Abstract
The excitations produced by fast electrons impinging perpendicularly on both metallic and semiconductor cylindrical nanowires are investigated within the framework of dielectric theory. The dependence of the electron energy-loss spectra (EELS) on the nanowire radius is studied in detail, and so is the spatial extension of the induced-charge fluctuations associated to the modes that are excited during the loss process. The limits of applicability of dielectric theory to nanowires are discussed. In particular, comparison between the present theory and EELS measurements performed with silicon nanofibers support the use of dielectric theory at the scale of a few nanometers in diameter, and it is shown that this positive result is justified in terms of the longitudinal pattern of the induced surface plasmons. Finally, the effect of nanowire termination on the electron energy-loss probability for electrons passing near the edge is calculated using the boundary charge method, showing that the range of this effect can extend up to tens of nanometers for low-energy $m=0$ modes.
Highlights
Technical developments in nanofabrication have allowed in recent years the production of structures of nanometric size with different shapes and compositions
EELS spectra obtained for electrons traveling perpendicularly to thin wires of a few nm in radius have been studied within the frame of classical dielectric theory, first by modeling the nanowires as infinite cylinders and later by considering edge effects using the BCM method
The general dependence of both surface- and bulk-plasmon excitations on the size of the target has been analyzed for metallic Drude wires and compared with results obtained for spherical particles and thin films, finding a similar dependence with the length of the electron path inside the target
Summary
Technical developments in nanofabrication have allowed in recent years the production of structures of nanometric size with different shapes and compositions. This has stimulated considerable theoretical and experimental work leading to a better general understanding of these nanostructures and the relevant physics at this length scale While some of these structures are very promising candidates for applications in nanoscale electronic devices, wires or nanotubes of a few nanometers in radius and some tens or hundreds of micrometers in length are interesting from a fundamental point of view due to their quasi-one-dimensional character. It is in this latter case where the analysis of the spectra relies more on theories such as the one developed in this work
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