九州シンクロトロン光研究センター
県有ビームライン利用報告書
課 題 番 号 ： 1905035S

Ｂ Ｌ 番 号 ： 12（様式第 5 号）

バイアス印加基板に堆積した超ナノ微結晶ナノダイヤモンド膜の化学結合構造
Studies on chemical bonding structures of ultrananocrystalline diamondfilms deposited on cemented carbide substrates biased negatively
アリ モハメド アリ，エギザ モハメド，星野光一朗，田中佑樹，大植英生，吉武 剛
Ali Mohamed Ali, Mohamed Egiza , Koichiro Hoshino, Yuki Tanaka, Hideki Ohue,and Tsuyoshi Yoshitake
九州大学大学院総合理工学府量子プロセス理工学専攻

Department of Applied Science for Electronics and Materials, Kyushu University※１※２※３※４

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１．概要（注：結論を含めて下さい）
Ultrananocrystalline diamond/amorphous carbon composite (UNCD/a -C) films were
deposited on negatively biased cemented carbide (WC-Co) substrates by coaxial arc
plasma deposition. The deposition rate is increased to be 0.9 nm/s, which isapproximately 3 times larger than that of films deposited under no bias condition. Inaddition, the critical load in sc ratch tests was enhanced to be 31 N, which is 4 times
more than that of the no bias films. On the other hand, the hardness was slightly
degraded by employing the negative bias. From electrical diagnostics of the biasapplication, it was found that the nega tive bias is immediately compensated by thearrival of highly-dense positive carbon ions at the substrate and the substrate is
weakly positively charged after the compensation. This might be the main reason forthe degraded hardness by the bias application , Since the positive bias deaccelerate
carbon ions, which facilities the formation of sp2 bonds.

２．背景と目的The hardness, adhesion, wear resistance, smoothness, and maximum film thickness are important key factors
for the hard coating applications. It is well known that negative bias application to substrates enhances theirmechanical key factors, particularly the hardness and adhesion strength, of DLC films prepared by physicalvapor de- position. Concretely, it was reported that the hardness increases by 10–20 GPa as compared with thatof films without biases and the ad- hesion strength is apparently improved by applying high negative bias
voltages to substrates [1–2]. In addition, the overall compressive stress in films decreases by applying biases tosubstrates, which results in the maximum film thickness to be deposited without being peeled off from thesubstrates.
On the other hand, there have a few research on the effects of negative bias application to UNCD/a-C films.
Although it was reported that the formation of high-density nanocrystalline diamond (NCD) and UNCD on
non-diamond substrates was achieved by bias enhance nucleation (BEN) and growth (BEG) for the deposition
by microwave plasma CVD, the bias effects have never been studied for UNCD/a-C films prepared by CAPD
thus far. In this work, to improve the mechanical key factors of UNCD/a-C films prepared by CAPD, negativebias voltages were applied to WC-Co substrates, and theeffect on the mechanical properties of the films wereinvestigated. In addition, the electrical diagnostics wasemployed for investigating the bias process.
３．実験内容（試料、実験方法、解析方法の説明）
UNCD/a-C films were deposited on negatively-biased
WC-Co substrates at base pressures of less than 10−4 Pa by
CAPD with a graphite target (purity 99.99%). A voltage of100 V was applied to an arc plasma gun equipped with a 720
μF capacitor. The repetition rate of discharges was 1 Hz. A
distance between a coaxial arc gun and the substrate was 15mm. A substrate holder that was electrically isolated fromthe vacuum chamber of a CAPD deposition apparatus wasconnected to a Tru-Plasma Bipolar 4020 power supply, andquasi-DC bias of −100 V was applied in pulse with aduration of 8.7 μs at frequencies of 40, 60, and 80 kHz. The
formation of UNCD grains in the deposited films wasconfirmed by Raman spectroscopy. X-ray photoelectron andnear-edge X-ray absorption fine structure (NEXAFS)
spectroscopies were employed for characterizing thechemical bonding structures of the films at beamline
12 of Kyushu Synchrotron.

Fig. 2. Typical C1s X-ray photoelectron spectra offilms deposited at (a) un-bias, and bias frequency of(b)40 kHz and (c)80 kHz. Inset show survey
spectra.

