In-situ twistable bilayer graphene

Abstract

The electrical and optical properties of twisted bilayer graphene (tBLG) depend sensitively on the twist angle. To study the angle dependent properties of the tBLG, currently it is required fabrication of a large number of samples with systematically varied twist angles. Here, we demonstrate the construction of in-situ twistable bilayer graphene, in which the twist angle of the two graphene monolayers can be in-situ tuned continuously in a large range with high precision. The controlled tuning of the twist angle is confirmed by a combination of real-space and spectroscopic characterizations, including atomic force microscopy (AFM) identification of crystal lattice orientation, scanning near-field optical microscopy (SNOM) imaging of superlattice domain walls, and resonant Raman spectroscopy of the largely enhanced G-mode. The developed in-situ twistable homostructure devices enable systematic investigation of the twist angle effects in a single device, thus could largely advance the research of twistronics.

Near-field optical characterization of atomic structures and polaritons in twisted two-dimensional materials

“…转，进而使叠层二维材料实现转角操作(如图 5a-c) [23] 。最近，Cheng Hu 等人 发展出了一种使用 AFM 探针操纵双层二维原子晶体转角的原位调控技术(如图 5d 和 e) [24] 。利用二维原子晶体在非公度状态下的超滑效应，可以使得其层间轻 易的发生相对滑动 [25,26] 。该技术的独特之处在于，在上下两层石墨烯之间，插 入了原子级厚的六方氮化硼(hBN)空心齿轮结构，在齿轮的中间空心区域，上 下两层石墨烯接触，形成转角区域。使用 AFM 探针推动 hBN 齿轮，能够精确地 控制石墨烯重叠区域的扭转角度。 这一技术为研究双层石墨烯的转角效应提供了 机会，可以在很大程度上推进转角光电子学的研究。 图 5 转角二维原子晶体的原位调控技术。 (a-c)使用 PDMS 微型半球状聚合物凝胶操纵叠 层二维材料实现转角操作。图 a，b 为方法示意图，图 c 展示了样品转角前后的光学成像。 标尺为 40μm。 [23] (d，e)使用 AFM 探针操纵双层二维原子晶体转角的原位调控技术。图 d 为方法示意图，图 e 为样品转角前后的 AFM 成像。 [24] (出自文献 [23,24] ，已获得授权) is the AFM images before and after twisting. [24] (Reproduced with permission from Ref. [23,24] ) 16,27] 、 晶界 [5] 、台阶 [28] 的极化激元性质已有大量的研究，可以预见，叠层石墨烯会提供 更丰富的光电性质。…”

“…[24] (Reproduced with permission from Ref. [23,24] ) 16,27] 、 晶界 [5] 、台阶 [28] 的极化激元性质已有大量的研究，可以预见，叠层石墨烯会提供 更丰富的光电性质。…”

Moiré straintronics: a universal platform for reconfigurable quantum materials

“…In contrast to in situ tuning of θ [41][42][43], 2D strain has the potential to tune the size and shape of the moire pattern via the three independent strain parameters c , s and φ s . In the following section, we will focus on the case of pure heterostrain (µ = 0) on homo-and heterobilayer structures and show how the different types of strain can affect the moiré lattice geometry.…”

“…In contrast to in situ tuning of θ [41][42][43], strain tuning allows a more diverse variation of the moiré size and shape. In this section, we discuss the topic from the experimental point of view.…”

“…The fabrication of magic angle graphene is challenging due to the precise rotational alignment at the angle 1.1 • [2, 3,30,74]. Recently, there have been efforts of allowing in situ tuning the stacking angle using an atomic force microscope tips [41][42][43]. However, the experimental setup involves using bulk hexagonal boron nitride rotors which lowers the flexibility of the moiré sample structure.…”