J. F. Trigo

Pulsed laser deposition and electrodeposition techniques in growing CdTe and CdxHg1-xTe thin films

Abstract CdTe and CdxHg1−xTe (CMT) thin films were grown by a cathodic electrodeposition technique Also CdTe was deposited using a Pulsed Laser Deposition (PLD) technique. Optical and XPS analysis techniques have been used to characterise them. Important differences were found in adherence, composition, band gap, refractive index, absorption coefficient, really useful for these materials in solar cells. Variables like energy of the laser pulse and temperature of substrate are determinants to improve the structural and optical properties. The presence of Hg in CdTe films is able to control the bandgap although it carries some problems, like segregation and diffusion, found in XPS measurements, that have to be solved. PLD technique could be really of interest in order to avoid this kind of problems.

Dielectric Properties of Ti, TiO2 and TiN from 1.5 to 60 eV Determined by Reflection Electron Energy Loss Spectroscopy (REELS) and Ellipsometry

The dielectric properties of metallic Ti and thin films of TiO2 and TiN in the energy range from 1.5 to 60 eV have been determined by quantitative analysis of the respective electron energy loss spectra in the reflection mode (REELS). The energy loss function (ELF) of every material, that is proportional to Im {1/e}, is obtained by trial and error until a good quantitative agreement between the simulated and experimental inelastic electron scattering cross-sections at three different primary electron energies (i.e. 0.5, 1 and 1.5 keV) is achieved. Kramers-Kronig transformation is then used to obtain real and imaginary parts of the dielectric function e(ω). In addition, spectroscopic ellipsometry was used to improve the ELF in the 1.5 to 4.5 eV energy range where it is strongly affected by the experimental energy resolution and the presence of the elastic peak. The characteristic differences among the spectra of the particular compounds are discussed in terms of different electronic properties.

Calibration of the Probing Depth by Total Electron Yield of EXAFS Spectra in Oxide Overlayers (Ta2O5, TiO2, ZrO2)

Calibration of the probing depth by x-ray absorption spectroscopy (XAS) in oxide materials is intended by measurement of the total electron yield (TEY) of electrons ejected by absorption of the radiation. Measurements have been carried out for three series of electrolytic metal oxide overlayers with different thickness. The experiments have been conducted at the Ti K, Ta L III and Zr K edges Analysis of the XAS spectra is carried out by factor analysis and conventional Fourier transformation and fitting analysis. The data showed that the information depth by XAS follows the order Zr 2 > TiO 2 > Ta 2 O 5 at the Ti K, Ta L III and Zr K edges. As an alternative, the absorption spectra of the same samples were measured in the conversion electron yield (CEY) mode: i.e. by measuring the current of He + ions produced by the ejected electrons in an atmosphere of He in contact with the sample. Here, the information depth is slightly different from that obtained by TEY.

Thin BN films obtained by dual-ion-beam sputtering: an FT-IR and spectroscopic ellipsometry characterization

Abstract Thin BN films (100–250 nm) have been deposited on Si(100) substrates in a double-ion-beam sputtering system from a h-BN target. The films have been characterized by FT-IR spectroscopy and spectroscopic phase-modulated ellipsometry as a function of the deposition and irradiation parameters. Assistance with Ar+ ions result in boron rich films with refraction indexes above 2 or even higher as the deposited energy of the assisting ions increases. N2+-bombardment causes stoichiometric and even nitrogen-rich BN films characterized by refraction indexes around 1.85. The stability of the films is enhanced when the deposited energy of the N2+ ions is above 30 eV/atom and/or the deposition is performed on substrates at temperatures above 100°C.

Structural behavior of sputtered Co/Cu multilayers

Abstract Sputtered Co/Cu multilayers of different wavelength modulation have been prepared over different substrates. The study of Co layers by X-ray absorption spectroscopy shows that a significant change in the cobalt environment happens when the Cu thickness is smaller than 20 A. This result is in agreement with a non layer-by-layer growth mode of cobalt over copper, which means that Co-films consist of disconnected islands. The dependence of some physical properties at this copper thickness range will be regarded as the basis of this local arrangement of Co.

Characterization of Zr thin films grown by dual ion-beam sputtering

Abstract Zr thin films (100–600 nm) have been deposited on pyrex substrates at different temperatures (50–200°C) in a double ion beam sputtering system (residual pressure −7 torr) using Ar + ions for both sputtering and irradiation of the growing film. The films have been characterized by XRD, resistivity measurements and optical microscopy. The results show that, depending on the flux and energy of the ions impinging the growing film, the films develop compressive and tensile stresses which clearly influence their adherence and consequently their stability against exposure to the atmosphere.

Optical properties of Zr films grown under ion bombardment

Abstract Zr films (300–600 nm) have been deposited on Si〈100〉 in a double-ion-beam system (residual pressure, less than 10−7 Torr) using Ar+ for both sputtering and irradiation of the growing film. The films have been optically characterized by spectroscopic phase-modulated ellipsometry in the range 1.5–4.5 eV as a function of the deposition variables. The results show significant changes in the real part n and in the imaginary part k of the complex refractive index ( N = n + i k) . These changes mainly depend on the flux and energy of the Ar+ ions impinging the growing film. Furthermore, the stability of the films against the exposure to atmosphere and annealing in vacuum (10−7 Torr) was also investigated. The results are discussed in terms of packing densities, damage and surface oxidation of the films.

Structural behavior of Co/Cu multilayers studied by X-ray absorption spectroscopy☆

Abstract The study of the Co environment in Co/Cu multilayers by X-ray absorption spectroscopy shows that a significant change in the cobalt environment occurs when the Cu thickness is smaller than 20 A. Data are explained in terms of an island structure of the Co layers. This result agrees with a non layer-by-layer growth mode of cobalt over copper. The temperature dependence of the magnetization presents also differences for these samples according to the structural behavior.