Direct Femtosecond Laser Processing for Generating High Spatial Frequency LIPSS (HSFL) on Borosilicate Glasses with Large-Area Coverage
Round 1
Reviewer 1 Report
This manuscript investigated the formation of large-region HSFL on Borosilicate Glasses systematically. The results are reasonable although many similar works have been performed. I recommend a minor revision after addressing the following issues.
1. It can create LIPSS on metals, semiconductors and even dielectrics [8–10], Some references are not updated should be replaced by recently published papers or reviews such as Scripta Materialia 227 (2023) 115276, Opto-Electron Sci 1, 220005 (2022), Materials 2022, 15, 1378.
2. The formation of High Spatial Frequency LIPSS (HSFL) has been debated, with vari-48 ous theories suggesting self-organization [12], nanoplasmonic excitations [15,16], interfer-49 ence and second-harmonic generation [17–19], etc. Another mechanism of liquid vortex and flows and Marangoni bursting [ACS Appl.NanoMater.2020,3,1855] is recently proposed, which deserves to be mentioned here.
3. Laser ablation performed in liquid has opened new opportunities for obtaining, straightforwardly, very stable colloidal nanoparticles suspensions without the use of either reactive chemicals or stabilizers. Reference is missing here. Reference such as Sci. China-Phys. Mech. Astron. 65, 274203 (2022), Chem.Rev.2017,117,3990, Appl. Phys. Rev. 9, 041314 (2022)
4. There are too many SEM images, which lacks the quantification of LIPSS region or periods. In addition, LIPSS depth or width uniformity could be discussed to see give more valuable information.
5. For large region scanning, whether a macroscopic image can be provided. Iridescence is an indicator for LIPSS uniformity. Could it be supplemented and discussed?
6. Wettability strongly depend on the processing parameters so there should be some difference among them. More CA data should be supplemented and discussed in combination with the analysis of the structure morphology.
Author Response
Response to Reviewer 1
Point 1: It can create LIPSS on metals, semiconductors and even dielectrics [8–10], Some references are not updated should be replaced by recently published papers or reviews such as Scripta Materialia 227 (2023) 115276, Opto-Electron Sci 1, 220005 (2022), Materials 2022, 15, 1378.
Response 1: Thank you for the valuable suggestions. We have updated the manuscript refereces with recently published article. Line (40)
Point 2: The formation of High Spatial Frequency LIPSS (HSFL) has been debated, with various theories suggesting self-organization [12], nanoplasmonic excitations [15,16], interference and second-harmonic generation [17–19], etc. Another mechanism of liquid vortex and flows and Marangoni bursting [ACS Appl.NanoMater.2020,3,1855] is recently proposed, which deserves to be mentioned here.
Response 2: Thank you for the suggestion. We have added the suggested mechanism of HSFL formation with reference. (Line 50, 70-72)
Point 3: Laser ablation performed in liquid has opened new opportunities for obtaining, straightforwardly, very stable colloidal nanoparticles suspensions without the use of either reactive chemicals or stabilizers. Reference is missing here. Reference such as Sci. China-Phys. Mech. Astron. 65, 274203 (2022), Chem.Rev.2017,117,3990, Appl. Phys. Rev. 9, 041314 (2022)
Response 3: Sorry. There is no such sentence quoted in the manuscript to add the suggested references.
Point 4: There are too many SEM images, which lacks the quantification of LIPSS region or periods. In addition, LIPSS depth or width uniformity could be discussed to see give more valuable information.
Response 4: Thank you very much for this suggestion. We have added map of ratio of melt zone to crater area as a function of fluence and number of shots for the quantification of LIPSS region and melt zone (Figure 4, line 231-237). Also two-dimensional fast fourier transform(2D FFT) and dispersion of the LIPSS Orientation Angle (DLOA) analysis are done for the qauantification of the LIPSS. (figure 6, line 277-296)
Point 5: For large region scanning, whether a macroscopic image can be provided. Iridescence is an indicator for LIPSS uniformity. Could it be supplemented and discussed?
Response 5: Thank you for the suggestion. We have included a macroscopic image of the iridescence exhibited by the LIPSS.(figure 8a, line 305-306)
Point 6: Wettability strongly depend on the processing parameters so there should be some difference among them. More CA data should be supplemented and discussed in combination with the analysis of the structure morphology.
Response 6: Since the study aimed to obtain surface with unifrom HSFL formation we have only focused on the best set of process parameters for large area processing. So the optical and wetting studies are done only on the large area surface processed with the best process parameters.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript by Rajendran et al. reports on the morphological and optical characterization of Laser Induced Periodic Surface Structures (LIPSS) on borosilicate glasses and, in particular, the possibility to extend the surface processing to large areas.
The manuscript contains a systematic study on the LIPSS morphological dimension using Scanning Electron Microscopy and Atomic Force Microscopy. LIPSS were evaluated as laser fluence and number of pulses changed.
The manuscript also presents the evaluation of optical properties (reflectivity and transmissivity) of the processed borosilicate glasses and a study on the wettability after processing.
