Transmission Electron Microscopy and Molecular Dynamic Study of Ion Tracks in Nanocrystalline Y2Ti2O7: Particle Size Effect on Track Formation Threshold
, Jacques O’Connell 2, Alisher Mutali 1,3,4, Ruslan Rymzhanov 1,4 and Vladimir Skuratov 4,5,6
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper discusses the results of TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7 focusing on the particle size effect on track formation threshold.
I recommend major revision of the manuscript. The reasons are described below.
The main objective of this paper is to analyze the threshold Se value of track formation. The abstract of the paper stated that the threshold Se value to form amorphous tracks in nanoclusters and isolated nanoparticles were estimated as ~10 keV/nm and ~4 keV/nm respectively. However, the threshold value of track formation presented in the paper seems to be unreliable. For example, Se value of 4 keV/nm for isolated nanoparticles totally rely on the previous study of Y2Ti2O7 irradiated with 148 MeV Xe. (In the literature, the value of 3.5 keV/nm was presented.) On the other hand, in the present study it is difficult to deduce the threshold Se value of track formation from Fig.6, where data of three kinds of irradiations were plotted. Persuasive explanation using figures is definitely needed.
Moreover, it is extremely difficult to deduce the threshold Se value of track formation from Fig.5 (clusters of nanoparticles). (The origin of x- and y-axis is not shown in Fig.5, and it makes even more difficult to examine the threshold Se value.)
If the authors still want to claim that these values are reliable, they have to draw a curve in Fig. 5 and 6 to deduce the threshold Se value. However, in my opinion it is extremely difficult to draw a proper curve because the data are scattered.
Other comments:
p.1 line 18
10 keV/nm 4 keV/nm àNot reliable as explained above.
p.1 line 19
Definition of “the critical diameter of particles affecting the formation of SHI tracks” is vague. Especially, the word “affecting” should not be used. More concrete phrase should be used. Although MD simulation is useful to examine how the lattice evolves during irradiation, it is not useful to extract the critical parameter, such as critical diameter, since some artificial assumptions such as 0.5 nm skin to cool the nanoparticle are introduced in the simulation. Therefore, at least, the authors should mention that this result (critical diameter) is deduced from MD simulation.
p.1 line 31
said tracks à above-mentioned tracks?
p.4 Figure 2. Caption
The authors claimed that the tracks are amorphous, but it is not evident in the figure. They have to present magnified image of tracks to show it is amorphous. Showing a diffused ring in the Fourier transforms is also useful to prove the presence of amorphous phase.
p.4 Figure 2 and p.5 Figure 4
Both images represent the irradiation condition of 8 keV/nm. Are they the same samples? If not, the ion species and ion energy should be described in the captions. If they are the same samples and same irradiation condition, either of them should be deleted to reduce redundancy.
Moreover, it seems contradicting that the tracks in Fig.2(b) are amorphous, while those in Fig.4(b) are imaged as strained region. (Both of tracks are formed in the center of a nanoparticle.) The authors should explain the reason.
p.5 line 187
red marks in Figure 5a à red marks in Figure 4a
p.7 Figure 5.
The authors should change the setting of axis, so that the origin of x- and y-axis can be seen.
p.7 line 207 and 210 (Captions)
The authors used the word “average radius”, but the definition is not clear. They claimed that even for the same grain the track radius varies depending on the location of the tracks (near the edge or far from the edge). Moreover, sometimes they are amorphous and sometimes they are imaged as strained regions. Did they analyze only the amorphous tracks and excluded the strained tracks during the analysis? They should explain which tracks are chosen during the analysis.
p.8 line 250
Comparing sim TEM images è Comparing “the” TEM images?
p.9 Figure 8 and p.6 Figure 6
It seems that the data are not identical. Please check the data. For example, the data of 148 MeV Xe at 23.1 keV/nm are not the same.
p.9 Figure 8
The data showing zero track diameter is not distinguishable. Please revise the marks, so that we can recognize the irradiation condition.
p.9 Figure 8
Is it proper to plot Skuratov’s data? According to the authors’ previous paper (ref.[26]), velocity effect should be taken into account, and two curves were drawn in Fig.4 of ref.[26] to demonstrate the velocity effect. The velocity effect should be discussed.
