José G. Bañuelos

Thin films of polyaniline–polyacrylic acid composite by chemical bath deposition

Polyaniline (PANI)–polyacrylic acid (PAA) composite thin films were deposited at room temperature on glass and polymethyl methacrylate substrates by introducing these into a freshly prepared chemical bath of HCl, PAA, aniline monomers and (NH4)2S2O8. Compared to the single PANI films, which were obtained from the same bath constitution but without PAA solution, the composite films showed a red shift at the maximum optical transmittance peak and a slightly lower electrical conductivity. Fourier transform infrared spectroscopy studies of the PANI composite thin films indicated the presence of the acid-base reaction product between PANI and PAA, as well as PAA molecule incorporation in the films. Atomic force microscopy analysis also showed morphologic and mechanical elasticity differences between the single PANI film the composite films deposited by the chemical bath method.

Morphological, optical, and nonlinear optical properties of fluorine-indium-doped zinc oxide thin films

Chemically sprayed fluorine-indium-doped zinc oxide thin films (ZnO:F:In) were deposited on glass substrates. A mixture of zinc pentanedionate, indium sulfate, and fluoride acid was used in the starting solution. The influence of both the dopant concentration in the starting solution and the substrate temperature on the transport, morphological, linear, and nonlinear optical (NLO) properties were fully characterized with atomic force microscopy (AFM), scanning-electron microscopy (SEM), UV-VIS, and photoluminescence (PL) spectroscopies, and the second-harmonic generation (SHG) technique, respectively. A decrease in the resistivity was observed for increasing substrate temperatures, reaching a minimum value of 1.2 × 10−2 Ω cm for samples deposited at 500°C. The surface morphology was also dependent on the dopant concentration in the starting solution and on the substrate temperature. The X-ray diffraction (XRD) patterns revealed that the ZnO:F:In thin solid films are polycrystalline in nature fitting with a hexagonal wurtize type and showing (002) preferential growth for all of the studied samples. The optical transmittance of these films was found to be higher than 80%, from which the optical band gap of these samples was determined. Finally, a clear dependence on the quadratic NLO properties of the developed semiconducting ZnO:F:In thin films with the substrate temperatures was established, where huge x(2)-NLO coefficients on the order of x33(2) = 37 pm V−1 were measured for high substrate temperatures.

Thermal spikes in Ag/Fe and Cu/Fe ion beam mixing

Abstract Ion beam mixing has been studied since 1980, and since then a lot of experimental and theoretical work has been done and knowledge has been gathered. Nevertheless, there are still many fundamental aspects that need to be clarified and with that aim many experiments need to be performed. Copper and iron are miscible in the liquid state, while silver and iron are not. However, both systems are thermally immiscible in the solid state. In order to have an insight into the importance of mixing within thermal spikes during ion beam irradiation, we deposited Cu/Fe and Ag/Fe bilayers onto Si substrates and irradiated them at room temperature with 2 MeV Cu and 2.5 MeV Au ions. A combination of Rutherford backscattering spectrometry (RBS) and atomic force microscopy (AFM) was used to analyze the atomic transport at the interface and the morphology changes of the samples. From the element profiles at the interface we conclude a mixing efficiency, which is indeed larger than the prediction of the ballistic model in the Cu/Fe system and smaller in the Ag/Fe system. Since ballistic mixing is expected in any case, we argue that demixing and phase separation in the Ag/Fe system occur in the thermal spike phase of the cascade as a consequence of the positive heat of mixing. Further mixing does occur in the thermal spike in the Cu/Fe system and they remain mixed even at the solid state because of the high cooling rate. In addition, ion irradiation induces a large surface roughening of the Ag and Cu top layers as proven by AFM. This effect is important for the correct interpretation of the results. Furthermore, this recrystallization affects also the interface, producing a rough interface, that appears in the RBS spectra as an atomic ‘diffusion’ at the interface.

