Synthesis of β-Mo(2)C thin films

Thin films of stoichiometric β-Mo(2)C were fabricated using a two-step synthesis process. Dense molybdenum oxide films were first deposited by plasma-enhanced chemical vapor deposition using mixtures of MoF(6), H(2), and O(2). The dependence of operating parameters with respect to deposition rate and quality is reviewed. Oxide films 100-500 nm in thickness were then converted into molybdenum carbide using temperature-programmed reaction using mixtures of H(2) and CH(4). X-ray diffraction confirmed that molybdenum oxide is completely transformed into the β-Mo(2)C phase when heated to 700 °C in mixtures of 20% CH(4) in H(2). The films remained well-adhered to the underlying silicon substrate after carburization. X-ray photoelectron spectroscopy detected no impurities in the films, and Mo was found to exist in a single oxidation state. Microscopy revealed that the as-deposited oxide films were featureless, whereas the carbide films display a complex nanostructure.     

Preparation and characterization of poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonate) composite thin films highly loaded with platinum nanoparticles

In this work, we propose a simple and efficient, low-temperature (∼120 °C) process to prepare transparent thin films of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) loaded with high concentration (up to 22.5 wt%) of platinum (Pt) nanoparticles. Firstly, an improved polyol method was modified to synthesize nano-sized (∼5 nm) and mono-dispersed Pt particles. These nanoparticles were incorporated into the matrix of PEDOT:PSS thin films via a spin coating/drying procedure. The electrochemical activities of the PEDOT:PSS thin film modified electrodes with respect to the I⁻/I₃⁻ redox reactions were investigated. It was found that the modified electrode of PEDOT:PSS thin film containing 22.5 wt% Pt exhibited the electrochemical activity comparable to the conventional Pt thin film electrode, suggesting that this electrode has good potential to serve as a counter electrode in dye-sensitized solar cells.     

Swift heavy ion induced ordering and piezoelectric β-phase in poly(vinylidene fluoride)

Ion flux dependent swift heavy ions (SHI) induced structural changes have been reported for pristine poly(vinylidene fluoride) (PVDF). Ordering phenomena has been observed first followed by its transformation from α to β-form (polar metastable piezoelectric phase). The ordering of (020) plane become prominent at higher ion flux SHI irradiation and its further increase induces structural change from α to β phase as revealed by XRD and FTIR analyses. Structural changes are also supported by morphological evidence and thermal studies before and after SHI irradiation.     

Growth, electrical and structural characterization of β-GaSe thin films

GaSe thin films were deposited onto the glass substrates kept at 200° and 300°C by the thermal evaporation of GaSe crystals under the pressure of 10^–5 Torr. X-ray analysis of the films revealed that films grown at 200°C are amorphous in nature while the films grown at 300°C are polycrystalline -GaSe. The temperature dependent electrical conductivity measurements in the region of 320–100 K for the films grown at 300°C showed that the transport mechanisms are the thermionic emission of charged carriers and the variable range hopping above and below 180 K, respectively. Space charge limited current (SCLC) studies have also been performed on these films through the current-voltage measurements at different temperatures and a dominant hole trap at 0.233 eV from the top of the valance band with a trap density of 1.6 × 10¹¹ cm^–3 is identified.     

High resolution transmission electron microscopic observation of β-Sn thin films

Thin films of β-Sn were studied by high resolution transmission electron microscopy (HRTEM). Diffraction patterns and experimental images agreed with those calculated on the basis of the known crystal structure of β-Sn. By matching the observed images to those calculated, the thicknesses of the films were estimated. Defects were observed as illustrated by a high resolution image of a [100] tilt grain boundary (Σ = 13, θ = 27°). The 20 nm thick films were found to be covered by a carbonaceous deposit. The presence of small clusters of β-Sn in the amorphous contamination layers covering the films was also revealed by HRTEM and by their conversion into SnO₂ particles in the electron beam.     

Dielectric behaviour of thin films of β-PVDF/PZT and β-PVDF/BaTiO3 composites

Thin films of the composites formed between poly(vinylidene fluoride) (PVDF) and lead zirconium titanate (PZT) and also barium titanate with 0–3 connectivity, have been obtained by dispersion of the ceramic powder in a solution of PVDF in dimethylacetamide DMA. Evaporation of the solvent at 65 °C allowed crystallization of PVDF predominantly in the polar phase, regardless of the amount of PZT or BaTiO₃ powder added upto 40 vol %. The relative permittivity and loss index values were determined for the pure components and for the composites with different ceramic contents, in the frequency range of 100 Hz to 13 MHz. An increase in PZT or BaTiO₃ content resulted in an increase in the relative permittivity of the composites, and the experimental results are shown to be in good agreement with those calculated from the theoretical expression of Yamada et al. [1]. The de electrical conductivity of composites with different compositions was also determined.     

