The microstructural characterization of materials is essential for the understanding of diffusion, reaction, interaction and deformation processes. Transmission electron microscopy is a tool to identify some of these processes with atomic-scale resolution. Projects of Dr. Heinrich are on interfaces and chemical reactions in thin-film solar cells, on metastable phases in Al- und Ni-alloys and on magnetic intermetallics.

The absorber layers in thin-film solar cells have a direct band-gap and layers of a few micrometers thickness absorb light very efficiently. In contrast to conventional Si-based solar cells the costs for the materials used in possible large-scale production are low. Efficiencies of 16% for CdTe/CdS cells and 18% for Cu(In,Ga)Se2 devices (CIGS) are obtained in some cases, but the reproducibility of processing parameters is poor. To understand and improve processing, adhesion between Mo and CIGS, Na diffusion, chemical gradients in CIGS, and new materials replacing CdS for the p-n junction are investigated. Focussed-ion beam cutting for electron microscopy in combination with electron-beam induced current measurements is used to select and characterize defect structures in these multilayer systems.

The phase transformation sequences during the decomposition of alloys with face-centered cubic structure frequently involve metastable nanoscaled precipitates coherently embedded in the matrix material. Metastable phases like Guinier-Preston zones act as nucleation sites for precursors of a stable phase. The formation mechanisms of precursor phases with hexagonal close-packed structure in Al- and Ni-alloys are investigated using transmission electron microscopy. Electron microscopy is also used to characterize the microstructural evolution of magnetic alloys with L1₀ structure.


Selected Publications

P. Müllner, B. E. Bürgler, H. Heinrich, A. S. Sologubenko and G. Kostorz, “Observation of the shear mode of the e to t phase transformation in a Mn-Al-C single crystal”, Phil. Mag. Lett. 82, pp. 71-79, 2002.

H. Heinrich, A. Vananti, G. Kostorz, “Stress fields near interfaces of aluminium-based metal-matrix composites”, Phil. Mag. A 82, pp. 2269-2285, 2002.

R. Erni, H. Heinrich, G. Kostorz, “Quantitative characterisation of chemical inhomogeneities in Al-Ag using high-resolution Z-contrast STEM”, Ultramicroscopy 94, pp. 125-133, 2003.

H. Xu, H. Heinrich, J.M.K. Wiezorek, “Microstructural changes during annealing of Fe-Pd based thin films”, Intermetallics 11, pp. 963-969, 2003.

M. Terheggen, H. Heinrich, G. Kostorz, A. Romeo, D. Baetzner, A.N. Tiwari, A. Bosio, N. Romeo, “Structural and chemical interface characterization of CdTe solar cells by transmission electron microscopy”, Thin Solid Films 431-432, pp. 262-266, 2003.

R. Erni, H. Heinrich, G. Kostorz, “On the internal structure of Guinier-Preston zones in Al-3 at.% Ag“, Phil. Mag. Lett. 83, pp. 599-609, 2003.