Thin films prepared from tungstate glass matrix

Vitreous samples containing high concentrations of WO3 (above 40% M) have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. These films were characterized by X-ray diffraction (XRD), perfilometry, X-ray energy dispersion spectroscopy (EDS), M-Lines and UV-vis absorption spectroscopy. In this work, experimental parameters were established to obtain stable thin films showing a chemical composition close to the glass precursor composition and with a high concentration of WO3. These amorphous thin films of about 4 mu m in thickness exhibit a deep blue coloration but they can be bleached by thermal treatment near the glass transition temperature. Such bleached films show several guided modes in the visible region and have a high refractive index. Controlled crystallization was realized and thus it was possible to obtain WO3 microcrystals in the amorphous phase. (C) 2007 Elsevier B.V. All rights reserved.

Thickness and Annealing Temperature Effects on the Optical Properties and Surface Morphology of Layer-by-Layer Poly(p-phenyline vinylene) plus Dodecylbenzenesulfonate Films

The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV)+dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 degrees C had a dichroic ratio delta = 2.3 and order parameter r = 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with delta = 1.0 for a 75-layer LbL PPV + DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the self-covariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 206-213, 2011

Immobilization of Ibuprofen-Containing Nanospheres in Layer-by-Layer Films

Liposomes have been applied to many fields as nanocarriers, especially in drug delivery as active molecules may be entrapped either in their aqueous interior or onto the hydrophobic surface. In this paper we describe the fabrication of layer-by-layer (LbL) films made with liposomes incorporating the anti-inflammatory ibuprofen. The liposomes were made with dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl glycerol (DPPG) and palmitoyl oleoyl phosphatidyl glycerol (POPG). LbL films were assembled via alternate adsorption of the polyamidoamine dendrimer (PAMAM), generation 4, and liposomes containing ibuprofen. According to dynamic light scattering measurements, the incorporation of ibuprofen caused DPPC and DPPG liposonnes to become more stable, with a decrease in diameter from 140 to 74 nm and 132 to 63 nm, respectively. In contrast, liposomes from POPG became less stable, with an increase in size from 110 to 160 nm after ibuprofen incorporation. These results were confirmed by atomic force microscopy images of LbL films, which showed a large tendency to rupture for POPG liposomes. Film growth was monitored using nanogravimetry and UV-Vis spectroscopy, indicating that growth stops after 10 bilayers. The release of ibuprofen obtained with fluorescence measurements was slower for the liposomes, with decay times of 9.2 and 8.5 h for DPPG and POPG liposomes, respectively, than for the free drug with a decay time of 5.2 h. Ibuprofen could also be released from the LbL films made with DPPG and POPG liposomes, which is promising for further uses in patches.

Low-Frequency Noise in Field-Effect Devices Functionalized With Dendrimer/Carbon-Nanotube Multilayers

Low-frequency noise in an electrolyte-insulator- semiconductor (EIS) structure functionalized with multilayers of polyamidoamine (PAMAM) dendrimer and single-walled carbon nanotubes (SWNT) is studied. The noise spectral density exhibits 1/f(gamma) dependence with the power factor of gamma approximate to 0.8 and gamma = 0.8-1.8 for the bare and functionalized EIS sensor, respectively. The gate-voltage noise spectral density is practically independent of the pH value of the solution and increases with increasing gate voltage or gate-leakage current. It has been revealed that functionalization of an EIS structure with a PAMAM/SWNTs multilayer leads to an essential reduction of the 1/f noise. To interpret the noise behavior in bare and functionalized EIS devices, a gate-current noise model for capacitive EIS structures based on an equivalent flatband-voltage fluctuation concept has been developed.

SURFACE-ENHANCED RAMAN SCATTERING: METAL NANOSTRUCTURES COATED WITH LANGMUIR-BLODGETT FILMS

This review deals with surface-enhancved Raman scattering (SERS) employing Langmuir-Blodgett (LB) films, which serve as model systems for developing theoretical and experimental studies to elucidate the SERS effect. In addition, LB films have be used as integral parts of molecular architectures for SERS-active substrates. On the other hand, SERS and surface-enhaced resonant Raman scattering (SERRS) have allowed various properties of LB films to be investigated, especially those associated with molecular-level interactions. In the paper, emphasis is placed on single molecule detection (SMD), where the target molecule is diluted on an LB matrix of spectral silent material (low Raman cross section). The perspectives and challenges for combining SERS and LB films are also discussed.

