Thermal balance of tungsten monocrystalline nanoparticles in high pressure magnetron discharges

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.

Spatial distributions of plasma parameters in conventional magnetron discharges in presence of nanoparticles

“…It has been shown (Arnas et al 2019) that the mean size of NPs synthesized from tungsten sputtering in magnetron discharges similar to those described above is around 20 nm after a 15 s discharge. The charging of an isolated dust particle is calculated classically using the orbital motion limited model where it is supposed that the ions and electrons have an orbital trajectory around the particle (Bernstein & Rabinowitz 1959).…”

“…The experimental set-up was already presented (Arnas et al. 2019) and is schematized in figure 1. Experiments are conducted in a stainless steel cylinder of 40 cm in length and 30 cm in diameter.…”

“…The discharge current is maintained constant at 0.3 A using a DC current-regulated power supply (Glassman HV, 1 A-1 kV) and the discharge voltage self-adjusts to approximately −200 V. The formation of NPs and then their sampling are carried out on stainless steel polished substrates, which are pushed one after the other under a hole drilled in the centre of the anode disc. The description of their formation in such discharge conditions and geometry as well as their structural properties were already reported in Arnas et al (2019) and will not be discussed in this article.…”

“…Many studies have explored the mechanisms of nanoparticle (NP) formation in low-temperature plasmas for various applications extending from electronics (Grieve, Mulvaney & Grieser 2000), optics (Kelly et al 2003), magnetism (Wei et al 2009) and catalysis (Cuenya 2010) to biology or medicine since nanoscale materials present enhanced properties compared to those of bulk materials (Chauduri & Paria 2012). Various ionization sources can be used in this domain such as radio-frequency discharges (Couedel et al 2010), microwave electron cyclotron resonance discharges (Ouaras et al 2015;Rojo et al 2019) and DC discharges (Kishor Kumar, Couedel & Arnas 2014;Michau, Hassouni & Arnas 2017) as well as magnetron sputtering discharges in a gas-aggregation system (MS-GAS) (Kashtanov, Sirnov & Hippler 2007;Hartmann et al 2012;Caillard et al 2015) and conventional magnetron discharges that we use for basic studies on NP formation (Arnas et al 2019). For a given plasma source, NP formation depends strongly on the discharge conditions (geometry, magnetic field configuration if any, discharge current and voltage, gas pressure and temperature).…”

Tungsten Nanoparticles Produced by Magnetron Sputtering Gas Aggregation: Process Characterization and Particle Properties

“…These observations are supported also by the SAED patterns presented as insets in Figures 7a and 8a, both presenting only bright spots. Details regarding the chemical composition of the W NPs and their oxidation in ambient air can be found elsewhere [28,52]. We briefly mention here that the amorphous layers which can be observed on the edges of the nanoparticles (see HRTEM images from Figures 7b and 8b) are due to post synthesis oxidation.…”