General comments
The systematic study of LIPSS morphology for borosilicate glasses as a function of pulse energy and pulse numbers is a strong point of the submission as well as the accompanying evaluation of optical properties and wettability after extending the surface processing to large areas.
The manuscript is written in a clear way, using a good English. The work is interesting and will be appreciated by the scientific community. In fact, the topic of LIPSSs is still of great interest and the work of Rajendran et al. presents an easy replicable method for the fabrication of said structures on a technological interesting class of materials.
The references presented in the work are appropriate and are used wisely to strengthen the scientific validity of the obtained result.
However, the homogeneity evaluation of the produced surface structures is rather hurried and only provides a qualitative aspect; therefore, while the work is very interesting and provides elements of novelty, I suggest publication only after addressing this matter along with other minor issues that were spotted during the peer review process.
Specific comments
1. Figure 1: is it the movement of the laser a raster scan?
2. The authors introduce the parameters S (incubation coefficient) and states that when it is equal to 1 the effect of accumulation is null. But they do not analyse their result (S = 0.68 ± 0.03). I suggest adding a short paragraph on the meaning of this value.
3. Have the authors measured the depth of the produced “craters”? And of the produced “lines”? Was it considered as a factor when producing the large area samples? Especially to optimize the analysed properties?
4. How where the LIPSS periodicities measured? I imagine it was carried out by analyzing fourier transorm images, but it was not mentioned in row 223/224.
5. The authors only provide a qualitative demonstration on the uniformity of LIPSS, basing their conclusions on selected SEM images and citing redeposition and melt formation. Have the authors analysed the different FFT images? Recent works in literature, such as:
a. https://doi.org/10.3390/ma16072883
have demonstrated how it is possible to obtain a quantitative analysis of LIPSS homogeneity based on FFT parameters. I think this is an important part to clarify.
6. In the reflectivity and transmissivity paragraph the background bibliography could be enriched by providing other results obtained by nanotexturing transparent materials along Ref.34, such as:
a. Enhancement of absorption in the visible spectrum in diamond: https://doi.org/10.1021/acs.nanolett.1c01310
b. Bioinspired antireflective nanostructures on optical glass: https://doi.org/10.1016/j.jnoncrysol.2022.122016
7. No information on the physical dimension of the large areas samples is provided by the authors. What is the size of the irradiated area?
Author Response
Response to Reviewer 2
Point 1: Figure 1: is it the movement of the laser a raster scan?
Response 1: No. it is line by line scanning of the target material. The target is positioned on a XY translational stage. Laser alignmennt is fixed.
Point 2: The authors introduce the parameters S (incubation coefficient) and states that when it is equal to 1 the effect of accumulation is null. But they do not analyse their result (S = 0.68 ± 0.03). I suggest adding a short paragraph on the meaning of this value.
Response 2: Thank you for the suggestion. We have inserted a short description of the incubation parameter into the article. (line 191-195)
Point 3: Have the authors measured the depth of the produced “craters”? And of the produced “lines”? Was it considered as a factor when producing the large area samples? Especially to optimize the analysed properties?
Response 3: The depth profile analysis is carried out only for the LIPSS on the large area sample.
We haven’t measured the depth of crater or the line. The analysis were limited to optimise the uniformity of the LIPSS structures. In order to achieve that the topography of the LIPSS is analysed for different process parameters and the best one with unifrom structures and less nanoparticle redeposition is choosen for large area processing.
Point 4: How where the LIPSS periodicities measured? I imagine it was carried out by analyzing fourier transorm images, but it was not mentioned in row 223/224.
Response 4: Thank you for this valuable suggestion. We have added the details with 2D-FFT image of the crater.(figure 5c, line 242-248)
Point 5: The authors only provide a qualitative demonstration on the uniformity of LIPSS, basing their conclusions on selected SEM images and citing redeposition and melt formation. Have the authors analysed the different FFT images? Recent works in literature, such as:
- https://doi.org/10.3390/ma16072883
have demonstrated how it is possible to obtain a quantitative analysis of LIPSS homogeneity based on FFT parameters. I think this is an important part to clarify.
Response 5: Thank you very much for the suggestion. We have done the quantitative analysis of the LIPSS using the suggested methods. (figure 7, line 277-296)
Point 6: In the reflectivity and transmissivity paragraph the background bibliography could be enriched by providing other results obtained by nanotexturing transparent materials along Ref.34, such as:
- Enhancement of absorption in the visible spectrum in diamond: https://doi.org/10.1021/acs.nanolett.1c01310
- Bioinspired antireflective nanostructures on optical glass: https://doi.org/10.1016/j.jnoncrysol.2022.122016
Response 6: Thank you very much for the suggestion. We have enriched the bibilography with the suggested references. (line 327)
Point 7: No information on the physical dimension of the large areas samples is provided by the authors. What is the size of the irradiated area?
Response 7: Thank you for the suggestion. We have included a macroscopic image of the iridescence exhibited by the LIPSS. The size of the irradiated area is 5 x5 mm2. (figure 8a)
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors replied satisfactorily to all the points raised during the review process, therefore I suggest pubblication in present form.