This means that they have to discuss whether the results of MD simulation belong to low velocity group or high velocity group in Figure 8. As long as I understand, the data of MD simulation are similar to the high velocity group rather than the low velocity group, although the irradiation condition is in the low velocity group. If this is true, the results of MD simulation may give large systematic error. If so, the authors should not hide this fact.
p.9 Figure 8 caption
The data of Skuratov is not properly cited.
Ref.[24] should not be “Skuratov, V.A.; Uglov, V.V.; O’Connell, J.; Sohatsky, A.S.; Neethling, J.H.; Rogozhkin, S.V. Radiation stability of the ODS alloys against swift heavy ion impact. J. Nucl. Mater. 2013, 442, 449-457. doi: 10.1016/j.jnucmat.2013.07.017”. It should be “V.A. Skuratov et al., J. Nucl. Mater. 456 (2015) 111–114.”. The track data appear only in the latter paper.
p.10 line 309
The authors claimed that the estimated threshold values are 308
7.7 ≤ Sth < 8.6 keV/nm and 4 keV<Sth<5.4 keV/nm, respectively. However, this conclusion is not well proven by the data or figure. Please show us clearer explanation by drawing proper curves in Fig.5 and 6 (or in Fig.8).
If the results of MD simulation are used to decide the threshold Se value, the authors should take account of possible errors mentioned above. They should not totally rely on MD simulation. I believe TEM results are more reliable than the results of MD simulation.
Author Response
Thank you very much for taking the time to review our manuscript entitled “TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7: particle size effect on track formation threshold”. Your comments are constructive and have helped us to improve our article by adding more details of experimental data and making a deeper analysis. Please find our responses in the file attached and the corresponding revisions/corrections in the re-submitted files.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript discusses about the ion tracks in nanocrystalline Y2Ti2O7 by combining TEM and MD. The subject of this manuscript fits with the scope of Crystals, however, it needs a large improvement to make it suitable for publication, as suggested in the following:
Major:
1.) Page 2, line 80 to 86: 1.) could the authors comment on how was the gran size was measured in this study ? 2.) could the authors provide the venders for the chemicals listed here ? 3.) could the authors comment on why the PH=8 is important here ?
2.) Page 4, Figure 1: there are scale bars in these images, however, there is no indication what dimensions these scale bars indicate. Could the authors take care of this ? In Figure 1 (a), there are two classes of particles: 1.) dark particles with light-contrasted amorphous dots; 2.) light particles with dark-contrasted dots. Could the authors comment on what are the two particle classes and what are the dots contrast from in each of them ?
3.) Page 4, Figure 2: 1.) could the authors add an indication number for the scale bar in Figure 1(b) ? 2.) could the authors why it is concluded that tracks are more efficiently produced with decreasing electronic energy loss, and if this can be quantified in some way ? This seems not very obvious in Figure 2.
4.) Page 5, Figure 3: could the authors add an indication number for the scale bars here ?
5.) Page 5, Figure 4: 1.) could the authors provide the imaging conditions for (a) DF TEM, why are the two particles show so different contrast ? 2.) could the authors add an indication number for the scale bar in (b) ?
6.) Page 5, line 170 to 176: this paragraph is a duplicate of Page 4 line 154 to 160.
7.) Page 5, line 177 to 181: this part is a duplicate of Page 4, line 161 to 165.
8.) Page 5, line 187: it is mentioned “see red marks in Figure 5a”, this should be Figure 4 (a).
9.) Page 6, line 188 to 189: it is mentioned “these defected regions remain crystalline”, could the authors comment on how are the tracks determined to be amorphous ? Could the authors show some experimental data to prove amorphous tracks exist ?
10.) Page 7, line 222: it is cited Figure 9 here, could the authors double check this is the right figure to cite here ?
