Enhanced extraction efficiency of the sputtered material from a magnetically assisted high power impulse hollow cathode

Abstract

The high power impulse hollow cathode sputtering (HiPIHCS) technique was pioneered by researchers attempting to combine the high ionization degree of sputtered species in a high power impulse magnetron sputtering discharge with the highly energetic electrons from a hollow cathode (HC) in order to obtain high-density and high-energy fluxes of sputtered metal species. Hence, this novel technique may open new horizons in surface engineering, offering the ability to control, enhance and tailor coating properties by using additional electric and/or magnetic fields. However, there are still many issues to be solved, including the ionization degree of the sputtered material and the deposition rate, as well as the extraction efficiency. This work reports on the improvement of the extraction efficiency of the sputtered material in an HiPIHCS process when an external magnetic field is applied. The HiPIHCS discharge was operated with ultrashort pulses (5 μs) of high voltage (600-800 V) applied directly on the HC. The obtained experimental results show that the extraction efficiency of both neutral and ionized sputtered material increases at least by a factor of two when an external magnetic field of only 15 mT is applied in the HC discharge region.

Secondary electron emission under magnetic constraint: from Monte Carlo simulations to analytical solution

“…It acts along the entire trajectory of the secondary electrons, assuming that the sheath thickness is twice as large as the Larmor radius of the secondary electrons. This is a valid assumption for magnetic fields of the order of , as in magnetron sputtering devices 30 and tokamaks 39 , but it may fail for lower magnetic fields ( ), as in Hall thrusters 9 or hollow cathode discharges 28 , 29 . The schematic representation of magnetic field B , electric field E and secondary electron velocity vectors is plotted in Fig.…”

“…The effective SEY is obtained by subtracting the number of recaptured electrons from the number of secondary electrons released by a single primary particle. It is a crucial parameter in various applications assisted by a magnetic field, such as: magnetically confined plasma in fusion devices 27 , Hall thrusters 8,9 , hollow cathode discharges 28,29 , or magnetron sputtering reactors 16,30,31 ; electron guidance by magnetic immersion lenses in scanning electron microscopy 32 ; magnetic suppression of the SEE from the beam screen of a high-energy accelerator 33 or from the negative electrode of a beam direct energy converter 34 . Therefore, the effective secondary electron emission under magnetic field influence has been investigated, independently or in connection with the mentioned applications.…”

Plasma Synthesis and Self-Assembly of Magnetic Nanoparticles

“…Recently, there are studies done which seek to combine the hollow cathode effect with the entrapment of electrons through magnetic fields, to further increase the efficiency of the hollow cathode sputtering technique. [16] Although interesting, this is not a topic of this thesis, and will therefore not be discussed further.…”

“…However, since hollow cathodes are used and not magnetrons, the correct term for the technique would be High Power Impulse Hollow Cathode Sputtering (HiPIHCS, "pronounced high-picks"). [16] The reason for using this pulsed technique is the large fraction of ionized species generated, and extracted, compared to DC. [15] The benefits of having ionized species for nanoparticle formation is discussed in the section "Nucleation and growth of nanoparticles".…”

Secondary electron emission under magnetic constraint: from Monte Carlo simulations to analytical solution

“…The SEE is influenced and may be controlled by the presence of a magnetic field at the emitting surface. It is the case of various applications: magnetically confined plasma in fusion devices [16], Hall thrusters [5,6], hollow cathode discharges [17,18] or magnetron sputtering reactors [13,19,20]; electron guidance by magnetic immersion lenses in scanning electron microscopy [21]; magnetic suppression of the SEE from the beam screen of a high-energy accelerator [22] or from the negative electrode of a beam direct energy converter [23].…”