The Etching Behaviour and Fluorine-Based-Plasma Resistance of YOF Coatings Deposited by Atmospheric Plasma Spraying

To the esteemed reviewer：

Thank you so much for taking the time to review this manuscript. Your comments and suggestions have been invaluable in helping us revise and improve our paper, as well as providing valuable guidance for our research. We had thoroughly studied the comments and implemented the necessary corrections. Thank you again for your positive and constructive comments and suggestions on our manuscript. We hope you will find our revised manuscript acceptable for publication.

1. To the esteemed reviewer：

Thank you so much for taking the time to review this manuscript. Your comments and suggestions have been invaluable in helping us revise and improve our paper, as well as providing valuable guidance for our research. We have studied these comments and suggestions carefully, and made corresponding modifications in the revised manuscript which were highlighted in red. The following is a summary of the point-by-point response to these comments.

2. Point-by-point response to Comments

Comments 1: There are many missing points about experimental methodology description: paper presents measurement for which no description of the machines used and of the methods employed is provided in the “Material and Methods” section: roughness (line 111), porosity (line 115) and TEM characterization (line 206), and FESEM-EDS (line 118, in this case the FESEM model is indicated but no information is given on the EDS detector and on the software used for quantification).

Response 1: Thank you for pointing this out. In the revised manuscript, we added the corresponding description of the machines used and of the methods employed in the “Material and Methods” section: roughness (lines 66-67), porosity (lines 67-68), TEM characterization (lines 68-69), and FESEM-EDS (line 65).

Changes in the revised manuscript:

The following comment was added: (Lines 65-69, page 2)

“An Xplore 30 EDS detector was used, and Oxford software was employed for quantification. A Mitutoyo Surftest SJ-310 was used to measure the surface roughness of the sample. The porosity was obtained by processing the color distribution of the SEM image through software (Granularity). The microstructure of the cross-section of the coating was characterized via TEM (F200S, Thermoscientific Talos). “

Comments 2: incomplete or missing part of the sentence at line 66, towards the end

Response 2: Thank you for pointing this out. We have revised the description of the XPS experimental conditions in the revised manuscript. (Lines 70-71, page 2)

Changes in the revised manuscript:

Lines 70-71, page 2

“X-ray photoelectron spectroscopy (K-Alpha, Thermo Scientific) was operated using a monochromatic Al-Kα X-ray source at a passing energy of 50 eV with a spot size of 450 μm.”

Comments 3: a sentence is truncated before reaching complete meaningfulness at line 95

Response 3: Thanks for your careful checks. This sentence has been completed in the revised manuscript. (Lines 101-103, page 3)

Changes in the revised manuscript:

Lines 101-103, page 3

“As shown in Figure 2 (a), (b), the peaks indicated by the rhombuses represent the crystalline structure of trigonal YOF, and the peaks indicated by the reverse triangles represent the crystalline phases of cubic Y₂O₃.”

Comments 4: table 2 is introduced too early in the text, well before the part of text referring to it, its caption should contain more details (like that these are data obtained by EDS quantification)

Response 4: Thanks for your suggestion. In the revised manuscript, Table 2 has been moved to a new location, and additional information has been added to the caption. (Page 6)

Changes in the revised manuscript:

Page 6

Table 2. The relative atomic percentages of Y, O, and F elements in the coatings before and after plasma exposure (data were obtained via EDS quantification). （For the figures and tables in the reply manuscript, please see the attachment "Reply to Reviewer 2.docx."）

Comments 5: Figure 4 as a whole is not much meaningful in itself: the color intensity of each figure is not a clear indication of the elemental contents and all figure appear quite homogeneous with just few holes due to the granular structure of the sample, which is already shown in SEM images. I would advise to remove it and to only show table 2. Actually, in table 2 the precision of the results is too high: data are provided up to 0.01% of accuracy but it is actually completely unreasonable for EDS, this method does not provide results with an accuracy down to this extent. For a reliable EDS measurement, the quantification should be obtained on a certain number of fixed size areas across each sample and the tabulated results should provide the mean of all measurements taken on a certain sample +/- the standard deviation of the different results distribution. Authors should also take into account that with EDS the quantification of light elements is particularly critical since the low-energy lines of the spectrum are frequently affected by strong background and discuss a bit more on the software used for analysis of spectra and quantification of elements. Comparison with XPS results should also help as this technique is generally more accurate, despite being limited to the topmost layer of the sample, within few nanometers form its surface.

