T. de los Arcos

Preparation and characterization of TiN–Ag nanocomposite films

Abstract Thin nanostructured films of TiN–Ag are deposited by a plasma vapour process consisting of co-sputtering of Ti and Ag from three magnetrons in an Ar–N 2 gas mixture. The coatings are characterized by in situ photoelectron spectroscopy, energy-filtered transmission electron microscopy and scanning electron microscopy. The dependence of the film structure and silver cluster distribution on total silver content, substrate biasing and substrate temperature was investigated.

Optical characterization of alignment and effective refractive index in carbon nanotube films

We have characterized the thickness and effective refractive index of carbon nanotube forests by fitting reflectance measurements in the visible and near infrared ranges. The measurements were performed with polarized light. An effective medium layer consisting of a mixture of graphite and air was used to simulate the nanotube film. The proposed model accurately described the behaviour of the reflected s-polarized component (Rs), which allowed for the precise determination of the thickness and porosity of the films, in very good agreement with SEM measurements of film thickness. The p-polarized component (Rp), on the other hand, could not be described in terms of the developed model. In badly aligned samples, where there is a mixture of Rs and Rp behaviour, the model fails to fit the Rs component as well. This effect can therefore be taken as an indirect indication of lack of alignment in the samples.

Diagnostics and modeling of glow discharges by time-resolved IR absorption spectroscopy

In this work, several applications of time resolved absorption spectroscopy, with different time scales and spectral resolutions, are described for the diagnostic and modeling of cold plasmas produced in square wave modulated hollow cathode discharges. These methods have revealed a very sensitive and efficient way to test the relevance of the different individual mechanisms, in comparison with the usual plasma diagnostic methods of the stationary state.

Gas phase FT-IR absorption spectroscopy as a quantitative diagnostic method for cold plasmas: Application to hollow cathode discharges of acetylene and sulfur reduced compounds (DMS and DMDS)

Abstract Gas phase compounds produced in low pressure dc hollow cathode flowing discharges of acetylene, dimethylsulfide (DMS) and dimethyldisulfide (DMDS) have been, by the first time, identified and quantitatively measured through in situ FT-IR absorption spectroscopy. Experimental discharge parameters have been varied in the ranges where stable enough plasmas were produced. A high conversion of precursors to non-volatile compounds is observed. Only diacetylene has been detected in the infrared spectra of acetylene/inert gas discharges, with yields between 3 and 13%. Its appearance indicates that the C 2 H radical is the main intermediate species produced in such discharges. CS 2 , CH 4 and C 2 H 2 have been the most abundant products detected in the infrared spectra of DMS and DMDS plasmas, their maximal yields being in the range 5–20%. The concurrent production of CO, CO 2 and OCS, with yields one to two orders of magnitude lower, must be attributed to oxidation processes of the precursors due to air traces in the discharge cell. No final gaseous compounds, either oxygenated or not, suggesting the production of the CH 3 S radical as intermediate species were detected in these plasmas. The results presented clearly prove that hollow cathode discharges (HCD) produce cold plasmas where high temperature chemistry is conducted.

Time-resolved FTIR absorption and emission spectroscopy of plasmas produced in low-frequency-modulated N2O hollow cathode discharges

Low frequency modulated N2O hollow cathode discharges have been studied using time-resolved FTIR absorption and emission spectroscopy. Some experimental absorption data corresponding to slow transients of the discharge, as well as the temporal behavior of the different bands observed in the emission spectra, are presented here. A general exposition of the chemical reactions included in the kinetic model that explain with a satisfactory agreement that experimental stationary and time-resolved data is also given.

Time-resolved FTIR absorption and emission spectroscopy of species produced in hollow cathode molecular discharges

The study of the different experimental variables affecting the dissociation processes of molecular species, when using hollow cathode discharges as excitation method, and the characterization of the corresponding plasmas, have been made using FTIR absorption and emission spectroscopy. Mass spectrometry has also been employed for diagnosis purposes. The availability of step-scan mode and time resolved possibilities in our FTIR spectrometer, allowed to follow the excitation processes when using modulated discharges. Nitrous oxide, N2O, for which no data in hollow cathode discharges were available, has been employed as test compound for checking the possibilities of our experimental setup.