Refractive Index Evaluation in Active TDBC Layers for Photonics Applications
, Tessa Albaric 3, Adam Habouria 3, Deru Lian 3, Clémentine Symonds 3, Jean-Michel Benoit 3, Joel Bellessa 3 and Alban Gassenq 3
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsPlease see in attachment.
Comments for author File: 
Comments.pdf
Quality of English is low. Many sentences are unclear or should be noticeably corrected. Thus, the text should be tested and corrected by professional interpreter.
Author Response
Reviewer 1
We would like first to thanks the reviewers 1 for the careful reading. He proposes many grammatical improvements in the manuscript. It clearly improves the English level of our article. All the modified sentences have highlighted in yellow in the revised version of the manuscript. Furthermore, you can find below the answers and the associated modifications regarding the scientific questions.
1) However, for fosc different values are reported which can correspond to the use of PVA/TDBC mixture or to the evaluation method. Furthermore, different values are also observed but note that the fit uncertainty is high, especially when the data are plotted with the dielectric convention [5–7].
What is a “dielectric convention” in this context.
Dielectric convention (or formalism) is when we use epsilon imaginary and real part – bottom part of the Figure 1, as explained in line 61. We added “(i.e using Equation 4)“ at the end of this sentence for clarification and we replaced the words “convention” by “formalism”.
2) Fitting was computed with EASE software with the Lorentz-Drude model with two transitions.
Citation should be given for the software source
It is the commercial software of the ellipsometer. No reference is needed since CompleteEASE can be easily found. We change the word EASE by “CompleteEASE (J.A Woolam)” for an easier finding.
3) For the 220 nm, such energy appears thus to be the second absorption transitions of the molecule
given enough high oscillator strength to be detected by ellipsometry.
What is a "second absorption transitions of the molecule"?
The well-known fundamental transition in TDBC J aggregate is 590 nm (HUMO-LUMO), the second one is at around 250 nm (see ref. [21]). As explained to reviewer 3, it is already indicated in the text : the UV “absorption band have been already used for comparing Raman spectroscopy in active and bleached TDBC [21]“. Since we did not want to add detail about that because we already explained such phenomena in our ref [21], we only added : “As expected, only the fundamental transition is removed by the bleaching probably because the layer were bleached in the visible range, as studied in ref [21].” Furthermore, we rewritten the sentence: “The 220 nm transition is identified as the second absorption transitions of the molecule, detectable by ellipsometry due to its high oscillator strength.”
4) Figure 2c presents the extracted refractive index with the n and k convention, which have been
fitted with the ellipsometry data.
What is a "n and k convention"?
n an k convention (or formalism) is when we use n and k to plot the refractive index – top part of the Figure 1 (see line 61). We added “(Equation 1)“ at the end of this sentence. We replaced the word “convention” by “formalism”.
What is the reflection model used in the calculation of dispersive refractive index on the base of measured Psi and Delta?
It is the usual ellipsometry model (see Wikipedia for instance). We think that no reference is needed.
Besides refractive index, dispersive dielectric constant is shown in the bottom panel of Figure 2c, and some comments are needed about.
We are sorry, we don’t understand your question. As presented in Equation 1 both formalisms can be used to plot the refractive index. Ref [19] was added as example in the sentence : “The refractive index can be plotted with two equivalent conventions [19]“.
5) For the transition width ΔE=0.1 eV, we found a larger value compared to the literature probably
due to the thickness variation evaluated at around 5 nm by the fit.
What is a "transitions width"?
ΔE is the absorption spectral width (see Table 1). "transition width" have been replaced by “absorption spectral width (Table 1)”
Please give the description of the method used to determine the thickness variation.
The thickness variation is obtained by the ellipsometry fitting with CompleteEASE (J.A Woolam) software. An explanation has been also added for reviewer 4 : ...for a fixed thickness of 17 nm.
6) Indeed, since the fitting with ellipsometry method is highly dependent of the thickness evaluation it could be interesting to compare such result to other methods.
No problems. Please compare the thickness evaluation obtained by ellipsometric method with the
results yielded by other methods.
We did not succeed in performing such extra experiments. Indeed, it does not work with profilometer because the material is soft. Furthermore, it is difficult with AFM because micro-patterning is needed (scratch technics gives no abrupt interfaces). You can read the reply to the reviewer 4 and to your question 8.
7) Since the normalized absorption width does not change between the different speeds (bottom part of the Figure 3a), we assume a constant refractive index for all the layers.
What is an "absorption width"? Delta E (ΔE). The word spectral has been added to the manuscript (see your question 5).
How is it possible to assume "constant refractive index" for dispersive refractive index?
When the material is pure the refractive index does not change between the different thicknesses. We are right “constant” is not an appropriate word that we replaced by ”the same”.
8) Thus, the relative film thickness values were estimated in reference to the film fabricated at 2500
rpm (17 nm), as reported in [16].
The fidelity of this determination is unclear. In my opinion, it is topical to determine the film thicknesses directly by SEM of AFM and compare to the ellipsometric results.
Yes, SEM experiment could be interesting but not on SiO2 substrate because it cannot be properly cleaved. Since we cannot compare thickness with Si and SiO2, because surface tension are different, we added: “Thickness is indeed difficult to accurately evaluate since it is a soft material difficult to micro-pattern.”
9) In that case we found a better agreement with the literature compared to ellipsometry measurement but the result is also very sensitive to the thickness evaluation presented here in the Figure 3b.
This sentence is unclear.
Indeed the oscillator strength evaluation is related to the thickness evaluation (k and x in the Equation 5). We added “(Equation 5)“ in this sentence.
