Review Reports

Round 1

Reviewer 1 Report

The authors point out that there they "selected a few recent articles describing some innovative solutions to achieve on-surface chemistry on inert surfaces." This is an important area of scientific inquiry and the review is appropriate in its design of look at various substrates and correlating the outcomes of various reactions with the reaction triggers. It does, however, present itself as a fairly narrow review and also lacks a few additional details that are needed as outlined below. 

 

The authors highlight a range of publications in their review. Their own prior art are cited a number of times. Although they aim to have a focus to this review as stated above, there is still (I believe) the possibility to expand this to include additional examples that both highlight the diversity of work in the field and highlight other researchers in the field. 

 

Throughout the article the authors should review where they can add further details. For example, adding the composition of the STM tip when used in the reactions, the level of the vacuum used for the reactions (e.g., UHV or otherwise), and other "reaction" details would greatly improve the clarify of the manuscript within its intended focus. 

 

The AFM data all need to have height scale bars added to the plots. 

 

The authors present a detailed discussion around the work in Figure 7, for example. It would be good to add further in depth discussion regarding the reaction mechanisms wherever possible. I understand this is limited by the nature of the studies presented in the literature, but this is also an opportunity to point out the areas for further work. And when depth is not possible, the authors should highlight the breadth of work that has been done in the various areas into which they have organized the themes of the manuscript.

 

Some phrases need to be rechecked for clarity, such as "tunnel electron to dissociate of a molecule through" and "injected electrons in on NaCl bilayer on". 

 

In the introductory section of the "Non-silicon based semiconductors" section of the review, the authors mention a number of metallic substrates in the context of the work they set out to discuss. These substrates, and all substrates throughout the review, should be specified. In general this is an aspect they do well throughout the thesis, but it should be done thoroughly. 

 

In the same section on "Non-silicon based semiconductors" the authors cite a number of substrates that are the most active, but they should present a balanced case and present those that are less active as well. 

 

The authors should quantify their statements wherever possible. For example, "on the TiO2 surface, the cyclodehydrogenation is possible but it is the limiting step of the process, with a higher activation barrier than cyclodehydrofluorination reaction" should have the activation barrier quantified in the discussion. In the context of discussing surface reactions this is an important aspect of these reactions that is in general missing from this review for understanding the reaction barriers and the probabilities on various surfaces. 

 

The statement "Electronic properties, determined by STS," needs to be clarified. What is STS? Did they mean STM? 

 

The authors state that "the observations support that the initial supramolecular networks have been transformed onto more stable 1D di-acetylene polymers due to the thermally-induced reaction between carbon-carbon triple..." How do they know it is more stable? That is unclear. And relative to what? 

 

Overall there are some important outcomes learned in this review, but it should also be prepared for a more broad audience. Statements early on should review the techniques needed for cleaning substrates, the importance of adsorbed species, the importance of atmospheric control during these steps, etc. This clarification would expand on the minimal statements in the introduction and would enable more readers to access the content herein. 

 

I am unsure that the authors answered in detail all of the questions that they sought to answer, such as "How to compensate the desorption or uncontrolled diffusion of all involved chemical species..." They should reflect on the aims of the review and ensure that these are all met in a detailed manner. Possibly additional discussion is required to put in perspective all of the lessons learned in each of the subsections. 

 

The Figures are numbered out of sequence. This should be cleaned up to be sure they are sequentially numbered. (e.g., Fig. 7 is before Fig. 5 and 6). 

Author Response

Reviewer 1

The authors point out that there they "selected a few recent articles describing some innovative solutions to achieve on-surface chemistry on inert surfaces." This is an important area of scientific inquiry and the review is appropriate in its design of look at various substrates and correlating the outcomes of various reactions with the reaction triggers. It does, however, present itself as a fairly narrow review and also lacks a few additional details that are needed as outlined below. 

 

The authors highlight a range of publications in their review. Their own prior art are cited a number of times. Although they aim to have a focus to this review as stated above, there is still (I believe) the possibility to expand this to include additional examples that both highlight the diversity of work in the field and highlight other researchers in the field. 

Author’s reply: We have selected and described in details 9 examples, 2 being from Lackinger’s group, two others from Amsharov’s group and only 2 are from our works. We estimate that these 9 articles are enough to give a non-exhaustive, but relevant overview of the field.

 

Throughout the article the authors should review where they can add further details. For example, adding the composition of the STM tip when used in the reactions, the level of the vacuum used for the reactions (e.g., UHV or otherwise), and other "reaction" details would greatly improve the clarify of the manuscript within its intended focus. 

