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In this study, a novel amphiphilic nonlinear optical (NLO) molecule which can form a monolayer at the air-water interface was demonstrated. Also, in-plane coherence and long-range order in multilayered thin films are achieved by manipulating the experimental parameters such as temperature, surface pressure, rate of compression, and transfer ratio. A fundamental understanding of how molecules come together to form a monolayer was gained and the process of transferring the monolayer from the air-water interface to the solid (glass) substrates was optimized. It therefore allows control over thin film properties governed by structural order at the molecular level. NLO measurement is used as a complementary tool in determining the structure related thin film properties. The quadratic increase of a second harmonic signal with increasing film thickness implies the sign of sustaining noncentrosymmetric order throughout the film.

We report here a novel approach to synthesize chiral PANI nanofibers in an aqueous solution. This new approach requires the following conditions: (1) Polymerization was carried out in concentrated camphor sulfonic acid solutions. (2) Aniline oligomers were used to accelerate the polymerization reaction. (3) Ammonium persulfate (oxidant) was added incrementally to the aniline solution. The high anisotropy factor of these PANI nanofibers is likely due to the "autocatalytic effect" resulting from lower oxidation potentials of aniline oligomers. Our chemical synthesis of the chiral PANI nanofibers is enantioselective and, under the optimized conditions, has an anisotropy factor (g = Deltaepsilon/epsilon) of 2.3 x 10-2.

The excited state electronic structure of $\pi$ conjugated phenylene-acetylene oligomers is calculated using time-dependent density functional theory (TD-DFT) approaches. The theoretical fluorescence spectra are analyzed in terms of Frank-Condon active nuclear normal modes and shown to compare well with experiment. Theoretical and experimental results for the optical absorption and emission spectra of these molecules indicate that the conjugation length can be significantly reduced by conformational rotations about the triple-bonded carbon links. This has serious implications on the electronic functionalities of polyphenylene-acetylene based molecular wires and their possible use as charge/energy conduits in nano-assemblies.

We have fabricated unilayer electroluminescent devices from soluble poly(p‐pyridine) (PPy). The solubility of PPy in weak acids allows direct spin casting of the polymer films. The electroluminescence spectrum peaks at 2.5 eV (497 nm) corresponding to white light weighted towards the blue end of the spectrum. The photoluminescence spectrum peaks at 2.35 eV (530 nm). The operating voltages of the devices ranged from 4 to 12 V with current densities of 6 to 8 mA/mm2. We compare our devices with similar blue emitting devices based on poly(p‐phenylene).

Nanostructured Cu/304 stainless steel (SS) multilayers were prepared by magnetron sputtering at room temperature. 304SS has a face-centered cubic (fcc) structure in bulk. However, in the Cu/304SS multilayers, the SS layers exhibited fcc structure for layer thickness of less than or equal to 5 nm. For 304SS layer thickness larger than 5nm, bcc 304SS grains were observed to grow on top of the initial ≈ 5 nm of fcc SS. The maximum hardness of Cu/304SS multilayers was ≈ 5.5 GPa (factor of two enhancement compared to rule of mixtures hardness) achieved at a layer thickness of 5nm, with a decrease in hardness with decreasing layer thickness below 5 nm. The hardness of fcc/fcc Cu/304SS multilayers (layer thickness ≤ 5 nm) is compared with Cu/Ni, another fcc/fcc system, to gain insight on how the mismatch in physical properties such as lattice parameters and shear moduli of the constituent layers affect the peak hardness achieved in these nanoscale systems.

DNA sequence-dependent photoluminescence enhancement is found for a cationic polyelectrolyte complexed with single stranded DNA and described as a result of an interplay between electrostatic attraction and the π-π stacking between the polyelectrolyte's backbone and DNA's bases.

