Extraordinary Field Emission of Diamond Film Developed on a Graphite Substrate by Microwave Plasma Jet Chemical Vapor Deposition

Round 1

Reviewer 1 Report

Appreciation of the article “Extraordinary field emission of diamond film developed on a graphite substrate by Microwave Plasma Jet Chemical Vapor Deposition”, submitted by Hua-Yi Hsu, Jing-Shyang Yen, Chun-Yu Lin, Chi-Wen Liu, Kaviya Aranganadin, Chii-Ruey Lin, Jwo-Shiun Sun, and Ming-Chieh Lin to “APPLIED SCIENCES” (ISSN 2076-3417).

 

TITLE: “Extraordinary field emission of diamond film developed on a graphite substrate by Microwave Plasma Jet Chemical Vapor Deposition”

AUTHORS: Hua-Yi Hsu, Jing-Shyang Yen, Chun-Yu Lin, Chi-Wen Liu, Kaviya Aranganadin, Chii-Ruey Lin, Jwo-Shiun Sun, and Ming-Chieh Lin

DATE: January, 2023 (2023-01-18)

Manuscript ID: applsci-2176050

 

SUMMARY ASSESSMENT

In this article, the authors present the work they carried out to improve an MPJCVD (microwave plasma jet chemical vapor deposition) system used in the manufacture of thin diamond films in the presence of an environment containing a mixture of  and  gases, at a pressure of 70 Torr.

This work had a numerical simulation component using the finite element method implemented in COMSOL Multiphysics using a three-dimensional model of the plasma as a fluid that solved the dynamics of the interaction of the low temperature plasma (=1000K) with the 2.45 GHz electromagnetic wave frequency, in a self-consistent way for the MPJCVD system. The equations used were the conventional ones, which are integrated in the COMSOL plasma module. Modelling was carried out considering several relevant parameters, including reactor geometry, microwave power and working gas pressure. In the simulation, they used argon and hydrogen separately as working gases. These numerical simulations provided, according to the authors, a greater understanding of the manufacturing process, which allowed optimizing parameters that were used in the experimental work of manufacturing thin diamond films deposited on a graphite substrate.

The article is interesting and is generally structured in an understandable way, making a potential contribution to a more efficient design of the MPJCV system.

The text is written comprehensively and specifically with regard to English, generally of a good level.

I suggest the Editors that the article be published in “Applied Sciences” journal after being revised according to the recommendations and suggestions set out below.

 

GENERAL RECOMMENDATIONS AND SUGGESTIONS:

 

- Why is Ar used in the modeling section when the working gas in the reactor is the  mixture, even with different percentages of ? The simulation part could and should have been done using the  mixture. For the effect of the kinetics of the species present in this mixture (neutrals, electrons and ions) there are tables in the literature with the main reactions, there are effective cross sections of electronic collision, etc. Undoubtedly, the work would be more robust. Why simulate argon if it is not considered experimentally afterwards?

I think the authors should provide an explanation in the article about this issue.

- Lines 198-199: "...electric field , which is defined by ..." => ...electric field , where  represents, as usual, the gradient of the electric potential ...

- With regard to equation (4), the meaning (and how to obtain) the parameter  must be indicated.

- On line 208: "" =>

- On line 209: "" =>

- In equation (8), indicate the meaning of .

- Equation (9) is written in a correct but pedantic way, so to speak.  is the electrical permittivity of the vacuum (and it is a constant, as its name indicates and is well known) and  is the relative electrical permittivity (or dielectric constant) of the medium - it remains to mention the respective meanings in the text - also admitted as a constant. Right? I would then write this equation (9) in the traditional way:

If the authors want to keep only one line, put parentheses:

- In equation (10), indicate the meaning of

- In equation (11), indicate that  is the angular frequency of the electromagnetic wave,  is the relative magnetic permittivity and .

- In equation (14), the  must appear more separated from the  expression, despite the comma. In fact, this  is not used later and can be incorporated into the equation for the  parameter.

- On line 241, which boundary conditions do the authors refer to? Only geometric? There are, of course, in the reactor (walls, for example) boundary conditions to which the electromagnetic field must obey. But they are not referred to in the model. It would be useful to the interested reader the authors indicate the electromagnetic boundary conditions used. What are, for example, in terms of voltage, the boundary conditions imposed?

- Why is it that on line 245 the size of the mesh is a length and not an area (or a volume)? From a numerical simulation point of view, the problem is two-dimensional, right? Or three-dimensional? Never just one dimension, I think. It is necessary for the authors to clarify this point.

