Evidence for the presence of the multipole plasmon mode on Ag surfaces

Abstract

Collective surface electronic excitations on Ag͑111͒ and Ag͑110͒ have been studied by energy-lossspectroscopy LEED. The data allow separation of the contribution to the loss intensity due to monopole and to multipole surface plasmons, thus demonstrating the existence of the latter mode also on noble-metal surfaces. Multipole plasmons are therefore a general property of the optical response of metal surfaces whenever the charge-density profile at the interface is not too abrupt. ͓S0163-1829͑96͒51544-4͔ EVIDENCE FOR THE PRESENCE OF THE MULTIPOLE . . .

Electronic excitations on silver surfaces

“…In ELS-LEED measurements, where work function reduction is not required, a feature at 3.74 eV for Ag͑110͒ and Ag͑111͒ surfaces has been observed and identified to be the multipole surface plasmon. 17 The reason for the difference in the multipole plasmon position between our measurement ͑3.7 eV͒ and with ELS-LEED ͑3.74 eV͒ is because in photoyield the q ʈ ϭ0 mode is observed, while in ELS the detected mode is q ʈ Ϸ0 due to the finite aperture of the detector. 48 The existing theoretical results on Ag do not support the existence of a Ag multipole plasmon below p .…”

“…The collective excitation modes on Ag have been a topic of controversy in recent years because of the disagreement between time-dependent local-density approximation ͑TDLDA͒ based theoretical calculations 16 and energy-lossspectroscopy low-energy electron diffraction ͑ELS-LEED͒ measurements 17 about the existence of the multipole plasmon m mode on Ag. In the q ʈ ϭ0 limit of the ELS-LEED spectra, a peak at 3.74 eV was obtained by subtracting the data for two different impact energies.…”

“…Hence, by default, the feature was interpreted to be the Ag multipole plasmon. 17 The s-d model based TDLDA calculations, on the other hand, predicted the existence of the multipole plasmon above the interband offset at 6.7 eV. 39 An early study for polycrystalline Ag films using total photoyield spectroscopy shows features near 3.7 eV and 3.85 eV that were assigned to monopole plasmon induced by surface roughness and a spurious signal, respectively.…”

Collective excitations of thin films of disordered potassium adsorbed on Ag(110)

“…The energy loss spectra were recorded by energy loss spectroscopy of low-energy electron diffraction ( ELS-LEED), a new spectrometer system with both high momentum and high energy resolution [8] and therefore particularly apt for surface plasmon dispersion measurements [9][10][11]. In the present experiment we worked with a momentum resolution of 0.02 Å −1, as determined from the to-noise ratio for the losses.…”

Edge plasmons in graphene nanostructures

“…11 Xia and Quinn showed that systems with gradual edge density profiles support several types of edge waves (multipole modes) 12 that can be thought of as standing-wave plasmons fitting into the diffuse edge layer. This notation is very similar as 3D multipole surface plasmons [13][14][15][16][17][18] that have been observed experimentally on K, Na, and Ag surfaces 19,20 and, very recently, in graphene-coated Ir and SiC. 21 Basic requirements for the existence of such higher-multipole modes include gradual edge density profile and dispersion of bulk plasmon.…”