Seminars Archive

X-ray microscopy and spectromicroscopy in environmental sciences

Abstract


Monday, May 19, 2003, 14:30
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza

X-ray microscopy and spectromicroscopy in environmental sciences


Juergen Thieme

( Institute for X-Ray Physics, University of Goettingen, Germany)
Abstract
X-ray microscopy achieves a much higher resolution than light microscopy. This is due to the much shorter wavelength of X-rays compared to visible light. The smallest structures that can be seen in an X-ray microscope at present are about 20 nm in size. In addition, X-ray microscopy is capable of imaging specimens directly in aqueous media. By tuning the wavelength of the X-radiation appropriately, it is possible to perform spectromicroscopy studies. Comprising, it is a tool very well suited to study structures showing colloidal dimensions in the environment. Due to their surface activity these structures are principally involved in various chemical and physical processes. Substances can be bound and immobilized or transported, colloids can attach to microorganisms building up microhabitats, and organic substances as humic substances can flocculate due the interaction with metals. A great variety of these structures have been studied with X-ray microscopy using its high spatial resolution as well as its high spectral resolution. Dispersions extracted from soils and groundwater aquifers have been imaged to visualize first of all the appearance of the colloidal structures. The effect of changing chemical conditions in an aqueous environment has been studied, too. The change in the appearance of colloidal structures has been imaged and evaluated using fractal geometry. Using spectromicroscopy, the distribution of organic substances on inorganic soil colloids has been studied. The obtained spectra have been analyzed for major chemical components. A large fraction of these are humic substances. Spectra have been taken from humic substances with and without a coagulation agent. Different functional groups have been identified and changes have been mapped. Clay dispersions and microhabitats as well as morphological effects of biologically induced redox changes of humic substances have been imaged tomographically. Tilt series of images have been obtained with an X-ray microscope; the specimen was then reconstructed from these images. This reconstruction conveys a detailed three-dimensional impression of the specimen structure, as will be shown.