In pulsed laser deposited YBa2Cu3O7−x thin films containing 5 mol. % Ba2YNbO6 pinning additions, we show that a growth rate of 1 nm/s (10 Hz laser repetition rate with an instant rate ∼0.1 nm/pulse) gives remarkably strong c-axis correlated pinning which is associated with the presence of Ba2YNbO6 nanocolumns. This is different to the behaviour of other well-studied pinning additions where only random nanoparticles of the pinning phase are present at high growth rates and is an important finding for industrial fabrication of coated conductors where fast growth is required.

Using subpicosecond transient absorption spectroscopy, we have investigated the primary photoexcitations in thin films and solution of several phenylene-based conjugated polymers and an oligomer. We identify two features in the transient absorption spectra and dynamics that are common to all of the materials which we have studied from this family. The first spectral feature is a photoinduced absorption (PA) band peaking near 1 eV which has intensity-dependent dynamics which match the stimulated emission dynamics exactly over two orders of magnitude in excitation density. This band is associated with singlet intrachain excitons. The second spectral feature (observed only in thin films and aggregated solutions) is a PA band peaking near 1.8 eV, which is longer-lived than the 1 eV exciton PA band, and which has dynamics that are independent (or weakly-dependent) on excitation density. This feature is attributed to charge separated (interchain) excitations. These excitations are generated through a bimolecular process. By comparing to samples in which charged excitations are created deliberately by doping with C 6 O, we assign these secondary species as bound polarons.

We report on the optical characterization of a series of multi-layered organic superlattices made by polyelectrolyte self-assembly. Using a high molecular weight, water-soluble, anionic form of poly-phenylene vinylene, self-assembled films can be formed which show high photoluminescence quantum efficiency (QE). A dramatic red shift of the luminescence and increase in QE is observed as additional PPV layers are added. We attribute the red shift and increasing QE to a changing conformation of the polymer chains as the superstructure is assembled, together with efficient Frster energy transfer in a preferred direction away from the substrate toward layers with longer effective conjugation length. Upon adding a C60 top layer, the luminescence spectrum is strongly quenched. We attribute this to charge transfer of from the top-most polymer layer to the C60 layer. We discuss the possibilities of exploiting this directional charge transfer in an ultrafast holographic device along with other optics for increasing the temporal diffraction efficiency of polymer-based mediums.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present our recent advances toward the development of high-performance solid-state optical limiting devices using reverse saturable absorption (RSA) dyes doped into optical host materials. Femtosecond transient absorption spectroscopy was employed to determine both the spectral regions of strong RSA, and the singlet-triplet excited-state dynamics. The optical limiting in the visible spectrum in both metallo-phthalocyanines and metallo-porphyrins is due to a combination of singlet and triplet RSA. Optical limiting performance was studied for RSA dyes in dual tandem limiters (both in solution and solid-state). Our best results in the solid-state yielded an attenuation of 400X, and a damage threshold of up to several mJ at f/5 focusing. The optical limiting at f/5 is further enhanced, particularly in the solid-state, by self-defocusing thermal nonlinearities.

Publisher Summary The concept of gel-inhibitory agents that improve the solution processing parameters of the emeraldine base is introduced in the chapter. These agents are quite sensitive to the concentration range and the gel inhibitor/emeraldine base (GI/EB) molar ratio between 1 and 4. The preparation of highly concentrated EB solutions utilizing high molecular weight polyaniline is easily achieved with this processing advantage. The solutions are stable for periods of time sufficient to dry–wet spin fiber. The fiber moduli, strength, and DC conductivity are improved by stretch alignment. Mineral acids tend to weaken the fibers following doping protocols, while organic acids such as benzene phosphinic acid (BPA) preserve good mechanical and conductive properties. In the study described in the chapter, all of the doped samples showed temperature- dependant DC conductivity. This data can be fit to disorder models such as the quasi-one- dimensional variable-range hopping (VRH) model. Acetic acid is an anomalously poor dopant, and for polyaniline BPA is a good dopant.

