Glancing Angle Deposition and Growth Mechanism of Inclined AlN Nanostructures Using Reactive Magnetron Sputtering

Round 1

Reviewer 1 Report

The authors present interesting work on glancing angle deposition (GLAD) of AlN nanostructures by reactive magnetron sputtering. The data gives a good basis for an overall study. Thus, I recommended it to be published in Coatings after some revisions. My particular comments are as follows:

• The authors claim that “Higher working gas pressures resulted in longer individual columns with larger diameters” and “highly coalesced and faceted nanocolumnar morphology”. To my knowledge, higher working gas magnetron-sputtering deposited films show more porous structure and smaller grain size. The SEM images in Figure 2 also demonstrate that the grain size of the AlN nanocolumns increase with lower deposition pressure.
• How did you measure the thickness of the AlN films? The deposition rates fluctuate significantly when the deposition pressure reduces from 10 to 1.5 mTorr. The growth rate of the AlN films deposited at higher deposition pressure should be lower as there are thicker AlN layer formed on the surface of the Al target, thus the DC deposition current will reduce, resulting in lower deposition rate.
• Did you measure the composition of the AlN by XPS? The XRD (Figure 6) measurement shows that the composition of the films deposited at different pressures are different.
• The scale bars of the SEM images (Figure 2) should be the same.

Author Response

Dear Reviewer,

Please find the attached Response Letter with point - by - point responses to your comments. These changes have been highlighted in YELLOW in the revised manuscript.

Thank you for taking the time to read our manuscript and provide us with valuable comments, we very much appreciate it.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. Authors used the different magnification of SEM  top-view images (Fig. 2a-d) for comparison. Should be used the uniform magnification.
2. Authors indicated the film growth directions are arbitrarily in the SEM (Fig. 2e-h). Should be check.
3. Should be explain the GLAD correctly.
4. Should be correct the grammatical corrections throughout the manuscript.
5. Conclusion section should be trimmed with important points.
6. Fig.12 – labels are missing. Also, Fig. 12(a), left panel, initial and final growth directions are arbitrary.
7. Figure 8, 9 and 10 – Should be positioned the figures without inferring the text flow.
8. Fig.6 – Should be provide the well-organized image.
9. Why authors used multiple illustration for the same purpose, should be avoided.

Author Response

Dear Reviewer,

Please find the attached Response Letter with point - by - point responses to your comments. These changes have been highlighted in YELLOW in the revised manuscript.

Thank you for taking the time to read our manuscript and provide us with valuable comments, we very much appreciate it.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors, very interesting work. I would like to propose the followings:

1. At the start, within the introduction, give some examples of thin film applications and the importance of crystal growth orientation with respect to functionality of films and associated benefits along with relevant references. 
2.  line 108....   which 'was' equipped....
3. line 113, elaborate on native oxide. 
4. Can you elaborate on why you have decided to conduct your simulation study with 10cm diameter magnetron while your physical experiments are with a 7.62cm diameter target? 
5. The target distance in your physical study was 10cm and in your simulation study was 12cm, can you elaborate on why you decided to go with 12 and not 10cm?
6. For your simulation study you mentioned that you chose a 500L cylinder model. What is the chamber volume of your plasma deposition system? Give some explanation of why choosing 500L. 
7. The XRD pole figure results are very interesting, however, you need to give some explanation of this method of data presentation for those less familiar. 
8. In figures 3 and 5 where you are presenting the pole figures. Give some explanation of how the contours are interpreted.  
9. In figure 7, again give an slight description of how you are interpreting the data in the figure caption. 
10. line 252, discussing the change in energy of the sputtered flux, you refer to Ep reduction from 5ev to 2.5ev.  I am not sure if I am understanding this reduction by looking at the figures 9a to 9d. According to your colour bar, green is 0 energy 6.4 is also within green, above which there is a blue section. So how does the figure 9d indicate 2.5ev? Similar confusion applies in rest of figure 9(e-h)
11. Overall in figure 9, the ev range you are discussing is from 2.5ev to 14ev.    Why do you have a colour bar extending to 32?  perhaps reducing the range of the colour bar may better demonstrate the results. 
12. Figure 11(a).  Total average scattering angle ranging from 0 to 800. Do you mean 80? 
13. if figure 13, we see a linear like relationship considering Nitrogen gas. However, with Argon a sudden shift between 3 and 5 mTorr pressure is observed.  Please explain and elaborate on this observation. 
14. I suggest slightly shortening the summary section and integrate it to the conclusion. 
15. As a recommendation, I think it’s best to integrate your results and discussion sections.  Describing the results as they are presented gives a better flow to the story. 

Author Response

Dear Reviewer,

Please find the attached Response Letter with point - by - point responses to your comments. These changes have been highlighted in YELLOW in the revised manuscript.

Thank you for taking the time to read our manuscript and provide us with valuable comments, we very much appreciate it.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Please confirm that "at higher pressure the nanocolumns grow more closer to each other". This contraries to common sense.

Author Response

Dear Reviewer,

Thank you for taking the time to review our manuscript again. Please find our response attached.

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors made the necessary modifications. 

Author Response

Dear Reviewer,

Thank you for taking the time to review the manuscript once again.