In Situ Growth of PbS Nanoparticles without Organic Linker on ZnO Nanostructures via Successive Ionic Layer Adsorption and Reaction (SILAR)

Round 1

Reviewer 1 Report

No experimental details are provided for any of the characterization techniques mentioned in the paper. Which instruments were used for SEM, TEM, XRD, PL measurements, etc?? what were their operating conditions??

"All authors contributed equally to the manuscript" Doesn't make sense when there are multiple authors.

My decision: "reject"

Author Response

Thank you for the opportunity to revise my paper. I have commented below on each of the points raised by the referees. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors present the growth, structural and optical properties of PbS nanoparticles/QDs on ZnO nanowires using successive ionic layer adsorption and reaction technique. The paper presents a study of the change in structural and optical properties as a function of the number of SILAR cycles. The paper is grammatically well written, however, I believe the citations in the introduction and results are not sufficient. The authors need to present previous comparable work as an argument to convince that the technique and materials used are promising candidates for photovoltaic applications. More references are also needed for the techniques mentioned in line 78-86. The results presented can be convincing and the paper can be published after the authors address and incorporate the following comments/questions in the manuscript:

1. I believe figure 1 is self explanatory through the text; figure 2 is missing a defined band for the conduction band in the ZnO circle. 

2. The authors state that the substrates become dark after deposition of PbS nanoparticles. Can the authors present absorption data for the phenomenon? Generally, it is viewed as a positive property for good photovoltaic materials but the argument should be supported with absorption data. 

3. The authors state the observed sized of the PbS nanoparticles using SEM. I noticed that the size is 3.6 nm for 5 cycles, which is much lower than the resolution of the SEM. The authors need to present a range (average and standard deviation) of the size data for accuracy.

4. From the SEM images, it seems that the nanowires degrade after PbS deposition. Do the authors agree with the observation? If yes, can they comment on why this happens and what future optimizations can be done to avoid the problem? Are the nanowires size and density for different samples the same or were there variations in nanowire morphology before PbS deposition? If yes, how does this affect the results presented?

5. The authors present an extensive TEM imaging for PbS QDs on ZnO NWs. Were any defects observed due to strain relocation in the TEM images? The presence of defects (which is a function of the cycles deposited) can severely harm the optical properties. 

6. I recommend the authors to maintain color consistency in Figure 7 spectra and inset. 

7. Can the authors explain the intensity trends in the PL spectra - why is the DLE intensity of 10 cycles > 5 cycles >16 cycles? Why is the NBE intensity for samples similar, despite different sized QDs? What power and temperature was the PL performed at? 

8. The wavelength shift in PbS QDs for different deposition conditions is minor, despite the size changes observed in TEM. I understand the wavelength is dependent on quantum confinement and the strain state - the authors need to explain how both the factors are playing a role in the emission wavelength and which effect is stronger. Larger size of QDs should encourage higher strain relaxation and less quantum confinement - why do the authors see a larger blueshift? Though the authors mention that strain causes the blueshift, the lattice constant and the complex state of strain (compressive/tensile?) should be discussed. 

9. The authors mention the incorporation of oxygen vacancies - which, in theory should be detrimental to the optical properties. How do the vacancy incorporation depend on the number of cycles in SILAR?

Author Response

Thank you for the opportunity to revise my paper. I have commented below on each of the points raised by the referees. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors reported the in-situ growth of PbS nanoparticles on the surface of ZnO nanowires at different cycle times by successive ionic layer adsorption and reaction techniques. The morphology, composition and optical properties of the composites were characterized in detail. The work data of the paper are detailed, but the key conclusions of the author need to be further refined. In addition, the author also needs to pay attention to the following details.

The x-axis and y-axis in Fig. 8 are not marked.

The "s1-5" and "S1-3" in Fig. 8 are not described. The reader does not know what samples are referred to?

The sentence in lines 188-189 is a separate paragraph. Why?

Figure 10 needs to be described in detail.

The conclusion paragraphs need to be further summarized.

Author Response

Thank you for the opportunity to revise my paper. I have commented below on each of the points raised by the referees. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The current version may be considered for acceptance.

Author Response

Thank you very much its much appreciated