Jürgen Niemeyer

Characterization of refractory organic substances by NEXAFS using a compact X-ray source

PurposeWe present the characterization of environmental samples using near-edge X-ray absorption fine structure (NEXAFS) spectra recorded with an in-house device. We want to point out the feasibility of such an easily accessed complementary technique, if not sometimes alternative to NEXAFS studies performed with synchrotron radiation, as the number of compact setups is increasing.Materials and methodsThe experiments were carried out using a laser-driven plasma source. We studied heterogeneous samples like refractory organic substances to demonstrate the potential of NEXAFS spectra, achieved by such an instrument, concerning specimens of high chemical complexity.Results and discussionFrom the respective resonance peaks in the spectra, the presence of certain functional groups, such as aromatic or carbonyl groups, is verified, and the elemental composition is estimated. The results of the reference samples are consistent with the literature. For the environmental samples, external influences of the extraction solvent or fertilizers can be determined from the spectra.ConclusionsThis could provide the possibility to perform test experiments with samples, which are later studied in more detail with synchrotron light and might as well give an impulse on the broader spread of the application of NEXAFS spectroscopy.

Table-top soft X-ray microscopy with a laser-induced plasma source based on a pulsed gas-jet

A table-top soft x-ray microscope based on a long-term stable and nearly debris-free laser plasma from a pulsed nitrogen gas jet target is presented. The microscope operates in the “water window” region at 2.88 nm wavelength. The emitted soft x-ray radiation is focused by an ellipsoidal condenser mirror into the object plane and a sample is imaged using a Fresnel zone plate onto a CCD camera. The spatial resolution of the microscope is about 50 nm demonstrated for a Siemens star test pattern.

X-Ray Spectromicroscopy Studies of Nanoparticles in Aqueous Media

X-ray microscopy is capable of imaging particles in the colloidal size range directly in their aqueous environment with high spatial resolution. It is possible to combine this with high spectral resolution for spectromicroscopy studies. Two types of microscopes are common in X-ray microscopy, the transmission X-ray microscope and the scanning transmission X-ray microscope; their setups are shown in this chapter. While the former takes high resolution images from an object within seconds or faster, the latter as an analytical instrument is suited for spectromicroscopy. As examples for visualization of the morphology, zinc containing particles and samples of clay and soil have been imaged with a transmission X-ray microscope. Images are shown from a cryo-tomography experiment based on X-ray microscopy images to obtain information about the three-dimensional structure of clusters of humic substances. The analysis of a stack of images taken with a scanning transmission X-ray microscope to bring together morphology and chemistry within a soil sample is shown.

Protolytic Weathering of Montmorillonite, Described by Its Effective Surface Fractal Dimension

Octahedral coordinated aluminum is released by the attack of protons from clay minerals like montmorillonite. Apart from other effects, this leads to an alteration of the form of the surface of the clay particles. We used fractal geometry to describe this change in form. The effective surface fractal dimension (D) was determined before and after acid treatment by using the dependency: number of yardsticks necessary to cover the surface versus size of the yardstick area. We used n-alkanols with different cross sectional areas to determine this dependency. This resulted in a D: 2.55 for the untreated and a D: 2.85 for the acid treated clay.