Nanostructured Semi-Transparent TiO2 Nanoparticle Coatings Produced by Magnetron-Based Gas Aggregation Source
Round 1
Reviewer 1 Report
1. There are several places in the manuscript that the author needs to polish again: “More beneficial” in lines 59; “;” in lines 63 and etc.
2. Please explain the similarities and differences between the technology used in the manuscript and the magnetron sputtering method.
3. Please explain whether the radius of columnar structure obtained by this deposition method can be accurately controlled and its practical application.
4. If this method can only obtain the coating mentioned in the manuscript in a limited small area.
5. Can the author add some research progress about this new way and explain the innovation of the article.
Finally, I recommend the paper for publication in Coatings but after minor revision.
Author Response
- There are several places in the manuscript that the author needs to polish again: “More beneficial” in lines 59; “;” in lines 63 and etc.
ANSW: Additional ‘polishing’ was performed as suggested by the referee.
- Please explain the similarities and differences between the technology used in the manuscript and the magnetron sputtering method.
ANSW: We have tried to modify the manuscript to stress the key differences between magnetron sputtering and nanoparticle deposition by means of m-GAS systems (i.e., used pressures, complete decoupling of nanoparticle production from their deposition, and directionality).
- Please explain whether the radius of the columnar structure obtained by this deposition method can be accurately controlled and its practical application.
ANSW: This is an interesting question, but we must confess that we do not have a definite answer to it. In principle, the radius of formed columns could be controlled by structuring the substrate prior to the deposition of nanoparticles. However, more detailed studies are needed to confirm
- If this method can only obtain the coating mentioned in the manuscript in a limited small area.
ANSW: The referee is right that in our case only small areas can be decorated with the nanoparticles. This is, however, more a technical issue that can be solved, e.g., by using a slot-like orifice or gradual movement of the substrate. This is added into the Conclusion part of the manuscript.
- Can the author add some research progress about this new way and explain the innovation of the article?
ANSW: In our opinion, the possibility to produce highly porous coatings composed of individual TiO2 nanoparticles and with tailor-made architecture is an important step toward novel and effective photo-active coatings needed in a wide range of applications. Furthermore, preliminary tests have already confirmed that this technique can also be used for the production of heterogeneous TiO2/metal nanostructures with variable plasmonic performance. This is a subject of ongoing study.
Reviewer 2 Report
This manuscript provides a method to produce semi-transparent nanoparticle TiO2 films. It should be interesting to some readers. However, before accepting for publication, some revisions are suggested to improve the quality.
1. Based on the SEM images in Fig 3, the diameter of the circular opening is 50 um. The center-to-center distance should be much larger than 50 um.
2. For Fig 7, high-quality SEM images of the nanoparticle films formed at tilting angle of 60 degrees are required to show the difference to that of the case at 0 degrees. Moreover, to well understand the effect of the tilting angle on the morphology, two levels may not be sufficient for study. Normally, at least three levels are required. Also, more parameters, like the porosity and pore size, would be helpful to support your conclusion.
3. For the relation between the tilting angle α and the growth angle β, even though there is a reference, I still suggest giving some explanation or graphs there to help readers to understand.
4. For optical application, how is the effect of tilting angle on the optical properties? It is worth studying and can improve the quality of your manuscript.
Author Response
- Based on the SEM images in Fig 3, the diameter of the circular opening is 50 um. The center-to-center distance should be much larger than 50 um.
ANSW: Thank you for this comment. The value of centre-to-centre distance was corrected
- For Fig 7, high-quality SEM images of the nanoparticle films formed at tilting angle of 60 degrees are required to show the difference to that of the case at 0 degrees. Moreover, to well understand the effect of the tilting angle on the morphology, two levels may not be sufficient for study. Normally, at least three levels are required. Also, more parameters, like the porosity and pore size, would be helpful to support your conclusion.
ANSW: Figures 7 and 8 were modified to show the increased porosity and nanocolumnar character of the Ti/TiO2 nanoparticle films. We fully agree that more deposition angles are advantageous. In this context, we added a reference to our previous article focused on vanadium nanoparticle films. In this study, 3 tilting angles were used, and the validity of the tangent rule was confirmed. Concerning the porosity and the characterization of the morphology of the nanoparticle films, this is a subject of ongoing research.
- For the relation between the tilting angle α and the growth angle β, even though there is a reference, I still suggest giving some explanation or graphs there to help readers to understand.
ANSW: The reason for different deposition and growth angles is still under debate. First, one has to consider that the deposition source is not strictly punctual, and the nanoparticles do not have a single angular direction. In addition, the short-range interaction that occurs between incoming nanoparticles and a substrate may change the trajectories of deposited nanoparticles close to the substrate and cause the growth of columns at an angle different to the angle at which nanoparticles arrive at the substrate (so-called surface trapping mechanism). This information was added to the manuscript.
- For optical application, how is the effect of tilting angle on the optical properties? It is worth studying and can improve the quality of your manuscript.
ANSW: The motivation of this study was to introduce a new technique that enables the production of highly porous TiO2 coatings composed of individual nanoparticles. The applications of such coatings, including their optical properties, photo-activity or ability to be used as a material for water cleaning were not studied so far and are a subject of ongoing investigations.
Reviewer 3 Report
I can recommend the publication of the manuscript after a minor revision.
Write in alphabetical order the keywords.
Lines 89, 90, 93, and so on: insert correctly the symbol degree (°).
Line 95: Can you insert a picture with the system used in research?
Insert a reference for eq. (1).
How many samples where used in analyses.
Kindly insert a short paragraph with Statistical analyses, and explain the method, the software used, and all the parameters related to these statistical experiments.
Insert for tools (company, country, and so on).
