Imaging with plasmon energy loss electrons

Abstract

Collision of electron with the specimen in electron microscope are either elastic or inelastic. There are mainly two types of characteristic energy loss: the plasmon energy loss and the inner shell ionization loss. In metals and semiconductors the plasmon energy loss Ep is proportional to , where Nf is the number of free electrons in unit volume. Normally Ep is 10 - 20 eV and the plasmon peak in EELS is well defined. In insulators, the plasmon peak usually has a broad maximum in the range 20-30eV. If the separation of plasmon peaks of species in a multi-phase sample is large enough, they can be distinguished by means of energy filtered imaging technique. In this paper we report two examples to illustrate the ability of this method in material science. The machine used is a TEM Opton CEM 902 at 80 kV.The first example is a-Si:H/C:H superlattice sample. Fig. 1a shows the CTEM image. Fig. 1b and 1c show the inelastic images. The energy window are set at about the plasmon energy loss of Si( E = 16 eV) and a-carbon( E=26 eV respectively. In Fig.1b the bright strips are a-Si layers.