Broad background in electron diffraction of 2D materials as a signature of their superior quality

Abstract

An unusually broad bell-shaped component (BSC) has been previously observed in surface electron diffraction on different types of 2D systems. It was suggested to be an indicator of uniformity of epitaxial graphene (Gr) and hexagonal boron nitride (hBN). In the current study we use low-energy electron microscopy and micro-diffraction to directly relate the BSC to the crystal quality of the diffracting 2D material. Specially designed lateral heterostructures were used to map the spatial evolution of the diffraction profile across different 2D materials, namely pure hBN, BCN alloy and pure Gr, where the alloy region exhibits deteriorated structural coherency. The presented results show that the BSC intensity has a minimum in the alloyed region, consequently showing that BSC is sensitive to the lateral domain size and homogeneity of the material under examination. This is further confirmed by the presence of a larger number of sharp moiré spots when the BSC is most pronounced in the pure hBN and Gr regions. Consequently, it is proposed that the BSC can be used as a diagnostic tool for determining the quality of the 2D materials.

Interplay of Kinetic Limitations and Disintegration: Selective Growth of Hexagonal Boron Nitride and Borophene Monolayers on Metal Substrates

“…In addition to the moiré satellites, all h BN integer order spots exhibit a broad bell-shaped component (BSC) of diffuse intensity; see Figure (a) and the intensity line profile shown in Figure (b). Such BSC is not caused by defects, and has also been reported for high-quality layers of several other 2DMs. ,,, …”

“…The pattern exhibits 3-fold symmetry reflecting the underlying symmetry of the Ir(111) substrate and the 3-fold symmetry of the h BN layer . It is well-known that many 2D systems form moiré networks as result of the different lattice spacing and possible rotation of the 2D layer and substrate. ,− For h BN on Ir(111) such moiré pattern has been observed in diffraction ,,− and STM. , In the SPA-LEED images of Figure the unambiguous identifier of such h BN related moiré pattern is a hexagonal network of satellite spots surrounding the (00) spot and all integer order diffraction spots.…”

Probing the Intrinsic Strain in Suspended Graphene Films Using Electron and Optical Microscopy

“…Further characterization using low‐energy electron diffraction (LEED) can be beneficial to quantify CVD graphene quality and complement the current findings. [ 31 , 32 ] Although, doping and strain properties of our graphene films can be characterized using the methods presented in our work, extensive atomic‐scale characterization is essential and complementary to assess the graphene quality.…”