The Influence of Recrystallization on Zinc Oxide Microstructures Synthesized with Sol–Gel Method on Scintillating Properties

Round 1

Reviewer 1 Report

The authors have improved the quality of the manuscript.

Author Response

The authors have improved the quality of the manuscript.

Thank you very much for your comment. We have made every effort to improve the quality of a paper.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors present interesting properties of ZnO layer on Al2O3 support. However additional comments and/or explanations should be added before publications.

Table 1- sample 1000-50: the thickness is much lower than the 800-50 one. As the characterizations indicate the existence of a ZnAl2O4 interface, it will be useful to better characterize this interface thickness and the residual ZnO layer one.

Table 2- the nature of the percentage must be indicated (weight? Atomic?)

Figure 2- the author announced bigger crystallites in the 800°C sample but the pictures (800/1000) and the size distributions look similar.

Line 292- 3.06 to 3.18 eV or nm?

Emission part-The emission curves are complex due to the existence of both excitonic and defect contribution. Excitation graphs may help to better understand the nature of the visible band

Figure 10/11 Thermolumimescence: It would be interesting so as to complete the discussion, to add the emission curves at about 410K, 450K, 525K. In figure 11, the contribution of the Al2O3 support is high as well as the emission linked to the ZnAl2O4 interface. Thus it is difficult to make a direct link between the emission and the nature of the defect cited in litterature

Author Response

The authors present interesting properties of ZnO layer on Al2O3 support. However, additional comments and explanations should be added before publications.

Thank you very much for this remark. We will try to improve everything that should be additionally explained.

Table 1- sample 1000-50: the thickness is much lower than the 800-50 one. As the characterizations indicate the existence of a ZnAl2O4 interface, it will be useful to better characterize this interface thickness and the residual ZnO layer one.

Due to your suggestion, we have conducted the measurments of the 1000_50 sample cross-section, analyse them and include into a paper. We would like to really thank for this suggestion. It opened our eyes on another, better explanation of the spinel sub-phase creation.

Table 2- the nature of the percentage must be indicated (weight? Atomic?)

Thank you very much for this remark. The values relate to atomic percentage. The correction is supplied onto an article.

Figure 2- the author announced bigger crystallites in the 800°C sample but the pictures (800/1000) and the size distributions look similar.

Thank you very much for the comment. The distribution for both samples looks quite similar, but the sample fired in 800 ^oC has most of the crystallites in the range of 2-8 μm.  The remark is introduced into the manuscript.

Line 292- 3.06 to 3.18 eV or nm?

Thank you the remark. It should be a value in eV.

Emission part-The emission curves are complex due to the existence of both excitonic and defect contribution. Excitation graphs may help to better understand the nature of the visible band

Thank you very much for this suggestion. We agree, that the photoluminescence results may be ambiguous. Due to your suggestion, we have conducted the measurements of emission. Unfortunately, the result obtained with our system has very poor quality, has very bad signal-to-noise ratio and doesn’t give any additional information. The obtained measurement is supplied below.

Figure 10/11 Thermolumimescence: It would be interesting so as to complete the discussion, to add the emission curves at about 410K, 450K, 525K. In figure 11, the contribution of the Al2O3 support is high as well as the emission linked to the ZnAl2O4 interface. Thus it is difficult to make a direct link between the emission and the nature of the defect cited in literature

We agree that to complete the discussion; it would be great to add the emission curves. Unfortunately, our hardware doesn't allow preparing such measurements.

We also agree that in the case of sample 1000_50, we may deal with the emission linked to the ZnAl2O4 interface. Thus, a short mention was added.

The authors present interesting properties of ZnO layer on Al2O3 support. However, additional comments and explanations should be added before publications.

Thank you very much for this remark. We will try to improve everything that should be additionally explained.

Table 1- sample 1000-50: the thickness is much lower than the 800-50 one. As the characterizations indicate the existence of a ZnAl2O4 interface, it will be useful to better characterize this interface thickness and the residual ZnO layer one.