Lines: 149-154, 183-188, 224-229, 233-235, insert more explanations and details.
Line 159: improve the resolution of fig. 5c.
Line 189: improve the resolution of fig. 6.
Specify the limits of this study.
Insert a distinct Section “5. Conclusions” (and specify clearly with technical data your findings; also indicate the direction for future research and recommendations well documented).
Minor mistakes in References, such as ref [14], [17], [18], [20], and so on. Use only a single style (abbreviation of all journal titles).
Ref. [4] is an article or a book?
Even though the work is relevant to the journal's scope, i.e., Coatings, I do not find even a single article published in the journal in the list of references.
If possible, I recommend the following references:
[1] https://doi.org/10.1016/j.rinp.2017.08.018
[2] https://doi.org/10.1007/s11082-020-02584-2
[3] https://doi.org/10.1002/pssb.200540026
[4] https://doi.org/10.1016/j.cattod.2015.09.018
[5] https://doi.org/10.7508/JNS.2013.01.001
I will recommend the present scientific manuscript for further publication once all the aforementioned suggestions will be properly fixed.
Author Response
Write in alphabetical order the keywords.
ANSW: Corrected as it was suggested.
Lines 89, 90, 93, and so on: insert correctly the symbol degree (°).
ANSW: This typo was corrected throughout the manuscript.
Line 95: Can you insert a picture with the system used in research?
ANSW: We believe that the schematic sketch is sufficient.
Insert a reference for eq. (1).
ANSW: The reference has been added as suggested.
How many samples where used in analyses.
Kindly insert a short paragraph with Statistical analyses, and explain the method, the software used, and all the parameters related to these statistical experiments.
ANSW: As suggested, we have added the following text that describes the statistical evaluation of the mean size of Ti/TiO2 nanoparticles : The mean size of nanoparticles, both as-deposited and annealed ones, was determined from SEM images. For the statistical analysis, the sizes of more than 100 individual nanoparticles were measured. The results are presented as mean values along with the standard deviations.
Insert for tools (company, country, and so on).
ANSW: Required information was added.
Lines: 149-154, 183-188, 224-229, 233-235, insert more explanations and details.
ANSW: Short explanations were added into the manuscript as suggested
Line 159: improve the resolution of fig. 5c.
Line 189: improve the resolution of fig. 6.
ANSW: Figures were improved as required.
Specify the limits of this study.
Insert a distinct Section “5. Conclusions” (and specify clearly with technical data your findings; also indicate the direction for future research and recommendations well documented).
ANSW: The limits of the study from the point of view of deposition technique per-se are mostly connected with the small area that can be coated with the nanoparticle films. From the application point of view, further development will require proper control of the crystallinity of TiO2 NPs and their optical bad gap. This information has been added in to the manuscript (Conclusion).
ANSW:
Minor mistakes in References, such as ref [14], [17], [18], [20], and so on. Use only a single style (abbreviation of all journal titles).
Ref. [4] is an article or a book?
ANSW: References were corrected
Even though the work is relevant to the journal's scope, i.e., Coatings, I do not find even a single article published in the journal in the list of references.
If possible, I recommend the following references:
[1] https://doi.org/10.1016/j.rinp.2017.08.018
[2] https://doi.org/10.1007/s11082-020-02584-2
[3] https://doi.org/10.1002/pssb.200540026
[4] https://doi.org/10.1016/j.cattod.2015.09.018
[5] https://doi.org/10.7508/JNS.2013.01.001
ANSW: New references were added where appropriate including 2 articles published in the journal Coatings.
Round 2
Reviewer 2 Report
This study introduce a new technique that enables the production of highly porous TiO2 coatings composed of individual nanoparticles. In my previous comments, I thought more supporting analysis are needed to imrpove the depth of the manuscript. It can be about the producing parameters, morphonogy, property, or application. However, based on author's reply, the method and morphology study have been reported in someother publications. It makes me have more concerns on the novelty of this study. So, I still suggest the author to provide more supporting analysis to show its novelty.
Author Response
Dear editors, we fully respect the opinion of the referee and his/her concerns related to the originality of our manuscript. However, in our opinion, the manuscript demonstrated for the first time the important and key advantages of investigated strategy for the production of semi-transparent TiO2 porous coatings, namely the simplicity of the production step, the possibility to form patterned and/or nanocolumnar nanoparticles films composed of high-purity nanoparticles with well-defined size, the possibility to change the architecture of mesoporous TiO2 films by the oblique angle deposition, the solvent-free and linker-free character of the fabrication process as well as its compatibility with the commonly used transparent and conductive substrates. These principal advantages are now stressed in the Conclusion part of the manuscript. We do believe that this manuscript, despite the fact that it is intentionally not primarily focused on any particular application of produced coatings, might be of interest to the broad research community as the fabrication procedure is highly original and, as far as we know, and it was not investigated in the past.
Round 3
Reviewer 2 Report
I stand by my earlier opinion.
Author Response
We are sorry that we have not convinced you in our previous replies and we fully respect your opinion. However, we believe, that our manuscript is original and brings new findings related to the fabrication of novel coatings (patterning, focusing). According to our knowledge, there is no other published study that demonstrated the possibility to produce TiO2 columnar films composed of individual nanoparticles. This result, together with the solvent- and linker-free vacuum character of the deposition process opens the way for the production not only of TiO2 nanocolumnar nanoparticle films but also advanced heterogeneous structures in a controlled manner combining, for instance, photoactive TiO2 nanoparticles with nanoparticles of plasmonic metals (e.g., by low pressure sputtering). This topic is currently under study in our labs.
Anyway, we appreciate your effort and wish you Merry Christmas and Happy New Year.
