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作者简介:

陈东旭,男,1984年出生,博士,讲师,硕士研究生导师。主要研究方向为材料表面改性层的腐蚀与防护。E-mail:dxchen11b@alum.imr.ac.cn

通讯作者:

周艳文,女,1966年出生,博士,教授,博士研究生导师。主要研究方向为等离子体物理。E-mail:zhouyanwen1966@163.com

中图分类号:TG174

DOI:10.11933/j.issn.1007−9289.20211230001

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目录contents

    摘要

    为了提高不锈钢的耐局部腐蚀性能,采用等离子体增强化学气相沉积(Plasma-enhanced chemical vapor deposition, PECVD)技术,在 316L 不锈钢表面制备含氢类金刚石(Diamond-like carbon, DLC)薄膜,研究不同脉冲偏压对薄膜的杂化结构及腐蚀行为的影响,并对相关影响机制进行讨论。结果表明,脉冲偏压主要影响 316L 不锈钢表面 DLC 薄膜的杂化结构及微观形貌,并最终影响其腐蚀行为。随着脉冲偏压的增加,等离子体电离程度增大,沉积过程中的热峰效应和溅射效应增强,DLC 薄膜中的氢含量减少,降低了薄膜局部腐蚀敏感性,薄膜点蚀坑数量减少。但同时薄膜中 sp2 杂化结构的相对含量会随脉冲偏压升高而增加,导致薄膜腐蚀速率加快,点蚀坑半径增大。随着偏压从 1.4 kV 增加到 2.6 kV,316L 不锈钢的年腐蚀速率由 9.33 nm/y 增大到 62.4 nm/y。脉冲偏压为 1.4 kV 时,虽然年腐蚀速率最低,但薄膜最易发生点蚀,其长期服役寿命较差;而偏压为 2.6 kV 时,等离子体能量过高,薄膜被过度刻蚀,导致其缺陷增多,耐蚀性变差。在研究范围内,脉冲偏压为 2200 V 时,DLC 薄膜具有较高的耐点蚀能力和较低的年腐蚀速率,表现出最佳的综合耐蚀性能。

    Abstract

    In order to improve the localized corrosion resistance of stainless steel, plasma-enhanced chemical vapor deposition (PECVD) technology is used to prepare hydrogen-containing diamond-like carbon (DLC) film on the surface of 316L stainless steel. The effects of different pulsed bias on the hybrid structure and corrosion behavior of the film are investigated, and the related influence mechanisms are also discussed. The results are showed that pulse bias voltage mainly affects the hybrid structure and microstructure of the DLC film on 316L stainless steel surface, and finally the corrosion behavior is affected. With the increase of pulse bias voltage, the degree of plasma ionization increases, the thermal peak effect and sputtering effect during the deposition process are enhanced, the hydrogen content in the DLC film decreases, the local corrosion susceptibility of the film is reduced, and the number of pitting pits in the film is reduced. But at the same time, the relative content of sp2 hybrid structure in the film also increases with the increase of pulse bias voltage, which leads to the accelerated corrosion rate of the film and the increase of the pit radius. As the bias voltage increases from 1.4 kV to 2.6 kV, the annual corrosion rate of 316L stainless steel increases from 9.33 nm/y to 62.4 nm/y. When the pulse bias voltage is 1.4 kV, although the annual corrosion rate is the lowest, the film is most prone to pitting corrosion, and its long-term service life is poor. When the bias voltage is 2.6 kV, the plasma energy is too high, and the thin film is etched excessively, resulting in increased defects and poor corrosion resistance. In the research range, when the pulse bias voltage is 2.2 kV, the DLC film has high pitting corrosion resistance and low annual corrosion rate, showing the best comprehensive corrosion resistance.

