Abstract
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.
*The experimental characterization of the materials by M.H. was supported by the US Department of Energy (DOE) Basic Energy Sciences grant DE-SC0021984. The development of the heterostructure stacking equipment was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515. The characterization of stacking processes on this system more broadly (beyond hBN/hBN) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract DE-AC02-76SF00515. M.H. acknowledges partial support from the National Security Agency through the Graduate Fellowship in STEM Diversity program. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award ECCS-2026822.
