Electrochemical Properties and Chemical Oxygen Demand Depending on the Thickness of Boron-Doped Diamond
Round 1
Reviewer 1 Report
The work by Song et al. (Electrochemical Properties and Chemical Oxygen Demand Depending on the Thickness of Boron Doped Diamond) reports the fabrication boron-doped diamond (BDD) film via hot-filament chemical vapor deposition (HFCVD) using acetone as a carbon source and trimethyl boron (TMB) as a boron source. They manipulated the film thickness by tuning the deposition time. They determined that no remarkable difference was detected in their electrochemical activation or catalytic activity with film thickness.
In general, the manuscript is well-organized and easy-to-follow. I recommend the publication of the manuscript,after the some major points given below are addressed.
In the Abstract, please first use the open name of the TMB and then its abbrevation.
Please summarize the major reactions in Figure 1 for the clarification.
Line 110-113
I think this part must be removed to discussion part for Figure 3. If it is SEM data, please provide relavant data. Please reconsider this section.
Line 124
What is Ref C? Please fix this part.
In additon to Raman data, the authors must provide direct data showing the boron content in the film.
Figure 6
Please use the same units in the figure and text (mg/mL or ppm).
Label a and b for the graphs in Figure 6. What is the second graph in Figure 6? It was not mentioned in the manuscript.
It would be better to add some data for commercially available electrodes in CV and COD analysis. With these data, the authors can compare BDD thin films with other systems and discuss their advantages/disadvantages.
Author Response
Our reply) We carefully read your comments and tried our best in revising our manuscript according to them. All revisions are highlighted, using the "Track Changes" function in Microsoft Word.
In the Abstract, please first use the open name of the TMB and then its abbrevation.
Our reply) In the Abstract, we added the open name of the TMB
Before) TMB
After) trimethyl borate (TMB)
Please summarize the major reactions in Figure 1 for the clarification.
Our reply) We summarized the major reactions in Figure 1.
Before) In addition, acetone and trimethyl borate (TMB) were injected into the HFCVD chamber through a bubbling system instead of using methane gas to reduce the cost of BDD coating. At this time, the temperature of the acetone and TMB solution was adjusted at 0 ℃ using a thermostat.
After) The carbon source was acetone and the reaction gas was hydrogen. In addition, TMB was used to dope diamond with boron. Acetone and TMB were bubbled with hydrogen carrier gas and supplied into the chamber. The temperature of the acetone and TMB solution was adjusted using a thermostat. The antifreeze liquid was placed in a thermostat, and the bubbler containing the acetone and TMB solutions were immersed in the antifreeze at 0 °C to keep the temperature of the solutions at 0 °C. Hydrogen gas as a reactive gas, acetone as a carbon source, and TMB for boron doping were supplied to the chamber using a separate flow control device.
Line 110-113
I think this part must be removed to discussion part for Figure 3. If it is SEM data, please provide relavant data. Please reconsider this section.
Our reply) We removed the related part by referring to the part you said.
Line 124
What is Ref C? Please fix this part.
Our reply) We added reference.
In additon to Raman data, the authors must provide direct data showing the boron content in the film.
Our reply) Boron content has been added to the manuscript.
Before) Raman analysis showed that there were significant changes as boron doping occurred, and there was no difference between the 12 hours and 60 hours results. The Raman spectra of BDD are quite different from those of non-doped diamond films. The corresponding diamond characterization peak at 1332 cm-1 in Figure 4 is absent.
After) Raman analysis showed that there were significant changes as boron doping occurred, and there was no difference between the 12 hours and 60 hours results. In this experiment, the amount of boron doping was made equal to 11,400 ppm, this obtained through calculation based on the amount of acetone and TMB used in the experiment. The Raman spectra of BDD are quite different from those of non-doped diamond films. The corresponding diamond characterization peak at 1332 cm-1 in Figure 4 is absent.
Figure 6
Please use the same units in the figure and text (mg/mL or ppm).
Label a and b for the graphs in Figure 6. What is the second graph in Figure 6? It was not mentioned in the manuscript.
It would be better to add some data for commercially available electrodes in CV and COD analysis. With these data, the authors can compare BDD thin films with other systems and discuss their advantages/disadvantages.
Our reply) Thanks for your comment. We have revised and added the description and content of figure 6 based on your comments. In addition, the IrO2 electrode, which is commonly used as a water treatment electrode, was compared with the BDD electrode.
Please see the attached manuscript for detailed modifications.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript reports 1) the results on boron-doped diamond (BDD) deposition in the multi-filament CVD reactor with acetone as a carbon source and TMB as a boron source and 2) various characterization (morphology, growth rate ~100 nm/h, electrochemical properties, COD measurements) of the BDDs obtained at two deposition times,12 and 60 hours. As it might be expected the different thickness of these BDDs does not affect their properties. COD measurements show that BDD electrodes are more useful (but more expensive) as water-treatment electrodes than existing ones. The discussion of the results is a rather scarce.
The manuscript with minor corrections/additions (to address the remarks below) can be recommended for publication in Coatings.
Distance between the filaments Dff is two times higher than the distance Dfs between the filament plane and substrate holder (Table 1). Is the ratio Dff/Dfs=2 too high to provide uniform diamond deposition (and doping) without holder rotation? I remember the modeling results for multi-filament CVD reactors where Dff/Dfs~1 was required for uniform deposition. Author’s comments on deposition uniformity could be interesting for readers.
Page 4, line 124. [Ref C] should be replaced by a real reference.
