Influence of the angular distribution function of incident particles on the microstructure and anomalous scaling behavior of thin films

The microstructure and the scaling properties of films grown by plasma enhanced chemical vapor deposition are reproduced with a discrete model that takes into account the angular distribution function of the particles and the lateral growth of the films. Both the experimental and simulated surfaces exhibit a granular microstructure and an anomalous scaling behavior characterized by values of the growth exponent β that vary with the scale of measurement. Depending on the angular distribution function used in the model, values of β ranging from 0.86 to 0.2 are obtained

Scaling behavior and mechanism of formation of Si O2 thin films grown by plasma-enhanced chemical vapor deposition

This paper reports a study of the kinetic roughening of Si O2 thin films prepared by plasma-enhanced chemical vapor deposition (PECVD). Tetramethylsilane has been used as a precursor, and the synthesis has been carried out under remote and in-plasma configurations. The analysis of surface topography of the films by atomic force microscopy shows an anomalous scaling behavior that cannot be represented by the Family-Vicsec scaling relation of dynamic scaling theory. The application of different methods for obtaining the roughness exponent α yields different values of this exponent (α=0.7 for the height-height correlation function and α=1.3 for the power spectral density function for long deposition times) in all experimental conditions. Moreover, a strong variation of the α exponent with deposition time has been determined for the samples grown in remote mode. This correlates with the presence of a crossover region of the growth exponent β, which varies from a first value of 1.3 for low deposition times to another of 0.3 for longer deposition times. Such a variation is not found for the samples grown in the plasma, characterized by a β value of 0.28. The results obtained can be explained by the combined effect in the growth process of a low diffusivity of the physisorbed species along with the existence of nonlocal interactions due to shadowing effects. These two assumptions are in agreement with the empirical knowledge existing about the kinetics of the growth of Si O2 thin films by PECVD and establish a link between the scaling properties of the films with the surface chemistry during the film growth.Ministerio de Educación y Ciencia MAT2004-01558 y MAT2007-6576

Relationship between scaling behavior and porosity of plasma-deposited TiO2 thin films

The growth of TiO2 thin films prepared by plasma enhanced chemical vapor deposition has been studied by analyzing their roughness with the concepts of the dynamic scaling theory. Differences in the growth and roughness exponents have been found depending on the composition of the plasma by using either O2 or mixtures Ar+ O2 as plasma gas and titanium isopropoxide as the precursor. The slope of the representations of the film roughness against the deposition time yielded values of the exponent β of 0.45 and 0.32 for, respectively, thin films prepared with plasmas of O2 or mixtures Ar+ O2. Meanwhile, values of the exponent α of 1.15 and 1.89/0.35 were deduced from the power spectral density representations for the films prepared under these two experimental conditions. These values are congruent with growth processes dominated, respectively, by shadowing or diffusion processes. A columnar microstructure was observed by scanning electron microscopy for the thin films prepared with pure oxygen. Meanwhile, homogeneous films were obtained with mixtures of Ar+ O2. The open porosity of the films was determined by measuring water adsorption-desorption isotherms with a quartz crystal monitor. This analysis showed that in the samples prepared with mixtures of Ar+ O2 the porosity consisted exclusively of micropores (d2 nm). It is concluded that the different growth mechanisms found by just changing the chemistry of the plasma are responsible for the quite distinct microstructures, porosities, and optical properties obtained for the films.Ministerio de Educación y Ciencia NAN2004-09317-C04-01 y MAT2007-6576

Measuring the electron temperature by optical emission spectroscopy in two temperature plasmas at atmospheric pressure: A critical approach

