Plasmageactiveerde CO2-neutrale brandstofproductie

In een samenwerking van de Technische Universiteit Eindhoven (faculteit Technische Natuurkunde) en het FOM-instituut DIFFER (Dutch Institute for Fundamental Energy Research) zoeken we naar productieprocessen om CO2 om te zetten naar een brandstof. Aan de basis van het productieproces staat een gasontlading. De energie die nodig is om het resulterende plasma te laten branden zal in de toekomst afkomstig zijn van duurzame energiebronnen. Een succesvolle methode zal leiden tot verminderde CO2-emissies en opslag van duurzaam opgewekte energie

Parameterization of the optical function of hydrogenated amorphous carbon by means of B-splines

ellipsometry (SE) is a non-invasive optical diagnostic that measures the change in polarization of light reflected on a thin film. To extract both the optical function and thickness of the film from SE data, a (multi-layered) model is required that describes the interaction of the incident light with the film. For amorphous materials this interaction is commonly modeled by the Tauc-Lorentz oscillator and is used to parameterize the optical function [1]. However, a fully mathematical Kramers-Kronig consistent description of the optical function by means of B-splines is also possible [2]. The B-spline parameterization requires no pre-existing knowledge about the interaction of light with the film. The layer structure for this model consists of a substrate, the bulk layer, of which the optical function is represented by Bsplines, and a roughness layer. The roughness is modeled by an effective medium approximation of 50% bulk material and 50% voids. This layer structure is verified by cross-sectional scanning electron microscopy (SEM) measurements. The roughness is in good agreement with values determined by atomic force microscopy (AFM). When the B-spline model is applied to SE data obtained during growth, it has been found that the optical function for every measured thickness is the same, thereby ascertaining the homogeneity of the bulk layer of the a-C:H. During etching of a-C:H with a hydrogen plasma, the optical function of the film - due to the homogeneity of the bulk material - can be fixed throughout the entire etch process, which enables real time in situ monitoring of the thickness evolution. Further parameterization of the dielectric function, as found by the B-spline model, by a physics-based model is possible. For a-C:H films, the bulk layer is described by two Tauc-Lorentz oscillators, from which the sp2/sp3 ratio has been, tentatively, determined from SE data up to 6.5 eV [3]. In all, the B-spline model is an accurate and fast method to determine thickness, roughness and optical constants for numerous types of thin films, including - as has been shown - hydrogenated amorphous carbon. The determined film properties can also be used as input parameters for physicsbased models

Role of carbon atoms in the remote plasma deposition of hydrogenated amorphous carbon

The aim of this article is to determine the role of carbon atoms in the growth of hydrogenated amorphous carbon (a-C:H) films by means of an argon/acetylene expanding thermal plasma. Cavity ring down absorption spectroscopy is used to detect metastable carbon atoms by probing the 1s2 2s2 2p 3s 1P11s2 2s2 2p2 1S0 electronic transition. In addition to absorption measurements, the emission of the same transition is monitored by means of optical emission spectroscopy. These two measurements provide information about the local production of the C atoms and about their reactivity in the gas phase. It will be shown that under growth conditions in an Ar/C2H2 expanding thermal plasma, the metastable carbon density is also representative for the ground state carbon density. From obtained results it is concluded that the carbon atoms react rapidly with acetylene in the gas phase and therefore their contribution to the growth of hard diamond-like a-C:H films can be neglected. Only at low acetylene flows, the condition when soft polymer-like films are deposited, carbon atoms are detected close to the substrate and can possibly contribute to the film growth

Experimental study of the erosion of Ar/H2 plasma facing carbon surfaces: optical emission spectroscopy, mass spectrometry and spectroscopic ellipsometry measurements

Carbon materials could be used for divertor plates in the ITER fusion device. Numerous studies (experimental or modeling) have been undertaken to better understand the chemical processes involved in carbon erosion by hydrogen atoms or ions. These works have been performed for several kinds of carbon layers and different hydrogen (or deuterium) ion fluxes. Results of an experimental study on carbon-material erosion under hydrogen bombardment will be presented. Optical emission spectroscopy and mass spectrometry have been employed to determine the presence of excited and stable molecules that are formed under these conditions. Ex situ spectroscopic ellipsometry has been used to calculate the erosion rate. In order to determine this erosion rate during plasma exposure and with a better precision, preliminary results on in situ spectroscopic ellipsometry will be presented

