Microstructural Transformations in Solid-State Annealed Al/Ag/Al Diffusion Couples Examined via High-Voltage Electron Microscopy (HVEM)

Round 1

Reviewer 1 Report

This study works on the Al-rich intermediate phases within Ag/Al diffusion couples and characterizes the phase evolution in this system by HVEM, but the work is worse written. Before consideration,the work should be checked carefully.

1)    In lines 151-152, the description“upper/lower region” is not consistent with Fig. 1.

2)    In Figure 1a, different phase regions should be indicated.

3)    In Fig. 1, the mentioned annealing time is different for figure a and b, why different samples are selected?

4)    “Dashed line indicates …”should be “Solid line indicates …”.

5)    Lines 196-198 are not relevantto the main text.

6)    In Figure 2, the phase in 2b is identified as Ag, but I thought it may be Al.

7)    The most confusing part is the TEM images discussed in the text, such as Lines 250-255, which mentioned Fig. 2 as TEM results, but actually, it is not, and similar problems are found for Figures 4, 5, 7, etc.

Author Response

Reviewer 1

This study works on the Al-rich intermediate phases within Ag/Al diffusion couples and characterizes the phase evolution in this system by HVEM, but the work is worse written. Before consideration,the work should be checked carefully.

: Thank you for your feedback, which we highly value. We appreciate your thorough review, and your input has significantly contributed to improving the quality and clarity of our manuscript. We have meticulously reviewed your comments and suggestions and incorporated the necessary revisions into our manuscript. To facilitate your review of the changes, we have highlighted the revised sections in red for your convenience.

 
1)    In lines 151-152, the description“upper/lower region” is not consistent with Fig. 1.
: Thank you for your valuable feedback. Based on your comment, we have made revisions to our manuscript.

2)    In Figure 1a, different phase regions should be indicated.
: We express our gratitude for your comments. In response to your feedback, we have revised our manuscript.

3)    In Fig. 1, the mentioned annealing time is different for figure a and b, why different samples are selected?
: We express our gratitude for your comments. There are no specific reasons for this.

4)    “Dashed line indicates …”should be “Solid line indicates …”.
: Thank you for your valuable feedback. Based on your comment, we have made revisions to our manuscript.

5)    Lines 196-198 are not relevant to the main text.
: Thank you for your valuable feedback. We have incorporated your suggestions into our revision.

6)    In Figure 2, the phase in 2b is identified as Ag, but I thought it may be Al.
: We genuinely appreciate your invaluable feedback. We acknowledge the critical mistake on our part regarding the phase identification as Al, as mentioned in the main text. After considering your comment, we have revised the figure in our manuscript to address this issue.

7)    The most confusing part is the TEM images discussed in the text, such as Lines 250-255, which mentioned Fig. 2 as TEM results, but actually, it is not, and similar problems are found for Figures 4, 5, 7, etc.

: Thank you very much for your comments. We sincerely apologize for the errors in indexing figure numbers. We made extensive revisions to the manuscript structure prior to submission, and we conducted a thorough review. Your feedback has been instrumental in improving the overall quality of our work.

Reviewer 2 Report

Manuscript reports on detailed study of interface formed between Al and Ag plates after diffusion by a set of microscopic techniques. In general, I found the manuscript to be a well-designed and prepared research worthy a publication in the Metals. There are several minor comments:

1. lines 144-146 ‘X-ray diffraction (XRD) analysis was conducted using a Rigaku Smartlab instrument to determine the crystal structure of the equilibrated Ag-Al alloy [6]. ’and Figure 2b. Authors report the application of XRD technique to study phase composition of sample with Ref 6. It is not clear if the presented results are original or previously reported in work [6]. In case of primer, please give the detailed description of XRD experimental setup (wavelength, geometry, monochromators etc).

2.Figure 2(a) shows the cross-section of samples as viewed by optical microscopy. Obviously, the thickness of intermetallic layer varies along the sample. Thus, the measured values of thickness, l, requires the e.s.d. values to be presented in Figure 1(c) as error bars.

3.Figure 3(a) shows electron microscopy image of sample in virtually the same scale as in Figure 1, but the thickness of interface layer are different. Moreover, Figure 3(a) shows no various layers within the sample. Please clarify. Scale bar in Figure 3(a) is poorly visible, please improve.

