Oral: In-Situ Alkali Metal Deposition in Graphfullerene for Cryogenic Near-Field Microscopy

The recent synthesis of graphfullerene flakes, a carbon allotrope with

fullerene molecules arranged in a hexagonal lattice through covalent in-

plane bonds and van der Waals out-of-plane interactions, can provide

insights into alkali-metal-doped 2D fullerene networks. By integrating an

alkali-metal evaporator into the sample preparation chamber of our cryo-

genic near-field optical microscope, we perform in-situ deposition and

nano-IR measurements, facilitating continuous re-dosing and characteri-

zation of alkali-metal stoichiometries, such as KxC60. By preparing sam-

ples with and without thin (<5nm) hBN encapsulation, we differentiate

between the optical responses of surface-bound and intercalated potas-

sium, revealing changes in the optical properties of graphfullerene due to

alkali-metal intercalation. Low-temperature magnetic force microscopy

(MFM) can potentially detect correlated electronic behavior and the on-

set of superconductivity. Further confirmation of superconductivity may

be achieved through terahertz near-field reflectance imaging. These tech-

niques also theoretically allow the visualization of Josephson plasmons and

other correlated phenomena in 2D superconductors. Certain stoichiome-

tries of alkali-metal-doped fullerene thin films are well known to exhibit

superconductivity at low temperatures; however, the impact of the cova-

lent in-plane bonds in graphfullerene on its superconducting properties

remains unexplored.