Raman spectroscopy analysis of structural photoinduced changes in GeS(2) + Ga(2)O(3) thin films

Photoexpansion and photobleaching effects have been observed in amorphous GeS(2) + Ga(2)O(3) (GGSO) thin films, when their surfaces were exposed to UV light. The photoinduced changes on the surface of the samples are indications that the structure has been changed as a result of photoexcitation. In this paper, micro-Raman, energy dispersive X-ray analysis (EDX) and backscattering electrons (BSE) microscopy were the techniques used to identify the origin of these effects. Raman spectra revealed that these phenomena are a consequence of the Ge-S bonds` breakdown and the formation of new Ge-O bonds, with an increase of the modes associated with Ge-O-Ge bonds and mixed oxysulphide tetrahedral units (S-Ge-O). The chemical composition measured by EDX and BSE microscopy images indicated that the irradiated area is oxygen rich. So, the present paper provides fundamental insights into the influence of the oxygen within the glass matrix on the considered photoinduced effects. (C) 2010 Elsevier B.V. All rights reserved.

Bismuth germanate films prepared by Pechini method

Bismuth germanate films were prepared by dip coating and spin coating techniques and the dependence of the luminescent properties of the samples on the resin viscosity and deposition technique was investigated. The resin used for the preparation of the films was obtained via Pechini method, employing the precursors Bi(2)O(3) and GeO(2). Citric acid and ethylene glycol were used as chelating and cross-linking agents, respectively. Results from X-ray diffraction and Raman spectroscopy indicated that the films sintered at 700 degrees C for 10 h presented the single crystalline phase Bi(4)Ge(3)O(12). SEM images of the films have shown that homogeneous flat films can be produced by the two techniques investigated. All the samples presented the typical Bi(4)Ge(3)O(12) emission band centred at 505 nm. Films with 3.1 mu m average thickness presented 80% of the luminescence intensity registered for the single crystal at the maximum wavelength. Published by Elsevier B.V.

Enzyme Activity of Catalase Immobilized in Langmuir-Blodgett Films of Phospholipids

A major challenge for producing low cost biosensors based on nanostructured films with control of molecular architectures is to preserve the catalytic activity of the immobilized biomolecules. In this study, we show that catalase (HRP) keeps its activity if immobilized in Langmuir-Blodgett (LB) films of dipalmitoyl phosphatidylglycerol (DPPG). The incorporation of catalase into a DPPG monolayer at the at interface was demonstrated with surface pressure and surface potential isotherms, in addition to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). According to the PM-IRRAS data. catalase was not denatured upon adsorption on a preformed DPPG monolayer and could be transferred onto a solid substrate. The catalytic activity of catalase in a mixed LB film with DPPG was ca. 13% higher than in solution. The control of molecular architecture and choice of a suitable phospholipid matrix allows catalase-containing LB films to be used in sensing hydrogen peroxide.

Influence from the sulfonate group (RSO(3)(-)) on the conversion process and emission efficiency of poly(p-phenylene vinylene)

The discovery of an alternative route to convert poly(xylyliden tetrahydrothiophenium chloride) (PTHT) into poly(p-phenylene vinylene) (PPV) using dodecylbenzenesulfonate (DBS) has allowed the formation of ultrathin films with unprecedented control of architecture and emission properties. In this work, we show that this route may be performed with several sufonated compounds where RSO(3)(-) replaces the counter-ion (Cl(-)) of PTHT, some of which are even more efficient than DBS. Spin-coating films were produced from PTHT and azo-dye molecules, an azo-polymer and organic salts as counter-ions of PTHT. The effects of the thermal annealing step of PTHT/RSO(3)(-) films at 110 and 230 degrees C were monitored by measuring the absorption and emission spectra. The results indicate that the exchange of the counterion Cl(-) of PTHT by a linear long chain with RSO(3)(-) group is a general procedure to obtain PPV polymer at lower conversion temperature (ca. 110 degrees C) with significant increase in the emission efficiency, regardless of the chemical position and the number of sulfonate groups. With the enhanced emission caused by Congo Red and Tinopal as counter-ions, it is demonstrated that the new synthetic route is entirely generic, which may allow accurate control of conversion and emission properties. (C) 2010 Elsevier B.V. All rights reserved.

