A Computational Study of Solid Si Target Dynamics under ns Pulsed Laser Irradiation from Elastic to Melting Regime

Round 1

Reviewer 1 Report

Please see attached PDF for comments and suggestions for authors.

Comments for author File: Comments.pdf

Author Response

Reply to Reviewer #1

Comment 1. Overall, the review paper is good; good jobs from authors! I recommend the paper for publication. However, the authors will have to address several concerns and issues before it can be successfully published.

Authors’ response: We thank the Referee for his/her kind words. All the recommendations were considered on the revised manuscript. 

Reviewer #1. Recommendation 1: No doubt that the abstract is well written, but it is too qualitative. Authors should reflect some of the results in the abstract aiming at addressing/highlighting how the research gaps are addressed and the important contributions, with relation to practical applications.

Authors’ response: The abstract was changed according to the recommendation.

Reviewer #1. Recommendations 2 and 11: The originality/novelty of the analysis is not really highlighted in Section 1 Introduction. The written paragraph focused more on what is not done, and thus will be conducted. The paragraph should elaborate more the importance, and addresses/highlights the research gaps and contributions, with relation to practical applications (give examples).

This investigation is on dynamic behaviour of solid Si targets irradiated by nanosecond laser pulses through computational study by transient, thermοmechanical three-dimensional finite element method simulations. This is definitely of interest for a wide range of applications such as medicine [a], chemistry [b], biology [c] and microfluidics [d,e]. Statement of the importance of current work can be discussed along with the suggested references to further enhance the introduction section, as well as strengthen the significant and novelty of the paper:

2018. Zhong, et al., 2018. Assessing the dynamic characteristics of a femtosecond laser micro plasma expansion process with an optical fiber sensing probe. In Frontier Research and Innovation in Optoelectronics Technology and Industry (pp. 235-239). CRC Press. b. Kautek, et al., 2005. Physico-chemical aspects of femtosecond-pulse-laser-induced surface nanostructures. Applied physics A, 81, 65-70. c. Doukas, et al., 1996. Physical characteristics and biological effects of laser-induced stress waves. Ultrasound in medicine & biology, 22(2), 151-164. d. Lin, et al., 2021. Femtosecond laser precision engineering: from micron, submicron, to nanoscale. Ultrafast Science. e. Lim, et al., 2023. Effect of Microchannel Diameter on Electroosmotic Flow Hysteresis. Energies, 16(5), 2154.

Authors’ response: The last two paragraphs of Introduction were changed according to the recommendation. All the suggested references were added.

 
Reviewer #1. Recommendation 3:  In 2. Numerical modeling and simulation, the acoustomechanical dynamic response of the Si solid target is studied by a FEM model simulated in LS-DYNA. Can the authors justify the use of LS-DYNA in comparison with other conventional software platforms? What are the advantages applicable to the current research?

Authors’ response:  LS-DYNA, a Finite Element Analysis software, excels in addressing high-speed transient events through its explicit dynamic analysis capabilities. It is adept at precisely representing material responses to large deformations, nonlinearities, and contact interactions. LS-DYNA provides a wide range of material models and element types tailored for dynamic simulations. A key distinguishing factor from other software platforms lies in the incorporation of elastoplastic temperature dependent material properties, coupled with the utilization of a suitable equation of state, like Gruneisen. This combination enables the accurate representation of a physical system's behaviour concerning its thermodynamic properties, including pressure, volume, and temperature. Thus LS-DYNA proves effective in accurately simulating the behaviour of Si targets during the laser Si interaction where intense heating induces significant stresses and deformations.

Reviewer #1.  Recommendations 4 and 5:  In 2. Numerical modeling and simulation, what is the convergence criterions being applied for the numerical investigation?

What is the total number of mesh employed? The authors should provide details on the mesh convergence test for the current investigation?

Authors’ response: Mesh convergence criteria were applied for the numerical investigation to ensure that the results of an analysis are not affected by changing the size of the mesh. The quantities of temperature, and vertical displacement converged to a repeatable solution with decreasing element size. The initial size of each element was 5 μm × 0.6 μm × 5 μm (for X × Y × Z axes) and gradually the mesh size was reduced to the size 0.5 μm × 0.3 μm × 0.5 μm. After evaluating the outcomes, it was determined that a uniform discretization of 1μm×0.3μm ×1μm for each element was employed. This decision was based on the observation that further reduction in mesh size yielded minimal alterations (~1%) in displacement values, with no discernible change in temperature.

 Moreover, the workpiece, with dimensions of 450 μm × 9 μm × 450 μm along the X, Y, and Z axes, utilized a uniform discretization of 1 μm × 0.3 μm × 1 μm for each element to simulate the response of the silicon target. The model consisted of ~ 6,000,000 elements.

Additions were made on the second to last paragraph of Numerical modeling and simulation.

Reviewer #1.  Recommendations 8,6 and 7: In 2. Numerical modeling and simulation, the authors should construct a flowchart to illustrate the procedure for solving the governing equations?