Due to your suggestion, we have conducted the measurments of the 1000_50 sample cross-section, analyse them and include into a paper. We would like to really thank for this suggestion. It opened our eyes on another, better explanation of the spinel sub-phase creation.

Table 2- the nature of the percentage must be indicated (weight? Atomic?)

Thank you very much for this remark. The values relate to atomic percentage. The correction is supplied onto an article.

Figure 2- the author announced bigger crystallites in the 800°C sample but the pictures (800/1000) and the size distributions look similar.

Thank you very much for the comment. The distribution for both samples looks quite similar, but the sample fired in 800 ^oC has most of the crystallites in the range of 2-8 μm.  The remark is introduced into the manuscript.

Line 292- 3.06 to 3.18 eV or nm?

Thank you the remark. It should be a value in eV.

Emission part-The emission curves are complex due to the existence of both excitonic and defect contribution. Excitation graphs may help to better understand the nature of the visible band

Thank you very much for this suggestion. We agree, that the photoluminescence results may be ambiguous. Due to your suggestion, we have conducted the measurements of emission. Unfortunately, the result obtained with our system has very poor quality, has very bad signal-to-noise ratio and doesn’t give any additional information. The obtained measurement is supplied below.

Figure 10/11 Thermolumimescence: It would be interesting so as to complete the discussion, to add the emission curves at about 410K, 450K, 525K. In figure 11, the contribution of the Al2O3 support is high as well as the emission linked to the ZnAl2O4 interface. Thus it is difficult to make a direct link between the emission and the nature of the defect cited in literature

We agree that to complete the discussion; it would be great to add the emission curves. Unfortunately, our hardware doesn't allow preparing such measurements.

We also agree that in the case of sample 1000_50, we may deal with the emission linked to the ZnAl2O4 interface. Thus, a short mention was added.

Author Response File: Author Response.docx

Reviewer 3 Report

The article is devoted to the recrystallization of a ZnO film grown on a sapphire substrate by sedimentation of particles from a suspension in an organic medium. The suspension was prepared in a solution of zinc acetate dihydrate in the presence of diethanolamine. The film thickness was adjusted by repeated sedimentation cycles. Recrystallization was investigated by annealing of the film in an ambient atmosphere at 650, 800 and 1000 °C for 2 hours. Interesting results have been obtained on physical properties of the film which depended on the state of defects formed under the initial conditions of the film formation and its subsequent transformation accompanied with a change in the morphology and structure under the influence of the substrate on the recrystallization process. However, the description of the experimental work and the discussion need a correction.

 

A general comment on terminology in the text of the article should be noted. When describing the heat treatment of prepared ZnO layers, the authors use the term “annealing”, but it would be more correct to use the term “firing”. For heat treatment of prepared layers, the term “firing” is better suited. In addition, when discussing the structure of films with particles up to several microns, the authors use the term crystallites. However, the term crystallite refers to a block, mosaic structure of a single crystal. It would be more correct to call faceted particles in ZnO layers crystals.

There is no characterization of the initial state of the film after its preparation by heating at 120 °C. The changes occurring in the film during the recrystallization are compared with its state after the first stage of firing at 650 °C. The description of the film state lacks an initial stage of its evolution. In the results section, the change in the histogram of the crystal size distribution with the firing temperature is shown as well as photographs of the film at low magnification. The change in crystal morphology could be traced in images obtained using a scanning electron microscope, SEM images. But the SEM images are not shown. At the same time, the constructed size distributions include submicron crystals. The merit of the work is the analysis of the size of 3000 particles. However, it is not stated how their dimensions were obtained. The work does not show the average crystal size and its dependence on the firing temperature. If we approximate the histogram data using a lognormal function, then the parameters of the obtained size distribution would contain the average crystal size. The average crystal size could also be determined by averaging all the 3000 particle sizes obtained.

When describing Raman microscopy, it would be possible to note how scattering can be observed on the surface and in the cross section of both the ZnO film and the substrate. This method is not obvious for every reader.

Table 2 shows the percentage of sample 650_18. The sum of the percentage is not 100%.

