This review traces the development of X-ray mapping from its beginning
50 years ago through current analysis procedures that can reveal otherwise
obscure elemental distributions and associations. X-ray mapping or
compositional imaging of elemental distributions is one of the major
capabilities of electron beam microanalysis because it frees the operator
from the necessity of making decisions about which image features contain
elements of interest. Elements in unexpected locations, or in unexpected
association with other elements, may be found easily without operator bias
as to where to locate the electron probe for data collection. X-ray
mapping in the SEM or EPMA may be applied to bulk specimens at a spatial
resolution of about 1 μm. X-ray mapping of thin specimens in the TEM
or STEM may be accomplished at a spatial resolution ranging from 2 to 100
nm, depending on specimen thickness and the microscope. Although mapping
has traditionally been considered a qualitative technique, recent
developments demonstrate the quantitative capabilities of X-ray mapping
techniques. Moreover, the long-desired ability to collect and store an
entire spectrum at every pixel is now a reality, and methods for mining
these data are rapidly being developed.