Response 5: Thanks for your suggestion. According to your suggestion, we deleted the EDS figure from the original paper and put it in Figure S1 in the supplementary material. The description of the change in fluorine content of the coating before and after dry etching was moved to lines 134-143, Page 6. Regarding the accuracy of EDS data, your point is correct. We consulted the experimenters who conducted the EDS test and discovered that the last digit is a floating point that is not precise. We performed EDS tests three times on different parts of the sample and provided the standard deviation of the elements. The test results are shown in Table S1 in the supplementary material. In the revised manuscript, we put the mean values ​​of the test results in Table 2. The EDS system had been calibrated and the impact of background on the test results of light elements had been minimized. We have discussed the XPS data in the article, which is consistent with the EDS conclusion that the YOF 6% coating has the best NF3 plasma resistance.

Changes in the revised manuscript:

Lines 134-143, page 5

“The fluorine content of the coatings before and after dry etching was evidently different. The YOF 3% powder mixture, consisting of the most YF3 and the fewest YOFs, resulted in the highest relative fluorine percentage and the lowest relative oxygen percentage in the coating. On the other hand, the YOF 9% powder mixture, consisting of the least YF3 and the most YOFs, resulted in the lowest relative fluorine percentage and the highest relative oxygen percentage in the coating. The YOF 3%, YOF 6%, and YOF 9% coatings had fluorine concentrations of 47.15, 45.72, and 46.62 atomic % after the NF₃ plasma etching, respectively. High amounts of fluorine occurred near the boundary or valley in the Y₂O₃ sample. This increase in the fluorine content was due to the creation of a fluorinated layer. Table 2 lists the relative atomic percentages of the Y, O, and F elements in each coating.”

Table S1. The EDS results of Y, O, and F elements in the coatings before and after plasma exposure.

Comments 6: The sentence at line 165 "binding energy has increased due to electron transformation from oxygen atoms to fluorine atoms" is totally unclear

Response 6: Thanks for pointing this out. In the revised manuscript, we corrected the sentence to explain the reason for the difference in binding energy between Y-O and Y-F bonds.

Changes in the revised manuscript:

Lines 172-172, page 7

“As previously reported, the difference in binding energy between Y–O and Y–F bonds is caused by the difference in electronegativity between oxygen and fluorine [31,32].”

Comments 7: About TEM data, where was SAED acquired? Is it possible to mark it? In my opinion it would be better to get on each sample 2 SAED patterns, one on the fluorinated portion and one from the unaltered substrate. About EDS images, I actually think Fluorine images by itself do not say much on the concentration profile. Many EDS analysis software provide the option to extract a line profile across the image and plot the concentration of different elements along the line. It would be more recommendable to provide the STEM image with the indication of the line with alongside the plot profile with the concentration of the different elements along the line, for a line drawn perpendicular to the sample surface, hence showing the concentration of Y, O and F along sample depth.

Response 7: Thanks for your question. We have made modifications to the image based on your feedback; the modified image is shown in Figure 8. There are two SAED patterns on each sample, one on the fluorinated portion and one on the unaltered substrate. The specific location of the SAED is marked by a red arrow in the image.

For EDS results, thanks for your suggestion. The diffusion of the F element can be clearly observed after NF₃ etching, as shown in Figure 8(d). The formation of a fluoride layer indicates that Y₂O₃ could react with F. Thus, the EDS results are sufficient to demonstrate the distribution of elements in the coating.

Changes in the revised manuscript:

Page 10

Figure 8. TEM cross-sectional images of the (a)YOF 6% and the (b) Y₂O₃ coating, and the TEM-EDS mappings of the (c) YOF 6% and the (d) Y₂O₃ coating

3. Response to Comments on the Quality of English Language

Comments: A little revision of English is needed in my opinion, particularly about sentence structure and punctuation. Some of the sentences, particularly on the discussion part, do not appear completely clear to me.

Response: Thanks for your suggestion. We revised the whole manuscript carefully to avoid language errors. In addition, we consulted a professional editing service and asked several colleagues who are native English speakers to check the English. We hope the revised manuscript could be acceptable for you.

1. To the esteemed reviewer：

Thank you so much for taking the time to review this manuscript. Your comments and suggestions have been invaluable in helping us revise and improve our paper, as well as providing valuable guidance for our research. We have studied these comments and suggestions carefully, and made corresponding modifications in the revised manuscript which were highlighted in red. The following is a summary of the point-by-point response to these comments.

2. Point-by-point response to Comments

Comments 1: What would be the behavior if SF₆ is used instead of NF₃?

Response 1: Thanks for your question. As we know, the etching characteristics of fluorocarbon gases, such as CF₄ and C₄F₈, have been widely studied. However, etching with these gases is often accompanied by the formation of unwanted fluorocarbon polymer layers. In engineering practice, we found that CF₄ or SF₆ would produce additional by-product deposition on the surface of silicon wafers. Recently, completely dissociated NF₃ has been used to minimize these unwanted reactions and to achieve high etch rates. Therefore, in order to avoid other influences on the experimental results, we chose NF₃ for research.

