Fabrication and Characterization of Ag–Ta Thin Films by Co-Magnetron Sputtering as Alternative Layer for High Reflection of NIR Radiation

Round 1

Reviewer 1 Report

In the manuscript, authors write that the main aim of their research “…single layer to develop industrial low-emission coating for cost-effective, clean, and easy adaptation to a large area coating”. Nevertheless, it is well known that “A low-e coating for glazing should show spectral selectivity, i.e. have a high transmittance in the visible range of the spectrum to allow visible light inside, and at the same time provide high reflectance in the near infrared part of the spectrum” (see for example, doi.org/10.1016/j.enbuild.2015.03.024). Authors state that their film “The AgTa alloy thin film deposited for 30 s exhibits higher reflectance in NIR region. It demonstrates an average reflectance of about 80% and slightly decreased to 75% after keeping in the air atmosphere for 28 days”. The optimized film has averaged reflectance more than 80% that is not be accepted for low-e coating application. For the Ag (and Ag-based) coatings is should be Light Transmittance (not Reflectance) more than 80 % (DOI: 10.5772/67085). Moreover, author report that their coating degrades by the time, that is very critical for industrial applications. There are already many well-known methods how to avoid it, see for example in the Ref. DOI: 10.5772/67085.

There are several more comments on the binning parts:

Abstract

1) alloy composition should be mentioned;

2) “deposition time” seems like process parameter, that lead to variation in films’ thickness. I suggest to change for “films’ thickness” as the main investigated parameter;

3) In abstract should be mentioned in which range there was variation of the films’ thickness;

4) “monotonic increase in FCC and BCC phase of Ag and Ta” – increase of the amount of signal? If there is more material the stronger the signal, isn’t it obvious?

5) “The work function and …. were investigated”. What does it mean “work function”?

6) “The potential low-emission coating application as reflectance in the NIR region property was investigated by a UV-VIS-NIR spectrophotometer in the 29 range of 300-2,000 nm.”

6.1) English should be improved, too long sentence;

6.2) Author begin the sentence as NIR region and in the end write the range from 300-2,000 nm. Better to split in several sentences;

7) “The AgTa alloy thin film deposited for 30 s exhibits higher reflectance in NIR region” – conclusion does not have any physical sense.

8) English and terms should be improved. Authors mixing and using various terms like “thin film”, ”coating” and not clear the difference.

9) “NIR radiation” – may the authors explain what was and how radiated?

10) it should be added more keywords related to work;

There are even more question for further parts.

Authors shows the “atomic concentration of oxygen is ranged from 40 to 50 %”, which tells about significant oxidation. All the investigated properties might be influenced by this effect.

I recommend to rework manuscript completely, change/add experiments and explanation.

Author Response

We have revised the manuscript as of your commendations. Enclosed plase find the attached file of the response to reviewer#1 and the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

The work is dedicated to the formation of metal thin films using simultaneous sputtering of Ag and Ta for the sun-heating-protection application. Prepared coatings based on Si and glass substrates were studied successfully using XRD, SEM, XPS, deep UV spectroscopy, and UV-Vis-NIR spectroscopy. As a result, NIR-protection properties of prepared coatings as well as their time stability up to 30 days were revealed. To sum up, the manuscript under review seems to be a high-quality work, which will fit the publication criteria after the major revision.

The following major points should be commented/revised:
1. SEM images – grains are not distinguished. Authors are advised to provide SEM data with higher magnification. Otherwise, statistic distributions of the grains size should be included. Moreover, graphs with grain size / coating thickness dependencies on the deposition time are of interest.
2. According to authors, coatings consist of AgTa alloy. However, any evidence is not provided. Contrary, XRD data demonstrate the maxima of pure-phase Ag and Ta. Why the term “AgTa alloy” is used?
3. Figs 7,8,9 illustrate reflectivity of the prepared coatings in VIS range. However, transmittance is of interest because the possible practical application includes the sun-heating-protection coatings for glass buildings.
4. The upper boundary of deposition times is of interest. Why coatings with higher thickness are not considered?
5. Two substrates are used for sputtering (Si and glass). According to practical point of view, glass is a good choice. But what about silicon? In particular, why Si substrates are used for XRD measurements? Reviewer is supposing that the single-crystal Si substrates can influence on the crystallinity of coatings under study.
6. Table 1 – How work function values were calculated? Reference or equation is required. Moreover, error values are of interest.

