Atomic structure and defect dynamics of monolayer lead iodide nanodisks with epitaxial alignment on graphene

Lead Iodide (PbI2) is a large bandgap 2D layered material that has potential for semiconductor applications. However, atomic level study of PbI2 monolayer has been limited due to challenges in obtaining thin crystals. Here, we use liquid exfoliation to produce monolayer PbI2 nanodisks (30-40 nm in diameter and > 99% monolayer purity) and deposit them onto suspended graphene supports to enable atomic structure study of PbI2. Strong epitaxial alignment of PbI2 monolayers with the underlying graphene lattice occurs, leading to a phase shift from the 1 T to 1 H structure to increase the level of commensuration in the two lattice spacings. The fundamental point vacancy and nanopore structures in PbI2 monolayers are directly imaged, showing rapid vacancy migration and self-healing. These results provide a detailed insight into the atomic structure of monolayer PbI2, and the impact of the strong van der Waals interaction with graphene, which has importance for future applications in optoelectronics.

The paper by Sinha et al. discusses synthesis of 2D monolayer Lead Iodide on graphene substrate using liquid exfoliation method, and further explored the atomic structure, defect structures and structural change under electron beam using scanning transmission electron microscopy. Despite that the authors put lots of interesting information in one paper, the paper still lacks the depth and novelty that are required by a journal like nature communications. The results are 'routine' and there is very loose relationship between different sections. The defect structure, edge structure, electron beam effect and self-healing are all well-known effect for 2D materials under the electron beam. For example, under electron beam irradiation, holes can form for basically any 2D materials. The hole expansion process is more or less the same for all the TMDs. The edge structure is mainly zigzag for TMDs, which is not surprising that such edge structure is also observed for monolayer PbI2. The atoms are extremely mobile around defects and could form interesting transient structures, leading to self-healing or hole expansion depending on the local structure. The paper reports lots of observations, but I am not sure how those observations are special for PbI2, and how those observations extend our current understanding of defect structure of 2D materials, under electron beam. And it is not clear how the observations can be related to the physical or functional properties of PbI2, as the authors have nicely discussed in the introduction, such as band gap, mobility. To summarize it, this is a decent characterization paper for monolayer PbI2 synthesized using liquid exfoliation, but it does not really provide more information than we have already known about this 2D material. This paper would fit better in ACS Nano.

Reviewer #2 (Remarks to the Author):
This manuscript describes the preparation and structural analysis, via electron microscopy, of the 2D transition metal dichalcogenide system PbI2, a candidate material for optoelectronic applications in the green-to-UV region of the spectrum. The 2D form of this material has received less attention than its multilayered form, in part due to the difficulties of obtaining high quality monolayers. Main results include the preparation of the monolayer (2D) form in a manner amenable to electron microscopy imaging, its adoption of a preferred phase and orientation relation with the graphene substrate, and the observation of various beam induced defect structures and their evolution over time. I will leave any criticisms warranted of the materials preparation to reviewers better qualified to comment on it, and focus on the electron microscopy.
Though adequate signal-to-noise is a challenge for any thin sample, as evident in the images shown, PbI2 is well-suited to annular dark field scanning transmission electron microscopy (ADF-STEM) because the strong scaling of the signal with atomic number allows ready discrimination between the Pb and I atoms (with low contribution from the light graphene support), and the structure of the two phases (T-phase and H-phase) are clearly distinguishable by ADF-STEM contrast. Drawing not only on the directly interpretable nature of ADF-STEM for thin samples but also on comparison with electron scattering (multislice) simulations, the authors demonstrate the phase and monolayer nature of their prepared samples and proceed to catalogue a range of (beam-induced) structural defects, many of which evolve dynamically under electron irradiation but some of which, once formed, seem reasonably stable. The figures are generally of high quality and used to good explanatory effect. While this kind of electron microscopy analysis is no longer unusual, the present analysis seems to me generally done well, and the significance of the material should help this work appeal to a wide cross-section of the materials research community. I would ask the authors to consider the points raised below by way of minor revision before the paper be accepted for publication.

