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The most severe problem for the vacuum arc deposition (VAD) technique is the formation of micron-size particles on the films. These particles degrade the films' properties. The present work studied the generation mechanisms and characteristics of the droplets that are produced in the carbon films deposited by vacuum arc technique. To achieve a better control of the generation mechanism of these droplets, the effect of the arc current, arc duration time, cathode spot temperature and distance between cathode and substrate on the size and population of the micro-droplets are studied. / The micro-droplets are in the range of 0.3 $ mu$m to 2 $ mu$m in diameter, and have a graphite structure. The most probable origin for these particles are the cathode. The size and population of these particles are directly proportional to the cathode spot temperature (i.e., to the arc current and/or arc duration time), and inversely proportional to the distance between the cathode and the substrate. The droplet production is mainly due to the heating effect.

The self preserving free jet in streaming flow has been investigated by studying the equations of mean motion for two-dimensional turbulent flow. It is found that at high Reynolds nurnber the jet may be self preserving if the free stream velocity varies as the downstream co-ordinate to a power which in turn depends on the non-dimensional velocity of the jet. The growth of the jet is then linear. The effect of an upstream boundary-Iayer on the outside of the slot is also considered. This analysis is then applied to the outer part of a wall jet in a similar pressure gradient. The effect of the inner boundary layer on the outer part of the flow is considered and formulae for the growth of the inner boundary-Iayer and the variation of skin friction are given. Also a form for the non-dimensional mean velocity profile including the inner boundary-layer is suggested. The predictions of the theory are found to be in substantial agreement with measurements of the mean velocity, the static pressure and the skin friction in wall jets with an equilibrium pressure gradient. Experimental measurements have also been made for wall jets in streaming flow with zero pressure gradient and wall jets in still air. The results of these experiments compare weIl with those of previous investigators . The law-of-wall and the velocity defect law for wall jets are investigated and the former is found to be limited in application. A simple power law appears to be useful for representing the whole boundary-layer velocity profile and forms the basis for the analysis of the inner boundary-layer .