γ-Fe₂O₃-Based MEMS Gas Sensor for Propane Detection

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

You present in your manuscript a high-quality study over propane detection using MOX based-MEMS devices. Prior to manuscript acceptance you must fulfill the following requirements:

1. Out of the 3S-parameters which a commercial sensor must fulfill you have checked only 2 (sensitivity and selectivity). The sensor stability parameter (over time) must be shown in your manuscript, as you reported only good signal reproducibility. Please insert in the manuscript a separate figure with measurements regarding sensor signal stability in a matter of months (6 months is standard).
2. As your sensing mechanism involves the O^- species, please insert a separate figure with your sensors response to humidity, as this is of paramount importance when real-life applications are predicted for your sensors. Were your target and carrier gas dried?
3. Please specify at the corresponding section the gas suppliers, and the MFC system used (or how you calibrated your target gas concentrations).
4. You specify that your LOD is below 1 ppm propane (Fig. 5b). How did you come to this conclusion? Please explain this thoroughly, so the average reader will understand.
5. Fig. 8 must be revised, as there are typing errors all over it.
6. Please describe your data acquisition system, and if the signal was filtered or not.
7. Were your sensing measurements performed with inert or air as carrier gas, as this was not mentioned in the manuscript?
8. How thick were your sensitive layers, as determined from tilted SEM imagery (if any?). Please specify this in your manuscript, as this orients your sensors towards a specific class (thick or thin).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study focuses on experimental comparisons to demonstrate that the γ-Fe₂O₃ is the best catalyst for propane gas detection. The sensor prepared using ZnO as the substrate combined with γ-Fe₂O₃ as the catalyst has better refrigerant sensing performance. Overall quality of this study is relatively high, but the following questions need to be answered and resolved before publishment:

1. Please add a fabrication flow chart and indicate the sensor dimensions as well, because these are very important information about the sensor.
2. MEMS gas sensors widely use Pt, Pd, Au, Cr, and Al, please explain clearly why you chose ZnO instead of other substrate materials. Have you conducted any control experiments with different substrate materials?
3. From the experiment in figure 6 only, the author concludes that the double-layer sensor with ZnO as the substrate and γ-Fe₂O₃ as the catalyst demonstrates a superior sensing effect than the single-layer sensor. Single experimental data is not convincing enough. Have you considered any theoretical aspect to explain this observation? For example, the structural advantage of the double layer? The material advantage of the double layer?
4. In your 2.8 Gas sensing experiment, was the temperature of the gas measured in real time during the whole experiment? Did any temperature changes occur? Does this affect the accuracy of your sensor? Please show your experimental data to prove this.

Comments on the Quality of English Language

Please do more thorough proofreading. For example, in the conclusion section on line 268, you repeated the same text twice. Similar formatting and expression errors must be avoided.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

the manuscript was greatly improved after revision.