![]() ![]() The EM interference reduction for the case of FOCP probe is proved in the article, where a comparison of fiber optics and standard nickel catalytic probes was made by the inventors of FOCP. ![]() This is the main reason why a fiber optic catalytic probe (FOCP) has been invented. Because the measured values of the thermocouple are in mV range and the wires of a thermocouple act as a receiver the RF interference distorts the electric signal and therefore the measurement is unusable. The main problem of the standard catalytic probe is EM interference when measurement takes place near RF discharge region. The standard catalytic probe uses a thermocouple to measure the catalyst temperature. From the temperature curve of the catalyst the density of neutral atoms can be calculated. They use the fact that a catalyst is heated by the dissipation of energy caused by heterogeneous surface recombination of atoms. ![]() The advantages of catalytic probes over other methods are that they are simple, easy to use, quantitative and can be used in plasma discharge regions. This method is very popular since it is noninvasive and the equipment is not so expensive, but actinometry is based on an assumption that is usually questionable: it predicts that oxygen atoms are directly excited to a radiative state by electron impact excitation from the ground state.Īmong all methods for the estimation of neutral atom density in plasma, catalytic probes are the oldest. In this gas mixture the density of noble gas atoms is known and with the use of intensities ratio we can calculate the density of neutral O-atoms. The deficiencies of these methods are quite expensive equipment and the fact that the method is also only effective in afterglow where atoms are already in the ground state and not in the excited states as they are in the discharge region.Īctinometry is basically optical emission spectroscopy, where a comparison between the intensities of two emission lines, one suitable oxygen emission line and a noble gas (usually argon) emission line, determines O-atom density. To achieve this, rather powerful lasers should be used. Because excitation energies of radiative states suitable for this method are quite high, about 11 eV, at least two photons must be absorbed simultaneously. Optical absorption spectroscopy techniques are often realized by monitoring the florescence of the laser light absorbed by atoms. Density in plasma is only estimated with an appropriate model. The main deficiency of this method is that NO titration can only be used in a flowing afterglow, while in the discharge region NO is destroyed by electron impact. The intensity of this emission is a linear function of NO flow rate and from the slope of this curve the density of O-atoms is determined. Excited NO 2 molecules are formed and then de-excited by light emission. A known amount of NO is leaked in a flowing afterglow region, where NO interacts with O. NO titration is a pretty reliable chemical method for the determination of O-atom densities, but titration uses toxic NO gas which for safety reasons is usually used in a mixture with Ar. ![]() Methods for oxygen atom density measurement include NO titration, optical absorption spectroscopy, actinometry and catalytic probes. For different purposes in terms of treatment of solid materials by reactive oxygen atoms different densities are needed and therefore it is very useful to know the density of atoms in plasmas as precisely as possible. However, these values can vary for a few orders of magnitude dependent on discharge parameters. A typical neutral oxygen atom density in low pressure oxygen plasmas is around 10 21 m −3. The best way to produce neutral atoms is with electromagnetic discharges. They are being mainly used in nanoscience for synthesis of large quantities of metal oxide nanoparticles, in biomedical science for sterilization of delicate biocompatible materials and in surface science for changing the surface properties, e.g., activation of polymer materials. The importance of neutral atoms as a reactive particle in modern sciences is increasing. ![]()
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