We present our recent advances toward the development of high-performance solid-state optical limiting devices using reverse saturable absorption (RSA) dyes doped into optical host materials. Femtosecond transient absorption spectroscopy was employed to determine both the spectral regions of strong RSA, and the singlet-triplet excited-state dynamics. The optical limiting in the visible spectrum in both metallo-phthalocyanines and metallo-porphyrins is due to a combination of singlet and triplet RSA. Optical limiting performance was studied for RSA dyes in dual tandem limiters (both in solution and solid-state). Our best results in the solid-state yielded an attenuation of 400x, and a damage threshold of up to several mJ at f/5 focusing. The optical limiting at f/5 is further enhanced, particularly in the solid-state, by self-defocusing thermal nonlinearities.

Publisher Summary This chapter presents the results obtained for wet-spun emeraldine base (EB) fiber prepared when non-toxic heptamethyleneimine (HPMI) is used in place of 2-methylaziridine. The “gel inhibitor” assisted processing of ultra-high molecular weight EB into wet-spun fiber uses small amounts of secondary amine additives—for example, 2-methyl aziridine (2MA)—to form thermodynamically stable, particle-free, and highly concentrated (20% w/w) EB solutions. Wet-spun fibers with similar physical characteristics may be obtained by utilizing nontoxic heptamethyleneimine (HPMI) as the gel inhibitor. UV–Vis data shows that the oxidation state of EB polymer in solution and in the fiber is unaltered by the presence of HMPI. Acid doping of as-spun EB fibers leads to conductivity values ranging from 10″ to 3.3 S/cm. The volatile weak acetic acid is removed by mechanical pumping in vacuum, which explains the reduced conductivity value compared to the other samples. Acid doping of the EB fiber results in changes in fiber volume, and thus fiber density. Differences in failure strength and strain of the fibers compared to other reported fibers are likely due to differences in the molecular weight of the EB utilized for each study.

The authors present recent results of broadband femotosecond (fs) transient absorption (TA) and broadband nanosecond (ns) optical limiting (OL) studies of C{sub 60} and derivatized C{sub 60}. Improvements in measurement techniques for fs TA spectra provide sensitivity to 10{sup {minus}5} in differential transmission, allowing detailed comparison of excited-state spectra with established energy level diagrams, as well as comparison of the ratio of triplet to singlet excited-state absorption cross sections from TA spectra with those obtained by modeling time transients at different wavelengths. For derivatized fullerenes, which provide enhanced solubility and a ground-state absorption extended into the infrared compared with C{sub 60} there is no spectral region where the triplet absorption cross section dominates the singlet as strongly as demonstrating broadband limiting in all 6, 6 mono-adducts and neat C{sub 60}. The authors report new approaches to processing sol-gel encapsulated fullerenes to improve the OL performance of solid-state materials to approach the response of solution limiters.

We review our results from spectral studies of the ultrafast excited-state absorption in fullerenes and derivatized fullerenes. These results allow determination of both the spectral response of reverse saturable absorption (RSA) nonlinearities such as optical limiting (OL) in fullerenes, and the dynamical response for different morphologies. We have investigated the effects of thin film and various sol-gel glass environments on the nanosecond OL and femtosecond dynamics of derivatized fullerenes. These data provide evidence of decay pathways which compete with the intersystem crossing to a triplet from the initial singlet states. With appropriate processing, however, the OL response of derivatized-fullerene sol-gel glasses can be enhanced to approach that of the same molecule in solution, while significantly enhancing the optical damage threshold. The optical limiting of these derivatized fullerenes is compared with that of various porphyrin and phthalocyanine molecules.

A Li-O2 battery based on the Mn3O4/RGO nanocomposite (monodispersed Mn3O4 nanoparticles supported on RGO) cathode exhibits excellent ORR activity and an outstanding initial discharge capacity as high as 16,000 mA h g(-1).