The meaning of reference [18] on line 167 when discussing recrystallization is not entirely clear, since the article [18] describes the morphology of tin layers during the galvanic process.

Lines 168-169 show the presence of small pits in the film layers. They meant pits or through holes to the substrate, visible in Fig. 2 how glowing voids? It is not described how tightly the film is attached to the substrate, can crystals fall out?  

On line 182, the authors write film deposited at 650 ° C - I mean ... annealed ...?

In the phrase "As shown in Figure 3D, the interatomic distances (d) for individual planes are quite similar" on lines 192-193, the authors probably wanted to say about a similar change in interatomic planes.

The data for the lattice parameters in Tables 3 and 4 are duplicated in Fig. 3 and 4a, b.

In the lines 217-218, there is a significant decrease in the ratio of c/a parameters with an increase in the firing temperature, i.e. deformation of the unit cell is observed. The reason for the effect is not commented. This can be a consequence of the "burnout" of the carbon impurity with the formation of oxygen vacancies, as well as thermally activated processes of the formation of structural defects and the diffusion of aluminum ions from the substrate.

Interesting results were obtained in the study of Raman scattering of light. When describing the results of Raman scattering shown in Fig. 5, and speaking about the Raman spectra of film cross sections, the authors note (line 248-250): It is worth noticing that these peaks overlap the positions of substrate related peaks, so it is impossible to obtain valuable information from their behavior. However, there was no comment on the fact that the Raman spectra of the growth surface and the substrate cross sections practically do not change with an increase in the firing temperature. For the Raman spectra of the substrate cross section, this seems obvious, but for the growth surface it is not very clear. In this case, the most noticeable changes are observed in the Raman spectra of the cross section of the ZnO layer, which reflects changes in the state of ZnO crystals during recrystallization. If the authors plot on fig. 5 positions of the Raman peaks maxima, the corresponding discussion would be easier to understand. In the presented figure 5 it is necessary to use the narrow lines of the substrate as reference marks to estimate the positions of the peaks for the ZnO layer. In this case, the position of the peaks in the region 645-662 in Fig. 5b for cross-section of ZnO and Al₂O₃ may not correspond to the text of the description. Interestingly, after firing at 650°C, a broad peak at about 578 cm^-1 is observed for the layer of ZnO crystals (Fig.5a), which is probably related to the oxygen vacancies mentioned above. The correspondence between the oxygen vacancy and the Raman peak at 576 cm-1 is shown in [Y. Song, S. Zhang, C. Zhang, Y. Yang, K. Lv. Raman Spectra and Microstructure of Zinc Oxide irradiated with Swift Heavy Ion. Crystals 2019, 9 (8), 395. https://doi.org/10.3390/cryst9080395]. And also [P. Camarda, F. Messina, L. Vaccaro, S. Agnello, G. Buscarino, R. Schneider, R. Popescu, D. Gerthsen, R. Lorenzi, F. M. Gelardi, M. Cannas. Luminescence mechanisms of defective ZnO nanoparticles. Phys. Chem. Chem. Phys., 2016, 18, 16237-16244. https://doi.org/10.1039/C6CP01513A]

Firing at 800°C leads to a decrease in intensity and to broadening of the main peak at 437 cm^-1, and the maximum of the Raman scattering peak of the oxygen vacancy shifts. After firing at 1000°C, the peak of the oxygen vacancy disappears, and the intensity and width of the peak at 437 cm^-1 is restored. In addition, a narrow peak appears evidently at 662 cm^-1. Annealing at 800°С and 1000°С leads to the appearance of a weak peak at about 645 cm – 1 in the Raman spectrum of the {0001} plane of the substrate. This peak was not observed after firing at 650°C. The appearance of a peak after treatment at high temperatures can be associated with the formation of the ZnAl₂O₄ phase.

 

In the section on luminescence, the phrase is incomprehensible «One can assume that it may be correlated with the suppressed thickness of a sample.» (line 289)

 

In fig. 8c it is necessary to correct the error in the range of values on the upper axis: Energy (eV).

