White Paper: Characterizing the atomic lattices of 2D crystals with AFM
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MATERIALS NEWS Similarly, ultrahigh-resolution imaging can be performed on other 2D materials. Figure 2 shows graphene grown by hightemperature molecular beam epitaxy.3 In Figure 2a, two regions of graphene, separated by a central crack, display hexagonal moiré patterns that arise from lattice mismatch between the graphene and the hexagonal boron nitride (hBN) substrate. Defects and variable periodicity in the moiré patterns represent strain-induced spatial variations in the graphene lattice constant. In the smaller-scale images in Figure 2b–d, the vectors indicate that both graphene regions (Figure 2b and d) have the same lattice orientation and are aligned with the hBN substrate (Figure 2c). The impressive spatial resolution in these images was achieved through the instrument design of Cypher AFMs. In the lateral direction, closed-loop control provides more accurate XY scanning than the open-loop operation of older AFMs. Use of symmetric design, thermally stable materials, and smaller enclosures has reduced additional scanning distortion due to thermal drift. In the vertical direction, Cypher’s noise floor has been lowered to
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