Abstract
The alkali halides are ionic compounds. Each alkali atom donates an electron to a halogen atom, leading to ions with full shells. The valence band is mainly located on halogen atoms, while, in a traditional picture, the conduction band is mainly located on alkali atoms. Scanning tunnelling microscopy of NaCl at 4 K actually shows that the conduction band is located on Cl− because the strong Madelung potential reverses the order of the Na+ 3s and Cl− 4s levels. We verify this reversal is true for both atomically thin and bulk NaCl, and discuss implications for II-VI and I-VII compounds.
Highlights
Introduction(The Madelung potential is the potential at any ion position in an ionic crystal due to the combined electrostatic potentials of the infinite number of ions in the crystal.) such a calculation (and similar considerations) alone is not decisive proof of this reality because of confounding factors such as the large spatial extent of s orbitals and nonunique assignments of charges to ions
We perform an experimental study of the conduction band of NaCl using scanning tunnelling microscopy (STM) providing a real space picture of states, which are centred on the Cl− ions across the entire band gap
Because few experimental techniques can characterise the conduction band character of the alkali halides with atomic resolution, we investigated the NaCl(100) surface with STM
Summary
(The Madelung potential is the potential at any ion position in an ionic crystal due to the combined electrostatic potentials of the infinite number of ions in the crystal.) such a calculation (and similar considerations) alone is not decisive proof of this reality because of confounding factors such as the large spatial extent of s orbitals and nonunique assignments of charges to ions For exactly this reason, we perform an experimental study of the conduction band of NaCl using scanning tunnelling microscopy (STM) providing a real space picture of states, which are centred on the Cl− ions across the entire band gap
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