Mónica M. Gómez

Thickness Dependence of the Optical Properties of Sputter Deposited Ti Oxide Films

Abstract Amorphous and crystalline Ti oxide films were obtained by reactive magnetron sputtering onto substrates at different temperatures. Optical constants of the films were determined from spectrophotometric measurements of reflectance and transmittance. The amorphous films had a band gap of ∼3.4 eV and a wide absorption tail extending to lower energies. The crystalline films displayed a band gap of 3.3–3.35 eV and a more narrow absorption tail. The optical constants were dependent on film thickness. The crystalline films showed evidence of structural inhomogeneities leading to diffuse scattering in the thicker films as well as to a grading of the refractive index.

Photo-electrocatalytic degradation of 4-chlorophenol over sputter deposited Ti oxide films

Abstract Ti oxide films with thicknesses in the 1.9–8.0 μm range were sputter deposited onto electrically conductive transparent glass substrates. X-ray diffraction indicated a dominating rutile structure. The films were used to investigate photo-electrocatalytic degradation of 4-chlorophenol in water solution, employing a specially designed reactor. UV light was used for the photocatalysis, and a bias potential was applied for avoiding electron-hole recombination. The photocurrent and the kinetics of the catalytic reaction were tested with potentiostatic and spectrophotometric measurements. The reaction products were investigated using different arrangements of a Ti oxide working electrode and a Pt counter electrode. UV irradiation through the glass substrate yielded an enhancement of the reaction kinetics for increased film thicknesses and applied bias potential.

Nanocrystalline Ti-oxide-based solar cells made by sputter deposition and dye sensitization: Efficiency versus film thickness

Nanocryst. TiO2-based films with a special penniform microstructure were prepd. by reactive d.c. magnetron sputtering followed by dye sensitization. The films were integrated in a solar cell configuration and were able to yield a higher photocurrent than sol-gel-produced titanium oxide-based films of similar thickness. The photoelec. conversion efficiency reached 4% in ∼10-μm-thick sputter deposited films.

Photoelectrochemical studies of dye-sensitized polycrystalline titanium oxide thin films prepared by sputtering

Abstract Titanium oxide thin films were prepared by reactive DC magnetron sputtering of Ti in O 2 +Ar onto SnO 2 :F coated glass. A dye consisting of Cis-dithiocyanato- N -bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) was incorporated by dipping the films into a solution of the dye in ethanol. The amount of dye incorporation was found to be highly dependent on the microstructure and the thickness of the film, as apparent from optical measurements. Incident photon-to-current efficiency was studied as a function of sputtering parameters using a three-electrode cell with an electrolyte consisting of an aqueous 0.1 M KI solution purged with nitrogen as well as using a two-electrode system with acetonitrile with a LiI/I 2 solution as the electrolyte.

Reactively Sputter-Deposited Titanium Oxide Coatings with Parallel Penniform Microstructure

Reactively Sputter Deposited Titanium Oxide Coatings with Parallel Penniform Microstructure

Photoelectrochemical effect in dye sensitized, sputter deposited Ti oxide films : The role of thickness-dependent roughness and porosity

Ti oxide films were made by reactive DC magnetron sputtering onto electrically conducting glass substrates. The films were dye sensitized with an Ru complex, thereby yielding nanocrystalline solar cells. We investigated the microstructure of the films by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and cyclic voltammetry on viologen-containing samples. The internal surface area was enhanced with increasing film thickness, and this property could be correlated with an enlarged photoelectric conversion efficiency.

Sputter-deposited Ti oxide films used for photoelectrocatalytic degradation of 4-chlorophenol

Ti oxide films were made by reactive magnetron sputtering under conditions yielding “penniform” structures with large porosity. X-ray diffractometry showed that rutile-like and anatase-like films were produced depending on the oxygen content in the sputter plasma. Rutherford backscattering spectrometry documented some oxygen overstoichiometry. Spectral optical measurements were used to analyze the absorption around the fundamental band gap and to give evidence of some hydration and hydroxylation in the films. The various Ti oxide films were brought in contact with 4-chlorophenol (4-CP), whose photo-electrocatalytically induced degradation under ultraviolet irradiation was investigated in a reactor allowing optical probing of 4-CP as well as of intermediate reaction products such as benzoquinone. A rutile-like structure was conducive to the degradation of 4-CP, which can be reconciled with the band gap being suitable for producing photoinduced holes capable to effecting oxidation of the pollutant.

Adsorption of As(V), Cd(II) and Pb(II), in multicomponent aqueous systems using activated carbons

  This paper studies the use of two activated carbon samples made of cocoa pod husk (CPH-AC) and one commercial activated carbon sample in the adsorption of As(V), Cd(II) and Pb(II) from multicomponent synthetic solutions and from the Puyango-Tumbes River water, a river located in northwest Peru. The characterization of the activated carbon samples was conducted. The CPH-AC samples exhibited a specific surface area (SBET) between 709 and 1117 m2/g and a pH point of zero charge (pHPZC) between 4.4 ± 0.2 and 5 ± 0.2, while the commercial material gave an SBET value of 775 m2/g and a pHPZC value of 7.6 ± 0.1. All the evaluated samples displayed the capacity to adsorb As(V), Cd(II) and Pb(II) from both aqueous systems. The adsorption efficiency for Pb was outstanding reaching the value of 89%. A pseudo-second order kinetic model was satisfactorily applied for most of the activated carbon samples.

Bactericidal, structural and morphological properties of ZnO 2 nanoparticles synthesized under UV or ultrasound irradiation

Nanoparticles of ZnO2 were synthesized by a sol‐gel method using Zn(CH3COO)2 and H2O2 in an aqueous solution exposed to either ultraviolet (UV) or ultrasound irradiation. X-ray diffraction and scanning electron microscopy showed that the nanostructures consisted of spherical blackberry-like clusters. Nanoparticles fabricated by using UV irradiation had smaller sizes and narrower size distributions than nanoparticles prepared by using ultrasound. Bacillus subtilis (B. subtilis), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used as test microorganisms, and the antibacterial activity of the ZnO2 nanoparticles was studied by use of the well diffusion agar bacteriological test. ZnO2 nanoparticles synthetized using UV had the best antibacterial properties. The inhibition zone was largest for B. subtilis but was present also for S. aureus and E. coli.

Alternating Current Characterization of Sputter Deposited Ti Oxide Films

Ti oxide films with varying stoichiometries and different crystal structures were prepared by reactive direct current magnetron sputtering in oxygen-depleted plasmas. The complex dielectric permittivity was determined in the 10-3 -107 Hz range from measurements using a capacitor configuration. The real and imaginary parts of displayed power-law dependences from ~10 Hz up to a value between 1 and 10 kHz. Our data could be rationalized in terms of a model for screened hopping of vacancy-induced charge carriers, but the details remain poorly understood.