Calculated Shockley-type surface states for Cu (110) are shown by full lines in the diagrams. Occupied states occur at energies below that marked Ef . Circles represent current experimental data. Unshaded regions represent bulk band energy gaps.

Alkali metals adsorbed onto particular noble metal surfaces produce quantum well energy states that an electron may occupy. These systems have potential for device application at room temperature.

The detailed form of the surface barrier potential in the energy region where it joins to the top row of atoms of the noble metal is of fundamental importance for describing the unoccupied states in the quantum well. The unoccupied surface states arise primarily because of the surface barrier above the occupied energy states but also depend on the details of the surface potentials at lower energies. These surface potentials can be probed if they give rise to occupied surface states.

As part of a complete study of prominent copper (Cu) surfaces we have used a layer-by-layer scattering method to calculate all occupied and unoccupied surface states of the Cu (110) surface. This method has not been used before in the calculation of occupied surface states.

The major result of our calculation is that we predict the occurrence of occupied Shockley states and resonances due to this lower energy region of the surface barrier potential. Surface states arising from this mechanism have not been identified before for this system or any other. The states occurring in bulk band gaps have long lifetimes and should be detectable by modern experimental techniques. For Cu (110) no such experimental data exists at the present time.

We anticipate that this study and further studies of other Cu surfaces will lead to detailed experimental exploration in these energy regions. Combined experimental and theoretical analysis will provide fundamental information about the details of the potentials at the surface interface region.

Marlene Read and Joe Qiu