The Influence of Ion Beam Bombardment on the Properties of High Laser-Induced Damage Threshold HfO2 Thin Films
Round 1
Reviewer 1 Report
In principle the topic is of high relevance. The experimental approach is ok. Some important issues are within the paper, however. In the following a list of comments are given (some are more important as others):
- LIDT with CW Lasers is commonly determined by defects. This effect was not investigated.
- line 51: The explanation, monitoring by photoelectricity is not possible. You mean: Monitoring using a photoelectrical sensor (or something like that)
- line 55: Where was the ion flux measured? At position of substrate?
- Ellipsometry: Was the backside of the glass included in the analysis?
- The refractice indices dispersion is given later. This must be strongly improved. The dispersion shown in the later diagram is not common with HfO2 layers, especially the drop at the short wavelengths. I suspect this is due to the limited dispersion model used.
- The reafrctive index data should be compared with other literature data
- line 119: It is surprising that the films are polycrystalline since they are deposited by evaporation. Is there any comparison with literature.
- What is the grain size of the polycristalline film?
- line 123: What is PVDF ? (check please also the other abbreviations)
- line 143: Discussion of n is questionable. It can also be due to densification and not only stoichiometry? Another measurement might be needed to check this.
- Figure 6: Are there any results from literature which can be used for comparison?
- The results should be more compared with results from literature, for example, there should be many more papers in the literature investigating ion effects on HfOx films.
Author Response
（1）LIDT with CW Lasers is commonly determined by defects. This effect was not investigated.
Yes, for optical oxide films such as HfO2 thin films and TiO2 thin films, nodular defects are one of the main causes of laser damage. Because this article focuses on the analysis of the influence of ion beam post-treatment on HfO2 film with different ions and energies, and the ion beam bombardment is mainly to correct the microstructure, density and oxygen mismatch of the film,So we did not mention the effect of film defects.
（2）line 51: The explanation, monitoring by photoelectricity is not possible. You mean: Monitoring using a photoelectrical sensor (or something like that)
We are very sorry that the wrong expression in original manuscript misled you.. For optical thin films deposited by electron beam evaporation, we usually use the photoelectric extremum method to monitor the film thickness. The photoelectric extremum method uses the extreme value of the light signal in the evaporation process to control the wavelength or its integer multiple change. The principle is that the intensity of the transmitted light changes with the thickness of the film, and the photomultiplier is used to monitor the change of the center wavelength. When the product of the thickness of the film and its refractive index is an integer multiple of 1/4 wavelength, the transmittance appears extreme. In our experiment，The light signal of the center wavelength were detected by photomultiplier in our equipment
（3）Where was the ion flux measured? At position of substrate?
Yes, the ion flux measured is measured at the position of the substrate using a Faraday cup designed by ourselves.
（4）Ellipsometry: Was the backside of the glass included in the analysis?
No，In order to avoid the effect of the backside of the glass on measure accuracy. The back fo
K7 glass was painted in black ink pen during Ellipsometry measure
（5）The refractice indices dispersion is given later. This must be strongly improved. The dispersion shown in the later diagram is not common with HfO2 layers, especially the drop at the short wavelengths. I suspect this is due to the limited dispersion model used.
Yes, since there is no BK7 glass substrate data in the ellipsometer database, we established the substrate data after measuring the BK7 glass. BK7 glass has already absorbed less than 370nm in the short-wave range, so anomalous dispersion appears.
（6）The reafrctive index data should be compared with other literature data
Most of the refractive index measurement is done on fused silica or silicon substrate, and the processing conditions are also different, so we have not compared with the refractive index curve in other documents, the refractive index of HfO2 thin films in the visible light range is not much different(1.81~1.95).
（7）line 119: It is surprising that the films are polycrystalline since they are deposited by evaporation. Is there any comparison with literature.
The film is prepared at a temperature of 200°C. After the deposition, it must be held in a high vacuum at 200°C for 30 minutes, which may be the main reason for the crystallization of the film. Figure 4 shows the XRD spectrum peaks of HfO2 thin films we measured. The（）、（121）、（311）can be observed from the XRD spectrum. Therefore, we believe that the prepared HfO2 is polycrystalline.Related literature on the preparation of HfO2 thin films by thermal evaporation[1][2]
（8）What is the grain size of the polycristalline film?
According to Scherrer's formula, the size of the crystal grain can be estimated, , where D is the crystal grain size, k is the Scherrer constant, 0.89, B is the half-width of the diffraction peak, and q is the diffraction angle, which can be calculated the size of each crystal grain. From Fig.4,The size of grains are about 4.98nm~12.41nm.
（9）line 123: What is PVDF ? (check please also the other abbreviations)
Sorry, this is our mistake, so we didn’t check carefully, this should be HfO2 film.
