Origami folded 2D-crystals

Details

Supervisors

Hackens, Benoît

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux

Abstract

After the discovery of graphene, 2D crystals raised a huge interest and researches around this area have kept growing ever since. Amongst those 2D materials, hBN stands out. With its structure analogue to graphene and its large band gap, it is a basic building block of complex architectures (heterostructures,...). As any other material, 2D crystals develop defects (vacancies, wrinkles,...) that affect strongly their properties. In hBN deposited on a SiO2 substrate, wrinkles produced by high-temperature annealing have been reported. They seem oriented in a peculiar way linked somehow to the symmetry of the crystal. For this work, a similar experiment on hBN was performed with BaF2 as substrate. The topography of the resulting wrinkles was measured by atomic force microscopy and their geometrical parameters were studied as a function of critical experimental parameters. Moreover, electrostatic force microscopy revealed a local polarisation around the wrinkles. Indeed, a particular mechanical-electrical coupling was predicted for such crystal: a gradient of deformation should induce a local polarisation. This properties is known as flexoelectricity and could be exhibited by the wrinkles. A significant difference in the surface potential between the flat and the wrinkled regions of hBN flakes has been detected.