Measurement of Sub-Surface Microstructures Based on a Developed Ultrasonic Atomic Force Microscopy
Round 1
Reviewer 1 Report
Dear Author,
The manuscript entitled "Measurement of Sub-surface Microstructures Based on a Developed" is relevant to Applied Sciences. The authors work on current topics related to the resonant frequency method. The article is based on an original and up-to-date experiment. In general, the work is well prepared.
The method approached is a complex and topical one.
The finite element method by simulation is being used more and more lately, and the authors have done this with a lot of professionalism. The results are some estimated by the authors which is a plus to this paper. The AFM images are clear and concise, and the graphics show the success of the tests.
The article only required small tweaks:
Introduction: Please provide some information on the alloys or materials used for the tests.
I think a few more references can be added in the field of carbon fiber reinforced polymer.
It is generally a well-prepared paper and can be published with corrections in the mirror.
Author Response
Thank the reviewer very much for the careful review of our paper. The precious comments and suggestions, which have greatly helped us to improve the paper, are highly appreciated. The paper has been revised in response to all the comments and suggestions from the reviewers. It should be noted that some minor modifications have also been made to the manuscript to correct typos and add some references. The responses to the comments are attached as an additional file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This study proposed a new contact resonance method to enlarge the detectable buried depth by ultrasonic atomic force microscopy (AFM). The authors combined simulations and experiments to illustrate the effect of subsurface burial depth on the detection capability. The manuscript is clear, relevant for the field, and presented in a well-structured manner. The manuscript is scientifically sound and the experimental design is appropriate to test the hypothesis. I have the following questions and comments for the authors:
- This study demonstrated a large buried depth of the subsurface microstructures measured by ultrasonic AFM (~34.5 um) which is significantly higher than the limit (less than 0.5 um) reported by the previous studies. However, even though the authors showed results from both simulations and experiments, there is no solid and detailed interpretation of how the method developed in this study could achieve such a big improvement. The authors claimed that the major difference between this study and previous research is the use of resonance frequency as the feedback signal. Could the authors elaborate more on how the feedback is used (by providing more data on the frequency measurement and spectrum analysis) and why it can improve the measurement capability?
- The authors mentioned that a sweep signal is applied to the probe to determine the contact resonance frequency between the probe and the sample. Did the authors only measure this frequency at a fixed single point or scan an area on the sample? I believe it is not practical to obtain contact resonance frequency maps by sweeping the spectra pixel-by-pixel.
- What is the acquisition rate of your method? Is your acquisition rate better than previous studies? How big is your scanning area? How many data points did the authors collect to produce a scanning image as shown in figure 6c?
- For all your measurement results, did you show the average result with any filter function or did you just show a single trail? How many repeats have you done for a single measurement?
Author Response
Thank the reviewer very much for the careful review of our paper. Your questions and suggestions are very helpful for our experiments at this stage and for the subsequent research and we are very grateful for your review. The paper has been revised in response to all the comments and suggestions from the reviewers.
Author Response File: Author Response.docx