 

When discussing the results, it is necessary to consider the change in the crystal size and their reorientation established in the work. The change in the size of the crystals and their reorientation indicate a thermally activated solid-phase mobility of the structure, due to which diffusion processes of mass transfer between crystals occur during firing of the film. The mobility of the structure leads to the reorientation of crystals with of the formation of the preferred direction (002) under the influence of the crystal field of the substrate. At firing temperatures of about 650°C, the processes of formation and interaction of defects are already taking place, which are influenced by impurities and the composition of the environment. The appearance of the ZnAl₂O₄ phase after firing is due to the diffusion of zinc ions into the substrate [D. L. Branson. Kinetics and Mechanism of the Reaction Between Zinc Oxide and Aluminum Oxide. J. Amer. Ceram. Soc. 2006. 48 (11): 591-595. DOI: 10.1111 / j.1151-2916.1965.tb14679.x]. The change in the state of ZnO crystals is affected by the diffusion of aluminum ions from the substrate.

 

The Phrase

Therefore, it is likely that the process of synthesis and deposition and the annealing could 360 lead to the appearance of imperfections in the lattice that can significantly affect the 361

samples' properties. The best feature to estimate the layers' quality may be the c/a ratio 362 calculated by the XRD measurements (Figure 4C). 363

is too cautious, because the results obtained allow us to definitely state that annealing significantly changes the state of defects in the ZnO structure.

 

The phrase on line 365 "... the sintering atoms may be less compressed in the c-axis direction than in the other ranges ..." is incorrect, crystals are sintered. In this case, their structure is deformed.

 

Notes to the conclusions.

 

... the appearance of carbon may be one reason for the formation of peaks induced by an additional strain in a lattice. + Samples exhibited the DARS peaks on their surface, which may implicate the appearance of additional stresses resulting from imperfections of the crystal lattice.

The carbon impurity is the reason for the increased formation of defects, namely oxygen vacancies, accompanied by structural disordering and lattice imperfection.

 

Polycrystalline films exhibited the reorientation of grains under the conditions of annealing changes. This issue was easily visible in confocal microscopy images.

The reorientation of grains is proved by the results of Raman scattering. An increase in the average grain size during film annealing indicates a redistribution of mass between crystals because of thermal activation of the solid-phase mobility.

Structural mobility leads to reorientation of crystals with the formation of the preferred direction (002) under the influence of the crystal field of the substrate.

 

Although the XRD pattern for a sample 1000_50 shows the intermediate phase formation between sapphire and ZnO, the c/a parameter value changes could be induced.

The change of c/a value couldn’t be associated with the formation of a different phase in the substrate.

 

Comments for author File: Comments.pdf

Author Response

The article is devoted to the recrystallization of a ZnO film grown on a sapphire substrate by sedimentation of particles from a suspension in an organic medium. The suspension was prepared in a solution of zinc acetate dihydrate in the presence of diethanolamine. The film thickness was adjusted by repeated sedimentation cycles. Recrystallization was investigated by annealing of the film in an ambient atmosphere at 650, 800 and 1000 °C for 2 hours. Interesting results have been obtained on physical properties of the film which depended on the state of defects formed under the initial conditions of the film formation and its subsequent transformation accompanied with a change in the morphology and structure under the influence of the substrate on the recrystallization process. However, the description of the experimental work and the discussion need a correction.

 At a begining, we would like to thank you for your very detailed review. Due to the detailed comments, we will try to improve most of the problematic issues or explain our perspective.

A general comment on terminology in the text of the article should be noted. When describing the heat treatment of prepared ZnO layers, the authors use the term "annealing", but it would be more correct to use the term "firing". For heat treatment of prepared layers, the term "firing" is better suited. In addition, when discussing the structure of films with particles up to several microns, the authors use the term crystallites. However, the term crystallite refers to a block, mosaic structure of a single crystal. It would be more correct to call faceted particles in ZnO layers crystals.

Thank you very much for this remark. We fully agree; thus, the correction is added to a manuscript.

