Acoustic surface plasmon on Cu(111)

¹  Department of Physics and Materials Science Program, University of New Hampshire - Durham, NH 03824, USA
²  CNISM, IMEM-CNR and Dipartimento di Fisica, Università di Genova - Genova, Italy, EU
³  Departamento de Física de Materiales and CFM (CSIC-UPV/EHU), Facultad de Ciencias Químicas, Universidad del País Vasco - Apdo. 1072, 20080 San Sebastián/Donostia, Spain, EU
⁴  Donostia International Physics Center (DIPC) - P. Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain, EU
⁵  IKERBASQUE, Basque Foundation for Science - 48011 Bilbao, Spain, EU

Corresponding author: karsten.pohl@unh.edu

Received: 13 April 2010
Accepted: 1 June 2010

Abstract

Contrary to previous reports we show that the acoustic surface plasmon (ASP) exists also at noble-metal surfaces, thus demonstrating the generality of this phenomenon in the presence of partially filled Shockley surface states. Angle-resolved high-resolution electron energy loss spectroscopy measurements and calculations of the surface loss function indicate that for Cu(111) the ASP is a sharp feature up to a loss energy of about 0.4 eV. The dispersion is indeed linear (acoustic) with a slope (sound velocity) of (4.33± 0.33) eVÅ in good agreement with recent theoretical predictions. The ASP can play important roles down to the meV regime, precluded to ordinary surface plasmons, for electron, phonon and adsorbate dynamics, as well as chemical reactions and advanced microscopies.