LSAT Substrates Research Articles

Consequences of phase separation on magnetotransport in dc magnetron sputtered Sm0.50Sr0.50MnO3 thin films on LSAT substrate

Single crystalline thin films of Sm0.50Sr0.50MnO3 (SSMO) (thickness ∼200 nm) were prepared on LSAT (100) single crystal substrates by dc magnetron sputtering. The X-ray diffraction θ‒2θ and ω-2θ scan reveals that these films (i) have very good crystallinity, (ii) are oriented along out-of-plane c-direction, and (iii) are under small tensile strain. Temperature and magnetic field dependent electrical transport of these films shows (i) sharp paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition, (ii) large enhancement in TIM when subjected to magnetic field, (iii) hysteretic variation in resistivity with magnetic field, and (iv) huge occurrence of magnetoresistance near PMI-FMM transition. The magnetic state in the FMM (T < TC) regime resembles cluster glass, which is formed by the presence of charge ordered-antiferromagnetic clusters in the ferromagnetic matrix. The results shown in the present study could be regarded as the consequence of strong nature of phase separation in these films due to competing FMM and AFM-COI phases in these films which is known to be the generic feature of low bandwidth manganites.

In situ monitoring of atomic layer epitaxy via optical ellipsometry

We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity. Ruddlesden–Popper thin films of SrO(SrTiO3)n=4 were grown by means of metalorganic aerosol deposition in the atomic layer epitaxy mode on SrTiO3(1 0 0), LSAT(1 0 0) and DyScO3(1 1 0) substrates. The measured time dependences of ellipsometric angles, Δ(t) and Ψ(t), were described by using a simple optical model, considering the sequence of atomic layers SrO and TiO2 with corresponding bulk refractive indices. As a result, valuable online information on the atomic layer epitaxy process was obtained. Ex situ characterization techniques, i.e. transmission electron microscopy, x-ray diffraction and x-ray reflectometry verify the crystal structure and confirm the predictions of optical ellipsometry.

Transport phenomena in SrVO3/SrTiO3 superlattices

Epitaxial [(SrVO3)7/(SrTiO3)4]r (SVO/STO) superlattices were grown on (0 0 1)-oriented LSAT substrates using a pulsed electron-beam deposition technique. The transport properties of the superlattices were investigated by varying the number of repetitions of the SVO/STO bilayers r (1 ⩽ r ⩽ 9). A single SVO/STO bilayer (r = 1) was semiconducting, whereas an increase in the number of repetitions r resulted in metallic behavior in the superlattices with r ⩾ 3. The transport phenomena in the SVO/STO superlattices can be regarded as conduction through parallel-coupled SVO layers, the SVO layer embedded in the superlattices showed a great enhancement in the conductivity compared with the single SVO layer. This work provides further evidence of electronic phase separation in the SVO ultrathin layer that has been recently discovered, the SVO ultrathin layer is considered as a 2D Mott insulator with metallic and insulating phases coexisting, the coupling between SVO layers embedded in the SVO/STO superlattices creates more conduction pathways with increasing number of repetitions r, resulting in a crossover from insulating to metallic behavior.

Epitaxial growth and properties of Nb-doped anatase TiO2 films on LSAT by MOCVD

High quality single crystalline Nb-doped anatase phase TiO2 films with different Nb concentrations were deposited on LSAT (100) substrates by metal organic chemical vapor deposition (MOCVD) at 600 °C. The influences of Nb concentration on the structural, electrical and optical properties of the films have been investigated. The obtained films were single crystalline anatase TiO2 and the epitaxial relationship between the films and the substrates was confirmed as TiO2 (001) || LSAT (100) with TiO2 [010] || LSAT [010]. The resistivity of the films was reduced by almost 8 orders of magnitude after Nb doping and a minimum resistivity of 4.0 × 10−2Ω⋅cm was obtained in 0.6% Nb-doped samples. The films achieved a maximum mobility as high as 13.5 cm2⋅V−1⋅s−1. The carrier concentration was in a range of 9.4 × 1017–1.7 × 1019 cm−3. The optical transmittance of the films in the visible range exceeded 93% and the optical band gap was varied from 3.48 to 3.53 eV.

