Sputtering in vacuum: A technology for ultraclean metallization and space propulsion

Sputtering is a well known coatings technology belonging to the group of physical vapor technologies. In contrast to cathodic arcs, sputtering can easily be scaled and does not produce the unwanted, ldquoinfamousrdquo macroparticles. Sputtering is conventionally done in the presence of a sputtering gas such as argon. For reactive deposition, argon is mixed with reactive gases such as nitrogen (for nitrides) or oxygen (for oxides). In this contribution we will report about a new development that allows sputtering in high or even ultrahigh vacuum to occur, without the addition of any gas at any time. This ldquogasless sputteringrdquo enables the deposition of ultra-clean metal coatings, in which even trace amounts of argon can be avoided. The key ldquoingredientsrdquo for gasless sputtering to work is (i) providing a short pulsed plasma flow aiming onto the magnetron target, and (ii) provide enough voltage (and power) to the magnetron that the discharge can run away into the so-called sustained self-sputtering (SSS) mode. We will describe the physical principles of operation, and outline further uses of the hardware, such as thrusters for space propulsion.