Grütter and his fellow McGill and GM researchers describe the "quantum weirdness" in a paper appearing in Proceedings of the National Academy of Sciences. The researchers investigated an ultra-small contact between gold and tungsten, two metals currently used in combination in semiconductors to connect different functional components of a device.
Grütter's lab used advanced microscopy techniques to image a tungsten probe and gold surface with atomic precision, and to bring them together mechanically in a precisely-controlled manner. The electrical current through the resulting contact was much lower than expected, they said. Mechanical modeling of the atomic structure of this contact was done in collaboration with Yue Qi, a research scientist with the General Motors R&D Center in Warren, Mich.
Electrical modeling confirmed this result, showing that dissimilarities in electronic structure between the two metals leads to a fourfold decrease in current flow, even for a perfect interface, the researchers said. They also found that crystal defects—displacements of the normally perfect arrangement of atoms—generated by bringing the two materials into mechanical contact was a further reason for the observed reduction of the current.
McGill student Till Hagedorn peers into a field ion microscope.
"The size of that drop is far greater than most experts would expect—on the order of 10 times greater," Grütter said.
According to Grütter, the results point to a need for future research into ways to surmount this challenge, possibly through choice of materials or other processing techniques. "The first step toward finding a solution is being aware of the problem," Grütter said. "This is the first time that it has been demonstrated that this is a major problem" for nanoelectronic systems."