Conformal and Transparent Al2O3 Passivation Coating via Atomic Layer Deposition for High Aspect Ratio Ag Network Electrodes
and Han-Ki Kim 1,*Round 1
Reviewer 1 Report
Reviewer comments on manuscript: “Conformal and transparent Al2O3 passivation coating via atomic layer deposition for high aspect ratio Ag network electrodes”.
In reviewed manuscript Authors describe conformal Al2O3 passivation using ALD technique of a transparent and flexible Ag network electrode. This type of electrodes are recently widely used.
The reviewed manuscript may be published after minor revision.
Reviewer has noticed several issues that need to be cleared or fixed:
line 73: "film" word is repeated;
Figure 3 (line 195): images c) - f) have scales that doesn't allow to distinguish differences between values during the process. Please change it.
Figure 4 (line 225): images c), d) same here
Figure 6 d) - do the coloured images have same scale? Please comment.
Author Response
Reviewer 1
Reviewer comments on manuscript: “Conformal and transparent Al2O3 passivation coating via atomic layer deposition for high aspect ratio Ag network electrodes”.
In reviewed manuscript Authors describe conformal Al2O3 passivation using ALD technique of a transparent and flexible Ag network electrode. This type of electrodes are recently widely used.
The reviewed manuscript may be published after minor revision.
Reviewer has noticed several issues that need to be cleared or fixed:
line 73: "film" word is repeated;
Answer) As reviewer recommended, we correct the line 73.
Figure 3 (line 195): images c) - f) have scales that doesn't allow to distinguish differences between values during the process. Please change it.
Answer) As reviewer suggested, we changed the scale in Figure 3 c-f.
Figure 4 (line 225): images c), d) same here
Answer) As reviewer suggested, we added the bending mode in the Figure 4.
Figure 6 d) - do the colored images have same scale? Please comment.
Answer) The color images were obtained from IR camera to show temperature uniformity. All images are same scale.
Reviewer 2 Report
Manuscript ID: metals-2211564
Title: Conformal and transparent Al2O3 passivation coating via atomic layer deposition for high aspect ratio Ag network electrodes
This manuscript reports the development of a silver (Ag) electrode with improved stability by using a Al2O3 passivation layer. The authors demonstrated an enhancement of the stability and reliability of the Al2O3/Ag network-based transparent thin-film heaters. The ALD-grown Al2O3 film was found to prevent the introduction of moisture and impurities into the Ag network with a high aspect ratio. Better stability of the electrode using an Al2O3 passivation layer and without compromising the optoelectronic properties seems relevant in the context of the development of transparent and flexible electrodes; nevertheless, some issues should be clarified before considering this paper for publication.
1) The authors claim “However, the scarcity of indium elements and use of vacuum-based systems can increase the production cost of flexible ITO films”. How about the cost of fabricating Ag or Al2O3? Both are widely prepared by vapor deposition methods.
2) “ITO films deposited on flexible substrates via magnetron sputtering have been predominantly employed as transparent electrodes in flexible optoelectronic devices, owing to their low resistivity, high transmittance, easy scalability, and mature thin-film process” – I think that this correct description of the ITO films deserved more literature references. I would suggest the following recent ones: https://doi.org/10.1016/j.vacuum.2021.110056; https://doi.org/10.1016/j.optmat.2022.113040; https://doi.org/10.3390/colloids6030046; https://doi.org/10.3390/coatings11020144.
3) The silver electrode was fabricated employing a solution methodology. Any particular reason for that? How about the stability of these metallic films compared to those that are usually prepared by thermal evaporation or sputtering?
4) The authors should clarify the choice of 85 °C/85% relative humidity (RH) (why 85?) test to demonstrate the feasibility of ALD-grown Al2O3 thin-film passivation.
5) Figure 1: Please introduce the scale on the SEM images. In addition, the authors could describe the main differences between the morphology of the Ag network before and after the passivation. The SEM images are similar…
6) “Moreover, ALD-grown Al2O3 layers can be prepared at relatively low temperatures and are suitable for application as polymer substrates”. References should be provided!
7) Figure 2: the surface morphology of both Al2O3-covered and uncovered regions on the Ag network template exhibits the presence of slits. Some comments would be useful.
8) The authors have used a passivation layer of (thin Al2O3 film) with a thickness of 60 nm. Why? Did the authors explore the effect of using lower/higher thicknesses?