We compare detailed dynamics of the excited-state absorption for C60 in solution, thin films, and entrapped in an inorganic sol-gel glass matrix. Our results demonstrate that the microscopic morphology of the C60 molecule plays a crucial role in determining the relaxation dynamics. This is a key factor for applications in optical limiting for nanosecond pulses using reverse saturable absorption. We find that the dynamics of the C60-glass composite occur on long timescales, comparable to that in solution; thin film samples, by contrast, show rapid decay. These results demonstrate that the C60-sol-gel glass composites contain C60 in a molecular dispersion, and are suitable candidates for solid-state optical limiting. Multispectral analysis of the decay dynamics in solution allows accurate determination of both the intersystem crossing time and the relative strengths of the singlet and triplet excited-state cross sections as a function of wavelength from 450-950 nm. The triplet excited-state cross section is greater than that for the singlet excited-state over the range form 620-810 nm.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Holographic recording has been demonstrated in conducting polymer/C60 blends. These materials allow ultrafast holographic recording and the ability to tailor the decay dynamics of the recorded hologram. Diffraction efficiencies up to 1.6 percent have been measured in these materials for gratings recorded with individual laser pulses. Results are presented that demonstrate that an improved signal-to-noise ratio is obtained when holographic detection is used to observe the dynamics of photo-induced absorption.

We present a study of the morphology dependence of the photoluminescence (PL) properties of the pyridine-based polymers poly(p-pyridyl vinylene), poly(p-pyridine), and poly(p-pyridyl vinylene p-phenylene vinylene) (PPyVPV). The photoluminescence of solution samples is characterized by high quantum efficiency (g70% in PPyVPV), weak coupling to vibrational modes (Huang-Rhys parameter \ensuremath{\sim}0.5) and a single-exponential decay (radiative lifetime \ensuremath{\sim}1 ns). On the other hand, film samples display strongly redshifted, featureless emission with low quantum yield (20%) and highly nonexponential decay dynamics. Through consideration of absorption and excitation spectra, the ``site-selectivity'' of the PL, and the concentration dependence of the PL spectrum, we demonstrate that the redshifted film spectra are a result of the formation of low-energy aggregate sites due to strong interchain interactions. Time-resolved measurements suggest a longer radiative lifetime for the aggregate vs solution, leading to the lower efficiency. Aggregate formation is found to be morphology dependent, and is minimal in ``powder'' samples which are precipitated after polymerization. \textcopyright{} 1996 The American Physical Society.

Transient holographic gratings using third-order nonlinear optical processes have been suggested as possible elements for a variety of optical applications, particularly in the areas of interconnection networks and optical computing. Many of the materials suggested for applications relating to holographic optical processing rely on effects such as photorefractivity or photo-isomerization, both of which occur on time scales of milliseconds to minutes [1]. While these materials are well suited to applications such as optical storage, faster materials have a higher probability of proving useful for real-time processing. Recently it has been discovered that in certain polymers doped with C60, charge transfer occurs after excitation across the π – π * energy gap of the polymer to the dopant C60 molecules [2]. Using transient absorption measurements, it has been shown that this charge- transfer process occcurs at times shorter than 300 fs, and can persist up to millisecond time-scales. Since the third order nonlinear optical susceptibility, χ(3), includes a component which is related to the excited charge distribution, charge transfer to C60 can be used to increase the lifetime of this incoherent contribution to χ(3) in polymers.

Poly(2,5-methoxy-propyloxy sulfonate phenylene vinylene) (MPS-PPV) and DAB-Am-16, a generation 3.0 polypropylenimine hexadecamine dendrimer (DAB), are shown to form a tunable photoresponsive polyelectrolyte assembly in aqueous solution with an enhanced emission signal of up to 18-times that of MPS-PPV alone.