Electrical properties of γ-CuCl thin films

The electrical properties of thin film CuCl, a wide band gap material with potential applications in the optoelectronic industry, has been studied using admittance spectroscopy in the frequency range 10 mHz–1 MHz and temperature range 280–400 K. The electrical conductivity of CuCl films was found to be mainly ionic and the temperature dependency follows the Arrhenius relationship. The power-law exponent of the AC dispersive regimes was found to be almost temperature independent. Further to this, DC electronic hole conductivity of the order of 2.3 × 10⁻⁷ S/cm was deduced to be in coexistence with Cu⁺ ionic conductivity using irreversible electrodes (Au), while a total conductivity of the order of 6.5 × 10⁻⁷ S/cm was obtained using reversible electrodes (Cu) at room temperature.     

The intergranular embrittlement of Cu-AI-Ni β-phase alloys

Intergranular embrittlement in the Cu-Al-Ni -phase alloys has been investigated. Results of various experiments, which included an Auger electron spectroscopic analysis of freshly fractured grain boundary surfaces, lead to the conclusion that impurities do not play any significant role in the intergranular embrittlement of these alloys.     

An investigation about thin films of poly[2-methoxy-5-(2′-ethyl-hexyloxy) phenylene vinylene] (MEH-PPV) prepared by Langmuir-Schaefer technique

The Langmuir monolayer behaviour of poly[(2-methoxy-5-(2-ethyl-hexyloxy) phenylene vinylene] (MEH-PPV) conducting polymer was investigated at air-water interface at different subphases containing anions. A uniform deposition of MEH-PPV monolayers was shown by UV-visible, electrochemical techniques, where the influence of anions on redox properties was investigated by cyclic voltammetric surveying. The nature of anions revealed significant changes in redox properties of the MEH-PPV LS films. The photoelectrochemical response of MEH-PPV LS conducting polymer was also investigated at length.     

Nickel β-diketonate complexes as precursors for the photochemical deposition of nickel oxide thin films

In this paper we report the utilization of amorphous films of Ni(II) diketonate complexes as precursors for the direct photochemical deposition of thin films of nickel oxides. The UV photolysis of amorphous thin solid films of Ni(PhCOCHCOPr)₂ results in the loss of all ligands from the coordination sphere. The acetylacetone derivative was chosen for the solid state photochemistry because the presence of the long carbon chains or highly branched hydrocarbons substituents, lowers the intermolecular interactions and allows the formation of high quality films upon spin-coating. The surface morphology of the films was observed by scanning electron microscopy and showed excellent quality without islands or other imperfections. The formation of NiO was determined by X-ray difraction and Auger spectroscopy analysis. The photochemical deposition of patterns of NiO was shown to be compatible with standard lithographic techniques by the lithography of 100 × 2 m lines.     

Isothermal crystallization kinetics of poly(vinylidene fluoride) in the α-phase in the scope of the Avrami equation

Isothermal melt crystallization of poly(vinylidene fluoride) (PVDF) at different crystallization temperatures was studied by differential scanning calorimetry. Analysis by the two different approaches of the Avrami equation was performed: first the classical double logarithmic approximation was used, but a non-linear least squares search showed to clearly improve the fit of the model to the experimental isotherms. The differences found by both methods in the Avrami parameters are discussed. The limitation of the Avrami equation in this polymer has to do not only with the fitting procedure to determine the parameters but also with the lack of a consistent physical interpretation of their temperature evolution. The melting behavior of the samples was analyzed and an equilibrium melting temperature of 190.9 °C was obtained by the Hoffmann–Weeks extrapolation. The samples crystallize in a spherulitic structure, as observed by optical microscopy with polarized light (OMPL). Lauritzen–Hoffmann theory was applied to analyze the crystallization kinetics and the Regime III was found for the crystallization of α-PVDF.     

Fabrication of flexible conductive films derived from poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) (PEDOT:PSS) on the nonwoven fabrics substrate

In this research, conducting poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) (PEDOT:PSS) aqueous dispersion was synthesized at first via chemical oxidative polymerization and followed by mixing it with poly(styrene-r-butyl acrylate) P(St-BA) aqueous latex, creating a conductive material with outstanding stretchability. The elastic conductive composite were then film formed on the glass and poly(ethylene terephthalate) (PET) nonwoven fabric substrate by spin coating and dip coating, respectively. Composite films with various contents of PEDOT:PSS polymer (10–100 wt.%) had been prepared. From the conductivity measurements, the conductivity was still kept as high as 88 S cm⁻¹ even the PEDOT:PSS content was lowered to 10 wt.%. Furthermore, the elasticity of conductive films on the PET-nonwoven fabric substrate was evaluated by the 180° bending test repeating 100 times. With introducing soft P(St-BA) material in the PEDOT:PSS phase, the surface resistance increased merely 3–6 times after bending 100 times, while the surface resistance for pure PEDOT:PSS film could reach 18–20 times.     

