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 ： 1911112S

Ｂ Ｌ 番 号 ： 12（様式第 5 号）

タ ン グ ス テ ン バ ッ フ ァ 層 を 有 す る 超 硬 合 金 基 板 及 び Si 基 板 上 に 堆 積 し た ナ ノ
ダイヤモンドコンポジット膜の機械特性と化学結合構造との相関の解明（Ⅱ）
Study on relationship between mechanical properties and chemical bonding
structures of nanodiamond composite films deposited on cemented carbide withtungsten buffer layer and Si substrates (II)エ ギ ザ モ ハ メ ド ， ア リ モ ハ メ ド .ア リ , 田 中 佑 樹 , 星 野 光 一 朗 , 吉 武 剛
Mohamed Egiza, Ali M. Ali, Yuki Tanaka, Koichiro Hoshino, 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
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１．概要（注：結論を含めて下さい）
Nanodiamond composite (NDC) films, which comprise nano-diamond crystals embedded inamorphous carbon matrix (a-C) can be applied in a variety of fields owing to their superior
electrical, optical, and mechanical properties. The high hardness and extremely smoothsurfaces of NDC films as compared with those of polycrystalline diamond films are keys
for the application to hard coating on cemented carbide and silicon substrates, which arerepresentative substrates for cutting tools and electronic devices, respectively. NDC films
were deposited by coaxial arc plasma deposition (CAPD) on cemented carbide (WC-Co)
substrates directly and with tungsten (W) intermediate layers.
The films deposited on W intermediate layers achieved an evident enhancement in thehardness to 67.5 GPa and Young’s modulus to 719 GPa, as compared with the hardness of
50 GPa and Young’s modulus of 520 GPa of films deposited directly on the substrate s. Thissignificant improvement in the mechanical properties is consistent with enhanced C-C sp 3
fractions in the films. It was found that the W intermediate layers suppress Co catalytic
effects that induces graphitization specially at the interface and thus improve formation of
diamond crystals and enhances films adhesion .

２．背景と目的
Diamond and related hard carbon coatings haveattracted attention because they are effectively applicable
to cutting non-ferrous and abrasive materials due to theirunique features such as high hardness and excellent moldrelease. The physical properties of carbon materials arestrongly influenced by the ratio of sp3 (diamond-like) tosp2 (graphite-like) bonds. Nanodiamond composite(NDC) films deposited directly on WC-Co at room
substrate-temperature exhibit maximum hardness of 50
GPa and a young’s modulus of 520 GPa [1]. It wasdemonstrated that low substrate temperature is effective
to diamond growth and suppressing the Co catalytic
effects at the interface. Furthermore, the diffusion of Co
atoms into the films hardly occurs even at the substratetemperature of 550 ºC. To further understand the role of
Co catalytic effects on the properties of the films, W
intermediate layer was sputtered prior to the film
deposition, because it was reported that the insertion of
W intermediate layer can improve diamond growth ratewith finer grain structure, achieve highest nucleation
density of diamond comparing to other strong
carbide-forming elements (Ti and Cr), and suppress Co
catalytic effects and compressive stress at the interface,which improves films adhesion.
The effects of W buffer layer on the films growth, thehardness, and Young’s modulus of the films were studied.
In addition, the chemical bonding structures of the films
were investigated by X-ray photoemission spectroscopy
and near-edge X-ray absorption fine-structure
spectroscopies to understand the physical origin of thefilms properties due to insertion of W intermediate layer.
３．実験内容（試料、実験方法、解析方法の説明）
WC–Co substrates (K-type cemented tungsten carbide)with a dimension of 10 × 4.5 mm were employed forfilm deposition. Only the pretreatment of roughening thesubstrates surface was chemically made in the roughness
average range of 0.15–0.2 μm to enhance the adhesion of
the films. Prior to the film deposition, the surfaces of thesubstrates were cleaned in acetone and methanol
ultrasonic bathes for 7 min, respectively.
NDC films were deposited on WC-Co substrates at room
substrate-temperature by CAPD with pure graphitetargets. The inside of a vacuum apparatus was evacuatedto base pressures of less than 10-4 Pa by a turbo
molecular pump. An arc plasma gun equipped with a 720µF capacitor was operated at an applied voltage of 100 V.
The films were deposited directly and with sputtered W
intermediate layer at various thicknesses as shown in Fig.
1. The hardness and Young’s modulus of the depositedfilms were investigated by nano-indentation. The
deposited films were characterized by X-ray
photoemission spectroscopic at beamline 12 of Kyushu
Synchrotron.

Fig. 1 schematic diagram of NDC films deposited on
WC-Co substrates after insertion of W intermediatelayer.

Fig. 2 Raman spectra of NDC films deposited on
WC-Co substrates.

C-C

*C-C

*HOPGPCDFig. 3 C K-edge NEXAFS spectra of NDC films
deposited on WC-Co substrate (a) with and (b) without
W intermediate layer, and (c) reference spectrum of highoriented pyrolytic graphite (HOPG) and polycrystalline
diamond (PCD).

４．実験結果と考察
The films deposited directly on WC-Co substrates exhibit a hardness of approximately 50 GPa and Young’s
modulus of 520 GPa. A Raman spectrum of the films is shown in Fig. 2. A peak detected at 1337 cm−1 might bedue to UNCD grains. The peak position is slightly shifted from that of bulk diamond peak (1333 cm−1 ) and its
peak is broaden, which might be due to phonon confinement effects and scattering in nano-sized grains anddue to the coexistence of D-band peak coming from a-C. Moreover, a broad peak around 1580 cm−1 wasobserved, which attributed to G-band of amorphous carbon matrices due to the bond stretching of carbon atoms
in sp2 hybridization. By the insertion of W intermediate layer, the hardness and Young’s modulus wereimproved to 67.5 GPa and 719 GPa, respectively. This improvement might be attributed to the suppression ofCo catalytic effects that induces films graphitization and in turn reduces films hardness and Young’s modulus.
Also, the adhesion between NDC film and WC-Co substrate was successfully enhanced due to the buffer layer
enhanced the chemical compatibility between the film and substrate.
Figure 3 shows NEXAFS spectra of NDC films deposited with and without inserted W intermediate layer. TheNEXAFS spectra show intense C-C  peak to the films deposited on W intermediate layer comparable to thedirectly deposited films. The inserted W intermediate layer improved the diamond formation in the films,
which enhances films hardness. Additionally, the center of  peak is shifted to the high energy side, whichmight be attributed to suppressing films compressive stress due to insertion of W intermediate layer.
５．今後の課題
This experiment shows the role of W intermediate layer in the suppression of Co catalytic effects, and therelationship between the film’s hardness and C-C sp3 fraction were investigated. The results demonstrated thatthe insertion of the buffer layer to form chemical compatibility can significantly increase the adhesion of NDC films
on WC-Co substrates.

６．参考文献[1] Hiroshi Naragino et al. Appl. Phys. A, 122, (2016).
[2] Y.S. Li, A. Hirose, J. Appl. Phys. 101, 073503 (2007).
[3] Y.S. Li, A. Hirose, Surf. & Coat. Technol. 202, 280 (2007).
[4] Mohamed Egiza et al. Coatings, 8, 359 (2018)

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).
▪ Mohamed Egiza et al. Coatings, 8, 359 (2018)▪ Ali M. Ali et al. Diamond relat. Mat. 96, 67 (2019)▪ Mohamed Egiza et al. Japanese Journal of Applied Physics 58 (7), 075507 (2019)
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, Raman, Hardness, NEXAFS, W intermediate layer
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）