Gregory Clarke

Measurement of energy transfer at an isolated substrate in a pulsed dc magnetron discharge

The power density delivered by particles to an electrically isolated substrate in an asymmetric bipolar pulsed dc unbalanced magnetron has been quantified. The plasma source was operated in argon with a titanium target, and measurements were made using both a calorimeter probe and time-resolved Langmuir probe incorporated into a specially made substrate holder. The main results from the calorimeter probe show clearly that with increased pulse frequency (from dc to 350kHz) and reduced duty cycle (90%–50%), the particle power density (from ions, electrons, sputtered Ti, and backscattered Ar) at the substrate increases significantly. For instance, at 350kHz and 60% duty cycle, the total power density is 83mW∕cm2, about 60% higher than in dc mode for the same time-average discharge power. However, from an inventory of the individual particle contributions to the total power density derived from time-resolved Langmuir measurements and a simple model of the substrate sheath and plasma internal processes, we pre...

Time resolved 2-D optical imaging of a pulsed unbalanced magnetron plasma

Using wavelength filtered two dimensional (2-D) optical imaging, the temporal and spatial evolution of selected excited species in a pulsed magnetron discharge has been studied. A titanium target was sputtered at a pulse frequency of 100 kHz, in an argon atmosphere, at an operating pressure of 0.27 Pa. The radial information of the emissivity was determined using the Abel inversion technique. The results show strong excitation of the observed species above the racetrack in the on-time, and the possible development of an ion–acoustic wave, initiated after the off–on transition. The on–off transition is accompanied by a burst of light from the plasma bulk consistent with the transient plasma potential reaching about +200 V. During this phase, we argue that there is a release of secondary electrons from the grounded substrate and walls due to ion bombardment, as well as an increased confinement of energetic plasma electrons. The characteristic decay times of the selected transitions at 750.4, 751.5, 810.4 and 811.5 nm (ArI), present within the bandpass width of our filters, is briefly discussed in terms of the production of fast electrons in the system.

Time-Resolved Imaging of a Silicon Micro-Cavity Discharge Array

Time-resolved imaging of an array of silicon based micro-cavity discharge devices, operating in helium at 700 Torr, is presented. The array is shown to ignite four times per cycle, with the brightest emission corresponding to a distinct current peak in the negative phase of the applied sinusoidal voltage. The cavities do not ignite simultaneously and the instantaneous intensity across the array is non-uniform. Before the brightest emission peak is reached, optical imaging shows some of the cavities to be ignited. During the emission peak, neighboring cavities are successively ignited, resulting in two emission regions which propagate across the array with wavefront velocities of 3 and 6 km/s.

Image processing virtual circuitry for physics based applications on field programmable gate array technology

Presented in this paper are the designs of several algorithms which enable the identification and tracking of various regions within a series of images using FPGA technology. Two example probLem domains in the areas of plasma physics and observational astronomy have been expolored. In the plasma physics application, an initial pixel extraction technique has been expanded to include spatial (related to the distance from a cathode) and value measurements (based on intensity values), which are subsequently merged in order to identify different intensity / emissivity regions within a plasma assisted deposition system. The optimum combination of these and other techniques are discussed, together with their reasons for selection. The control signals, decoding method and subsequent processing steps, associated with how a point within individual images is selected, will also be presented. In the astronomical application, a variation of a scene change detection mechanism is shown and how this system was adapted in order to track and chart the motion of Near-Earth Objects (NEOs).

Time-Resolved Optical Imaging of an AC Magnetron Discharge

Magnetron sputtering has proved to be an important and versatile technique for the production of thin films. In this paper, time-resolved optical imaging has been used to investigate the effect of an alternating-current (ac) waveform on plasma emission. The results suggest the formation of a secondary discharge, during the positive half of the pulse cycle, that is adjacent to the magnetrons anode.