Nanoscale domains of ordered oxygen-vacancies in LaCoO3 films

High-quality LaCoO3 (LCO) thin films were epitaxially grown on SrTiO3 (STO), (La,Sr)(Al,Ta)O3 (LSAT) and LaAlO3 (LAO) substrates using pulsed laser deposition technique. Nanoscale domains with either horizontally or vertically modulated dark stripes are observed in the LCO films on STO and LSAT substrates, whereas only horizontally-modulated domains are found in the films on LAO substrate. The domain sizes and directions strongly depend on the strain state of the films due to lattice mismatch between film and substrate. The lattice strains in the films are mainly relaxed through change of the domain directions. The oxygen deficiency of the films has been revealed by X-ray photoelectron spectroscopy. As confirmed by high-angle annular dark field (HAADF) observations and high-resolution transmission electron microscopy (HRTEM) image simulations, the modulated dark stripes stem from oxygen-vacancy ordering, which causes local lattice expansion. The saturation magnetization increases with the tensile strain in the films. The ferromagnetic character is correlated with the oxygen deficiency, strain state and vertically modulated domains.

The influence of the in-plane lattice constant on the superconducting transition temperature of FeSe0.7Te0.3 thin films

Epitaxial Fe(Se,Te) thin films were prepared by pulsed laser deposition on (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT), CaF2-buffered LSAT and bare CaF2 substrates, which exhibit an almost identical in-plane lattice parameter. The composition of all Fe(Se,Te) films were determined to be FeSe0.7Te0.3 by energy dispersive X-ray spectroscopy, irrespective of the substrate. Albeit the lattice parameters of all templates have comparable values, the in-plane lattice parameter of the FeSe0.7Te0.3 films varies significantly. We found that the superconducting transition temperature (Tc) of FeSe0.7Te0.3 thin films is strongly correlated with their a-axis lattice parameter. The highest Tc of over 19 K was observed for the film on bare CaF2 substrate, which is related to unexpectedly large in-plane compressive strain originating mostly from the thermal expansion mismatch between the FeSe0.7Te0.3 film and the substrate.

The effect of fission-energy Xe ion irradiation on dissolution of UO2 thin films

The aim of this work was to study the effect of fission fragment damage on the dissolution of UO2 thin films in water. For this purpose, thin films of UO2 on LSAT (Al10La3O51Sr14Ta7) substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate the fission damage and induce chemical mixing that occur within nuclear fuels. The dissolution experiment was conducted under a nitrogen atmosphere (200–900 O2 ppm in N2) to study the effect of the induced irradiation damage and mixing on the dissolution of the UO2 matrix. The irradiated samples showed a decrease in the amount of dissolved uranium, as compared to the corresponding unirradiated samples. This was ascribed to the irradiation-induced chemical mixing of the UO2 films with the substrate elements, which resulted in stabilisation of the UO2 matrix and increased its aqueous durability. Secondary phases were also observed on the surface of the UO2 films after the dissolution experiment.

Influence of substrate induced strain on B-site ordering and magnetic properties of Nd2NiMnO6 epitaxial thin films

Epitaxial thin films of double perovskite Nd2NiMnO6 (NNMO) have been successfully grown on (001) oriented substrates of (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT), SrTiO3 (STO) and LaAlO3 (LAO) by pulsed laser deposition under optimum growth conditions. X-Ray diffraction and reciprocal space maps of the asymmetric (103) peak reveal that the films deposited on LSAT and STO substrates are fully relaxed, while a large in- plane compressive strain has been observed in film grown on LAO. This results into the coexistence of anti-site disorder and orthorhombic phase in the film deposited on LAO, which is further confirmed from observed shift and broadening in the antisymmetric vibrations in the Raman spectra. The temperature dependent magnetization shows a ferromagnetic transition close to 200K in all the three samples. However, film grown on LAO substrate shows an additional upturn transition at ~96K (T′), which could be ascribed to the formation of antisite disorders further responsible for reduction of saturation magnetization (~1.8×105 A/m) in hysteresis curve of the sample. The ordered structure obtained on LSAT and STO exhibit in-plane easy axis with a large coercivity of ~0.2T, while, the film deposited on LAO does not show any preferred anisotropic direction.

Structural effects in UO2 thin films irradiated with fission-energy Xe ions

Uranium dioxide thin films have been successfully grown on LSAT (Al10La3O51Sr14Ta7) substrates by reactive magnetron sputtering. Irradiation by 92 MeV 129Xe23+ ions to simulate fission damage that occurs within nuclear fuels caused microstructural and crystallographic changes. Initially flat and continuous thin films were produced by magnetron sputtering with a root mean square roughness of 0.35 nm determined by AFM. After irradiation, this roughness increased to 60–70 nm, with the films developing discrete microstructural features: small grains (∼3 μm), along with larger circular (up to 40 μm) and linear formations with non-uniform composition according to the SEM, AFM and EDX results. The irradiation caused significant restructuring of the UO2 films that was manifested in significant film-substrate mixing, observed through EDX analysis. Diffusion of Al from the substrate into the film in unirradiated samples was also observed.

