Phase and Orientation Control of NiTiO3 Thin Films

Abstract

Subtle changes in the atomic arrangement of NiTiO3 in the ilmenite structure affects its symmetry and properties. At high temperatures, the cations are randomly distributed throughout the structure, resulting in the corundum structure with R−3c symmetry. Upon cooling, the cations order in alternating layers along the crystallographic c axis, resulting in the ilmenite structure with R−3 symmetry. Related to this is the R3c symmetry, where the cations alternate both perpendicularly and along the c axis. NiTiO3 with the latter structure is highly interesting as it exhibits ferroelectric properties. The close relationship between structure and properties for ilmenite-related structures emphasizes the importance of being able to control the symmetry during synthesis. We show that the orientation and symmetry of thin films of NiTiO3 formed by atomic layer deposition (ALD) can be controlled by choice of substrate. The disordered phase (R−3c), previously only observed at elevated temperatures, have been deposited at 250 °C on α-Al2O3 substrates, while post-deposition annealing at moderate temperatures (650 °C) induces ordering (R−3). We have in addition explored the symmetry and epitaxial orientation obtained when deposited on substrates of LaAlO3(100), SrTiO3(100) and MgO(100). The presented work demonstrates the possibilities of ALD to form metastable phases through choice of substrates.

Area-selective atomic layer deposition of molybdenum oxide

“…In the current work, simple post-deposition annealing in air has been performed. This has been done using rapid thermal processing (RTP), a tool commonly used in our group [128,129]. RTP uses lamps to heat the samples and was originally developed to anneal silicon wafers in the semiconductor industry, as it has a much more limited thermal budget than traditional furnaces [130].…”

Effect of Subcycle Arrangement on Direct Epitaxy in ALD of LaNiO3

“…This very often leads to an amorphous potpourri of binary constituents that require postdeposition annealing to facilitate crystallization of a ternary compound. Note that some processes facilitate direct epitaxy by this approach, such as the growth of NiFe 2 O 4 , NiTiO 3 , LaMnO 3 , BaTiO 3 , and SrZrO 3 . − In multilayer deposition, binary films of some thickness (nanometer scale) are deposited and intermixing/diffusion takes place after deposition to create the ternary compound, usually aided by postdeposition annealing. An example of this is found in the deposition of epitaxial films of BiFeO 3 .…”

Influence of sputtering conditions and annealing parameters on structure and morphology of NiTiO3 ilmenite thin films

“…In most of the above-mentioned technologies, materials must be designed in the form of thin films to improve their life span under operating conditions or to reduce their dimensions for 3 miniaturization constrains. NiTiO3 thin films were grown by several techniques such as Atomic Layer Deposition [17,18], Pulsed Laser Deposition [19] and by Plasma Sputtering [6,15,20,21]. Among all these techniques, magnetron sputtering is a versatile one, suitable for the deposition of high-quality and well-adhered layers of a wide range of materials at commercially useful scales.…”