Mixing alternating copolymers containing fluorenyl groups with phospholipids to obtain Langmuir and Langmuir-Blodgett films

The control of molecular architectures may be essential to optimize materials properties for producing luminescent devices from polymers, especially in the blue region of the spectrum. In this Article, we report on the fabrication of Langmuir-Blodgett (LB) films of polyfluorene copolymers mixed with the phospholipid dimyristoyl phosphatidic acid (DMPA). The copolymers poly(9.9-dioetylfluorene)-co-phenylene (copolymer I) and poly(9,9-dioctylfluorene)-co-quaterphenylene) (copolymer 2) were synthesized via Suzuki reaction. Copolymer I could not form a monolayer on its own, but it yielded stable films when mixed with DMPA. In contrast, Langmuir monolayers could be formed from either the neat copolymer 2 or when mixed with DMPA. The surface pressure and surface potential measurements, in addition to Brewster angle microscopy, indicated that DMPA provided a suitable matrix for copolymer I to form a stable Langmuir film, amenable to transfer as LB films, while enhancing the ability of copolymer 2 to form LB films with enhanced emission, as indicated by fluorescence spectroscopy. Because a high emission was obtained with the mixed LB films and since the molecular-level interactions between the film components can be tuned by changing the experimental conditions to allow For further optimization, one may envisage applications of these films in optical devices such as organic light-emitting diodes (OLEDs).

Adsorption kinetics and charge inversion in layer-by-layer films from nickel tetrasulfonated phthalocyanine and poly(allylamine hydrochloride)

Layer-by-layer (LBL) films of nickel tetrasulfonated phthalocyanine (NiTsPc) alternated with poly(allylamine hydrochloride) (PAH) have been prepared, whose surface charge has been evaluated using surface potential measurements. From adsorption kinetics results, we obtained the immersion time of similar to 40 s, which was used to assemble layers of NiTsPc. The effect of gold (Au) and aluminum (Al) electrodes on the charge behavior was examined. We found that the surface potential (i.e. surface charge) was inverted each time a layer of PAH was alternated with another of NiTsPc molecules for the two types of electrodes, which was attributed to charge overcompensation between positive charges of PAH molecules, and negative charges from NiTsPc molecules. (C) 2009 Elsevier B.V. All rights reserved.

A Multitechnique Study of Structure and Dynamics of Polyfluorene Cast Films and the Influence on Their Photoluminescence

This article describes the microstructure and dynamics in the solid state of polyfluorene-based polymers, poly(9,)-dioctylfluorenyl-2,7-diyl) (PFO), a semicrystalline polymer, and poly [(9,9-dioctyl- 2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)- 1,4-phenylene vinylene}, a copolymer with mesomorphic phase properties. These Structures were determined by wide-angle X-ray scattering (WAXS) measurements, Assuming a packing model for the copolymer structure, where the planes of the phenyl rings are stacked and separated by an average distance of similar to 4.5 angstrom and laterally spaced by about similar to 16 angstrom, we followed the evolution of these distances as a function of temperature using WAXS and associated the changes observed to the polymer relaxation processes identified by dynamical mechanical thermal analysis. Specific molecular motions were studied by solid-state nuclear magnetic resonance. The onset of the side-chain motion at about 213 K (beta-relaxation) produced a small increase in the lateral spacing and in the stacking distance of the phenyl rings in them aggregated Structures, Besides, at about 383 K (alpha-relaxation) there occurs a significant increase in the amplitude of the torsion motion in the backbone, producing a greater increase in the stacking distance of the phenyl rings. Similar results were observed in the semicrystalline phase of PFO, but in this case the presence of the crystalline structure affects considerably the overall dynamics, which tends to be more hindered. Put together, Our data explain many features of the temperature dependence of the photoluminescence of these two polymers.