- Figures 6 and 8 show, in the upper left corner, the enlargement of the antenna tip, with the colors indicative of the values of the different parameters that the authors intend to show, as well as their spatial distributions, but they are not very understandable and, therefore, difficult to read and consequently interpret. As it is not possible to understand what is being shown, basically because the presentation space is too small, the camera view cannot be excluded and just shown the figure with the tip of the antenna and the nearby region, but with dimensions that allow a good visualization of what's going on or, alternatively, look for another angle to make the figure of the tip of the antenna?

In the legends of these figures, the units of the physical quantities associated with the lateral color code are not indicated.

- The authors must indicate where to find it in the literature or, if that is the case, how they calculated the reaction coefficients in Tables 1 and 2. For collisional processes involving electrons, there are libraries of effective sections and it must also be indicated whether in the case for Ar or , if the Boltzmann kinetic equation is solved for electrons to obtain the distribution function for the energy (or speeds) of electrons or if Maxwellian distributions are used. In the latter case, how do you obtain the electronic temperature? Is it an ad-hoc parameter? I think this issue needs clarification from the authors as simulation is a very important component of the article.

 

                                                                                                                    2023, January, 26

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you so much for your review. It’s our honor to have your recommendations. We have modified this manuscript according to your suggestions and those of other reviewers. Please see the attached file. We have also replied to your comments in detail as below. Mainly we have reorganized the formulation to improve the readability and added more figures to enhance the understanding of the results. More references are included accordingly. A marked copy showing the changes is also provided. 

Thank you very much!

Sincerely yours,

Ming-Chieh Lin and Coauthors

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript describes on numerical and experimental studies of reconditioning a microwave plasma jet chemical vapor deposition (MPJCVD) system for the growth of diamond film. The authors have done a great job. But there are a few notes:

1. In Fig.6, 7, enlarge the small drawings (top left).

2. Authors must clearly state the purpose of the work.

3. On SEM images, make the dimensional segments larger.

4. What is the film thickness?

5. In conclusion, the authors write about the homogeneity of the film. As a rule, the presence of drops (or particles) on the surface of films (or coatings) is considered to be a defect. The SEM image in Fig. 12a shows a large number of particles with a size of 60-70 µm. I don't know how the authors can claim that their film has relatively high uniformity and continuity.

6. "The SEM image reveals the presence of a diamond film uniformly distributed with particles at a size of ~1 μm" - show these particles in the image. Is this an average size? On what area of the film surface were particle size measurements taken to make this claim? Give a histogram of particle size distribution.

7. Fig.12b the structure is not like the presence of grains or particles. Here the structure is similar to lamellar. From this image it is impossible to agree that the film has high uniformity and continuity.

8. What is the surface roughness of the film?

Author Response

Dear Reviewer,

Thank you so much for your comments and encouragement. We have replied to your comments point by point and modified the manuscript according to your comments and those of other reviewers. Please see the attached file. Mainly we have reorganized the formulation to improve the readability and added more figures to enhance the understanding of the results. More references are included accordingly. A marked copy showing the changes is also provided.

Thank you very much!

Sincerely yours,

Ming-Chieh Lin and Coauthors

Author Response File: Author Response.pdf

Reviewer 3 Report

In this paper, the authors report the recondition of a micro plasma jet chemical vapor deposition (MPJCVD) system for developing diamond films. Optimal performance of the system was simulated using the COMSOL Multiphysics 3D plasma model under various parameters including reactor geometry, microwave power and working gas pressure. The successful deposition of diamond layer has been proven by experimental work using optimal system conditions.

In general, this paper is good. It has demonstrated the successful implementation of MPJCVD system recondition for the fabrication of diamond films. Therefore I would suggest to accept this paper for publication with minor revision. However, some issues  should be considered to improve the paper quality:

SECTION1: It is important to explain the difference between the previous system and the current system (after recondition)

SECTION3, LINE200: please put References for the Equations.

SECTION 4.2: It is mentioned that the electron density can reach 2×10power20 m-3. What does it mean? Further clarification is required to clarify the range of parameters specified as appropriate for the deposition process

SECTION4.3: It is stated that a very strong electric field is concentrated at the tips of the antenna. What level of electric field is required for the deposition process? Please revise the figures to show the electric field characteristics more clearly at the tips. please Zoom in the tips of the antenna to show the electric field configuration that appears on the antenna .

PART5: How can the authors claim that the diamond film has been created?.

SECTION 5: It is mentioned that a very low operating voltage and a high current density have been obtained. Are these a specific property of the diamond film ?.

 

 

Author Response

Dear Reviewer,

Thank you so much for reviewing our work. Your comments and encouragement are valuable to us. We have replied to your comments point by point and modified the manuscript according to your comments and those of other reviewers. Please see the attached file. Mainly we have reorganized the formulation to improve the readability and added more figures to enhance the understanding of the results. More references are included accordingly. A marked copy showing the changes is also provided.

Thank you very much!

Sincerely yours,

Ming-Chieh Lin and Coauthors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

no comments