Comments 2: The XPS spectra presented must be evaluated in terms of stability of the fitting. Please provide the values and errors for all peaks.

Response 2: Thanks for your suggestion. In the revised manuscript, we provided the values of the corresponding Y-O bond and Y-F bond fitting peaks after exposure to the NF₃ plasma, as shown in Figure 6. The errors of all fitted peaks are listed in Table S2 in the Supplementary Material. (For the figures and tables in the reply manuscript, please see the attachment "Reply to Reviewer 3.docx.")

Changes in the revised manuscript:

Page 8

Figure 6. Peak positions of the XPS spectra of (a) YOF 3%, (b) YOF 6%, (c) YOF 9% and (d) Y₂O₃ surface after exposure to the NF₃ plasma.

Table S2. Standard errors for all peaks of the XPS spectra.

Comments 3: The quality of XPS figures can be improved.

Response 3: Thanks for pointing this out. In order to improve the quality of XPS figures, we increased the font size. At the same time, we used pink solid lines to represent the fitted Y-F bond energy, blue solid lines to represent the fitted Y-O bond energy, and marked the corresponding peaks, as shown in Figure 6.

Comments 4: Please provide spectra of the samples before treatments.

Response 4: Thanks for your suggestion. In order to compare the changes in the bond energy of the Y-F bond and the Y-O bond before and after exposure to NF₃ plasma, we put the XPS figures before exposure to NF₃ plasma in the Supplementary Material, as shown in Figure S2.

Figure S2. Peak positions of the XPS spectra of (a) YOF 3%, (b) YOF 6%, (c) YOF 9% and (d) Y2O3 surface before exposure to the NF₃ plasma.

1. To the esteemed reviewer

Thank you so much for taking the time to review this manuscript. Your comments and suggestions have been invaluable in helping us revise and improve our paper, as well as providing valuable guidance for our research. We have studied these comments and suggestions carefully, and made corresponding modifications in the revised manuscript which were highlighted in red. The following is a summary of the point-by-point response to these comments.

2. Point-by-point response to Comments

Comments 1: Statistical scattering of the results, reported in Table 2 should be reported.

Response 1: Thanks for your suggestion. We performed EDS tests three times on different parts of the sample and provided the standard deviation of the elements. The mean of three EDS tests is listed in Table 2. The test results are shown in Table S1 in the supplementary material. (For the figures and tables in the reply manuscript, please see the attachment "Reply to Reviewer 4.docx.")

Changes in the revised manuscript:

Page 6

Table 2. The relative atomic percentages of Y, O, and F elements in the coatings before and after plasma exposure (data were obtained via EDS quantification).

Table S1. The EDS results of Y, O, and F elements in the coatings before and after plasma exposure.

Comments 2: I strongly recommend to the authors to study the wetting properties of the reported surfaces.

Response 2: Thanks for your suggestion. We conducted tests on the wetting characteristics of the coatings using Optical contact angle measuring and contour analysis systems (HR1500 Data physics, OCA25). The findings indicate that the YOF coating exhibits hydrophobic properties, whereas the Y₂O₃ coating has hydrophilic properties. Furthermore, YOF 6% coating exhibits the largest wetting angle which is 121.8°, suggesting superior hydrophobicity.

Figure S3 in the supplementary material displays the test results.

Figure S3. Peak positions of the XPS spectra of (a) YOF 3%, (b) YOF 6%, (c) YOF 9% and (d) Y2O3 surface before exposure to the NF3 plasma.

Comments 3: Figure 4 is unclear.

Response 3: Thanks for your reminder. Since the color intensity of each figure is not a clear indication of the elemental contents, all figures appear quite homogeneous due to the granular structure of the sample, which is already shown in SEM images. We have included Figure 4 in the supplementary material and improved its resolution. The modified EDS image is shown in Figure S1 below.

Figure S1. EDS maps before and after NF₃ plasma etching.

Comments 4: The shape of the YOF particles depicted in Figure 1 calls for explanation.

Response 4: Thanks for your suggestion. We have added explanation about the shape of YOF powders in the revised manuscript. (Line 76, Line 79-80)

Changes in the revised manuscript:

Line 76, page 2

“Centrifugal spray granulation of ceramic slurry to form spherical morphology.”

Line 79-80, page 3

“In addition, spheres with a kind of dent morphology were also observed in the YOF powder samples (Figure 1(a), (b), and (c), marked with red arrows). “

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