Researchers break the geometric limitations of moire pattern in graphene heterostructures

Dec 23, 2019
Researchers break the geometric limitations of moire pattern in graphene heterostructures (Nanowerk News) Researchers at The University of Manchester have uncovered interesting phenomena when multiple two-dimensional materials are combined into van der Waals heterostructures (layered ‘sandwiches’ of different materials).
These heterostructures are sometimes compared to Lego bricks – where the individual blocks represent different atomically thin crystals, such as graphene, and stacked on top of each other to form new devices.
Published in Science Advances ("Composite super-moiré lattices in double-aligned graphene heterostructures"), the team focus on how the different crystals begin to alter one another’s fundamental properties when brought into such close proximity.

Fourier transformation of an AFM image of moiré patterns, showing two sets of distinct hexagonal patterns (red and green dashed hexagons).
Of particular interest is when two crystals closely match and a moiré pattern forms. This moiré pattern has been shown to affect a range of properties in an increasing list of 2D materials. However, typically the geometry of the moiré pattern places a restriction on the nature and size of the effect.
A moiré pattern is due to the mismatch and rotation between the layers of each materials which produces a geometric pattern similar to a kaleidoscope.
The team have broken this restriction by combining moiré patterns into composite ‘super-moiré’ in graphene both aligning to substrate and encapsulation hexagonal boron nitride.
The researchers demonstrate the nature of these composite super-moiré lattices by showing band structure modifications in graphene in the low-energy regime. Furthermore, they suggest that the results could provide new directions for research and devices fabrication.
Zihao Wang and Colin Woods authors of the paper said: “In recent years moiré pattern have allowed the observation of many exciting physical phenomena, from new long-lived excitonic states, Hofstadter’s Butterfly, and superconductivity.
Our results push through the geometric limitation for these systems and therefore present new opportunities to see more of such science, as well as new avenues for applications.”

Source: University of Manchester

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