Lab talk
Apr 26, 2012
Nano-ponds modify properties of hexagonal boron nitride layers
Hexagonal boron nitride (h-BN) is well suited as a substrate to form ultra-fast transistors with graphene. In many examples and prototypes that have been reported, h-BN layers are mechanically exfoliated onto silicon oxide supporting substrates. In a subsequent step, graphene layers are laid on the h-BN layer, which enables the fast carrier transport in graphene. Now, researchers at Universidade Federal de Minas Gerais, Brazil, have studied the influence of trapped water nano-ponds on the properties of such h-BN layers.
The team has observed that, during normal exfoliation procedures, a thin water layer is trapped between the h-BN flake and the silicon oxide substrate (click on image for detail). Using electric force microscopy experiments and theoretical simulations, the scientists have shown that this confined water layer has a peculiar behaviour: a preferred electrical polarization direction.
Due to confining effects, a net polarization, perpendicular to the h-BN surface that sandwiches the water layer, affects its response to an electric field. In other words, there is an anomalous response of h-BN flakes to electric fields applied in its surface normal direction. Since this is the direction used to gate transistors, h-BN-based devices are likely to respond differently than expected due to the water effect.
Full details can be found in the journal Nanotechnology.
About the author
Camilla Oliveira and Matheus Matos are graduate students in the Physics Department of Universidade Federal de Minas Gerais. This work is the result of a collaboration between the Condensed Matter theory group (Matheus Matos, Prof. Mario Mazzoni and Prof. Helio Chacham) and the SPM group (Camilla Oliveira and Prof. Bernardo Neves). Both groups have several projects in common, focused mainly on the physical properties of carbon nanostructures (graphene, nanotubes, etc) and other 2D materials (h-BN, MoS2, etc).
