*3.1. Plasma Treatment*

The schematic drawing and photograph of the experimental set-up for the inductively coupled radio-frequency plasma irradiation (27.12 MHz) [28] of the multiwall WS2 nanotubes is depicted in Figure 10.

In these experiments, non-thermal plasma with electrons, atoms and ions, having different temperatures each, was used to irradiate powders of multiwall WS2 nanotubes (INT-WS2), inorganic fullerene-like (IF) quasi spherical nanoparticles and different transition metal dichalcogenides microcrystalline 2H-platelets. A plasma power in the range of 400–600 W was applied for 5, 10, 20, 40 and 80 min. The electron temperature in these experiments was in the range of 1.7 × 104 –2.3 × 104 °K (1.5–2 eV), and the electron density was in the range of ~1012/cm3 [29].

The argon gas pressure was 10 Pa, and the flow speed of the Ar gas was 30–35 cm3 /s, while the base pressure before the Ar gas was 10<sup>í</sup><sup>4</sup> Pa. The temperature of the neutral Ar atoms and Ar+ ions is approximately two orders of magnitude smaller than that of the electrons. The plasma energy impact on the substrate surfaces was 2.3 W/cm2 at 400 W and 3.1 W/cm2 at 600 W [30]. The plasma parameters, pressure and energy impact were constant over the treatment time. The temperature of the substrate increased with time and depended on the heat conductivity and the quality of the thermal contact between the powder and the susceptor. The nanoparticles temperature was different from that of the gas. It was influenced by a number of factors, including the electron and ion bombardment, electron-ion recombination, reaction enthalpy from the chemical surface reaction, energy loss by heat radiation and conduction. The temperature of the nanotubes could be estimated to be in the range of a few hundred degrees centigrade [31].

**Figure 10.** (**a**) Schematic representation and (**b**) Photograph of the experimental set-up for the plasma treatment of the multiwall WS2 nanotubes.
