Periodic Relief Fabrication and Reversible Phase Transitions in Amorphous Ge2Sb2Te5 Thin Films upon Multi-Pulse Femtosecond Irradiation
, Aleksandr Kolchin 1,2, Dmitrii Shuleiko 1,2, Denis Presnov 1,3,4, Tatiana Kaminskaya 1, Petr Lazarenko 5, Victoriia Glukhenkaya 5, Tatiana Kunkel 6,7, Sergey Kozyukhin 7 and Pavel Kashkarov 1,8Round 1
Reviewer 1 Report
Review of the manuscript "Periodic relief fabrication and reversible phase transitions in amorphous Ge2Sb2Te5 thin films upon multi-pulse femtosecond irradiation" by Stanislav Zabotnov, Aleksandr Kolchin, Dmitrii Shuleiko, Denis Presnov, Tatiana Kaminskaya, Petr Lazarenko, Victoriia Glukhenkaya, Tatiana Kunkel, Sergey Kozyukhin and Pavel Kashkarov
(ID: Micro-1554623)
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The manuscript deals with the formation of laser-induced periodic surface structures (LIPSS) in a Ge2Sb2Te5 (GST225) on SiO2/Si substrate via femtosecond irradiation. The analysis find out the presence of two periodic structures (or "gratings"), one at the same wavelength of the laser (1250 nm) and another at with much shorter spatial period. The gratings form at different "dosages" of laser radiation, i.e. the formation of the first grating is first observed at fewer laser pulses, then the second appears after additional irradiation.
Based on traditional understanding, the formatino of the first grating has to be ascribed to propagation of surface polasmon polaritons, which can be formed thanks to the metallic-type (negative) dielectric associated to free carriers (Drude polarizability).
By using a modeling the authors ("modelling of LIPSS formation") determine an estimation of the (negative) complex refractive index needed to support the SPP and generate the first grating, while the second has been attributed to laser-induced hydrodynamic instabilities which occur after more prolonged irradiation.
The work appears to be technically sound and deal with a interesting topic. Overall, the exposition is clear overall, altough there are some points which are not (see later). The English form is also acceptable, even if some revisions shall be necessary in specific points.
Therefore, I recommend to accept the manuscript after some minor revisions (as listed below):
1) Abstract, Line 27 "Additionally, formation of the lattices with the higher period..."
After reading tre manuscript it is understandable that here the authors refer to the grating at 1250 nm period. Howeever, as written in the present form is not clear from the beginning and one might doubt if there is some additional grating with longer spatial period that shall be expected/predicted (based on some kind of model).
Therefore, I suggest to rephrase this sentence by stating something such as "the formation of the lattice whise spatial period is equal to that of the laser wavelength (i.e. the longer
Also notice that the period is "longer" (or maybe "larger") but "higher" is not very appropriate here. Moreover, "approved" is also a strange choice: I would say (line 28) that the presence of the grating "can be modelled by considering free carrier contribution...".
2) Line 43: "... might be increased sufficiently". What do the author mean here by "sufficiently"? I'd suggest to explain the point.
3) Line 43 "It is usually explained..". What the author mean by "it" ? The sentence is quite obscure.
4) Line 207: "So, it might be assumed, that...". The second comma shall be removed while insted the first is ok ("So, it might be assumed that...").
5) Line 264: "The first type gratings with wavelength period..". Once again, this is not very clear. I would recommend to reword the sentence as follows "The first kind of gratings, i.e. those whose spatial period is equal to the laser wavelength..."
6) Line 266. ".. the second type have subwavelength period...". Here I would also say something as "the second type have a spatial period horter than the laser wavelength..."
Author Response
We thank the reviewer for high evaluation of the relevance of our manuscript.
We have improved the manuscript text in accordance with the comments and marked up the corrections using the “Track Changes” function in MS Word.
Point 1: Abstract, Line 27 "Additionally, formation of the lattices with the higher period..."
After reading the manuscript it is understandable that here the authors refer to the grating at 1250 nm period. However, as written in the present form is not clear from the beginning and one might doubt if there is some additional grating with longer spatial period that shall be expected/predicted (based on some kind of model).
Therefore, I suggest to rephrase this sentence by stating something such as "the formation of the lattice whise spatial period is equal to that of the laser wavelength (i.e. the longer
Also notice that the period is "longer" (or maybe "larger") but "higher" is not very appropriate here. Moreover, "approved" is also a strange choice: I would say (line 28) that the presence of the grating "can be modelled by considering free carrier contribution...".
Response 1: Thank you for the careful reading. We absolutely agree with you. To avoid misunderstanding we corrected Abstract by the following way:
Lines 27 – 28. “Additionally, formation of the lattices whose spatial period is close to the impacted laser wavelength can be modelled by considering free carrier contribution at intensive photoexcitation.”
Point 2: Line 43: "... might be increased sufficiently". What do the author mean here by "sufficiently"? I'd suggest to explain the point.
Response 2: We absolutely agree with you comment. We improved and extended the statement: “In a case of femtosecond laser treatment, the rate and energy efficiency of triggered crystallization [5–7] and amorphization [8–10] might be increased up to several times compared with impact by nanosecond or longer laser pulses.”
Point 3: Line 43 "It is usually explained..". What the author mean by "it" ? The sentence is quite obscure.
Response 3: Really, this is a bad wording! We corrected it: “Such increase is usually explained by the non-thermal nature of melting and quenching processes exactly at femtosecond laser treatment [11,12].”
Point 4: Line 207: "So, it might be assumed, that...". The second comma shall be removed while instead the first is ok ("So, it might be assumed that...").
Response 4: Thank you very much for the careful reading. We deleted second comma.
Point 5: Line 264: "The first type gratings with wavelength period..". Once again, this is not very clear. I would recommend to reword the sentence as follows "The first kind of gratings, i.e. those whose spatial period is equal to the laser wavelength..."
Response 5: We absolutely agree with you again. The sentence was reworded: “The first type gratings whose spatial period is close to the laser wavelength can be induced by SPP’s excitation.”
Point 6: Line 266. ".. the second type have subwavelength period...". Here I would also say something as "the second type have a spatial period horter than the laser wavelength..."
Response 6: We agree with you and accept your comment. The sentence was reworded: “The structures of the second type have a spatial period noticeably shorter than the laser wavelength…”
Reviewer 2 Report
The publication is complete. In the introduction, the authors explain precisely what the described novelty is. The description of the experiment includes all the key steps and parameters. This is visible, from setting the parameters of recording the laser information to the physical interpretation and photographic visualization of the recorded information. For these reasons, readers should be pleased. Such a set of the precisely given information, even inviting you to repeat the experiment, rarely happens. The text can be accepted as is. Congratulations to the authors.
Author Response
The publication is complete. In the introduction, the authors explain precisely what the described novelty is. The description of the experiment includes all the key steps and parameters. This is visible, from setting the parameters of recording the laser information to the physical interpretation and photographic visualization of the recorded information. For these reasons, readers should be pleased. Such a set of the precisely given information, even inviting you to repeat the experiment, rarely happens. The text can be accepted as is. Congratulations to the authors.
Response: We thank the reviewer for high evaluation of the quality and readiness of our manuscript.
