Parabola-Like Gold Nanobowtie on Sapphire Substrate as Nano-Cavity

Round 1

Reviewer 1 Report

In the reviewed article, the authors performed a numerical analysis of  a nano-cavity for confining light in a nanoscale gap region. The proposed scheme is interesting, but there is no in-depth discussion of several issues:

1. Recently, several unique concepts of resonance nano-cavities have emerged, e.g. Graphene-based tunable hyperbolic microcavity. Sci Rep 11, 74 (2021); Resonant nanocavity-enhanced graphene photodetectors on reflecting silicon-on-insulator wafers. Applied Physics Letters, 119(23), 232104; Deep subwavelength flow-resonant modes in a waveguide-coupled plasmonic nanocavity. Physical Review B, 101(24), 245420, etc. Authors should mention these concepts and highlight the advantages of their concept when compared with other architectures.
2. Why the parabola-like gold nano-bowtie shape was chosen? What is behind its uniqueness?
3. The numerical model has not been precisely described, i.e. what were the boundary conditions, what was the size of the numerical grid, what is the accuracy of the obtained results?
4. Can the proposed model of the device be additionally optimized in terms of increasing the operational parameters of the device, i.e. both scattering and absorption ratio as well as enhancement ratio? How can this be done? This point should be discussed in depth.

Author Response

This is the response for Reviewer 1.

Author Response File: Author Response.doc

Reviewer 2 Report

The authors present FDTD calculations on parabola-like gold bowties, and the effect that the variation of the width, height and gap have on several optical properties.

While the research itself is interesting, the level of English in very low, with multiple errors in every sentence. It is essential to get it professionally edited, because it is almost impossible to read it and understand the meaning behind some statements.

Additional editing points:

• Parabola-like gold nanobowtie is mentioned too many times, in almost every sentence, especially in the abstract and introduction. Consider finding an acronym or a shorter name.
• Figure captions are too repetitive.
• Line 170; L is not depicted in Figure 1, and I suggest changing the font in the figure
• 5 and 7 need to be altered so that the effect is visible

 

1. Line 320: what is the explanation for the jump that occurs in Fig 2?
2. It is not properly explained what influence the substrate makes, i. e. why is sapphire chosen?
3. The discussion and conclusions are lacking any in-depth analysis, the authors only present the data without any further elaboration.
4. The paper would benefit from a table or two, with neatly presented shifts or % o the change.

Overall, the paper has some potential but it has to be rewritten and modified.

Author Response

This is the response for reviewer 2.

Author Response File: Author Response.docx

Reviewer 3 Report

1-Strong language correction is needed… When the authors use have or has, they should use is or are (not was or were). This should be corrected in the whole doc.

2-Which Software did the authors use? I think Lumerical but which year product? Those must be added in the revision. Also, the mesh sizes...2D or 3D FDTD? What are the considered boundary conditions? Those information must be added in the revsion.

3-They have given some equations in the paper without preparing their references in the text. The references of the formula are needed as well in the revision.

4-Why did the authors use Sapphire as the substrate as it is expensive? Why not using SiO2 for example? They should explain the reason in the first paragraph of the 'design and methods' Section.

5-Bowtie antenna is investigated widely before...The authors should give a table before the conclusion Section and they should compare their Bowie antenna with at least 5 previously lately published ones.

Author Response

This is a response for reviewer 3. Please see the attached file.

Author Response File: Author Response.docx

Reviewer 4 Report

The current manuscript could be considered for publication after the authors carefully address the following issues:

1. English can be improved, mostly in writing style and grammar mistakes.
2. Notation should be improved. For example, instead of having 1e3, it should be written as 10^-3. 
3. Remove the sentence 'It is available online at......' from supplementary material.
4. The novelty of the paper is weak. Bow-tie nano-antennas have been described by Capasso a long time ago. The main difference is that instead of a triangular, the shape now is parabolic. Also, a comparison with a triangular structure 'could' strengthen the paper.
5. Since this is a purely theoretical paper, feasibility can be argued. A very high resolution focused ion beam or electron beam lithography/ICP would be needed to fabricate such device. Also, gaps of less than 50 nm are hard to be fabricated. 

Author Response

This is a response for Reviewer 4. Please see the file attached. Thanks.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Accept

Reviewer 4 Report

 Some of the issues have been answered, but the novelty remains weak. In any case, I leave the journal to make a final decision.