Ultrahigh-Speed Deposition of Diamond-like Carbon on a Pipe Surface Using a Scanning Deposition Method via Local High-Density Plasma

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The local high-density plasma method used to deposit DLC films is an effective way. While, in this work, there lacked typical microstructure, phases analysis and the comparison of the deposition between the traditional method and the new one. It is essential for the new products by the new method.

Author Response

Comments 1: The local high-density plasma method used to deposit DLC films is an effective way. While, in this work, there lacked typical microstructure, phases analysis and the comparison of the deposition between the traditional method and the new one. It is essential for the new products by the new method.

Response 1: We appreciate the valuable comment and fully understand the importance of clarifying the microstructural differences between the traditional and the new methods.

To compare these differences, we conducted Raman spectroscopy on regions of the pipe’s outer surface, away from the metal antenna (Figure 12). The regions influenced by both microwave and DC plasma are shown as Positions A–C in Figure 12(a). To provide a clearer comparison, we newly added Positions D and E along with their corresponding Raman spectra (Figure 12(c); lines 334–349, reference 18 and 19 highlighted in yellow). Note that the film growth at Positions D and E is considered to be driven solely by DC plasma. As a result, a distinct structural difference was observed between the two regions. The Raman spectra at Positions A–C exhibit a typical DLC spectrum, which includes two broad peaks: the D band and G band, reflecting the disordered sp²-bonded carbon network and graphitic vibrations, respectively. This indicates a hard amorphous structure. In contrast, the spectra at Positions D and E show a higher slope due to the involvement of photoluminescence components, which suggests that these regions possess a hydrogen-rich, polymer-like carbon (PLC) structure rather than “diamond-like” structure [1].

Furthermore, for a more detailed microstructural analysis, it is necessary to clarify differences in the chemical composition within the coatings in addition to the Raman-based structural evaluation. Such interpretation can be achieved through energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In particular, XPS would enable quantitative evaluation of the Si content and the sp²/sp³ ratio of the coatings. However, these analyses require additional sample preparation (e.g., specimen cutting) and scheduling of analytical instruments. Therefore, due to the limited response period (one week), we regret that it was not possible to perform these analyses within the current revision; they are planned as part of our future work.

 Reference

[1] Choi, J., Ishii, K., Kato, T., Kawaguchi, M., & Lee, W. "Structural and mechanical properties of DLC films prepared by bipolar PBII&D," Diam. Relat., vol.20, pp. 845-848, 2011, 10.1016/j.diamond.2011.04.003.

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the attached file.

Comments for author File: Comments.pdf

Author Response

Comments 1: Is it possible to compare the methods of obtaining a DLC C:H-Si film(using microwave and, alternatively, in a glow discharge) in terms of structure?
What are the advantages of the DLC deposition method in microwave plasma beside increasing the coating rate?
For example, in PLATIT's411+DLC installation, a high-quality coating (dark gray in color) with  a uniform thickness is implemented could the installation you have designed have?

Response 1: We appreciate the valuable comment and fully understand the importance of clarifying the microstructure of DLC deposited by the current methods. To understand this, we conducted Raman spectroscopy on regions of the pipe’s outer surface, away from the metal antenna (Figure 12). The regions influenced by both microwave and DC plasma are shown as Positions A–C in Figure 12(a). To provide a clearer comparison, we newly added Points D and E along with their corresponding Raman spectra (Figure 12(c); lines 334–349, reference 18 and 19 highlighted in yellow). Note that the film growth at Points D and E is considered to be driven solely by DC plasma. As a result, a distinct structural difference was observed between the two regions. The Raman spectra at Points A–C exhibit a typical DLC spectrum, which includes two broad peaks: the D band and G band, reflecting the disordered sp²-bonded carbon network and graphitic vibrations, respectively. This indicates a hard amorphous structure. In contrast, the spectra at Points D and E show a higher slope due to the involvement of photoluminescence components, which suggests that these regions possess a hydrogen-rich, polymer-like carbon (PLC) structure rather than “diamond-like” structure [1].

A significant structural difference was observed with the introduction of microwave irradiation. Therefore, it can be concluded that microwave irradiation is essential for forming a “diamond-like” coating on the outer surface of the pipe to achieve a low-friction and durable protective film.

Regarding uniform thickness, in this study, we found that rotation of the pipe contributes to uniformity of film thickness along the circumferential direction (this point has also been included in the Conclusion lines 468-469 highlighted in yellow). Based on this finding, it is expected that combining circumferential rotation with axial reciprocating scanning could achieve overall uniformity in film.

An additional advantage of the high-speed DLC deposition achieved by the current method lies in its ability for low-temperature processing. In this approach, DLC films with thicknesses of several micrometers can be deposited within a few minutes. In particular, for coating the outer surface of pipes, the antenna does not remain stationary but rotates during deposition. In our future research, a combined rotational and vertical-motion system will be developed to enable coating of the entire outer surface of the pipe. As a result, the substrate temperature is expected to decrease further, allowing this process to be classified as a low-temperature deposition technique. This characteristic makes the method highly suitable for heat-sensitive materials offering a versatile and effective approach for DLC deposition.

Reference

[1] Choi, J., Ishii, K., Kato, T., Kawaguchi, M., & Lee, W. (2011). Structural and mechanical properties of DLC films prepared by bipolar PBII&D. Diamond and related materials, 20(5-6), 845-848.

