Abstract
Twisted bi-layer graphene (tBLG) has attracted much attention because of its unique band structure and properties. The properties of tBLG vary with small differences in the interlayer twist angle, but it is difficult to accurately adjust the interlayer twist angle of tBLG with the conventional fabrication method. In this study, we introduce a facile tBLG fabrication method that directly picks up a single-crystalline graphene layer from a growth substrate and places it on another graphene layer with a pre-designed twist angle. Using this approach, we stacked single-crystalline graphene layers with controlled twist angles and thus fabricated tBLG and twisted multi-layer graphene (tMLG). The structural, optical and electrical properties depending on the twist angle and number of layers, were investigated using transmission electron microscopy (TEM), micro–Raman spectroscopy, and gate-dependent sheet resistance measurements. The obtained results show that the pick and place approach enables the direct dry transfer of the top graphene layer on the as-grown graphene to fabricate uniform tBLG and tMLG with minimal interlayer contamination and pre-defined twist angles.
Highlights
Bi-layer graphene, in which two sheets of monolayer graphene are stacked, has unique physical and electrical properties that are different from monolayer graphene [1,2]
Twisted bilayer graphene, in which two sheets of monolayer graphene are stacked with a twist angle, has received considerable attention because its unique properties depend on a twist angle such as van Hove singularities [5], tunable optical conductivity [6], and renormalization of Fermi velocity [7,8]
The polypropylene carbonate (PPC)/PDMS stamp had a weak adhesion with graphene but a strong adhesion with gold, so the gold pattern and the underlying graphene could be selectively lifted from the Ge substrate
Summary
Bi-layer graphene, in which two sheets of monolayer graphene are stacked, has unique physical and electrical properties that are different from monolayer graphene [1,2]. Instead of single-layer graphene without a bandgap, AB stacked bi-layer graphene has been studied as a channel material of a new transistor structure [4]. Twisted bilayer graphene, in which two sheets of monolayer graphene are stacked with a twist angle, has received considerable attention because its unique properties depend on a twist angle such as van Hove singularities (vHSs) [5], tunable optical conductivity [6], and renormalization of Fermi velocity [7,8]. TBLG has been fabricated by folding [6,11] or stacking [12,13,14] exfoliated graphene flakes
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