Metal-organic chemical vapor deposition of β-In2S3 thin films using a single-source approach

Dithioimidobisdiisopropylphosphinato indium chloride In[(SPⁱPr₂)₂N]₂Cl has been shown to be an effective single-source precursor for the deposition of indium sulfide films by aerosol-assisted chemical vapor deposition (AACVD). X-ray powder diffraction (XRPD) studies indicated that polycrystalline -In₂S₃ films with the tetragonal phase have been deposited on glass substrates (425–475 °C). The morphology of films was confirmed by scanning electron microscopy (SEM). Energy dispersive X-ray analysis (EDAX) indicates the presence of indium and sulfur.     

Mechanical properties of nanocomposite metal–ceramic thin films

Thin film composites consisting of metallic nanocrystals embedded in an insulating host have been synthesized using alternating-target pulsed laser deposition of Ni and Al₂O₃ on silicon (100) substrate. The evaluation of structural quality of the thin film composites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number contrast has revealed the formation of a biphase system with thermodynamically driven segregation of Ni and alumina during pulsed laser deposition. The best hardness values of the thin film composites, measured using nanoindentation techniques, were found to be 20–30% larger than pure alumina films fabricated under identical conditions. Fracture toughness measurements of the composite showed slight toughening due to embedding of Ni nanoparticles.     

Effect of annealing on optical properties of thin films with β-FeSi2 quantum dots

Reactive deposition epitaxy was used to prepare β-FeSi₂ nanodots on a Si(001) surface. The influence of annealing on optical properties has been studied. Annealing increases the particle size and decreases absorption. The indirect optical transition at 0.84-0.89 eV dominates the absorption spectra below 1.3-1.5 eV. The film with smaller nanoparticles exhibits higher absorption with direct optical transition energies in the 1.3-1.5 eV range. It suggests that direct transition is dominant only in small (around 3 nm diameter) β-FeSi₂ nanodots. Larger particles are dominated by the indirect optical transition.     

Structural and optical properties of Cd x Zn(1 − x)Te thin films

Seven Cd _x Zn_{(1 ? x} Te solid solutions with x = 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 were synthesized by fusing stoichiometric amounts of CdTe and ZnTe constituents in silica tubes. Each composition was used in the preparation of a group of thin films of different thicknesses. Structural investigation of the obtained films indicates they have a polycrystalline structure with predominant diffraction lines corresponding to (111) (220) and (311) reflecting planes, which can be attributed to the characteristics of growth with the (111) plane. The optical constants (the refractive index n, the absorption index k, and the absorption coefficient α) of Cd _x Zn_{(1 \s -x)} Te thin films were determined in the spectral range 500–2000 nm. At certain wavelengths it was found that the refractive index, n, increases with increasing molar fraction, x. It was also found that plots of α² (hv) and α^1/2 (hv) yield straight lines, corresponding to direct and indirect allowed transitions respectively obeying the following two equations: $$\begin{gathered} E_g^d = 1.583 + 0.277x + 0.197x^2 \hfill \\ E_g^{ind} = 1.281 + 0.111x + 0.302x^2 \hfill \\ \end{gathered}$$      

X-ray and electron microscopical studies of thin films of (Cd1−xZnx)S solid solution

A series of (Cd_1–x Zn _x )S powders phosphors and thin layers prepared by thermal evaporation of solid solution were studied. The phosphors used were 41% ZnS: 59% CdS with a cobalt concentration from 0 to 0.325%. The analysis of the structure of films of different thicknesses using X-ray diffraction technique confirms that the calculated relative intensities of the planes show considerable differences from the experimental results. For film thicknesses 70 nm thea axis is normal to the substrate, while at greater thicknesses (273 nm) thec axis is practically normal to the substrate. The effect of the electron beam on the solid solution indicates that layers decomposed leaving the grain boundaries decorated by metallic cadmium and zinc particles.     

In vitro and in vivo degradation of poly(l-lactide-co-glycolide) films and scaffolds

Poly(l-lactide-co-glycolide) (PLGA) was synthesized using a biocompatible initiator, zirconium acetylacetonate. In vitro and in vivo degradation properties of PLGA films (produced by solvent casting, 180 μm thick) and PLGA scaffolds (produced by an innovated solvent casting and particulate leaching, 3 mm thick) were evaluated. The samples were either submitted for degradation in phosphate buffered saline (PBS) at 37 °C for 30 weeks, or implanted into rat skeletal muscles for 1, 4, 12, 22 and 30 weeks. The degradation was monitored by scanning electron microscopy, atomic force microscopy, weight loss, and molecular weight changes (in vitro), and by microscopic observations of the materials’ morphology after histological staining with May-Grunwald-Giemsa (in vivo). The results show that the films in both conditions degraded much faster than the scaffolds. The scaffolds were dimensionally stable for 23 weeks, while the films lost their integrity after 7 weeks in vitro. The films’ degradation was heterogenous—degradation in their central parts was faster than in the surface and subsurface regions due to the increased concentration of the acidic degradation products inside. In the scaffolds, having much thinner pore walls, heterogenous degradation due to the autocatalytic effect was not observed.