Investigation of the Influence of Sublayer Thickness on Pairing of Metallic MEMS Shutter Blades
Round 1
Reviewer 1 Report
- Highlight better which is the novelty of the work?
- What is the status of the literature according to your work? Make a comparison between the results obtained by you and another previous research.
- Add disadvantages/limitation for this investigation.
- Add more conclusions. Complete the conclusions with the limitations of the proposed methodology.
- Generally, the quality of the writing could be improved.
Author Response
We thank the Reviewer for the detailed, useful and pertinent criticism of our manuscript. We have modified the manuscript concerning all the points raised. Changes in the manuscript are shown via the tracking method of Office.
Point 1: Highlight better which is the novelty of the work?
Response 1: This point has been stated and clarified in the introduction section.
Point 2: What is the status of the literature according to your work? Make a comparison between the results obtained by you and another previous research.
Response 2 This point is considered in the introduction section.
Point 3: Add disadvantages/limitations for this investigation.
Response 3: the limitations of our methods are existing in the multistep fabrication process, mainly in the drying process where there are turbulences created by the isopropanol vapour on the surface of the sample, please, refer to the video at the supplementary material.
Point 4: Add more conclusions. Complete the conclusions with the limitations of the proposed methodology.
Response 4: Please, refer to the previous point (point 3)
Point 5: Generally, the quality of the writing could be improved.
Response 5: The manuscript has been revised for typos, grammar, and quality of writing.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Reviewer Comments
In this paper, 3D self-assembly of microstructures, the net intrinsic stress within a hybrid metal layer stack is utilised to study the dynamics of the pairing of metallic MEMS shutter blades representing a highly nonlinear Casimir system. The study focuses on two main geometries: i) unpaired (free-standing) and ii) paired metallic MEMS shutter blades. The hybrid metal stack comprises three metal layers, including intrinsic stress, to enable the curling of the freestanding shutter blades. The top aluminum layer thickness is varied systematically, creating tailored stress in the shutter blades resulting in different curling of the freestanding as well as the paired shutter blades. However, the followings should be carefully addressed in the revision to be published in JMSE.
1- The novelty of the work must be clearly addressed and discussed, compare your research with existing research findings and highlight novelty, (compare your work with existing research findings and highlight novelty).
2- The authors should be followed the instruction of the journal in all parts and sections in this manuscript. Also, similarity index must be reduced to not more than 20% with not more than 3% from a source.
3- Complete mathematic calculation model with all nomenclature missing
4- The abstract needs more quantitative results. The abstract section is an important and powerful representation of the research. It is better that the results should be presented with the support of specified data.
5- The main objective of the work must be written on the more clear and more concise way at the end of introduction section,
6- Introduction section must be written on more quality way, i.e. more up-to-date references addressed. Research gap should be delivered on more clear way with directed necessity for the conducted research work,
7- The authors should indicate this technique to enhance system performance. Also, the author should add more references that discuss the effect of using this technique. It is recommended that the authors carry out wide analysis and comparison with the state-of-the-art studies.
8- Most tables and figures are needed improve the quality of all tables and figures.
9- Add references for all equations.
10- I would also expect to validate with two more experimental works available in the literature.
11- The literature review must be improved. Please highlight in the literature review the differences between previous papers and your paper. Please clearly indicate the knowledge gap and prove that it is a really not analyzed area of the field. Please indicate new approach / new methods in a comparison to the existing investigations (literature review should be extended and add below references). Numerical Investigations of Transient Flow Characteristic in Axial Flow Pump and Pressure Fluctuation Analysis Based on the CFD Technique..Numerical investigation of flow field behaviour and pressure fluctuations within an axial flow pump under transient flow pattern based on CFD analysis method.
12- You need to add error analysis of your results and add the error bars in your graphs to indicate your accuracy measurements.
13- Improve work justification. Also, add more analysis about velocity and pressure contours.
14- More quantitative conclusions should be presented. Please prepare additional comparisons, some percentage differences. There is a lack of quantitative conclusions which should contain main findings from the paper and highlight the new and high novelty and contribution of your work to the field.
15- Present the mathematical equation of the boundary conditions and initial condition.
16- Conclusion section is missing some perspective related to the future research work, quantify main research findings.
17- The conclusion section on lacks in summative conclusions. The main results, novelty and academic contributions should be emphasized in this section. Moreover, are the results obtained in this paper really applicable in other similar researches?
18- In the discussion development, it is very important to emphasize points of agreement or disagreement between results in this work and others cited in references part of manuscript.
19- Authors should discuss limitations of the current study and possible improvements for future directions/research works.