  • 0 前言

  • 奥氏体不锈钢由于其优异的耐蚀性和综合力学性能,被广泛应用于机械、电子、能源、交通及生活等领域[1-3]。然而在苛刻水化学环境中长期服役后,不锈钢容易因局部腐蚀而失效[4-5],从而带来严重的经济及安全问题,严重制约其在相关行业的发展及应用。因此,如何减轻及控制奥氏体不锈钢的局部腐蚀,成为亟待解决的问题之一而备受关注。

  • 表面改性技术,可以在保障基体材料自身性能的同时,提高材料表面的物理化学性能,以满足不同服役环境的需求[6-7]。等离子体增强化学气相沉积( Plasma enhanced chemical meteorological deposition,PECVD),是利用高功率电压产生高能量等离子体进而实现低温成膜的一种镀膜技术。由于成膜效率高、成膜均匀致密及可实现复杂工件镀膜等优点而被广泛应用在金属材料表面改性领域[8-9]。其中,类金刚石(Diamond like carbon,DLC) 薄膜具有优异的化学稳定性及优异的摩擦学特性而备受关注[10-11]。然而,DLC 作为一种非晶态碳膜虽然惰性较高,但在腐蚀介质中,薄膜中的 sp 2 杂化碳原子具有电子传输能力较强的 π 键,会导致薄膜在电化学作用下发生腐蚀失效[12-13]。KHUN 等[14] 认为,DLC 的腐蚀主要来自薄膜与电解液中电化学活性物质的反应,并且溶液的 pH 值对 DLC 膜的腐蚀行为有显著影响。另外,DLC 膜中的孔隙也会诱发严重的局部腐蚀,导致薄膜的破坏以及基体金属的加速溶解[15-16]。DENG 等[17]研究了 Si 掺杂对 DLC 薄膜腐蚀行为的影响。研究表明,虽然 Si 的掺杂会减少 sp 2 杂化键的含量,但同时会使薄膜中 sp 3 杂化键数量增加,造成薄膜中孔隙增多,耐蚀性能降低。

  • 综上所述,DLC 膜中的 sp 2 和 sp 3 杂化键含量对其耐蚀性能有显著影响,而脉冲偏压是影响 PECVD 技术制备 DLC 薄膜中等离子体能量及密度的主要因素之一,直接决定了薄膜中的杂化键合结构。关于脉冲偏压对不锈钢表面 DLC 薄膜耐蚀性能影响相关研究较少,其影响机理也没有得到阐明。因此,本文采用 PECVD 技术,在 316L 不锈钢表面制备DLC 薄膜,研究脉冲偏压对 DLC 薄膜键合结构及腐蚀行为的影响规律,并探讨相关的影响机制及腐蚀机理。

  • 1 试验准备

  • 1.1 试样及 DLC 薄膜制备

  • 本试验选用 316L 不锈钢,其主要成分(质量分数)如下:0.14%C,0.44%Si,1.35%Mn,0.02%P, 15.84%Cr,8.14%Ni,1.33%Mo,其余为 Fe。将 316L 不锈钢切割成 10 mm×10 mm×3 mm 的试样,经超声清洗之后,依次使用 240#、400#、800#、1200#、 1500#、2000#金相砂纸打磨,再使用粒度为 1.5W 的金刚石研磨膏抛光处理至镜面。最后超声清洗,烘干密封袋保存待用。

  • 将制备完成的 316L 不锈钢放入图1 所示的真空腔中,在其表面制备 DLC 薄膜;打开机械泵和分子泵,将真空度抽至 2 mPa。之后打开加热电源,将腔体加热到 110℃,以确保去除真空腔内的水蒸气;待真空腔的真空度降低至 1 mPa,向真空腔内通入 100 mL / min 的氩气(Ar),持续 10 min。然后减小 Ar 流量至 50 mL / min,通气 20 min,以达到除气的目的;打开高压脉冲电源,从 800 V 开始逐渐升高电源电压,直至高于制备工艺电压 200 V,对试样进行 30 min 的高压清洗,以去除试样表面可能存在的氧化膜或污染物;高压清洗结束,将真空腔内的温度降低到 100℃,脉冲宽度设定为 15 μs,Ar 流量调整至 20 mL / min,C2H2 流量为 60 mL / min,腔体气压为 2 Pa,分别在 1.4 kV、1.8 kV、2.2 kV 和 2.6 kV 脉冲偏压下进行 2 h 的镀膜。

  • 图1 PECVD 设备示意图

  • Fig.1 Schematic diagram of PECVD equipment

  • 1.2 薄膜性能测试及表征

  • 利用(Alpha-step D-100)台阶仪对 DLC 薄膜的厚度进行表征。利用(CspM5500/5500A)扫描探针原子力显微镜(Atomic Force Microscope,AFM) 对薄膜的形貌进行观测。利用 Vertex. C. EIS 电化学工作站,在质量分数为 3.5%的 NaCl 溶液中,采用三电极测量体系,对不同脉冲偏压下制备的 DLC 薄膜进行动电位极化曲线的测量,并对其强极化区进行 Tafel 拟合。分别利用激发波长为 532 nm 的可见光 Raman 光谱仪(XploRA PLUS)和红外光谱仪 (Cary 630FTIR),对 DLC 薄膜成分和结构进行表征。利用蔡司公司制造的光学显微镜(Axio Vert. A1) 对 DLC 薄膜表面改性试样被腐蚀后的微观形貌进行观察。