Main concern:
Though some motivation is provided in the introduction and conclusion, the discussion of Figs. 4-9 provides a great enumeration of defect structures encountered, but does not convey to me a sense of conceptual framework or practical significance. Especially given that these defects seem to be electron-beam induced, I feel the manuscript would be significantly strengthened if the unity of purpose and significance of these findings could be more clearly conveyed.
Minor considerations: * Line 132: given the time between images shown is many orders of magnitude greater than most atomic dynamics, that holes are seen in Fig. S3 (rather than, say, "thinning") seems to me to be a less than conclusive demonstrating that the sample is indeed only a monolayer thick. Could the authors please elaborate on why holes would be expected to open up layer-wise? * Line 168-170: "The smaller the difference in the relative lattice spacings between the two crystals, the larger the van der Waals interaction is likely to be. The best lattice match occurs when the PbI2 adopts 1H phase and is aligned to the arm-chair direction, which agrees with our experimental findings." Please consider spelling out this connection in greater detail in reference to , especially since the green lines indicating the "minimum distance where Pb atom overlaps a C-C bond in graphene, indicating loss of commensuration" seem to me to be of comparable length between Figs. 3(s) and (v). * In Fig. 4(j-l), what was used as the basis of relative alignment? Given the mobility of defects asserted elsewhere, it is not entirely obvious to me that the orange lines on those three successive images correspond to the same set of atoms.
* The weak contrast at the centre of the defect in Fig. 5(b) is interpreted to indicate a single vacancy (rather than two I vacancies one above the other). However, there seems to me to be similar remnant contrast present in the centre in Fig. 5(b), (j) and (k) but those cases are interpreted as complete vacancies. Please elaborate on how the interpretation / assignment of these experimental images to particular simulated configurations was made. * In Figs. 8(f-h), (n-p), what is the significance of the red arrows? It seems to imply a direct thisatom-moved-from-here-to-here interpretation that I would consider questionable given the time frame of atomic dynamics relative to the time elapsed between images. * In the supplementary material, I find the discussion comparing what Fig. S4 shows to what Fig.  S5 shows confusing, especially given the differences in format of the two figures. Please clarify.
* In section S5, I find it hard to make the connections between Figs. S5(c) and (d) on the basis of relative column intensities, though the intercolumn spacing is persuasive. Should this be explicitly stated?
* I also find it hard to see Fig. S6(c) as being the "high resolution image of the area boxed in red color in figure a" -not least, the extent of the fields of view appear to be quite different. Please confirm the correct image has been provided.
Trivial points: * In line 222, "The red arrow indicates the ejection of the electrons…" should presumably refer to the ejection of atoms? (At the risk of being especially pedantic, I'd also argue that what is shown in Fig. 4(i) is a red line, not an arrow since it lacks a head.) * In line 380: "Sigma Aldrick" should read "Sigma Aldrich". The authors for the first time reported the synthesis of 2D monolayer Lead Iodide nanodisk with diameter of 30-40 nm using liquid-exfoliation method. Then interface it with graphene to form van der Waals heterostructure which may be important for future applications in opto-electronics. Defective dynamic in 2D PbI2 is also studied. The topic is interesting. All the experimental synthesis and characterization are basically sound. I would recommend it publishing in Nature Communications after some minor revisions.
(i) The band gap of PbI2 is quite large. The Most practical applications should be discussed.
(ii) Many defects have been formed and observed. Which has the lowest formation energy?
Reviewer #4 (Remarks to the Author): In this work, Jamie H. Warner and co-workers report the liquid-exfoliation of PbI2 nanodisks and systemically study the interaction between PbI2 and graphene. The fundamental atomic structure and different defects as well as the edge states under electron beam irradiation are well studied. The method is simple, and the solid experiment has been conducted by ADF-STEM. The interaction between graphene and PbI2 is illustrated. Some comments, especially the detailed structure information, should be addressed before its acceptance. 1) The authors claim that only 2 flakes with bilayer structure are found among more than 300 flakes. However, in figure 1c, 1e and figure s1 and s2, there are small flakes showing thickness is above bilayer. The authors use the supernatant of the dispersion for preparing TEM samples. Where (bottom or top) is the dispersion taken from the container? Do the flakes have the similar thickness in the bottom or top of the container? The authors should consider all the few-layer PbI2 not only the monolayer and bilayer. Meanwhile, the experiment conditions of liquid-exfoliation for the 300 flakes should be provided in the manuscript. 2) Why the PbI2 prefers the orientation of zigzag aligned to graphene armchair direction rather than the graphene zigzag direction. The detailed reason should be discussed and offered in the manuscript.
3) The authors claim that the best lattice matching occurs in the 1H-PbI2 with direction aligning to the graphene arm-chair. On the contrary, what's the structure of PbI2 (1H or 1T) when its direction aligning to the graphene zigzag? 4) What's the graphene direction when the edges of PbI2 are etched to form sharp zig-zag faceted terminations after electron beam irradiation? 5) Different defects are induced by electron beam irradiation such as 4-membered ring configuration, atoms missing. As for the defects, the significant issue is the stability. Do these structures can be stable in air? 6) What's the effect of the accumulation of the atoms in Fig (i-j). To form a new material or only a new structure of PbI2? It should be clarified.

