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Influence of ultra-low ethylene partial pressure on microstructural and compositional evolution of sputter-deposited Zr-C thin films

Abstract : Zr-C thin films are grown on single-crystalline MgO(001) substrates via ultra-high vacuum dc magnetron sputtering of Zr target in 10 mTorr Ar-C$_2$H$_4$ gas mixtures with ethylene partial pressures ($P_{C2H4}$) between 2 × 10$^{−7}$ Torr and 2 × 10$^{−4}$ Torr at substrate temperature $T_s$ = 923 K and using $P_{C2H4}$ = 2 × 10$^{−6}$ Torr at 723 K ≤ $T_s$ ≤ 1123 K. The as-deposited layer microstructure and composition are determined using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. We find that the layers sputter-deposited at $T_s$ = 923 K using the lowest $P_{C2H4}$ = 2 × 10$^{−7}$ Torr are polycrystalline, close-packed hexagonal structured Zr:C solid solutions. At higher $P_{C2H4}$ = 2 × 10$^{−6}$ Torr and 2 × 10$^{−5}$ Torr, we obtain films composed of free‑carbon (C) and NaCl-structured ZrC$_x$, $x$ ≤ 1. The amount of C increases 104% with ten-fold increase in $P_{C2H4}$ from 2 × 10$^{−6}$ Torr to 2 × 10$^{−5}$ Torr. At the highest $P_{C2H4}$ = 2 × 10$^{−4}$ Torr, the layers are X-ray amorphous with $\sim$49 at.% C. Films grown at 723 K ≤ $T_s$ ≤ 1123 K using constant $P_{C2H4}$ = 2 × 10$^{−6}$ Torr exhibit qualitatively similar microstructures, irrespective of $T_s$, composed of dense columnar ZrC$_x$ grains surrounded by C and corrugated surfaces. Our results suggest that the compositional and microstructural evolution of Zr-C films during reactive sputter-deposition of Zr is highly sensitive to ethylene partial pressure, with as little as 0.02% of the total pressure sufficient at $T_s$ ≥ 723 K to obtain ZrC$_x$ films.
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Hicham Zaid, Angel Aleman, Koichi Tanaka, Chao Li, Pascal Berger, et al.. Influence of ultra-low ethylene partial pressure on microstructural and compositional evolution of sputter-deposited Zr-C thin films. Surface and Coatings Technology, Elsevier, 2020, 398, pp.126053. ⟨10.1016/j.surfcoat.2020.126053⟩. ⟨cea-02884587⟩

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