F.F. Castillón

Tungsten nitride films grown via pulsed laser deposition studied in situ by electron spectroscopies

Abstract Tungsten nitride (WNx) films were grown on silicon and glass slide substrates by laser ablating a tungsten target in molecular nitrogen ambient. By in situ Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), the films density, elemental composition and chemical state were determined. Ex situ, the films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Also, the transmittance and resistivity of the film on glass substrates were determined. The results show that the reaction of tungsten and nitrogen is effective; the nitrogen is integrated in the tungsten matrix changing gradually the electronic configuration, chemical states and film properties. Since with this preparation method the obtained films are of high quality, low resistivity and dense, this makes attractive to growth tungsten nitride films for technological applications.

XPS and HRTEM characterization of cobalt-nickel silicide thin films

Abstract We studied by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) films of Co–Ni/p-Si deposited by PLD on Si(100) substrates. They were thermally treated in vacuum to promote silicide formation. By means of XPS in-depth profiles, it was observed that the deposited metal film contains more Co than Ni. The Co and Ni 2p transitions present shifts characteristic of silicide at respective ranges of 778.3–778.6 and 853.2–853.6 eV, while the Si2p transition appears at 99.2–99.5 eV, as determined by XPS. By means of HRTEM, nanocrystalline regions belonging to CoSi2, Ni2Si and NiSi2 structures were identified. Some grains of CoSi2 are large in size, more than 20 nm in diameter, while Ni2Si and NiSi2 nanocrystals are of the order of 10 nm. There are several regions where no crystalline ordering seems to be apparent. The SiO2 layer acted as an effective diffusion barrier suppressing mobility of metal into the Si(100) substrate. The observed tendencies of the Co and Ni concentrations as a function of depth agree with a model of CoSi and NiSi structure separation and subsequent formation of CoSi2 and NiSi2.

Enzymatically synthesized polyaniline film deposition studied by simultaneous open circuit potential and electrochemical quartz crystal microbalance measurements

The chemical and enzymatic deposition of polyaniline (PANI) films by in situ polymerization was studied and the resulting films were characterized. The film formation and polymerization processes were simultaneously monitored by the evolution of the open circuit potential and quartz-crystal microbalance measurements. Different substrates, such as Indium-Tin oxide electrodes and gold-coated quartz-crystal electrodes were used as substrates for PANI deposition. Electroactive PANI films were successfully deposited by in situ enzymatic polymerization at low oxidation potential. The electrogravimetric response of the enzymatically deposited PANI film was studied by cyclic voltammetry in monomer-free acidic medium. The morphology of the films was observed by scanning electron microscopy, revealing a granular structure in enzymatically deposited PANI. The PANI films were also characterized by thermogravimetric analysis, electrochemical impedance spectroscopy, and X-ray photoelectron and Fourier-transformed infrared spectroscopy. The simultaneous use of quartz crystal microbalance and open circuit potential is presented as a very useful technique to monitor enzymatic reactions involving oxidoreductases.

Influence of preparation on the structure and co conversion of γ-Bi2MoO6 catalysts

The effect of treatment conditions during preparation and activation of γ-Bi2MoO6 catalysts was investigated. Catalytic evaluation shows that CO conversion is much higher for catalysts obtained under vapor controlled evaporation conditions (CE) than for standard evaporation catalysts (SE). Characterization results show that preparation under SE conditions induces segregation of Bi2O3 on the surface of Bi2MoO6 catalysts decreasing their catalytic activity. Catalysts treatment under hydrogen reactivates the catalytic properties of SE samples.