 

 

 

 

Author Response

Manuscript reports on detailed study of interface formed between Al and Ag plates after diffusion by a set of microscopic techniques. In general, I found the manuscript to be a well-designed and prepared research worthy a publication in the Metals. There are several minor comments:

Thank you for your valuable feedback, which we greatly appreciate. Your thorough review has been instrumental in enhancing the quality and clarity of our manuscript. We have carefully examined your comments and suggestions, and have diligently incorporated the required revisions into our work. To assist you in identifying the changes, we have highlighted the revised sections in blue for your convenience.

 

 

1. lines 144-146 ‘X-ray diffraction (XRD) analysis was conducted using a Rigaku Smartlab instrument to determine the crystal structure of the equilibrated Ag-Al alloy [6]. ’and Figure 2b. Authors report the application of XRD technique to study phase composition of sample with Ref 6. It is not clear if the presented results are original or previously reported in work [6]. In case of primer, please give the detailed description of XRD experimental setup (wavelength, geometry, monochromators etc).

: Thank you for your insightful comment on our manuscript. We apologize for any confusion in our previous description. In response to your inquiry, the X-ray diffraction (XRD) analysis presented in our work (Figure 2b) is indeed original and not previously reported in reference [6]. We understand the importance of providing a detailed description of the XRD experimental setup, and we appreciate your interest in this aspect. We also moved the citation number location to make sure everything is clear. 

 

2.Figure 2(a) shows the cross-section of samples as viewed by optical microscopy. Obviously, the thickness of intermetallic layer varies along the sample. Thus, the measured values of thickness, l, requires the e.s.d. values to be presented in Figure 1(c) as error bars.

: Thank you very much for highlighting this crucial aspect. In our experiment, we determined the average thickness by calculating the intermetallic compound's area within the cross-section of each diffusion zone sample and then dividing it by the horizontal length as shown in below schematic diagram. This approach allows us to obtain more reliable average thickness data than repeatedly measuring length at various positions. However, it's important to note that this method doesn't provide error bars since it doesn't involve the repetitive collection of data points. We have revised our manuscript by adding the necessary explanation for the thickness measurement.

 

Figure 6. Schematic image of the intermetallic layer at the interface of the diffusion couple in Ref. [25] O, M.; Tanaka, Y.; Kobayashi, E. Microstructure Evolution at the Interface between Cu and Eutectic Sn-Bi Alloy with the Addition of Ag or Ni. Journal of Materials Research and Technology 2023, doi:10.1016/J.JMRT.2023.09.159.

 

3. Figure 3(a) shows electron microscopy image of sample in virtually the same scale as in Figure 1, but the thickness of interface layer are different. Moreover, Figure 3(a) shows no various layers within the sample. Please clarify. Scale bar in Figure 3(a) is poorly visible, please improve.

: Thank you very much for your comments. You are correct in noting that Figure 3(a) presents an electron microscopy image captured by TEM, which does differ in scale compared to Figure 1. The interface layer shown in Figure 3(a) represents a localized region, while Figure 1 provides a broader view of the entire diffusion couple.

The variations in the thickness of the interface layer between the two figures can be attributed to the different scales and the fact that Figure 1 offers a more comprehensive perspective. In Figure 3(a), we aimed to focus specifically on the microstructure of the interface layer without including the multiple layers seen in Figure 1.

We appreciate your feedback on the visibility of the scale bar in Figure 3(a) and have made the necessary improvements to enhance its clarity.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Author,

 

After a careful and thorough review, below are my considerations.

Based on the data presented and the discussion conducted, the present manuscript needs improvement before it can be accepted for publication.

 

TITLE

As described in the ABSTRACT, where it is stated that an Al/Ag/Al sandwich was prepared, I suggest including this information in the title, which only says Ag/Al, and updating it to Al/Ag/Al.

 

ABSRACT

Some information about the results of the study is presented here, such as the description of two stable intermediate phases, referred to as μ and δ phases. What is missing, however, is an explanation to the reader of the importance of studying these intermediate phases and of the advances that this study makes possible for materials science and engineering, including in the context of electronic device fabrication. Simple questions need to be answered: What advances does this study provide? Why are the results of this study important to the electronic device industry? Highlight the novelty of the study.

