04Aa11-C12A7 エレクトライドの仕事関数ならびに負イオン生成挙動

H production and the work function behavior of C12A7 electride in low temperature plasmas
笹尾真実子1, L. ターリ2, G. カートリ2, J.M.ラエット2, M. ミニザーリ2,A. ハイラー3,4, R. フリードル3, U. ファンツ3,4, 尾藤圭太5, 和田元5
M. Sasao1, L. Tahri２, G. Cartry２, Jean-Marc Layet２, M. Minissale２, A. Heiler３,4, R. Friedl4, U. Fantz３,4,K. Bito5, M. Wada5
同志社研究開発機構1, マルセイユ大学2, アウグスブルグ大学3, マックスプランンクプラズマ物理研究所4, 同志社大学理工学部5
Office of R&D Promotion, Doshisha University1, Aix-Marseille Université2,Max-Planck-Institut für Plasmaphysik3, Universität Augsburg4,Graduate School of Science and Engineering, Doshisha University5
C12A7 electride is considered as one of thepossible plasma electrode materials of Cs-free
negative hydrogen isotope (H⁻/D⁻/T⁻) ion sources.
We have been carried out the work function
measurements [1], H⁻/D⁻ ion spectra measurementsfrom a C12A7 surface facing to a low-density
hydrogen plasma [2], and extraction of negativeions from a small aperture of a C12A7 plasma
electrode [3,4], and favorable results were reported.
Recently, C12A7 electride material is studied
with regard to the work function behavior in ahydrogen and deuterium plasma environment on thelaboratory experiment device ACCesS [5, 6]. The
material has proven to be resilient to hydrogen anddeuterium plasma exposure at ion source relevant
conditions. After initial conditioning of the surface
by thermal annealing and plasma exposure, shortplasma pulses lead to a work function to ~3.2 eV,
and the application of a positive bias potential
further lowers the work function to slightly below 3eV. In contrast, the application of a negative bias
potential leads to an increase of the work function
and a strong decrease of the photoelectric yield of
the surface [7].
Similar behavior on change of the work function
by the plasma bombardment at a positive bias wasobserved from a C12A7 electride target on a device,
PIIM, and PYS (photoelectron yield spectroscopy)in Aix- Marseille University [8, 9]. The lowest
value of the work function observed was ~2.5 eVafter annealing up to higher temperature. This value
was confirmed by UPS measurement with thesimilar conditioning procedure.
H-/D⁻ spectra from a C12A7 electride target
immersed in a hydrogen plasma were measured
simultaneously at PIIM. Fig. 1 shows NegativeIon (H-/D-) counts measured with EQP 300, vs.
work function measured by PYS. Peak counts aremostly contributed by desorption by scattering.
The target was biased negatively at 60V, and thesurface was bombarded by positive ions, mainly
H3+. The dependence on the work function is weak,
and the negative ion yield by D3+ ion bombardment
is lower than by H3+. The peak counts from C12A7
are one order higher compared with those from aclean molybdenum (shown by 2 solid lines).

Fig. 1 H- yield dependence on work function
References
1. M. Sasao, et al., AIP Conference Proceedings 1869,020005 (2017).
2. M. Sasao, et al., Applied Physics Express 11, 066201(2018).
3. M. Kobayashi, et al., AIP Conference Proceedings
2052, 020003 (2018).
4. T. Eguchi et al., Rev. Sci. Instrum. 91, 013508(2020).
5. R. Friedl, Rev. Sci. Instrum. 87, 043901 (2016)
6. S. Cristofaro et al., Plasma Res. Express 2, 035009(2020)
7. A. Heiler, et al., accepted by AIP Conference
Proceedings, NIBS2020
8. G. Cartry, et al., New Journal of Physics, 19(2),025010 (2017).
9. L. Tahri, et al., presented at JSI, 22-24 janvier 2020.