20- English language should be carefully checked and carefully check paper for language typos.
21- Any authorship changes will need to have a specific, valid reason for the update that will be evaluated by the Editor according to journal defining authorship guidelines.
Author Response
We thank the Reviewer for the detailed, useful and pertinent criticism of our manuscript. We have modified the manuscript concerning all the points raised. Changes in the manuscript are shown via the tracking method of Office
Point 1: The novelty of the work must be clearly addressed and discussed, compare your research with existing research findings and highlight novelty, (compare your work with existing research findings and highlight novelty).
Response 1: This point is now considered in the introduction section.
Point 2: The authors should be followed the instruction of the journal in all parts and sections in this manuscript. Also, similarity index must be reduced to not more than 20% with not more than 3% from a source.
Response 2: MDPI did not send us a file with listed conflicts with other papers and corresponding percentage of overlap.
Point 3: Complete mathematic calculation model with all nomenclature missing.
Response 3: We are not using a theoretical model calculation model, here. Our simulations on the Casimir force were published in the past in one of our previous papers [16] but they are not directly relevant here and therefore those results have been only cited in the manuscript.
Point 4: The abstract needs more quantitative results. The abstract section is an important and powerful representation of the research. It is better that the results should be presented with the support of specified data.
Response 4: The abstract has been modified, considerably.
Point 5: The main objective of the work must be written on the more clear and more concise way at the end of introduction section.
Response 5: This point is clarified at the end of the introduction section.
Point 6: Introduction section must be written on more quality way, i.e. more up-to-date references addressed. Research gap should be delivered on more clear way with directed necessity for the conducted research work.
Response 6: The introduction section has been modified, to consider the point raised by the reviewer.
Point 7: The authors should indicate this technique to enhance system performance. Also, the author should add more references that discuss the effect of using this technique. It is recommended that the authors carry out wide analysis and comparison with the state-of-the-art studies.
Response 7: This investigation provides more understanding of the process of self- assembly of the paired shutters and identifies a process working window and the possible geometrical changes within the defined window, allowing further studies on the structure as well as on the Casimir forces in upcoming investigations. In the revised version of our manuscript this is now stated in the summary and outlook section as future work. See also our extended answer to point 17. Here is a short summary of our answer to point 17. Future applications in systems could address (i) drug delivery, mass transport and sensorics and (ii) lightweight constructions targeting material resource efficiency and weight reduction in construction.
Point 8: Most tables and figures are needed improve the quality of all tables and figures.
Response 8: The paper includes no tables. The description of Figure 1 is modified for a better understanding along with the text. Figure.2 has also been modified and adapted better to the article’s needs. We believe that the rest of the figures are in good quality.
Point 9: Add references for all equations.
Response 9: No equations were included in the previously submitted version of our manuscript. In the current version, the eccentricity equations were included in section 4.1 together with a new reference.
Point 10: I would also expect to validate with two more experimental works available in the literature.
Response 10: Without specifying which two references it is difficult to identify reviewer’s intention. We added 5 more references and compared the results in sections 1 and 5.
Point 11: The literature review must be improved. Please highlight in the literature review the differences between previous papers and your paper. Please clearly indicate the knowledge gap and prove that it is a really not analyzed area of the field. Please indicate new approach / new methods in a comparison to the existing investigations (literature review should be extended and add below references). Numerical Investigations of Transient Flow Characteristic in Axial Flow Pump and Pressure Fluctuation Analysis Based on the CFD Technique..Numerical investigation of flow field behaviour and pressure fluctuations within an axial flow pump under transient flow pattern based on CFD analysis method.
Response 11: The first part of point 11 has been considered, see also our answer to point 10.
Concerning reviewer’s second point: Our manuscript is not at all studying Transient Flow fields in Axial Flow Pump and Pressure Fluctuation Analysis based on the CFD Technique.
Point 12: You need to add error analysis of your results and add the error bars in your graphs to indicate your accuracy measurements.
Response 12: The provided graphs already include error bars, yet the description of the evaluation methodology has been modified for a better understanding.
Point 13: Improve work justification. Also, add more analysis about velocity and pressure contours.
Response 13: Our manuscript is not studying velocity and pressure contours. It is not related to our manuscript. No action possible here like for the second part of point 11.
Point 14: More quantitative conclusions should be presented. Please prepare additional comparisons, some percentage differences. There is a lack of quantitative conclusions which should contain main findings from the paper and highlight the new and high novelty and contribution of your work to the field.
Response 14: The summary and outlook section has been extended, considerably.
Point 15: Present the mathematical equation of the boundary conditions and initial conditions.
