José Cotrino

Reforming of ethanol in a microwave surface-wave plasma discharge

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 C2* depends on the plasma mixture. The temperature of the OH* species was determined by analyzing the shape profile of its emission band.

Type of Plasmas and Microstructures of TiO2 Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition

TiO 2 thin films have been prepared at temperatures between 298 and 523 K by plasma enhanced chemical vapor deposition at working pressures of 4 × 10 -3 and 4 × 10 -4 Torr, in this latter case by using electron cyclotron resonance conditions. Ti isopropoxide has been used as the precursor and oxygen or mixtures of oxygen + argon as the plasma gas. The refraction indexes of the films (from 1.95 to 2.4) have been correlated with their microstructure and surface roughness as observed, respectively, by scanning electron microscopy and atomic force microscopy. Optical emission spectroscopy analysis of plasma indicates a higher fragmentation of the precursor in a plasma of pure O 2 than in another of Ar + O 2 . Heating at T > 503 K induces the crystallization of the films into the anatase structure. The differences in the structure, microstructure, and optical properties are accounted for by assuming that the type of interactions of the plasma species with the growing film change with the deposition conditions.

Evaluation of different dielectric barrier discharge plasma configurations as an alternative technology for green C1 chemistry in the carbon dioxide reforming of methane and the direct decomposition of methanol.

Carbon dioxide reforming of methane and direct decomposition of methanol have been investigated using dielectric barrier discharges (DBD) at atmospheric pressure and reduced working temperatures. Two different plasma reactor configurations are compared and special attention is paid to the influence of the surface roughness of the electrodes on the conversion yields in the first plasma device. The influence of different filling gap dielectric materials (i.e., Al(2)O(3) or BaTiO(3)) in the second packed configuration has been also evaluated. Depending on the experimental conditions of applied voltage, residence time of reactants, feed ratios, or reactor configuration, different conversion yields are achieved ranging from 20 to 80% in the case of methane and 7-45% for the carbon dioxide. The direct decomposition of methanol reaches 60-100% under similar experimental conditions. Interestingly, the selectivity toward the production of hydrogen and carbon monoxide is kept almost constant under all the experimental conditions, and the formation of longer hydrocarbon chains or coke as a byproduct is not detected. The maximum efficiency yields are observed for the packed-bed reactor configuration containing alumina for both reaction processes (approximately 1 mol H(2) per kilowatt hour for dry reforming of methane and approximately 4.5 mol H(2) per kilowatt hour for direct decomposition of methanol).

Synthesis of SiO2 and SiOxCyHz thin films by microwave plasma CVD

Abstract Plasma enhanced chemical vapour deposition of SiO2 and polymeric SiOxCyHz thin films has been carried out at room temperature in a microwave electron cyclotron resonance (ECR) reactor. Si(CH3)3Cl has been used as volatile precursor of Si and pure oxygen as plasma gas. Plasma conditions were characterised by optical emission spectroscopy as a function of the relative flow rates of oxygen and precursor. The oxygen plasma was characterised by emission lines and bands due to O* and O2+ species whose relative intensity decreased as the flow rate of the precursor increased. Then, the plasma was dominated by the emission lines of H* species formed by dissociation of the precursor molecules. From the evolution of the intensity of the emission of oxygen and hydrogen lines as a function of the relative concentration of oxygen and precursor and by considering the composition and microstructure of the obtained thin films, a model is proposed for the decomposition mechanism of the precursor. According to this model, Si–Cl bond would dissociate in a first step. Then a series of reactions would follow with the activated oxygen species that, depending on the relative flow rate of oxygen, lead to the formation of SiO2 or a polymeric SiOxCyHz material. The chemical composition of the films was analysed by Rutherford backscattering spectroscopy (RBS), electron recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS), while their structure and microstructure were investigated by means of transmission electron microscopy (TEM), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FT-IR). It has been also shown that the SiOxCyHz thin films, with typical compositions such as Si:1, O:2, C:3.6, H:5.5, yield SiO2 thin films by exposure to a plasma of oxygen. These SiO2 thin films were smoother than the parent SiOxCyHz samples and the silica films prepared by PECVD under oxygen rich conditions.