There is no characterization of the initial state of the film after its preparation by heating at 120 °C. The changes occurring in the film during the recrystallization are compared with its state after the first stage of firing at 650 °C. The description of the film state lacks an initial stage of its evolution.

After the first stage of annealing, the film consists of a gel correlated with the zinc-diethanolamine complexes, which was investigated with the Raman spectroscopy (the spectra is shown below). The changes occurring during the recrystallization weren't the main scope of an article. Although, we have described the changes occurring during annealing in different articles, which is also during the review process. Thus, we can add the appropriate citation in the text or add this information as a supplementary document – there we would like to refer to your suggestion.

In the results section, the change in the histogram of the crystal size distribution with the firing temperature is shown as well as photographs of the film at low magnification. The change in crystal morphology could be traced in images obtained using a scanning electron microscope, SEM images. But the SEM images are not shown. At the same time, the constructed size distributions include submicron crystals. The merit of the work is the analysis of the size of 3000 particles. However, it is not stated how their dimensions were obtained. The work does not show the average crystal size and its dependence on the firing temperature. If we approximate the histogram data using a lognormal function, then the parameters of the obtained size distribution would contain the average crystal size. The average crystal size could also be determined by averaging all the 3000 particle sizes obtained.

The crystallites' size was estimated with a FiJi ImageJ software from confocal micrographs, which were prepared in 4096x4096 px resolution. Due to obtained scale, we have estimated the equivalent of one micrometer in pixels; after measuring the length of 3000 grains (in the case of 800_50 sample (picture below_) in pixels, we have calculated their equivalent in micrometers. If you suggest adding high-resolution micrographs as supplementary material, we can do so.

Due to the huge amplitude in the highest and the lowest measurements, we have believed that the average value may introduce some misleading conclusions. Although, we may agree that these values can be pretty helpful in the case of comparison. Thus, we have included them in an article.

 

 

 

When describing Raman microscopy, it would be possible to note how scattering can be observed on the surface and in the cross section of both the ZnO film and the substrate. This method is not obvious for every reader.

Thank you for this suggestion. The annotation is added to the instrumental analysis description.

Table 2 shows the percentage of sample 650_18. The sum of the percentage is not 100%.

Thank you for pointing this out. The values were obtained as an averaged values, and it made the percentage was problematic. Thus, the values were normalized to 100% (where the sum of all compounds was 100%).

The meaning of reference [18] on line 167 when discussing recrystallization is not entirely clear, since the article [18] describes the morphology of tin layers during the galvanic process.

Thank you for this remark. We have corrected the reference for much appropriate.

Lines 168-169 show the presence of small pits in the film layers. They meant pits or through holes to the substrate, visible in Fig. 2 how glowing voids? It is not described how tightly the film is attached to the substrate, can crystals fall out?  

The pits are visible in Figure 2 as more immense glowing voids (smaller voids are correlated with focusing on particular crystallites at specific heights). We have added the annotations about the brittleness of films (in micro-structures); layers are very susceptible to scratching (although we haven't conducted further experiments on the mechanical properties of structures).

On line 182, the authors write film deposited at 650 ° C - I mean ... annealed ...?

Yes, the correction is added to a manuscript.

In the phrase "As shown in Figure 3D, the interatomic distances (d) for individual planes are quite similar" on lines 192-193, the authors probably wanted to say about a similar change in interatomic planes.

Thank you, that is right. The correction is added to a manuscript.

The data for the lattice parameters in Tables 3 and 4 are duplicated in Fig. 3 and 4a, b.

We have duplicated the data because we feel that this presentation may be more straightforward for analyzing and observing changes with the annealing temperature.

In the lines 217-218, there is a significant decrease in the ratio of c/a parameters with an increase in the firing temperature, i.e. deformation of the unit cell is observed. The reason for the effect is not commented. This can be a consequence of the "burnout" of the carbon impurity with the formation of oxygen vacancies, as well as thermally activated processes of the formation of structural defects and the diffusion of aluminum ions from the substrate.

