Effect of a Discontinuous Ag Layer on Optical and Electrical Properties of ZnO/Ag/ZnOStructures

Round 1

Reviewer 1 Report

In this manuscript “Effect of discontinuous Ag layer on optical and electrical properties of ZnO/Ag/ZnO structures”, the authors proposed highly efficient transparent ZnO/Ag/ZnO structures deposited at room temperature which are especially suitable for application as TCO layer. The results seem interesting, and the idea is quite straightforward and beneficial for future transparent electrode research. The manuscript can be published in “Coatings” after a suggested minor revision.

1.       In line 173, the authors need to explain why sheet resistance decreases with increasing the deposition time (physical phenomena).

2.       In Figure 4, why authors separated the transmittance graph for samples 2 and 5? All the transmittance spectra from samples 1 to 5 can be drawn in one graph. Is there any specific reason to separate them? It is better to draw them in one graph so that differences can be clearly observed.

3.       In lines 196-197, the authors mentioned that “This effect was attributed to the coupling between the incident light and surface plasmon polaritons (SPPs)”, have authors performed Raman Spectroscopy for their claim that this effect is due to coupling between incident light and SPPs? If not, then revise it.  

4.       Some related literature needs to be cited, for reference see

                                 I.            https://doi.org/10.1007/s10854-019-02418-2

                               II.            https://doi.org/10.3390/nano12132192

Author Response

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Reviewer 2 Report

The manuscript reports about the optical and electrical properties of ZnO/Ag/ZnO trilayer stuctures fabricated by radiofrequency sputtering. Such systems, so as other metal oxide/Ag/metal oxide structures  have been widely investigated as potential ITO substitutes. The authors should therefore better underline in the introduction the novelty of their findings. Moreover, some technical aspects should be solved, as explained below.

 1) The term Ag nanoparticles (Ag NPs) used in the abstract and in other parts of the manuscript seems not very appropriate. The authors, in fact, seem to have obtained by RF sputtering a ultrathin Ag layer, made by Ag nano-grains more than Ag NPs. This can be observed by the AFM images.

 2) Please specify the type of glass and Si substrates used. Transmittance of bare glass substrate (Figure 3) seems low in comparison with data from the literature.

 3) Sputtering parameters such as RF power and Ar working pressure used for the deposition of ZnO and Ag layers should be specified.

 4) The thickness of Ag layers corresponding to the different sputtering times (7 and 10 s) should be indicated.

 5) Fitting of ellipsometric data has been done only for Sample 4 and Sample 5, which are made by only ZnO layers of different thickness (29 nm+29 nm and 29 nm +63 nm, respectively). It could be interesting also to  perform the fitting of the whole ZnO/Ag/ZnO structure, to estimate the refractive index, extinction coefficient and thickness of the Ag layer embedded in the dielectric structure, as reported also in the literature by other authors (doi: 10.1063/1.4820266).

 6) Table 2 reports the sheet resistance and the transmittance values of three different ZnO/Ag/ZnO structures. Generally, the sheet resistance of these structures is strongly influenced by the resistance of the metal layer. If the Ag layer is obtained with the same sputtering conditions for all the samples, and if the sputtering is reproducible, a lower sheet resistance should be expected for the structure with the highest Ag deposition time. Instead, the authors found a lower sheet resistance for Sample 2 and attribute it to the higher thickness of the ZnO top layer. Please, discuss about this point, providing also the sheet resistance of the ZnO layer. For such thin ZnO layer, the sheet resistance should be quite high, having this layer the main effect of protecting the silver film and acting as antireflecting coating.

 7) At line 155 please correct Haake in Haacke.

 8) Please discuss formula 2. The value of g does not seem to have been calculated.

Author Response

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Reviewer 3 Report

In this paper, the authors managed to fabricate ZnO/Ag/ZnO nanolaminate structures by deposition utilizing consecutive RF sputtering at room temperature. The optical transparency, sheet resistance, and figure of merit were determined. The deposition time of Ag nanoparticles and the film thickness of the ZnO top layer were investigated and their influence on the key parameters was highlighted. The paper is well-written, and the study provides interesting results. Here are some comments to improve the work:

1.     The introduction should give more information about the state-of-the-art and show the difference between the presented work and other research studies. So, some modifications in the introduction are needed to emphasize this.

2.     Table 1: the dimensions of the different layers should be listed.

3.     Lines 139 to 141: missed references for the statement.

4.     I recommend combining Table 2 with Table 3 to provide a comparative figure.

5.     It is recommended to measure the Hall mobility of the different samples.

6.     The conclusions should be rewritten to include more quantitative results.

7.     The text should be proofread to minimize typographical and grammatical errors

Author Response

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Round 2

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

The authors managed to address the raised issues from the previous revision. So, my recommendation is to accept the publication of this paper.

Author Response

The authors managed to address the raised issues from the previous revision. So, my recommendation is to accept the publication of this paper.

We appreciate the reviewer useful remarks and recommendations.

Round 3

Reviewer 2 Report

The authors have discussed Referee’s suggestions.

However,

1) the thickness of Ag layer was not indicated, which instead could have been provided easily by sputtering rate.

2) Discussion about the discontinuous Ag layer formation was not improved, despite the many suggested papers could have helped it. AFM data seem to show the formation of a porous layer containing percolating Ag grains/clusters. In a discontinuous layer, if Ag nanoclusters were not connected,  the resistivity of Ag layer could not be a few Ω/square, as instead observed. SEM images of the surface of Ag layers (grown for 7 and 10 s) could have helped in showing more clearly the Ag morphology. However, it is not productive to discuss further on these points.

 Minor corrections:

3) Typos are still present at lines: 27, 48 (TCO’s instead of TCOs), 87, 155, 166, 167, 220, 265, 305, 308, 314 and must be corrected.

4) Please correct “alternate low-cost” into “ITO-alternative low-cost”.

Author Response

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