Cleavage-Driven Laser Writing in Monocrystalline Diamond

Round 1

Reviewer 1 Report

In this paper, the possibility of graphitization of micro-channels by ultrafast laser is discussed. In order to achieve the high quality microwires, different strategies are proposed and tested.

The novelty is evident. The manuscript is well written, and easy to understand / follow. Notwithstanding, there are a couple of weaknesses need addressing before further consideration for publication.

First of all, the incentive of the study is for applications such as PCAs. And it is known that the current applications of graphitic wires are highly dependent upon their electrical properties, which suggest that a reduction of resistivity will have great impact in obtaining superior performance for the relevant devices. Therefore, an obvious question is whether these wires produced at different conditions offer same resistivity for intended applications. Another related question is the influence of the fracture / cleavage reported in this manuscript on the conductivity/resistivity of the wires written. A brief discussion should be given in section 3. Seeing the authors recent publication (ref.20), I wonder if it would be even more insightful if authors provide some resistivity measurement results.

Second, the authors may also want to comment on how deep these features can go, and is this a limiting factor for the targeted applications.

A couple of minor remarks are noted in the manuscript.

At last but not at least, English needs polishing. It is ok to read, but faults are clearly visible.

In conclusion, this report is interesting and with potential to provide useful insights for the community. I kindly ask the author to carry out a major revision. Some descriptions and discussion in the current version need to be strengthened.

Comments for author File: Comments.pdf

Author Response

%% Q1. First of all, the incentive of the study is for applications such as PCAs. And it is known that the current applications of graphitic wires are highly dependent upon their electrical properties, which suggest that a reduction of resistivity will have great impact in obtaining superior performance for the relevant devices. Therefore, an obvious question is whether these wires produced at different conditions offer same resistivity for intended applications. Another related question is the influence of the fracture / cleavage reported in this manuscript on the conductivity/resistivity of the wires written. A brief discussion should be given in section 3. Seeing the authors recent publication (ref.20), I wonder if it would be even more insightful if authors provide some resistivity measurement results.
A1. 1. The questions concerning the appropriateness of these buried electrodes for HV applications, like PCA, are indeed of quite importance. We strongly expanded the discussion about possible conductivity of produced threads and put it to the section 3:
"As was already mentioned, the possible application fields of the buried threads cover a wide variety of electronic devices including photoconductive antennas, detectors of ionizing radiation, etc.
There are two major requirements which produced graphitized electrodes should satisfy as far as possible.
The first one is high conductivity, the second is an intact surrounding diamond matrix.
And the last requirement is even more important, because the high conductivity is vitally significant for the only high speed devices, while the possible electronic-active defects interfere with current flows at any operation frequency.  
The future studies should investigate both the aspects.

To this moment, the resistivity of a graphitized zig-zag fracture produced by nanosecond pulses in diamond was found to be close to the resistivity of polycrystalline graphite \cite{Ashikkalieva:2022internal}.
The conductivity of the cleavage-driven graphitized threads is expected to be even higher due to the higher structural perfection of the graphite produced.
The information about the structural defects in the vicinity of laser produced conducting phase is rather limited.
We know only few works encountered this problem \cite{Pimenov:2016et}.
However, some deterioration of operation of the diamond-based detectors was attributed to the presence of electronic traps located in regions close to electrodes \cite{Salvatori:2019diamond}.
The degree of the diamond damage in the cleavage-driven process should be studied and compared with the damage induced in the customary regime of a graphitized thread formation."

2. Unfortunately, there are no measurements of their electrical properties. We work with that and plan to publish these data elsewhere.

%% Q2. Second, the authors may also want to comment on how deep these features can go, and is this a limiting factor for the targeted applications.
A2. We specify this moment in the section 2:
"After adjustment of a correction collar the threshold of optical breakdown was very close to a constant ($\sim 1.0 \mu$J) in the range of 50 $\mu$m to 350 $\mu$m beneath the diamond surface.
As a matter of fact, this range determines a region size where laser writing could be realized without the readjustment of the correction ring. 
The graphitized structures described below were produced at $\sim 100 \mu$m depth beneath the surface."

%% Q3. A couple of minor remarks are noted in the manuscript.
A3. Everything was fixed in the current version in accordance with the recommendations.

 

Reviewer 2 Report

This research is interesting for diamond-based THz antenna and other optical devices. After carefully reading, I have some little comments and/or suggestions as follows:

(1) How to quantitatively control the graphite wire thickness during the laser writing process?

(2) Could you provide an illustration of the evolution mechanism and laws from the image information (e.g., Fig.3 and Fig. 4)?

(3) What is graphitization energy for your research in Fig. 6? This nomination is not clear to readers. Any preconditions were necessary for the following statement after Fig. 6.