Nonlinear optical performance of poled liquid crystalline azo-dyes confined in SiO2 sonogel films

The catalyst-free sonogel route was implemented to fabricate highly pure, optically active, hybrid azo-dye/SiO2-based spin-coated thin films deposited onto ITO-covered glass substrates. The implemented azo-dyes exhibit a push–pull structure; thus chromophore electrical poling was performed in order to explore their quadratic nonlinear optical (NLO) performance and the role of the SiO2 matrix for allowing molecular alignment within the sonogel host network. Morphological and optical characterizations were performed to the film samples according to atomic force microscopy (AFM), ultraviolet-visible (UV-Vis) spectroscopy and the Maker-fringe technique. Regardless of absence of a high glass transition temperature (T g) in the studied monomeric liquid crystalline azo-dyes, some hybrid films displayed stable NLO activity such as second harmonic generation (SHG). Results show that the chromophores were homogeneously embedded within the SiO2 sonogel network, where the guest–host molecular and mechanical interactions permitted a stable monomeric electrical alignment in this kind of environment.

SHG-Activity of Polar Nano-Structures of LC-RED-PEGM-7 Based Sono-Gel Hybrid Materials

The synthesis of sol-gel materials induced by ultrasonic action (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic and optical properties. A newly synthesized liquid crystalline mesogen (named here RED-PEGM-7) was introduced as dopant specie within the SiO2 matrix in order to create an active nonlinear optical hybrid material at room temperature. A comparative characterization of the structural properties between a pure reference sample and several doped composites was performed by X-ray diffraction (XRD) and atomic force microscopy (AFM); where, an optimal dissolution concentration of tetraethoxysilane (TEOS) and the liquid crystalline (LC) mesogen, to obtain good mechanical and nonlinear optical properties in thin film layers has been found.

Corrosion Resistance of AA2024-T3 Coated with Graphene/Sol-Gel Films

Graphene is a two-dimensional network of carbon atoms with optimal thermal, electronic and chemical stability properties that promise different and versatile applications in various fields including the protection of metals from corrosion phenomena. For this reason in this paper graphene was employed and studied as an agent dopand incorporated into hybrid sol-gel coatings to enhance their resistance in saline media and to improve the durability of these films. Graphene was obtained by using an electrochemical method involving oxidation and reduction reactions in a sodium lauryl sulfate solution. On the other hand, the hybrid sol-gel was synthesized from the combination of inorganic and organic precursors, zirconium (IV) n-propoxide (TPOZ) and 3-glycidoxipropiltrimetoxysilane (GLYMO) respectively. In order to obtain the coating system (graphene/sol-gel) two different procedures were applied onto clean aluminum plates: a) the electrodeposition of graphene and b) the graphene-doped sol-gel coating. Differential scanning calorimetry, scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the results, which demonstrate an improvement of the corrosion properties of the films with the incorporation of graphene compounds.

Optical Properties of Fluorinated Bent-Core Liquid Crystals Confined in Anodic Alumina Nanotubes

In the present work, oxalic amorphous porous anodic alumina membranes with highly ordered porous arrays and average nanometric porous dimensions of 70 nm in diameter and 17 microns in depth (nanotubes) were prepared and successfully used as host matrix for fluorinated bent-core liquid crystals. Atomic force microscopy studies were performed on the organic-inorganic hybrid samples in order to explore surface morphology and optimal insertion of these liquid crystalline (LC)-compounds into this environment. The quadratic nonlinear optical (NLO) and spectroscopic properties of the implemented mesogen with the nanotube-like confinement were systematically studied in order to evaluate its optical performance. Bent core molecules have shown interesting optical properties which have not yet been intensively investigated in solid-state hybrid structures. Hence, the obtained hybrid composites represent a promising field of investigation in the route to functional bent-core based materials, where different bent-core mesomorphic structures can be obtained and are of interest for new and improved applications in nanotechnology.

Growth of C 60 Fullerene Films on Semiconductor Surfaces

We report on a study of vacuum-deposited thin films of C 60 fullerene on Si (100) and InP (100) semiconductor surfaces. The film morphology and C 60 —substrate interactions were investigated by using atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). For the film deposition, both patterned Si aand InP surfaces were used. It was found that the stronger interactions occur between C 60 molecules and Si surface, than between C 60 molecules and InP surface. On InP surface with microrelief of parallel V-grooves oriented in [011] direction, C 60 films grow preferentially above the groove walls, with C 60 grains arrayed in the direction perpendicular to the groove axis.