Internal electronic structure of adatoms on Fe(110) and Fe(100) surfaces: A low-energyLi+scattering study

Abstract

The neutralization of 400-3000 eV 7 Li ϩ ions scattered from clean and adsorbate-covered Fe͑110͒ and Fe͑100͒ surfaces was measured with time-of-flight spectroscopy. Li singly scattered from bromine, iodine, and cesium adatoms has a consistently larger neutral fraction than that for scattered from substrate sites. This suggests that the local electrostatic potential directly above these adatoms is reduced from that of the clean substrate. The neutral fraction of Li scattered from halogen adatoms is surprising in that it decreases as the emission angle moves off-normal, yet increases in the usual manner for cesium and silver adatoms. This indicates that the charge distribution associated with a halogen adsorbate is nonuniform, most likely due to internal polarization. A semiquantitative theoretical analysis shows that a nonuniform internal electron density would give rise to the observed behavior. The polarization of halogen adatoms is likely responsible for anomalous work function changes observed previously. Alkali-ion scattering is shown to be an effective tool for detecting the internal electronic structure of an adatom.

Internal Polarization of Oxygen Adatoms on Polycrystalline Ta Investigated by Na-Ion Scattering

“…In earlier ion scattering work with I and Br adsorbates, our group provided experimental evidence to support this conclusion for halogens [7,8]. Alkali-metal ions were scattered from the adatom sites, and the change in the NF was consistent with the outward pointing dipole (no.…”

“…Internal polarization, which had earlier been experimentally demonstrated for larger and more easily polarizable halogen adatoms [7,8], results from the interaction of the negative charge in the adatom with its image in the metal.…”

“…It was observed, however, that the magnitude of the effect is independent of the size of the halogen, as it is almost same for I and Br, and it is also independent of whether the halogen is adsorbed on a metal [7,8] or semiconductor surface [17]. In addition, the system studied by Wu and Klepeis [6] was Cl adsorbed on Ta, which shows a strong polarization with the relatively smaller Cl adatom.…”

Charge exchange between low energy alkali ions and cerium oxide surfaces

“…Neutralization in large-angle alkali ion scattering is sensitive to the inhomogeneous LEP associated with electropositive and electronegative adsorbates on metal surfaces [13,[18][19][20][21][22][23][24][25][26][27][28][29], and should therefore also be useful in probing an inhomogeneous metal oxide surface [30]. Previous experiments investigating charge exchange between low energy projectiles and metal oxide surfaces [16,17] were performed in a small scattering angle configuration (67°), which does not allow for separation of scattering from different sites.…”

Hydrogen ion scattering from a potassium impurity adsorbed on graphene

“…The collision of low energy alkali ions with alkali and halogen covered metal surfaces has been studied by several groups [13][14][15][16][17][18][19]. A conclusive remark from these works can be found in the phrase of Gauyacq et al [19]: "Because of the importance of local effects, the resonant charge transfer process appears to be a rather sensitive probe of the local electronic properties of an adsorbate-substrate system.…”