Reviewer#1
The paper by Sinha et al. discusses synthesis of 2D monolayer Lead Iodide on graphene substrate using liquid exfoliation method, and further explored the atomic structure, defect structures and structural change under electron beam using scanning transmission electron microscopy.
Reviewer#1 1) Despite that the authors put lots of interesting information in one paper, the paper still lacks the depth and novelty that are required by a journal like nature communications. The results are 'routine' and there is very loose relationship between different sections. The defect structure, edge structure, electron beam effect and self-healing are all wellknown effect for 2D materials under the electron beam. For example, under electron beam irradiation, holes can form for basically any 2D materials. The hole-expansion process is more or less the same for all the TMDs.

Our response:
We have now revised our manuscript to emphasis the novelty and make clear the depth of our findings. It has been now structured in three sub-parts which describes the (a) synthesis of predominantly monolayer PbI2 (b) 1-H atomic structural phase of PbI2 (c) atomic scale defects. All these results are novel and provide insight into the special structure of PbI2.
The results are new as well as quite different from other 2D materials. Hole expansion process is not same for PbI2, as we have seen a big restructuring, very stable new defects as well as different pathway of hole formation. Different hole expansion process can lead to different types of defect formation on large scale and different influence on the semiconducting properties, and thus makes all the 2D materials different on the monolayer scale. We have also replied to this in more details with the 3 rd question. We have now restructured our paper as well as added more comparisons with other 2D material in our main text to strengthen the paper. 2) The edge structure is mainly zigzag for TMDs, which is not surprising that such edge structure is also observed for monolayer PbI2.
Our response: PbI2 is not a TMD, so it is not valid to assume that the behaviour seen in TMDs will apply to PbI2. For example, in other 2D materials such as Graphene, a mixture of armchair and zig-zag edges can exist. To date, there is no experimental evidence on the nature of edges in PbI2 monolayers, so prior to our report, it is only theoretical predictions. Our results provide the very first evidence on the edge terminations on PbI2 monolayer crystals. In our edge-study the PbI2 maintains the zigzag structure to the armchair direction of the graphene even whilst etching. It etches away in three possible directions which is specific to graphene orientation. This is very unique and we have added more information to the main text as well as added a new figure in S.I. 11.
3) The atoms are extremely mobile around defects and could form interesting transient structures, leading to self-healing or hole-expansion depending on the local structure.
The paper reports lots of observations, but I am not sure how those observations are special for PbI2, and how those observations extend our current understanding of defect structure of 2D materials, under electron beam.
