Surface of room-temperature-stable electride [Ca24Al28O64]4+(e-)4: preparation and its characterization by atomic-resolution scanning tunneling microscopy

ACS Nano. 2011 Mar 22;5(3):1907-14. doi: 10.1021/nn102839k. Epub 2011 Mar 1.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aluminum Compounds / chemical synthesis*
  • Calcium Compounds / chemical synthesis*
  • Electric Conductivity
  • Macromolecular Substances / chemistry
  • Materials Testing
  • Microscopy, Scanning Tunneling / methods*
  • Molecular Conformation
  • Nanostructures / chemistry*
  • Nanostructures / ultrastructure*
  • Particle Size
  • Surface Properties
  • Temperature


  • Aluminum Compounds
  • Calcium Compounds
  • Macromolecular Substances
  • calcium aluminate