9) Figure 4 should be updated. The graphs are very small and imperceptible for the readers.
10) “Figure 5b shows photographs of the bare Ag and Al2O3/Ag network electrodes before and after the environmental degradation test. The bare Ag network electrode exhibited a color change and decreased transparency.” Looking at the images, this affirmation is not so clear. It seems that there is also a change in color for the Al2O3/Ag network electrode after the environmental degradation test. Some comments should be provided.
11) In the conclusions section, the authors could elaborate and explain the fact that the Al2O3 thin film prevents the corrosion of the Ag network and deterioration of the electrode. Does the Al2O3 film play a more relevant role in the thermal stability of the electrode or the stability under relative humidity?
With my best regards.
Author Response
Reviewer 2
his manuscript reports the development of a silver (Ag) electrode with improved stability by using a Al2O3 passivation layer. The authors demonstrated an enhancement of the stability and reliability of the Al2O3/Ag network-based transparent thin-film heaters. The ALD-grown Al2O3 film was found to prevent the introduction of moisture and impurities into the Ag network with a high aspect ratio. Better stability of the electrode using an Al2O3 passivation layer and without compromising the optoelectronic properties seems relevant in the context of the development of transparent and flexible electrodes; nevertheless, some issues should be clarified before considering this paper for publication.
1) The authors claim “However, the scarcity of indium elements and use of vacuum-based systems can increase the production cost of flexible ITO films”. How about the cost of fabricating Ag or Al2O3? Both are widely prepared by vapor deposition methods.
Answer) Considering the cost of vacuum-based sputtering system, the cost of solution coating system for Ag network and atomic layer deposition (ALD) system for very thin Al2O3 passivation is much lower. In addition, the expression is claiming that the price of ITO is increasing due to the cost of indium, which is a material used in ITO. As a result, there is a development of new materials to replace it.
2) “ITO films deposited on flexible substrates via magnetron sputtering have been predominantly employed as transparent electrodes in flexible optoelectronic devices, owing to their low resistivity, high transmittance, easy scalability, and mature thin-film process” – I think that this correct description of the ITO films deserved more literature references. I would suggest the following recent ones: https://doi.org/10.1016/j.vacuum.2021.110056; https://doi.org/10.1016/j.optmat.2022.113040; https://doi.org/10.3390/colloids6030046; https://doi.org/10.3390/coatings11020144.
Answer) As reviewer suggested, we changed above references
3) The silver electrode was fabricated employing a solution methodology. Any particular reason for that? How about the stability of these metallic films compared to those that are usually prepared by thermal evaporation or sputtering?
Answer) To implement the Ag network structure at a low cost, a solution coating method was introduced, and detailed experimental methods are indicated in the reference 22 and 27. The Ag network structure is implemented using the surface energy of the substrate, making wet-coating technology suitable. Furthermore, it is generally challenging to implement the Ag network structure using conventional sputtering or evaporation methods, so it is typically produced using solution coating technology.
4) The authors should clarify the choice of 85 °C/85% relative humidity (RH) (why 85?) test to demonstrate the feasibility of ALD-grown Al2O3 thin-film passivation.
Answer) The 85 °C/85% test is a well-known standard temperature-humidity test known for testing thin film protective coatings in displays, and most research on thin film packaging is conducted through the 85 °C/85%test
5) Figure 1: Please introduce the scale on the SEM images. In addition, the authors could describe the main differences between the morphology of the Ag network before and after the passivation. The SEM images are similar…
Answer) As reviewer suggested, we added scale bar in Figure 1
6) “Moreover, ALD-grown Al2O3 layers can be prepared at relatively low temperatures and are suitable for application as polymer substrates”. References should be provided!
Answer) As reviewer suggested, we added reference.
7) Figure 2: the surface morphology of both Al2O3-covered and uncovered regions on the Ag network template exhibits the presence of slits. Some comments would be useful.
Answer) To distinguish between the area covered with a Al2O3 film and the area without, a tape was applied on top of an Ag network to create a barrier for the Al2O3 film. Afterwards, the film's unevenness created by removing the tape appears as a slit. As reviewer suggested, we added comments in manuscript.
8) The authors have used a passivation layer of (thin Al2O3 film) with a thickness of 60 nm. Why? Did the authors explore the effect of using lower/higher thicknesses?
