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ICMCTF - 2014
Matthias Bartosik (M. Bartosik)
"Thermal Expansion and Elasticity of metastable cubic B1-AlN"
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Aluminum nitride is an important material for various applications due to its specific properties. Whereas the stable wurtzite structure is well characterized, only little is known for the metastable high-pressure phase face centered cubic (B1, rock-salt type) AlN. By coherency strains to lattice matched materials, like B1-CrN, AlN can be stabilized in the metastable B1 crystal structure even under ambient conditions. However, the maximum thickness of fully stabilized B1-AlN is limited to a few nm because the high chemical driving force for transformation into its stable wurtzite allotrope prevents the existence of bulk free-standing pieces of this phase.
The experimental characterization of phases in such small dimensions is a challenging task. Here, an approach is proposed that combines in-situ wafer curvature experiments with continuum mechanics modeling to determine the in-plane coefficient of thermal expansion (CTE) and elastic properties of B1-AlN. In the experiments CrN/AlN superlattice films on Si (100) are investigated with 1 nm thick AlN layers stabilized in the B1 structure as confirmed by high-resolution transmission electron microscopy. The continuum mechanics approach is formulated as inverse problem solved by means of finite element methods.
To cross-validate the results, the temperature dependent CTE is calculated using ab initio methods. The elastic properties of B1-AlN are reproduced from previous studies, emphasizing the significant difference of B1-AlN compared to other nitride materials used as hard protective coating materials.

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