Defined as a semiconductor structure where the chemical composition changes with position. (Often sandwiched layers)
Structures stacked intimately during growth process. Chemically: L or g to grow particles, ALD, CVD, Spin coating. Physically: Sputtering
Ex: Oxides, GaN+GaAntimonid, heterometallics
Two perovskites can have same structure but different symmetries.
The grain boundaries/surfaces are interesting!
Parameters for good epitaxy
Similar crystal structure
In lattice constant size (1-2% deviation between phases is ok)
Perovskite structure phase termination
The center termination can have charge neutrality if the cation is in 2+ ox state.
The leftmost termination type can be charge neutral if the cation is in 2+ ox state.
If the caton terminations are exposed to atmosphere, the “undercoordinated” cations will undergo surface reconstruction in order to be happy. Or the surface can adsorb water, oxygen or other to satisfy bonds.
Phase ternimations can also be challenged if one of the phases has electrically charged layers, while the other has neutral layers.
SrTiO and LaAlO heterostructures is the most documented one.
Magnetization Hysteresis of SrTiO3|LaAlO3
Proves ferro or ferrimagnetism (as only these have open hysteresis loop)
SrTiO3 are diamagnetic, LaAlO3 is diamagnetic, not expected to be ferro/ferrimagnetic when put together.
Probably an effect of the charge layer mismatch
Super rare to have coexistence of ferromagnetism and superconducting properties.
Can you have heterostructures of two Rocksalt structures?
Ex: MgO | NiO
Possible, same crystal structure, same unit cell size
However, intermixing of Mg and Ni may occur over the surface region
More prone to intermixing when using high energy synthesis methods (e.g. sputtering). Low temp methods, ALD, Spin coatings can help avoid intermix.
