Ion implantation in plasmas with diminishing positive column

This work is basically designed as an attempt to understand the consequence of the contact between the sheath edge and as anode and to exploit them in favor of industrial and technical goals, if possible. The sheath edge may arrive at the anode either during the formation of the ion matrix or during the expansion phase. Regarding the consequences the picture at the instant of contact is qualitatively the same in both cases, namely, the cathode-anode gap will be occupied by a uniform distribution of ions in the former case, and a nonuniform distribution of ions in the latter. What happens afterwards is a strongly non-linear process, involving the motion of ions subject to the applied potential and their diminishing space charge effect. If the contact is the established as the sheath thickness approaches the Child-Langmuir limit ( Child law sheath ), where the ion current density is restricted to the rather low value ( n0evd ) by the speed with which the ions enter the sheath from the neutral plasma then the ion current may exhibit a peak due to the abolition of this restriction. However, the current is soon to disappear, since the ion supplying neutral plasma no more. Hence, the heat deposition in the cathode should be considerably less than the deposition by longer lasting arc currents and the target is likely to remain unharmed. It is probably true that the discharge will be cut off for a brief period of time after all the ions in the sheath are collected by the cathode. However, each ion energies, and these electrons are expected to regenerate the plasma shortly afterwards, upon ionizing the neutral gas existing in the anode-cathode gap. The consequence of allowing sheaths to expand up the anode is then likely to be automatic generation of periodically appearing, high ion current peaks, which may even be advantageous due to the resulting large implation dose rates and possibly un necessitating the sophisticated, high voltage triggering electronics