Novel two-dimensional materials and their heterostructures constructed in ultra-high vacuum

Compared with the three-dimensional bulk materials, two-dimensional (2D) materials exhibit superiorelectronic, optical, thermal, and mechanical properties due to the reduced dimensionality. The quantumconfinement effect of 2D materials gives rise to exotic physical properties, and receives extensive attention ofthe scientists. Lots of routes to fabricate the 2D materials have been proposed by the material scientists,including the traditional mechanical exfoliation, chemical vapor deposition, molecular beam epitaxy under ultra-high vacuum (UHV), and so on. Among them, fabricating materials under ultra-high vacuum has theadvantages of constructing large-scale and high-quality samples, and is therefore widely adopted in the 2Dmaterial growth. In this paper, we review three different strategies of growing 2D materials under UHVconditions, including molecular beam epitaxy, graphene intercalation and manual manipulation by nano probes.We compare the advantages and drawbacks among those methods in creating 2D materials, and try to providesome guidance to the community, especially those who are new to the field.