Some studies of lead and iron adsorption on the W(100) surface by field emission microscopy

The behaviour of lead and iron adsorbed on the W(100) surface has been studied by probe hole field emission microscopy, field desorption, and by measurement of the total energy distribution (TED) of field-emitted electrons. Lead adsorbed at 300 K which reduces the work function of W(100) can be completely removed at 78 K by field desorption below 3.2 V Å^?1 and the resulting surface has both the work function and TED, which are characteristic of the clean plane. Condensation at 800 K followed by field desorption, results in a plane surface of work function 4.17 eV and an altered TED. This effect is attributed to the microfacetting, which is observed by LEED. The Swanson peak in the W(100) TED which is removed by submonolayer amounts of lead re-emerges at monolayer coverage when lead adopts the (1 × 1) structure. Such behaviour is consistent with the model proposed by Kar and Soven. A spectral peak observed when lead is adsorbed on the reconstructed W(100) surface is thought to derive from the atomic ¹D state. Adsorption of iron on a W(100) surface reduces φ considerably due to dipole formation and efficiently quenches the Swanson peak. Higher coverages introduce other peaks in the TED enhancement curve, and by adopting an energy scale based on the work of Hagstrum, an attempt is made to interpret the observed peaks in terms of the known energy structure of the free iron atom. One of the three spectral peaks is assigned to the 4s² ground state of the iron atom, and the remaining two peaks are tentatively attributed to atomic p-states. It is concluded that while the excited state structure of the iron atom is too complex to permit complete interpretation of the spectra, this approach offers the hope that, for simpler atoms, such features may be interpreted in this way.