Author’s reply: We agree with this remark concerning the level of vacuum used for each detailed experiment. However, the composition of the tip is not mandatory for a short review.

 

The AFM data all need to have height scale bars added to the plots. 

 Author’s reply: In the original manuscript of Richter, there is no scale bars corresponding to the height. Therefore, we have decided to adopt a common presentation for each figure, i.e. without any scale bar.

 

The authors present a detailed discussion around the work in Figure 7, for example. It would be good to add further in depth discussion regarding the reaction mechanisms wherever possible. I understand this is limited by the nature of the studies presented in the literature, but this is also an opportunity to point out the areas for further work. And when depth is not possible, the authors should highlight the breadth of work that has been done in the various areas into which they have organized the themes of the manuscript.

 Author’s reply: We have chosen to describe more deeply some parts but concerning the other ones, explanations are not so detailed in terms of reaction mechanisms.

Some phrases need to be rechecked for clarity, such as "tunnel electron to dissociate of a molecule through" and "injected electrons in on NaCl bilayer on". 

Author’s reply: We agree and we made the corresponding corrections.

In the introductory section of the "Non-silicon based semiconductors" section of the review, the authors mention a number of metallic substrates in the context of the work they set out to discuss. These substrates, and all substrates throughout the review, should be specified. In general this is an aspect they do well throughout the thesis, but it should be done thoroughly. 

Author’s reply: We agree and we made the corresponding corrections by adding also the required references (lines 269-70).

In the same section on "Non-silicon based semiconductors" the authors cite a number of substrates that are the most active, but they should present a balanced case and present those that are less active as well. 

Author’s reply: We do not agree because it is not the topics of this review to deeply describe unreactive semiconductor substrates.

 

The authors should quantify their statements wherever possible. For example, "on the TiO2 surface, the cyclodehydrogenation is possible but it is the limiting step of the process, with a higher activation barrier than cyclodehydrofluorination reaction" should have the activation barrier quantified in the discussion. In the context of discussing surface reactions this is an important aspect of these reactions that is in general missing from this review for understanding the reaction barriers and the probabilities on various surfaces. 

Author’s reply: We agree, however, these details are not in the straight line of this review. If the readers want to have a full description, they can read the corresponding articles.

The statement "Electronic properties, determined by STS," needs to be clarified. What is STS? Did they mean STM? 

Author’s reply: We agree and we made the corresponding corrections (lines 319-20).

The authors state that "the observations support that the initial supramolecular networks have been transformed onto more stable 1D di-acetylene polymers due to the thermally-induced reaction between carbon-carbon triple..." How do they know it is more stable? That is unclear. And relative to what? 

Author’s reply: We agree and we made the corresponding corrections by adding also the required references (lines 269-70).

Overall there are some important outcomes learned in this review, but it should also be prepared for a more broad audience. Statements early on should review the techniques needed for cleaning substrates, the importance of adsorbed species, the importance of atmospheric control during these steps, etc. This clarification would expand on the minimal statements in the introduction and would enable more readers to access the content herein. 

Author’s reply: We do not agree with these remarks concerning the description of the experimental part of the chosen articles. These features can be found in the original articles, if some readers are interested.

I am unsure that the authors answered in detail all of the questions that they sought to answer, such as "How to compensate the desorption or uncontrolled diffusion of all involved chemical species..." They should reflect on the aims of the review and ensure that these are all met in a detailed manner. Possibly additional discussion is required to put in perspective all of the lessons learned in each of the subsections. 

Author’s reply: We agree and we made the corresponding corrections as also suggested by referee 2.

The Figures are numbered out of sequence. This should be cleaned up to be sure they are sequentially numbered. (e.g., Fig. 7 is before Fig. 5 and 6).

Author’s reply: We apologize for that mistake and we made the corresponding corrections.

Author Response File: Author Response.pdf

Reviewer 2 Report

In their mini-review Geagea and co-workers present and discuss recent advances in the on-surface synthesis on non-metallic substrates. As these substrates behave mostly chemically inert in the reaction, new paradigms are required to induce covalent bond formation as photochemistry or the local injection of charge carriers from the tip of a Scanning-Probe-Microscope.

Even though this topic was already tackled by recent reviews (e.g. ACS Materials Lett. 2021, 3, 1, 56–63 and Dalton Trans., 2021,50, 10020-10027), the present submission still adds to the existing work and provides a unique perspective.

