Ion survival in grazing collisions of H− with vicinal nanosurfaces as a probe for subband electronic structures

Abstract

We study the electron dynamics at a monocrystalline Pd(111) surface with stepped vicinal nanostructures modeled in a simple Kronig-Penney scheme. The unoccupied bands of the surface are resonantly excited via the resonant charge transfer (RCT) interaction of the surface with a hydrogen anion reflected at grazing angles. The interaction dynamics is simulated numerically in a quantum mechanical wave packet propagation approach. Visualization of the wave packet density shows that, when the electron is transferred to the metal, the surface and image subband states are the most likely locations of the electron as it evolves through the superlattice. The survival probability of the interacting ion exhibits strong modulations as a function of the vicinal-terrace size and shows peaks at those energies that access the image state subband dispersions. A simple square well model producing standing waves between the steps on the surface suggests the application of such ion-scattering at shallow angles to map electronic substructures in vicinal surfaces. The work also serves as the first proof-of-principle in the utility of our computational method to address, via RCT, surfaces with nanometric patterns.

Resonant Charge-Transfer in Grazing Collisions of H− with Vicinal Nanosurfaces on Cu(111), Au(100) and Pd(111) Substrates: A Comparative Study

“…This may be due to the fact that the textured surfaces are modifying the energies of the band gap, the surface state and the image states represented by the parameters of the pseudopotential we are using to model. It was found in our previous publication [13] that the distance d between vicinal steps is one important surface structure property that effects the position of the modulation peaks. As mentioned earlier, D cl = 1 a.u.…”

“…Results for a particular vicinally stepped surface, therefore, should modify based on these three parameters as was shown in Ref. [13]. However, the comparison of vicinal RCT among various metals, the focus of the present study, will partly borrow from their flat-substrate properties as will be shown.…”

“…The potential, V vi-surf , of the vicinal surface will have two components: (i) A one-dimensional potential model in z obtained from pseudopotential local-densityapproximation calculations for simple and noble metal surfaces [32,33] that represents the flat precursor substrate. This is the model, with free electron motion in the x direction, that was employed in our previous work with flat surfaces [27][28][29][30] and, more recently, with a vicinal Pd(111) surface [13]. A graph of this potential appears in Fig.…”

“…The H − ion is described by a single-electron model potential, V ion , which includes the interaction of a polarizable hydrogen core with the active electron [34]. However, we employ an appropriately re-parametrized version of this potential [27], as was also applied in our other publications [13,[28][29][30]. This form is commensurate with our two-dimensional propagation scheme and produces the correct ion affinity level energy E ion = 0.0275 a.u.…”

“…For vicinal surfaces with periodic arrays of terraces, the confinement driven reflections of electrons from steps can further modify the free electron dispersion into subband dispersion enriching the RCT process. We recently applied this techniques to study RCT between the H − ion and vicinally stepped Pd(111) surfaces and computed the ion survival probability [13]. The natural next step therefore is to extend the method to other metallic vicinals to explore general similarities and detailed differences as a function of altering surface band structures.…”