  • 2 结果与讨论

  • 2.1 偏压对 DLC 薄膜形貌及厚度影响

  • 图2 为不同偏压下制备的 DLC 薄膜表面形貌 AFM 图片。可以发现,脉冲偏压对 316L 不锈钢表面 DLC 的微观形貌有显著影响。随着偏压从 1.4 kV 增加到 2.2 kV,薄膜的平均粗糙度逐渐降低。DLC 膜形成主要经历原子沉积、形核、团簇、岛状生长及扩散等过程[18-20]。脉冲偏压增加会使等离子体能量增加,沉积的原子能量较高,更容易向四周扩散生长,最终使薄膜更加均匀致密。然而,当偏压增大至 2.6 kV 时,高偏压对膜的刻蚀作用增强[21],使薄膜中出现缺陷,平均粗糙度增加、致密性变差。

  • 图2 不同偏压下 DLC 薄膜表面形貌 AFM 图片

  • Fig.2 AFM images of DLC film surface morphology under different bias voltages

  • 图3 所示为不同偏压下 316L 不锈钢表面 DLC 薄膜厚度结果。可以发现,台阶仪测得的平均膜厚均在 1.70~1.75 μm,说明脉冲偏压对 316L 不锈钢表面 DLC 膜的厚度影响较小。

  • 图3 不同偏压下 DLC 薄膜厚度结果

  • Fig.3 Thickness results of DLC films under different bias voltages

  • 2.2 偏压对薄膜 sp 2 及 H 含量影响

  • DLC 膜的耐蚀性能与薄膜形貌及键合结构相关[22]。图4 为不同偏压下制备的DLC 薄膜的Raman 光谱结果。可以发现,随着偏压从1.4 kV 增大至2.6 kV, D 峰和 G 峰面积比(I(D)/I(G))的值由 1.34 增大至 1.65,随着脉冲偏压的增加,碳离子的注入行为会产生局部热峰效应,导致 sp 3 结构向 sp 2 结构转化, DLC 薄膜中 sp 2 杂化结构的相对含量增加。研究认为 DLC 薄膜中 sp 2 /sp3 的比值越高,薄膜的电阻率越低[23]。sp 3 轨道杂化结构由 4 个 σ 键组成,sp 2 轨道杂化结构与之相比,少了 1 个 σ 键,但同时多了一个 π 键。π 键传输电子的能力超过 σ 键,这导致含 sp 2 轨道杂化结构较多的 DLC 薄膜具有更高的电导率,耐蚀性能降低。Raman 结果与极化曲线强极化区拟合结果一致,进一步说明脉冲偏压升高会导致 DLC 膜中 sp 2 含量增加,最终导致薄膜耐蚀性能下降。

  • 图4 不同偏压下制备 DLC 薄膜的 Raman 光谱

  • Fig.4 Raman spectra of DLC films prepared at different bias voltages

  • 利用 PECVD 技术制备 DLC 薄膜时,使用 C2H2 气体作为工作气体,所以沉积的薄膜中氢主要以 C-Hx 的形式存在,图5 为不同偏压下制备的 DLC 薄膜的红外光谱结果。可以发现位于 2 860 cm−1 (sp 3 C-H3,对称)、2 910 cm−1 (sp 3 C-H)、2 930 cm−1 (sp 3 C-H2,对称)和 2 970 cm−1 (sp 3 C-H3,非对称)4 个位置的主要特征峰[24-25]。随着偏压从 1.4 kV 增加到 2.6 kV,DLC 薄膜 C-Hx对应的特征峰越来越不明显。一般认为随着偏压的增加,沉积 DLC 薄膜过程中等离子体中的粒子团电离程度增大,并且热峰效应和溅射效应也更明显,导致沉积薄膜中的氢含量降低[26]

