide abstract] ABSTRACT: Polyaniline (PANI) is used for the preparation of “molecular” electrodes in heterojunctions, which include either Langmuir–Blodgett (LB) films or LB assemblies composed of thin layers of different compounds. Langmuir–Schaefer (LS) technique is applied to provide high speed of film deposition. The uniformity of polyaniline films is achieved due to the deposition of mixed polyaniline/polycyanoacrylate films with further dissolution of polycyanoacrylate fraction. The required configuration of the heterojunction is produced by irradiating polyaniline films with an electron beam through the masks and pattern development in 1-methyl-2-pyrrolidone (NMP). Current–voltage characteristics of heterojunctions are measured to demonstrate the applicability of developed approach.
Materials Science and Engineering C 01/2002; 22(2):239-244. · 2.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Langmuir–Schaefer (LS) technique is applied to deposit uniform films of poly(methacrylate) derivative with fluorocarbon groups in the side chains. The films of this compound cannot be deposited with the ordinary Langmuir–Blodgett (LB) technique while the Langmuir–Schaefer technique version used in the present study allows to achieve fast deposition at low surface pressure. The films are sensitive to an electron beam. Positive patterns can be produced in the deposited multilayers in a definite range of exposure doses. The sensitivity and the contrast are equal to 42.4 μC/cm2 and 1.2, respectively. Strong irradiation results in film cross-linking and negative pattern formation. High quality of deposition of ultrathin layers and their sensitivity to an electron beam allow the use of the studied compound for the development of nanostructured materials.
Materials Science and Engineering C 01/2002; 22(2):295-299. · 2.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Langmuir–Blodgett (LB) assemblies composed of monolayers of different compounds alternating in a predetermined sequence are potential candidates for development in the field of nanoelectronics. However, their poor mechanical stability restricts the possibility of fabrication of interconnected electronic elements because LB films can be easily destroyed during the deposition of metal electrodes. In this work, we present a technique for the fabrication of junctions for the electrical characterization of one-component LB films and LB assemblies enclosed between thin molecular electrodes. The molecular electrodes are produced using LB films of a charge-transfer salt. Such an application of these films became possible due to considerable improvements in their conductivity, quality of deposition and stability in comparison with the properties of films of similar compositions studied previously. Lateral patterning of electrodes is carried out by the irradiation of conductive films with an electron beam, which results in the loss of their conductivity. In this way, it is possible to prepare the samples for electrical investigations without any damage to incorporated LB films. The LB films of barium stearate, polycyanoacrylate, mixture of surfactant donor and acceptor, porphyrins, as well as the LB assemblies composed of thin layers of these compounds deposited in various sequences were enclosed between the molecular electrodes and studied. Probable conduction mechanisms are discussed on the basis of obtained data.
Thin Solid Films 01/2002; 405(1):276-289. · 1.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Present communication is concerned with the application of monolayer engineering, in particular of ‘protective plate’ technique, for the fabrication of alternate-layer assemblies based on enzyme penicillin G acylase. Several structures are compared with each other. The deposited films are tested to determine the values of enzymatic activity and the level of protein detachment in aqueous solutions. As the result, the deposition procedure is found, which enables to obtain biocatalytic media with enhanced performances. The biocatalyst efficiency is proved by three independent techniques including direct yield determination with HPLC. The advantage of applied method of enzyme immobilization with respect to other techniques is demonstrated.
[Show abstract][Hide abstract] ABSTRACT: We report on the modifications in morphology and microscopic structure induced by photoexcitation of homo- and heterostructures of a side chain liquid crystalline polymer, namely a polyacrylate with an azobenzene moiety in the side chain. The structures were molecular mono- and multilayers deposited with the Langmuir-Schaefer technique. The structural and morphological determinations were performed with synchrotron radiation X-ray reflectometry and Grazing Incidence Diffraction (GID). We observe extensive photoinduced effects on the nanoscale: expansion of the multilayers independently of number of layers, reduction of surface roughness, and destruction of order to yield a glasslike phase. The study of superlattices composed of alternate layers of barium behenate and our polymer indicates a general reduction of photoinduced structural effects on the polymer multilayer. Finally, we discuss these effects as a function of temperature from the range of the glass transition to the clearing point.
Molecular Crystals and Liquid Crystals. 01/2002; 375(1):689-699.
[Show abstract][Hide abstract] ABSTRACT: Macroscopic conductance was observed in Langmuir–Blodgett (LB) bilayers deposited by two versions of the Langmuir–Schaefer (LS) technique. Bilayers of several compositions on the basis of donor compounds and donor–acceptor mixtures doped in ferric chloride solutions after the deposition were studied. Relatively high conductivity for such super-thin films was obtained due to the application of specific methods of substrate surface preparation and optimized procedure of doping. The conductivity values were in the range of 0.2–1.0 S cm−1 for bilayers and 10–30 S cm−1 for the films composed of 12 monolayers. This difference can be caused by the formation of bilayers of heterogeneous X-type/Y-type structure, which is in a good agreement with the results of surface potential measurements. Bilayers deposited by the LB technique either are non-conductive or possess very low conductivity. The most probable reason of such a behaviour is their discontinuity at the microscopic level. This conclusion is based on the data obtained by FT-IR spectroscopy, surface potential, and optical microscopy techniques as well as by transfer ratio measurements.
Colloids and Surfaces A-physicochemical and Engineering Aspects - COLLOID SURFACE A. 01/2002; 198:689-701.