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.

Two-dimensional spatial measurements of magnetic field and plasma parameters have been performed in conventional magnetron DC discharges during the formation of metallic nanoparticles. Correlations between the electron density and temperature distributions, and the magnetic field geometry and strength have been established. A sharp increase of the plasma potential is found on the edge of the last magnetic arch followed by a decrease towards the anode plate and edges. It is shown that the spatial variation of the plasma potential is at the origin of a potential well that can trap negatively charged nanoparticles.

Abstract. In this article, plasma parameters during tungsten nanoparticle growth in a high-pressure direct-current magnetronsputtering discharge were studied over a wide range of gas pressures and discharge currents. Langmuir probe and optical emission spectroscopy measurements were performed. Correlation between nanoparticle size distribution and probe and spectroscopy measurements are discussed.

Two-dimensional measurements of magnetron discharge plasma parameters are used to calculate the forces applied to an isolated nanoparticle in conditions where nanoparticles are produced from cathode sputtering. Plasma spatial inhomogeneities, which are specific to magnetron discharges, also induce inhomogeneities in the charging mechanism and applied forces. It is shown that the nanoparticle transport is due to electric, thermophoretic and ion drag forces, and that the dominant one proportional to the nanoparticle size varies according to position. For a given plasma, these spatial differences explain the segregation of size in the nanoparticle deposits, which are observed inside the device.