10) Figure 4a presents different microstructures, which have been fabricated on SiO2 with insolation for different doses. Please report the doses used in the experiment.
The dose are indicated in Figure 4-b, we added “R in the insolated region as function of the Dose (D) (used in Figure 4a) “
11) What is a “grey intensity extraction”?
The greyscale is a number starting from 0 for black up to 255 for white, it come from image treatment. It is usual in image processing. We changed the word “grey intensity” by “grayscale”.
12) Figure 4. TDBC microstructures made by local photo-bleaching using (a) a optical microscope for
TDBC on SiO2 and a laser writer for TDBC on Ag on SiO2; (b) Extracted reflectivity; (c) deduced refractive index. What is a "laser writer for TDBC on Ag on SiO2"?
It is a typing mistake. The Figure 4 legend have been fully rewritten: “Figure 4. Study of the refractive index as a function of the photo-bleaching with (a) the top view images of the layers for different bleaching levels; (b) theoretical reflectivity as a function of the bleaching dose and Fcv; (c) deduced refractive index as a function of the bleaching dose. “
13) Therefore, the layer bleaching can also influence the refractive index evaluation in the layer.
It is not clear how method of evaluation of refractive index can be dependent of bleaching?
Oscillator strength decreases with bleaching up to 0 when the layer is fully bleached, as presented in Figure 4. We are sorry, we don’t understand your question. For instance ellipsometry use a laser which can potentially bleach the layers during the measurement if the power is too high. We added “since optical characterization can potentially bleach the layers”.
14) Some discrepancies where first highlighted, especially when TDBC is mixed with PVA. We have
then measure pure TDBC layer by ellipsometry.
These sentences are unclear and they should be corrected.
Sorry, the sentences have been corrected by “Some discrepancies were first highlighted”
15) A very high oscillator strength is measured, as expected, but with an upper-evaluated spectral width probably due to the layer roughness.
It is not clear how the oscillator strength can be measured. What is the method for this?
The Fcv is extracted by the ellipsometry fitting with the software. Once again, we think that no reference is needed because it is not an article about ellipsometry. We used ellipsometry as usual tools for studying our layers. Note that such experiment in TDBC have never been conducted in literature to our knowledge.
16) In Conclusion section, please test and correct each sentence from the grammar point of view.
Practically, all sentences contain evident mistakes.
Sorry about that, indeed 10 errors were corrected in the conclusion.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsThe report attached.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this paper, the authors prepared a pure TDBC layer and measured it through elliptical polarization and absorption spectroscopy. This work shows that although the precise refractive index evaluation of pure TDBC layers depends on the measurement method, its oscillator strength force still remains very high without bleaching. I believe that publication of the manuscript may be considered only after the following issues have been resolved.
- In the curve fitting with refractive index in the upper part of Figure 1, why is the disengagement phenomenon at the wave peak so obvious for the curve fitted from the green dot data?
- In Figure 2, (a) and (b) are comparisons before and after activation. The active material exhibits significant transitions at 220 nm and 590 nm. Why does (b) still show a curve change nearly identical to that in (a) at 220 nm?
3. In the introduction section, in order to improve the readability of the article, it is suggested that the author supplement some of the latest work on refractive index, such as, Tunable Metamaterial Absorption Device based on Fabry–Perot Resonance as Temperature and Refractive Index Sensing; Specialty optical fibers for advanced sensing applications; Exceptional-point-enhanced sensing in an all-fiber bending sensor.
4. The experiments in Section 3.1 were conducted with a thickness of 5 nm, while Section 3.2 only discusses thicknesses greater than 5 nm. Why not discuss thicknesses less than 5 nm?
- The ellipsometry measured the refractive indices of two samples at different angles, but only three sets of comparative data were measured, which is too few for a meaningful comparison.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsReferee’s comments
The authors presented both experimental and simulative studies (spectroscopic ellipsometry measurements) on extracting complex refractive index of TDBC films. Overall, the data seems reliable and the corresponding explanations are reasonable, which make it possible to be published in PHOTONICS. However, several problems, which are quite important for improving the quality of the manuscript, still need to be addressed before the final acceptance.
1. The terminology in the text should be consistent, for example, the author use both “Drude-Lorentz model” and “Lorentz-Drude model” in the text, this need to be corrected.
2. The author use the well-known Drude-Lorentz model on Page 2, where they use EG2 instead of Ep2(plasma energy) in numerator in equ. (1), why? Related explanation should be given for this replacement. In addition, the author use EG in equ. (1) and Eg in equ. (4), this must be a mistake.
3. It’s quite unclear that how does the TDBC layer prepared? i.e., what is the concentration of TDBC? Which solvent was used for dissolving TDBC here? What is PDAC on page 3? The description on page 3 is unambiguous.
4. The thickness of the TDBC film used for spectroscopic ellipometry in Figure 2 was not given, it’s important to add this value.
5. In part 3.2, the author “assume a layer thickness at 17 nm for the 2500 rpm speed”, why do not directly measure the thickness of the film by experiment such as profilometer or AFM?
Minor revisions:
Line 42 “In this works” to “In this work”; Line 66 “light spectra” to “optical intensity”; Line 77 “with straight lines” to “with curves”;
The author should make Figure 2c larger.
Comments on the Quality of English LanguageThe language of the manuscript should be polished!
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAfter the revision, this paper is sufficiently improved and it can be published in the present state.
Author Response
Comment of reviewer:
After the revision, this paper is sufficiently improved and it can be published in the present state
Reviewer 2 Report
Comments and Suggestions for AuthorsSee the review report attached
Comments for author File: Comments.pdf
Minor editing of English language required
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsAccept in present form
Author Response
Comment of reviewer:
Accept in present form
