New view of nanoribbons


Rebecca Pool

Thursday, August 9, 2018 - 21:15
Scanning tunneling microscope image of a hybrid nanoribbon composed of wide and narrow segments. 
US-based researchers have fabricated hybrid nanoribbons with new electronic and magnetic properties that hold huge potential in 1D material design and quantum computing.
Stunning scanning tunnelling microscopy images of a nanoribbon superlattice reveal electrons trapped at the junction between wide and narrow ribbon segments, that have been joined together.
"We've spent years changing the properties of nanoribbons using more conventional methods," highlights Professor Michael Crommie from the University of California Berkeley. "But playing with their topology gives us a powerful new way to modify the fundamental properties of nanoribbons that we never suspected existed until now."
Only last year, theoretical physicist Professor Steven Louie from UC Berkeley predicted that joining two types of nanoribbon - with different electron topologies - would yield a unique material that immobilises single electrons at the junction between the graphene structures.
Excited by this concept, Berkeley colleagues Crommie and Professor Felix Fischer set out to experimentally demonstrate that the junction of nanoribbons with the appropriate topology would trap electrons.
Fischer developed a new method to chemically synthesise atomically precise nanoribbon structures from the complex carbon compound, anthracene, which, crucially, displayed the necessary properties to form electron-trapping junctions.
STM image shows a hybrid graphene nanoribbon composed of a topologically non-trivial nanoribbon (9 carbon atoms across) joined to a topologically trivial nanoribbon (7 carbon atoms across). Electrons are trapped at each junction.
The complex molecules were heated on a gold catalyst in a vacuum chamber to form nanoribbons, with Crommie then using STM to image the nanoribbon electronic structure.
According to the researchers, STM results perfectly matched Louie's theoretical calculations, with the hybrid nanoribbons having between 50 to 100 junctions, each occupied by an individual electron that could quantum mechanically interact with its neighbours.
“When you heat the building blocks, you get a patchwork quilt of molecules knitted together into this beautiful nanoribbon,” says Crommie. “But because the different molecules can have different structures, the nanoribbon can be designed to have interesting new properties.”
According to Fischer, the length of each segment of nanoribbon can be varied to change the distance between trapped electrons, changing how these charged particles interact quantum mechanically.
For example, when close together the electrons interact strongly and split into two quantum states whose properties can be controlled, allowing the fabrication of new 1D metals and insulators. 
However, when the trapped electrons are slightly more separated, they act like small, quantum magnets that can be entangled and are ideal for quantum computing.
“This provides us with a completely new system that alleviates some of the problems expected for future quantum computers, such as how to easily mass-produce highly precise quantum dots with engineered entanglement that can be incorporated into electronic devices in a straightforward way,” says Fischer.
Research is published in Nature.
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