Data for: Deterministic fabrication of graphene/hexagonal boron nitride moire superlattices

The electronic properties of moire heterostructures depend sensitively on the relative orientation between layers of the stack.
For example, near-magic-angle twisted bilayer graphene (TBG) commonly shows superconductivity, yet a TBG sample with one of the graphene layers rotationally aligned to a hexagonal Boron Nitride (hBN) cladding layer provided the first experimental observation of orbital ferromagnetism. To create samples with aligned graphene/hBN, researchers often align edges of exfoliated flakes that appear straight in optical micrographs. However, graphene or hBN can cleave along either zig-zag or armchair lattice directions, introducing a 30 degree ambiguity in the relative orientation of two flakes. By characterizing the crystal lattice orientation of exfoliated flakes prior to stacking using Raman and second-harmonic generation for graphene and hBN, respectively, we unambiguously align monolayer graphene to hBN at a near-0 degrees, not 30 degrees, relative twist angle. We confirm this alignment by torsional force microscopy (TFM) of the graphene/hBN moire on an open-face stack, and then by cryogenic transport measurements, after full encapsulation with a second, non-aligned hBN layer. This work demonstrates a key step toward systematically exploring the effects of the relative twist angle between dissimilar materials within moire heterostructures.

莫尔异质结（moire heterostructures）的电子性质对堆叠层间的相对取向具有极强的敏感性。例如，近魔角扭转双层石墨烯（twisted bilayer graphene, TBG）通常表现出超导性，而将其中一层石墨烯与六方氮化硼（hexagonal Boron Nitride, hBN）包覆层旋转对齐的TBG样品，则首次实验观测到了轨道铁磁性。为制备石墨烯/六方氮化硼对齐样品，研究者通常会对齐在光学显微图像中呈现为直线的剥离薄片的边缘。然而，石墨烯或六方氮化硼可沿锯齿型（zig-zag）或扶手椅型（armchair）晶格方向解理，这会为两片薄片的相对取向带来30度的不确定性。我们分别利用拉曼（Raman）光谱和二次谐波产生（second-harmonic generation）对石墨烯与六方氮化硼的剥离薄片进行堆叠前的晶格取向表征，从而将单层石墨烯与六方氮化硼以近0度（而非30度）的相对扭转角实现精准对齐。我们通过对开放式堆叠的石墨烯/六方氮化硼莫尔结构进行扭转力显微镜（torsional force microscopy, TFM）表征，并在使用第二层非对齐六方氮化硼层完成完全封装后开展低温输运测量，验证了该对齐效果。本研究为系统探究莫尔异质结中不同材料间相对扭转角的影响迈出了关键一步。