Long-Term Plasmonic Stability of Copper Nanoparticles Produced by Gas-Phase Aggregation Method Followed by UV-Ozone Treatment
Round 1
Reviewer 1 Report
I only have a few comments on this manuscript.
1) Page 4: Figure 2: Please state the total number of the particles counted for bot (a) and (b).
2) Page 5: Figure 4: Why are the data from as treated (right after the UV-zone treatments) are not presented?
3) Page 6: Figure 5: Labeling the plots (a), (b), (c), and (d) as “19nm untreated,” “24nm UV-untreated,” “19nm UV-ozone treated,” and “24nm UV-ozone treated, ”will enable the readers understand the plots better. Lines are too thin to be able to be able to distinguish them, in my opinion.
4) It seems that the effect of UV-ozone treatments is to lower the rate of red shifts in relative extinction spectra. Would these optical property differences between the untreated and UV-ozone treated CuNPs make any significant differences in the applications mentioned in this article (opto-electronics, photovoltaics and especially in sensing)?
Author Response
The response is provided in the attached file
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this MS, UV-ozone treatment was used for rapid oxidation of CuNPs, showing the long-term stability of SPR property about 50 months. It is an interesting observation but some key points are missing in the main context.
1.What is the experimental detail for UV-ozone treatment?
- What is the layer thickness of oxide species on the surface of CuNPs?
- The quantitative check for different cupper oxide species should be done for understanding the protection mechanism.
- It is suggested to perform applications of treated CuNPs, such as quenching fluorescent molecules or SERS.
- The mechanism of improved stability of such UV-ozone CuNPs is still vague.
- What is the reason that SPR intensity of untreated CuNPs is increasing with time in Figure 5?
Author Response
The response is provided in the attached file
Author Response File: Author Response.pdf
Reviewer 3 Report
This article is for stabilization of Cu nanoparticles using a passive layer of CuO formed by UV-ozone method. Highly-pure Cu nanoparticles with two sizes (19 nm and 24 nm) were formed by a spattering method, and compared between 2 series: untreated and UV-ozone treated. The surface chemical species were found to mainly be Cu(OH)2 and Cu2O for untreated Cu nanoparticles, while the Cu nanoparticles were covered by CuO after the UV-ozone treatment. Under ambient conditions for 5 months, the untreated Cu nanoparticles exhibited a gradual red-shift in plasmon absorption band, while the treated Cu nanoparticles changed its plasmon absorption band to the longer wavelength immediately after the treatment and didn’t significantly change for 5 months. These shifts were attributed to the oxide layers on metallic Cu, and showed a time dependency with good agreement with approximate curves of t^(1/3).
In my opinion, this study is a minor update of the author’s previous works (ref. 20), as mentioned in the main text. The passivation of Cu nanoparticles by the UV-ozone treatment is already reported. Although some new results were added (time dependency curves), explanation for this was not sufficient. Therefore, regretfully, I can’t recommend this manuscript for publication before a major update.
- Explanation of shell formation process (from time-dependency curves).
- XPS or AES for oxygen can be applied to analyze the structures of Cu2O and CuO shells (e.g. oxygen vacancy and hydration of CuO shell).
- Grazing incidence XRD analysis for crystallinity of metallic Cu and Cu-oxide shells.
and such analyses can improve the quality of this manuscript.
Author Response
The response is provided in the attached file
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The manuscript is improved but I insist that the SERS application of such Cu nanoparticles must be performed.
Author Response
Response to the comment of reviewer 2
“The manuscript is improved but I insist that the SERS application of such Cu nanoparticles must be performed. “
Similar comment requesting SERS or other plasmonic-based testing of the Cu NPs was present in the previous report of the same reviewer. Our answer was following: “We agree with the reviewer that such measurements would provide a strong impact on application-oriented use of the samples under the study. However, goal of the current work is to investigate the long-time trends in plasmonic properties as well as to provide insights on the reasons for their change. Testing the samples in SERS (or similar) is a different task, which requires additional resources and time. Thus, the requested measurements can not be performed as addition to the current paper. But of course, we will plan such studies in the future.”
We added a sentence in lines 286-288 “However, additional studies are required to test the UV-ozone treated Cu NPs in particular plasmonic-based methods such as, for example, surface enhanced Raman spectroscopy or photovoltaics.”
Unfortunately, we can not add much to the above statement. It explains clearly our position.
Reviewer 3 Report
After revision, a model for the wavelength shift was given. Then, I think that this manuscript can be published by the applied nano with a minor modification as below.
- For convenience, the parameters used in equation 2 (e.g. dielectric constants of Cu oxides) around line 215.
Author Response
Response to the comment of reviewer 3
After revision, a model for the wavelength shift was given. Then, I think that this manuscript can be published by the applied nano with a minor modification as below.
- For convenience, the parameters used in equation 2 (e.g. dielectric constants of Cu oxides) around line 215.
We added the requested information and corresponding reference in line 219.