Thank you for your comment. The description and possible reason for the increase of c/a parameter were already discussed in a Discussion paragraph (this form enabled the correlation c/a ratio with other measurements).

Interesting results were obtained in the study of Raman scattering of light. When describing the results of Raman scattering shown in Fig. 5, and speaking about the Raman spectra of film cross sections, the authors note (line 248-250): It is worth noticing that these peaks overlap the positions of substrate related peaks, so it is impossible to obtain valuable information from their behavior. However, there was no comment on the fact that the Raman spectra of the growth surface and the substrate cross sections practically do not change with an increase in the firing temperature. For the Raman spectra of the substrate cross section, this seems obvious, but for the growth surface it is not very clear. In this case, the most noticeable changes are observed in the Raman spectra of the cross section of the ZnO layer, which reflects changes in the state of ZnO crystals during recrystallization. If the authors plot on fig. 5 positions of the Raman peaks maxima, the corresponding discussion would be easier to understand. In the presented figure 5 it is necessary to use the narrow lines of the substrate as reference marks to estimate the positions of the peaks for the ZnO layer. In this case, the position of the peaks in the region 645-662 in Fig. 5b for cross-section of ZnO and Al₂O₃ may not correspond to the text of the description. Interestingly, after firing at 650°C, a broad peak at about 578 cm^-1 is observed for the layer of ZnO crystals (Fig.5a), which is probably related to the oxygen vacancies mentioned above. The correspondence between the oxygen vacancy and the Raman peak at 576 cm-1 is shown in [Y. Song, S. Zhang, C. Zhang, Y. Yang, K. Lv. Raman Spectra and Microstructure of Zinc Oxide irradiated with Swift Heavy Ion. Crystals 2019, 9 (8), 395. https://doi.org/10.3390/cryst9080395]. And also [P. Camarda, F. Messina, L. Vaccaro, S. Agnello, G. Buscarino, R. Schneider, R. Popescu, D. Gerthsen, R. Lorenzi, F. M. Gelardi, M. Cannas. Luminescence mechanisms of defective ZnO nanoparticles. Phys. Chem. Chem. Phys., 2016, 18, 16237-16244. https://doi.org/10.1039/C6CP01513A]

Firing at 800°C leads to a decrease in intensity and to broadening of the main peak at 437 cm^-1, and the maximum of the Raman scattering peak of the oxygen vacancy shifts. After firing at 1000°C, the peak of the oxygen vacancy disappears, and the intensity and width of the peak at 437 cm^-1 is restored. In addition, a narrow peak appears evidently at 662 cm^-1. Annealing at 800°С and 1000°С leads to the appearance of a weak peak at about 645 cm – 1 in the Raman spectrum of the {0001} plane of the substrate. This peak was not observed after firing at 650°C. The appearance of a peak after treatment at high temperatures can be associated with the formation of the ZnAl₂O₄ phase.

Thank you for a detailed glance at the Raman measurements. To start – due to your suggestion, we have confirmed the position of ZnO-related peaks conducting the comparative analysis for 20 different spectra of each sample. We found out that the peaks are red-shifted with the increase of annealing temperature, which is an interesting observation regarding XRD measurement. The observation is included in the manuscript.

As suggested, for clarification, we have plotted the position of Al2O3 peaks for a better correlation to text.

Thank you very much for marking the peak at 578 cm^-1 correlated with oxygen vacancies. We have noticed it, and it indeed disappears in sample fired in 1000 ^o C. In analyzing a few spectra for 650_18 and 800_50 samples, the shifting was not observed. The observation was included in a manuscript. Also, after analyzing the sample annealed in 800 ^oC, the decrease of intensity varies for a different position in the sample. Thus, we couldn't add this observation to a manuscript.

Additionally, we have included your observation due to the 646 cm-1 peak.

In the section on luminescence, the phrase is incomprehensible «One can assume that it may be correlated with the suppressed thickness of a sample.» (line 289)

Thank you very much for this suggestion. The fragment is rephrased.

