Surface of Room-Temperature-Stable Electride [Ca24Al28O64]4+(e-)4: Preparation and Its Characterization by Atomic-Resolution Scanning Tunneling Microscopy

The nanocage compound crystal [Ca24Al28O64](4+)(e(-))(4) (C12A7:e(-)) is a room-temperature-stable electride. Although bulk C12A7:e(-) exhibits metallic conduction, the surface of an as-prepared sample or one prepared by mechanical fracture In ultrahigh vacuum is almost insulating and exhibits distinct non-ohmic contact. We studied whether the Intrinsic surface of this electride exhibits metallic conduction or not by examining various conditions for preparing the Intrinsic surface :A combination Of sputtering with thermal annealing led to the emergence of metallic conductivity in a specific condition. Suitably prepared surfaces revealed ohmic contact even In an ambient atmosphere. Atomic-resolution scanning tunneling microscopy (STM) images of the surfaces were consistent with a,structural,model,in which the cage structure in the bulk C12A7:e(-) electride is conserved at the surface.