Structural and spectroscopic characterization of poly(styrene sulfonate) films doped with neodymium ions

This work reports the structural and spectroscopy characterization of poly(styrene sulfonate) (PSS) films doped with neodymium (Nd) ions. Nd-PSS films were processed using the acid of poly(styrene sulfonate) - H-PSS and neodymium nitrate - Nd(NO(3))(3); the maximum incorporation of Nd ions in the polymeric matrix was equal 19.3%. The absorption in the UV-Vis-NIR spectral region presents typical electronic transitions of Nd 3, ions, with well resolved peaks. The infrared spectra present the transition bands of PSS with characteristic line shape broadening, and the presence of vibrational modes of N-O groups in the range of 1400-720 cm(-1), prove the permanence of Nd(NO(3))(x), with x = 1, 2 and/or 3. in the H-PSS matrix. UV-Vis site selective photoluminescence data indicate that the incorporation of Nd 31 introduces a blue shift in PSS emission (325-800 nm), decreasing the interaction between adjacent PSS lateral groups (aromatic rings). Nd(3+) reabsorption and energy transfer effects between the PSS matrix and Nd(3+) were also observed. The IR emission of Nd-PSS films at 1076 rim ((4)F(3/2) -> (4)I(11/2)) present constant efficiency, independent on Nd(3+) concentration. The Judd-Ofelt theory was employed to analyze radiative properties. The excitation spectra prove the energy transfer between the polymeric matrix and Nd(3+). Complex impedance data was used to probe relaxation processes during the charge transport within the polymeric matrix. (C) 2008 Elsevier B.V. All rights reserved.

Temperature dependence of molecular dynamics and supramolecular aggregation in MEH-PPV films: A solid-state NMR, X-ray and fluorescence spectroscopy study

This article presents an investigation of the temperature induced modification in the microstructure and dynamics of poly[2-methoxy-5-(2`-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) cast films using Wide-Angle X-ray Scattering (WAXS), solid-state Nuclear Magnetic Resonance (NMR), and Fluorescence Spectroscopy (PL). MEH-PPV chain motions were characterized as a function of temperature by NMR. The results indicated that the solvent used to cast the films influences the activation energy of the side-chain motions. This was concluded from the comparison of the activation energy of the toluene cast film, E(a) = (54 +/- 8) kJ/mol, and chloroform cast film, E(a) = (69 +/- 5) kJ/mol, and could be attributed to the higher side-chain packing provided by chloroform, that preferentially solvates the side chain in contrast to toluene that solvates mainly the backbone. Concerning the backbone mobility, it was observed that the torsional motions in the MEH-PPV have average amplitude of similar to 10 degrees at 300 K, which was found to be independent of the solvent used to cast the films. In order to correlate the molecular dynamics processes with the changes in the microstructure of the polymer, in situ WAXS experiments as a function of temperature were performed and revealed that the interchain spacing in the MEH-PPV molecular aggregates increases as a function of temperature, particularly at temperatures where molecular relaxations occur. It was also observed that the WAXS peak associated with the bilayer spacing becomes narrower and its intensity increases whereas the peak associated with the inter-backbone planes reduces its intensity for higher temperatures. This last result Could be interpreted as a decrease in the number of aggregates and the reduction of the interchain species during the MEH-PPV relaxation processes. These WAXS results were correlated with PL spectra modifications observed upon temperature treatments. (C) 2008 Elsevier Ltd. All rights reserved.

TEM, XRD and AFM study of poly(o-ethoxyaniline) films: new evidence for the formation of conducting islands

The existence of conducting islands in polyaniline films has long been proposed in the literature, which would be consistent with conducting mechanisms based on hopping. Obtaining direct evidence of conducting islands, however, is not straightforward. In this paper, conducting islands were visualized in poly(o-ethoxyaniline) (POEA) films prepared at low pH, using Transmission Electron Microscopy (TEM) and atomic force spectroscopy (AFS). The size of the islands varied between 67 and 470 angstrom for a pH=3.0, with a larger average being obtained with AFS, probably due to the finite size effect of the atomic force microscopy tip. In AFS, the conducting islands were denoted by regions with repulsive forces due to the double-layer forces. On the basis of X-ray diffraction (XRD) patterns for POEA in the powder form, we infer that the conducting islands are crystalline, and therefore a POEA film is believed to consist of conducting islands dispersed in an insulating, amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasi-one dimensional variable range hopping (VRH) mechanism.