Influence of the interelectrode distance on the production of nanoparticles by means of atmospheric pressure inert gas DC glow discharge

This work is aimed at investigating the influence of the inter-electrode spacing on the production rate and size of nanoparticles generated by evaporating a cathode on an atmospheric pressure dc glow discharge. Experiments are conducted in the configuration of two vertically aligned cylindrical electrodes in upward coaxial flow with copper as a consumable cathode and nitrogen as a carrier gas. A constant current of 0.5 A is delivered to the electrodes and the inter-electrode distance spanned from 0.5 to 10 mm. Continuous stable nanoparticle production is attained by optimal coaxial flow convection cooling of the cathode. Both the particle production rate and the primary particle size increase with the inter-electrode spacing up to nearly 5 mm and strongly decrease with an increasing inter-electrode distance beyond 5 mm. Production rates in the range of 1 mg h-1 of very small nanoparticles

Electric field measurements in atmospheric-pressure plasma jets

Atmospheric pressure non-thermal plasmas are researched for many applications. They became popular with plasma medicine, where restrictions on the plasmas are rigorous - they have to be at room temperature and not transfer significant amount of charge to the target, while still providing a mixture of reactive species, charge, field, to be efficient in medical applications. The intended applications soon extended to the treatment of different types of targets, where it is either important to treat them at atmospheric pressure (e.g. water) or with a plasma at room temperature. Atomic layer deposition is a good example of a traditionally low pressure technology being extended into the atmospheric pressure, and so is plasma catalysis. Another family of applications is in food and agriculture, where plasmas present a promising technology applied to a wide range of surfaces, dielectrics of different permittivities, in atmospheric air but also in humid conditions.The discharges used in these developments very often belong to the family of non-thermal atmospheric pressure plasmas - these are transient discharges, highly non-uniform in both space and time, small-scale (sub-mm), low ionization level, low light output, and most importantly sensitive to their environment. For example, a He plasma jet working in a kHz bullet mode changes its properties when impinging on a target with respect to the case when it expands freely into the ambient atmosphere. This is an important aspect to be kept in mind when bringing non-thermal atmospheric pressure plasmas intoapplications. It is also the motivation for the research presented in this talk. This work focuses on the fundamental properties of non-thermal plasmas such as the electric field, charge density and electron temperature. The work was performed on a non-thermal atmospheric pressure He plasma jet working in a kHz-driven mode with one ionization wave produced per voltage period or pulse. These fundamental properties of the discharge were measured in a freely expanding jet as well as when impinging on targets of different types, from low-permittivity dielectrics such as glass, to water, to metal. The measurements were performed in the plasma plume, but also in a target when a high-permittivity dielectric (er = 56) was used.The results bring one of the first sets of data concerning the E field, electron density and electron temperature, which are relatable to each other through the fact that they were all obtained on the same discharge. The effect of the gas flow speed is significant in the freely expanding jet, showing that the increased flow extends not only the visible length of the plasma plume, but also its electric field profile. In addition, the electron density and temperature were shown to respectively fall and rise within the plasma plume with increasing the distance from the end of the glass capillary.The presence of the target influences the plasma plume in several different ways. For low-permittivity targets, such as plastic or glass, the presence of the target does not significantly influence the plasma properties in the plume, but it does initiate surface discharges belonging to the family of ionization waves. The electric field induced in the target material by those surface ionization waves were measured, both axially, in the direction through the material, and radially. When the permittivity of the target is increased, the surface ionization waves are replaced by one or several return strokes and a significantly altered electric field profile, along with increased electron density and temperature. In the extreme case of the metallic target, combined with much higher electron densities, the duration of the discharge on the metal surface is extended to a microsecond. The work shows not only that the presence of the target influences the plasma, but that the properties of the target determine the plasma parameters, also in the gas phase

Influence of molecular processes on the hydrogen atomic system in an expanding argon-hydrogen plasma

An expanding thermal arc plasma in argon–hydrogen is investigated by means of emission spectroscopy. The hydrogen can be added to the argon flow before it enters the thermal arc plasma source, or it can be flushed directly into the vacuum expansion vessel (1–20 vol¿% H2). The atomic state distribution function for hydrogen, measured at a downstream distance of 20 mm, turns out to be very different in the two cases. For injection in the arc, three-particle recombination is a primary source of hydrogen excitation, whereas measurements with hydrogen injected into the vessel clearly point to a molecular channel (dissociative recombination of formed ArH+) populating atomic hydrogen levels