Raman microscopy investigation of beryllium materials

Abstract

We report for the first time on the ability of Raman microscopy to give information on the structure and composition of Be related samples mimicking plasma facing materials that will be found in ITER. For that purpose, we investigate two types of material. First: Be, W, Be 1 W 9 , and Be 5 W 5 deposits containing a few percents of D or N, and second: a Mo mirror exposed to plasma in the main JET chamber (in the framework of the first mirror test in JET with ITER-like wall). We performed atomic quantifications using ion beam analysis for the first samples. We also did atomic force microscopy. We found defect induced Raman bands in Be, Be 1 W 9 , and Be 5 W 5 deposits. Molybdenum oxide has been identified showing an enhancement due to a resonance effect in the UV domain.

Preparing the future post-mortem analysis of beryllium-based JET and ITER samples by multi-wavelengths Raman spectroscopy on implanted Be, and co-deposited Be

“…the answer is not necessarily "yes". For example in [27] we were not able to detect Be-N nor Be-D bonds whereas we were able to do so in [38] by identifying BeD 2 hydrides. Then, here by "defects", we mean every kind of defects that can modify the long range crystallographic order of a pristine crystal, the holy grail to reach with this technique being to be defect-sensitive for every material studied.…”

“…This work follows two precedent works [27,38] where we were able to detect the growth of BeD 2 crystals under D implantation conditions. Here we focus on the finger print of defects in the Raman spectra of Be due to deposition process with some impurities (D 2 , or N 2 atmospheres) codeposits (with C) or D implanted samples that generate defects, whatever they are (single interstitial atom, vacancy, di-vacancy, chemical bond creation,...).…”

“…Broad bands lying at 645, 887 and between 1008 and 1113 cm -1 have been attributed to defect induced bands in [27]. We will investigate it deeper when describing figure 3.…”

“…The logarithmic scale used here allows to distinguish several additional broad bands (413, 544 and 616 cm -1 ) that were first evidenced in [27], and called defect induced bands. As explained in [27], all these bands are similar whatever D or N being included in the material, meaning these bands are not directly related to Be-D or Be-N vibrators, but their inclusion produces defects in the crystal giving rise to these bands, which are interpreted as Phonon Density of States (PDOS).. Selection rules are relaxed by defects as defects break the translational symmetry of the crystal.…”

“…Raman microscopy is a nondestructive, non-contact, and local (≈1m 2 lateral resolution [23]) technique that has been proved to be sensitive to Be stretching modes [24], beryllium oxide modes [25], bending and stretching tungsten oxide modes [26], Be x W y mixed samples density of states [27], Be-C-W irradiated samples [28], and give information when a pristine material is implanted by hydrogen ions [27,29,30]. First Raman analyses in ILW-tokamaks were performed on several molybdenum JET mirrors [27], showing that the technique is sensitive to thin (≈10 nm) deposited layer composed of ≈33% Be, ≈33% C and ≈33% O and to the underlying molybdenum oxidized mirror, the atomic percent being obtained by X-ray Photon spectroscopy (XPS). C-O and C=O modes have been detected in that layer, and defective or beryllium mixed with O and/or C have been found without possibility to identify the phases rigorously up to now, because of a poor benchmarking of the technique for these materials.…”