Adsorption of sodium on the W(100) surface was studied at room temperature by angular resolved ultraviolet photoemission spectroscopy and low-energy electron diffraction. A reconstruction of the W(100) surface induced by sodium adsorption was observed at least at low coverage. The high-lying tungsten surface states situated at 0.4eV below the Fermi level at normal emission ( Gamma ) suffer a continuous shift towards higher binding energies when sodium coverage increases. With a monolayer of sodium, the shift attains 2 instead of 1eV for caesium. The low-lying surface state located at 4.2eV below the Fermi level at Gamma shifts towards higher binding energies in contrast with caesium adsorption. These effects reveal a stronger sodium atom-substrate interaction than that which occurred in caesium. The description of the Cs/W(100) system could be extended to Na/W(100): the d(z2)-like surface states of W(100) hybridise with the sodium 3s valence states to form a polarised covalent bond.

Sodium-Induced Modifications in the Electronic Structure of the W(100) Surface. J.Cousty, R.Riwan, P.Soukiassian, F.Mila: Journal of Physics C, 1986, 19[16], 2883-91