1. INTRODUCTION

A contextualization of the study carried out is presented, with information on the importance of using specific dissimilar materials that undergo heat treatments with the aim of obtaining, through the diffusion of atoms from dissimilar materials, superior physical properties, improving the performance. of electronic devices.

The authors present some studies from the literature, such as the study by Fouracre [10], who carried out a study with Ag/Al thin film diffusion couples annealed at 473 K, identifying the presence of the Ag₂Al phase between the Ag and Al thin films.

Following this reasoning, the authors comment: "Turning our attention to the binary Ag-Al system, the phase diagram indicates the presence of two stable intermediate phases, μ and δ, at temperatures below 723 K [8,9]". In the reference [8], McAlister comments that the μ phase still needs more studies to be understood, and for the δ phase, the same author presents information on the temperature at which the phase is stable, in addition to the atomic % composition Al at different temperatures. For both phases, the phase diagram is shown with the location of the two phases. In the study by Bem and Olubambi [9], more information about the μ and δ phases is presented. In addition to the phase diagram, the authors also present a description of the formation of the phases, which enriches the study carried out and allows progress in the understanding of these phases.

Based on these observations, I ask the authors to add to the study the phase diagram of the Ag/Al system, with the identification of the respective phases, in addition to the information on the chemical composition, since only the names of the phases are presented.

The aims of the study are not well defined in the last paragraph of the introduction. In addition to investigating the growth behavior of intermediate phases within the binary Ag-Al system, it is necessary to state the reason for conducting this study, i.e., the novelty of this study that will advance the aims of the study. Why are intermediate phases important?

 

3. RESULTS

The scale of Figure 2(a) should be improved. It is impossible to observe.

Add scale to Figure 3 (a) and improve the resolution of Figure 3 (a) and (b).

Show the indexing of the diffraction pattern in Figure 3 (b).

In Figure 4 (a) and (b), insert the corresponding indexes of the diffraction patterns. Figure 5 does not include the figure caption describing it. In addition, include the indexing of the diffraction pattern in Figure (a).

In Figure 6, adjust the scale size as the scale is too large for very small precipitates. In figure (c), insert the indexing of the diffraction pattern.

As shown in the study, two phases (μ and δ) were identified. What is the chemical composition of these two phases?

 

4. DISCUSSION

Here it was necessary to establish a relationship with the aims of the study and also with the progress that the results of the study can provide for the field of electronic component design, as presented in the introduction section. In this sense, dealing with the results and the progress they represent is a very important point that must be taken into consideration when discussing the study.

 

5. CONCLUSIONS

The authors comment on the dynamic evolution of microstructures and the growth of intermediate phases within Ag/Al diffusion pairs. However, the two phases found are not well described, their respective compositions, and how these intermediate phases can be beneficial for use in electronic devices. Based on the title, the information presented in the introduction section, and the aims (which should be better written), present in the conclusion the advance that the findings can represent.

Minor editing of English language required.

Author Response

Dear Author,

 

After a careful and thorough review, below are my considerations.

Based on the data presented and the discussion conducted, the present manuscript needs improvement before it can be accepted for publication.

: Thank you for your valuable feedback. We have carefully reviewed your comments and made the necessary revisions to our manuscript. To facilitate your review of the changes, we have highlighted the revised sections in orange for your convenience.

TITLE

As described in the ABSTRACT, where it is stated that an Al/Ag/Al sandwich was prepared, I suggest including this information in the title, which only says Ag/Al, and updating it to Al/Ag/Al.

: Thank you for your comments regarding the title. We have revised it based on your advice.

 

ABSRACT

Some information about the results of the study is presented here, such as the description of two stable intermediate phases, referred to as μ and δ phases. What is missing, however, is an explanation to the reader of the importance of studying these intermediate phases and of the advances that this study makes possible for materials science and engineering, including in the context of electronic device fabrication. Simple questions need to be answered: What advances does this study provide? Why are the results of this study important to the electronic device industry? Highlight the novelty of the study.

: Thank you for your valuable feedback on the abstract. We have thoroughly reviewed and revised it based on your comments and suggestions.

