S. Jiménez-Sandoval

High transmittance CdO thin films obtained by the sol-gel method

Abstract CdO thin films have been prepared by the sol-gel technique, from a novel precursor solution based on Cd(OOCCH 3 ) 2 ·2H 2 O, ethylene glycol, glycerol, and triethylamine, on slide glass substrates. The films were annealed in open atmosphere at 200°C and were characterized by UV-VIS spectroscopy, X-ray diffraction and atomic force microscopy. The CdO thin films obtained have a high polycrystalline quality and, outstandingly, they show a transmission of 95% at a wavelength of 600 nm, which increases to virtually 100% from 700 to 1100 nm. The indirect and direct band gap energy values were found to be 2.06 and 2.59 eV, respectively. The resistivity of the films was 2×10 −2 Ω cm.

A study of the dielectric characteristics of aluminum oxide thin films deposited by spray pyrolysis from Al(acac)3

Abstract The dielectric characteristics of aluminum oxide thin films deposited by the spray pyrolysis technique are reported. The films were deposited with different molarities from a spraying solution of aluminum acetylacetonate and N , N -dimethylformamide. The films were deposited on silicon substrates at temperatures ranging from 450 to 650°C. The addition of water mist during the deposition process led to a remarkable improvement of the overall characteristics of the films. Films with excellent dielectric characteristics and low surface roughness were obtained. The results of the characterization indicate that there is a significant presence of carbon in the films. This carbon in the films modifies the electrical conduction characteristics leading to behavior similar to that displayed by off-stoichiometric silicon oxide (SiO 2 ) films. It is observed that the overall resistivity of the film decreases when both the molarity of the solution and the deposition temperature increase. This behavior correlates with the increase in the amount of carbon remaining inside the film. The films as deposited have a surface state density in the range of 10 11 1/eV-cm 2 and are able to stand electric fields higher than 5 MV/cm without observing dielectric breakdown.

Influence of annealing temperature on the formation and characteristics of sol-gel prepared ZnO films

ZnO thin films have been obtained by the sol-gel method from a Zn(OOCCH3)2 precursor on soda lime glass and silicon wafer substrates. The films, obtained by a single dipping procedure, were characterized by Fourier transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies, atomic force microscopy, x-ray diffraction and ellipsometry measurements. Thermally untreated and annealed (100–450 °C) films were studied in order to analyze the influence of temperature on the formation and properties of the ZnO coatings. Remarkably, these results indicate that ZnO forms at considerably lower temperatures than 450 °C, which is usually considered in the literature as a reference temperature for the formation of ZnO. Thus, a sharp absorption edge of ZnO at ∼380 nm can be easily observed in the UV-vis spectra of films annealed at 200 and 300 °C, accordingly, and the FTIR data indicate the absence of organic groups at these temperatures. The atomic force microscopy results show a uniform, void-free surface...

Raman study of copper and iron oxide particles embedded in an SiO2 matrix

The structure of heat-treated sol–gel-made SiO2 samples containing copper or iron in various amounts was studied using Raman spectroscopy and x-ray diffraction. The treatments were in air in the temperature range 200–800 °C. Copper and iron concentrations were in the range 7–55 wt%. It was found that in the samples containing copper, the metal is mainly dissolved in the SiO2 network when the thermal treatment is at low temperatures. For higher annealing temperatures, first a copper silicate is formed and then most of the copper forms cupric oxide particles at temperatures of about 800 °C. In samples containing iron, the formation of particles with nanometric size of the γ-Fe2O3 (maghemite) phase is observed after annealing at 500 °C. At 800 °C the maghemite phase is transformed into the stable hematite (α-Fe2O3) phase. Copyright

Raman-scattering and structure investigations on porous SiC layers

Raman scattering spectroscopy, scanning electron microscopy, and scanning acoustic microscopy were studied on porous SiC layers prepared by different technological routes and subjected to reactive ion treatment. The Raman spectra revealed a number of features specific for nanocrystallite materials, which can be used for characterization and diagnostics of porous SiC layers for technological applications.

Micro-Raman spectroscopy: a powerful technique for materials research

Abstract Since the development of the holographic notch filters during the last decade and novel detectors such as charge coupled devices, Raman spectroscopy instrumentation has evolved rapidly, so that modern spectrometers are orders of magnitude faster, present much lower signal-to-noise ratio and simplified optics than their predecessors. These advances have also had a significant effect in the construction of novel micro-Raman-dedicated spectrometers that currently use lasers with powers of the order of a few tens of mW. In the present work, a brief overview of current Raman spectroscopy technology in traditional spectrometers and of different applications of modern micro-Raman spectroscopy to the study of materials, ranging from epitaxial semiconductor thin films of interest to the optoelectronics industry, to biomaterials of interest to medical science, is presented. An emphasis is given to different acquisition modes that are possible when the excitation laser light is passed through a microscope objective and the sample is placed in a computer controlled XY stage.

