Volume 86, Issue 6, 15 September 1999
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
86(1999); http://dx.doi.org/10.1063/1.371158View Description Hide Description
We have performed a simulation of ion and fast neutral transport in the sheath region of a direct current magnetron discharge under different pressures by using the Boltzmann equation and the database from the two-dimensional (2D) results of a plasma structure, which was given by a hybrid model. Evolution of the erosion profile on the target surface has been predicted by using the 2D energy distributions of ions and fast neutrals incident on the target (cathode) surface. We confirmed that an accurate prediction of the erosion profile can be obtained by assuming that the constant sputtering yield corresponds to the cathode voltage under conditions of low pressures that make use of the film deposition processes.
Modeling of ionization of argon in an analytical capacitively coupled radio-frequency glow discharge86(1999); http://dx.doi.org/10.1063/1.371159View Description Hide Description
A hybrid Monte Carlo-fluid model has been developed for the description of electrons, argon ions, and fast argon atoms in a capacitively coupled radio-frequency (rf) glow discharge used in analytical spectroscopy. Typical operating conditions are about 6 Torr pressure and 10 W electrical power. The discharge cell is rather small and is characterized by a much smaller rf-powered electrode than grounded electrode, which yields a high dc bias voltage. The electron density at these conditions is in the order of The computation time to simulate all these electrons with a Monte Carlo or a particle-in-cell method was found to be too long. Therefore, the electrons are subdivided in two groups. The fast electrons emitted from the rf electrode, as well as the ones formed by ionization with sufficiently high total (=kinetic+potential) energy for further ionization, give rise to so-called γ ionization; these are described with a Monte Carlo method. The slow electrons, which can, however, be heated again by the fluctuating electric field, give rise to so-called α ionization; they are described with a fluid approach, which also treats the argon ions. Moreover, the fast argon ions and atoms are treated with a Monte Carlo model in the rf sheath. Typical results of this model include the electrical characteristics (i.e., dc bias and rf amplitude voltages, electrical current, potential, and electric field distributions), the electron densities and mean energies, the ionization rates due to the electron impact α and γ ionization and fast argon ion and atom impact ionization, and the relative contributions of these ionization mechanisms to the overall ionization.
Effects of resonant pumping on the temporal and spatial evolution of a laser produced lithium plasma86(1999); http://dx.doi.org/10.1063/1.371160View Description Hide Description
The spatial and temporal distribution of neutral and singly ionized lithium atoms has been investigated when slab targets are irradiated by ∼1 μs pulses of both resonant and nonresonant radiation from a flashlamp pumped dye laser. The ion population is enhanced when the laser is tuned to resonance with the line of neutral lithium and there is evidence for efficient ion production at distances up to 7.5 mm from the target surface. In particular, the rate of ionization is increased and the maximum ion population is attained between 120 and 200 ns earlier in the resonant case depending on distance above the target surface. However, the on-resonance ion population close to the surface is found to decrease significantly some 200 ns into the laser pulse. Ion and neutral drift velocities were measured by direct observation of the surface of the expanding plasma plume at a laser flux close to and were consistent with the value predicted by a dynamic source model for accelerated plasma expansion, as was the value for the electron temperature derived from line intensity ratios. Power density thresholds for ion production have been studied and in particular, the threshold for production is established.