The fabrication of well‐defined, atomically sharp substrate surfaces over a wide range of lattice parameters is reported, which is crucial for atomically regulated epitaxial growth of complex oxide heterostructures. By applying a framework for controlled selective wet etching of complex oxides on the stable rare‐earth scandates (REScO3), apseudocubic = 0.394 – 0.404 nm, the large chemical sensitivity of REScO3 to basic solutions is exploited, which results in reproducible, single‐terminated surfaces. Time‐of‐flight mass‐spectroscopy measurements show that after wet etching the surfaces are predominantly ScO2 ‐terminated. Moreover, the morphology study of SrRuO3 thin‐film growth gives no evidence for mixed termination. Therefore, it is concluded that the REScO3 surfaces are completely ScO2 ‐terminated.
engineering can be used to tune the specifi c thermoelectric material properties.Detailed thermoelectric characterization of Na x CoO 2 thin fi lms has been hindered by the chemical instability in ambient conditions. [ 7,8 ] However, a recently developed method to obtain chemically stable, single-phase Na x CoO 2 thin fi lms by pulsed laser deposition due to the in situ deposition of an amorphous AlO x capping layer enables us to exploit the intrinsic properties of these thermoelectric thin fi lms. [ 8 ] Here, we show that by structural engineering in chemically stable Na x CoO 2 thin fi lms the thermoelectric properties can be controlled and enhanced as compared to bulk samples. By changing the single crystalline substrate material we can control the structural properties and as a consequence the electronic and thermal properties of the thermoelectric thin fi lms. Tuning of the grain size within the Na x CoO 2 thin fi lms signifi cantly infl uences the achievable Seebeck coeffi cient. We demonstrate that preservation of the crystallinity in these thin fi lms with enhanced Seebeck coeffi cient results in minimal reduction of the electrical conductivity and, therefore, leads to a doubling of the thermoelectric power factor at room temperature.Here, structural engineering is applied as a tool to obtain improved control over the thermoelectric properties of Na x CoO 2 thin fi lms, which is unique for epitaxial thin fi lms and cannot be obtained in single crystal or polycrystalline samples. To study this effect, Na x CoO 2 thin fi lms were grown by pulsed laser deposition (PLD) on various single crystal substrates. All Na x CoO 2 thin fi lms were deposited under the same conditions and have a thickness of 60 nm. Independent of the substrate material and structure, all thin fi lms showed a preferred growth orientation with the (00l) direction parallel to the surface normal.Previously it was shown that the crystallinity of Na x CoO 2 thin fi lms does not strongly depend on the deposition temperature, [ 8 ] and an optimum deposition temperature of 430 °C was determined. However, the effect of oxygen deposition pressure on the crystallinity was not systematically studied yet. Here, we observe a signifi cant decrease in crystallinity when the deposition pressure was reduced by one and two orders of magnitude from the previously reported value of 0.4 mbar, [ 8 ] resulting in an increased resistivity by a factor of fi ve, together with a strong reduction of the Seebeck coeffi cient. Based on these results we can conclude that, although the deposition pressure can clearly be used to tune the crystallinity of these Na x CoO 2 thin fi lms, it will not provide the required enhanced control over the thermoelectric properties. Therefore the optimized deposition parameters [ 8 ] are used, which result in a combination of the optimum crystallinity and thermoelectric properties. Furthermore, all thin fi lms have been cooled down after growth in 1 atm. of oxygen at a rate of 10 °C min -1 to optimize the oxidation level.
With reduced dimensionality, it is often easier to modify the properties of ultrathin films than their bulk counterparts. Strain engineering, usually achieved by choosing appropriate substrates, has been proven effective in controlling the properties of perovskite oxide films. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. Here we report the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO_{3} films by the deposition of a SrTiO_{3} capping layer, which can be lithographically patterned to achieve local control. Using a scanning Sagnac magnetic microscope, we show an increase in the Curie temperature of SrRuO_{3} due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. This capping-layer-based technique may open new possibilities for developing functional oxide materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.