Rebeca Ribeiro (C2N Marcoussis) : On-demand band structure modification in graphene/BN heterostructures by active angle control

lundi 9 avr. 2018, 14:00 → 16:00 Europe/Paris

Amphi Charpak (LPNHE)

In situ band structure manipulation of 2D materials offers unique
opportunities toward understanding of multiple physical phenomena and the
design of novel opto-electronic devices. A simple, yet effective, way to
modify the band structure of these materials is by controlling the relative
orientation between the layers in van der Waals heterostructures. The
clearest example of this effect is graphene on hexagonal boron nitride
(BN), in which the layer orientation determines the wavelength of the Moiré
superlattice, which in turn modifies the native band structure of graphene
opening an energy gap and generating minigaps at higher energies. However,
current techniques are limited to fabrication of samples with fixed
interlayer angles. Studies of angular dependence are therefore limited to
static properties, and require multiple samples, which imposes experimental
challenges and introduces uncertainty due to sample-to-sample variations.
Here we present optical, mechanical and electronic characterization of
BN/graphene/BN heterostructures where the angle between layers is changed
continuously with a control of 0.2 degrees. In room-temperature
experiments, we confirm the layer alignment by measurement of the angle-
dependent broadening of the Raman 2D peak, consistent with previous
results. As the layers approach alignment, friction between the BN and
graphene increases and electronic transport measurements show satellite
resistance peaks growing and moving toward the main peaks at charge
neutrality. The energy gaps for the main and satellite peaks, as determined
from low-temperature measurements, show remarkably different angular
dependence. Combining these three measurements in the same device
demonstrates the new capability to precisely tune in situ optical,
mechanical and electronic properties of a van der Waals heterostructure.
Our new experimental technique opens the possibility to study the angle-
dependent properties of van der Waals heterostructures and in situ band
structure engineering of 2D materials.