Excited states of Na nanoislands on the Cu(111) surface

Abstract

Electronic states of one monolayer high Na nanoislands on the Cu͑111͒ surface are studied as a function of the nanoisland size. Properties of nanoislands such as one-electron states, the electron density, and the associated potential are obtained self-consistently within the density-functional formalism using a one-dimensional pseudopotential for the Cu͑111͒ substrate and the jellium model for Na. A wave packet propagation method is used to study the energies and lifetimes of quasistationary states localized at Na islands. For very large islands, island-localized states merge into the two-dimensional continuum of the Na quantum well state. Thus, we assign the quasistationary states studied as arising from the quantization of the two-dimensional quantum well continuum due to the finite island size. The scattering at the island boundaries results in the energy-conserving resonant electron transfer into the continuum of the substrate states broadening the island-localized states into resonances.

Localization, splitting, and mixing of field emission resonances induced by alkali metal clusters on Cu(100)

“…Indeed, the complex resonance pattern observed in this study calls for a guiding line allowing one to have a better understanding of the data. As follows from previous works, 15,16 in the absence of the STM tip the attractive potential associated with the alkali ad-island is sufficiently strong to lead to a series of island-induced quasistationary electronic states. The finite lifetime of these states is due to the coupling with the substrate, which enables population decay.…”

“…Importantly, the lifetime of the resonances with given n rapidly decreases with increasing energy ( quantum number). This is linked with an energy dependence of the electron escape through the island boundaries, [13][14][15][16] and it also explains why only a limited number of states could be observed.…”

“…We find that the presence of the alkali clusters of nm size (nanoislands) on the metal surface induces (i) new types of resonances with different azimuthal symmetry (m quantum number) 15,16 that originate from the island-localized imagepotential-like states pinned (for low quantum numbers) to the local vacuum level above the island, and (ii) the splitting of the original FER's spatially extended all over the metal surface. Depending on their spatial distribution and relative energy positions, the island-localized resonances can mix with the localized split component of the conventional FER's of the supporting metal surface giving rise to multiple structures observed in dI/dV maps and spectra.…”

Image potential states of supported metallic nanoislands

“…22 Here we are interested in the n = 1 IS case. As follows from the present DFT study, the vacuum level of 1 ML Na/ Cu͑111͒ is located at −1.53 eV with respect to the vacuum level of Cu͑111͒.…”

“…21 An extended description of the method including the choice of the nanoisland geometry and computational details can be found in our previous work. 22 Here we only briefly outline the theoretical approach based on the ab initio density-functional ͑DFT͒ calculations and the time-dependent wave packet propagation ͑WPP͒ study.…”