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
Ｂ Ｌ 番 号 ： 12
課 題 番 号 ： 1804026S（様式第 5 号）
基板への負バイアス印加が超ナノ微結晶ナノダイヤモンド膜の化学結合状態に与える影響
Effects of negative bias applied to substrates on the chemical bonding structures ofultrananocrystalline diamond films Softエ ギ ザ モ ハ メ ド ， 竹 市 悟 志 ， Ali Mohamed， 星 野 光 一 郎 ， 田 中 佑 樹 ， 吉 武 剛
Mohamed Egiza, Ali Mohamed Ali, Satoshi Takeichi, Koichiro Hoshino, Yuki Tanaka, andTsuyoshi 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 先 端 創 生 利 用 （ 長 期 タ イ プ ） 課 題 は 、 実 施 課 題 名 の 末 尾 に 期 を 表 す （ Ⅰ ）、（ Ⅱ ）、（Ⅲ）を追記してください。
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１．概要（注：結論を含めて下さい）
Ultrananocrystalline diamond (UNCD)/amorphous carbon (a -C) composite (UNCD/a-C) films
were deposited on WC-Co substrates, which were pulsed -biased at a voltage of 100 V andfrequencies from 40 to 80 kHz, by coaxial arc plasma deposition. The bias effects on themechanical and structural properties of the UNCD/a -C films were investigated. The depositio nrate increased approximately threefold by applying the bias, which implies that species ejectedfrom a coaxial arc plasma gun are ionized. A 9 µm UNCD/a -C film with a hardness of 49 GPa
was deposited at a low frequency of 40 KHz. With increasing pulse bi as frequency, thehardness was degraded. X-ray photoelectron and near-edge X-ray absorption fine-structure
spectroscopic measurements indicated that the amount of sp 3 bonds is evidently decreased dueto the undesirable surface charge up. It worked on reduc ing the negative bias voltage and ion
energy at the high bias frequency.

２．背景と目的
Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite (UNCD/a-C)
films are new candidates applicable to hard coating because of the high hardness and extremely smooth film
surface.1 It is well known that the physical properties of carbon materials are strongly influenced by the ratio ofsp3 (diamond-like) to sp2 (graphite-like) bonds. The mechanical properties of UNCD/a-C films, which
comprise a large number of UNCD grains and an a-C matrix, are expected to be strongly affected by the ratio
between sp3 and sp2 bonds.
In our previous studies, we realized the formation of 51-GPa-hardness UNCD/a-C films on cemented
carbide (WC-Co) substrates by coaxial arc plasma deposition (CAPD), without applying negative bias tosubstrates. They exhibited the sp3/(sp3+sp2) ratio of 57%, which was estimated from X-ray photoemission
measurements. To enhance the mechanical properties of UNCD/a-C films, the negative bias voltage wasapplied to substrates during the deposition. Since the application of the negative bias onto substrates enhances
the kinetic energies of ionized species, an improvement in the mechanical properties of resultant films isexpected.
According to a grain boundary mismatch model (GBM) and an ion-peening model (Ion-P.),6 which
describe the residual stress as a function of the ion energy,7 with increasing the ion energy the internal stress ofthe films gradually decreased. Therefore, the ratio of sp3 bonds is expected to increase by applying the negative
bias due to increasing the energy of deposited carbon ions and reducing the internal stress of the films. In thiswork, the effects of negative bias on the deposition of UNCD/a-C films on WC-Co substrates was studied, andthe chemical bonding structures of the films were investigated by X-ray photoelectron and near-edge X-ray
absorption fine-structure spectroscopies.
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. The
substrates were pulsed-biased at a negative voltage of 100 V
and frequencies of 40, 60, and 80 kHz. The hardness andYoung’s modulus of the UNCD/a-C films were estimated bynanoindentation at an applied indentation load of 0.5 mN. The
film thickness was evaluated from cross-sectional SEM images.
X-ray photoelectron and near-edge X-ray absorption finestructure (NEXAFS) spectroscopies were employed forcharacterizing the chemical bonding structures of the films atbeamline 12 of Kyushu Synchrotron Center/Saga Light Source.
４．実験結果と考察
It was found that the application of negative bias trembles thedeposition rate, as compared with that of the films deposited
without biasing. The critical load estimated from scratch tests
was improved by four times by biasing.
The hardness and Young’s modulus were hardly affectedby the bias frequency, as show in Fig. 1. The hardness was 49
GPa and the fraction of sp3 was 57% at a bias frequency of 40
kHz. Figure 2 shows X-ray photoemission spectra of the films
deposited at bias frequencies of 40 and 80 kHz. The hardness andsp3 fraction decreased with increasing bias frequency.
NEXAFS measurements were examined to study thechemical bonding structures of the films. Figure 3 shows
typical NEXAFS spectra of the films deposited at zero bias anddifferent bias frequency of 40 and 80 kHz. The intensity ofspectra was normalized at 330 eV and the background wassubtracted by using the Victorian –fit method. The spectra show asharp rise near 284.5 eV (π* C=C), which may be raised from
amorphous carbon matrixes in UNCD/a-C films. On the otherhand, there is a separated peak at 295 eV and a slightly deep
valley near 300 eV related to (σ* C-C) in UNCD/a-C film
deposited at zero bias condition. These separated peaks and deep
valley disappears for the films deposited at bias frequency of 40and 80 kHz.
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 thenegatively biased films. The surface charge up phenomena wasobserved during the films deposition, and it worked on reducing
the negative bias voltage and ion energy at the high bias
frequency. Therefore, the surface charge up produce moregraphitic carbon bonds and reduce the hardness. The results pointout that changing the pulsed bias parameters do affect UNCD/a-Cfilm properties. Therefore, we expect that the properties of
UNCD/a-C films can be controlled and improved by selecting
suitable bias conditions.

Fig. 1. Dependence of hardness,
Young’s modulus, deposition rate, andcritical load on bias frequency.

Fig. 2. Typical C 1s X-ray photoelectron
spectra of films deposited at bias
frequency of (a) 40 kHz and (b) 80 kHz.

Fig. 3. Typical NEXAFS profile ofUNCD/a-C films deposited on WC-Co atdeferent substrate bias conditions.

６．参考文献1Tang, Y., et al. (2010). Diamond & Related Materials, 19(5-6), 496-499.
Liu, N., et al. (2014). The Astrophysical Journal, 786(1), 66.
3Zhong, X. et al. (2009). Journal of Applied Physics, 105(3), 034311.
4
Chu, Y. et al. (2012). Journal of Applied Physics, 112(12), 124307.
5Chu, Y. et al. (2014). Journal of Applied Physics, 115(2), 024308.
2

6Hoffman, R. W., Thin Solid Films 34.2 (1976): 185-190.

7N. Woehr. Diamond Related Material 16 (2007) 748.

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）
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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, Negative bias voltage, Hard coating, Coaxial arc plasma deposition
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① 論文（査読付）発表の報告（報告時期：2020 年 12 月）