Answer) Considering the flexibility of the Ag network electrode, it is advantageous to have a thinner passivation inorganic film on Ag network. However, taking into account the passivation properties, it cannot be too thin, so a thickness of 60nm, which is typical for flexible inorganic films, was chosen as an optimal passivation thickness.
9) Figure 4 should be updated. The graphs are very small and imperceptible for the readers.
Answer) As reviewer suggested, we changed the Figure 4 and added indication of bending mode.
10) “Figure 5b shows photographs of the bare Ag and Al2O3/Ag network electrodes before and after the environmental degradation test. The bare Ag network electrode exhibited a color change and decreased transparency.” Looking at the images, this affirmation is not so clear. It seems that there is also a change in color for the Al2O3/Ag network electrode after the environmental degradation test. Some comments should be provided.
Answer) As reviewer recommended, we corrected the explanation of Figure 5b.
11) In the conclusions section, the authors could elaborate and explain the fact that the Al2O3 thin film prevents the corrosion of the Ag network and deterioration of the electrode. Does the Al2O3 film play a more relevant role in the thermal stability of the electrode or the stability under relative humidity?
Answer) As reviewer suggested, we changed the conclusion part. We added comments on the effective role of Al2O3 on thermal stability of the Ag network electrodes.
Reviewer 3 Report
In the present manuscript, Lee et al. have investigated the electrical stability of Ag films by ALD-based Al2O3 passivation. The authors have demonstrated the endurance of the Al2O3 passivation by testing it under typical standardized temperature and humidity conditions. Additionally, the authors have demonstrated that the films demonstrate a stable performance as flexible heating strips under tensile, compressive, and twisted forms. I can recommend the manuscript for publication once the following concerns are addressed convincingly.
Major revision:
1. The authors should include AFM images of the surface after bending cycles and twisting cycles.
2. For all practical purposes, the authors should also perform an 85/85 test in combination with or after the compressive or twisting endurance cycles, since the Al2O3 is prone to developing cracks whereby moisture and temperature are expected to have a stronger influence, which is a more realistic use case scenario. I am confident that it will still be relatively better than non-passivated Ag. However, it would have a lower performance metric in comparison with isolated representations of the 85/85 test prior to flexibility test.
Author Response
Reviewer 3
In the present manuscript, Lee et al. have investigated the electrical stability of Ag films by ALD-based Al2O3 passivation. The authors have demonstrated the endurance of the Al2O3 passivation by testing it under typical standardized temperature and humidity conditions. Additionally, the authors have demonstrated that the films demonstrate a stable performance as flexible heating strips under tensile, compressive, and twisted forms. I can recommend the manuscript for publication once the following concerns are addressed convincingly.
Major revision:
- The authors should include AFM images of the surface after bending cycles and twisting cycles.
Answer) As depicted in Figures 3 and 4, there was no change in resistance observed even under severe bending modes, indicating excellent mechanical stability of the Ag network/Al2O3 electrodes. While we are currently unable to provide surface AFM images due to issues with the ALD facility, we have strong confidence that there were no changes in surface morphology.
- For all practical purposes, the authors should also perform an 85/85 test in combination with or after the compressive or twisting endurance cycles, since the Al2O3 is prone to developing cracks whereby moisture and temperature are expected to have a stronger influence, which is a more realistic use case scenario. I am confident that it will still be relatively better than non-passivated Ag. However, it would have a lower performance metric in comparison with isolated representations of the 85/85 test prior to flexibility test.
Answer) As suggested by the reviewer, conducting an 85 °C/85% test under compressive or twisting endurance cycles is necessary to demonstrate the feasibility of the Ag network/Al2O3 electrode for practical purposes. However, performing this combinational test requires a new bending system design. Unfortunately, we do not currently have access to such an environmental test system, making it challenging to conduct the combinational test of Ag network/Al2O3 electrode. Nevertheless, we recognize the importance of conducting mechanical bending tests combined with the 85 °C/85% test. Therefore, we plan to report the results in this journal as soon as we obtain the necessary system.
Reviewer 4 Report
In this work, the authors have studied the effect of Al2O3 passivation on the properties of a solution processed Ag network. They have investigated the optical transmittance and mechanical flexibility of the Ag network before and after the deposition of Al2O3 layer. They also have evaluated the performance of the bare and passivated Ag networks for TFHs applications. The manuscript is well prepared however, the following comments must be addressed by the authors before the manuscript can be considered for publication:
· In the introduction, add the correct references for the following sentence “Among these TFE materials, ITO films …………. and mature thin-film process [18, 19]”
· Replace “printing processed” with “solution processed” in the following sentence “However, printing processed TFEs obtained via spin coating, bar coating, slot-die coating, and spray coating”.
