The Amorphous Carbon Layers Deposited by Various Magnetron Sputtering Techniques

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a comparative study of amorphous carbon (a-C) layers deposited by three magnetron sputtering techniques -  Pulsed Magnetron Sputtering (PMS), Gas Injection Magnetron Sputtering (GIMS), and High-Power GIMS (HiPGIMS). The authors aim to analyze how these techniques affect the sp3/sp2 hybridization ratio and, consequently, the structural and optical properties of the coatings. Although the experimental work is comprehensive, the paper requires major revision before it can be considered for publication.

- Table 1 omits several essential technological details discharge power, target current density, and substrate temperature which can make the experiments difficult to reproduce.
- The film thicknesses are mentioned in the Results section but their dependence on process parameters and their influence on Raman/XPS analysis are not addressed.
- All data are presented as single measurements with no error estimates, reproducibility tests, or discussion of measurement uncertainty.
- The Raman analysis relies solely on an empirical formula for sp³ estimation, without discussing the D and G band positions, intensity ratios, or possible effects of stress, clustering, or fluorescence background.
- The final section restates the main results without providing critical evaluation, practical implications, or directions for future research.
- The manuscript contains grammatical errors, inconsistent units, typographical mistakes. Careful English proofreading and technical editing are essential.

Author Response

Dear reviewer

On behalf of all the authors, I would like to express our appreciation for your time and suggestions during the review of our paper. We have considered all of your remarks during the revision and present a rewritten paper. All amendments are highlighted in yellow. Here is a detailed response to all of your comments:

1. "Table 1 omits several essential technological details discharge power, target current density, and substrate temperature which can make the experiments difficult to reproduce"

Thank you for pointing this out. In the original version of the text, we wanted to discuss the discharge parameters in the Results and Discussion section. However, we agree that it is worth providing all these values where readers are looking for them, i.e., in the methods section. We have also added information about the deposition temperature.

2. "The film thicknesses are mentioned in the Results section but their dependence on process parameters and their influence on Raman/XPS analysis are not addressed."

Thank you for pointing out these shortcomings. We have added a brief discussion of the kinetics of film growth (lines 392-397). In addition, we have commented on the XPS and Raman spectroscopy results in relation to the differences in film thickness (lines 355-361).

3. "All data are presented as single measurements with no error estimates, reproducibility tests, or discussion of measurement uncertainty."

Thank you for bringing this important aspect to our attention. We agree that when providing values, the error resulting from the measurement and estimation methods should also be provided. The revised manuscript was supplied with:

• Layer thickness estimation errors
• E_g estimation errors
• Sp³/sp² error evaluation by Raman spectroscopy
• Sp³/sp² error evaluation by XPS
• Short discussion about the uncertainty of OES spectra registration

4. "The Raman analysis relies solely on an empirical formula for sp³ estimation, without discussing the D and G band positions, intensity ratios, or possible effects of stress, clustering, or fluorescence background."

This is, in fact, a valuable comment that deserves consideration. I fully understand that there are several methods of sp³ estimation in carbon materials. I used to take into account all of them, including the ID/IG ratio, the G-band position, and the G-band FWHM. Moreover, as you noticed, several factors can affect the Raman spectrum of carbon-based materials (stress, clustering, fluorescence). I would add a few more, such as surface topography or other elements in the coating composition. In my honest opinion, the most reliable method is based on the G band position, as this is the most arbitrary factor in determining the carbon state. In the case where ID << IG, the IG can be prioritized during the fitting operation, ensuring its position is always as it should appear in the Raman spectrum. In contrast, the FWHM can be falsified by additional vibrations forming with -O, -OH, -H, and -COOH, which appear near the D and G band regions. Some of these bonds were revealed by the XPS method in our films. In my opinion, the I_D/I_G ratio evaluation is also tricky because the intensities can be affected by fluorescence.

Additionally, the change in ID/IG when sp3 is raised (according to Ferrari's 3-stage model of carbon amorphization) means that the ID/IG decreases very dynamically, making reliable sp3 evaluation impossible. This is why I believe the methods based on G peak position are the most reliable, and they are always used to match the XPS results in my studies. The Cui method used in our paper is based on the G peak position, which depends on the sp3 content and the energy of excitation. The Cui method allows us to compare the dynamics of the G band shift resulting from changes in sp3 content, which is further influenced by excitation energy. It brings another level of certainty to evaluated values. In my opinion, comparing the other mentioned methods with the Cui approach does not bring more reliability than the method we used. We admit that adding short information to the text that values of other parameters of D and G peaks like I_D/I_G ratio, G_FWHM, G_position are in ranges characteristic for a-C films containing ~20-50% sp³ is a good idea, because it suggests that our sp3 evaluation is reflected also in these factors.

