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Crystallisation of semiconductor amorphous film carries some special features. Besides explosive and spherulite modes less-known “transrotational” one (when crystals are growing with internal lattice bending round axis or axes lying in the film plane [1]) is observed. We use combination of transmission electron microscopy (TEM), including in situ and high resolution studies, with atomic force microscopy (AFM) to investigate amorphous-crystalline transformation and amorphous-crystalline interface in thin films (using the same definite grains and their local areas for both methods). Amorphous films were prepared by vacuum condensation (Se, with Te doping) and pyrolysis (Fe2O3), separated from the substrate and placed on TEM grids for subsequent electron beam annealing.
Complicated regular change in lattice orientations are indicated by regular bend contour patterns on the TEM images (main features presented earlier for both Se [2] and Fe2O3 crystals [1]).
AFM has been used to visualize the surface structure of the amorphous matrix, crystals and amorphous-crystalline interface including the details (e.g. globular size and its distribution in initial amorphous material inherited by the crystals grown herein).
Concentric zones of different orientations and imperfection revealed by TEM are also seen in AFM, based on the variations in mean height (for Se) and on the character of fibrous structure (for Fe2O3) which differs for two types of crystals. Both types have also radial elongated nodes and hollows of different character revealed by AFM.
Probably most important observation is obtained for the amorphous-crystalline interface for crystallization of Fe2O3 phase: there are strong variations in crystal height, probably associated with variations of lattice orientations. It should be taken into account for advanced models of crystallisation in amorphous films. Anyway it is evident, that simple concept: flat crystal growing along the inside of amorphous film, powered primarily by tensile stresses (caused by the density changes) is inadequate.
[1]. V.Yu. Kolosov and A.R. Tholen, Acta Mater. v. 48 (2000), p. 1829.
[2]. I.E. Bolotov and V.Yu. Kolosov, Phys. Stat. Sol. v. 69a (1982), p. 85.
*This work was partially supported by INTAS (00-100), pending support from RFBR
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