Response 15: We are not using a theoretical model calculation model, here. Our simulations on the Casimir force were published in the past in one of our previous papers [16] but they are not directly relevant here and therefore those results have been only cited in the manuscript. No action possible also here.
Point 16: Conclusion section is missing some perspective related to the future research work, quantify main research findings.
Response 16: The conclusion section has been extended to include the required parts.
Point 17: The conclusion section on lacks in summative conclusions. The main results, novelty and academic contributions should be emphasized in this section. Moreover, are the results obtained in this paper really applicable in another similar research?
Response 17: The conclusion section has been extended. As already mentioned in the manuscript we already started to study the possibilities to detach the metal blades again. Studies with variable FIB trenches show a threshold area necessary to keep them attached by the Casimir force. We also mentioned that roughness studies in the overlapping region of the metal blades are under work, currently and will be published soon in a forthcoming publication. We appreciate reviewer’s comments and also added more about applications and our future outline on that field: a) the particle transport in the magnetic stray field tubes [21] for drug delivery, mass transport and sensorics. The Yin and Yang shape is superior to the circular diameter used in [22] and opens additional attractive research fields using these new structures. b) Lightweight construction for material resource efficiency and weight reduction in construction are another perspective application, in macro and micro field. Applications are e.g., in the field of buildings and mobile systems such as planes, cars and drones.
Point 18: In the discussion development, it is very important to emphasize points of agreement or disagreement between results in this work and others cited in references part of manuscript.
Response 18: the formed tubes of the unpaired shutters have been achieved and researched by so many researchers however the yin-yang geometry is not yet studied.
Point 19: Authors should discuss limitations of the current study and possible improvements for future directions/research works.
Response 19: The limitation of the study is mainly arising from the multistep fabrication process, which is now stated in the fabrication technology section. Especially, the dynamic drying process is highly complex and sensitive. Furthermore, in the recent investigation stiction of part of the shutter blades (shutter A of formed shutter pair) to the substrate was observed deflecting its elliptical geometry hence affecting the Yin-Yang shape unintentionally. Future work will focus on geometrical changes in shutter design to overcome this issue and enable superior applications/functionalities.
Point 20: English language should be carefully checked and carefully check paper for language typos.
Response 20: The manuscript has been carefully revised for typos and grammatical issues.
Point 21: Any authorship changes will need to have a specific, valid reason for the update that will be evaluated by the Editor according to journal defining authorship guidelines.
Response 21 We did not apply for changes in the author list.
Author Response File: Author Response.docx
Reviewer 3 Report
Notes attached.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 3
We thank the Reviewer for the detailed, useful and pertinent criticism of our manuscript. We have modified the manuscript concerning all the points raised. Changes in the manuscript are shown via the tracking method of Office
Point 1: all typos and missing spaces.
Response 1: The manuscript was carefully revised.
Point 2 Modification of the title
Response 2: The title has been modified to ‘Investigation of the influence of sublayer thickness on pairing of metallic MEMS shutter blades’
Point 3: Figure 1 modification
Response 3: The figure caption has been modified along with the text to adapt it better to the needs of the article.
Point 4: also, a trivial drawing - adapt to the needs of this article, e.g. taking into account (Under specific parameters see figure 2)
Response 4: Figure 2 has been modified, considerably. The parameters are now explained in section 3: Fabrication technology.
Point 5: It is advisable to post a photo of the stand (drying set up)
Response 5: A scheme of the set-up as well as drying process steps in time domain is now included in Figure 3. In the supplementary material, a photograph of the stand is included.
Point 6: why only dAl2 was changed and dCr was not changed
- give a competent explanation
-or extend the research by changing dCr and expand the obtained results and graphs
-Clarification needed.
Response 6: Among others the pairing of the two blades is used to study the role of attractive Casimir forces. For the Casimir force, the interacting material is only Al. The change in the stressed metal layer thicknesses has the goal to adjust different ROCs. This can be done via changing dAl2 or dCr or via changing both. In order to obtain clear results, the number of parameters changed a time has be kept minimum. Therefore, only dAl2 has been changed.
Point 7: Change the position of figure 3.
Response 7: The position has been changed; the figure numbering is now changed to Figure 4.
Point 8: State how many samples of the given thicknesses were present
Response 8: The number of samples with further explanation is now stated in the fabrication technology section.
Point 9 : where do these differences in the size of the marked errors come from?
Response 9: The error bars and the shown differences are now explained in the discussion section.
Point 10: where did this disorder come from?
Response10: It is not a disorder, yet as stated, the evaluation is done statistically, and the average value has been used to demonstrate the decreasing trend of RoCs shown in figure 6.
