Research Interests

Cosmic dust is an important and very active component in the universe. The interstellar dust starts its epic voyage inside a star and is injected into the interstellar medium by expanding circumstellar envelopes, supernovea and novae. Eventually, it will be mixed in interstellar and molecular clouds which can contract and form proto-solar nebula, the birthplaces of new suns and planets.

We can learn more about cosmic dust in different ways. The direct way is the investigation of interstellar grains isolated from meteorites or IDPs (Interstellar Dust Particles). Another way is the investigation of cosmic dust analogs and the measurement of their spectral properties at different levels of chemical and structural processing.

Dust introduces the problems of solid-state and surface physics and chemistry into astrophysics. The goal of our laboratory work is the production, structural analysis and measurement of the spectral properties of cosmic dust analogs in a wavelength range relevant for comparisons with astrophysical observations and the improvement of our knowledge on dust condensation and processing in different astrophysical environments.

The main components of cosmic dust comprises amorphous and crystalline magnesium and magnesium-iron silicates, amorphous and amorphous hydrogenated carbon grains, but also minor components such as oxides, sulfides, carbonates and silicides. My laboratory work is mainly focused on silicates and carbon materials.

Silicates

Synthesis of amorphous and crystalline magnesium and magnesium-iron silicates by using different production methods like
conventional melting and quenching technique Sol-Gel synthesis, and laserablation.

Careful determination of the chemical composition, internal homogeneity in a nanometer scale, morphology and structural properties of the solid grains by using wet-chemical quantitative methods, scanning electron microscopy (SEM), transmission and high resolution transmission electron microscopy (TEM and HRTEM), energy dispersive X-ray analysis (EDX), and Raman spectroscopy.

Measurement of the spectral properties of the silicate material in a broad wavelength range comprising FUV, UV/VIS/NIR/MIR and FIR (100nm - 500 micron) and derivation of optical constants using Kramers-Kronig relation and Lorentz-oscillator-fit methods.

Investigation of spectral properties of natural minerals in relation to their chemical composition and internal structure.

Investigation of the chemical and structural processing of silicate grains in different astronomical environments.
Experiments on the conversion of amorphous silicates into crystalline material by thermal annealing and investigation of the influence of Si-OH groups on the crystallization behavior of silicates.

Experiments on the effect of ion irradiation (energy range keV-MeV) on amorphous and crystalline silicates.

Carbonaceous Grains

Simulation experiments on the condensation of carbon nanoparticles in astrophysical environments by vapor-phase condensation of carbon nanoparticles in quenching gas atmospheres. We use two different carbon sources (1.) laserablation with a pulsed Nd-YAG LASER (532 nm) and (2.) laserpyrolysis of acetylene and other precursor gases using a pulsed CO₂ laser.

Structural and morphological variation of the condensed grains can be achieved by changing the conditions in the production process, for example, varying the laser power, gas pressure, total gas flow, precursor gas, precursor gas ratios, target material, composition of the quenching gas atmosphere.

Structural and morphological analyses of the grains by using TEM and HRTEM in combination with EELS (state of order, size of graphitic subunits, quantitative ratio of sp²/sp³ hybridized C atoms), EDX (content of hetero atoms), and electron diffraction (internal structure), Raman spectroscopy (state of order, crystallite sizes of graphitic subunits, phase identification) and NMR (bond ratio).

Measurements of the spectral properties of the condensed carbon grains from the FUV up to the IR in relation to morphology and internal structure of the grains.

Investigation of the spectral behavior of interstellar nanodiamonds isolated from the Murchison and Allende meteorites.