Influence of Proximity to Supporting Substrate on van der Waals Epitaxy of Atomically Thin Graphene/Hexagonal Boron Nitride Heterostructures

Abstract

Combining graphene and the insulating hexagonal boron nitride (h-BN) into two-dimensional heterostructures is promising for novel, atomically thin electronic nanodevices. A heteroepitaxial growth, in which these materials are grown on top of each other, will be crucial for their scalable device integration. However, during this so-called van der Waals epitaxy, not only the atomically thin substrate itself must be considered but also the influences from the supporting substrate below it. Here, we report not only a substantial difference between the formation of h-BN on single- (SLG) and on bi-layer epitaxial graphene (BLG) on SiC, but also vice versa, that the van der Waals epitaxy of h-BN at growth temperatures well below 1000 °C affects the varying number of graphene layers differently. Our results clearly demonstrate that the additional graphene layer in BLG enhances the distance to the corrugated, carbon-rich interface of the supporting SiC substrate and thereby diminishes its influence on the van der Waals epitaxy, leading to a homogeneous formation of a smooth, atomically thin heterostructure, which will be required for a scalable device integration of 2D heterostructures.

The impact of ultraviolet laser excitation during Raman spectroscopy of hexagonal boron nitride thin films

“…Another complication is added when h‐BN is combined with graphene in vdW heterostructures: The h‐BN E 2g phonon mode might interfere with the relatively broad defect‐related D peak of graphene appearing in the same spectral regions for visible excitation. [ 20,21 ] A similar problem is found for heterostructures formed of h‐BN and epitaxial graphene on SiC(0001), where even in the absence of a D peak, the h‐BN signal can superimpose with the Raman signal originating from the 6(√3 × √3) R 30° interfacial layer between graphene and SiC (also known as buffer layer), [ 18 ] which consists of broad bands spreading over 1200 and 1660 cm −1 . [ 23 ]…”

“…For their preparation, various methods have been employed, the most common still being mechanical exfoliation of micrometer-sized flakes from bulk h-BN crystals. [12,13] Nevertheless, aiming at the realization of large-area synthesis-a crucial step towards applications-scalable approaches such as chemical vapor deposition (CVD), [14] metalorganic vapor phase epitaxy, [15] atomic layer deposition, [16] and molecular beam epitaxy (MBE) [10,[17][18][19][20][21] have been explored as well. Here, it is particularly important to be able to evaluate the quality of the synthesized films regarding their structure and optoelectronic properties and compare it, for instance, with results achieved for state-of-the-art bulk h-BN crystals.…”

“…[25] This avoids overlapping between the D peak and the E 2g optical phonon of h-BN, which has been proven highly beneficial for the evaluation of the individual properties of h-BN co-existing with graphene in large-area heterostructures. [18,21] Finally, for the case of atomically thin h-BN grown on top of metallic substrates such as Ni, another benefit of Raman analysis under UV excitation is the absence of an inhomogeneous luminescence originating from the underlying metal, [21] which results in a strong background signal and is observed when visible wavelength excitation is employed. [17] Such an asset of UV Raman is also anticipated to hold true for broad luminescence signals originating from precursor impurities during CVD-based synthesis or residual contamination associated with transfer processes of h-BN layers.…”

Controllable Preparation of 2D Vertical van der Waals Heterostructures and Superlattices for Functional Applications

“…[47][48][49] In addition to CVD technology, magnetron sputtering and MBE can also enable the growth of h-BN on graphene. [50][51][52] High-quality multilayer h-BN films with controllable layers on Ru(0001) or Gr/Ru(0001) substrates have been generated by the magnetron sputtering of B in N 2 /Ar (Figure 3b,c). [50] Interestingly, direct growth on Ru(0001) produces h-NB with A-A′-A stacking, whereas the termination of the Ru surface with ML graphene preferentially forms h-BN with A-B-C stacking (r-BN) (Figure 3d).…”

“…[ 50 ] r‐BN provides a more facile, diffusionless pathway for the transformation to cubic BN. Heilmann et al [ 51 ] demonstrated the strong influence of the number of graphene layers on the vdW epitaxial growth of h‐BN by MBE. The additional layer in bilayer graphene enhances the distance to the corrugated, carbon‐rich interface of the supporting SiC substrate and thus diminishes its influence on the vdW epitaxy, contributing to the homogeneous formation of h‐BN and thereby forming atomically smooth heterostructures (Figure 3e).…”