posted on 2021-02-16, 02:13authored byJanne-Petteri Niemelä, Anish Philip, Nadia Rohbeck, Maarit Karppinen, Johann Michler, Ivo Utke
State-of-the-art
atomic layer deposition (ALD) thin-film technology
which is well-integrated with microelectronics and beyond is currently
strongly extending toward hybrid materials where organic fragments
are inserted within the inorganic matrix through so-called molecular
layer deposition (MLD) cycles. This allows the fabrication of nanoscale
inorganic–organic superlattices and multilayers directly from
the gas phase. These materials are particularly promising for enhancing
the mechanical flexibility of rigid inorganics. Here we demonstrate
for ALD/MLD-grown ε-Fe2O3/Fe-terephthalate
superlattice structures that nanoscale (1–10 nm) Fe-terephthalate
interlayers significantly improve the flexibility of ε-Fe2O3 thin films without sacrificing their unique
high-coercive-field magnetic characteristics. Nanoindentation evaluation
indicates that the elastic modulus can be reduced by a factor of 2
down to 70 ± 20 GPa, while in situ tensile fragmentation testing
demonstrates that the crack onset strain and critical bending radius
can be tuned by a factor of 3. Modeling of the tensile fragmentation
patterns through Weibull statistics shows that cohesive and interfacial
shear strain, following the trend for crack onset strain, increase
with increasing organic content, while gains for the respective strengths
are limited by the simultaneous reduction in elastic modulus. The
Fe-terephthalate film exhibits high interfacial shear strain/strength
and low tendency for buckling, which highlights its potential to act
as an adhesion layer for the ferrimagnetic ε-Fe2O3 layers. The results are particularly interesting for magnetic
recording applications in sustainable next-generation flexible electronics.