Combined high-resolution scanning Auger spectroscopy and energy dispersive X-ray analysis of soil samples

Abstract

Soil samples are usually non-conductive which leads to charging phenomena at their surfaces if microanalysis using electron beams is to be performed. During the last decade, however, various submicroscopic techniques have been developed which give acceptable accuracy of analysis of soil materials present on the surface of thin sections of soils. Laser analysis and electron- and ion microscopy were applied but AES (Auger electron spectroscopy) has, until recently, remained unsatisfactory due to charging phenomena. However, if a very thin section (< 30 μm) of the sample was glued to the sample holder using carbon paste, the surface was treated with argon ions and the probe current was kept low, AES on soil samples became possible.These precautions almost completely eliminated the charging phenomena. The use of a combination instrument allowed simultaneous AES and EDX (energy dispersive X-ray analysis) measurements on the same spot on a thin section. AES gave surface information whereas EDX gave information on the bulk (subsurface) of the soil material as well. A larger area was analysed with XPS (X-ray photoelectron spectroscopy) in the same instrument. AES measurements, also supplying information on the lighter elements, make this type of analysis interesting for studies of decomposition and impregnations of organic matter in soils and are also important for environmental research in situ.