Role of the 2D Surface State Continuum and Projected Band Gap in Charge Transfer in Front of a Cu(111) Surface

Abstract

Electron capture by Li+ and H projectiles in grazing scattering from Cu(111) and Cu(110) surfaces is studied experimentally and theoretically. Whereas data for Cu(110) can be described by established theoretical methods treating resonant charge transfer with a free-electron metal, data for Cu(111) show pronounced deviations from this approach. We interpret our observations by the effect of the projected L-band gap of the Cu(111) surface. In particular, the quantum states of reduced dimension (2D surface state continuum) play a dominant role in electron transfer.

Wave packet propagation study of the charge transfer interaction in the F−–Cu(111) and –Ag(111) systems

“…This was attributed to the blocking of the resonant charge transfer in [28,48] which was shown to be important for a formation of F − , even at rather low collision energy [13]. Consequently, we cannot quantitatively compare our results with theirs.…”

“…Second, a fluorine has a much larger electron affinity than a hydrogen. Thanks to a better overlap of the wave functions, the 2D surface state continuum, when energetically allowed, is a dominating decay channel for an ion state lying within the band gap [23,28,46]. Moreover, when the binding energy of a negative ion is close to that of the surface state, a coupling of the ion level with the 2D surface state continuum is more efficient than its coupling with the 3D continuum of the free-electron metal states (see a discussion in [46]).…”

“…First, there exist very long lived states in the alkali-Cu(111) systems [24,26,27]. Second, there is a parallel velocity dependence of the probability of an electron capture by the atom from Cu(111) surfaces in grazing scattering experiments that is characteristic of a 2D electronic continuum [28]. Third, there exits an avoided crossing between the energy level of the projectile and the bottom of the surface state continuum [23].…”

H−formation in collisions of hydrogen atoms with Al(100) surfaces

“…The TDOS shifts toward high energies close to ionization threshold, which enhances electron loss and reduces the efficiency of H − formation via electron capture from the Fermi sea. Similar effects are found in the measured hydrogen negative-ion yields near Cu(111) and Cu(110) surfaces [3].…”

“…Theoretical schemes for modeling charge exchange in ion-surface collisions can reveal deviations from the adiabatic evolution of the initial charge state of the projectile and provide reliable estimates for the fractions of minority charge states of the atom after its reflection from the surface. A number of such scattering experiments has been performed in the past, allowing for the scrutiny of various theoretical models [1][2][3].…”