Flexible Silicon Dimer Nanocavity with Electric and Magnetic Enhancement

Round 1

Reviewer 1 Report

Please see the attached document with the comments

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In their work Pan and co-workers exploit dimers electric and magnetic Mie-type resonances in high-index Si dimers of different sizes to enhance the emission properties of R6G molecules. The Authors also performed simulations of the electromagnetic field distributions and decomposed the contributions of electric and magnetic modes to the system response to understand the R6G enhanced fluorescence signal. The article content is quite clear (just few minor typos and the need to add more details about the methodology – see my comments below) and it might be suitable for publication in Photonics, although I would like the Authors to address the following comments before giving a final opinion.

1. I am a bit puzzled about the novelty of this work compared to the state-of-the art, which is not well described. To me it is not clear what novelty brings this work since enhancement of photoluminiscence and other effects (e.g., fluorescence and Raman) using dielectric dimers and/or trimers has been reported by many groups in the recent years. From my perspective this study does not highlight in the introduction the novelty that it brings to the community and it does not cite relevant works in the field. Ideally, the Authors should contextualize better their work, comparing their approach/system also with more effective systems (both plasmonic and all-dielectric) based on dimers to achieve molecular emission enhancement. Important key references from many groups around the world are missing. Here some examples:
   1. Nature Communications 6:7915 (2015)
   2. ACS Photonics2(7), 913–920 (2015)
   3. Optics Express 20(13), 13636-13650 (2012)
   4. Optics Express 20(18), 20599-20604 (2012)
   5. Nanoscale 8, 10576-10581 (2016)
   6. Scientific Reports 8:12652 (2018)
2. The Authors should be more precise and quantify what “moderate” means already in the abstract. Based on their result, they achieve a factor-2 enhancement, which is already an improvement compared to the bare molecules, but it should be better discussed.
3. The part regarding the simulated electric and magnetic field distributions and decomposition of the modes of the nanocavity to analyse the contribution of electric and magnetic modes to the R6G enhanced fluorescence is discussed very briefly. Moreover, it might be important to understand what are the contributions to the enhancement coming from either absorption or scattering. This analysis might help to explain better the moderate enhancement factor. Usually the electric mode, which here looks to be the dominating one, is mostly radiative, thus explaining the low enhancement of the fluorescence, which can be enhanced better if the molecule is coupled to an antenna through a non-radiative process.
4. A comparison with other systems should be made, in particular, it is well known that electric and magnetic modes can be obtained with other systems which are easier to fabricate, in particular metal-insulator multilayers, see for instance Nano Lett. 13(12), 6033–6039 (2013), Nano Lett. 15(3), 1952–1958 (2015), Nano Lett. 19(3), 1851–1859 (2019), and Adv. Photon. Research https://doi.org/10.1002/adpr.202100286.
5. Table 2 is wrong: decay times is not reported, it is a copy of table 1. Please correct.
6. Why do the Authors not plot the fluorescence decay time curves? They claim to study fluorescence emission, but they plot only PL, which I interpret as photoluminescence (the acronym is in fact not defined in the text).
7. A TEM image of the dimer might make more sense, what is the reason to show just one particle?
8. Details on the analytical/numerical technique to decompose the dimer response in magnetic and electric components are missing (what method has been used)? Please provide details or at least one reference.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Please find the review report in the attached file.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

This work constructed heterogeneous silicon nanosphere dimers in sizes by probe nanomanipulation method and studied the fluorescence response of R6G film on the dimers. R6G enhanced fluorescence endowed by silicon dimer nanocavities was observed, and the simulated electric and magnetic field distributions and decomposed mode of nanocavity showed that electric and magnetic mode enhancements are responsible for the R6G fluorescence enhancement when exciting the dimers under longitudinal and transverse directions relative to the dimer axis, respectively. This concept will have great potentials in the fields of all-dielectric plasmonic nanostructures and this work is deserved to be accepted for publication. Reviewer has the following questions:

1.     The R6G membrane was thermally evaporated on the silicon dimer. Could authors give more experimental details for this procedure? Furthermore, how to get the R6G thickness?
2.  In the paper, the R6G fluorescence intensity changes as a function of the excitation polarization. However, the definitions of the "longitudinal" and "transversal" excitations are absent.
3. Authors find that there is no hot spot for perpendicular excitation. Does "perpendicular" refer to incident direction or polarization? Some clarification is needed. Furthermore, a zoom-in electric field map for perpendicular direction is recommended in Fig.5 to support the argument.
4. The color coding used in Fig.6 needs double check.
5. Table 2 is the same as the Table 1. Table 2 needs double check.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I recommend the article for its publication 

Author Response

Dear Reviewer,

Thank you very much for your review and recommendation.

Reviewer 2 Report

The Authors addressed all the comments of the reviewers. Thus, I support the publication of the article.

Just a minor point: please revise the references, some authors' names are spelled wrong (e.g. Ref. 7, current: Angelis, F. D., it should be : De Angelis, F.).

Author Response

Dear reviewer,

Thank you for your suggestions. We revised our manuscript according to your comment.

Response to the comment of reviewer 2

Just a minor point: please revise the references, some authors' names are spelled wrong (e.g. Ref. 7, current: Angelis, F. D., it should be : De Angelis, F.).

Author reply: The authors' names in reference 7 was revised in Page 10 from Line 357 to 359 in the revised manuscript. Besides, we also checked other references.

“7. Ardini, M.; Huang, J.A.; Sánchez, C.S.; Mousavi, M.Z.; Caprettini, V.; Maccaferri, N.; Melle, G.; Bruno, G.; Pasquale, L.; Garoli, D.; De Angelis, F. Live Intracellular Biorthogonal Imaging by Surface Enhanced Raman Spectroscopy Using Alkyne-Silver Nanoparticles Clusters. Sci. Rep. 2018, 8, 12652.”