Moreover, the following minor issues should be fixed:
7. Line78 – “in the NIR region from 300-2000 mm-wavelength”
8. Line148 – remove “Showing:”
9. Line161 – Fermi
10. Line299,316,318 – just check DOI
11. Line177 – “XPS is sensitive to surface region probed in 3 nm below surface” – reference is required
12. Figure 5b - composition percentage in at. %?
13. Lines188-194 - variety of the fitting functions should be explained
14. Line209 – “The lower oxidation state (Ta1+) can also be from alloy with silver” – reference is required
15. Figures 8 and 9 – error bars are of interest

Author Response

We have revised the manuscript as of your commendations. Enclosed plase find the attached file of the response to reviewer#2 and the revised manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

1) The Reviewers have not answered the main question underlined in the very beginning.

In the manuscript, authors write that the main aim of their research “…single layer to develop industrial low-emission coating for cost-effective, clean, and easy adaptation to a large area coating”. Nevertheless, it is well known that “A low-e coating for glazing should show spectral selectivity, i.e. have a high transmittance in the visible range of the spectrum to allow visible light inside, and at the same time provide high reflectance in the near infrared part of the spectrum” (see for example, doi.org/10.1016/j.enbuild.2015.03.024). Authors state that their film “The AgTa alloy thin film deposited for 30 s exhibits higher reflectance in NIR region. It demonstrates an average reflectance of about 80% and slightly decreased to 75% after keeping in the air atmosphere for 28 days”. The optimized film has averaged reflectance more than 80% that is not be accepted for low-e coating application. For the Ag (and Ag-based) coatings is should be Light Transmittance (not Reflectance) more than 80 % (DOI: 10.5772/67085). Moreover, author report that their coating degrades by the time, that is very critical for industrial applications. There are already many well-known methods how to avoid it, see for example in the Ref. DOI: 10.5772/67085.

I have splitter in several question as  in my view the manuscript does not scientifically sound and the experimental design is not appropriate to test the hypothesis

1.1) What might be the application for the coating (as in work optimized Ag-Ta coating are not applicable for low-e coating for glazing)? In a current form manuscript could not be published.

1.2) Part of results were done on fresh films and other part of the results on already heavily oxidized films.

Authors commented that

Answer

The atomic concentrations of Ag, Ta, O and C are given in the Fig.5(b). The formation of O2 oxidation was already discussed in page 6. However, in the conclusions, we already added one sentence: “The atomic concentration of elements of AgTa films as investigated by XPS showed that the concentrations of Ag, Ta, O2 and C were found to be about 20, 20, 40 and 20%, respectively, in all prepared films. This means that Ag and Ta oxide films were formed during the deposition or the waiting time for characterization in which this problem is unavoidable.”

In practice, in Thailand, so far only two XPS systems (in Chiangmai University and Thai Synchrotron National lab) are available for XPS characterization. Therefore, normally it took about 3 months for XPS characterization. For long waiting time in this case, the oxidation already occurred particularly for Ag which is easily oxidized by oxygen. This problem cannot be avoid for research like this work in Thailand.

It means that authors selected not appropriate method for investigation. These results can not be used for the explanation of the results of current results. It is hard to say if such oxygen came to not propriety made experiments of due to easily oxidation. Both these options are not acceptable for application.

If authors wish to report on the oxidation process of the films than all the investigation should be fully reworked.

The manuscript’s results are not reproducible based on the details given in the methods section

2) Comment    1)                      alloy composition should be mentioned;

Answer

The alloy composition of AgTa films was investigated by XPS in terms of atomic concentration and the details were already discussed from Fig.5(b). However, we summarized the results again in the “Conclusions” of the revised manuscript.

3) authors’ manuscript is not well-structured. Results should not appear for the first time in conclusions.

4) Investigated films are not novel and in results there are not deep explanation and comparison with already published literature

Author Response

Frist of all, we would like to thank for your valuable comments.

Enclosed, please find  our responses to your comments. We hope that the answers to all topics of your commentare are clear and satisfactory.

Best regards,
Surachart Kamoldilok

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript was carefully revised according to reviewer's suggestions.

Author Response

Frist of all, we would like to thank for your valuable comments.

Best regards,
Surachart Kamoldilok