How can metal atoms be trapped inside fullerene cages?

To produce endohedral fullerene species, in which a metal atom is physically trapped inside a carbon cage, scientists typically use a vaporization technique. Specifically, graphite disks or rods are impregnated with the desired metal—such as an alkali metal, alkaline earth metal, or early lanthanoid—and then vaporized.1

This process allows the metal atoms to be encapsulated within the forming fullerene structures. The resulting compounds are assigned formulas such as M@C${}_{60}$, where M represents the trapped metal atom.1

While this method is standard for metals, other substances can be trapped using different techniques. For instance, helium can be introduced into the cage by heating C${}_{60}$ in helium vapour under high pressure.1