Fig. 1. Raman spectra of films deposited at (a)un-bias, and bias frequency of (b) 40kHz and(c)80 kHz.

Fig. 3. Typical C1s X-ray photoelectron spectra offilms deposited at (a) un-bias, and bias frequency of(b)40 kHz and (c)80 kHz. Inset show survey
spectra.

４．実験結果と考察
It was found that The deposition rate of the UNCD/a-C films was drastically increased by the negative bias
application. The deposition rate increases with increasing substrate current. Since the substrate current isattributed to the arrival of positively-ionized carbon species, this implies that carbon species ejected from thegraphite cathode are almost positively ionized and they are attracted by the negative bias. The film thickness is
in- creased to be approximately 9 μm without the film being peeled off from the substrate. Raman spectroscopy
is a standard characterization technique for carbon system. Fig. 1 exhibiting the typical peaks associated withUNCD/a-C composited films. A distinct Raman band at 1337 cm−1 shows a typical behavior for diamondbonded of the deposited films.
X-ray photoelectron spectroscopy is an appropriate technique to assess the chemical composition ofUNCD/a-C films. Fig. 2 shows X- ray photoemission spectra of the films deposited at different bias

frequencies measured using synchrotron radiation. The inset shows survey spectra measured with a MgKα line.
Intense C 1s and O 1s peaks are observed at binding energies of 284.5 and 532.5 eV, respectively. To analyze
the spectra more precisely, the C 1s spectra are decomposed into C=C (sp2), C-C (sp3), C-O, and C=O peaks
with Voigt function after the backgrounds being subtracted by Shirley method. The sp3/(sp2 +sp3) ratio,
namely sp3 fraction, was estimated from the areas of the decomposed sp3 and sp2 peaks.
NEXAFS measurements were examined to investigate the chemical structures of the films. NEXAFS spectraof the films deposited at no bias and different bias frequencies of 40 and 80 kHz are shown in Fig. 3. Thespectra show sharp absorption due to π∗ transition, and it was decomposed into peaks due to π1∗ C=C, π2∗ C=C,and π∗ C≡C peaks located at photon energies of 284.8, 285.6, and 287.27 eV, respectively.
５．今後の課題
In this work, we could confirm the decreased sp3 content responsible for the regarded hardness and Young’s
modules of the negatively biased films. In addition, the results indicated from Raman spectroscopy strongly
agree with that indicated from XPS and NEXAFS. The surface charge up phenomena was observed during thefilms deposition, it worked on reducing the negative bias voltage and ion energy at the high bias frequency.
Therefore, the surface charge up produce more graphitic carbon bonds and reduce the hardness. The results
point out that changing the pulsed bias parameters do affect UNCD/a-C film properties. Therefore, we expectthat the properties of UNCD/a-C films can be controlled and improved by selecting suitable bias conditions.
６．参考文献1 Zhong, X. et al. (2009). Journal of Applied Physics, 105(3), 034311.
2 Chu, Y. et al. (2012). Journal of Applied Physics, 112(12), 124307.

７．論文発表・特許（注：本課題に関連するこれまでの代表的な成果）▪ Hiroshi Naragino et al., Evergreen, 03, 1-5 (2016)▪ Mohamed Egiza et al., Evergreen, 03, 32-36 (2016)▪ Hiroshi Naragino et al., Jpn. J. Appl. Phys 55, 030302 (2016)▪ Hiroshi Naragino et al. Appl. Phys. A, 122, (2016).
▪ Ali M. Ali, et al., 17 (ALC17) Proceedings pp. 194-196 (2017).
▪ Ali M. Ali, et al., Proceedings of CSS pp. 204-205 (2017).
▪ Egiza, M., et al., Coatings, 8(10), 359 (2018).
▪ Ali M. Ali, et al., Proceedings of IEICES (2018).
８．キーワード（注：試料及び実験方法を特定する用語を２～３）
Nanodiamond, Hard coating, Coaxial arc plasma deposition, CAPD, Raman, Nanoindentation, Soft X-rayspectroscopic, Si doping

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① 論文（査読付）発表の報告（報告時期：2022 年3 月）