Single‐Electron Deexcitation of Volume Plasmons Induced by Heavy Ions in Thin Solid Foils

Abstract

In heavy ion (C+, N+) induced electron spectra ( E , < 30 eV) differential in angle and energy, of thin C (z = 370 nm), Cu (z = 100 nm), and AI (z = 160 nm) targets pronounced structures in forward direction superimposed on the flanks of the "true" secondary electron peak are observed. The energies of these structures are well correlated with the plasmon energies h o p of the materials in question. The present data offer good evidence for the existence of the single-electron deexcitation process of volume plasmons in thin solid films.I n winkel-und energiedifferentiellen, ioneninduzierten (C+, N+) Elektronenspektren (E, < < 30 eV) von diinnen C-(z = 370 nm), Cu-(5 = 100 nm) und AI-(z = 160 nm) Targets werden ausgepragte Strukturen in Vorwartsrichtung beobachtet, die den Flanken des ,,wahren" Maximum der Sekundiirelektronen uberlagert sind. Die Energien dieser Strukturen sind gut korreliert mit den Plasmon-Energien h 9 der in Frage stehenden Materialien. Die mitgeteilten Werte ergeben gute Hinweise fur die Existenz des Einelektronenzerfallsprozesses der Volumenplasmonen in dunnen Festkorperschichten.The description of solid materials in terms of a quasi-free electron gas implies the possible excitation of collective longitudinal oscillations of the electron plasma with discrete plasmon energies E = hop, op being the plasma frequency. Plasmons are of prime importance because they represent a direct proof of the existence of a collective excitation of the whole valence electron system in solids in contrast to the second kind of a low-lying excited state of a many-body system, the modified single-particle excitation [l].The excitation of plasmons can e.g. be induced by electrons (1 keV 5 EL 5 10 keV) penetrating thin solid films by inelastic collisions with the electron plasma [2, 31. Even in collisions of ions with solids plasmon generation has been reported [4, 51.The following deexcitation of plasmons may take place either by emission of light or by transformation into phonons or possibly by emission of quasi-free valence electrons. When escaping from the solid surface, those electrons produced by plasmon decay have to overcome the work function @ specific for the solid material. Their final kinetic energy E , is given by According to the above relation, the single-electron deexcitation of plasmons should lead to a n additional portion of electrons with discrete energies in the low energy electron spectra, superimposed on the monotonically decreasing "true" secondary electron background [6]. I n electron spectra induced by electron impact corresponding structures have been reported by several authors (see e.g. [7, 81). It is of importance 1) August-Euler-Str. 6, D-6000 Frankfurt (Main), FRG.

Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter

“…Figure ) using the collecting electric field of 65 V/cm and the energy filtered measurements without a collecting field, we find that 90% of the electrons have an energy of well below 15 eV. Our findings compare well with energy distributions of ion-impact-induced electrons emitted from 3D targets reported in the literature. − Still, previously, LEEs from thick samples were interpreted as the result of an inelastic electron scattering cascade converting initially high energetic electrons from Auger processes into many LEEs. With the help of a 2D material, we can now show that the electrons have low energies from the beginning on.…”

Excitation of volume plasmons in glancing collisions of protons with Al(111) surfaces

“…The excited electron resulting from plasmon decay may be emitted outside the solid, where it has been observed to produce a distinct structure in the energy distribution of electrons emitted in ion-solid interactions. [6][7][8][9][10][11] Plasmon decay constitutes an important fraction of the total electron emission. 11,12 Because of the strong inelastic electron-electron interactions in solids, electrons from plasmon decay are attenuated exponentially with depth; those observed originate from shallow depths of the order or smaller than the electron escape depth of about 1 nm.…”