XPS Study of Ion Irradiated and Unirradiated UO2 Thin Films.

XPS determination of the oxygen coefficient kO = 2 + x and ionic (U(4+), U(5+), and U(6+)) composition of oxides UO2+x formed on the surfaces of differently oriented (hkl) planes of thin UO2 films on LSAT (Al10La3O51Sr14Ta7) and YSZ (yttria-stabilized zirconia) substrates was performed. The U 4f and O 1s core-electron peak intensities as well as the U 5f relative intensity before and after the (129)Xe(23+) and (238)U(31+) irradiations were employed. It was found that the presence of uranium dioxide film in air results in formation of oxide UO2+x on the surface with mean oxygen coefficients kO in the range 2.07-2.11 on LSAT and 2.17-2.23 on YSZ substrates. These oxygen coefficients depend on the substrate and weakly on the crystallographic orientation. On the basis of the spectral parameters it was established that uranium dioxide films AP2,3 on the LSAT substrates have the smallest kO values, and from the XRD and EBSD results it follows that these samples have a regular monocrystalline structure. The XRD and EBSD results indicate that samples AP5-7 on the YSZ substrates have monocrystalline structure; however, they have the highest kO values. The observed difference in the kO values was probably caused by the different nature of the substrates: the YSZ substrates provide 6.4% compressive strain, whereas (001) LSAT substrates result only in 0.03% tensile strain in the UO2 films. (129)Xe(23+) irradiation (92 MeV, 4.8 × 10(15) ions/cm(2)) of uranium dioxide films on the LSAT substrates was shown to destroy both long-range ordering and uranium close environment, which results in an increase of uranium oxidation state and regrouping of oxygen ions in uranium close environment. (238)U(31+) (110 MeV, 5 × 10(10), 5 × 10(11), 5 × 10(12) ions/cm(2)) irradiations of uranium dioxide films on the YSZ substrates were shown to form the lattice damage only with partial destruction of the long-range ordering.

Microstructure and growth of epitaxial nano-scale LaBaCo2O5.5+δ islands on (La,Sr)(Al,Ta)O3 substrate

Epitaxial nano-scale LaBaCo2O5.5+δ (LBCO) islands are prepared on (La,Sr)(Al,Ta)O3 (LSAT) substrates by pulsed laser deposition technique. The microstructure of these islands is investigated by aberration-corrected (scanning) transmission electron microscopy. These islands exhibit morphologies of truncated octahedron with {111}LBCO side surfaces and form on nano-sized {111}Co3O4 faceted Co3O4 secondary phase that grows directly on the substrate. The crystallographic orientation relationships between the LBCO film and the LSAT substrate, as well as between the LBCO film and the Co3O4 secondary phase are determined. The atomic structure of the coherent interfaces between the Co3O4 phase and the LBCO islands is revealed by the atomic-resolution high-angle annular dark field images. Based on the obtained structural results, the growth mechanism of the islands is proposed and discussed.

Substrate Effects on In-Plane Magnetic Anisotropy and Verwey Transition Temperatures of (100) Magnetite (Fe3O4) Films

(100) Fe3O4 films were grown on five different (100)-oriented substrates: MgO, MgAl2O4 (MAO), (PbMg0.33Nb0.67)1– x :(PbTiO3) x (PMNT), SrTiO3 (STO), and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), to investigate the substrate effects on structural, magnetic, and transport properties of the films. The X-ray diffraction measurements suggested that the epitaxial (100) Fe3O4 films were grown, although the lattice mismatch between the Fe3O4 and the substrates varied from +0.25% to −7.8%. Remarkably, the (100) Fe3O4 films grown on MAO, PMNT, and STO substrates exhibited a distinctive in-plane magnetic anisotropy with the magnetic easy axis along the [010] and [001] directions. In contrast, the (100) Fe3O4 films on the MgO and LSAT substrates showed a very weak anisotropy in the [011] easy direction. The Verwey transition temperature of the (100) Fe3O4 film was found to have a minimum value of $\sim 110$ K for MgO and a maximum value of $\sim 122$ K for STO. These results suggest that the magnetic anisotropy and Verwey transition behaviors of the (100) Fe3O4 film can be tuned by film growth on a specific substrate.

