Scientists at the Department of Energy’s Oak Ridge National Laboratory have made the first direct observations of a one dimensional boundary separating two different, atom-thin materials, enabling studies of long-theorised phenomena at these interfaces.
Theorists have predicted the existence of intriguing properties at one dimensional (1D) boundaries between two crystalline components, but experimental verification has eluded researchers because atomically precise 1D interfaces are difficult to construct.
‘While many theoretical studies of such 1D interfaces predict striking behaviours, in our work we have provided the first experimental validation of those interface properties,’ said ORNL’s An-Ping Li in a statement.
The new Nature Communications study builds on work by ORNL and University of Tennessee scientists published in Science earlier this year that introduced a method to grow different two dimensional materials – graphene and boron nitride – into a single layer only one atom thick.
The team’s materials growth technique unlocked the ability to study the 1D boundary and its electronic properties in atomic resolution. Using scanning tunnelling microscopy, spectroscopy and density-functional calculations, the researchers first obtained a comprehensive picture of spatial and energetic distributions of the 1D interface states.
‘In three dimensional (3D) systems, the interface is embedded so you cannot get a real-space view of the complete interface – you can only look at a projection of that plane,’ said Jewook Park, ORNL postdoctoral researcher and the lead author of the work. ‘In our case, the 1D interface is completely accessible to real-space study,’
‘The combination of scanning tunnelling microscopy and the first principles theory calculations allows us to distinguish the chemical nature of the boundary and evaluate the effects of orbital hybridisation at the junction,’ said ORNL’s Mina Yoon, a theorist on the team.
The researchers’ observations are said to have revealed a highly confined electric field at the interface and provided an opportunity to investigate a phenomenon called a ‘polar catastrophe,’ which occurs in 3D oxide interfaces. This effect can cause atomic and electron reorganization at the interface to compensate for the electrostatic field resulting from materials’ different polarities.
‘This is the first time we have been able to study the polar discontinuity effect in a 1D boundary,’ Li said.
Although the researchers focused on gaining a fundamental understanding of the system, they note their study could culminate in applications that take advantage of the 1D interface.
‘For instance, the 1D chain of electrons could be exploited to pass a current along the boundary,’ Li said. ‘It could be useful for electronics, especially for ultra-thin or flexible devices.’
The team plans to continue examining different aspects of the boundary including its magnetic properties and the effect of its supporting substrate.
The study is published as ‘Spatially resolved one dimensional boundary states in graphene–hexagonal boron nitride planar heterostructures.’
Coauthors are ORNL’s Jewook Park, Jaekwang Lee, Corentin Durand, Changwon Park, Bobby Sumpter, Arthur Baddorf, Mina Yoon and An-Ping Li; the University of Tennessee’s Lei Liu, Ali Mohsin, and Gong Gu; and Central Methodist University’s Kendal Clark.