Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

It is an interesting work. However, the authors need to address these questions/comments:

1. The term used in Figure 1 “Pre doped” is confusing. Does it mean just sputtered AlScN without any ion implantation and after sputtering?
2. There is no data provided on the thickness of each of the layers.
3. Can the authors explain why they used Ti layer and Diamond substrate?
4. The Ti layer was not detected by any of the characterization techniques. Any reason for that?
5. How much was the accelerating voltage of EDS?
6. Although the authors mentioned that 43% atomic percentage of Sc in AlScN gives the best piezoelectric performance, the ion implantation technique did not provide that high percentage of Sc in AlScN. Any reason for that?
7. It would have been nice to provide the values of piezo electric coefficient for all the samples.

Author Response

please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript deals with the important topic of searching for efficient SAW device materials. The topic is current and fits well with the journal's scope. The idea of the study is interesting. If the proposed two-step method of doping AlN with scandium proves effective, it could be a convenient way to enrich the ScAlN crystal without inducing an unfavorable structural phase transition. The methods used are reasonably chosen, but the presented results are inconsistent, and their analysis is superficial and ignores their important features. This means that the conclusions drawn from the conducted research are not well-founded.

1. While Fig. 2b shows a similar (or possibly slightly higher) aluminum content after removal of the oxidized layer, in the case of the scandium-doped crystal (Fig. 2e) the peak assigned to Al 2p decreases dramatically and, moreover, its energy differs significantly from that assigned to Al-N in the spectrum acquired at the surface. This non-obvious difference in the properties of similar materials is not commented on in any way.
2. The peaks assigned to Al-N and Al-O have different binding energies for the two investigated crystals, which is not commented on in any way, and what is more, their relative chemical shift is clearly different, which is not consistent with the statement in the text (lines 123 and 124).
3. Both peaks (in Fig. 2e) are asymmetric, as if composed of at least two components. This is unlikely to be a spin-orbit splitting of the Al 2p level, which is 0.4 eV and not resolved in Figure 2b. So what could it be? And why only for ScAlN?
4. Based on the XPS results, the authors report a Sc content in the subsurface layers of 2.4-0.5 at% for implanted AlN and 10-9.6 at% for implanted ScAlN. Simultaneously, EDS data show approximately 10 at% for AlN and over 30 at% for ScAlN. What does "at%" mean in both cases? How should this be interpreted? How was the scandium content calculated for the XPS data?
5. In my opinion, in Fig. 3 the Sc content simply decreases with sample depth and no Gaussian-like profile can be distinguished within experimental precision (see line 148).
6. In conclusion, the authors state that the XPS and EDS results confirm that the Sc atoms are bonded with nitrogen and are distributed uniformly up to 200 nm below the surface (line 185). From the cited EDS data it is not possible to draw any conclusions about the chemical bonding of Sc atoms (it is generally difficult to do so based on EDS). Fig. 3 shows the depth range up to 80 nm and, especially in Fig. 3a, indicates that deeper than 70 nm the scandium content drops to zero. In the XPS data, which binding energy of the Sc 2p peaks corresponds to the Sc-N configuration? Was it observed for AlN or for ScAlN? In particular, Fig. 2f shows a shift in the Sc peaks between 15 nm and 30 nm (the N 1s binding energy is constant). What does this mean? A change in chemical bonding?

And two minor, technical remarks:

7. How was the sputtering rate calibrated for a reference AlN sample?
8. What is the meaning of the oval drawn with a dashed line in Fig. 1 a and b?

In summary, in my opinion, the manuscript is not suitable for publication until the authors have seriously considered the issues mentioned above.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript seems to be improved now. The current form is okay to publish. 

Reviewer 2 Report

Comments and Suggestions for Authors I fully accept the changes to the manuscript and the authors' clarifications in response to my comments.
I particularly appreciate the detailed analysis of the XPS results presented in the revised text.