On April 28, it was announced that Junhao Lin, a Vanderbilt University Ph.D. student and visiting scientist at Oak Ridge National Laboratory (ORNL), has managed to create metallic wires that are only three atoms wide. This is three orders of magnitude smaller than the width of wires that are used in most modern electronics.
“Junhao took this project and really ran with it,” said Sokrates Pantelides, University Distinguished Professor of Physics and Engineering at Vanderbilt University and Lin's advisor. “The technique represents an exciting new way to manipulate matter at the nanoscale and should give a boost to efforts to create electronic circuits out of atomic monolayers, the thinnest possible form factor for solid objects.”
The nanowires are made from transition-metal dichalcogenides (TMDCs), a family of semiconducting materials that naturally form monolayers. TMDCs consist of a transition metal (found in the d-block and f-block of the Periodic Table) and two atoms of a chalcogen element (found in group 16 of the Periodic Table). Nanowires composed of molybdenum or tungsten combined with sulfur or selenium have been predicted to be metallic, and electrical measurements have now confirmed this.
“Junhao used a scanning transmission electron microscope (STEM) that is capable of focusing a beam of electrons down to a width of half an angstrom (about half the size of an atom) and aims this beam with exquisite precision,” said Wu Zhou, ORNL Wigner Fellow and Lin's microscopy mentor.
Atomic monolayers are the focus of many materials scientists because of their exceptional electron mobility, flexibility, strength, and transparency. Graphene, a single layer of carbon atoms arranged in a honeycomb-like lattice, was the first such material, but TMDCs have proven to have more practical applications. Other research groups have created transistors and flash memory gates from TMDCs, but they have had to use other materials to connect them.
“This will likely stimulate a huge research interest in monolayer circuit design,” Lin said. “Because this technique uses electron irradiation, it can in principle be applicable to any kind of electron-based instrument, such as electron-beam lithography.” In addition, Lin envisions that the STEM technique could be used to create three-dimensional circuits by stacking TDMC monolayers and connecting them with the newly discovered nanowires.
“If you let your imagination go, you can envision tablets and television displays that are as thin as a sheet of paper that you can roll up and stuff in your pocket or purse,” Pantelides commented.