Abstract
This perspective considers the enormous promise of epitaxial functional transition metal oxide thin films for future applications in low power electronic and energy applications since they offer wide-ranging and highly tunable functionalities and multifunctionalities, unrivaled among other classes of materials. It also considers the great challenges that must be overcome for transition metal oxide thin films to meet what is needed in the application domain. These challenges arise from the presence of intrinsic defects and strain effects, which lead to extrinsic defects. Current conventional thin film deposition routes often cannot deliver the required perfection and performance. Since there is a strong link between the physical properties, defects and strain, routes to achieving more perfect materials need to be studied. Several emerging methods and modifications of current methods are presented and discussed. The reasons these methods better address the perfection challenge are considered and evaluated.
Highlights
Since the discovery of high-temperature superconductivity in perovskite oxides in 1986, the unearthing of a huge range of physical phenomena in transition-metal oxides (TMOs) has been nothing short of remarkable, e.g., new magnetics, ferroelectrics, multiferroics, semiconductors, transparent conductors, calorics, plasmonics, catalysts, and ionic conductors, from prominent solid state chemistry groups, e.g., Refs. 1–6
Optimum physical properties have been achieved in (La, Sr)MnO3 and BiFeO3.27,28 We note that the non-TMO perovskites, e.g., BaSnO3, are less susceptible to variable electronic conduction from cation defects since mixed valence of the non-TMO cations is less prevalent scitation.org/journal/apm and any n-type defects are completely compensated by acceptor defects.[29]
The methods are at different stages of understanding/development, some being at very early stage but showing tantalizing property enhancements to warrant much deeper investigation. (A) adsorption-controlled growth by Molecular Beam Epitaxy (MBE); (B) hybrid growth processes, i.e., Pulsed laser deposition (PLD) + soft chemical; (C) interval growth in PLD; (D) amorphous phase epitaxy (APE), (E) liquid assisted growth, (F) vertically aligned nanocomposites, and (G) laser-heated substrates with localized high temperature heating
Summary
Since the discovery of high-temperature superconductivity in perovskite oxides in 1986, the unearthing of a huge range of physical phenomena in transition-metal oxides (TMOs) has been nothing short of remarkable, e.g., new magnetics, ferroelectrics, multiferroics, semiconductors, transparent conductors, calorics, plasmonics, catalysts, and ionic conductors, from prominent solid state chemistry groups, e.g., Refs. 1–6. The very urgent need to reduce power consumption to slow global warming makes TMO devices, with their unrivaled stability, all-encompassing properties, in most cases low toxicity, and ability to be made in large areas, of unprecedented importance. For this reason, a paradigm shift in thinking is needed to put funding of materials engineering of TMO films on, at the very least, an equal footing with the basic science funding. In the case of TMOs, both anion and cation non-stoichiometry is the key challenge, rather than the purity of materials
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