(4) After the research results, could any quantitative statements provide in the conclusion section?

Author Response

%% Q1. How to quantitatively control the graphite wire thickness during the laser writing process?
A1. We believe that there are 2 sizes: width and thickness. Width can be controlled with changing lens. In the case the variation range is not wide: 1-3 um, we suppose. Thickness can be controlled via multiple scanning. We don't measure the thickness yet. It can be done after polishing with SEM. We guess it is around 100 nm after a single scan.

%% Q2. Could you provide an illustration of the evolution mechanism and laws from the image information (e.g., Fig.3 and Fig. 4)?
A2. As far as we could understand question, the reviewer asks add some marks in the Figs 3 or 4, which assist to see mechanisms more clearly. It is quite difficult to provide this as the images are small enough. For the illustration of processes revealed and corresponding mechanisms we use Fig 1 (b-c) for the seed-graphitization process and Fig 5(c) for cleavege formation. We also rewrite the Fig.4 caption to be more clear. Now it:
"The optimum seed-based laser writing and build-up of graphite wire thickness. Seed stage parameters: $E_s = 1.0$~$\mu$J, $V_s = 0.2$ mm/s. Graphitization stage parameters: $E_g = 0.3$~$\mu$J, $V_g = 0.05$ mm/s. The first image demonstrates the seed scan. The second, fourth, fifth and subsequent images correspond to the first, second, third and subsequent graphitization scans. The third image demonstrates 2-nd graphitization scan in the progress."

%% Q3. What is graphitization energy for your research in Fig. 6? This nomination is not clear to readers. Any preconditions were necessary for the following statement after Fig. 6.
A3. For clarity now we define both the parameters "seed energy" and "graphitization energy" in the text like:
"The seed energy, i.e. the pulse energy in the seed stage, was limited by range around single pulse graphitization threshold: $0.9 \cdot E_{th} < E_s < 1.1 \cdot E_{th}$."
and then
"The graphitization energy, i.e. the pulse energy in the graphitization stage, varied in much wider range."
Regarding the last part of this question, we don't understand what the statement do you mean after Fig6.

%% Q4. After the research results, could any quantitative statements provide in the conclusion section?
A4. We add next comment in the Conclusion
"The continuous structures were produced at the seed energy which is close to the threshold of the single pulse graphitization ($\sim 1.1 \mu$J) and the graphitization energy ranged from $\sim 0.2 \mu$J to $\sim 1 \mu$J."

 

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

%% Q1. Please define abbreviations HPHT and CVD where they first appear.
A1. Thank you, it has been fixed.

%% Q2. Authors write in the 22 line: "Surface conductivity of an untreated diamond is relatively high and threshold for a surface breakdown is comparable to that of air $\sim 10$ kV/cm. " It is known that diamond is a dielectric material. Please clarify why the surface conductivity of diamond is relatively high? The surface breakdown value needs a reference.
A2. It is quite valuable remark. The surface conductivity significance for any material is a common fact. Here we do not mean that diamond surface resistance is expessially low. We mean it is somewhat lower than bulk resistance. The question about surface breakdown threshold is complex because it strongly depends on the history of the particular sample. The 10 kV/cm was observed in our experiments and to clarify this point we rewrite this sentence as:
"Surface conductivity of an untreated diamond is relatively high and, for instance, in the experiments described below the threshold for a surface breakdown was comparable to that of air $\sim 10$ kV/cm. "

 

Reviewer 4 Report

I think this is very nice paper. I even don't have any questions to ask. 

Author Response

Thank you, sir

Round 2

Reviewer 1 Report

The quality of the manuscript has been improved in this revised version. Some insights and limitations of the current research results have been added, which is good for the readers.

There a re still a few minor grammer issues: acrynom "THz" should be defined before being used. I feel aslo "face(s)" in lines 111 and 112 should be replaced by "surface", but not 100 percent sure about this myself - please cross check.

I think also, according to MDPI general codes, the supplier, brand and address of the supplier of the instruments and materials should be given in the text. One more thing, there should be a space between digits and the following units.

Author Response

%% Q1. There a re still a few minor grammer issues: acrynom "THz" should be defined before being used. I feel aslo "face(s)" in lines 111 and 112 should be replaced by "surface", but not 100 percent sure about this myself - please cross check.
A1. 'Thz' was defined.
When the orientation is told the term 'face' is preffered.
When we point out the treatment process (polishing) the both terms ('face' and 'surface') are allowed. We remain this point unchanged. 

%% Q2. I think also, according to MDPI general codes, the supplier, brand and address of the supplier of the instruments and materials should be given in the text. One more thing, there should be a space between digits and the following units.
A2. Everything was fixed.