Graphene has been hailed as the wonder material for the post-silicon era slated to start circa 2028 by theInternational Technology Roadmap for Semiconductors. Its electron mobility at room temperature is already over 10-times that of silicon (15.000 cm2/Vs compared to 1,400 cm2/Vs, respectively). Now, however, a group for researchers at the University of British Columbia (UBC) had pushed it to infinity—superconductivity—by doping it with lithium and cooling it to 5.9 degrees Kelvin. But this is only the beginning, since UBC professor Andrea Damascelli hopes to push doped graphene into higher temperatures of criticality (Tc is when it becomes superconducting) using the same methods as his predecessors, plus a little secret sauce of his own.

"Increasing the ultimate value of Tc achievable on monolayer graphene is at present our key goal," Damasdcelli told EE Times. "We are exploring specific combinations of new substrates and dopants in order to further enhance and stabilize superconductivity, in much the same way that enhanced transition temperatures have been achieved in other two-dimensional quantum materials, such as single-layer FeSe."

Damasdcelli has already been experimenting with all sort of dopants in single atomic layers (monolayers) of graphene, measuring whether the adsorbed atoms (adatoms) are diffusing over the surface and get stuck (intercalate) within the graphene lattice.

"The key advantages of one dopant versus the other are the easiness in donating the right amount of electrons to monolayer graphene, the stability of the adatoms on the graphene surface (some diffuse or intercalate more easily than others, which may be detrimental to stabilizing superconductivity), as well as the modification they induce in the interaction between electrons and atomic vibration of the graphene layer which in the end directly controls the strength of superconductivity and the value of the critical temperature. Finding the ideal dopants—the most stable and the ones leading to the highest Tc—is crucial for possible future applications."

Damasdcelli was assisted in his work by the Max Planck Institute (Stuttgart, Germany) where his samples were fabricated in the lab of researcher Ulrich Starke under the Graphene Flagshipprogram, the E.U.s biggest ever research project.

"Our monolayer graphene was epitaxially grown [under an argon atmosphere on hydrogen-etched silicon carbide substrates] by our collaborators at the Max Planck Institute in Stuttgart, in re4searcher Ulrich Starke's group. These samples were reconditioned [annealed at 500 degrees Celsius] immediately before the angle resolved photo emission spectroscopy (ARPES) measurements in our chamber at UBC in the Quantum Materials Lab, to obtain atomically-clean pristine graphene," Damasdcelli told us. "Lithium adatoms were then deposited in ultra-high-vacuum conditions from a commercial alkali metal source, with the graphene samples held at a temperature of 8 degrees Kelvin. The low temperature turned out to be key in being able to decorate graphene with a well ordered Li-superstructure, which in turn is essential for observing superconductivity."

Next Damasdcelli group at UBC, with associates worldwide, is tuning all the parameters of his doped graphene material in hopes of eventually getting it to superconduct at normal atmospheric pressures and at room temperature, or at least at temperatures that are more convenient for commercial products (such as the temperature of liquid nitrogen, 77 degree Kelvin, which is relatively easy to maintain in equipment).

Also contributing to the work was Bart Ludbrook, a former post-doctoral researcher in Damascelli’s group at UBC.