 

1. INTRODUCTION

A contextualization of the study carried out is presented, with information on the importance of using specific dissimilar materials that undergo heat treatments with the aim of obtaining, through the diffusion of atoms from dissimilar materials, superior physical properties, improving the performance. of electronic devices.

The authors present some studies from the literature, such as the study by Fouracre [10], who carried out a study with Ag/Al thin film diffusion couples annealed at 473 K, identifying the presence of the Ag₂Al phase between the Ag and Al thin films.

Following this reasoning, the authors comment: "Turning our attention to the binary Ag-Al system, the phase diagram indicates the presence of two stable intermediate phases, μ and δ, at temperatures below 723 K [8,9]". In the reference [8], McAlister comments that the μ phase still needs more studies to be understood, and for the δ phase, the same author presents information on the temperature at which the phase is stable, in addition to the atomic % composition Al at different temperatures. For both phases, the phase diagram is shown with the location of the two phases. In the study by Bem and Olubambi [9], more information about the μ and δ phases is presented. In addition to the phase diagram, the authors also present a description of the formation of the phases, which enriches the study carried out and allows progress in the understanding of these phases.

Based on these observations, I ask the authors to add to the study the phase diagram of the Ag/Al system, with the identification of the respective phases, in addition to the information on the chemical composition, since only the names of the phases are presented.

The aims of the study are not well defined in the last paragraph of the introduction. In addition to investigating the growth behavior of intermediate phases within the binary Ag-Al system, it is necessary to state the reason for conducting this study, i.e., the novelty of this study that will advance the aims of the study. Why are intermediate phases important?

: Thank you for your detailed comments and suggestions.

1. Phase Diagram and Chemical Composition: We understand the importance of providing a phase diagram of the Ag/Al system and detailing the chemical composition of the intermediate phases. In our revised manuscript, we included a phase diagram showing the locations of the μ and δ phases and information on the chemical composition of these phases. This addition will enhance the understanding of our study.
2. Clear Aims and Importance of Intermediate Phases: We have also revised the last paragraph of the introduction to explicitly state the aims of our study and emphasize the importance of investigating intermediate phases. We highlighted how understanding these phases can lead to advancements in materials science and engineering, particularly in electronic device fabrication. This will provide clarity on the significance of our research.

 

3. RESULTS

The scale of Figure 2(a) should be improved. It is impossible to observe.

: Thank you for your comment. We have revised it based on your comment.

 

Add scale to Figure 3 (a) and improve the resolution of Figure 3 (a) and (b).

: Thank you for your feedback. The scales of Figure 3(a) and (b) are the same. Thus, one was omitted in the original manuscript. We have revised it in the revised version of the manuscript.

 

Show the indexing of the diffraction pattern in Figure 3 (b).

: Thank you for your comment. We have revised our manuscript based on your suggestion.

 

In Figure 4 (a) and (b), insert the corresponding indexes of the diffraction patterns. Figure 5 does not include the figure caption describing it. In addition, include the indexing of the diffraction pattern in Figure (a).

: Thank you for your comment. We have revised our manuscript based on your suggestion.

 

In Figure 6, adjust the scale size as the scale is too large for very small precipitates. In figure (c), insert the indexing of the diffraction pattern.

: Thank you for your comment. We have revised our manuscript based on your suggestion.

 

As shown in the study, two phases (μ and δ) were identified. What is the chemical composition of these two phases?

: Thank you for your question. You can refer to the EPMA data to determine the chemical compositions of the two phases. The μ phase has a chemical composition of Ag - 20-21 at.% Al, while the δ phase contains 23-31 at.% Al.

 

4. DISCUSSION

Here it was necessary to establish a relationship with the aims of the study and also with the progress that the results of the study can provide for the field of electronic component design, as presented in the introduction section. In this sense, dealing with the results and the progress they represent is a very important point that must be taken into consideration when discussing the study.

: We appreciate your valuable comments. Our manuscript has undergone careful revisions based on your insightful feedback. 

5. CONCLUSIONS

The authors comment on the dynamic evolution of microstructures and the growth of intermediate phases within Ag/Al diffusion pairs. However, the two phases found are not well described, their respective compositions, and how these intermediate phases can be beneficial for use in electronic devices. Based on the title, the information presented in the introduction section, and the aims (which should be better written), present in the conclusion the advance that the findings can represent.

