Beniamino Rovagnati

A reaction model for plasma coating of nanoparticles by amorphous carbon layers

A detailed chemical kinetics scheme of the reactions occurring in a CH4∕H2 plasma, namely, electron-neutral, ion-neutral, and neutral-neutral reactions, is implemented for the prediction of the species fluxes toward the surface of a submicron particle in a low-pressure environment. Surface reactions at the particle surface are also accounted for. Kinetic theory is applied in the collisionless region within a distance of one mean free path away from the particle, while continuum theory is implemented to solve for species transport in the outer region where reactive-diffusive phenomena occur. These regions are bounded by appropriate boundary conditions. The self-consistent electric field is obtained by solving the Poisson’s equation in the continuum region. The charged and neutral species distributions are calculated and the growth rate of the amorphous carbon layer at the particle surface, as well as particle charging, are predicted. The predicted growth rate is within the range of experimental data from l...

Lateral motion of a dust particle in magnetized plasma sheath

In this paper, lateral mobilization of a dust particle through application of an oblique magnetic field in a plasma sheath with infinitely long lateral dimensions is studied. A weakly collisional two-fluid model is implemented to simulate the plasma. A single submicrometer-sized particle is released at the sheath edge with zero initial velocity and is tracked in Lagrangian frame, taking into account various forces. Various characteristics of the particle lateral motion such as time history of its horizontal position, velocity, and acceleration components are presented and discussed. Through investigation of power spectra of plasma and particle variables, the particle drift in the horizontal plane is explained. While varying parameters such as magnetic field intensity, particle density, and its radius, the particle horizontal velocity components are calculated. The variation of these velocity components is then explained by considering the ion velocity components at the particle location.

Effect of collisions on dust particle charging via particle-in-cell Monte-Carlo collision

In this paper, the effect of collisions on the charging and shielding of a single dust particle immersed in an infinite plasma is studied. A Monte-Carlo collision (MCC) algorithm is implemented in the particle-in-cell DEMOCRITUS code to account for the collisional phenomena which are typical of dusty plasmas in plasma processing, namely, electron-neutral elastic scattering, ion-neutral elastic scattering, and ion-neutral charge exchange. Both small and large dust particle radii, as compared to the characteristic Debye lengths, are considered. The trends of the steady-state dust particle potential at increasing collisionality are presented and discussed. The ions and electron energy distributions at various locations and at increasing collisionality in the case of large particle radius are shown and compared to their local Maxwellians. The ion-neutral charge-exchange collision is found to be by far the most important collisional phenomenon. For small particle radius, collisional effects are found to be imp...

A kinetic model to study film deposition during dusty plasma chemical vapor deposition process

A simplistic numerical kinetic model to predict the deposited film morphology in dusty plasma chemical vapor deposition reactors is developed. The morphological accretion of a circular object is studied in a two-dimensional geometry and the most important deposition phenomena are taken into account, i.e., surface diffusion and surface ion bombardment. Both isotropic and anisotropic plasmas are considered. It is shown that when the particle is located in an isotropic plasma, the deposited film maintains the original particle sphericity. Whereas, if the particle is assumed to levitate in the (pre) sheath forming around the bottom electrode of the reactor and ions contribute considerably to the deposition, the film develops in a nonuniform manner similar to experimental observations.

Effect of ion-neutral collisions on the charging of a dust particle

of ion-neutral charge-exchange collisional process on the charging and shielding of a single dust particle immersed in an infinite plasma under dierent operating conditions is studied. The fully kinetic evolution of the plasma is accounted for by use of a two-dimensional Particle-in-Cell method in a cylindrical symmetric geometry, where both ion and electron species are tracked. Collisions are considered as probabilistic events which depend on the specific collision frequency. The variation of the steady-state dust particle potential with increasing collisionality is presented and discussed. The ions energy distributions at various locations and at increasing collisionality are shown and compared to their local Maxwellian distributions.