Procedure for Fabrication and Characterization of van der Waals Heterostructures

A step-by-step description of the technique for manufacturing various van der Waals heterostructures is provided. First, the procedure to obtain monolayer and few-layer flakes from layered materials, in particular graphite and hexagonal boron nitride, is discussed. Next, different approaches to their assembly depending on the required final structure are considered. Finally, the procedure for making ohmic contacts is described in detail and the parameters for plasma chemistry and metal deposition are given. The field effect is discovered in transport measurements carried out at various temperatures, but a number of features, such as a strong shift of the charge neutral point from the zero-gate voltage, a large resistance away from the charge neutral point, and a low mobility, indicate a poor quality of the resulting devices. Nevertheless, one of the fabricated devices demonstrates good quality: the maximum mobility is estimated as 15 000 cm²/(V s), and the magnetic field dependences demonstrate the quantum Hall effect that is standard for high-quality graphene. Unexpectedly, scanning electron microscope images of the resulting devices reveal a large amount of contamination on the surface of the flakes, which may explain the corresponding quality of our devices. Preliminary results of flakes cleaning with chemical compounds and thermal treatment are presented.