However, I’m somewhat confused by the structure of the manuscript. I understand that the main classification is the substrate (passivated metals, semiconductors, bulk insulators), but this separates some experiments that should be discussed alongside (e.g. photochemistry appears twice in different sections).  I am not sure how to resolve this, maybe an overview table would already be helpful. On the other hand, I do not see an in depth discussion of the specific roles of the different classes of substrates, which would justify the present organization of the manuscript.

In my opinion the conclusion section needs major revision. It is currently extremely short and almost without content. Here I would like to learn more about the author’s main visions, potential ideas for the field, further reaching goals, current limitations, necessary developments, principal problems etc.

More specific points:

-line 45: “uncontrolled diffusion” sounds strange. I do not know what it means and it also implies that controlling diffusion is possible

-line 95: “the absence of surface electrons” also appears odd; every substrate has electrons also bulk insulators; maybe this should be rephrased by saying the substrate does not have a chemical contribution due to the absence of electronic states in the respective energy window

-line 100: What are Ag(111)-I and Au(111)-I surfaces?

-line 117 & 214-2145: “(free) radical polymerization” is misleading as the reactions are not propagating; “radical addition” would be better;

-section 2.1.3: The yield of “STM tip activated reactions” is extremely low, in most cases a few molecules only; accordingly, this approach only qualifies for basic research. This should be clearly stated and a comparison to the other approaches would be beneficial.

-line 131:” In order to determine the best theoretical approximation” is confusing; I think the authors want to express that eventually experimental results were required to verify / falsify specific theoretical approaches

-line 160: Why an “economic challenge”? I think the authors want to express something like industry / application relevant

-line 165: unpassivated silicon surfaces can even decompose molecules; the severity of this strong interaction should be more clearly stated

-Fig. 7a: It would be helpful to illustrate the reaction in more detail already in the figure. If I understood correctly, the alkoxy chains are cleaved and dimerize via radical addition. This should become clear in the figure.

-line 240: I can understand the dimerization, but how can longer oligomers be formed? This requires a more detailed explanation.

-section 2.2: When reading this section obtains the impression that on-surface synthesis has been broadly established on transition metal oxide surfaces, which is clearly not the case. But the only work I know of was carried out on TiO2. Moreover, some of the reactions also require a catalytic contribution of the TiO2 surface. To avoid any misconception this section should be revised accordingly.

-Fig 8a: I would not call the reaction product a “polydiacetylene” as it does not have any acetylene moieties anymore.

-line 333: How does the electrostatic surface anchoring work. Is the carboxylic group deprotonated under these conditions? This should be clarified.

Author Response

Reviewer 2

In their mini-review Geagea and co-workers present and discuss recent advances in the on-surface synthesis on non-metallic substrates. As these substrates behave mostly chemically inert in the reaction, new paradigms are required to induce covalent bond formation as photochemistry or the local injection of charge carriers from the tip of a Scanning-Probe-Microscope.

Even though this topic was already tackled by recent reviews (e.g. ACS Materials Lett. 2021, 3, 1, 56–63 and Dalton Trans., 2021,50, 10020-10027), the present submission still adds to the existing work and provides a unique perspective.

Author’s reply: We thank the referee for this comment.

 

 

However, I’m somewhat confused by the structure of the manuscript. I understand that the main classification is the substrate (passivated metals, semiconductors, bulk insulators), but this separates some experiments that should be discussed alongside (e.g. photochemistry appears twice in different sections).  I am not sure how to resolve this, maybe an overview table would already be helpful. On the other hand, I do not see an in depth discussion of the specific roles of the different classes of substrates, which would justify the present organization of the manuscript.

Author’s reply: We agree with this comment. Basically, it is a choice. We have decided to organize this mini-review by substrates because to address this review for the point-of-view of the surface science. In the case of silicon-based surfaces or bulk insulators, we have mentioned the interest of these substrates. We agree, it is not a “in depth discussion of the specific roles of the different classes of substrates” as you propose but we are convinced that is enough clear for the readers.

In my opinion the conclusion section needs major revision. It is currently extremely short and almost without content. Here I would like to learn more about the author’s main visions, potential ideas for the field, further reaching goals, current limitations, necessary developments, principal problems etc.

Author’s reply: We agree and we made the corresponding corrections (lines 421-445).

More specific points:

-line 45: “uncontrolled diffusion” sounds strange. I do not know what it means and it also implies that controlling diffusion is possible

Author’s reply: We agree and we made the corresponding corrections.

-line 95: “the absence of surface electrons” also appears odd; every substrate has electrons also bulk insulators; maybe this should be rephrased by saying the substrate does not have a chemical contribution due to the absence of electronic states in the respective energy window

Author’s reply: We agree and we made the corresponding corrections.