5. "The final section restates the main results without providing critical evaluation, practical implications, or directions for future research."

We have added proper fragments at the end of the Results Discussion and Conclusions sections.

6. "The manuscript contains grammatical errors, inconsistent units, typographical mistakes. Careful English proofreading and technical editing are essential."

We have reviewed the article for linguistic accuracy and corrected any language errors.

Reviewer 2 Report

Comments and Suggestions for Authors

This is a well-structured and timely piece of research that addresses a significant challenge in materials science: controlling the sp^3 content in Diamond-Like Carbon (DLC) films synthesized by magnetron sputtering, which is a less energetic technique compared to filtered cathodic arc deposition. The systematic comparison between PMS, GIMS, and HiPGIMS is highly valuable, as it clearly delineates the advantages and trade-offs of using pulsed and gas-injection modifications to conventional sputtering. The results, particularly the achieved high sp^3 content under specific HiPGIMS conditions, are noteworthy and represent an important contribution to the field of thin film technology.

Specific revisions is required below

• Gas Injection Control: Please provide a more detailed discussion of how the Gas Injection (GI) mechanism was implemented, especially for GIMS and HiPGIMS. Was the pulse frequency, duration, and duty cycle of the gas injection valve varied systematically? This detail is crucial for reproducibility.
• Target Power: HiPGIMS is defined by high instantaneous power. Please ensure that the specific peak power density and average power for the HiPGIMS experiments are clearly stated and compared against the PMS method, as this is the primary difference between the two pulsed modes.
• Kinetic Energy Mechanism: The core finding relates the increased plasma energy (due to pulsing and Ne gas) to higher sp^3 content, consistent with the subplantation model. The discussion section should dedicate a paragraph to explicitly linking the measured plasma parameters (e.g., ion flux, ion energy distribution, if measured or estimated) to the resulting sp^3/sp^2 ratio across all three techniques. A figure schematically comparing the ion energy distribution for PMS, GIMS, and HiPGIMS would greatly enhance the paper.

Author Response

Dear reviewer

On behalf of all the authors, I would like to express our appreciation for your time and suggestions during the review of our paper. We have considered all of your remarks during the revision and present a rewritten paper. All amendments are highlighted in yellow. Here is a detailed response to all of your comments:

1. "Please provide a more detailed discussion of how the Gas Injection (GI) mechanism was implemented, especially for GIMS and HiPGIMS. Was the pulse frequency, duration, and duty cycle of the gas injection valve varied systematically? This detail is crucial for reproducibility."

We are grateful for bringing this to our attention, regarding the insufficient description of GIMS and HiPGIMS's technological details. We have revised these fragments, and we believe they are now clarified.

2. "HiPGIMS is defined by high instantaneous power. Please ensure that the specific peak power density and average power for the HiPGIMS experiments are clearly stated and compared against the PMS method, as this is the primary difference between the two pulsed modes."

We agree that it is essential to provide arbitrary parameters that differ between GIMS and HiPGIMS from PMS. We supplied the revised paper with average current density, mean power density, and duty cycle. We have also introduced the power density of the power peak and discussed it in the Results and Discussion section.

3. "The core finding relates the increased plasma energy to higher sp^3 content, consistent with the subplantation model. The discussion section should dedicate a paragraph to explicitly linking the measured plasma parameters (e.g., ion flux, ion energy distribution, if measured or estimated) to the resulting sp^3/sp^2 ratio across all three techniques. A figure schematically comparing the ion energy distribution for PMS, GIMS, and HiPGIMS would greatly enhance the paper."

Thank you for this suggestion. We have added a section at the end of the Results, which includes a discussion, where we clearly outline the key relationship between the plasma states of three different MS techniques and the phase composition of the deposited films. We wish that we could fulfill the requirements of comparing the parameters, such as the distribution of ion or electron temperatures, at this stage of our study. We are currently developing a self-designed Langmuir probe dedicated to pulsed processes, as presented in the paper. It was too early to use this device in this experiment, but we look forward to sharing our findings in one of our future works very soon.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed all my comments/concerns in this revised manuscript. I have no additional concerns regarding this manuscript. The manuscript could be recommended for publication in this form