Forschergruppe FOR 759
The Formation of Planets:
The Critical First Growth Phase
We first investigated PLD thin films with Mg2SiO4 composition deposited on a Si wafer, which were annealed in different sequences.
... from IR Spectroscopy
Fig. 1 shows two IR spectra (normalised to the uncovered reference) of such a sample before (black) and after (red) annealing at 800°C for 128 hours. During annealing forsterite has crystallized, as indicated by the several characteristic peaks (green bars, according to Hofmeister, 1997). The strong band at 1080 cm-1 is related to SiO2-bands (Koike, 2003).
... from SEM (Fig.2) and AFM (Fig. 3a,b) investigations of the surface topography
Figs. 2 and 3 a, b show the surface topography after annealing in air at 1080°C for 10 days (= 240 hours).
In contrast to the original amorphous thin film, the surface is no longer smooth but rough with deep cavities. Some of them contain small spheres which are probably single crystals. The diameter of the spheres was determined to approx. 1µm.
Remaining open questions:
- Why do cavities appear on the surface of the PLD film?
- Are they related to dewetting of the film on the surface of the substrate due to volume decrease during the crystallisation process?
Experimental series with different starting materials, different annealing times and temperatures are on the way.
Results and observations are continuously compared with the results of the evaporation, condensation and annealing experiments on SiO and SiO2 carried out by M. Klevenz at KIP.