Electrical charges interact strongly with colloidal particles whose diameters are about 25 Å in diameter, typical of silver particles in a photographic image. Here we see a charge passing close to an ordered colloid. The image charges induced in the colloid are left behind and exert a retarding force on the particle causing it to lose energy. An alternative view is that electromagnetic energy tunnels from the particle into the colloid where it is dissipated in the complex mode structure.
Howie and Walsh (Micros. Microanal. Microstruc.,
2, 171, 1991) have
studied aluminium colloids with an electron microscope fitted with
energy analysis capabilities. They can choose to create an image using
only electrons with a certain energy loss. On the right is an image of
a colloid created from electrons with a 6eV loss. scale:
1cm = 100 Å
Using our theory we can calculate the probability of a given energy loss by electrons in colloids. We assume that it is the density of the colloid that determines the loss properties (this sample has a 12% filling fraction), and replace the disordered sample of the experiment with the ordered colloid of our theory. Here we see the dominant 6eV loss feature reproduced. The nature of modes absorbing energy is explored in the other pages.
last updated Wed Apr 08 16:25 bst 1998 by RAE