In Situ Monitoring of Growth of Vertically Stacked h-BN/Graphene Heterostructures on Ni Substrates and Their Interface Interaction

Round 1

Reviewer 1 Report

The authors report on the vertically stacked h-BN/graphene heterostructures with high coverage are synthesized by chemical vapor deposition (CVD) of h-BN on Ni substrates followed by segregation growth of graphene at h-BN/Ni interfaces, which are monitored by in situ surface microscopy and surface spectroscopy. They used synchrotron-based local XPS and XPEEM to reveal that the stacking order of the heterostructure is h-BN upper on graphene and the monolayer and multilayer graphene both from underneath the h-BN. The h-BN/Ni interfaces are decoupled by the graphene interlayers, and the decoupling effect is enhanced by the thicker graphene layers. Besides, a boundary confinement effect of h-BN on the underneath graphene is rationally proposed, where the segregated graphene layers underneath h-BN hardly extend across h-BN domain boundaries. This work provides more insights into the understanding of the fabrication, the stacked structure, and the interface interaction for h-BN/graphene heterostructures. I find the manuscript well-structured and in general convincing. I recommend this article for the publication in Surfaces after minor revision, along the lines suggested hereafter.

Comment 1: They authors emphasize that near-surface C species is the main source for graphene segregation, which is critical for producing the heterostructures. How to control the near-surface C concentration and further the graphene layers? Does the method combining CVD for h-BN and segregation for graphene be available to prepare the vertical h-BN/graphene heterostructures on other substrates?

Comment 2: The description and explanation for the boundary confinement effect are simple but elegant. Under the h-BN domains, graphene is keeping segregation for a long time (156 min) and cannot grow across the h-BN domain boundary. If the concentration of near-surface C species increases, the driving force of graphene segregation would be enhanced, which may provide a possibility to assist the graphene to extend outside the h-BN domain boundary. How do you think the effect of this enhanced growth driving force on overcoming the h-BN boundary trapping? Please give a reasonable comment.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Paper has scientific value for facilitating the synthesis and applications of Van der Waals heterostructures. However, its English needs to be changed.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper by Wei et al. reports on the interfacial interactions of vertically stacked heterostructures formed by h-BN/graphene/Ni(111). The degree of innovation is good, as well as the potential impact, also considering the high relevance of the topic. However, different amendments are mandatory before publication:

• Energy calibration in XPEEM has some imperfections. It is well known that in graphene on Ni(111) the C-1s has two main components around 284.7 and 284.4 eV ¹ arising from two coexisting graphene structures, with minor components at 283.2 eV (surface nickel carbide) and 283.8 eV (interstitial carbon dissolved into the near surface Ni layers). Perhaps a calibration with Au reference could be helpful.
• The I(V) curve for Ni is featureless, so that the reflectivity seems to have a monotonic decrease with increasing energy. However, in crystalline materials the phase relations in the scattering between the atoms focusses the scattered electrons into diffracted beams and modifies the backscattered intensity with pronounced maxima. The behavior of I(V) for clean Ni(111) in Ref. ² seems to differ from that in Fig. 2c. Similarly, a comparison with the behavior of I(V) in graphene/Ni(111) in LEEM experiments by Locatelli and coworkers should be provided, in consideration of some existing differences ³.
• In the Introduction, the authors write that “Previous studies mainly focus on preparation methods, while interface interaction in the heterostructures has not been explored”. This is quite generic. Readers would benefit from a clear picture regarding the state of the art with a careful survey of existing literature. Moreover, it is not properly correct that no surface-science techniques were used up to now. Other sentences in the Introduction are quite generic (e.g. the first sentence of the Introduction) with some redundant bibliography.
• Both Conclusions and Discussion should be extended.
• The readability of axis labels in graphs should be improved.
• Some grammar errors are present (e.g. “are choose”).

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The revised version of the manuscript is ready for publication