  • 图5 不同偏压下制备 DLC 薄膜的红外光谱

  • Fig.5 Infrared spectra of DLC films prepared at different bias voltages

  • 2.3 偏压对 DLC 薄膜电化学行为影响

  • 图6 给出不同偏压下的 DLC 薄膜在质量分数 3.5%的 NaCl 溶液中的极化曲线。表1 给出极化曲线强极化区 Tafel 拟合结果。从拟合结果中可以发现,随着偏压从 1.4 kV 增加到 2.6 kV,自腐蚀电位 (Ecorr)从 170 mV 下降到-80 mV,自腐蚀电流密度从 0.803 nA / cm2 增加到 73.6 nA / cm2。腐蚀速率的结果表明,DLC 薄膜的耐腐蚀性能随偏压的增加而降低。值得注意的是,这一结论仅是由强极化区拟合结果得出的。

  • 图6 不同偏压下 DLC 薄膜在质量分数 3.5 %的 NaCl 溶液中的极化曲线

  • Fig.6 Polarization curves of DLC films deposited with different bias voltages in the solution of 3.5 wt.% NaCl

  • 另外,当测试电位大于 500 mV 时,可以发现在 1.4 kV 和 1.8 kV 的极化曲线上,腐蚀电流密度出现急剧增大,极化曲线中出现“台阶”,表明此过程中 DLC 薄膜发生明显的局部腐蚀现象。金属在发生局部腐蚀之前,一般会存在孕育期,此阶段的腐蚀电流密度随着电位的升高而逐步增加。而一旦进入增殖期,由于小阳极-大阴极效应,腐蚀电流密度会迅速增加[27-28]。而在脉冲偏压增加至 2.2 kV 以上时,并没有出现明显的“台阶”,此时并没有明显的局部腐蚀发生,薄膜的主要失效形式为均匀腐蚀。

  • 表1 极化曲线强极化区 Tafel 拟合结果

  • Table1 Tafel fitting results in the strong polarization region of the polarization curves

  • 2.4 DLC 膜腐蚀行为分析及讨论

  • Raman 光谱(图4)、红外光谱(图5)和动电位极化曲线(图6)的测试分析结果表明,不同偏压下在 316L 表面制备的 DLC 薄膜具有不同的耐蚀性能。影响薄膜耐腐蚀性能的主要因素是 DLC 薄膜中的氢含量和 sp 2 杂化结构的含量。腐蚀初始阶段, DLC 薄膜主要发生均匀腐蚀,局部腐蚀仍处于孕育阶段。此时 DLC 薄膜的电化学过程主要受到膜中 sp 2 杂化结构含量的影响,DLC 薄膜的 sp 2 /sp3 比值越高,耐蚀性能越差。随着均匀腐蚀的发展,DLC 薄膜的局部腐蚀逐渐取代均匀腐蚀成为影响腐蚀速率的主导因素,DLC 薄膜中的氢溶解到电解液中引起了局部化学环境的改变,而局部化学环境的不均匀为局部腐蚀的发生提供条件。

  • 图7 为不同脉冲偏压在 316L 表面制备的 DLC 薄膜在质量分数 3.5%的 NaCl 溶液中腐蚀后点蚀坑形貌。可以发现,从 1.4 kV 到 2.2 kV,脉冲偏压低 (即 DLC 薄膜中氢的含量越高),点蚀坑的数量越多,说明其的发生点蚀的概率越大。而当偏压增至 2.6 kV 时,由于刻蚀作用造成缺陷,腐蚀介质更容易在缺陷处侵蚀 DLC 膜使其发生均匀腐蚀,而并没有出现明显的点蚀坑。腐蚀形貌结果与 AFM 和极化曲线结果相符。进一步说明,点蚀和均匀腐蚀是偏压对 316L 不锈钢表面 DLC 膜耐蚀性能影响的主要因素。另外可以发现,随着沉积偏压从 1.4 kV 增加到 2.2 kV,点蚀坑的直径也逐渐增大。根据极化曲线的结果,按照式(1)对不同薄膜的极化电阻(Rp) 值进行计算

  • Rp=babc/2.3Icorr ba+bc
    (1)
  • 图7 不同偏压下在 316L 表面制备 DLC 薄膜的腐蚀坑形貌

  • Fig.7 Corrosion pit morphology of 316L with DLC films at different bias voltages