: We appreciate your valuable comments. We have made careful revisions based on your feedback. 

Round 2

Reviewer 1 Report

The authors have made considerable revisions to their original version, here are some minor issues:

1)     The zone axis in the paper should be indicated in “[]” instead of “()”

2)     What is the composition of the hcp lamellar phase in Figure 4? I guess it is Ag2Al.

3)     In the caption of Fig. 5, “a hcp (011) zone” should be “a fcc [011] zone”, and check the expression carefully.

4)     The small spots in Fig. 6c originate from double diffraction.

 

5)     Phai zone should be mentioned in the section on HVEM characterization.

Author Response

The authors have made considerable revisions to their original version, here are some minor issues:

1)     The zone axis in the paper should be indicated in “[]” instead of “()”

Thank you for your comment. We have revised our manuscript based on your comment.

2)     What is the composition of the hcp lamellar phase in Figure 4? I guess it is Ag2Al.

Yes, the hcp lamellar phase is Ag2Al with the 65 at.%Ag.

3)     In the caption of Fig. 5, “a hcp (011) zone” should be “a fcc [011] zone”, and check the expression carefully.

Thank you for your comment. We have revised the expression.

4)     The small spots in Fig. 6c originate from double diffraction.

Thank you for your comment. We believe that the satellite spot originates from the incoherency of the precipitates within the fcc matrix.

5)     Phai zone should be mentioned in the section on HVEM characterization.

Thank you for your comment. The term "Phai zone" corresponds to the section labeled as "3.2.3. Intermediate Phases in the Al Side within 40 µm from the Initial Ag/Al Interface."

Reviewer 3 Report

Dear Author,

After carefully reviewing the first revision of the manuscript, there are still some corrections to be made.

My comments are as follows:

1)    Title is adequate;

 2)    Abstract contains 311 words. However, the limit is 250 words. Also, the practical applications that the study makes possible are not yet well described in the abstract. I noticed that in Figure 7 (containing the binary Al-Ag phase diagram calculated by ThermoCalc), which is on page 485 to 491, this sentence can be used in the abstract to inform the reader about the advance that this study can provide. I ask the authors to rewrite the abstract, up to 250 words, taking into account what has been discussed in the lines mentioned.

 3)    Keywords: Please, correct “Ag2A” to “Ag2Al”

 4)    Discussion: In Figure 7, make the lines thicker to make it easier to identify the phases shown in the legend.

5) Conclusions: Important information about the benefits that this study can provide is also presented here. These benefits can also be included in the abstract to add more information about the study conducted.

Author Response

Dear Author,

After carefully reviewing the first revision of the manuscript, there are still some corrections to be made.

My comments are as follows:

Thank you for your comments. We have revised our manuscript in response to your comments.

1)    Title is adequate;

Thank you for your feedback.

 2)    Abstract contains 311 words. However, the limit is 250 words. Also, the practical applications that the study makes possible are not yet well described in the abstract. I noticed that in Figure 7 (containing the binary Al-Ag phase diagram calculated by ThermoCalc), which is on page 485 to 491, this sentence can be used in the abstract to inform the reader about the advance that this study can provide. I ask the authors to rewrite the abstract, up to 250 words, taking into account what has been discussed in the lines mentioned.

Thank you for your feedback. We have made revisions to our manuscript accordingly.

 3)    Keywords: Please, correct “Ag2A” to “Ag2Al”

Thank you for your comment. We have made the necessary revisions.

 4)    Discussion: In Figure 7, make the lines thicker to make it easier to identify the phases shown in the legend.

Thank you for your comment. We have made the necessary revisions.

5) Conclusions: Important information about the benefits that this study can provide is also presented here. These benefits can also be included in the abstract to add more information about the study conducted.

Thank you for your comment. We have revised our manuscript.

Round 3

Reviewer 3 Report

Dear Author,

I have checked the corrections that have been made on the basis of the last revision I made. All the points I mentioned have been taken into consideration and the manuscript now meets the requirements to be considered for publication.

Yours sincerely,
Reviewer