Bonding geometry engineering of metal–oxygen octahedra is a facile way of tailoring various functional properties of transition metal oxides. Several approaches, including epitaxial strain, thickness, and stoichiometry control, have been proposed to efficiently tune the rotation and tilt of the octahedra, but these approaches are inevitably accompanied by unnecessary structural modifications such as changes in thin‐film lattice parameters. In this study, a method to selectively engineer the octahedral bonding geometries is proposed, while maintaining other parameters that might implicitly influence the functional properties. A concept of octahedral tilt propagation engineering is developed using atomically designed SrRuO
3
/SrTiO
3
(SRO/STO) superlattices. In particular, the propagation of RuO
6
octahedral tilt within the SRO layers having identical thicknesses is systematically controlled by varying the thickness of adjacent STO layers. This leads to a substantial modification in the electromagnetic properties of the SRO layer, significantly enhancing the magnetic moment of Ru. This approach provides a method to selectively manipulate the bonding geometry of strongly correlated oxides, thereby enabling a better understanding and greater controllability of their functional properties.
A clear experimental explanation of the contribution of Mott and Peierls transitions to the insulator−metal transition (IMT) characteristics in vanadium dioxide (VO 2 ) is still lacking. Examining the crystal and electronic structures of epitaxial VO 2 films grown at various deposition temperatures, a Mott or a Peierls transition was observed. The VO 2 film deposited at 500 °C showed suppressed Peierls transition characteristics because of the large inplane compressive strain in the insulating phase. The VO 2 films deposited at 600 and 650 °C had a higher IMT temperature because of the relaxation of both the in-plane and out-of-plane strain, and there were abundant V 4+ states. Therefore, it was related to a collaborative Mott−Peierls transition. Finally, the VO 2 film deposited at 720 °C showed a suppressed Mott transition because of the abundance of V 3+ states in the insulating phase. Furthermore, an analysis of the electronic structure of the insulating and metallic phases using in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy provide a complete band diagram to support the above explanation of the deposition-temperature-dependent IMT characteristics.
Studies
on the hydrogen incorporated M1 phase of VO2 film have
been widely reported. However, there are few works on
an M2 phase of VO2. Recently, the M2 phase in VO2 has received considerable attention due to the possibility of realizing
a Mott transition field-effect transistor. By varying the postannealing
environment, systematic variations of the M2 phase in (020)-oriented
VO2 films grown on Al2O3(0001) were
observed. The M2 phase converted to the metallic M1 phase at first
and then to the metallic rutile phase after hydrogen annealing (i.e.,
for H2/N2 mixture and H2 environments).
From the diffraction and spectroscopy measurements, the transition
is attributed to suppressed electron interactions, not structural
modification caused by hydrogen incorporation. Our results suggest
the understanding of the phase transition process of the M2 phase
by hydrogen incorporation and the possibility of realization of the
M2 phased-based Mott transition field-effect transistor.
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