Influence of Surface Contaminations on Cathode Processes of Vacuum Discharges

Abstract

The influence of surface contaminations on the ignition and maintenance of vacuum discharges is discussed qualitatively. Surface analysis of the electrodes and gas analysis during the discharges demonstrate that fresh electrodes contain always impurities within the upper surface layers, which affect the behaviour of vacuum arcs and vacuum breakdowns. The most effective way for cleaning the surfaces are the dischnrges themselves, if they burn in UHV. During that cleaning the following variations have been found: Arc cnthodes spots change from rapid moving ones with small erosion (type 1) to slow ones with strong erosion (type 2). The ignition of nanosecond discharges needs higher field strength and field emission current density. Polishing effects by short discharges (< 5 n s ) become more pronounced. Erosion craters in nanosecond discharges increase.

A review comparing cathodic arcs and high power impulse magnetron sputtering (HiPIMS)

“…The rapid repeated initiation of cathode spot is closely associated with the presence of a very high electric field at the cathode surface, which can be readily achieved despite the low total voltage between cathode and anode (~ 20 V) because most of the voltage drops in a very thin space charge layer (sheath) adjacent to the cathode (also known as the cathode fall). The actual magnitude of the electric surface field is greatly affected by geometrical features such as microscopic protrusions [92] or cracks [93], as well as by non-metal features such as adsorbates, oxide layers, and dust particles [94].…”

“…In practical terms, the cutoff of self-similarity is expected in nanoseconds in time and 10 nm in length. The time cutoff is derived by the observation of smoothing of a surface, rather than crater formation, when the discharge pulse duration is less than 5 ns [94]. The lower limit of the length scale is found from the smallest macroparticles and crater sizes [118,119].…”

The fractal nature of vacuum arc cathode spots

“…Today it is firmly established that spot characteristics depend on surface conditions of the cathode. The distinction between spots of type 1 and 2 was introduced in the 1970s when the role of surface condition on spot formation and operation was fully recognized [19][20][21]. Unless the cathode is specially treated, e.g.…”

Field emission and explosive electron emission processes in vacuum discharges

“…150 , а не взрывом микроострий, как полагалось ранее 145 . Действи-тельно, на расстоянии в десятки микрон от первичного ЭЦ (характерное расстояние между фрагментами пятна) для реализации механизма пробоя включений и иленок требуются менее жесткие условия в прикатодном слое.…”