Page 6, Fig. 5b. Prominent peaks at ~0.35/0.18 V merit author’s comments (e.g., pseudocapacitance effect, ions and faradaic charge transfer processes responsible for this effect etc)
Author Response
Our reply) We carefully read your comments and tried our best in revising our manuscript according to them. All revisions are highlighted, using the "Track Changes" function in Microsoft Word.
Distance between the filaments Dff is two times higher than the distance Dfs between the filament plane and substrate holder (Table 1). Is the ratio Dff/Dfs=2 too high to provide uniform diamond deposition (and doping) without holder rotation? I remember the modeling results for multi-filament CVD reactors where Dff/Dfs~1 was required for uniform deposition. Author’s comments on deposition uniformity could be interesting for readers.
Our reply) If the distance of Dff is reduced to 10 mm like Dfs, the sagging phenomenon of Ta filament appears a lot, and it was confirmed that the diamond coating did not proceed smoothly because the Ta filament was evaporated to a high temperature before carbonization. In addition, if the Dfs distance was increased to 20 mm to set the value of Dff/Dfs to 1, the temperature of the substrate was low, so diamond deposition did not occur.
Therefore, when the diamond film is deposited using HFCVD, which is owned by our group, a uniform diamond film was obtained by selecting the method of rotating the susceptor itself to deposit a uniform diamond film.
Page 4, line 124. [Ref C] should be replaced by a real reference.
Our reply) We added and modified reference.
Page 6, Fig. 5b. Prominent peaks at ~0.35/0.18 V merit author’s comments (e.g., pseudocapacitance effect, ions and faradaic charge transfer processes responsible for this effect etc)
Our reply) Thank you. We have added and supplemented some of the contents of the manuscript based on what you said.
Author Response File: Author Response.docx
Reviewer 3 Report
This article reports on the use of Boron Doped Diamond films as electrochemical detector, exploring the effect of the BDD HF-CVD grown thickness on the electrochemical window.
This manuscript is a good experimental piece and might become useful for researchers working on semiconducting diamond applications. The theoretical frame is well exposed and conducted, but I’ve detected lack of references in some sections. In my opinion, there are several items to be revised in order to be published in “Coatings”:
- Authors state that: “The purpose of this study was to manufacture BDD at a lower cost and capable of better performance in comparison with the BDD that is currently used for industrial applications.” However, production costs or performance comparisons are not carried out on the manuscript. I suggest changing this sentence to fit to the experiments presented in the document.
- In the introduction, authors refer to previous experimental results [10, 11]. Such references are related to simulations that shouldn’t be considered experiments.
- There are minor English style mistakes throughout the document.
- Details on the “pretreatment” carried out on the silicon and niobium wafers must be presented in the “experimental details” section
- Results can be improved:
- Contrast in Fig.2 can be improved. Figure 2 has 4 sections
- I’m not very confident on the measurement of the thickness of the BDD layer. Authors provide x.xx um data… a quite precise measurement (two decimals) that is not fitting the experimental micrographies presented.
There are additional aspects which require some attention; I send attached a pdf revision of the manuscript. I couldn’t include further comments on the whole manuscript (particularly, on the “results” section) because of the urgency of the peer review, but I also suggest reviewing such section.
This manuscript can provide valid information to be incorporated to the knowledge base of diamond-based devices, but it needs major revision prior to being published on Coatings.
Comments for author File: 
Comments.pdf
Author Response
Please see attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I thin the authors great progress in the revised version of the manuscript.
I recommend the publication of the manuscript.
Author Response
Thank you for your valuable review comments. Thanks to your advice, I think I was able to take it a step further.
I was able to develop more and more by taking note of what you gave me. Thank you.
Author Response File: Author Response.docx
Reviewer 3 Report
This is the second round of revision of this manuscript, which I said to be a good experimental piece and that might become useful for researchers working on semiconducting diamond applications. Among the main modifications, I positively value that:
- Authors have included a more detailed description of the pretreatment in the “experimental details” section.
- Authors have included minor details about costs, and have re-focused the aim of the study to: “manufacturate a BDD electrode, evaluate (…) and further develop (…)”. Thus omitting references to the analysis of the costs and focusing on the experiments. This is the right way, in my opinion. Now, aims of the manuscript are in agreement to the experiments.
Authors have modified some aspects of the manuscript; better fitting to “Coatings” standard, but some minor aspects still needs attention, in my opinion:
- Authors have modified Figure 2, but there are still some errors. Author’s response that “BDD film thickness was measured using the function found in FE-SEM (hitachi, S-4800). At this time, only two decimal places were indicated, but I will learn a more accurate measurement method and apply it to the next study.”… However, this is not about learning more accurate methods for measuring the surface. My concern is about the interpretation of the result and the sentence used:
- Please note that authors state that the boron doped diamond layer in Figure a) and b) is 1.22um and 5.91um… this is incorrect. Please note that the roughness of the surface is about 0.2um in a) and 0.5um in b). See attached figure.
- Roughness of the surface is a limitation to the maximum accuracy that authors can provide to a measurement. Being precise, authors should state that “… the BDD film deposited for 12 hours showed a thickness of 1.1±2um…”
- Intending to provide layer thickness data with a precision that is almost in the range of the nanometer for a BDD layer that clearly shows 200nm surface roughness… is an interpretation error.
As I previously indicate in the previous revision round, this manuscript can provide valid information to be incorporated to the knowledge base of diamond-based devices. However, in the present version there is still a minor revision to be made before publishing in Coatings.
Comments for author File: Comments.pdf
Author Response
Thank you for your valuable review comments. Thanks to your advice, I think I was able to grow one step further.
Thank you. As you said, including roughness seems to be the right expression. Thus, the thickness including roughness is added to the main body of the manuscript.
Author Response File: Author Response.docx