CD SELF-DOPING OF CDTE POLYCRYSTALLINE FILMS BY CO-SPUTTERING OF CDTE-CD TARGETS

Cadmium self-doped CdTe polycrystalline films were grown on Corning glass substrates at room temperature by cosputtering from a CdTe–Cd target. The electrical, structural, and optical properties of the films were analyzed as a function of the Cd concentration. Films with a stoichiometric composition, and slightly below and above it, were prepared. In films where the Te exceeds 50 at. %, it is found segregation of Te and its electrical resistivity is about 107 Ω cm. In those with an excess of Cd, the electrical resistivity drops several orders of magnitude, the carrier concentration increases, and the resistivity activation energy drops. From these results, we concluded that using this deposition method, n-type Cd self-doped CdTe polycrystalline films can be produced.

Crystal structure and energy gap of CdTe thin films grown by radio frequency sputtering

We have investigated the influence of structural characteristics on the band gap of rf sputtered CdTe thin films grown at substrate temperatures in the 69–232 °C range. The results of scanning electron microscopy and x‐ray diffraction studies indicated that the films are a polycrystalline mixture of cubic and hexagonal phases with preferential growth of columnar type parallel to the cubic [111] direction. The band gap of the films was obtained from photoreflectance spectroscopy experiments carried out at room temperature. It was found that the films had a band gap larger than that of CdTe single crystals. This result has been correlated with the existence of lattice strain, quantum size effects, and hexagonal phase regions. By using theoretical models it was possible to estimate the contribution to the band gap shift due to strain and quantum size effects obtaining results in good agreement with the experiment. The study of annealed samples indicated that the effects of thermal treatments were to promote ...

Vibrational and optical properties of carbon nitride films prepared by reactive magnetron sputtering

Carbon nitride films were prepared by reactive magnetron sputtering of a graphite target in a nitrogen atmosphere at different pressures and temperatures. The films were characterized by infrared, Raman and ultraviolet-visible spectroscopies, as well as by ellipsometry. We obtained hydrogen-free dark films when a negative bias was applied to the substrates; the samples prepared at room temperature without bias were soft and hydrogen could be detected in their infrared spectra. The most prominent features, between 1000 and 1700 cm-1, in both the Raman and infrared spectra were modelled using two Gaussian curves. As the nitrogen content was varied, the ratio between their areas followed opposite trends in the Raman and the infrared spectra. The presence of hydrogen caused the main feature to absorb more strongly at lower frequencies but did not alter the trend. The presence of six and five membered heteroaromatic rings is suggested to explain the increase of the infrared vibrations associated with double conjugated double bonds. The index of refraction can be correlated with features in the infrared spectra, suggesting that its value increases as the number of carbon and nitrogen double bonds increases. Ion bombardment reduces nitrogen incorporation; it is responsible for the densification of the films and the introduction of several defects that make films prepared under bias more absorbing in the low energy region.

Lanthanide(III) Complexes with 4,5-Bis(diphenylphosphinoyl)-1,2,3-triazolate and the Use of 1,10-Phenanthroline As Auxiliary Ligand

New lanthanide complexes with 4,5-bis(diphenyl)phosphoranyl-1,2,3-triazolate (L(-)), LnL(3).nH(2)O (1-8) and LnL(3)(phen).nH(2)O (9-16) (Ln = La, Ce, Nd, Sm, Eu, Gd, Tb, Er), have been prepared and spectroscopically characterized. The structures of LnL(3).nH(2)O (Ln = La, Ce, Nd, Sm and Gd) were determined by X-ray crystallography. The metal centers exhibit a distorted trigonal dodecahedron coordination environment with two symmetrically O,O-bidentate ligands and one unsymmetrically O,N- ligand attached to the metal; two oxygen atoms from neighboring dimethyl sulfoxide (DMSO) molecules complete the coordination sphere. This unsymmetrical ligand coordination behavior was also identified in solution through (31)P{(1)H} NMR studies. Photoluminescence spectroscopy experiments in CH(2)Cl(2) for both types of complexes containing Eu(III) (6, 14) and Tb(III) (7, 15) exhibit strong characteristic red and green emission bands for Eu(III) and Tb(III), respectively. Furthermore, NdL(3) (phen).5H (2)O (11) displays emission in the near-infrared spectral region ((4)F(3/2) --> (4)F(9/2) at 872 nm and (4)F(3/2) --> (4)F(11/2) at 1073 nm). The complexes containing 1,10-phenantroline exhibit higher quantum yields upon excitation at 267 nm, indicating that this auxiliary ligand promotes the luminescence of the complexes; however, luminescence lifetimes (tau) in this case are shorter than those of the LnL(3).nH(2)O series.