Our response: We now include new DFT calculations of the sputtering energy for Pb and I atoms in monolayer PbI2 and compare these to the energy transferred by the electron beam. We also now include DFT calculations of the vacancy migration barrier for Pb and I vacancies in PbI2. These new results show that energy from the electron beam is not sufficient to sputter the Pb or I atoms, indicating that more complex vacancy mechanisms are occurring than knock-on damage alone. This includes ionization effects due to the large band gap of PbI2, known as radiolysis. We do show that the energy from the electron beam is more than sufficient to drive the vacancy migration. We observe both Pb and I vacancies, which are both mobile and this is different to most other 2D crystals made up of one heavy and one lighter element. This leads to unique vacancy and hole formation in PbI2 with rapid vacancy migration.
Furthermore, PbI2 is of special interest, because 3D crystal structures of PbI2 (2H and 4H) have been shown to comprise of 15-20% atomic positions and have been shown to change the structure. 1,2 This can just give an idea of how much importance the vacancies and defects are, in 2D-PbI2 and can have important consequence for its semiconducting properties. On this front, our work is novel, since no one has studied and characterized the atomic scale defects and vacancies of PbI2 at the atomic scale. In addition, it exhibits new kind of stable defects (figure 6) which is unlike any other 2D materials and may provide new insights into the bonding properties of lead and iodide.
Importantly, the hole formation differs from other 2D materials studied at room temperature. Defects and hole formation and propagation for different 2D materials have shown vastly different behaviour. For instance, monolayer hBN has nanopores that form and grow in size whilst maintaining triangular shape from a monovacancy. 3 Graphene has nanopores at room temperature that are generally round. At room temperature in TMDs, such as MoS2 and WS2, round holes form that are not well faceted shapes and the heavy metal aggregates around the hole edges and can form nanowires. However, in PbI2, the holes form well faceted shapes with zig-zag termination at room temperature, and this is due to the high mobility of vacancies under the electron beam and the electron beam induced displacement of both Pb and I atoms.
These results provide a detailed insight into the atomic structure and defects in monolayer PbI2. We have now added this to the main text to make the paper more informative.
4) And it is not clear how the observations can be related to the physical or functional properties of PbI2, as the authors have nicely discussed in the introduction, such as band gap, mobility. To summarize it, this is a decent characterization paper for monolayer PbI2 synthesized using liquid exfoliation, but it does not really provide more information than we have already known about this 2D material. This paper would fit better in ACS Nano.
Our response: Knowing the defects and the structure of the defects of 2D materials is crucial to understanding its effects on its physical and chemical properties. The accurate determination of the atomic structures of these defects and vacancies can contribute to precise estimation of its effects on the transport properties of the material. The impact of the strong van der Waals interaction with graphene is yet another important part of the work and is crucial while considering it for future applications in opto-electronics. References: (1) The Structure of PbI2 Polytypes 2H and 4H: A Study of the 2H-4H Transition. J. Phys.