We report the fabrication and properties of three-, four-, and five-layer electroluminescent devices fabricated from light emissive N-based heterocyclic novel polymeric derivatives of PPP and PPV with which they are isoelectronic. They include poly(pyridine vinylene), (PPyV), and poly(2,5-dihexadecanoxy phenylene vinylene pyridyl vinylene), (PPV.PPyV). Some of the devices operate in both forward and reverse bias modes thus enabling operation in an ac mode. One type of device has the general construction: M/I/polymer/I/ITO where M equals Cu or Al, I equals polyaniline (emeraldine base, EB) or poly(3-hexylthiophene), (P3HT), and polymer equals PPV.PPyV. Under low frequency ac (sinusoidal) driving, light pulses with twice the driving frequency were observed in a device where M equals Al or Cu, I equals EB and polymer equals PPV.PPyV; and in a device where M equals Al, I equals P3HT and polymer equals PPV.PPyV. In the latter device the electroluminescence spectrum in the reverse bias mode differed from that in the forward bias mode. It was also shown that blends of PPyV in Nylon 6,6 exhibit a lower operating voltage than the pure polymer.

Symmetrically configured ac light-emitting (SCALE) devices based on conjugated polymers utilizing indium-tin oxide (ITO) and aluminum as electrodes have been demonstrated recently. Here we report the fabrication of SCALE devices using a more stable high workfunction metal, such as gold, as a charge (both electron and hole) injection electrode. Also, a variation of such devices in which the electroluminescent polymer, instead of being separated from the insulating polymer, is dispersed in the insulating polymer to form a unified emitter-insulator is reported. These devices emit light in both forward and reverse dc bias with symmetric current- voltage characteristics. Under low frequency ac (sinusoidal) driving voltage, light pulses with double the driving frequency are observed. A model is proposed to account for the device operation.

Light emitting electroluminescent devices have been studied in which the conjugated light emitting polymer is separated on both sides from the device electrodes by a film of nonconducting polyaniline. The devices operate under an AC applied potential.Aluminum, copper or gold serve as the metal electrodes. Flexible, completely organic polymer dispersed liquid crystal light valves have been fabricated from transparent plastic substrates on which a conducting film of polypyrrole has been deposited. A new concept, “microcontact printing”, is being investigated for patterning the polypyrrole.

The spectroscopic properties of the pyridine-based polymer poly(p-pyridyl vinylene p-phenylene vinylene) (PPyVPV) are examined. The emission of PPyVPV in solution has small intrinsic Stokes shift with some vibronic structure. In contrast, emission from thick film samples is featureless, with a strong redshift of ˜0.5 eV versus solution. We attribute these observations to the formation of aggregate states in film samples. Time-resolved photoluminescence measurements are in accord with the diffusion of excitons to the aggregate sites. Photoinduced absorption also originates from excitons in aggregate states.

Porous polyaniline (PANI) asymmetric membranes were prepared using phase inversion technique and a density gradient was found along the cross-section of the membrane. A chemical vapor triggered monolithic actuator was constructed based on the PANI membrane. It was found that the monolithic actuator bends from dense side to porous side in organic vapor and recovers to its original position in air. The actuator shows different bending behavior in different vapors with the most extensive and the fastest bending movement observed in THF vapor. The bending-recovery movement is believed to be caused by the sorption-desorption of organic vapor, which leads to volume deformation that is density dependent. The dense side shows a greater volume expansion than the porous side after the sorption of organic vapors, which causes a bending movement towards then porous side, and the desorption of the organic vapor from the membrane prompts it to recover to its original position.

We demonstrate here a facile one-pot interfacial synthesis of Au nanoparticles and Au–polyaniline nanocomposites through the polymerization of aniline by HAuCl4, and the nanocomposites are efficient catalysts for the reduction of rhodamine B.

We here demonstrate a fast fabrication of homogeneous silver nanostructures on polyaniline films within one minute, which show highly sensitive response in SERS applications.