11.) Page 8, Figure 7: 1.) the simulation for TEM seems like for the STEM mode, could the authors verify on this ? 2.) why is the contrast in Figure 7 (e) is so different compared to other simulated images, could the author comment on where is the contrast from ?
12.) Page 8, line 259 to 262: it is only mentioned what are plotted in Figure 8, however, there is not any interpretation or discussions on what has been learnt from Figure 8. Could the authors comment on this ?
13.) In general, this manuscript is not well organized and written. There are also places sound like the authors are not sure, such as Page 5, line 170 “A possible explanation..”; Page 7, line 224 “Our results seem to ..”. Could the authors comment on this ?
Minor:
a.) Page2, line 69: there is a strange symbol “÷”, could the authors please take care of this ?
Based on the current status of the manuscript, I recommend a major revision.
Comments on the Quality of English Language1.) the language itself is not seriously bad
2.) the way of presenting and writing is much more concerned
Author Response
We are very grateful to you for having found the time to review our manuscript entitled “TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7: particle size effect on track formation threshold”. Your comments were very helpful for us to improve our article by adding more explanations in the text. Please find our responses in the attachment and the corresponding revisions/corrections in the re-submitted files.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn the manuscript entitled “TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7: particle size effect on track formation threshold” A. Ibrayeva et al. have evaluated the structural effects in nanocrystalline pyrochlore Y2Ti2O7 induced by high energy heavy ions in a wide range of electronic stopping powers by high-resolution transmission electron microscopy and molecular dynamics simulation considering the grain size effect.
First of all, do not use acronyms in the abstract.
Please, add more references in the introduction.
In the experimental section, add information about the used materials and instruments.
In all reported data, please, use the pristine material as reference.
Add the scale unit in all the reported TEM images.
Magnify Figures 5 and 6.
Add the error bar to all the reported data in the plot in Figure 8.
To evaluate the crystalline phases in the analysed materials, I suggest using SAED patterns obtained by TEM analysis or patterns from XRD.
In my opinion, the manuscript can be accepted with minor revision.
Author Response
Thank you very much for taking the time to review our manuscript entitled “TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7: particle size effect on track formation threshold”. Your comments are very helpful for our article improvement. We appreciate it a lot. Please find our responses in the file attached and the corresponding revisions/corrections in the re-submitted files.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsI find that the authors responded to the comments properly.
I suggest minor revisions of the manuscript.
(1) Revision of Figure 5.
After careful reading of the manuscript and authors' answers, I managed to understand how the threshold value of the track formation was deduced. However, it is not straightforward to understand it easily.
The reason for the difficulty is that the Se values of n/d of the ion tracks appear in Table 1, but they are not specified in Figures 5 and 6.
It is not possible to deduce the threshold value just by watching the figures, unless the figures are revised properly.
Therefore, I recommend a minor revision of figure 5 (and 6) to facilitate the understanding of the readers.
The example of the revision of figure 5 is shown in the attached file. By doing so, the readers can easily understand how the threshold value is deduced. Table 1 is shown in the same pdf file just for reference. (Table 1 is not revised.)
Figure 6 can be revised in the similar manner, if the authors find it necessary.
(2) Page 4 line 164
“withing” is not correct. “within” is correct.
Comments for author File: Comments.pdf
Author Response
Thank you very much for taking the time to review the revised version of our manuscript entitled “TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7: particle size effect on track formation threshold”. We appreciate it a lot. Your comments helped us to present our results more clearly. Please find our responses below and the corresponding revisions/corrections in the re-submitted files.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsI would like to thank the authors for their efforts and time on considering my comments and revising the manuscript accordingly. Based on the current status of the manuscript, I recommend acceptance of it for publication.
Author Response
Thank you very much for having found the time to review the revised version of our manuscript entitled “TEM and MD study of ion tracks in nanocrystalline Y2Ti2O7: particle size effect on track formation threshold”. Please find our response below.
Author Response File: Author Response.pdf