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

The 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.

Quantification of the H content in diamondlike carbon and polymeric thin films by reflection electron energy loss spectroscopy

A nondestructive method to determine the hydrogen content at the surface of diamondlike carbon and polymeric thin films is proposed. The method relies on the analysis of the elastic peak produced by backscattering of electrons from the hydrogen atoms present at the sample surface. Quantitative analysis of the H content at the surface is achieved through use of a phenomenological sensitivity factor for elastic electron backscattering by H atoms with respect to other atoms present at the surface of reference polymeric samples. The validity of the method is checked with elastic recoil detection measurements and infrared spectroscopy analysis of the same samples. The accuracy of the method in the determination of H content at the sample surface is estimated to be ±10%.

Low temperature synthesis of dense SiO2 thin films by ion beam induced chemical vapor deposition

Abstract This paper presents a comparative study of SiO 2 thin films prepared at room temperature by ion beam induced chemical vapor deposition (IBICVD) and plasma enhanced chemical vapor deposition (PECVD) methods. The films are characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Rutherford backscattering spectroscopy (RBS), electron recoil detection analysis (ERDA), nuclear reaction analysis (NRA), X-ray reflectometry and spectroscopic ellipsometry. While the films prepared by IBICVD are very compact and dense and have a high refractive index ( n =1.48 at λ=550 nm), those prepared by PECVD exhibit a lower refractive index value ( n =1.45 at λ=550 nm), lower density and have a higher surface roughness. The different microstructure and properties of the two sets of films are discussed in relation to the ballistic effects that occur by the action of the highly energetic ion beams (e.g. 400 eV) impinging on the surface of the films prepared by IBICVD.

Theoretical and experimental characterization of TiO2 thin films deposited at oblique angles

The microstructural features of amorphous TiO2 thin films grown by the electron beam physical vapour deposition technique at oblique angles have been experimentally and theoretically studied. The microstructural features of the deposited films were characterized by considering both the column tilt angle and the increase in the column thickness with height. A Monte Carlo model of film growth has been developed that takes into account surface shadowing, short-range interaction between the deposition species and the film surface, as well as the angular broadening of the deposition flux when arriving at the substrate. The good match between simulations and experimental results indicates the importance of these factors in the growth and microstructural development of thin films deposited at oblique angles.

Determination of bromide by low power surfatron microwave induced plasma after bromine continuous generation.

A simple continuous flow generation of volatile bromine is described for the determination of low concentrations of the elements by atmospheric-pressure argon microwave induced plasma (MIP) surfatron. Bromine is continuously generated by mixing the bromide with sulphuric acid and hypochlorite solutions. The bromine vapor is separated from the aqueous phase by a gas-liquid separator and is desiccated by passing it through concentrated sulphuric acid. The detection limit attained was 2 microg/l. and the precision was +/-0.7% (at the 80 microg/l. level). The proposed determination is very selective if oxidizing/reducing agents are absent. The procedure has been tested for bromide determination in two drug preparations. Good agreement between the experimental results and the certified values has been obtained.

Growth regimes of porous gold thin films deposited by magnetron sputtering at oblique incidence: from compact to columnar microstructures

Growth regimes of gold thin films deposited by magnetron sputtering at oblique angles and low temperatures are studied from both theoretical and experimental points of view. Thin films were deposited in a broad range of experimental conditions by varying the substrate tilt angle and background pressure, and were analyzed by field emission scanning electron microscopy and grazing-incidence small-angle x-ray scattering techniques. Results indicate that the morphological features of the films strongly depend on the experimental conditions, but can be categorized within four generic microstructures, each of them defined by a different bulk geometrical pattern, pore percolation depth and connectivity. With the help of a growth model, a microstructure phase diagram has been constructed where the main features of the films are depicted as a function of experimentally controllable quantities, finding a good agreement with the experimental results in all the studied cases.