· Replace “Another candidate for preparing” with “Another alternative candidate for” in the following sentence “Another candidate for preparing ITO films is a self-assembled Ag network”.
· Give more details on the synthesis of Ag nanoparticles and their size.
· After drying the self-assembled film, did the authors use thermal treatment to improve the particles contact and to form the conductive Ag network?
· Add the duration of the temperature-humidity test to the experimental details section.
· Add the scale bar to the images in figure 1c
· The scale of Y-axis of the inset in figure 2 is not clear
· Electrical measurements show an increase in the resistance of the sample after passivation by about 5 orders of magnitudes. What is the reason for such increase in the resistance after passivation? A detailed discussion must be added.
· The authors should consider previous reports on the transparent - flexible heaters (TFHs) and their stability to enhance the introduction and discussion parts of the manuscript.
· “This indicates that the bare Ag network exhibits highly conductive properties through the development of Ohmic Al contacts on the conductive Ag network” in the experimental details, the authors mentioned the use of Ag contacts not Al contacts, kindly correct the text.
· Correct the title of x-axis in figure 3e to “cycle (times)”
· “During the inner and outer bending tests, both electrodes exhibited no change in resistance. Regardless of the bending mode, both samples exhibited no change in resistance”, figure 3f (outer-bending test) shows variation in resistance (2 – 5 %), kindly correct the text.
· Although the authors reported an increase in the resistance of the passivated sample, the temperature profile before the temperature-humidity test of both samples (bare and passivated) is the same at each applied voltage. A proper detailed explanation of this point must be given.
Author Response
Reviewer 4
In this work, the authors have studied the effect of Al2O3 passivation on the properties of a solution processed Ag network. They have investigated the optical transmittance and mechanical flexibility of the Ag network before and after the deposition of Al2O3 layer. They also have evaluated the performance of the bare and passivated Ag networks for TFHs applications. The manuscript is well prepared however, the following comments must be addressed by the authors before the manuscript can be considered for publication:
- In the introduction, add the correct references for the following sentence “Among these TFE materials, ITO films …………. and mature thin-film process [18, 19]”
Answer) As reviewer suggested, we corrected references.
- Replace “printing processed” with “solution processed” in the following sentence “However, printing processed TFEs obtained via spin coating, bar coating, slot-die coating, and spray coating”.
Answer) As reviewer suggested, we corrected the sentence.
- Replace “Another candidate for preparing” with “Another alternative candidate for” in the following sentence “Another candidate for preparing ITO films is a self-assembled Ag network”.
Answer) As reviewer suggested, we corrected the sentence.
- Give more details on the synthesis of Ag nanoparticles and their size.
Answer) Detailed information of the Ag nano particles and size is shown in reference 17, 22, and 23. We added in manuscript.
- After drying the self-assembled film, did the authors use thermal treatment to improve the particles contact and to form the conductive Ag network?
Answer) Detailed information of the Ag nano particles and size is shown in reference 17, 22, and 23. We added in manuscript.
- Add the duration of the temperature-humidity test to the experimental details section.
Answer) As reviewer suggested, we added in experimental section.
- Add the scale bar to the images in figure 1c
Answer) As reviewer suggested, we added scale bar in Figure 1c
- The scale of Y-axis of the inset in figure 2 is not clear
Answer) as reviewer suggested, we corrected the inset of Figure 2.
- Electrical measurements show an increase in the resistance of the sample after passivation by about 5 orders of magnitudes. What is the reason for such increase in the resistance after passivation? A detailed discussion must be added.
Answer) The electrically insulating properties of the ALD-grown Al2O3 passivation resulted in a significant increase in resistance for the Al2O3-coated Ag network electrode.
The authors should consider previous reports on the transparent - flexible heaters (TFHs) and their stability to enhance the introduction and discussion parts of the manuscript.
Answer) As reviewer suggested, we added the reports on the transparent-flexible heaters with Ag network in manuscript.
- “This indicates that the bare Ag network exhibits highly conductive properties through the development of Ohmic Al contacts on the conductive Ag network” in the experimental details, the authors mentioned the use of Ag contacts not Al contacts, kindly correct the text.