Reviewer#2
This manuscript describes the preparation and structural analysis, via electron microscopy, of the 2D transition metal dichalcogenide system PbI2, a candidate material for optoelectronic applications in the green-to-UV region of the spectrum. The 2D form of this material has received less attention than its multilayered form, in part due to the difficulties of obtaining high quality monolayers. Main results include the preparation of the monolayer (2D) form in a manner amenable to electron microscopy imaging, its adoption of a preferred phase and orientation relation with the graphene substrate, and the observation of various beam induced defect structures and their evolution over time. I will leave any criticisms warranted of the materials preparation to reviewers better qualified to comment on it, and focus on the electron microscopy.
Though adequate signal-to-noise is a challenge for any thin sample, as evident in the images shown, PbI2 is well-suited to annular dark field scanning transmission electron microscopy (ADF-STEM) because the strong scaling of the signal with atomic number allows ready discrimination between the Pb and I atoms (with low contribution from the light graphene support), and the structure of the two phases (T-phase and H-phase) are clearly distinguishable by ADF-STEM contrast. Drawing not only on the directly interpretable nature of ADF-STEM for thin samples but also on comparison with electron scattering (multislice) simulations, the authors demonstrate the phase and monolayer nature of their prepared samples and proceed to catalogue a range of (beam-induced) structural defects, many of which evolve dynamically under electron irradiation but some of which, once formed, seem reasonably stable. The figures are generally of high quality and used to good explanatory effect. While this kind of electron microscopy analysis is no longer unusual, the present analysis seems to me generally done well, and the significance of the material should help this work appeal to a wide cross-section of the materials research community. I would ask the authors to consider the points raised below by way of minor revision before the paper be accepted for publication.

Main concern:
Reviewer#2 1) Though some motivation is provided in the introduction and conclusion, the discussion of Figs. 4-9 provides a great enumeration of defect structures encountered, but does not convey to me a sense of conceptual framework or practical significance. Especially given that these defects seem to be electron beam induced, I feel the manuscript would be significantly strengthened if the unity of purpose and significance of these findings could be more clearly conveyed.
Our response: Our work is first of its kind to synthesize pure monolayer PbI2 using liquid exfoliation method, study the monolayer structure as well as the defect dynamics. We have now sectioned the paper into three parts so as the manuscript can clearly demonstrate the purpose and significance of these findings.

Minor considerations:
The monolayer PbI2 has not been considered before because of the lack of synthesis method to produce predominantly monolayer structures. Knowing the importance of the monolayer PbI2 structure and material, this article presents the ways to synthesize and study it. Graphene has played an important tore in the other 2D materials and this article presents how graphene can influence and relate to the synthesis and the production of the 2D monolayer PbI2 as well as help us study its structure and deformation under microscope in its 2D form/. The monolete study on its structure and defects has never been carried out before and hence, we also present that to the readers for better understanding of the thin layered 2D-crystals. Moreover, this paper presents a detailed analysis on the study of the monolayer PbI2 which has never been done before, whilst at the same time, contributing to the large scale facile synthesis of it on top of a substrate. - Reviewer#2 2) Line 132: given the time between images shown is many orders of magnitude greater than most atomic dynamics, that holes are seen in Fig. S3 (rather than, say, "thinning") seems to me to be a less than conclusive demonstrating that the sample is indeed only a monolayer thick. Could the authors please elaborate on why holes would be expected to open up layer-wise?
3) Line 168-170: "The smaller the difference in the relative lattice spacings between the two crystals, the larger the van der Waals interaction is likely to be. The best lattice match occurs when the PbI2 adopts 1H phase and is aligned to the arm-chair direction, which agrees with our experimental findings." Please consider spelling out this connection in greater detail in reference to Fig. 3(s-v), especially since the green lines indicating the "minimum distance where Pb atom overlaps a C-C bond in graphene, indicating loss of commensuration" seem to me to be of comparable length between Figs. 3(s) and (v).

