Thermal balance of tungsten monocrystalline nanoparticles in high pressure magnetron discharges

TL;DR

This study investigates the thermal behavior of tungsten nanoparticles produced in high-pressure magnetron discharges, revealing their temperature and phase stability during synthesis.

Contribution

It introduces a thermal balance model for tungsten nanoparticles, explaining their temperature and phase stability in plasma conditions with residual oxygen.

Findings

Nanoparticles are core-shell with a beta-tungsten core and tungsten oxide shell.

The temperature of nanoparticles exceeds the gas temperature but does not induce phase transformation.

Metastable beta-tungsten phase remains stable during plasma synthesis.

Abstract

Nanoparticles are produced in sputtering magnetron discharges operating with a tungsten cathode at 30 Pa argon pressure. Structure analyses show that they are of core-shell type. The core is a monocrystal mainly in the metastable beta-tungsten phase and the shell is made of tungsten oxide. The origin of the metastable phase is attributed to the presence of residual oxygen in the device. Since this phase transforms into the stable alpha-tungsten phase by annealing, a standard model on the thermal balance of nanoparticles was used to find the temperature that they can reach under the considered experimental conditions. It is shown that this temperature is significantly higher than the gas one but not high enough to transform the monocrystalline metastable beta-phase during the plasma process.