The authors should provide the simulation domain figure including the mesh element type to aid the understanding by readers?

The authors should list out the boundary conditions in Table format for clarity to the readers?

Authors’ response: A flow chart is constructed and added in the manuscript according to the referee’s comment. Also, information for the simulation domain, the boundary conditions and the element type used are provided in the flow chart. As previously stated, a uniform mesh was utilized, and the dimensions of the simulation domain were 450 μm × 9 μm × 450μm along the X, Y, and Z axes. Regarding the mesh element type it was already stated that a hexahedral, eight-node, 3D-solid finite element is employed for conducting the transient analysis. To highlight all this information, we also included it in the new flow chart figure. Additionally, the laser is directed onto the upper surface of the target, with the focal spot centred at the origin (0, 0, 0). Non-reflective boundary conditions are enforced on all other surfaces. We believe that a tabular format is not needed, since it will not contain a substantial amount of information, and since we use a very dense uniform rectangular mesh a discretization image will not provide any additional information.

Additions were made on the second to last paragraph of Numerical modeling and simulation.

Reviewer #1.  Recommendation 9: In 3. Results and discussion, the authors deserve compliments for the large amount of nice data generated; excellent job authors! However, the authors should attempt to highlight as much as possible (which currently missing) what exactly is the originality/novelty of their results, in comparison to some existing literatures. This allows readers to differentiate their paper from others, and highlight their important contributions. This will add significance to the section greatly.

Authors’ response: We would like to thank the referee for his/her kind words and for the great recommendation. The second to last paragraph of the Results and discussion section was modified according to the recommendation. 

Reviewer #1.  Recommendation 10: In 4. Conclusions (it is stated as Section 5, which should be changed to 4), the link between the research outcomes and the importance of the research to actual applications can be established in the conclusion section.

Authors’ response: Changes were made according to the recommendation.

Reviewer 2 Report

This is an interesting and valuable research work and it is recommended for publication with satisfactory revising/updating:

1. A more explicit introduction of what is the research problem and its context;

2. how the previous research (Including your own ones) is explicitly related to the current research;

3. Before result section, there should be a section to state the problem, the idealisation, and the justification for the range of input energy used in this research?

4. Results can be grouped with subheadings? 

5. No section 4?

Author Response

Reply to Reviewer #2

Comment 1. This is an interesting and valuable research work and it is recommended for publication with satisfactory revising/updating.

Authors’ response: We thank the Referee for his/her kind words. All the recommendations were considered on the revised manuscript. 

Reviewer #2. Recommendations 1 and 2:A more explicit introduction of what is the research problem and its context.

How the previous research (Including your own ones) is explicitly related to the current research;

Authors’ response: The last two paragraphs of Introduction were changed according to the recommendations.

Reviewer #2.  Recommendation 3:  Before result section, there should be a section to state the problem, the idealisation, and the justification for the range of input energy used in this research?

Authors’ response: The current study, focus on the problem of the nanosecond pulsed laser Si interac-tion. The knowledge of the matter’s change from elastic to plastic and to melted regime is a consistently intriguing research problem due to its significant potential in various emerging applications. These applications span across diverse fields, including laser-based processing, metallization (deposition of thin metal films onto silicon substrates), wafering, nanofabrication, dewetting, as well as the creation of high-frequency ultrasounds for nondestructive material characterization. Furthermore, this is of interest for a wide range of applications such as medicine, chemistry, biology, and microfluidics.

The selection of the input energy range was guided by temperature considerations, specifically tailored to facilitate the transition of the Si sample through distinct phases—from its solid state to a plastic state, and ultimately to a molten phase. Thus, the needed energy threshold for the plastic state and melting regime was found based on numerous simulations.

More specifically, the lower laser fluence of 0.45 J/cm² was meticulously chosen to meet the demand for attaining a temperature high enough to induce elastic deformations in the silicon sample while simultaneously avoiding excessive heat that might lead to plastic deformations within the focal spot region. Subsequently, the laser fluence of 0.75 J/cm² was found, after numerous runs, to fulfill the requirement of maintaining the maximum temperature achieved comfortably below the melting point. This careful calibration was essential to prevent any undesired melting phenomena. However, the chosen fluence was still sufficiently high to provoke permanent deformation within the focal spot region. Finally, a laser fluence of 1.35 J/cm² was selected, after various runs, to address the demand for achieving a maximum temperature well above the melting point. It was crucial to strike a delicate balance, ensuring that the temperature remained significantly below the boiling point, thus avoiding material ablation and plasma formation.

Modifications were made in the first paragraph of the Results and discussion section according to the Referee’s recommendation.

Reviewer #2.  Recommendations 4,5:  Results can be grouped with subheadings? No section 4?

Authors’ response: Both recommendations were fulfilled.

Round 2

Reviewer 1 Report

The authors have well-addressed the comments and suggestions. The paper is now ready for publication. Congrats! Good job authors!

Author Response

Thank you for your great work in reviewing the manuscript!