Multiple plasmon excitations in adsorbed two-dimensional systems

• Published in: Journal of physics. Condensed matter Vol. 23; no. 11; pp. 112204 - 6
• Main Authors: Pfnür, H, Langer, T, Baringhaus, J, Tegenkamp, C
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 23.03.2011; Institute of Physics
• Subjects: Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dispersion; Electron and ion emission by liquids and solids; impact phenomena; Electron energy loss spectra; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Energy use; Exact sciences and technology; Excitation; Graphene; Impact phenomena (including electron spectra and sputtering); Physics; Plasmons; Silicon substrates; Surface and interface electron states; Two dimensional; Ultrathin films; Electron energy loss spectra; Two-dimensional systems; Silicon carbide; Graphene; Dispersion relations; Line widths; Momentum; Plasmonics; Two-dimensional electron gas; Surface plasmons
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/23/11/112204

Using monolayer graphene as a model system for a purely two-dimensional (2D) electron gas, we show by energy electron loss spectroscopy, highly resolved both in energy and momentum, that there is a significant probability for the excitation of not only one but two dispersing losses. The appearance of both losses is independent of the substrate (we tested graphene on the Si face of 6H-SiC(0001), and on Ir(111) without and with an intercalated Na layer), and the ratio of the slope in the dispersion curves varies between 1.4 (SiC) and 2. While the lower dispersion curve can be attributed to the excitation of the sheet plasmon, in agreement with theoretical model calculations, the upper dispersion branch has not been identified before for plasmonic excitations in a 2D electron gas, and we assign it tentatively to the excitation of a multipole sheet plasmon.