Abstract
Photon emission spectra from submicron silver particles induced by an electron beam have been measured using a light detection system combined with a 200-kV transmission electron microscope. Multiple peaks appear in the spectra associated with collective plasmon excitations produced in the particles by the incident electrons. The wavelengths of these peaks are observed to shift towards larger values with increasing particle diameter, as predicted by Mie theory. Moreover, photon maps have been obtained in a scanning mode and they indicate that those peaks correspond to the multipole modes of electromagnetic oscillations in metallic spheres (Mie resonances). The spectral shape of the emission and the dependence on particle size, impact parameter, and electron energy are well explained from theoretical calculations of the photon emission probability derived from a fully retarded analytical treatment of the interaction of fast electrons with metallic spheres.
Highlights
Photon emission induced by the passage of a fast electron through a material can occur via different mechanisms that include phenomena such as cathodoluminescence, Cherenkov radiation, and transition radiation
Photons emitted from submicron silver particles illuminated by fast electrons have been observed using a light detection system combined with a 200-kV TEM
Focusing the electron beam on a given position on or near the particles, the recorded emission spectraFigs. 2, 4, and 5͒ are seen to be characterized by several peaks that have been explained in terms of the excitation of collective plasmon modes
Summary
Photon emission induced by the passage of a fast electron through a material can occur via different mechanisms that include phenomena such as cathodoluminescence, Cherenkov radiation, and transition radiation. Our experimental setup combines the high spatial resolution of a TEM, which can focus an electron beam on a region of 1 nm in diameter at the position of the sample, and the high-energy resolution of a light detection system, below 1 meV in the optical region This energy resolution is much better than that of other techniques commonly used in TEM, such as energy dispersive x-ray spectroscopyEDXand electron energy loss spectroscopyEELS. The dependence of the observed emission peak wavelengths on beam position and particle size is discussed in the light of a fully retarded theoretical description of photon emission induced by fast electrons passing near a sphere.
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