Wet-Chemical Fabrication of Functional Humidity Sensors on a TiO₂-Coated Glass Substrate via UV Photodeposition

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors demonstrate a completely wet-chemical procedure for the fabrication of functional impedimetric humidity sensing devices on a titania (TiO2) surface. This manuscript is accurate in both experimental and simulation results and provides detailed explanations of the physical significance of these findings. Therefore, it is highly worthy of publication in this journal. While the results are intriguing, there is a need for improved explanations of the mechanisms involved and more comprehensive references. I recommend accepting this manuscript following a minor revision.

Suggestions for Revision:

1. In introduction Section, elaborate on the novelty of the work and clarify the unique properties of the proposed TiO2-based sensing devices compared to other optical sensors and include the related references, such as the SPR PCF sensor (Photonics, 2022, 9(12), 916) and plasmonic sensor (Photonics, 2023, 10(1), 82).
2. Figure 8a: (1) Mention the power of the light source and exposure time used in the Raman spectra in the text. (2) Elaborate in more detail on the results and mechanisms obtained from Figure 8a.
3. As is well known, if the TiO2-based sensing device incorporates metallic elements capable of supporting SPR, it could exhibit SPR effects, which can enhance the sensitivity of the sensor. If the device is purely based on TiO2 without any metallic components, it would not exhibit SPR. Indicate whether the proposed TiO2-based sensing device includes the surface plasmon resonance effect. If so, please include this point in the text and quote the related references.
4. Meticulously review the manuscript to correct any typos and grammatical errors.

Author Response

Thank you very much for the time and dedication to reviewing my manuscript, and for the valuable feedback provided and please find my response in the attached file below.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted work reports a completely wet-chemical procedure for the fabrication of functional impedimetric humidity sensing devices on TiO2 surface. It was found that while MeOx-functionalization can be employed to purposefully modulate the TiO2 layer response, improving its linearity in the 15 – 90%. The quality of the experimental data is adequate. Several issues are proposed herein for further improvement of the scientific quality of the submitted manuscript before it can be accepted for publication.

1. In line 148, please remove one of the 'substrates'.
2. The author should precise whatever they calculate the direct or indirect optical bandgap. Further discussions in this part should be added.
3. In line 408-409 'This might imply the blocking of photocatalytically active sites blocking during the Ni2+ photodeposition-functionalization.' How did the author draw this conclusion? 

4. Referring to Table 3, please elaborate more on the differences between the IDE patterned samples in row 3 and 4.

5. In line 489-491,'No observable RH-Z dependence was noticed, except for a small but measurable decrease in the case of pristine TiO2 at RH > 80%, which may be attributed to the formation of molecular H2O layers on its highly hydrophilic surface.' How did the author draw this conclusion?
6. Please cite relevant references to justify the discussion in line 504-505.

Comments on the Quality of English Language

English usage in the manuscript is good and easy to understand.

Author Response

Thank you very much for the time and dedication to reviewing my manuscript, and for the valuable feedback provided and please find my response in the attached file below.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This work presents a completely wet-chemical fabrication procedure of a TiO2-based humidity sensor.

The work is interesting and explained with all the necessary details to reproduce it. It is obvious that the author has dedicated time to perform the study and write the manuscript patiently.

Only very few typos were found along the manuscript including non necessary "a", missing "." at the end of one sentence, and a unit that appears as a square looking like an error.

For the rest, the manuscript can be published as it is.

Comments on the Quality of English Language

The quality of English is correct.

Author Response

Thank you very much for the positive feedback on my manuscript. A very thorough read-through has been carried in the revised version and hopefully the number of typos and errors that would be identified during copy-editting have been corrected. Regarding the sheet resistance unit “Ω □⁻¹” sometimes Ω/sq. is used instead, but the square symbol seems to be preferred by my colleagues in the faculty of electronic engineering, where our dept. is situated so I got used to it. I appologise that it looks like a missing symbol.

Reviewer 4 Report

Comments and Suggestions for Authors

A well written manuscript. Your material process was well described and material analysis was thorough. Congratulations.

The impedance results left me with some questions I hope you will explore:

1     The improved sensitivity at lower frequencies led me to ask for 10 Hz and DC results.

2   At a favorite frequency you should explore temperature dependence; an ongoing question with capacitive humidity sensors is whether the controlling parameter is  absolute or relative humidity.

3   The low sensitivity below 40%RH should be discussed.

4   The weakness of polymer-based humidity sensors is their impedance instability at RH >90%. You should explore this humidity region because because swelling of polymer films should not be a problem with your sensors. This alone would make your sensor a useful commercial product.

5   Drift is a problem with all metal oxides. You should run long term drift tests.

6 1 volt excitation across a narrow gap (is the gap 200um? not sure) is a reasonably strong field. There is a danger of ion diffusion in some designs, which may not be a problem in your design. Test, then apply a higher voltage (2-5V) for a period of a few days and then retest.

Two clarifications requested:

1  Line 40- please specify linearity as humidity response linearity.

2  Magnetron sputtering is very inexpensive, it is not costly (line 49). That PVD process would be the main competitor to your wet chemical deposition method.

 

 

Author Response

Thank you very much for the time and dedication to reviewing my manuscript, and for the valuable feedback provided and please find my response in the attached file below.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The paper has been thoroughly revised and is now suitable for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

Author has sufficiently addressed all the comments and improve the manuscript accordingly.