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 ： 2204029S

Ｂ Ｌ 番 号 ： 12（様式第 4 号）
同軸型アークプラズマ成膜法における負バイアスおよび窒素ドーピングが超硬基板
上 に 成 膜 し た 超 ナ ノ 微 結 晶 ダ イ ヤ モ ン ド /ア モ ル フ ァ ス カ ー ボ ン 混 相 膜 の 化 学 結 合 状 態に与える効果
Effects of Negative Bias and Nitrogen-doping on Chemical Bonding Structure ofUltrananocrystalline Diamond/Amorphous Carbon Films Deposited on WC-Co Substrates byCoaxial Arc Plasma Deposition
Ali Mohamed Ali, Hiroshi Naragino, Seishiro Saito, and Tsuyoshi Yoshitake
九州大学大学院総合理工学研究院
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University※１※２※３※４

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１．概要（注：結論を含めて下さい）
Hard nanodiamond composite films were fabricated on negatively biased tungsten carbide
substrates by coaxial arc plasma deposition. The deposition was performed at different
substrate bias voltage using a pure graphite target of arc gun at a pressure less than 10 -4 Pa
without inserted gases. The influences of the substrate bias voltage on the deposition process,mechanical and structural properties of the films were investigated. At appropriated bias
voltage, the accelerated positive carbon ions have shown prudent deposition condition
favorable for nanocrystalline diamond growth. As a result, hard films of 80 GPa wereperformed at a bias voltage of -120 V. The outcomes of X-ray photoelectron and near-edge
X-ray absorption fine structure spectroscopies certified the enhancement of sp 3 hybridization
carbon. This significant improvement in the mechanical properties is consistent with enhanced
C 1s→ σ* transitions in the deposited films.

２．背景と目的
Ultrananocrystalline diamond/ amorphous carbon(UNCD/a-C) coating, a suitable mechanical form ofcarbon nanomaterials with a composite structure ofamorphous carbon (sp2 and sp3 hybridization) and
nanodiamond

crystallites,

haveexcellent

hardness,chemical inertness, biocompatibility, wear-resistance andsurface smoothness as well as low friction coefficient.
Chemical vapor deposition (CVD) has been essentiallyemployed for nanodiamond films deposition. Recently,

Figure 1 Load–displacement curve of UNCD/a-C films

pulsed coaxial arc plasma deposition (CAPD) has been

deposited at negative bias voltage of -120 (red), -80

used as a typical physical vapor deposition (PVD) method(blue), -60 (black), -40 Volts (green), and no bias

with significantly improved properties over the CVD

voltage (yellow).

growth techniques.

.

To improve the deposition ability of the CAPD
system and increase the energy of the deposited plasma
species, the development of coating systems was driven
by negatively biasing the substrate during the deposition.
This work was primarily aimed to study the influence ofdifferent negative bias voltage on the growth of
UNCD/a-C films prepared by CAPD. The effects on themechanical and structural properties of the films wereinvestigated.
３．実験内容（試料、実験方法、解析方法の説明）

Figure 2 Adhesion strength measured by scratch testing

UNCD/a-C films were deposited on negativelyof UNCD/a-C films deposited at different bias voltage

biased WC-Co substrates at base pressures of less than
10−4 Pa by CAPD with a graphite target. WC–Co
substrates (K-type cemented tungsten carbide) with adimension of 10×4.5 mm were employed for film
deposition. A voltage of 100 V was applied to the arc
plasma gun equipped with a 720-µF capacitor. The
repetition rate of discharges was 1 Hz. The substrateholder was biased at a voltage of -40, -60, -80, -120 V.
The hardness and Young’s modulus of the films wereestimated by nanoindentation with an applied indentationload of 0.5 mN/10 s. The adhesion strength of theFigure 3 NEXAFS spectra of UNCD/a-C films withfabricated films was evaluated by a scratch test. X-raydifferent hardness.

photoelectron and near-edge X-ray absorption fine structure (NEXAFS) spectroscopies were employed forcharacterizing the chemical bonding structures of the films.
４．実験結果と考察
The hardness of the fabricated films were evaluated from the load-displacement curves obtained fromnanoindentation as shown in Fig. 1. It clearly shows that the hardness and Young’s modulus increases withincreasing the bias voltage. The hardness at -120 V was 80 GPa. The substrate with a negative bias
voltage has a major role in enhancing the mechanical properties, including hardness, whichindicates that the negative bias electrically attracts positively-charged carbon species to the substrates. The
adhesion strength measured by scratch testing of UNCD/a-C films has shown marked improvement withincreasing the negative bias voltage, as shown in Fig. 2. The presented Figure shows a micrograph of thescratch tested UNCD/a-C films fabricated at different bias voltage. The critical load of the films fabricatedwithout bias voltage was found to be 7 N which rose to 19 and 28 N when fabricated at bias voltage of -60 and-80 V, respectively. The top image presents how the film fabricated at -120 V was able to withstand ascratching load up to 40 N. For a complementary structural analysis, NEXAFS spectroscopy was obtained forthe deposited samples. Figure 3 shows NEXAF spectra exhibit sharp absorption bands from a C 1s→ σ* and C
1s→ * transitions, which are characteristic of sp2 and sp3 hybridized carbon (double bond) and (single bond),respectively. The relative intensity of σ* peak gradually enhanced compared with the * peak, with the bias
voltage, which agrees with hardness enhancement. This might imply that the negative bias plays a role inenhancing the formation of nanocrystalline diamond and reducing the internal stress of the films.
５．今後の課題
In this work, the role of negative bias in the enhancement of mechanical properties, and the relationshipbetween the film hardness and C 1s→ σ* and C 1s→ * transitions were investigated. The results
demonstrated that the use of negative bias enhance the formation of sp3 bonds which work on improving themechanical properties of the deposited films.
６．参考文献[1] A. M. Ali et al., Diam. Relat. Mat. 96, 67 (2019).
[2] Y. S. Li et al., J. Appl. Phys. 101, 073503 (2007).
[3] A. M. Ali et al., Appl. Phys. Express 13, 065506 (2020).
[4] A. M. Ali et al., Surf. Coat. Technol. 417, 127185 (2021).

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）
該当なし．
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, Coaxial arc plasma, negative bias, Hardness, near-edge X-ray absorption fine structure.

９．研究成果公開について① 論文（査読付）発表の報告（報告時期：2021 年 3 月）