Answer) We corrected error in manuscript.
- Correct the title of x-axis in figure 3e to “cycle (times)”
Answer) As reviewer suggested we correct error in Figure 3.
- “During the inner and outer bending tests, both electrodes exhibited no change in resistance. Regardless of the bending mode, both samples exhibited no change in resistance”, figure 3f (outer-bending test) shows variation in resistance (2 – 5 %), kindly correct the text.
Answer) As reviewer suggested, we corrected the manuscript.
- Although the authors reported an increase in the resistance of the passivated sample, the temperature profile before the temperature-humidity test of both samples (bare and passivated) is the same at each applied voltage. A proper detailed explanation of this point must be given.
Answer) The temperature profile in thin film heaters are mainly affected by Ag network electrode regardless of Al2O3 passivation layer, the profiles seem to be similar.
Reviewer 5 Report
The authors report the deposition of Al2O3 passivation layer on Ag network electrode via atomic layer deposition method. This Al2O3 passivation layer improves the stability and reliability of the Ag network electrode without significant degradation of the optical transmittance or mechanical flexibility of the electrode. This manuscript is overall good and presents a relevant topic with interesting results. I think this work is acceptable to our journal “Metals” if the following issues were discussed or addressed.
Comments:
In the “Results and Discussion” section, Line 132-160 describes the ALD process, I don’t think it is appropriate to put it in this section, it’s better to put it in the “Materials and Methods” section or put it as Supplemental Material.
Line 98: “60 nm thick Al2O3 films were grown on the Ag network electrode using …”, what is the dimension of the Ag network? Line 161-163: “The thickness of the Al2O3 passivation layer was 60 nm, which is very thin relative to the width of the Ag network electrode”, what is the width of the Ag network electrode?
Author Response
Reviewer 5
In the “Results and Discussion” section, Line 132-160 describes the ALD process, I don’t think it is appropriate to put it in this section, it’s better to put it in the “Materials and Methods” section or put it as Supplemental Material.
Answer) For understanding of reader regarding low temperature ALD process on Ag network was explained in results and discussion.
Line 98: “60 nm thick Al2O3 films were grown on the Ag network electrode using …”, what is the dimension of the Ag network? Line 161-163: “The thickness of the Al2O3 passivation layer was 60 nm, which is very thin relative to the width of the Ag network electrode”, what is the width of the Ag network electrode?
Answer) The dimension of Ag network substrate is 5 cm ´ 5 cm. And the width of Ag network is about 5~10 mm.
Round 2
Reviewer 2 Report
The authors tried to answer all the questions/comments comprehensively and made the requested changes. Consequently, the article was improved. In my opinion, I believe the manuscript is now suitable for publication.
Regards.
Author Response
Thanks for your kind review.
Reviewer 3 Report
The authors have stated the challenges they face addressing the concerns , but have indirectly assured of the validity based on the device performance. I can recommend the manuscript for publication, since this initial work seems promising for further investigations in this field.
Author Response
Thanks for your kind review.
Reviewer 4 Report
The authors have addressed most of the comments given previously. However, the following points should be considered/clarified:
- Replace “Another candidate for preparing ITO” with “Another alternative candidate for ITO is a self-assembled .....” in the following sentence “Another candidate for preparing ITO films is a self-assembled Ag network”.
- Authors should consider some of the previous reports on (TFHs) and their stability in both the introduction and discussion parts (compare their results with those reported in literature) to enhance the manuscript.
- Authors should add their response to the last comment "The temperature profile in thin film heaters are mainly affected by Ag network electrode regardless of Al2O3 passivation layer, the profiles seem to be similar." to the discussion of figure 6 (b-c).
Author Response
- Replace “Another candidate for preparing ITO” with “Another alternative candidate for ITO is a self-assembled .....” in the following sentence “Another candidate for preparing ITO films is a self-assembled Ag network”.
Answer) As reviewer suggested, we corrected above sentence.
- Authors should consider some of the previous reports on (TFHs) and their stability in both the introduction and discussion parts (compare their results with those reported in literature) to enhance the manuscript.
Answer) As reviewer suggested, we added the comparison in introduction parts
- Authors should add their response to the last comment "The temperature profile in thin film heaters are mainly affected by Ag network electrode regardless of Al2O3 passivation layer, the profiles seem to be similar." to the discussion of figure 6 (b-c).
Answer) As reviewer suggested, we added above sentence.