Point 12: why the authors omit in their analyzes the length of the sticking area of shutter A to the substrate.
Response 12: It is not omitted.
It is not of interest to us, as the formed Yin-Yang shape and the overlapping area between the two shutters are the focus of the investigation.
The sticking area of shutter A is increasing for decreasing layer thickness dAl2. It is calculated by multiplying the observed cross-sectional sticking length (varying between 0 up to over 400 µm) with the shutter width of 400 microns. Nevertheless, it is not quantitatively evaluated, as the formed Yin-Yang shape and the overlapping area between the two shutters are the focus of the investigation.
Point 13: This also results from the change in the stiffness of shutter A with the thickness (and consequently its RoC) - which the authors could also take into account in the article and introduce parameters related to the stiffness of the beam.
Response 13: The stiffness of the beam is at least qualitatively captured by the eccentricity (or RoC). To introduce quantitative parameters, simpler geometries (like a deflected cantilever) would have to be investigated. However, this is out of our investigation scope. Yet, eccentricity is a rough measure of stiffness. That means that a shutter blade of very high stiffness remains more circular ( and low stiffness leads to more pronounced elliptical shapes (
Point 14 : However, it is necessary to clarify – since shutter A and B are identical in construction and their RoC are different – then the same analysis as in this article should apply to RoCA and RoCB
Response 14: RoCs of UNPAIRED shutters are identical. During the drying process, the shutters are deflected by surface tension forces – enabling the pairing but these forces are not present anymore after drying. Therefore, RoCs of shutter A and B are not different before pairing (green curve in Figure 4a).
After pairing shutter A and shutter B are forming together a Yin-Yang shape. After pairing the curvatures of the two shutters A and B are different. The curvature contours of shutter A are shown in red and those of shutter B are shown in blue (see Figure 4b).
Point 15: why has this topic not been developed further
Response 15: Turbulences during the highly sensitive drying process affect the pairing considerably. For further improvements in process control, a more complex and cost-intensive setup design is needed.
Thus, drying process control can be seen as one limitation factor. Nevertheless, the scope of this investigation is aiming the trend of Yin-Yang geometries and the identification of process window for shutter pairing.
Point 16: Nowhere have the Authors analyzed Casimir's force itself as a parameter, nor its value, nor its impact - this sentence is not true!!!
Response 16: References regarding previous studies on the Casimir forces have been added in the manuscript.
Point 17: this is another sentence that has no coverage in the content of the article
Response 17: See point 16.
Point 18: To sum up - the article is premature and requires broader research material and in-depth analysis
Response 18: Further research and analysis have been added to the manuscript. Note that the article's aim has been pointed out more clearly in the introduction.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The paper was improved.
Author Response
No Specific points were mentioned.
However, the manuscript has been modified overall.
Reviewer 2 Report
Reviewer Comments
The followings should be carefully addressed in the revision to be published in JMSE.
1- The novelty of the work must be clearly addressed and discussed, compare your research with existing research findings and highlight novelty, (compare your work with existing research findings and highlight novelty).
2- The abstract still needs more quantitative results.
3- The main objective of the work must be written on the more clear and more concise way at the end of introduction section,
4- Most tables and figures still are needed improve the quality of all tables and figures.
5- You still need to add error analysis of your results and add the error bars in your graphs to indicate your accuracy measurements.
6- Conclusion section is missing some perspective related to the future research work, quantify main research findings.
7- Authors should discuss limitations of the current study and possible improvements for future directions/research works.
Author Response
Reviewer 2
Point 1: The novelty of the work must be clearly addressed and discussed, compare your research with existing research findings and highlight novelty, (compare your work with existing research findings and highlight novelty).
Response 1: An additional paragraph along with a new figure is added to the introduction section showing the different geometries and the separation distances for each, respectively, hence highlighting the novelty of the presented geometry within this work and its separation distances between the investigated shutter blades.
Point 2:The abstract still needs more quantitative results.
Response 2: Quantitative results have already been included in the abstract in the first revised version of our manuscript. Unfortunately, the abstract has not been updated by MDPI in the response document to the reviewers. In the second revised version we again followed reviewer’s important point. We included now all quantitative findings and results in the current version of the abstract. Such as the RoC range_(16.7 to 78.8 µm), overlapping length range (8µm to 31 µm), stiction length of shutter A range (0 up to 90 µm) and eccentricity range(0 to 0.76).
Point 3: The main objective of the work must be written on the more clear and more concise way at the end of introduction section,
Response 3: The main objective and goal of the investigation are stated clearly at the end of the introduction to show the extended evaluations. The added evaluations are the stiction length of shutter A to the substrate and the length of the tight attachment in the overlapping area between shutters A and B.