6 pages, 5 figures, 2 tables.-- PACS: 52.70.Kz; 52.25.Os; 52.20.Fs; 52.20.Hv; 52.25.FiThe measurement of the electron mean kinetic energy by identifying the electron temperature and the excitation temperature obtained by optical emission spectroscopy is theoretically studied for two temperature argon plasmas at atmospheric pressure. Using a 32-level collisional radiative model in which both electron impact and argon-impact inelastic collisions are taken into account, it has been found that under certain conditions the argon inelastic collisions may cause a decrease of the argon excitation temperature so that the relation Te>Texc>T0 is satisfied. This inequality also appears when electron losses due to diffusion are important and the electron density is lower than its equilibrium value.This research was partially supported by Grant Nos. MAT2001-2820 and PPQ2001-3108 and the Acción Integrada HP02-102 from the Dirección General de Investigación Científica y Técnica ( Spain) .Peer reviewe

Reforming of ethanol in a microwave surface-wave plasma discharge

3 pages, 2 figures, 3 tables.Hydrogen production through plasma reforming of ethanol at room temperature and moderate pressure has been carried out in a microwave surface-wave reactor. Both pure ethanol and mixtures ethanol-water have been studied. The reforming yield was almost 100% in all conditions with H2, solid carbon, CO and CO2 as the main reaction products. In the mixture ethanol-water the formation of solid C was avoided. The optical emission spectroscopy analysis has shown that the formation of the excited species CO*, CH* and C depends on the plasma mixture. The temperature of the OH* species was determined by analyzing the shape profile of its emission band.The authors thank the Ministerio de Ciencia y Tecnología for financial support (projects PPQ2001-3108 and FIT 120300-2003-14, this latter in collaboration with Instalaciones ABENGOA, S. A.).Peer reviewe

Si K-edge XANES study of SiOxCyHz amorphous polymeric materials

6 pages, 4 figures, 1 table.-- PACS number(s): 61.10.Ht, 81.05. t, 81.15.Gh, 81.07.PrThis work reports on x-ray absorption spectroscopy study at the Si K edge of several amorphous SiOxCyHz polymers prepared by plasma-enhanced chemical-vapor deposition with different C/O ratios. SiO2 and SiC have been used as reference materials. The comparison of the experimental Si K-edge x-ray absorption near-edge structure spectra with theoretical computations based on multiple scattering theory has allowed us to monitor the modification of the local coordination around Si as a function of the overall C/O ratio in this kind of materials.This work was partially supported by the Spanish CICYT (Grants MAT2005-06806-C04-04 and MAT2004-01558).Peer reviewe

LaLiga Lockdown: Conditioning Strategy and Adaptation to In-Game Regulations during COVID-19 Pandemic Prevented an Increase in Injury Incidence

The first division of Spanish professional football (LaLiga) was suspended for 12 weeks as part of the policies enforced by health authorities during the first wave of COVID-19. During this period, players were confined to home for 8 weeks, followed by a club-based retraining period of 4 weeks. Afterwards, LaLiga’s teams completed 11 matches, with approximately 3 days of recovery between matches, to finish the competition. The aim of this investigation was to determine whether there is a difference in mean injury incidence in LaLiga players between the pre-lockdown period and post-lockdown period. A total of 277 players belonging to 11 teams competing in LaLiga were monitored during the 2019–2020 season. Injury incidence in the 27 matchdays completed before the lockdown was compared to the last 11 matchdays completed after the resumption of the competition. In comparison to the period before the suspension, the resumption of the championship did not significantly affect the injury incidence (4.2 vs. 5.4 injuries per 1000 h of exposure, p = 0.338). Injury incidence before suspension and after resumption of the competition was similar for muscle (2.6 vs. 3.4 injuries per 1000 h of exposure, p = 0.152) and ligament injuries (0.8 vs. 0.4 injuries per 1000 h of exposure, p = 0.062). The resumption of the competition also did not modify the distribution of injury according to body location (p = 0.948), injury type (p = 0.766), mode of onset (p = 0.614), severity (p = 0.065), or player position (p = 0.295). In summary, mean injury incidence in LaLiga players was similar before and after the lockdown. It is probable that the conditioning strategy adopted by clubs before the resumption of LaLiga and the adaptation of some in-game regulations helped to avoid an increased injury rate after the lockdown