Improving the CO and CH₄ Gas Sensor Response at Room Temperature of α-Fe₂O₃(0001) Epitaxial Thin Films Grown on SrTiO₃(111) Incorporating Au(111) Islands

Round 1

Reviewer 1 Report

The authors reported a method for preparing composite films for gas-sensing. They used pulsed laser deposition to grow Au nanoparticles/α-Fe₂O₃ heterostructures on SrTiO₃ (STO) (111) substrates. And the authors explained the composition and crystal structure of the materials on the films through many characterization analyses. The prepared films showed an improved gas-sensing activity. But it is better to modify the manuscript according to the following suggestions:

1. The abstract part did not highlight the advantages of the films for gas sensing. It is better to modify the abstract to show the specific gas sensing performance of thin films.
2. The SEM images of α-Fe₂O₃ layer and Au/α-Fe₂O₃ bilayer grown on STO (111) substrate were shown in Figure 2a, but there is no comparison of cross-section. And if possible, please provide the pictures of real products.
3. There are many analyses to show the composition and crystal structure of Au/α-Fe₂O₃ system, so how do these factors affect the gas sensing performance of the thin films?
4. The prepared films showed improved gas-sensing activity at room temperature. But compared to other reported sensors, what are the advantages of the composite films?
5. If possible, how about the gas-sensing performance of the hybrid Au/α-Fe₂O₃ films at a lower temperature?
6. There are few tests on gas sensing. Are there other tests to prove the gas-sensing performance of the hybrid films?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors Aída Serrano et al in here present an epitaxial Au islands which have been grown on epitaxial α-Fe2O3 thin film by pulsed laser deposition on SrTiO3(111) substrate.The crystallographic coupling of lattices is confirmed with a rotation of 30º between the in-plane crystallographic axes of α-Fe2O3(0001) structure and those of SrTiO3(111) substrate and between the in-plane crystallographic axes of Au(111) and those of α-Fe2O3(0001) structure. What’s more, α-Fe2O3 is the only phase of iron oxide identified before and after its functionalization with Au nanoparticles. In addition, its structural characteristics are also preserved after Au deposition, with minor changes at short-range order.  And conductance measurements of Au(111)/α-Fe2O3(0001)/ SrTiO3(111) system show that the incorporation of Au islands on top of the α-Fe2O3(0001) layer induces an enhancement of the gas-sensing activity for CO and CH4 gas in comparison to a bare α-Fe2O3(0001) layer grown on SrTiO3(111). Though this is a topic of an incessant research interest, it also needs much careful revision to meet high publish demands of Coatings.

1. Compared to preciously published papers such as Qiu, Xuanbing, et al. "Early detection system for coal spontaneous combustion by laser dual-species sensor of CO and CH4." Optics & Laser Technology121 (2020): 105832.; Zhang, Saisai, et al. "Self-sacrificial templated formation of ZnO with decoration of catalysts for regulating CO and CH4 sensitive detection." Sensors and Actuators B: Chemical330 (2021): 129286.; Kopač, Drejc, Blaž Likozar, and Matej Huš. "How size matters: electronic, cooperative, and geometric effect in perovskite-supported copper catalysts for CO2 reduction." ACS catalysis 10.7 (2020): 4092-4102.; Schmidl, G., et al. "UV laser induced gold nanoparticle fabrication dependent on initial film properties." Optical Materials 99 (2020): 109592., the principle and innovation of this paper should be explained more in details.
2. There are some grammar errors which should be revised carefully.
3. Please give the full name of the abbreviation when it first appears.
4. In figure 7, why Gas sensor response curves for (a, b) are sharper than (c, d)?
5. Error bar in some figures should be included.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

1. The experimental setup for gas sensing is not clear , may be a figure will help.
2. How was the gas concentration was maintained?
3. Figure 7, is the only result that shows the gas sensing part of this work, but it did not mention the RH condition nor the concentration of gas used in testing. Describe these conditions
4. Both CO and CH4 are showing very similar characteristics in Fig 7, please explain how one can differentiate the result or can be quantified?
5. Conclusions made on improvement in sensing characteristics are not justified, please quantify in the conclusions. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The author answered all the questions, the manuscript can be accepted now.

Reviewer 2 Report

The authors present interesting data about Improving the CO and CH4 gas sensor response at room temperature of α-Fe2O3(0001) epitaxial thin films grown on SrTiO3(111) incorporating Au(111) islands. The authors have carefully reversed their manuscripts and answer the reviewer’s questions. The manuscript is well written, has important scientific value, and should be of great interest to the readers. And the results are well presented and the statistical analysis would help a lot for related readers. Though, there are a couple of other minor issues that need further revision according to the requirement of Guide for Authors. Overall, it is an important study, and should be considered for publication after some minor revision with the help of editor.