Adhesion of HIPIMS-Deposited Gold to a Polyimide Substrate
Round 1
Reviewer 1 Report
This rather short paper deals with the deposition of gold film on the polyimide substrate. It can be published after addressing following remarks:
Affiliation of the authors is missing.
Introduction - the references should be put in one bracket instead of puttin each in a new one.
Why do authors write elements (e.g. chromium, titanium, argon) and materials such as polyimide with capital letters?
How was thickness measured - in-situ or ex-situ? What equipment was used? What was uncertainty of the measurement? Why did authors choose such thickness? What about the homogeneity of the thickness of gold film?
All figure captions are too long. There is no point of explaining what are the results and what do they mean in the figure captions. Please move it to the discussion part.
Line 83 - mistake with figure number.
SEM from the cross section is blurry - is there a chance to make a high resolution SEM image of the cross section? Authors stated: "We see, that the resulting crystals have an orientation directed towards the surface, while not being columnar." I would be careful with such statement as, to be honest, it is not visible from the cross section.
Line 112 - "The Kapton-tape can be lifted off the surface without problems. The adhesive film could also be lifted off the surface without problems." Combine it into one sentence.
English revision is needed in some parts.
Author Response
Dear Reviewer,
Thank you for your revision.
Regards
Jürgen Guljakow
Author Response File: 
Author Response.docx
Reviewer 2 Report
This work tackles a PVD growth of gold on polyimide, without the need for an intermediary layer to compensate for the potential adhesion issues, which is a daring topic that may pose a high interest to material scientists.
Although the topic is an interesting one, there are some issues that require thought:
1. Minor
1a. In caption Figure 3, (b), there is a writing error regarding the 300 m thick gold film. In caption Figure 4, there is no need for the first ”of”.
1b. The upper image from the SEM is referred to as the above view, but when looking at the image itself, the sample appears to be tilted in the microscope. What is the reason for that?
1c. For the HIPIMS - the main and only technique for deposition used in this work - there are only two references in the manuscript, the latest one being from 2018.
2. Major
2a. The Polyimide was spun onto a Wafer. What kind of wafer? Later it is said that it is a silicon wafer. It should be stated when it is first mentioned, polycrystalline or preferentially oriented (100, 111, etc.). More details on the application of the polyimide on the wafer should be given, with a determination of the thickness after thermal treatment.
2b. What was the background pressure of the vacuum before introducing Argon? What was the sputtering time for the resulting film thickness of 300nm?
2c. The term ”structure” in ”3.3. Surface and structure of the gold-films” is misleading. For anyone to affirm something about the structure of the film or the orientation of crystals, an XRD, preferably done in Grazing Incidence (if not rocking curves to assess texture) should be used.
2d. The greatest issue regarding this work has to do with the lack of references for other methods of depositing gold directly on polyimide, for a 300 nm film. This should highlight the significance of this work’s content and the subsequent appropriate research design of the present manuscript.
The thickness of 300 nm seems arbitrary. It is true that residual stress emanating from the physical deposition process can induce a relaxation of the film via delamination, but this happens near a critical thickness which may be above 300 nm.
Also, there is no proper reference for a neural implant that contains gold in a thickness range of 300 nm; it is very relevant to the present work, as the mentioned application relates to neural implants. The alternative for enhancing the research design consists in growing multiple films of ~ 10, 50, 100, 500 nm and studying their adhesion behavior vs varying thickness. This way, the main conclusion of this manuscript: ”HIPIMS allows to omit the application of adhesive chromium layers and to deposit gold directly onto polyimide” can have a thorough justification, not only in an arbitrary scenario.
Author Response
Dear Reviewer,
Thank you for your report.
Regards
Jürgen Guljakow
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Manuscript can be published in a current form.
Reviewer 2 Report
The authors have answered all concerns and made significant improvements to the manuscript.