Point 4: Most tables and figures still are needed improve the quality of all tables and figures.
Response 4: The whole manuscript still includes no tables. All the included figures are original and high-quality. Also, the content of the figures has been double-checked again. The fading representation (unsharp edges) of the electromagnetic spectrum is intended in Figure 1 and all the other elements are 100% sharp. Note that the highlighted fading backgrounds of 5 out of the 8 depicted shutter blades are intended in Figure 7 as explained in the text, since they later reveal pairing in Figures 8 and 9, subsequently. This is now explained in more detail in the figure caption of Figure 7. All the other elements are 100% sharp.
Point 5: You still need to add error analysis of your results and add the error bars in your graphs to indicate your accuracy measurements.
Response 5: Every graph (already) contains error bars indicating an accurate processing of our measurements. As stated in the text, all included errors result from statistical evaluation, i.e. the error analysis is based on the standard deviation of a set of measurement values (at least 10). In the case of free-standing shutter blades, the trend in error size is related to the increasing RoC for increasing layer thickness.
Point 6: Conclusion section is missing some perspective related to the future research work, quantify main research findings.
Response 6: The conclusion section is now highlighting the main findings of this investigation which are explained below and includes various points and applications considered for future work
The quantitative evaluation and discussion have been extended considering the overlapping length and the stiction length of shutter A in case of pairing. Both measures are related to the three pairing scenarios explained and illustrated in figure 9. Starting from an average length of approx. 16 µm for overlapping in pairing scenario I, the length increases for scenario II, peaking at 31 µm (the most significant value which was observed in this investigation at dAl2 88 nm) and finally decreases again, reaching an observed minimum of 8 µm for scenario III at dAl270 nm. This is in accordance with the reported RoCs and eccentricities since more pronounced curling reveals larger intrinsic stress avoiding that outstretched flat overlapping areas are formed. The stiction length of shutter A is continuously increasing, starting from no stiction (0 µm) observed for a few paired shutters of scenario I and ending at up to 90 µm, meaning that only 50 µm of shutter A are not sticking to the substrate for scenario III. This can also be seen in figure 9 and is already explained in the text.
Point 7: Authors should discuss the limitations of the current study and possible improvements for future directions/research works.
Response 7: Limitations have been discussed: Multistep fabrication process (especially turbulences during the drying) and stiction to the substrate. The former is planned to be solved by improving the current setup and process parameters considerably, and the latter shall be avoided with new designs realized on the photomask.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors partly took into account the comments in the review - the explanations are quite sparse, the mathematical description is poor.
The authors have not decided to expand the content of the article, so it remains incomplete - it is not an argument that they will publish more articles.
In the text - fig. 7, replace it with fig. 8.
Author Response
Point 1: The authors partly took into account the comments in the review - the explanations are quite sparse, and the mathematical description is poor.
Response 1: We added the mathematical description to the supplement, including the ellipse equation, a diagram of a standard ellipse and a representation of the geometrical changes in ‘eccentricity ‘. In addition, more quantitative results, as well as more explanations (see point 2), have been added.
Point 2:The authors have not decided to expand the content of the article, so it remains incomplete - it is not an argument that they will publish more articles.
Response 2: The quantitative evaluation and discussion have now been extended considering the overlapping length and the stiction length of shutter A in case of pairing. Both measures are related to the three pairing scenarios explained and illustrated in figure 9.
Starting from an average length of approx. 16 µm for overlapping in pairing scenario I, the length increases for scenario II, peaking at 31 µm(the largest value which was observed in this investigation at dAl2 88 nm ) and finally decreases again, reaching an observed minimum of 8 µm for scenario III at dAl270 nm. This is in accordance with the reported RoCs and eccentricities since more pronounced curling reveals larger intrinsic stress avoiding that outstretched flat overlapping areas are formed.
The stiction length of shutter A is continuously increasing, starting from no stiction (0 µm) observed for a few paired shutters of scenario I and ending at up to 90 µm, meaning that only 50 µm of shutter A are not sticking to the substrate for scenario III. This can also be seen in figure 9 and is already explained in the text.
We hope that we now meet the expectations of the reviewer. Thank you for the reviewer’s important hints.
To mention what is planned for the future (what will be published in the future) was a point raised by another reviewer.
Point 3: In the text - fig. 7, replace it with fig. 8.
Response 3: The mentioned point is corrected in the latest manuscript version. All figures' numbering has been double-checked.
Author Response File: Author Response.pdf
