Twisted Bilayer Graphene: A Versatile Fabrication Method and the Detection of Variable Nanometric Strain Caused by Twist-Angle Disorder

Twisted bilayer heterostructures (TBHs) are materials whose physical properties depend on the twist angle between the two layers of two-dimensional (2D) materials. Those heterostructures are not found in nature, and it is quite common to fabricate them with a nonhomogeneous twist angle, giving rise to the so-called twist-angle disorder. The most reliable method used to fabricate TBHs is the tear-and-stack method, which enables production of TBHs starting from a crystal of hexagonal boron nitride that works as a stamp. However, the twisted 2D materials stay attached to the boron nitride permanently. In this paper, we present a pyramid trunk stamp that enables a versatile and easy fabrication of twisted heterostructures without the aid of boron nitride crystals. The semipyramidal stamp enables good visualization of the 2D materials, easy alignments, and transfer of 2D materials between different substrates, and the same stamp can be reused for many fabrications. We demonstrate our method producing twisted bilayer graphene (TBG), and we present an investigation based on nano-Raman hyperspectral imaging, which can be implemented to characterize regions of TBG under twist-angle disorder, strain, or doping.