Engineering Substrate-Mediated Localized Surface Plasmons in Gold Nanodiscs

Round 1

Reviewer 1 Report

I really enjoyed reading the manuscript “Engineering substrate-mediated localized surface plasmons in gold nanodiscs” and results of partly removing the substrate under the nanodiscs are certainly very interesting.

However, there are some minor corrections/modifications that should be considered before publication:

Line 80: Is the discs final thickness approximately 20nm in total or each Au/Cr layer. What is the approximate thickness of Au and thickness of Cr?

Line 131: Table 1, Figure 1: What is the obtained pillar height(s) in sample S2-S5. Is it always the same (150 nm?) independent of the pillar diameters? Maybe the table could also have a column with pillar heights. Maybe the pristine flat structure, S1, could also be included in the table.

Line 134: Figure 2 (e-h): Maybe the approximate tilt-angle for SEM images can be mentioned.

Line 137: Figure 3: There is no scale/numbers on the reflectivity axis. Usually, this should be between 0-100% and it is useful to indicate, at least approximately, the reflectivity level for each sample.

Line 156: Figure 4. There is no scale/numbers on the extinction efficiency axis. How efficient is the extinction? For instance, it could be shown in terms of extinction cross-section and better related to the flat nano-disc area.

Line 175: Figure 5 and caption. The letters “a”, “b”, and “c” are missing in the figure (cropped left of figure).

Line 183: Maybe change “But” to “However,”

Line 199: Figure 6 caption: “samples under the study.”  -> “samples S1 to S5.” (And referring to Table 1.)

Line 201: Figure 7. The insert likely shows a schematic of a p-MA molecule(?), but this is not mentioned in the caption or text.

Line 203-204: “The excitation laser polarization was set parallel to the x-axis” can be referred to the coordinate system in Figure 5. Maybe it is clearer to state “polarized parallel to the substrate / in the sample-plane”.

Line 203: The Figure 7b caption, mentions 1434 cm-1 being monitored, but in line 212 it states 1077 cm-1. Based on the SERS intensity levels it must be line 1077 cm-1 that should be mentioned in the caption. Why was exactly this line selected? Maybe it could be better with an average estimate, for instance from the five brightest lines?

Line 215-216: The experimental x50 SERS intensity increase could be related to more locations for chemisorption on the pillar structures compared to the flat structures (higher A_SERS) and it is not mentioned what ratio of areas (A_Raman/A_SERS) was used in the EF estimate.

Line 221: The graphical appearance/resolution of equation (1) is too low. For instance, PDF zoom on the equation appears very rough and edgy.  

Line 227: Here the peak 1434 cm-1 is used for SERS EF evaluation (and not the 1077 cm-1).

Line 230: “the electric filed produces in plasmon resonance with…” -> “the electric field produced in plasmon resonances with…”

Line 242-244: “On the other hand” is used twice in the same sentence.

Line 255: “N. N. Popok”  -> “V. N. Popok”.

Author Response

Please, see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have successfully demonstrated that 2D nanostructures formed on bulk dielectrics typically exhibit relatively low EM field enhancement due to significant dissipation into the substrate. The simulation conducted in this study also supports the observed changes in LSPR spectra and the strong near-field enhancement.  Overall, the findings of this study show promising scientific significance and should be accepted in the present form for publication.

Author Response

We would like to thank the reviewer for the very positive evaluation.

Reviewer 3 Report

This paper presents an interesting study on the effect of substrate engineering on the plasmonic response and electric field enhancement of gold nanodiscs supported by silicon pillars for SERS applications. However, there are several concerns needs to be addressed:

(1) the thickness of the nanodisk has a great influence on plasmonic response and SERS performance. The author assumes that the thickness of the nanodisk is the same for all samples, but in fact Authors does not provide sufficient evidence of consistent thickness.

(2) What is the optimal value of the pillar diameter for maximizing the electric field enhancement and SERS performance?

(3) Why is there a large discrepancy between the measured and calculated extinction spectra for samples S2?

(4) In the conclusion, the authors wrote: “We anticipate that this work offers a promising platform for tuning the plasmon modes and amplifying the EM fields by eliminating the substrate influence.” Completely eliminating the influence of the substrate is impossible, and the authors didn't prove it.

(5) In Fig. 5, the authors show the electric field distribution plots in the x-z plane for different samples and find that the electric field enhancement factor increases significantly as the silicon pillar diameter decreases. It is suggested that they add some qualitative explanation here as to why reducing the silicon pillar diameter leads to an increase in the electric field enhancement factor.

(6) The authors show the SERS spectrum of p-MA molecules on the optimal sample. It is recommended that they also present a plot of how the SERS signal intensity changes with the pillar diameter, so that readers can see this trend more intuitively. 

(7) The authors compare the SERS spectrum of p-MA molecules on different samples. Can they give some quantitative indicators to evaluate SERS detection efficiency? For example, have they measured how SERS signal intensity varies with molecule concentration? Have they estimated the detection limit or sensitivity of SERS detection? How sensitive and selective are their nanostructures for SERS detection of molecules?

(8) The authors should be better to compare their results with some previous studies on similar nanostructures.

In line 2 of conclusion, the "electric field" should be "electric field".

Author Response

Please, see the attached file.

Author Response File: Author Response.pdf