Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposited and freestanding single-crystalline Fe7Pd3 thin films across the martensite–austenite transition. We find experimental evidence that magnetic domain appearance is strongly affected by the presence and absence of nanotwinning. While the martensite–austenite transition upon temperature variation of as-deposited films is clearly reflected in topography by the presence and absence of a characteristic surface corrugation pattern, the magnetic domain pattern is hardly affected. These findings are discussed considering the impact of significant thermal stresses arising in the austenite phase. Freestanding martensitic films reveal a hierarchical structure of micro- and nanotwinning. The associated domain organization appears more complex, since the dominance of magnetic energy contributors alters within this length scale regime.
This study demonstrates an innovative approach to clean a polycrystalline seed layer surface for solid phase epitaxy of amorphous silicon (a-Si). The excimer laser cleaning (ELC) makes use of in situ excimer laser irradiation during the first stages of a-Si deposition leading to melting of the as deposited a-Si and parts of the seed layer. The increased diffusion in liquid silicon allows for "smearing out" of surface contamination species. After liquid phase epitaxy is finished, further a-Si is deposited and crystallized by solid phase epitaxy. Thanks to the "smearing out," the interface between the crystalline and amorphous silicon exhibits less contamination locally. SIMS measurements demonstrate a reduced carbon concentration at the seed layer surface after ELC. Numerical simulations, taking into account heat transfer and temperature dependent diffusion, support the reduction of carbon concentration. The simulations agree very well with experimental results. To get optimal solid phase growth conditions, the a-Si deposition temperature has to be below 200 8C. Above 200 8C deposition temperature, defective growth occurs resulting in poor crystallinity or even in nonepitaxial growth.
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