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In this study, in situ synchrotron x-ray diffraction was used to investigate a high-temperature phase transition in tensile-strained epitaxial NaNbO3/(110)DyScO3 films. A ferro-to-ferroelectric phase transition was found in the temperature range between 230 and 350 °C, with a very pronounced thermal hysteresis. While at room temperature the well known monoclinic a1a2 in-plane ferroelectric phase is present, here, a slightly disturbed orthorhombic ferroelectric a1/a2 phase with exclusive in-plane polarization was found at high temperatures. This phase appeared in four variants, indicating the occurrence of four types of superdomains. The orthorhombic symmetry and the corresponding domain morphology observed at high temperatures showed a striking similarity to K0.9Na0.1NbO3 thin films grown on a (110) NdScO3 substrate. [ABSTRACT FROM AUTHOR]

The three-dimensional arrangement and orientation of domain walls in ferroelectric K0.9Na0.1NbO3/(110)NdScO3 epitaxial thin films were investigated at different temperatures both experimentally by means of piezoresponse force microscopy and three-dimensional x-ray diffraction and theoretically by three-dimensional phase-field simulations. At room temperature, a well-ordered herringbone-like domain pattern appears in which there is a periodic arrangement of a1a2/MC monoclinic phases. Four different types of domain walls are observed, which can be characterized by out-of-plane tilt angles of ±45° and in-plane twist angles of ±21°. For the orthorhombic high-temperature phase, a periodic a1/a2 stripe domain pattern with exclusive in-plane polarization is formed. Here, two different types of domain walls are observed, both of them having a fixed out-of-plane domain wall angle of 90° but distinguished by different in-plane twist angles of ±45°. The experimental results are fully consistent with three-dimensional phase-field simulations using anisotropic misfit strains. The qualitative agreement between the experiment and the theory applies, in particular, to the wide phase transition range between about 180 °C and 260 °C. In this temperature range, a complex interplay of coexisting monoclinic a1a2/MC and orthorhombic a1/a2 phases takes place. [ABSTRACT FROM AUTHOR]

The properties of the conductance at the LaInO3/BaSnO3 heterointerface are reported. The heterointerface is formed by covering the semi‐insulating BaSnO3:La thin films with 10 nm LaInO3 films, which are all epitaxially grown on NdScO3 substrates. Structural properties of BaSnO3 thin films are investigated by means of X‐ray diffraction and transmission electron microscopy and exhibit a threading dislocation density of 6 × 1010 cm−2. Via capacitance–voltage (C–V) measurements, clear evidence is present for the accumulation of electrons at the interface within 2.5 nm in the BaSnO3 layer, confirming the formation of a 2D electron gas (2DEG). Additionally, temperature dependent Hall effect measurements reveal a semiconducting behavior of the electron density of the 2DEGs. The room temperature mobility of 22 cm2 V−1 s−1 at an electron density of 4 × 1013 cm−2 is found to increase as the temperature decreases to 25 K. [ABSTRACT FROM AUTHOR]

A high growth rate process above 1 µm/h was achieved for Si-doped (100) β-Ga2O3 homoepitaxial films grown via metalorganic vapor phase epitaxy (MOVPE) while maintaining high crystalline perfection up to a film thickness of 3 µm. The main growth parameters were investigated to increase the growth rate and maintain the step-flow growth mode, wherein the enhanced diffusion channel due to the formation of a Ga adlayer was proposed to be the possible growth mechanism. Si doping allowed precise control of the n-type conductivity of the films with electron concentrations ranging from 1.5 × 1017 to 1.5 × 1019 cm−3 and corresponding mobilities from 144 to 21 cm2 V−1 s−1, as revealed by Hall effect measurements at room temperature. Secondary ion mass spectrometry confirmed homogeneous Si doping through the film and a one-to-one correlation between the Si concentration and the electron concentration. Low defect density in the films was determined by x-ray diffraction measurements. The demonstration of a high growth rate process of β-Ga2O3 films with μm level thickness and smooth surface morphology via MOVPE is critical for high power electronics with vertical device architecture. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate that extremely thin strain-engineered K0.7Na0.3NbO3 (KNN) films are ideal candidates for highly sensitive and also potentially selective surface acoustic wave (SAW) sensor applications. The strength of the use of these films in SAW sensors is based on their piezoelectric properties and their thinness. The latter leads to a strong concentration of the SAW energy at the very surface of the sensor's delay line and the generation of higher harmonics with significant amplitudes. Thin epitaxial films of typically 30 nm in thickness are grown via liquid-delivery spin metal-organic vapor phase epitaxy on different (110)-oriented scandate substrates (TbScO3 and GdScO3). The epitaxial strain is induced by the lattice mismatch between a substrate and a film. The SAW signal of thin KNN films and the resulting sensitivity of an SAW thin KNN film sensor are compared with conventional bulk SAW sensors based on LiNbO3 (LN) using identical electrode designs for the generation and detection of the SAW for both systems. Compared to the conventional LN SAW sensor, our KNN-based sensor shows a sensitivity that is approximately 14 times higher. This was achieved using only the third and fifth harmonics. Using even higher harmonics, the improvement could potentially be boosted up to a factor > 40. Moreover, we showed that simultaneous sensor recording of mass loading at different harmonics is possible with the KNN sensor. Similar to other sensor concepts, the resulting multiple signals might provide a fingerprint of the detected material and, thus, lead to a selective detection of the mass load. [ABSTRACT FROM AUTHOR]