-line 100: What are Ag(111)-I and Au(111)-I surfaces?

Author’s reply: We agree and we made the corresponding corrections by adding also the required references (lines 101-105).

-line 117 & 214-2145: “(free) radical polymerization” is misleading as the reactions are not propagating; “radical addition” would be better;

Author’s reply: We disagree free radical polymerization is only addressed in lines 214-15 and it is a true radical polymerization with Initiation, propagation and termination. We have clarified this point (Lines 149-253)

-section 2.1.3: The yield of “STM tip activated reactions” is extremely low, in most cases a few molecules only; accordingly, this approach only qualifies for basic research. This should be clearly stated and a comparison to the other approaches would be beneficial.

Author’s reply: We agree and we made the corresponding corrections (lines 159-61).

-line 131:” In order to determine the best theoretical approximation” is confusing; I think the authors want to express that eventually experimental results were required to verify / falsify specific theoretical approaches

Author’s reply: We agree and we made the corresponding corrections (lines 135-36).

-line 160: Why an “economic challenge”? I think the authors want to express something like industry / application relevant

Author’s reply: We agree and we made the corresponding corrections (line 167).

 

-line 165: unpassivated silicon surfaces can even decompose molecules; the severity of this strong interaction should be more clearly stated

Author’s reply: We agree and we made the corresponding corrections (lines 172-74).

-Fig. 7a: It would be helpful to illustrate the reaction in more detail already in the figure. If I understood correctly, the alkoxy chains are cleaved and dimerize via radical addition. This should become clear in the figure.

-line 240: I can understand the dimerization, but how can longer oligomers be formed? This requires a more detailed explanation.

Author’s reply: We agree and we made the corresponding corrections (lines 249-53). However, we do not modify the figure which is link to the STM image described in Figure 5c.

-section 2.2: When reading this section obtains the impression that on-surface synthesis has been broadly established on transition metal oxide surfaces, which is clearly not the case. But the only work I know of was carried out on TiO2. Moreover, some of the reactions also require a catalytic contribution of the TiO2 surface. To avoid any misconception this section should be revised accordingly.

Author’s reply: We agree and we made the corresponding corrections (lines 325-27).

-Fig 8a: I would not call the reaction product a “polydiacetylene” as it does not have any acetylene moieties anymore.

Author’s reply: We agree and we made the corresponding corrections.

-line 333: How does the electrostatic surface anchoring work. Is the carboxylic group deprotonated under these conditions? This should be clarified.

Author’s reply: We apologize for that mistake and we made the corresponding corrections (347-49).

Author Response File: Author Response.pdf

Reviewer 3 Report

The review by Geagea et al. describes nanostructure topography studies on passivated surfaces. This work can be published after elaborating few aspects.

1) On surface structure can be important in studying biomolecules such as carbohydrates (e.g. Nature 2020, 582, 375-378)

2) The surface properties have strong effect on molecule properties on moleculare arrangement in an interface and nanostructures formed. (for example J. Am. Chem. Soc. 2020, 142, 17, 7737–7743, ChemPhysChem, 2008, 9, 20-42, and Chem. Commun. 2021, 57, 6233–6236).

Author Response

Reviewer 3

The review by Geagea et al. describes nanostructure topography studies on passivated surfaces. This work can be published after elaborating few aspects.

On surface structure can be important in studying biomolecules such as carbohydrates (e.g. Nature 2020, 582, 375-378)

Author’s reply: We agree and we add the corresponding reference in the introduction (new ref 20).

The surface properties have strong effect on molecule properties on moleculare arrangement in an interface and nanostructures formed. (for example J. Am. Chem. Soc. 2020, 142, 17, 7737–7743, ChemPhysChem, 2008, 9, 20-42, and Chem. Commun. 2021, 57, 6233–6236).

Author’s reply: The effects of the underlying surfaces is very important for the development of on-surface chemistry. This is the main reason for the organization of the manuscript. However, we disagree with this comment because the mentioned articles are not in the topics of on-surface chemistry. Indeed, J. Am. Chem. Soc. 2020 is entitled “Electric Dipole Descriptor for Machine Learning Prediction of Catalyst Surface−Molecular Adsorbate Interactions”, ChemPhysChem, 2008 “Self-Assembling Nanoparticles at Surfaces and Interfaces” and Chem. Commun. 2021 “The influence of surface proximity on photoswitching activity of stilbene-functionalized N-heterocyclic carbene monolayers”.  From our point-of-view, they are non-relevant in our mini-review.

Author Response File: Author Response.pdf