Magnetron Sputter Deposition of Nanostructured AlN Thin Films
and Kjeld Pedersen 1Round 1
Reviewer 1 Report
“Magnetron sputter deposition of nanostructured AlN thin films” by M. Chirumamilla et al.
High-performance piezoelectric materials play a pivotal role in a wide array of applications, spanning from medical diagnostics, telecommunications, and underwater navigation to sensors, transducers, and energy harvesting. Among these materials, Aluminum Nitride (AlN) stands out as a promising piezoelectric candidate due to its exceptional attributes, including minimal dielectric losses, high thermal stability, and integration with Complementary Metal-Oxide-Semiconductor (CMOS) technology. AlN thin films are particularly highly attractive for filters and resonator applications in telecommunications applications. Consequently, there has been a notable surge in interest surrounding the growth of AlN thin films. In this study, M. Chirumamilla employed reactive magnetron sputtering under both normal and glancing-angle conditions to deposit AlN thin films on TiN-buffered Si substrates. The authors also use metallic nanoparticles grown by e-beam deposition to promote the growth of AlN nanostructures. These films are further characterized by SEM, TEM, EDS, optical reflectance, AFM, and SHG. Authors show that the variation in the material and size of metal seed particles allows the control of nucleation growth of AlN nanostructures. Furthermore, deposition at a normal angle results in the growth of bud-shaped AlN nano-structures whereas deposition at a glancing angle results in dense individually grown nanostructures tilted at an angle of 33 degrees relative to the surface normal. The manuscript is well-written however the results and discussion lack sufficient novelty to be considered for publication. Authors are encouraged to focus on the following concerns:
1. In a recent study conducted by the authors (ACS Appl. Nano Mater. 2023, 6, 10, 8849–8856, also referenced as 9 in our current work), AlN thin films were grown on TiN-buffered Si using normal and glancing-angle reactive magnetron sputtering techniques, both with and without Ag nanoparticles. The films' morphology was also thoroughly examined through SEM, TEM, EDS, and AFM. The study revealed that Ag nanoparticles play a role in facilitating the growth of the AlN wurtzite phase, resulting in improved piezoelectric properties. While the current work appears to be an extension of the prior study, the resemblance in growth methods, characterization, outcomes, and discussion does not contribute any new scientific insights or knowledge and appear to be repetitive.
2. The novelty of this study appears to involve additional tests, such as exploring different seed materials and conducting optical reflectance and SHG experiments. Nevertheless, these characterizations alone do not seem to provide enough scientific outcomes to justify the publication of the manuscript. For example, the authors demonstrate that only films grown with a glancing angle exhibit an SHG response, which is however an expected outcome given how SHG characterization functions.
Comments for author File: 
Comments.pdf
Author Response
Please, see the reply in the attached pdf file.
Author Response File: Author Response.pdf
Reviewer 2 Report
After reading the document “Magnetron sputter deposition of nanostructured AlN thin films” it can be seen that the authors conduct studies about the development and the factor that affect the AlN films by magnetron sputtering deposition. Angle deposition of 85 ° facilitate the formation of wurtzite-like structure which are relevant for piezoelectric applications.
Comment 1:please define AlN (aluminum nitride)
Comment 2: In the introduction, the authors state“AlN nanostructures remain less explored”. There is a lot of research focused on that topic, add and cite recent articles
Comment 3: The introduction is too superfluous. Add relevant works related to AlN and magnetron sputter.
Comment 4: Add the branch of each chemical reagent used in the experimental part.
Comment 5: what is the XRD setup, current, voltage, scan rate, etc. The same for AFM and the other techniques.
Comment 6: In Figure 1 add the layer or section names (the TiN layer, the AlN layer) and the distances or dimensions.
Comment 7: In Figure 2 (a) and Figure 4(a) there are some particles between the two deposited layers, Please add tha mapping for this species and discuss in the text.
Comment 8: Authors stated “Preferential growth” but there is not any textural analysis (Harris texture coefficient). Please add the analysis (you can check this article or any that you want “Improvement of dye sensitized solar cell photovoltaic performance by using a ZnO-semiconductor processed by reaction bonded”
Comment 9: Explain differences in Figure 5, regarding crystallographic and structural defects. What about lattice parameter, interplanar distance, etc
Comment 10: What are the limitations and challenges of this work? What is the research question?, future work?.
Author Response
Please, see the reply in the attached pdf file.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript by Chirumamilla, et al. presents a comprehensive study on the magnetron sputtering growth and characterization of nanostructured AlN films on TiN/Si. The nanostructure morphology can be controlled using a glancing angle and pre-deposited metal seeds. Overall, the manuscript is well written. The following concerns need to be addressed before considering for publication:
1. The authors claimed the PZ response of the nanostructured film to be higher than bulk in the introduction section. How is the PZ response of the nanostructure film with glancing angle deposition and Ag nanoparticles compared to the regular film with normal deposition without metal particles? The authors should comment on this.
