ABSTRACT
Circular dichroism in XAS is related to some degree of chirality of the target, be that
a helical arrangement of scatterers in NMCD or a magnetically active transition in
XMCD. For a long time it has been thought that such chirality cannot be observed
with electron probes. But as will be demonstrated in this chapter, this is not true.
The chiral properties of the target are present in the double differential scattering
cross section (DDSCS), that is the probability of scattering as a function of energy
transfer and momentum transfer to the target. It was shown in Chap. 1 how details
on the electronic structure of the scatterer can be derived from this probability
distribution. A well known example is the dependence of white line intensity in
the L edge of 3d metal oxides on the oxidation state, caused by charge transfer from
the metal to the oxygen atom. Another example was also discussed in Chap. 1:
Anisotropies in the scattering distribution are interpreted in terms of bonding. This
is a simple case of symmetry breaking caused by directional bonding which in turn
causes a symmetry breaking of the dynamic structure factor.
