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Plasma diagnostic and mechanical properties of tetrahedral amorphous carbon (ta-C) Thin films deposited by varying pulse power and mixed discharge parameters using high-power impulse magnetron sputtering.

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Title: Plasma diagnostic and mechanical properties of tetrahedral amorphous carbon (ta-C) Thin films deposited by varying pulse power and mixed discharge parameters using high-power impulse magnetron sputtering.
Authors: Yang, Fu-Sen1,2 (AUTHOR), Kuo, Yu-Lin1 (AUTHOR), Chang, Chi-Lung1,2,3 (AUTHOR) clchang@mail.mcut.edu.tw
Source: Diamond & Related Materials. Jan2026, Vol. 161, pN.PAG-N.PAG. 1p.
Subjects: Amorphous carbon, Thin films, Plasma diagnostics, Magnetron sputtering, Mechanical behavior of materials, Pulsed power systems, Carbon films
Abstract: This study investigates the deposition of tetrahedral amorphous carbon (ta-C) thin films using high-power impulse magnetron sputtering (HiPIMS) with a graphite target under various pulse power parameters and discharge modes, including a mixed-mode HiPIMS combined with arc discharge. Plasma diagnostics revealed that both HiPIMS and mixed-mode HiPIMS+Arc configurations significantly enhanced plasma energy, ionization rate, and density. A peak power density of 5.9 kW/cm2 and a high-energy C+ ion distribution were achieved by adjusting the high-voltage pulse duration. Combined X-ray reflectivity (XRR) and atomic force microscopy (AFM) analyses showed that modifying the pulse count or the high-voltage pulse duration increased thin film density and reduced surface roughness, yielding a maximum density of 2.6 g/cm3 and a minimum roughness of 0.88 nm. Transmission electron microscopy (TEM) revealed that while the ta-C thin films remained predominantly amorphous, localized nanocrystalline i‑carbon (intermediate carbon phase, ICP) (110) structures with an interplanar spacing of 0.32 nm were formed under high-energy plasma conditions. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and nanoindentation demonstrated that both discharge modes improved the sp3 bonding ratio, I D /I G ratio, hardness, and Young's modulus. The highest sp3 content (37.2 %) and compressive stress (−2.79 GPa) were achieved using a three-pulse HiPIMS configuration, while the highest hardness (27.2 GPa) and modulus (219.6 GPa) were obtained at a high-voltage pulse duration of 80 μs. These findings confirm that mixed-mode HiPIMS+Arc discharge provides an effective approach for producing dense, smooth, and mechanically robust ta-C thin films with localized nanocrystalline structures. Energy distribution of the carbon plasma ions under different power modes and the corresponding SAED crystal structure variations of the tetrahedral amorphous carbon thin films. [Display omitted] • i-Carbon (intermediate carbon phase, ICP) nanocrystals identified by TEM/SAED at d ≈ 0.32 nm (110) plane. • sp3-rich bonding achieved through energetic ion bombardment control. • Mixed-mode discharge enhances carbon ionization and thin film densification. • ta-C thin films show improved hardness and structural compactness. [ABSTRACT FROM AUTHOR]
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Abstract:This study investigates the deposition of tetrahedral amorphous carbon (ta-C) thin films using high-power impulse magnetron sputtering (HiPIMS) with a graphite target under various pulse power parameters and discharge modes, including a mixed-mode HiPIMS combined with arc discharge. Plasma diagnostics revealed that both HiPIMS and mixed-mode HiPIMS+Arc configurations significantly enhanced plasma energy, ionization rate, and density. A peak power density of 5.9 kW/cm2 and a high-energy C+ ion distribution were achieved by adjusting the high-voltage pulse duration. Combined X-ray reflectivity (XRR) and atomic force microscopy (AFM) analyses showed that modifying the pulse count or the high-voltage pulse duration increased thin film density and reduced surface roughness, yielding a maximum density of 2.6 g/cm3 and a minimum roughness of 0.88 nm. Transmission electron microscopy (TEM) revealed that while the ta-C thin films remained predominantly amorphous, localized nanocrystalline i‑carbon (intermediate carbon phase, ICP) (110) structures with an interplanar spacing of 0.32 nm were formed under high-energy plasma conditions. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and nanoindentation demonstrated that both discharge modes improved the sp3 bonding ratio, I D /I G ratio, hardness, and Young's modulus. The highest sp3 content (37.2 %) and compressive stress (−2.79 GPa) were achieved using a three-pulse HiPIMS configuration, while the highest hardness (27.2 GPa) and modulus (219.6 GPa) were obtained at a high-voltage pulse duration of 80 μs. These findings confirm that mixed-mode HiPIMS+Arc discharge provides an effective approach for producing dense, smooth, and mechanically robust ta-C thin films with localized nanocrystalline structures. Energy distribution of the carbon plasma ions under different power modes and the corresponding SAED crystal structure variations of the tetrahedral amorphous carbon thin films. [Display omitted] • i-Carbon (intermediate carbon phase, ICP) nanocrystals identified by TEM/SAED at d ≈ 0.32 nm (110) plane. • sp3-rich bonding achieved through energetic ion bombardment control. • Mixed-mode discharge enhances carbon ionization and thin film densification. • ta-C thin films show improved hardness and structural compactness. [ABSTRACT FROM AUTHOR]
ISSN:09259635
DOI:10.1016/j.diamond.2025.113105