2. What is the additional information or advantage provided by low-magnification STEM image and EDS spectra in Figure 2 and Figure 4, over regular SEM and EDS? Considering the scale is quite large between 0.5 µm to 1 µm.
3. The data of Figure 5 seems to be identical to the one used in supplemental information of Reference [9]. It should not be used.
4. In Figure 7, can the authors provide the cross-sectional SEM image without seeded nanoparticles for side-to-side comparison? How is the deposition rate with Au nanoparticle compared to the without nanoparticle scenario?
5. The authors should justify the reasoning behind the claim of “catalytic enhancing” effect. From what has been provided in the manuscript, I could not find any evidence to support this claim. If there does exist the catalytic enhancing effect, is Pt nanoparticle supposed to behavior better?
Author Response
Please, find the reply attached as pdf file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The revised manuscript is sufficiently improved and can be published in Applied Nano.
Author Response
We would like to thank the reviewer for reading of the revised manuscript and recommendation to publication.
Reviewer 2 Report
After reading the document “Magnetron sputter deposition of nanostructured AlN thin films” it can be seen that the authors used glancing angle magnetron sputter deposition to develop AlN structures.
After checking the modification of the manuscript it can be seen that the authors do not attend the comments. The introduction part was not correctly modified, and the elemental map for Ag was not added. Even the author stated that the XRD pattern presented in the document is not high-resolution. So, precise lattice parameter, and interplanar distances can not be determined on this pattern. Considering the above-mentioned comments the manuscript does not meet the quality to be considered for publishing in this journal.
Author Response
We would like to thank the reviewer for the 2nd round of reviewing.
However, we do not agree with the comment “After checking the modification of the manuscript it can be seen that the authors do not attend the comments”. We have addressed all 10 comments suggested by the reviewer and made appropriate changes of the manuscript.
We are not sure what the reviewer means under “the introduction part was not correctly modified”. He/she should be more specific. In the previous review, the reviewer asked to “add relevant works related to AlN and magnetron sputter” and we did it by expanding the section and citing considerable amount of additional relevant papers. In the current revision, we have introduced 3 additional references to review articles; one on general applications of III-Nitride nanostructures ( https://doi.org/10.1016/j.mser.2020.100578), micro-and nanostructures of AlN and their synthesis (https://doi.org/10.1080/09506608.2019.1641651), and a systematic review of magnetron sputtering (https://doi.org/10.1016/j.matpr.2020.02.317). With these additions, which are highlighted in blue in the revised manuscript, we believe that the frame of the work is properly set.
Regarding the comment “the elemental map of Ag was not added” we must admit that in the previous review comment 7 formulated as "add the mapping for this species and discuss in the text" was somewhat unclear. However, in the latest review it was clarified that the reviewer is specifically asking for mapping of Ag. Accordingly, we have updated figures 2 and 4 by including Ag into the mapping.
Regarding the comment about the XRD pattern and lattice parameters we would like to state that the resolution of our XRD data is sufficient to enable the calculation of lattice parameters and interplanar distances, which aligns well with the AlN reference code 00-025-1133 from the International Centre for Diffraction Data (ICDD). In Figure 3d of the manuscript, FFT analysis of selected areas confirms that the pillars grow along the c-axis of a wurtzite-like crystal lattice. This finding is further corroborated by the SHG measurements presented in Figure 9, which also indicate that the AlN structure adheres to a wurtzite-like lattice arrangement.
Reviewer 3 Report
The authors have addressed my comments in their response.
Author Response
We would like to thank the reviewer for reading the revised version and positive opinion about our corrections.
Round 3
Reviewer 2 Report
The document “Magnetron sputter deposition of nanostructured AlN thin films” has been previously checked and some comments were submitted.
Regarding to the introduction in the first review the comment was: “ 2: In the introduction, the authors state“AlN nanostructures remain less explored”. There is a lot of research focused on that topic, add and cite recent articles “
The author only added slight modifications, but there is a lot of published work related to this topic. The introduction needs to be modified in this direction.
On the other hand, the previous response of the authors stated that XRD is not in high resolution. Lattice parameter, and interplanar distance require spectra with good quality. Then, in the last submitted file, they said that has good quality (they gave opposite responses) but didn’t calculate Harris coefficient.
“Thank you for this valuable comment. Our structures contain Si, TiN, Ag and AlN materials. To measure the Harris coefficient, we need a very high-resolution XRD spectrum.
Unfortunately, obtaining a high-resolution XRD spectrum for Harris coefficient calculation is not feasible with our current setup due to technical limitations. However, we have used Fast Fourier transformations (FFTs), as shown in Figure 3, to demonstrate that AlN pillars preferentially grow along the c-axis of the wurtzite-like crystal lattice. While we understand that FFTs are not a direct substitute for Harris coefficient calculations, they do offer supporting evidence for our claim about preferential growth. Please, see lines 168-170.”