  • 式中,Rp 为极化电阻,Icorr 为自腐蚀电流密度,babc 分别为阳极和阴极的塔菲尔斜率。图8 为不同偏压下 DLC 薄膜的 Ecorr Rp 结果。可以发现, Rp 的变化趋势与 Ecorr 相似,随着偏压从 1.4 kV 增加至 2.6 kV,Ecorr 的值从 0.17 V 降低至-0.08 V, Rp 从 59.2 MΩ·cm 2 减少到 1.1 MΩ·cm 2。这是由于 DLC 薄膜中 sp 2 杂化结构随偏压的增大而增多,导致薄膜的电阻降低,与前文讨论一致。

  • 结合上述试验结果讨论,氢和 sp 2 杂化结构的含量对 DLC 薄膜的腐蚀性能有显著的影响。局部腐蚀的发生受 DLC 薄膜中氢含量的影响,电导率则取决于 DLC 薄膜中 sp 2 杂化结构的含量。腐蚀初期,腐蚀反应来自于 DLC 薄膜与电解液中的电化学活性物质发生反应(C→C2++2e-)。DLC 薄膜作为阳极被腐蚀,释放的电子运动到阴极并参与阴极反应 (H+ +e- →H,2H→H2),构成完整的闭合回路。此时, DLC 薄膜发生腐蚀的速率由薄膜中 sp 2 杂化结构的含量主导。DLC 薄膜中 sp 2 杂化结构可以改善薄膜表面的电子交换能力,薄膜更容易与电解液中的电化学活性物质发生反应。随着腐蚀的进行,薄膜中的氢越来越多的被释放到溶液中,导致薄膜局部水化学环境的改变,为局部腐蚀的发生提供了条件。 DLC 薄膜中氢含量越多,发生局部腐蚀的几率越大,产生的点蚀坑数量越多。点蚀坑的直径则取决于 DLC 薄膜中 sp 2 杂化结构的含量,在同样的腐蚀条件下,薄膜电导率越高,孔洞沿着薄膜横向扩展越容易,点蚀坑直径越大。脉冲偏压过高会导致剧烈刻蚀效应,使 DLC 膜的缺陷增多,耐蚀性能下降。因此,不锈钢表面 DLC 薄膜长期使用过程中,必须同时考虑氢含量和 sp 2 杂化结构的含量对腐蚀性能的影响。

  • 图8 DLC 薄膜的 EcorrRp随偏压变化曲线

  • Fig.8 Corrosion potentials (Ecorr) and polarization resistances (Rp) of DLC films as a function of bias voltage

  • 3 结论

  • (1)脉冲偏压对 316L 表面 DLC 薄膜杂化结构及耐蚀性能有显著影响。随着偏压从 1.4 kV 增加到 2.6 kV,薄膜中的氢含量减少、sp 2 杂化结构含量增加。

  • (2)DLC 薄膜中的 sp 2 杂化结构可以提高电子运输能力,进而降低薄膜的耐腐蚀性能。随着 sp 2 杂化结构的增加,DLC 薄膜在均匀腐蚀阶段的年腐蚀速率由 9.33×10−6 mm/y 增大到 6.24×10−5 mm/y。

  • (3)薄膜中的氢的释放会改变溶液的局部水化学环境,加剧了 DLC 薄膜的局部腐蚀。随着 DLC 氢含量的增加,薄膜发生局部腐蚀的几率越大,产生的点蚀坑数量越多。点蚀坑的直径则主要取决于 DLC 薄膜中 sp 2 杂化结构的含量,薄膜中 sp 2 含量越多,孔洞沿着横向扩展越容易,点蚀坑直径越大。

  • (4)DLC 薄膜长期服役过程中,必须同时考虑氢含量和 sp 2 杂化结构的含量对腐蚀行为的影响。本研究范围内,脉冲偏压为 2.2 kV 时,制备的 DLC 薄膜具有较高的耐点蚀能力。而脉冲偏压升至 2.6 kV 时,等离子体能量过高,薄膜被过度刻蚀,薄膜表面孔隙及缺陷增多,会导致腐蚀性介质渗入,进而破坏薄膜的保护能力,耐均匀腐蚀性能降低。

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  • 参考文献

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    • [2] ECA B,KLA C,TVDD D,et al.Early stages of dissolution corrosion in 316L and DIN 1.497 0 austenitic stainless steels with and without anticorrosion coatings in static liquid leadbismuth eutectic(LBE)at 500 ℃[J].Materials Characterization,2021,178:111234.