（10）line 143: Discussion of n is questionable. It can also be due to densification and not only stoichiometry? Another measurement might be needed to check this.
Yes, the refractive index of the film is not only affected by the density of the film, but also by its chemical ratio. For HfO2 thin films, the problem of oxygen loss during thermal evaporation is also an important factor affecting the refractive index of the film. In this paper, one of the purposes of bombarding the film with oxygen plasma is to modify its chemical composition. In this article, we have added a set of results of the XPS composition of the film after bombarding with oxygen plasma at an energy of 1000eV. This result is different from the result of plasma bombardment. Compared with the thin film, the hafnium-oxygen ratio increased from 1:1.78 to about 1:86.
We apology for the error analysis in the original manuscript. We forgot remove Hf-OH peaks from O1s Peak, which could be caused by adsorbed water molecules into films. Through re- analysis, we found that the stoichiometric ratio of Hf:O in as-deposited film is 1:1.78, moreover, According to the reviewer’s request, The XPS of film irradiated O ion beam bombardment with 1000eV have been added to Fig2(b),From this XPS graph, we calculated the stoichiometric ratio of Hf:O reached 1:1.86 ,It indicated that changes in the refractive index was mainly caused by stoichiometric ratio which varied with O ion beam bombardment
（11）Figure 6: Are there any results from literature which can be used for comparison?
The results should be more compared with results from literature, for example, there should be many more papers in the literature investigating ion effects on HfOx films.
The laser damage threshold test is affected by many factors, including the type of laser, laser wavelength, pulse width, laser beam diameter, etc. In addition, the thickness of the film is also an important factor that affects the laser threshold test. The literature () tested the laser damage threshold for the samples prepared by thermal evaporation and the film after coating treatment. The test conditions of this literature are basically the same as this article (test conditions: Nd:YAG laser, 12ns, 1064nm wavelength), but different is that this article uses a laser spot diameter of 0.4mm, this article uses 0.8mm, and the test methods are all "1-on-1" methods.
Appendix literature：
[1] Congjuan Wang，YunxiaJin ，Dongping Zhang，et,al.A comparative study of the influence of different post-treatment methods on the properties of HfO2 single layers，Optics & Laser Technology,2009,41(5):570~573
[2] Jianping Hu,Jian Wang,Yaowei Wei et,al. Effect of film growth thickness on the refractive index and crystallization of HfO2 film, Ceramics International,2021,47(23):33751~33757
Reviewer 2 Report
Line 76 - "in situ" instead of "in-suit"
Line 77 - insert "1064 nm" before wavelength
Line 137 makes no sense. Not sure what was meant instead of deals.
Deals of porous and void-rich structure were formed easily in the HfO2 thin film
Line 139 could make the film become denser
Line 154 - 155 Experimental evidence is needed for the films becoming denser with ion bombardment treatment.
"As mentioned above in figure 5(a), thin film became dense after post-treatment with Ar+ plasma." feels like citing earlier speculation as fact.
Author Response
Reviewer2#
(1) Line 76 - "in situ" instead of "in-suit"
We have changed to“in situ”
(2)Line 77 - insert "1064 nm" before wavelength
We have inserted
(3)Line 137 makes no sense. Not sure what was meant instead of deals.
Deals of porous and void-rich structure were formed easily in the HfO2 thin film
Sorry are very sorry that wrong word. We have modified "Deals of" to "Lots of"
(4)Line 139 could make the film become denser
The error has been corrected according to reviewer’s proposal
(5)Line 154 - 155 Experimental evidence is needed for the films becoming denser with ion bombardment treatment.
"As mentioned above in figure 5(a), thin film became dense after post-treatment with Ar+ plasma." feels like citing earlier speculation as fact.
The error has been corrected according to reviewer’s proposal
Round 2
Reviewer 1 Report
There is some progress in the quality of the paper. The answers given should be included in the text, is possible. Please explain abbreviations, for example, "standard RCA cleaning" may not be known for every reader. A short reference (e.g. as found here: https://www.inrf.uci.edu/wordpress/wp-content/uploads/sop-wet-silicon-rca-1.pdf) might be enough.
I still not agree with the ellipsometric analysis. In figure 5 it is said, "refractive index of HfO2 films". This is not true since the unkown dispersion of the BK7 substrate is included in the system. Figure 5 shows not any physical refractive data unless correct dispersion of all components is included.
So, one option would be to reduce the spectral range in figure 5 to the visible, the other option is to include correct data and also correct model. I would recommend the first option. In principle, you also could limit the discussion on the refractive index at a single wavelength in the transparent region, e.g. 550nm.
Also: Please add the explanation given with the black paint for the backside to avoid backside reflections. By the way: Did you check if the black paint is also black in the infrared range?
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Corrections look fine.
Author Response
English language and style have been checked and revised