In this paper, we report low-field magnetoresistance observed in preferentially c-axis oriented La0.67 Sr0.33MnO3:MgO composite films fabricated on (001) LaAlO3 substrates using a hybrid solution route. Addition of MgO in the composite film results in lowering of Curie temperature (∼300 K) from that of the pure film (∼360 K). The resistivity increases and temperature of highest resistivity of the composite films decrease with the addition of MgO. This behavior is attributed to a small substitution of Mg2+ in the manganite lattice and the presence of MgO near the manganite grain boundaries, thus building tunneling barriers and enhancing the spin polarized tunneling in the composite films. The values of low-field magnetoresistance increase with MgO addition and the composite film with highest amount of MgO exhibits maximum MR of −33% at 0.5 T (5000 Oe) and 10 K.

Self-assembled, segmented nanorods of c-axis-aligned Ba2(Y /Gd)(Nb/Ta)O6 as well as randomly distributed nanoparticles of (Y /Gd)2O3 and (Y /Gd)Ba2Cu4O8 were grown into YBa2Cu3O7 − δ (YBCO) thin films by pulsed-laser deposition. The complex pinning landscape proves to be extremely effective, particularly at higher fields where the segmented vortices yield a plateau in critical current density (Jc) with field angle around 60°. In 0.3 µm thick films, the Jc values are higher than 1 MA cm − 2 at 2.5 T ( axis). Owing to the combined interactions of the vortices with the different pinning centres, interesting new features are observed at high fields in the angular dependence of Jc.

A free charge layer forms at the LaAlO3/SrTiO3 interface. We show the influence of the SrTiO3 (001) substrate miscut angle on its electronic and transport properties. Highly miscut substrates lead to a substantial mobility enhancement and a carrier density decrease at low temperature consistent with a two-carrier type model.

Thin films of Pr0.5Ca0.5MnO3 were fabricated on (001) oriented SrLaAlO4, NdGaO3, and SrTiO3 substrates using a hybrid solution route and spin coating techniques. Good crystalline and epitaxial quality of the films was confirmed with X-ray diffraction and transmission electron microscopy studies. Strain in the film grown on NdGaO3 substrate did not relax during annealing process and the film exhibited charge-ordered insulator phase at low temperatures even with magnetic fields up to 9 T. However, the films on SrLaAlO4 and SrTiO3 substrates (with partially relaxed compressive and tensile strain, respectively) displayed melting of the charge-ordered phase with applied magnetic fields of less than 5 T. The results suggest that strain-relaxation rather than only the type of strain plays an important role in lowering critical melting magnetic fields in these films.

We report the synthesis and characterization of multilayer self-assembled polymer films made from a water-soluble conjugated polymer, poly(2,5-methoxy-propyloxy sulfonate phenylene vinylene) (MPS-PPV). We observe a red shift of both the absorption and fluorescence spectra with increasing numbers of active MPS-PPV layers. We attribute this red shift to changing polymer conformation and efficient energy transfer. Upon adding a water-soluble C 60 or C 60 -VBA copolymer top layer, the luminescence spectrum is strongly quenched due to charge transfer. The estimated charge transfer quantum efficiency from PL quenching is ∼95%. We discuss in detail the unidirectional energy transfer followed by charge transfer in the self-assembled multilayered films.

Conducting polymers have been proved to be effective reducing agents in the synthesis of noble metal nanoparticles. We demonstrate here the fabrication of homogeneous Ag nanosheet assemblies on conducting polymer membranes with 5 wt% polyaniline (PANI) substituted by conductive additives like graphite (G) or multi-walled carbon nanotubes (CNTs). The inclusion of conductive additives that act as electrical connectors for the PANI particles changes the surface property and creates a homogeneous nucleation environment, leading to the membrane surface completely covered by the Ag nanosheet structures. The pack density of the nanosheets can be simply tuned by modulating the concentration of AgNO3 aqueous solution. The as-prepared Ag nanosheet assemblies with abundant interstitial sites show strong SERS responses toward the mercaptobenzoic acid (MBA) molecules, with a detection sensitivity down to 5 ppm. A proper acid etching of these Ag nanosheet structures in 0.1 M HNO3 aqueous solution makes the nanoparticles that form the nanosheets much more exposed to the analyte molecules, and an even stronger Raman enhancement can be obtained. We believe the homogeneous Ag nanosheet assemblies supported on conducting polymer membranes can be sensitive and cost-effective SERS substrates in molecule detection.

