Plasmon excitation by charged particles interacting with metal surfaces

Abstract

Recent experiments (R. A. Baragiola and C. A. Dukes, Phys. Rev. Lett. 76, 2547 (1996)) with slow ions incident at grazing angle on metal surfaces have shown that bulk plasmons are excited under conditions where the ions do not penetrate the surface, contrary to the usual statement that probes exterior to an electron gas do not couple to the bulk plasmon. We here use the quantized hydrodynamic model of the bounded electron gas to derive an explicit expression for the probability of bulk plasmon excitation by external charged particles moving parallel to the surface. Our results indicate that for each q (the surface plasmon wave vector) there exists a continuum of bulk plasmon excitations, which we also observe within the semi-classical infinite-barrier (SCIB) model of the surface.It is well known that charged particles interacting with solid surfaces can create electronic collective excitations in the solid. These are bulk [1] and surface [2] plasmons. In the absence of electron-gas dispersion, the scalar electric potential due to bulk plasmons vanishes outside the surface [3]; hence, in this case probes exterior to the solid can only generate surface excitations. That electron-gas dispersion allows external probes to interact with bulk plasmons was discussed by Barton [4] and Eguiluz [5], and more recently by Nazarov et al [6]. Nevertheless, the fact that within a non-local description of screening bulk plasmons do give rise to a potential outside the solid has been ignored over the years [7,8], even when electrongas dispersion has been included; also, current non-local theories of plasmon excitation by external charges have not shown evidence for bulk plasmon excitation outside the solid [8][9][10]. Recently, Baragiola and Dukes [11] have studied the emission spectra produced by slow ions that were incident at grazing angle; their data indicate that the bulk plasmon is importantly involved in the emission process, though the projectiles are not expected to have penetrated into the solid. Bulk plasmon excitation in electron emission spectra produced by slow multiply charged ions has also been investigated [12], with projectiles that may enter the solid.In this letter we derive, within the quantized hydrodynamic model of the bounded electron gas [13], an explicit expression for the probability of bulk plasmon excitation by external charged particles moving parallel to a jellium surface. Our model, which assumes a sharp electron density profile at the surface, neatly displays the role of bulk plasmon excitations in the interaction of charged particles moving near a metal surface. We also demonstrate that our results for the total energy-loss probability agree with standard calculations [14] derived either by solving the linearized Bloch hydrodynamic equations [15] or within the semi-classical infinite-barrier (SCIB) model of the surface [16,17] with the hydrodynamic approximation for the bulk dielectric function. Though it has been generally believed that when charged particles move outside the solid the energy l...

Volume plasmon ejection of ions in pulsed ultraviolet laser induced desorption from several metals

“…This is possible because the vol- ume plasmon extends slightly beyond the surface. Beraga et al, 26 Barton, 51 Eguiluz, 52 and Nazarov and Luniakov 53 showed that electron-gas dispersion allows external probes to interact with volume plasmons.…”

“…One example is the acceleration of charged particles moving near a grating or real-world surface by the Smith-Purcell effect. [21][22][23][24][25] Theoretical support for experiments involving the excitation of volume plasmons by charged particles moving near a metal surface was provided by Beraga et al 26 Laser experiments often seem to access somewhat different results from the traditional light sources in photonstimulated desorption experiments. LID experiments often produce ions with a Maxwell-Boltzmann kinetic-energy distribution associated with laser ablation related surface melting and photoionization in the ablation plume.…”

Theory of surface plasmons and surface-plasmon polaritons

“…However, it was shown explicitly in Refs. [254] and [257] that the continuum of bulkplasmon excitations dominating the energy-loss spectrum inside the solid [see Fig. 8] is still present for z coordinates outside, as shown in Fig.…”

Hydrodynamic approximation for the nonlinear response of a metal surface

“…Within the semi-classical approach, the role played by bulk and surface plasmons goes unnoticed; however, the quantized hydrodynamic model provides explicit separate expressions for the contributions to the induced potential coming from the coupling with bulk and surface plasmons. The role that bulk and surface plasmon excitation plays on the energy loss of charged particles interacting with metal surfaces has been investigated recently, 38 showing that bulk plasmons are excited even in the case of charged particles that do not penetrate into the solid.…”