On the epitaxy of twin-free cubic (111) praseodymium sesquioxide films on Si(111)

Abstract

Twin-free epitaxial cubic (111) praseodymium sesquioxide films were prepared on Si(111) by hexagonal-to-cubic phase transition. Synchrotron radiation grazing incidence x-ray diffraction and transmission electron microscopy were applied to characterize the phase transition and the film structure. As-deposited films grow single crystalline in the (0001)-oriented hexagonal high-temperature phase of praseodymium sesquioxide. In situ x-ray diffraction studies deduce an activation energy of 2.2eV for the hexagonal-to-cubic phase transition. Transmission electron microscopy shows that the phase transition is accompanied by an interface reaction at the oxide/Si(111) boundary. The resulting cubic (111) low-temperature praseodymium sesquioxide film is single crystalline and exclusively shows B-type stacking. The 180° rotation of the cubic oxide lattice with respect to the Si substrate results from a stacking fault at the substrate/oxide boundary.

Epitaxy of single crystalline PrO2 films on Si(111)

“…7 Postdeposition annealing in 10 −5 mbar O 2 transforms h-Pr 2 O 3 films into cubic c-Pr 2 O 3 films with bixbyite structure ͑Ia3͒ which are stable if exposed to air. 8 The bulk lattice constant of c-Pr 2 O 3 is approximately twice the bulk lattice constant of Si. The residual lattice mismatch is +2.6% taking into account the 2:1 relationship of the lattice constants.…”

Postdeposition annealing induced transition from hexagonal Pr2O3 to cubic PrO2 films on Si(111)

“…This explains the phase transition one observes when hexagonal Pr 2 O 3 , which is our original phase after the evaporation process, is transformed to twin-free cubic Pr 2 O 3 or Pr 2 O 3+␦ by annealing in nitrogen 11 or low pressure oxygen. 12 The phase transition and the formation of an interface layer were not observed after annealing in UHV. 11 If the substrate was oxidized before the evaporation process, the film grows in the cubic phase but with a high density of stacking twins.…”

“…In general, the phase transition is only observed after an interfacial layer was formed between film and substrate. 12 This has been interpreted as a disconnection of film and substrate. 12 As we observed that the lateral lattice constant does not change significantly during the annealing process, this disconnection cannot be the reason for the phase transformation.…”

“…12 This has been interpreted as a disconnection of film and substrate. 12 As we observed that the lateral lattice constant does not change significantly during the annealing process, this disconnection cannot be the reason for the phase transformation. In our opinion the reason for the transformation is as follows.…”

“…If h-Pr 2 O 3 ͑0001͒ films are annealed in 1 bar nitrogen 11 or 10 −5 mbar oxygen 12 atmosphere, an interfacial layer is formed and the films are transformed to cubic c-Pr 2 O 3 ͑bix-byite structure with Ia3 symmetry͒, 12 which is stable under normal temperature and pressure. The lattice constant of bulk c-Pr 2 O 3 is approximately twice as large as the lattice constant of Si.…”