    • [3] ARUNKUMAR S,SESHADRI S.Review on weldability prospects of super austenitic stainless steels[J].Applied Mechanics and Materials,2021,903:33-43.

    • [4] CHEN D X,LIU M N,LIU X H,et al.Oxidation behavior of 304 stainless steel with modified layer by plasma nitriding in high temperature and pressurized water[J].Corrosion Science,2021,186(1-25):109468.

    • [5] 肖金涛,鞠鹏飞,臧旭升,等.铝合金表面润滑耐蚀复合镀层的制备及性能分析[J].中国表面工程,2021,34(4):38-45.XIAO Jintao,JU Pengfei,ZANG Xusheng,et al.Preparation and performance analysis of lubricating and corrosion-resistant composite coating on aluminum alloy surface[J].China Surface Engineering,2021,34(4):38-45.(in Chinese)

    • [6] 徐星,苏峰华,李助军.脉冲偏压对直流磁控溅射沉积MoN薄膜结构及性能的影响[J].中国表面工程,2019,32(2):54-62.XU Xing,SU Fenghua,LI Zhujun.Effects of pulse bias on structure and properties of MoN filmdeposited by DC magnetron sputtering [J].China Surface Engineering,2019,32(2):54-62.(in Chinese)

    • [7] 李姣姣,刘燕红,李家平,等.自组装膜层微观结构对铝合金表面耐腐蚀性能的影响[J].中国表面工程,2020,33(5):30-39.LI Jiaojiao,LIU Yanhong,LI Jiaping,et al.Effects of self-assembled film microstructure on corrosion resistance of aluminum alloy surface [J].China Surface Engineering,2020,33(5):30-39.(in Chinese)

    • [8] MARCIANO F R,BONETTI L F,SANTO L V,et al.Antibacterial activity of DLC and Ag–DLC films produced by PECVD technique[J].Diamond and Related Materials,2009,18(5-8):1010-1014.

    • [9] 孙磊,熊计,杨天恩,金属陶瓷及硬质合金表面 CVD/PVD 涂层的摩擦与切削性能[J].中国表面工程,2019,32(6):45-55.SUN Lei,XIONG Ji,YANG Tianen.Friction and cutting properties of CVD/PVD coatings on cermet and cemented carbide surfaces[J].China Surface Engineering,2019,32(6):45-55.(in Chinese)

    • [10] WEI X,ZHANG M,SHANG L,et al.Enhancement in the corrosive and tribological properties of the inner wall of 6063Al and Cl pipes by thick multilayer Si-DLC coatings[J].Materials Research Express,2019,6:085634.

    • [11] LUBWAMA M,CORCORAN B,et al.Raman analysis of DLC and Si-DLC films deposited on nitrile rubber [J].Surface and Coatings Technology,2013,232(10):521-527.

    • [12] CHEN J Y,WANG L P,FU K Y,et al.Blood compatibility and sp3/sp2 contents of diamond-like carbon synthesized by plasma immersion ion implantation-deposition[J].Surface and Coatings Technology,2002,156(1-3):289-294.

    • [13] JELÍNEK M,SMETANA K,KOCOUREK T,et al.Biocompatibility and sp3/sp2 ratio of laser created DLC films[J].Materials Science and Engineering B,2010,169(1-3):89-93.

    • [14] KHUN N W,LIU E,ZENG X T.Corrosion behavior of nitrogen doped diamond-like carbon thin films in NaCl solutions [J].Corrosion Science,2009,51(9):2158-2164.

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    • [18] ZHANG Z.Atomistic processes in the early stages of thin-film growth[J].Science,1997,276(5311):377-383.

    • [19] WAN S H,WANG L P,XUE Q J.Electrochemical deposition of sulfur doped DLC nanocomposite film at atmospheric pressure[J].Electrochemistry Communications,2010,12(1):61-65.

    • [20] WEI Q,PAN Z Y,LI Z J,et al.Impact-energy dependence of atomic mobility in diamond like carbon film growth[J].Physical Review B,2003,68(23):235408.

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    • [23] ZENG A,LIU E,TAN S N,et al.Stripping voltammetric analysis of heavy metals at nitrogen doped diamond-like carbon film electrodes[J].Electroanalysis,2002,14(18):1294-1298.

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