Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

Abstract

A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

Centimeter-sized epitaxial h-BN films

“…The growth of h-BN in our experiments appears to be initiated from dense, multiple points on the Ni(111) surface, which already cover a large percentage of the whole area of the surface even after a duration of 30 s. This is in contrast to previous chemical vapor deposition works where individual grains with a low density grew larger and then covered the entire film. 15,16,21 As the growth time increases, each h-BN nucleus merged into several multilayered h-BN patches, and then films with complete coverage were finally formed (see Supplementary Figures S3a,b and Supplementary Information). Nevertheless, in our case, a strong epitaxial relationship between the h-BN film and the Ni(111) surface presumably led to the formation of a single-oriented h-BN film.…”

“…[17][18][19][20] Accordingly, large-area single crystalline h-BN layers are desired to fully realize the potential advantages of h-BN in device applications. To this end, efforts on controlling the size and direction of individual domains of h-BN have been reported; 15,16,21,22 however, obtaining large-scale single crystalline h-BN films remains challenging. Here, we report the synthesis of epitaxial h-BN films on the centimeter scale while maintaining a low cost of production by re-using the Ni(111) substrates via electrochemical delamination.…”

“…However, the large-area h-BN layers prepared by chemical vapor deposition usually exhibit polycrystalline structures with a typical average grain size of several microns [12][13][14] or tens of microns. 15,16 Grain boundaries or dislocations in polycrystalline h-BN can affect its electronic or mechanical properties, resulting in a lower band gap energy, higher leakage current and poorer mechanical strength. [17][18][19][20] Accordingly, large-area single crystalline h-BN layers are desired to fully realize the potential advantages of h-BN in device applications.…”

Probing the Atomic Structures of Synthetic Monolayer and Bilayer Hexagonal Boron Nitride Using Electron Microscopy

“…Variations in the chemical potential of constituent elements can occur experimentally when different processes and substrates are used or when the Cu substrates are subjected to a pretreatment (i.e., oxidation) (Zhang et al, 2016), as in this scenario. To date, several other experimental approaches to obtaining similar hexagonal-shaped domains have been reported (Stehle et al, 2015;Tay et al, 2016b;Wang et al, 2015a;Wu et al, 2015;Yin et al, 2015b). The coexistence of ZZ N and ZZ B edges is further verified by the observation of truncated triangular-shaped domains (Fig.…”

“…To identify the epitaxial relation between h-BN and Cu, the crystallography of the Cu substrate can be mapped using electron backscatter diffraction (EBSD) and the mapped region can then be correlated to the orientations of the h-BN crystals using the aforementioned atomic configurations (Wood et al, 2015;Wu et al, 2015). In particular, for this analysis, triangular-shaped domains are preferred for the identification of a crystal's orientation.…”