Our response:
The figure is now moved to SI as figure S11. The figure is used to show the distance to a position of commensuration between the Pb atom and the underlying graphene lattice. The green line for the 1H:Arm-chair case is more than twice the distance than all other cases. This helps to understand why it might have a preference for alignment. We have also now added a more definitive DFT calculation which shows the armchair PbI2 has local energy minima when aligned to the armchair or zig-zag graphene direction s( Figure. 3 (s-t)). This has been described in more details in the figure and the main text now.
- indicate a single vacancy (rather than two I vacancies one above the other). However, there seems to me to be similar remnant contrast present in the centre in Fig. 5(b), (j) and (k) but those cases are interpreted as complete vacancies. Please elaborate on how the interpretation / assignment of these experimental images to particular simulated configurations was made.
Our response: The interpretation and assignment of the experimental images to their simulated configurations were made on the line profile of the defects after normalizing their intensities.
We have now added the extra information in S.I. 14 on how we have calculated the single vacancy or complete vacancies of I atoms. During image acquisition, some vacancies will be produced during the imaging process and therefore some residual contrast may appear for some cases, and also during imaging an existing vacancy may be filled during the image acquisition, which also leads to some residue contrast. To gain a full understanding, we measured many point vacancies and draw conclusions from multiple measurements of the same structures.
Furthermore, we believe that if the contrast pattern is stable and repeated during multiple sequential images, then it represents a stable configuration of a defect, rather than a transition state. Capturing a structural transition in a vacancy defect can lead to unusual contrast patterns that could be misinterpreted, but these contrast patterns are rarely stable for multiple sequential images because the transition pathways in vacancy changes are rarely between just two stable states, they often involve multiple pathways and movements to nearby lattice sites.

Reviewer#2 6) *In Figs. 8(f-h), (n-p)
, what is the significance of the red arrows? It seems to imply a direct this-atom-moved-from-here-to-here interpretation that I would consider questionable given the time frame of atomic dynamics relative to the time elapsed between images.
Our response: Yes, it is not possible to tell the pathway of movement of the atoms given the time elapsed between capturing two consecutive images. TEM captures the positions of fixed stability. It is similar to stroboscopic imaging of fast dynamics. Every movie/video has frames that capture still images of a moving event. The red arrows indicate the possibility of migration of the atoms from one position to the other. The electron beam damages the material and forms the nanopore but at the same time, we are able to capture the fast migration of atoms and the self-healing process in the material in real time. However, prolonged exposure to the electron beam ultimately leads excessive sputtering of atoms than the self-healing itself leafing to a bigger nanopore formation. We have now added more text to the main text to explain the figure more properly.

Reviewer#2 8) *In section S5, I find it hard to make the connections between Figs. S5(c) and
(d) on the basis of relative column intensities, though the intercolumn spacing is persuasive.
Should this be explicitly stated? argue that what is shown in Fig. 4(i) is a red line, not an arrow since it lacks a head.) Our response: Thank you for pointing this out. Yes, the red arrow indicated the ejection of the electrons. We have now corrected this in the main text as well as the red arrow. Our response: Thank you for the useful comment. The band gap of PbI2 is 2.4 eV in its bulk form, whereas its 2D monolayer has an indirect bandgap of about 2.5 eV, with possibilities to tune the band gap between 1-3eV. This enables it to PbI2 to be frequently used for fabrication of organic-inorganic halide perovskite solar cells, and as a high-energy photon detector material for gamma-rays and X-rays. We have added more on this in the main text.
Our response: The lowest formation energy is that of the single iodide vacancy that takes about 3.15 eV to get sputtered out of the system. We have now calculated it using DFT and added it to the main text as well as S.I.14.

