Sol–Gel Synthesis of ZnO:Li Thin Films: Impact of Annealing on Structural and Optical Properties
, Benedicte Vertruyen 3 and Raphael Closset 3
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors of this paper investigate the effect of thermal annealing between 300 and 600°C on the morphological, structural, optical and electrical properties of Li-doped ZnO thin films. These thin films were processed by sol-gel and deposited by spin-coating on two types of substrates: crystalline silicon and quartz.
In order for the paper to be publishable, the authors must first highlight what they bring to the table in addition to everything else that has been published in the field. They must also address the following deficiencies:
1- In the Introduction, authors should cite the most recent work in the field, such as "Structural, Electrical and Optical Characterization of ZnO:Li Thin Films Prepared by Sol-Gel Spin Coating, Journal of Ultrafine Grained and Nanostructured Materials Vol. 56, No.1, June 2023, pp. 108-120". They should also cite the papers that correspond to what they are claiming as a result or property. For example, the statement that "ZnO band gap can be engineered by doping with Mg" is very restrictive, and this is true for all dopants including Li (Figure 7b). Furthermore, reference 12, which discusses the effect of the solvent on the optical properties of ZnO:Mn, is inadequate. Similarly, reference 14 has no bearing on the effect of Li on the photocatalytic properties of ZnO.
2- In the Materials and Methods section, the authors do not indicate the thickness of the deposited ZnO film, nor the doping level actually obtained. The way in which the optical gap is obtained should also be indicated.
3- In the Results section:
Some properties (morphological and structural) are measured on films deposited on silicon substrates, while other properties (optical and electrical) correspond to films deposited on quartz. However, under the same sol-gel and spin-coating conditions, film growth can be substrate-dependent, especially at such thin thicknesses, and the authors provide no evidence that they achieve exactly the same under their conditions.
In Table 3, the comparison of the properties of ZnO thin films grown by different methods would make sense if they were doped with the same dopant and at the same doping level. This is not the case.
Finally, the values of experimentally determined physical quantities must not be expressed with unreasonable precision (lattice constant to within 0.001 Å).
Author Response
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Reviewer 2 Report
Comments and Suggestions for Authors1. It is not clear what is new in your paper, since the system is studied in papers by other authors listed in the references. Please be more specific about the novelty of your work.
2. I don't agree with the annotation ZnO:Li system, because in reality the system is ZnO- Li2O. From the precursors inserted into solution you get Li2O, not Li. This is a common mistake in many papers, and I don't agree with it.
3. Please include the preparation steps, not just the reference for them. Please include the amounts of reagents and the actual chemical composition of the sol and the dried material obtained, as I understand it is not an equi-molar composition. Insert substrate surface cleaning method.
4. If available, please insert the apparatus error.
5. FTIR subchapter: "The other weaker lines at 460, 613, 139, 650 cm-1 are also related to the stretching mode of Zn-O bonds [35]." - These bands are not identified in Figure 1a. Please identify them in the figure or delete the corresponding sentence.
6. When introducing equations, please include the proper reference. See equation (1).
7. Please include uncertainties in tables.
8. XRD subchapter: “As can be seen, no diffraction peaks of Li or Li related oxides are detected indicating the introduction of lithium in the ZnO crystal structure.” – The reader can't see this because no ZnO XRD pattern is presented in Figure 2.
9. Please check the entire manuscript for English translation errors, such as, for example, at page 5: “…and respectively the the mean crystallite size calculated…” or, at page 10: “transmittance of semicindoctors”.
10. “XRD line can be widening by defects, internal stress, instrumental broadening and respectively the the mean crystallite size calculated by the Debye–Scherrer’s equation is smaller than the actual value [37].” – This is true, but irrelevant to the discussion, since similar problems exist for undoped ZnO.
11. How did you get the band gap values? I do not see any tangents on the optical transmittance curves.
12. Since Taverage10 is 90% transmittance, equation (4) does not fit the values in Table 2.
13. The data in Table 3 are meaningless unless you compare them with the data you have obtained. Please do so.
14. Improve Conclusions according to the above observations.
Comments on the Quality of English LanguagePlease check the entire manuscript for English translation errors, such as, for example, at page 5: “…and respectively the the mean crystallite size calculated…” or, at page 10: “transmittance of semicindoctors”.
Author Response
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Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe reviewer's comments are primarily intended to improve the paper for publication. The authors have everything to gain by taking them seriously.
As far as this paper is concerned, the authors have still not clarified what is new in their work compared to other work on the same topic.
If I'm not mistaken, the thicknesses of the ZnO:Li films are still not given. I still say that comparing the properties of ZnO thin films made by different methods is meaningless if the dopant is not the same and the doping level is not the same.
Finally, just because another author has expressed lattice constants to 1/1000 of the atomic distance, it doesn't necessarily make physical sense.
Author Response
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Round 3
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors should make the following changes in their manuscript:
1°/ In the introduction, please make it clear that compared to other works on sol-gel prepared ZnO:Li thin films, their work is distinguished by the fact that the prepared sol solutions remain stable for a period of five months, which is a very good technological achievement. In addition, the detailed study of the properties covers a wide temperature range from 300 to 600°C.
2°/ In the experimental section, please explain the values of the film thicknesses.
3°/ The authors should add the following comment to Table 3: "In order to highlight the effect of the preparation method on the FOM of the ZnO thin film, thin films with comparable doping in terms of dopant and doping level should be compared. Unfortunately, data on Li-doped ZnO thin films are not available."
Author Response
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