Effect of annealing on interfacial moiré relaxation in marginally twisted hexagonal boron nitride

In emerging twistronics, the precise control of interlayer twist angles is necessary to generate novel correlated states or engineer confinement within moiré potentials. Many of these van der Waals heterostructures (vdWh) are encapsulated in hexagonal boron nitride (hBN) using dry transfer techniques that may require high temperatures. There is a general concern that extended heating of vdWh may drive moiré relaxation and perturb the interfacial twist angle. Although moiré relaxation due to high temperature annealing has been studied in graphene and chalcogenide twisted bilayers, the thermal relaxation of the twisted hBN interface is poorly understood. Here, we study the relationship between thermal annealing and twist angle relaxation at twisted hBN interfaces using a combination of scanning probe microscopy and optical spectroscopy. Based on time-resolved annealing studies, we establish preliminary bounds on the thermal budget of the hBN/hBN moiré stability, and find that marginally twisted hBN shows no significant changes in twist angle after annealing for time intervals and temperatures consistent with – or even exceeding – standard dry transfers. These results suggest that some moiré interfaces exhibit greater stability against thermally-driven lattice relaxation, which will inform future efforts to control moiré interfaces.