Reviewer #4
In this work, Jamie H. Warner and co-workers report the liquid-exfoliation of PbI2 nanodisks and systemically study the interaction between PbI2 and graphene. The fundamental atomic structure and different defects as well as the edge states under electron beam irradiation are well studied. The method is simple, and the solid experiment has been conducted by ADF-STEM. The interaction between graphene and PbI2 is illustrated. Some comments, especially the detailed structure information, should be addressed before its acceptance. Our response: The other few-layer PbI2 is out of scope of this paper.
- ring configuration, atoms missing. As for the defects, the significant issue is the stability. Do these structures can be stable in air?
Our response: We have conducted all our experiments under vacuum since that's how we can get the microscope working. However, multilayer PbI2 is known to exhibit large number of stable vacancies, as discussed in the introduction and the conclusion section of the paper. Any defect in a 2D material that is exposed to air gets functionalized. This changes the nature of the defect from its intrinsic fundamental state, into an oxidized or functionalized version. Defects attract hydrocarbons to locally bind to them, which is why grain boundaries are often dirty compared to the rest of area of graphene growth by CVD. Studies of air functionalized defects is a separate study on its own. There are many fields of research such as batteries, where exposure to air is not done. Also there are many 2D crystals that are not stable in air, and gloveboxes are used to handle them to study their properties.
Our response: Iodine atoms are very light and they have very low sputtering energy (as calculated from DFT and added to the main text and S.I.) and hence, they get sputtered out from the system very easily. Also looking at the contrast, the single atoms imaged are that of Lead. The atoms aggregate to form clusters or get dispersed on the surface of graphene. We have added more results in S.I. 15. These are usually amorphous and have no special crystal structure. - The authors have revised the manuscript based on all reviewers' comments. The novelty and importance of the paper have now been greatly improved. DFT simulation has been used to support experimental observations such as orientation relationship between graphene and PbI2, and by providing formation energies of point defect and energy barrier for diffusion of atoms. Also, the characterization is now more quantitatively. Instead of merely reporting TEM images in previous version, the paper now provides a comprehensive investigation on this novel 2D materials. I therefore recommend acceptance of the paper.
Reviewer #2 (Remarks to the Author): The authors have addressed the points I raised. I recommend the manuscript for publication in Nature Communications. Reviewer #4 (Remarks to the Author): The authors have considerably revised their work and addressed some important issues. Nevertheless, there are a number of specific points I would like the authors to address before a final decision can be reached.
-The main text contains too much information, which may dilute the significance and novelty of the work. The conciseness should be improved by only keeping the most significant parts in the main text.
-Minor concerns: a) Figure 1g is not mentioned in the manuscript at all. b) Some grammar mistakes, e.g. "iodine atoms" instead of "iodide atoms", "the agglomeration of vacancies leads to a hole formation" etc. c) In the first paragraph of part II, "1c and 1g" should be "2c and 2g" based on the context. d) Some letters of figures are not visible, e.g. Figure 3s. e) Both " Figure" and "figure" are used throughout the text. Please make it consistent.
EDITORIAL REQUESTS: 1) Please remove ORCIDs present in author's information.
Response: It has now been removed.
2) Please remove the image present after Reference list.
Response: It has now been removed.
Novelty should be clear from the context.   Response: There is no data sources to add otherwise.

Response
12) Please supply an "Author Contributions" section after the Acknowledgement section that refers to all authors.
Response: "Author Contributions" section has been added after the Acknowledgement section that refers to all authors.
13) Please provide a "Competing Interests" section after the "Author Contributions" section that refers to all authors. If there are no competing interests, please add the statement "The authors declare no competing interests."

Response:
The statement "The authors declare no competing interests" has been added to the "Competing Interests" section after the "Author Contributions" section.
- Response: I wish to participate in transparent peer review.
23) An updated editorial policy checklist that verifies compliance with all required editorial policies must be completed and uploaded as a related manuscript file with the revised manuscript. All points on the policy checklist must be addressed; if needed, please revise your manuscript in response to these points. Please note that this form is a dynamic "smart pdf" and must therefore be downloaded and completed in Adobe Reader, instead of opening it in a web browser. Editorial policy checklist: https://www.nature.com/authors/policies/Policy.pdf

Response:
We have addressed all the point and responded to it in this cover letter.
24) Your paper will be accompanied by a two-sentence Editor's summary, of between 250-300 characters including spaces, when it is published on our homepage. Could you please approve the draft summary below or provide us with a suitably edited version. ''Imaging liquid phase exfoliated nanosheets on suspended graphene via annular dark field STEM can enable identification of various defects, vacancies and their migration. Here, the authors report matching of zig-zag edges of monolayer PbI2 with graphene arm-chairs leading to a phase shift from 1T to 1H structure to maximize commensuration of the lattices.''

Response:
We accept this.