W. de la Cruz

Preparation and characterization of SnO2 thin films deposited by spray pyrolysis from SnCl2 and SnCl4 precursors

Abstract Highly transparent and conducting SnO2 thin films have been deposited by spray pyrolysis using SnCl2 and SnCl4 as precursor solutions and NH4F and HF as sources of the doping impurities. The role of various deposition parameters has been studied in detail and the optimum preparation conditions were obtained. A comparative study showed that the samples prepared using SnCl2 as the precursor solution and HF as the source of the doping impurities, present lower values of resistivity than those obtained from a precursor solution of SnCl4 and NH4F as doping solution. SnO2 films with resistivities of about 2.5 × 10−4ωcm and transmittance greater than 90% were obtained in this work. X-ray diffraction measurements indicated that the SnO2 films, prepared from SnCl4, present a preferential growth along the (200) direction whereas the samples prepared from SnCl2 present a tendency to grow preferentially along the (101), (211) and (301) directions.

Copper nitride films produced by reactive pulsed laser deposition

Deposition of copper nitride films is of importance due to its technological applications. Copper nitride thin films are deposited by reactive pulsed laser deposition (nitrogen environments) on silicon substrates at room temperature. The resultant films are in situ characterized by Auger (AES), X-Ray Photoelectron (XPS) and Reflection Electron Energy Loss spectroscopies (REELS). The chemical bond is strongly linked to the stoichiometry, and both can be controlled by the deposition pressure. The mass density achieved for Cu3N is 5.91 g cm−3, close to the theoretical value of 5.84 g cm−3. We conclude that this deposition method offers a means for fine-tuning the properties of copper nitride.

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.

Yttrium nitride thin films grown by reactive laser ablation

Abstract Yttrium nitride thin films were grown on silicon substrates by laser ablating an yttrium target in molecular nitrogen environments. The composition and chemical state were determined with Auger electron, X-Ray photoelectron, and energy loss spectroscopies. The reaction between yttrium and nitrogen is very effective using this method. Ellipsometry measurements indicate that the films are metallic. We attribute this behavior to a small oxygen contamination. Each oxygen atom introduces two additional electrons to the unit cell, resulting in a complex semiconductor–ionic–metallic system. These results are corroborated by first principles total energy calculations of clean and oxygen doped YN.

Beryllium nitride thin film grown by reactive laser ablation

Beryllium nitride thin films were grown on silicon substrates by laser ablating a beryllium foil in molecular nitrogen ambient. The composition and chemical state were determined with Auger (AES), X-ray photoelectron (XPS) and energy loss (EELS) spectroscopies. A low absorption coefficient in the visible region and an optical bandgap of 3.8 eV, determined by reflectance ellipsometry, were obtained for films grown at nitrogen pressures higher than 25 mTorr. The results show that the reaction of beryllium with nitrogen is very effective using this preparation method in producing high quality films.

Morphological evolution of pulsed laser deposited ZrO2 thin films

Morphological evolution of ZrO2 thin films deposited during pulsed laser deposition of Zr in O2 atmosphere has been experimentally studied at two different film deposition temperatures, 300 and 873 K. The roughness exponent, α, the growth exponent, β, the coarsening exponent, 1/z, and the exponent defining the evolution of the characteristic wavelength of the surface, p, for depositions at 300 K amounted to β=1.0±0.1, α=0.4±0.1, 1/z=0.34±0.03, and p=0.49±0.03, whereas for depositions carried out at 873 K amounted to β=0.3±0.3, α=0.4±0.2, and 1/z=0.0±0.2. Experimental error becomes important due to the flat morphology of the films inherent to the deposition technique. The change in the surface topography with the film temperature has been studied with the help of a simple Monte Carlo model which indicates the existence of two different growth regimes: a shadowing dominated growth, occurring at low temperatures, characterized by calculated values β=1.00±0.04, α=0.50±0.04, p=0.46±0.01, and 1/z=0.35±0.02 and ...

Effect of electrode type in the resistive switching behaviour of TiO2 thin films

The influence of the electrode/active layer on the electric-field-induced resistance-switching phenomena of TiO2-based metal?oxide?metal devices (MOM) is studied. TiO2 active layers were fabricated by the reactive rf-sputtering technique and devices were made by sandwiching between several metal electrodes. Three different MOM devices were made, according with the junction type formed between the electrode and the TiO2 active layer, those where Ohmic?Ohmic, Ohmic?Schottky and Schottky?Schottky. The junction type was tested by electrical I?V measurements. It was found that MOM devices made with the Ohmic?Ohmic combination did not show any resistive switching behaviour in contrast with devices made with Ohmic?Schottky and Schottky?Schottky combinations. From a detailed analysis of the I?V curves it was found that transport characteristics are Ohmic for the low-resistance state for all the contacts combinations of the MOM devices, whereas in the high-resistance state it depends on contact combinations and can be identified as Ohmic, Schottky and Poole?Frenkel type. These conduction mechanisms in the low- and high-resistance states suggest that formation and rupture of conducting filaments through the film oxide is the mechanism responsible for the resistance switching.

Beryllium nitride: an alternative material to beryllium for extreme ultraviolet and soft X-ray uses

Abstract Extreme ultraviolet and soft X-ray optical systems require low absorbing materials for many technological applications. In this paper, the optical properties of beryllium nitride (Be3N2) are studied and compared with those of beryllium (Be), a widely used material in this context. Thus, the dielectric function of Be and Be3N2 are determined in the 4–100 eV energy interval by means of reflection electron energy loss spectroscopy. It is found that the absorption coefficient of Be and Be3N2 are similar in the 40–100 eV energies range. Thereafter, the superior chemical stability and mechanical properties of Be3N2 makes it a promising Be substitute as optical material in severe environments.

Growth of beryllium nitride films by pulsed laser deposition; dielectric function determination

Beryllium nitride thin films, which are candidates for optoelectronic applications, have been grown by pulsed laser deposition on silicon substrates. The films were prepared by ablating a beryllium foil in N environment at several pressures and substrate 2 temperatures. Real-time ellipsometric monitoring for the period of deposition were carried out by a multiwavelength ellipsometer in the 1.625(hn(4.405 eV photon-energy range. After its completion, the films were characterized in situ by electron spectroscopies and ex situ by atomic force and scanning electron microcopies. A model for the growth of beryllium nitride was applied to reproduce the optical measurement and concurrently, the refractive index from the visible to the near ultraviolet spectral region was calculated. The estimated optical bandgap correlates closely with previously published theoretical results. 2003 Elsevier Science B.V. All rights reserved.

Epitaxial α-Be3N2 thin films grown on Si substrates by reactive laser ablation

Beryllium nitride thin films were grown on (1 1 1) and (1 0 0) silicon substrates by laser ablating a beryllium foil in molecular nitrogen ambient from room temperature up to 900 °C. Resulting films were characterized using scanning and transmission electron microscopies, X-ray diffraction, Auger electron and X-ray photoelectron spectroscopies. Epitaxial films were achieved at substrate temperatures of 750 °C on (1 1 1)-Si. The diffraction measurements are in agreement with the α-Be3N2 phase. The orientation relationship between film-substrate corresponds to [110]Si[210]Be3N2and(111)Si(123)Be3N2.