A. Carlsson et al., HIGH-RESOLUTION PHOTOEMISSION FROM A TUNABLE QUANTUM-WELL - CU(111) NA/, Physical review. B, Condensed matter, 56(3), 1997, pp. 1593-1600
High-resolution photoemission (Delta E=5 meV) at a low photon energy (
3.82 eV) is used to probe discrete quantum-well-type subband states ne
ar, below, and above E-F for Cu(111) covered with 2 ML or less of Na.
A subband characteristic of the monolayer range shifts gradually to lo
wer energy as the coverage is increased, extending below the Fermi lev
el for coverages above 0.85 ML. Combined with previous observations of
shifts for filled and empty states the present results show that the
Na monolayer has continuously tunable quantum-well state energies. Bey
ond the monolayer range quantum-well states characteristic of both one
and two atomic layers an observed, indicating growth of the second la
yer via monolayer high islands. A small downshift, by 25 meV, with inc
reasing coverage in the second layer is ascribed to an increase of the
island size. Lorentzian photoemission line shapes are observed for we
ll-ordered samples. The linewidth varies linearly with temperature in
the probed range (130-295 K) and this is ascribed to the phonon contri
bution to the width. Structural disorder leads to an asymmetric line,
which is Lorentzian on the steeper, low-kinetic-energy side.