Comments 2: When applying the top standing DLC coating, you replace acetylene with methane. Please explain why you are doing this. What does this mean for the structure and properties of the film? 

Response 2: We appreciate your keen observation of our manuscript. In our previous study, we attempted to use acetylene as a precursor gas for the top DLC layer, aiming to achieve a higher deposition rate [1]. However, the resulting DLC frequently delaminated and did not exhibit the desired film quality. Moreover, the present study focuses on developing a high-rate deposition system capable of forming a hard protective layer on the outer surface of the pipe. Unfortunately, the characterization of films with different precursor gases (e.g., methane, acetylene, toluene) and deposition parameters is beyond the scope of this work. Nevertheless, we recognize that this is an important issue that warrants further investigation, and related experiments are currently in progress as part of our future work.

Reference

[1] A. Ito, K. Nonomura, H. Kousaka and T. Furuki, "Ultra-Fast Si-DLC Deposition using Non-Uniform High-Density Plasma Generated by Microwave Input from the Side of a Cylinder," J. Surf. Finish. Soc. Jpn., vol. 76, no. 4, pp. 183-189, 2025, 10.4139/sfj.76.183.

Reviewer 3 Report

Comments and Suggestions for Authors

Fig. 1 caption: Instead of repeating most of the lines of the text, the abbreviations used in the figure should be explained (e.g. EH, MFC).

Fig. 12: It should be indicated which of the peaks is the G peak and which the D peak.

Film characterization: if possible, a measurement of the Si content of the films should be added (the result inferred from the Raman spectra is only qualitative and very indirect). A closer look at the surface roughness would be nice, too.

Figure 14: "axical" (in the axis label) is not a word. Axial, perhaps?

Comments on the Quality of English Language

In several instances, an article (a/the) seems to be missing, e.g. l. 16 ("using [a] metal contactor"), l. 47 ("coming to [the] substrate"), etc.. The text should be checked again. 

l. 37/38 "have conventionally" been "employed" (add "been")

l. 33: "Diamond-like carbon (DLC) is one of the demanding materials as a protective coating due to its high hardness, superior wear resistance, and chemical inertness". Is "demanding" the correct word? This would mean it is challenging or difficult - but that doesn't fit with the second part of the sentence ("due to..."). Isn't it rather a material "in demand"?

Author Response

Comments 1: Fig. 1 caption: Instead of repeating most of the lines of the text, the abbreviations used in the figure should be explained (e.g. EH, MFC).

Response 1: Thank you for pointing this out. We have made the corrections you pointed out. (lines 73, 95 and 97 highlighted in yellow)

Comments 2: Fig. 12: It should be indicated which of the peaks is the G peak and which the D peak.

Response 2: Thank you for pointing this out. We have made the corrections you pointed out. (Figure 12)

Comments 3: Film characterization: if possible, a measurement of the Si content of the films should be added (the result inferred from the Raman spectra is only qualitative and very indirect). A closer look at the surface roughness would be nice, too.

Response 3: We fully agree that it is important to clarify the differences in the chemical composition within the coatings in addition to the Raman-based structural evaluation. Such analysis can be performed using energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In particular, XPS would allow quantitative evaluation of the Si content and the sp²/sp³ ratio of the coatings. However, these analyses require additional sample preparation (e.g., specimen cutting) and arrangement of analytical equipment. Therefore, due to the limited response period (one week), we regret that it was not possible to perform these analyses within the current revision; they are planned as part of our future work.

As you pointed out, we have added the roughness measurement results. (lines 331-333 highlighted in yellow) Regarding the surface roughness (Ra), the Si-DLC film deposited under microwave irradiation exhibited no significant change compared with the pre-deposition surface, although the measured value increased slightly from 0.515 µm to 0.555 µm.

Comments 4: Figure 14: "axical" (in the axis label) is not a word. Axial, perhaps?

Response 4: Thank you for pointing this out. We have made the corrections you pointed out and replaced the Figure 14.

Comments 5: In several instances, an article (a/the) seems to be missing, e.g. l. 16 ("using [a] metal contactor"), l. 47 ("coming to [the] substrate"), etc.. The text should be checked again.

Response 5: Thank you for pointing this out. We have rechecked the manuscript and corrected spacing, capitalization, and typographical errors. (lines 13, 16, 17, 20, 35, 38, 47, 53, 207, 242, 257, 313, 316, 321, 328-330, 376, 386, 396, 398, 407, 408, 414, and 432 highlighted in light blue)

Comments 6: l. 37/38 "have conventionally" been "employed" (add "been")

Response 6: Thank you for pointing this out. We have made the corrections you pointed out. (line 38 highlighted in light blue)

Comments 7: l. 33: "Diamond-like carbon (DLC) is one of the demanding materials as a protective coating due to its high hardness, superior wear resistance, and chemical inertness". Is "demanding" the correct word? This would mean it is challenging or difficult - but that doesn't fit with the second part of the sentence ("due to..."). Isn't it rather a material "in demand"?

Response 7: We agree with this comment. We have made the corrections you pointed out. (line 33 highlighted in light blue)

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Additional cross-sectional microstructure analysis should be applied to characterize the deposition thickness and the adhesion between the substrate and the film.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf