Rafael Perez-Casero

Er-doped ZnO thin films grown by pulsed-laser deposition

Crystalline erbium(Er)-doped zinc oxide thin films have been grown by pulsed-laser deposition and were analyzed by the complementary use of Rutherford backscattering spectroscopy, x-ray diffraction analysis, atomic force microscopy, and photoluminescence. The composition, structure, and surface morphology of films were studied, as a function of the growth conditions (temperature from 300 °C to 750 °C and oxygen pressure from 10−6 to 0.5 mbar) and Er-doping rate, and were correlated to the emission spectroscopy of Er in the infrared domain. While these studies lead to the determination of optimal conditions for the growth of high crystalline quality films, results of photoluminescence experiments show that the insertion of Er ions in the ZnO matrix does not follow a simple pattern. The Er ions are incorporated from two pathways, one population is found inside the crystallites and another one at the grain boundaries, as a consequence of the differences in valence and ionic radius of Zn and Er.

Growth of crystalline doped β-alumina thin films by laser ablation

Crystalline thin films of sodium β-alumina and β-aluminogallate for optical applications have been deposited onto various single-crystal substrates by the pulsed laser deposition technique. Films with a smooth surface morphology were obtained by using Cr-doped targets. Despite Na loss in the films with respect to the target composition, the β-alumina crystalline phase was grown at elevated temperature (700–800 °C), and highly textured (00l) films were obtained, whatever the substrates: MgO, ZrO 2 , Al 2 O 3 or Si. The optical properties were studied by measuring the refractive index of the films and performing the emission spectrum of the Cr 3+ ions, providing results very similar to those of the bulk single-crystalline material.

Growth of oxide thin films by laser ablation

The pulsed laser deposition is now routinely used for the growth of a variety of oxide materials in thin film form. Superconducting, ferroelectric, magnetic or biocompatible oxide films are easily grown in this way. Epitaxial films, multilayers or superlattices based on various oxide materials have been also realized using this deposition method. The quality of the oxide films grown by the pulsed laser deposition technique depends upon the various phenomena which occur during their formation. Thus, we discuss in this paper the influence of the precise growth conditions on the atomic composition, surface morphology, structural and chemical nature of the pulsed laser deposited films. A special attention has been paid to the problem of the epitaxial growth of BiSrCaCuO and BaTiO3 films on MgO single crystal substrates.

Kinetics and mechanism of plasma oxidation of tantalum silicides

Radio frequency (rf) plasma oxidation at the floating potential of tantalum silicides, TaSix (0.3≤x≤4.5), has been investigated. The oxidations were carried out in the 400–800 °C temperature range. Measurements of the overall oxygen (16O and 18O) and cation contents as well as their distribution in the films were carried out using Rutherford backscattering spectrometry and nuclear microanalysis techniques. The oxidation rate was found to be primarily controlled by the diffusion of the oxidizing species through the oxide. The influence of silicide composition, temperature, and substrate nature on the nature of the oxide has been analyzed. The rf plasma oxidation of TaSix silicides can be understood as the competition between two diffusion processes: oxygen diffusion from the plasma through the growing oxide and silicon migration from the silicide layer or from the silicon substrate. Both silicon and oxygen diffusion processes coexist and determine the nature of the grown oxide. The mechanisms of oxygen mov...

Oxidation of tantalum silicide thin films in an RF oxygen plasma

Abstract We have investigated the RF plasma oxidation at floating potential of tantalum silicide with a Si:Ta ratio of 2.2 on 〈100〉 silicon. The oxidation was carried out in the 500–800°C temperature range. Rutherford backscattering spectrometry and nuclear reaction analysis have been used to study the composition of the samples and to determine the oxide growth kinetics. The oxidation rate was found to be controlled by the diffusion of the oxidizing species through the oxide. The oxidation leads to the growth of a pure silicon oxide film on surface. The growth of pure SiO 2 is postulated to occur by the supply of silicon atoms from both the substrate and the silicide layer. The existence of a diffusion barrier of SiO 2 between the silicon and the silicide avoids the supply of free silicon from the substrate. In this case, after the initial growth of SiO 2 , the formation of an oxide layer where both silicon and metal atoms are present was observed.

Plasma oxidation mechanisms in tungsten silicide thin films

The oxidation of tungsten disilicide in a rf oxygen plasma at floating potential in the 300–900 °C temperature range has been investigated. The oxidation kinetics and the elemental depth distribution in the films have been analyzed by the complementary use of Rutherford backscattering spectrometry and nuclear reaction analysis. It has been found that the nature of the oxide largely depends on temperature. A mixture of WO3 and SiO2 is grown in the 300–650 °C range. The W:Si ratio in these oxides decreases monotonically with temperature reaching a minimum value at 650 °C. As a matter of fact, a SiO2 surface layer is formed when oxidation is carried out in the 650–900 °C range. Oxygen diffusion through the growing oxide seems to be the dominant rate controlling process. Despite the fact that oxygen diffusion is a process activated by temperature, oxygen diffusion through the mixture of WO3 and SiO2 proceeds more rapidly than through SiO2. This leads to an enhancement of the growth rate at temperatures near 4...

Plasma oxidation of TaSix thin films

We have investigated the RF plasma oxidation at floating potential of tantalum silicides, TaSix (1.6 ⩽ x ⩽ 3.6), in the 300–800°C temperature range. Rutherford backscattering spectrometry and nuclear reaction analysis have been used to study the composition of samples and to determine the oxide growth kinetics. Whatever the initial silicide composition there are two different regimes in the oxide growth depending on the temperature. The transition temperature between these two regimes is about 550°C. However, both temperature and silicide stoichiometry play an important role in the nature of the grown oxides. The fact that the silicide is silicon enriched with respect to the stoichiometric composition of a disilicide (i.e. x 2) leads to the growth of a pure SiO2 film on the surface in the 300–800°C range. On the other hand, if the silicide is tantalum enriched (i.e x < 2) the nature of the oxide depends on the temperature: almost pure SiO2 for T < 550°C and an oxide mixture (Ta2O5-SiO2) in the 500–700°C range. It has also been evidenced that it is possible to grow a pure SiO2 film on the surface even if the silicide is Ta enriched provided that the temperature is high enough ( ∼ 800°C).