Nitrogen-Doped Flower-Like Hybrid Structure Based on Three-Dimensional Graphene

Round 1

Reviewer 1 Report

Nitrogen-doped flower-like hybrid structure based on three-dimensional graphene

In this paper, the authors describe the synthesis of a “hybrid structure consisting of nitrogen-doped 3-dimensional graphene and vertically aligned graphene”. On the whole this is an interesting paper, which describes a novel material. I am happy for the paper to be published, if the following comments are taken into account. I do not need to see the paper again.

I think it would be useful to include a sketch of the hybrid structure, so that the reader can more easily visualise exactly what is being synthesized.

In the Introduction the authors discuss carbon nanotube-graphene hybrids. They might like to cite this paper:

Harris, P.J.F.; Suarez-Martinez, I; Marks, N.A. The structure of junctions between carbon nanotubes and graphene shells, Nanoscale, 2016, 8, 18849–18854

On p.2, line 61  they say “The electric fields associated with plasma are believed to play a significant role in the vertical growth of carbon nanostructures”. I think they should explain the role of the electric fields.

XPS is used to analyse the samples, but this is a surface technique. Are the results representative of the bulk sample?

Figure 1(c) is labelled “HRTEM image showing graphene layers”, but the graphene layers are too small to be visible. This part of the image needs to be enlarged (also Figure 6).

Reference 4 is incomplete.

I only spotted one typo:

Caption to Figure 9 (and elsewhere):               “Lorenzian” should be “Lorentzian”

Author Response

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Reviewer 2 Report

The paper by Dasgupta et al on N-doped has several flaws which must be addressed before consideration for publication. These are detailed below:

Page 3 – Characterization

Much more detail is required here. For example, What laser power was used for Raman, was the scan a single one or multiplex? Was the rate of damage investigated by the laser power so the authors can be confident little damage form the laser occurs?

Also, for the XPS details on pass energy, resolution, x-ray source (power, achromatic or monochromatic), step size., fitting software and procedure etc should be included.  Recall a manuscript should always have sufficient information for someone else to not only make materials but characterise them the same way too.  What is the system resolution under the operating conditions used (e.g FHWM of Ag3d5/2 peak or C1s peak of PTFE or PE?), how were samples mounted and what charge compensation was used?

Page 4 – In the discussion of Fig 1(d), I wonder if the ‘equivalent thickness’ should be quoted using the ratio indicated for undoped graphene sheets.

Page 5 – Figure 2, the final image with the interface zone needs o be better. It is more blurred than the rest, presumably from editing.

Page 6 – Figure 4.  I don’t feel this adds to the argument of the paper, the Ni is dispersed fully, but the C signal could be less due to shadowing.  The main image in the figure suggests the upper part is at a different angle so the electron beam analysis won’t be perfect.  Th feel more selective areas should be taken. As the Ni will show up better being a higher Z material.

Page 9 onwards – XPS Analysis

Firstly, by convention all XPS data is plotted in rising binding energy from right to left, all spectra should be changed. Fr all data a  greater width should be sown, for example the C1s data we really need to see from about 275 eV u to about 300 eV to assess the background and loss structure for any possible graphitic carbon etc.

At present, without required details in that discussed in relation to the characterisation on page 3, the XPS data is pretty poor. Firstly figure 9 the N1s spectra CANNOT be resolved in to two states 0.1 eV apart and definitely not with significantly different FHWM.  The N1s data is also ‘to clean’ it looks like it has been heavily processed which is not aided by the different plotting method of the other spectra.  The C1s peak certainly looks to have many more components than fitted and borne out by the FHWM.  If the nitrogen is attached to the carbon, where is the C-N bond?

Due to the core-hole lifetime of the 1s level I wouldn’t expect the C1s and N1s peak FWHM to be significantly different, yet the C1s peak in fig 9 looks to be over 3 or 4 eV wide – this is impossible for a 1s level under normal operating conditions.

Figure 10, the C1s level is now fitted with Lorentzian functions whereas Figure 9 was fitted with broad more gaussian functions, why would the authors expect these to change greatly?  A standard Voight type function would be better given the noise in the data.  Also the shift to 284.4 eV suggests significant graphitic character, this is not really commented upon

Fig 11 is just unacceptable.  The C(1s) peak fitted foes not fit the envelope and no mention of the species at higher binding energy is made.

For all XPS data, the O1s peaks should also be shown and the wide scan spectra (may be included in SI) to confirm no other species present

Author Response

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Reviewer 3 Report

In the submitted manuscript, the authors present their synthesis of a novel nano-material consisting of nitrogen doped 3D graphene and vertically aligned graphene. The technological process is described adequately and the details of the state-of-the-art characterisation of the material are also provided. Moreover, the authors attempt to explain the microscopic origins of the material's growth process. 

This paper can be of importance for materials scientists looking for a promising material for energy storage. The material is presented in a clear and comprehensive manner. Therefore, I would like to recommend the publication of the manuscript in its present form. 

Author Response

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Round 2

Reviewer 1 Report

The authors have responded to all my points. The paper can now be published.

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Reviewer 2 Report

There are still significant issues with the fitting of the XPS data.

For example figure 9 has a clear peak at ~ 283 eV which needs clarification -  is this a carbide like peak or in fact the C-C peak which means all data must be calibrated to this peak?Regardless, the lack of adequate and careful fitting is a major concern.

Author Response

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Round 3

Reviewer 2 Report

I thank the authors for addressing the concern of the C1s spectrum they have replied, however my original comment also alluded to the other spectra being checked.  The data should be presented over a wider background range assuming the data has been collected over the give range (I give recommendations below) and the peaks from the same orbital should generally be of a similar FWHM given the relaxation times of the core-hole etc.

Recommended ranges:

C1s = 275 – 300 eV

N 1s = 385 – 415 eV

These ranges allow the informed to assess the quality of the data and judge the background routines etc

Overall, there are still issues with all the XPS fitting for ALL spectra.  This may stem from the use of Origin as its not really designed (Despite having routines added) for fitting XPS data.  I would recommend the manufacturers software or CasaXPS which are designed for photoemission data

Author Response

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