For the first time ever, Columbia University engineers created “artificial graphene” in a semiconductor device. The material breakthrough, the researchers say, could advance the development of optoelectronics and data processing technologies.
The story of “real” graphene, a honeycombed structure consisting of a single layer of carbon atoms, took off in 2004, when Russian-born scientists Andre Geim and Konstantin Novoselov produced the material in their University of Manchester laboratory.
The 2D creation’s unique atomic arrangement led to a variety of exciting discoveries and observations.
For one, researchers learned that graphene is an exceptional conductor, due to its ability to scatter electrons over great distances. The electron-carrying properties are an ideal match for computing technologies like touchscreens, transistors, and flash storage.
Considered a kind of wonder material by many scientists, graphene also offers superior strength and thickness.
Natural graphene, however, is somewhat limited by its honeycomb-like structure. As a natural substance, graphene exists in one, fixed atomic lattice, and all experiments must revolve around the material’s constraints.
“This places limits on the scope of studies of novel quantum phenomena linked to the honeycomb topology of graphene,” Columbia researcher Lingjie Du told Tech Briefs.
Du, along with a team of researchers from Princeton University, Purdue University, and the Instituto Italiano di Tecnologia in Italy sought to create an artificial graphene with more “tunable” electronic states – an adjustable lattice with a wide range of spacing and configurations.
Princeton and Purdue researchers began the fabrication process by growing a blank piece of gallium arsenide (GaAs) – a standard semiconductor material. Taking a page from conventional chip technology development, the team used a layering process known as molecular beam epitaxy to create the compound.
Employing electron-beam lithography, the Columbia engineers then created an array of nanodots on the semiconductor surface. The variations etched into the honeycomb structure resulted in the modulation of electronic behavior.
The team patterned a hexagonal lattice of nanofabricated pillars in which the electrons were confined in the lateral direction. By placing the nanodot sites close to one another (at a distance of approximately 50 nanometers), the artificial atoms could interact quantum mechanically, similar to the way atoms share their electrons in solids.
“This nanodot array modulates the potential energy seen by electrons so that they behave as if they are in graphene,” said Du.
The engineers’ layered structure restricts the movement of electrons to within a very narrow layer, effectively creating a 2D sheet where the particles travel nearly unimpeded.
Because the spacing between the artificial graphene’s quantum dots is much larger than natural graphene’s inter-atomic spacing, the Columbia researchers observed even more exotic quantum phenomena than ever before.
Artificial graphene has been demonstrated in optical, molecular, and photonic lattices – platforms that lack the versatility offered by semiconductor processing technologies, according to Aron Pinczuk, professor of applied physics and physics at Columbia Engineering and senior author of the study.
The material milestone, said the Columbia researcher in a December 2017 university press release, offers the possibility of new device concepts, enabled by the electrical control of graphene, and new ideas in advanced optoelectronics and data processing.
“Semiconductor artificial graphene devices could be platforms to explore new types of electronic switches, transistors with superior properties, and even, perhaps, new ways of storing information based on exotic quantum mechanical states,” said Pinczuk.
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