Dependence of the damage in optical metal/dielectric coatings on the energy of ions in irradiation experiments for space qualification

Abstract

Terrestrial accelerator facilities can generate ion beams which enable the testing of the resistance of materials and thin film coatings to be used in the space environment. In this work, a [Formula: see text]/Al bi-layer coating has been irradiated with a [Formula: see text] beam at three different energies. The same flux and dose have been used in order to investigate the damage dependence on the energy. The energies were selected to be in the range 4-100 keV, in order to consider those associated to the quiet solar wind and to the particles present in the near-Earth space environment. The optical, morphological and structural modifications have been investigated by using various techniques. Surprisingly, the most damaged sample is the one irradiated at the intermediate energy, which, on the other hand, corresponds to the case in which the interface between the two layers is more stressed. Results demonstrate that ion energies for irradiation tests must be carefully selected to properly qualify space components.

Figure 1

Stopping range of ${\text{He}}^{+}$ ions determined by simulations of collision dynamics with the TRIM/SRIM software for the energies used in the experiments.

Figure 2

(a): Spectral reflectance of the ${\text{TiO}}_2$/Al samples irradiated at different energies. (b): Total integrated scattering (TIS) measured for indicated the samples.

Figure 3

Grazing incidence XRD spectra acquired for the various ${\text{TiO}}_2$/Al samples at $1^{\circ }$ in $\omega .$

Figure 4

${\text{TiO}}_2$ peaks candidates.

Figure 5

Cross-sectional TEM bright-field images (a, c, e, g) of the reference sample and the irradiated samples at 4 keV, 16 keV, and 100 keV, respectively as well as higher magnified (b, d) and high-resolution TEM images (f, h) for the areas marked in the corresponding overview images on the left side.

Figure 6

AFM images of the reference (a), the 4 keV-irradiated sample (b) and the 16 keV-irradiated sample (c,d).

Figure 7

SEM images of the samples irradiated with 16 keV (a,b) and 100 keV (c,d) He ions.

Figure 8

AFM image of the sample irradiated with 100 keV He ions (on the left). On the right: a height profile for the evaluation of the bubble sizes and the bubble count as function of their diameter.