Langmuir Probe Diagnostics and Spectroscopic Measurements in the Post-Discharge of a Dinitrogen/Methane Microwave Plasma

Measurements of electron temperature ($T_{\rm e}$) and ion density ($n_{+}$) are reported for mixtures of dinitrogen with methane in the afterglow of a high frequency discharge (2450 MHz). Methane is added upstream or downstream the discharge. Ion density is derived by means of the Su and Kiel theory (continuum theory based on Poisson's equation and continuity equations). Results are compared with values obtained by means of the theory of Šícha et al. (collisional theory). Both theories give results of the same order of magnitude in our experimental conditions. The influence of the location of the methane introduction, of the radio of methane in the mixture and of the microwave power is studied. A decay of ion density is observed when methane is added to the plasma. Spectroscopic emission measurements of N$^{+}_{2}$ (first negative) and CN (violet system) show simultaneous ion density decrease and new chemical species formation.L'influence de l'addition de méthane à un plasma microonde (2450 MHz) de diazote est étudiée. La température des électrons ($T_{\rm e}$) et la concentration des ions ($n_{+}$) sont déterminés dans la post-décharge du plasma quand le méthane est introduit soit en amont de la décharge soit dans la post-décharge. On étudie l'influence de la puissance microonde, de la quantité de méthane ajoutée au diazote et de la position d'introduction du méthane. La concentration des ions est déterminée en utilisant la théorie de Su et Kiel (modèle continuum basé sur l'équation de Poisson et sur les équations de continuité). Les valeurs obtenues sont comparées avec celles calculées en utilisant la théorie de Šícha et al. (modèle collisionnel). Les deux modèles donnent des densités ioniques du même ordre de grandeur dann nos conditions expérimentales. L'introduction du méthane provoque une diminution de la concentration des ions. Des mesures spectroscopiques de l'émission de N$^{+}_{2}$ (système premier négatif) et de CN (système violet) confirment la diminution de la densité ionique simultanément à la formation de nouvelles espèces chimiques

Computational study of plasma-surface interaction in plasma-assisted technologies

The influence of the unevenness of substrates immersed into plasma important for plasma-based treatment of materials were studied by computer experiment. The role of both substrate properties and plasma parameters was investigated. For this analysis the combination of multidimensional fluid modelling and particle simulation was used. The fluid part of our model consisted of continuity equations for all charged species, energy balance equation for electrons and Poisson equation. The basic scattering processes were also included. The particle simulation technique was used both for the calculation of electron energy distribution function and for the derivation of quantities characterising plasma-surface interaction. This approach enabled us to study in detail the structure of the sheath and presheath near metal substrates with realistic geometries and finite dimensions. The main attention was devoted to the influence of substrate geometry in both macroscopic and microscopic spatial scales on the local electric fields in plasma