Pulsed RF Plasma Research Articles

Molecular Tailoring of Surfaces: Pulsed Plasma Polymerization of Bromine Containing Monomers

The use of a variable duty cycle pulsed RF plasma is shown to provide film chemistry control during polymerization of saturated (CH2Br2) and unsaturated (CH2=CHCH2Br) bromine containing monomers. With both monomers, the degree of bromine atom retention in the films is observed to increase in a progressive fashion as the RF duty cycle employed during plasma polymerization is decreased. The film deposition rates, when expressed in terms of thickness per Joule of RF energy input, increase rapidly as the RF duty cycles are reduced. Additionally, the film morphology is observed to become increasingly smooth with decreasing RF duty cycles during deposition, as illustrated with the allyl bromide monomer. The film chemistry controllability of this study is demonstrated with monomers possessing the relatively weak C-Br bond. As such, the present work represents an important extension of the pulsed plasma polymerization approach to include retention of a labile bond during film formation. The introduction of reactive surface functional groups, at controlled densities, provides additional molecular tailoring possibilities via subsequent chemical derivatization processes.

Analysis and modelling of a pulsed-plasma reactor for silicon nitride deposition: reactor optimization

Numerical modelling of a RF pulsed plasma reactor for silicon nitride deposition from SiH4/NH3 mixture was carried out and a detailed treatment of both electrical and mass transfer phenomena performed. Starting from two-dimensional simulations of the concentration profiles, some a posteriori simplifications were made to shorten the calculation time. The resulting numerical procedure, which was much more rapid, was found to be very accurate. The homogeneous and heterogeneous chemical mechanisms selected were previously investigated for a continuous-wave plasma; the good agreement achieved between calculation and experiment suggests that, on the whole, realistic choices were made. In the case of a pulsed-plasma reactor, good agreement was also found between calculation and experiment. It was shown that the use of a pulsed discharge was necessary to obtain uniform thickness and composition over all samples when using a low silane percentage in the gaseous mixture. An attempted reactor preoptimization was satisfactorily performed, in the light of the experimental correlation between electrical properties and chemical bonding in the deposited films.

Molecular surface tailoring of biomaterials via pulsed RF plasma discharges.

A pulsed RF plasma glow discharge is employed to demonstrate molecular level controllability of surface film deposits. Molecular composition of plasma deposited films is shown to vary in a significant manner with the RF duty cycle. Three fluorocarbon monomers are used to illustrate the process. All three exhibit a trend towards increased surface CF2 content with decreasing pulsed RF duty cycle, including exclusion of oxygen. Significant variations in carbon-fluorine surface functionalities are obtained over a controllable range of film thickness. Film growth rate measurements reveal the occurrence of surface reactions during significant portions of the off portion of the duty cycle. Albumin adsorption on fluorocarbon-treated PET films is unchanged from PET controls for a 100-fold range of bulk concentrations and 60-fold range of adsorption times. However, increased retention of albumin is observed following incubation with protein-denaturing sodium dodecyl sulfate solution, the retention decreasing with increasing bulk concentration of albumin. The increased retention of albumin suggests the treated surfaces may have promise as biocompatible materials.

The time evolution of the ion density and the gas temperature in pulsed radio frequency plasmas

The kinetics of the formation and decay of pulsed nitrogen rf plasmas have been investigated with time and spatially resolved optical emission and laser induced fluorescence spectroscopy. At a gas pressure of 3 Pa the decay of the N2+ ions, after the power is switched off, is caused by dissociative recombination and ambipolar diffusion to the wall. At higher pressures (30 Pa) the formation of N4+ has to be taken into account. An accurate method to determine the ion density from the second order decay is presented. A numerical model of the time evolution of the ion concentration profile is developed, which renders good agreement with the experimental data. Kinetic measurements of the rotational (Tr) and vibrational (Tv) temperature of N2+ show that Tr and Tv of N2+ are in equilibrium with Tr and Tv of the N2 gas. The vibrational temperature is, however, much higher than the rotational temperature. This observation can be readily explained on the basis of the results of the kinetic measurements. The experimental excitation and cooling rates for the translational, rotational, and vibrational energy levels of the N2 molecules are compared to simulations.

Deposition of plasma-polymerized acetylene by an intense pulsed RF plasma source

An inductively coupled, intense, pulsed RF plasma source deposited plasma-polymerized acetylene at a rate of 127 AA per discharge. The potassium bromide substrate was located 18-cm downstream from the RF coil. A puff valve admitted parent acetylene gas just before the transient RF current was applied. Fourier transform infrared (FTIR) spectra showed that carbon-to-carbon double bonds were formed. Scanning-electron-microscope images showed that the film thickness after 79 discharges was 1 mu m. A photodiode showed substantial light emission for about 30 mu s during each discharge. >

Laboratory investigations of pulsed RF plasmas relevant to CW arc pluming at high-power aerials. Part 1: Critical breakdown under pulsed RF conditions

Laboratory investigations of pulsed RF plasmas relevant to CW arc pluming at high-power aerials. Part 1: Critical breakdown under pulsed RF conditions

Laboratory investigations of pulsed RF plasmas relevant to CW arc pluming at high-power aerials. Part 2: Relevance of scale-model studies based on pulsed RF techniques

The paper describes experiments which extend the observations of RF breakdown events in nonuniform fields reported in Part 1 of the paper. In particular, emphasis is given to examining the relevance of laboratory observations on pulsed RF discharges to the understanding of the ‘pluming’ phenomenon occurring under CW conditions at high-power aerial arrays. This is achieved by examining the effects of various scaling factors on the breakdown characteristics using both scaled sphere-to-plane and scaled toroid-to-plane geometries. It is shown how the intrusion of objects with needle-point geometries can lead to dramatic reductions in the critical electric fields needed to initiate the unwanted ‘pluming’ phenomeonon.