A gradient of novel silver nanostructures with widely varying sizes and morphologies is fabricated on a single conducting polyaniline-graphite (P-G) membrane with the assistance of an external electric field. It is believed that the formation of such a silver gradient is a synergetic consequence of the generation of a silver ion concentration gradient along with an electrokinetic flow of silver ions in the field-assisted model, which greatly influences the nucleation and growth mechanism of Ag particles on the P-G membrane. The produced silver dendrites, flowers and microspheres, with sharp edges, intersections and bifurcations, all present strong surface enhanced Raman spectroscopy (SERS) responses toward an organic target molecule, mercaptobenzoic acid (MBA). This facile field-assisted synthesis of Ag nanoparticles via chemical reduction presents an alternative approach to nanomaterial fabrication, which can yield a wide range of unique structures with enhanced optical properties that were previously inaccessible by other synthetic routes.

The critical current density (Jc) of very thin YBa2Cu3O7?? (YBCO) films can approach 10?MA?cm?2 at 77?K in self-field, but for such films Jc drops sharply as the film thickness is increased. We have shown previously that this strong thickness dependence results from an enhancement of Jc near the film?substrate interface. In the present paper we investigate interfacial enhancement using laser-deposited YBCO films on NdGaO3 substrates, and find that we can adjust deposition conditions to switch the enhancement on and off. We find that the 'on' state is accompanied by a dense array of interfacial misfit dislocations, while we do not observe dislocations in films prepared in the 'off' state. This result appears to be but one of many examples in which interfacial properties of electronic film materials are profoundly affected by stress-induced defects at the film?substrate interface; however, to our knowledge the present work is the only case in which electronic properties are shown to be enhanced by such defects.

The permeability of gases through thin polyaniline EB film depends upon the combined mobility and solubility of the gases at a given temperature and pressure. The gas transport behavior of an emeraldine base (EB) film was studied in detail. Permeability measurements were made using the manometric time-lag method of analysis for He, H2, CO2, O2, N2 and CH4, all as functions of varying temperature (15° to 40° C). These measurements allowed us to determine the activation energies for permeation, diffusion, and heat of solution for each gas tested. Permeability of the gases is temperature dependent, permeability increases with increasing temperature and permselectivity of the gas pairs He/N2, O2/N2, CO2/CH4 decreases with increasing temperature.

A study is presented on the evolution through thickness of the angular and magnetic field (H) dependence of the critical current density (Jc) for YBa2Cu3O7 films grown by the trifluoroacetate route. A clear relation between Jc at self-field (sf) and the thickness-dependent distribution of pinning centers parallel to the ab-planes is found and confirmed by microstructural analysis. Results indicate that stacking faults and their associated partial dislocations are relevant pinning centers for determining the thickness dependence of and Jc(sf), respectively, supporting the hypothesis that the thickness dependence of Jc is related to defect density.

YBa2Cu3O7−x (YBCO) thick films were grown by hybrid liquid phase epitaxy (HLPE) on (001) SrTiO3 (STO) substrates. In the presence of a 100 nm thick, 5 mol% Au-doped STO buffer, self-field critical current densities, Jcsf, at 77 K of ~2.4 MA cm−2 and critical currents, Icsf, up to 700 A (cm-width)−1 were achieved. The Jc value is virtually independent of thickness and the growth rates are very high (~1 µm min−1). From transmission electron microscopy (TEM), Y2O3 nanocloud extended defects (~100 nm in size) were identified as the pinning defects in the films. Enhanced random pinning was induced by the presence of Au in the buffer.