Homoepitaxial growth of SrTiO3 thin films on 0.5 wt% niobium doped SrTiO3 (100) substrates with high structural perfection was developed using liquid-delivery spin metal–organic vapor phase epitaxy (MOVPE). Exploiting the advantage of adjusting the partial pressures of the individual constituents independently, we tuned the Sr/Ti ratio of the gas phase for realizing, stoichiometric, as well as Sr deficient layers. Quantitative energy dispersive X-ray spectroscopy in a scanning transmission electron microscope confirm Sr deficiency of up to 20% in nominally off-stoichiometrically grown films. Our MOVPE process allows to grow such layers in phase pure state and without extended defect formation. Indications for oxygen deficiency could not be identified. Sr deficient layers exhibit an increased permittivity of ɛr = 202 and a larger vertical lattice parameter. Current–voltage characteristics (IVCs) of metal–oxide–semiconductor (Pt/SrTiO3/SrTiO3:Nb) structures reveal that Sr deficient SrTiO3 films show an intrinsic resistive switching with on–off ratios of three orders of magnitude at RT and seven orders of magnitude at 10 K. There is strong evidence that a large deviation from stoichiometry pronounces the resistive switching behavior. IVCs conducted at 10 K indicate a defect-based mechanism instead of mass transport by ion diffusion. This is supported by in-situ STEM investigations that show filaments to form at significant higher voltages than those were resistive switching is observed in our samples. [ABSTRACT FROM AUTHOR]

A benchmark experiment is reported that demonstrates the shortening of hard X‐ray pulses in a synchrotron‐based optical pump–X‐ray probe measurement. The pulse‐shortening device is a photoacoustic Bragg switch that reduces the temporal resolution of an incident X‐ray pulse to approximately 7.5 ps. The Bragg switch is employed to monitor propagating sound waves in nanometer thin epitaxial films. From the experimental data, the pulse duration, diffraction efficiency and switching contrast of the device can be inferred. A detailed efficiency analysis shows that the switch can deliver up to 109 photons s−1 in high‐repetition‐rate synchrotron experiments. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition (PLD) was employed to grow coherent NaNbO 3 thin films on several lattice matched substrates. Compressive (tensile) lattice strain was induced by the use of NdGaO 3 and SrTiO 3 (DyScO 3 and TbScO 3 ) single crystals. Deposition from a stoichiometric target at a 5 Pa O 2 pressure was found to result in sodium and oxygen deficient films. By increasing the oxygen background pressure up to 200 Pa the oxygen and sodium concentrations in films on all substrates could be increased. As an alternative way to enhance the compositional ordering in the films sodium excess ceramics were used as PLD targets. With a Na/Nb ratio up to 1.17, phase pure, well-ordered films with smooth surfaces were grown on all substrates. The film composition was found to have a crucial impact on the formation of ferroelectric domains in tensilely strained films on DyScO 3 substrates. Regularly arranged ferroelectric stripe domains were obtained at an oxygen partial pressure of 5 Pa using sodium rich growth parameters via the application of a 1.17 Na/Nb ratio PLD target. [ABSTRACT FROM AUTHOR]

Epitaxially strained NaNbO3 films were grown by liquid-delivery spin metal-organic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently grown compressively strained NaNbO3 films on NdGaO3 exhibit the orthorhombic c phase. With increasing in-plane strain a first structural phase transition to the monoclinic r phase and, further on, for films grown under tensile strain on rare earth scandates, a second phase transition to the aa phase, are observed. Our results are in good agreement with the pathway of phase transitions predicted by Diéguez, Rabe & Vanderbilt [ Phys. Rev. B, (2005), 72, 144101] for NaNbO3 films. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of different phases of lead-free sodium–bismuth–titanate were epitaxially grown on SrTiO3 and NdGaO3 substrates by metal–organic chemical vapor deposition. Aurivillius phases with m =3, m =3.5 and m =4 and the Na0.5Bi0.5TiO3 perovskite phase were obtained by varying the substrate temperature and the Na/Bi ratio in the gas phase. Investigations of the impact of crystallographic structure and incorporated film lattice strain on local piezo- and ferroelectric properties were carried out by piezoresponse force microscopy experiments using dual AC resonance tracking combined with a tip-sample contact modeling procedure to determine an effective value for the piezoelectric coefficient for each sample. Comparative piezoresponse force microscopy measurements revealed a significant increase of the average effective piezoelectric coefficient d zz when the film structure changed from an Aurivillius phase to the perovskite phase. Films of perovskite phase have also shown the possibility of local tip-induced polarization switching. [Copyright &y& Elsevier]