Morphological Changes of Tungsten Surfaces by Low-Flux Helium Plasma Treatment and Helium Incorporation via Magnetron Sputtering

Abstract

The effect of helium on the tungsten microstructure was investigated first by exposure to a radio frequency driven helium plasma with fluxes of the order of 1 × 10(19) m(-2) s(-1) and second by helium incorporation via magnetron sputtering. Roughening of the surface and the creation of pinholes were observed when exposing poly- and nanocrystalline tungsten samples to low-flux plasma. A coating process using an excess of helium besides argon in the process gas mixture leads to a porous thin film and a granular surface structure whereas gas mixture ratios of up to 50% He/Ar (in terms of their partial pressures) lead to a dense structure. The presence of helium in the deposited film was confirmed with glow-discharge optical emission spectroscopy and thermal desorption measurements. Latter revealed that the highest fraction of the embedded helium atoms desorb at approximately 1500 K. Identical plasma treatments at various temperatures showed strongest modifications of the surface at 1500 K, which is attributed to the massive activation of helium singly bond to a single vacancy inside the film. Thus, an efficient way of preparing nanostructured tungsten surfaces and porous tungsten films at low fluxes was found.

Plasma-assisted catalytic formation of ammonia in N2–H2plasma on a tungsten surface

“…For each step a new fresh 20 nm tungsten film was deposited on silicon wafer by means of pulsed-DC magnetron sputtering of a 99.95% pure W target (details about the deposition parameters can be found in ref. 40).…”

Surface Modifications Induced by High Fluxes of Low Energy Helium Ions

“… 4 5 6 7 More recently, significant surface modifications were observed on tungsten under low-energy He ion irradiation, with ion energies below the threshold for damage creation, and investigated as a function of surface temperature, ion flux and exposure time. 8 9 10 11 These studies revealed the formation of a fine nanostructure exhibiting a high porosity of up to 90% and high light absorption. 12 13 14 The size of those nanostructures and thickness of the nanostructured layer could be controlled by surface temperature and plasma exposure time, respectively.…”

Evolution of the properties of helium nanobubbles during in situ annealing probed by spectrum imaging in the transmission electron microscope

“…However, other potential applications have been demonstrated such as annihilation of dislocations in GaN [12], reducing the threading dislocation density via the enhancement of the strain relaxation of SiGe/Si heterostructures [13], * marie-laure.david@univ-poitiers.fr the proximity gettering of metallic impurities [14], or the fabrication of ultrathin buried oxide layers in silicon [15]. Finally, low-energy helium plasma treatments have recently received considerable interest for nanostructuration of surfaces with applications in domains of energy conversion and storage devices, by both bottom-up [16] or top-down approaches [17,18]. In particular, nanopores in amorphous silicon coatings produced using such methods have been revealed to contain a high helium density [19].…”