In fig. 8c it is necessary to correct the error in the range of values on the upper axis: Energy (eV).

 Thank you for the suggestion. We have recalculated the values one more time, and the presented values are correct.

When discussing the results, it is necessary to consider the change in the crystal size and their reorientation established in the work. The change in the size of the crystals and their reorientation indicate a thermally activated solid-phase mobility of the structure, due to which diffusion processes of mass transfer between crystals occur during firing of the film. The mobility of the structure leads to the reorientation of crystals with of the formation of the preferred direction (002) under the influence of the crystal field of the substrate. At firing temperatures of about 650°C, the processes of formation and interaction of defects are already taking place, which are influenced by impurities and the composition of the environment. The appearance of the ZnAl₂O₄ phase after firing is due to the diffusion of zinc ions into the substrate [D. L. Branson. Kinetics and Mechanism of the Reaction Between Zinc Oxide and Aluminum Oxide. J. Amer. Ceram. Soc. 2006. 48 (11): 591-595. DOI: 10.1111 / j.1151-2916.1965.tb14679.x]. The change in the state of ZnO crystals is affected by the diffusion of aluminum ions from the substrate.

Thank you very much for pointing out these features, which are valuable for further discussion, and attaching the article about the reaction mechanism between Zl2O3 and ZnO. The information is added to the manuscript.

The Phrase "Therefore, it is likely that the process of synthesis and deposition and the annealing could lead to the appearance of imperfections in the lattice that can significantly affect the samples' properties. The best feature to estimate the layers' quality may be the c/a ratio calculated by the XRD measurements (Figure 4C)." This is too cautious, because the results obtained allow us to definitely state that annealing significantly changes the state of defects in the ZnO structure.

Thank you very much for this comment. The sentence is rephrased.

The phrase on line 365 "... the sintering atoms may be less compressed in the c-axis direction than in the other ranges ..." is incorrect, crystals are sintered. In this case, their structure is deformed.

 Thank you very much for this suggestion. The correction was made.

Notes to the conclusions.

 ... the appearance of carbon may be one reason for the formation of peaks induced by an additional strain in a lattice. + Samples exhibited the DARS peaks on their surface, which may implicate the appearance of additional stresses resulting from imperfections of the crystal lattice.

The carbon impurity is the reason for the increased formation of defects, namely oxygen vacancies, accompanied by structural disordering and lattice imperfection.

Thank you very much for pointing this out. We have added the appropriate comment to the article.

Polycrystalline films exhibited the reorientation of grains under the conditions of annealing changes. This issue was easily visible in confocal microscopy images.

The reorientation of grains is proved by the results of Raman scattering. An increase in the average grain size during film annealing indicates a redistribution of mass between crystals because of thermal activation of the solid-phase mobility.

Structural mobility leads to reorientation of crystals with the formation of the preferred direction (002) under the influence of the crystal field of the substrate.

Thank you for stating that. The comment is added to an article.

 Although the XRD pattern for a sample 1000_50 shows the intermediate phase formation between sapphire and ZnO, the c/a parameter value changes could be induced.

The change of c/a value couldn't be associated with the formation of a different phase in the substrate.

Thank you, the correction is added.

In addition to the above comments, all spelling and grammatical errors have been corrected. We look forward to hearing from you in due time regarding our submission and to respond to any further questions and comments you may have.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have taken into account all the remarks. Some points cannot be improved because of experimental limitation of their device.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Dear authors,

Your work lacks in novelty because sol-gel method was already demonstrated in many works. Moreover, there's no dicussion of your results presented, only is a poor description. Figures and images are not well presented in the overall manuscript.

Reviewer 2 Report

The work looks more like the report on properties of three samples (annealed under not controlled environment), using all available at the premises equipment. The drawn conclusions are based on these three samples and are not supported by statistical measurements. The scientific reliability of this work is low.

Reviewer 3 Report

The manuscript reports a research on processing-structure-properties relationships of ZnO micro-films grown on a sapphire substrate by using sol-gel method and further annealed at different temperatures.