Terahertz ellipsometry study of the soft mode behavior in ultrathin SrTiO3 films

We present a combined study with conventional far-infrared and time-domain terahertz ellipsometry of the temperature dependent optical response of SrTiO3 thin films (85 and 8.5 nm) that are grown by pulsed-laser deposition on LSAT substrates. We demonstrate that terahertz ellipsometry is very sensitive to the optical response of these thin films, in particular, to the soft mode of SrTiO3. We show that for the 85 nm film the eigenfrequency of the soft mode is strongly reduced by annealing at 1200 C, whereas for the 8.5 nm film it is hardy affected. For the latter, after annealing the mode remains at 125 cm-1 at 300 K and exhibits only a weak softening to about 90 cm-1 at 10 K. This suggests that this ultrathin film undergoes hardly any relaxation of the compressive strain due to the LSAT substrate.

Quality-enhanced GaN epitaxial films grown on (La, Sr) (Al, Ta)O3 substrates by pulsed laser deposition

High-quality GaN films have been epitaxially grown on (La, Sr) (Al, Ta)O3(LSAT) substrates by pulsed laser deposition (PLD) with an in-plane alignment of GaN[112¯0]//LSAT[11¯0]. The as-grown ~300-nm-thick GaN films grown at 450°C show very flat surface with a root-mean-square surface roughness of 0.9nm, full-width at half-maximums for GaN(0002) and GaN(101¯2) X-ray rocking curves of 0.06° and 0.10°, respectively, and sharp and abrupt GaN/LSAT hetero-interfaces. Moreover, with the increase in growth temperature, the surface morphology, crystalline quality and interfacial property of as-grown GaN films are deteriorated gradually. The high-quality GaN films grown on LSAT substrates by PLD are of great importance for the preparation of GaN-based devices.

Ferroelectric transition in compressively strained SrTiO3 thin films

We report the temperature dependent capacitance-voltage characteristics of Pt/SrTiO3 Schottky diodes fabricated using compressively strained SrTiO3 thin films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates. The measurements reveal a divergence of the out of plane dielectric constant of SrTiO3 peaked at ∼140 K, implying a ferroelectric transition. A Curie-Weiss law fit to the zero-bias dielectric constant suggests a Curie temperature of ∼56 K. This observation provides experimental confirmation of the theoretical prediction of out of plane ferroelectricity in compressively strained SrTiO3 thin films grown on LSAT substrate. We also discuss the roles of the field-dependent dielectric constant and the interfacial layer in SrTiO3 on the extraction of the Curie temperature.

B23-P-17Microstructural Analysis of Lithiated Sn/Sn Interface in Gelatin-Coated Sn Particle

LSAT:(La0.3Sr0.7)( Al0.65Ta0.35)O3 is one of the most preferable substrates for GaN thin film growth. However, there reported a few studies concerning the surface structures of LSAT substrate. In this study, we investigated annealing conditions for constructing surface step-terrace structure and directly observed the surface structure mainly by Z-contrast imaging. Commercially available LSAT (001) substrates were annealed at 800°C~1300°C for 0.5h~5h in air and Ar-5%H2. After annealing, the surface structures were analyzed by SEM, AFM, TEM and STEM. As results, the surface structure was found to depend on the annealing conditions. Precipitates were formed at the surface annealed at 1300°C irrespective of oxygen partial pressure. The amount of the precipitates was largely decreased by lowering annealing temperature. The surface smoothness at lower annealing temperature varies by oxygen partial pressure. The surface is atomically rough in air while the surface is atomically flat to form step-terrace structure in Ar-5%H2. Figure shows an example of the obtained step-terrace structure. The step height is a unit cell length of LSAT and the terraces are terminated at B-sites. The surface structure change due to the variation of annealing conditions will be presented. HAADF STEM image of step-terrace structure. B23-P-17 doi:10.1093/jmicro/dfv291 Microstructural Analysis of Lithiated Sn/Sn Interface in Gelatin-Coated Sn Particle

B23-P-18Step-terrace structures formed at LSAT (001) substrate surface

B23-P-18Step-terrace structures formed at LSAT (001) substrate surface

Influence of Lattice Strain on Phase Separation and Percolative Behaviors in La&lt;sub&gt;0.325&lt;/sub&gt;Pr&lt;sub&gt;0.3&lt;/sub&gt;Ca&lt;sub&gt;0.375&lt;/sub&gt; MnO&lt;sub&gt;3&lt;/sub&gt; Thin Films

The compressive and tensile strains induced by different substrates on La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.325</sub> Pr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.375</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LPCMO) thin films have been investigated. It is found that the in-plane compressive strain favors the ferromagnetic metallic phase by increasing the hopping amplitude between neighboring elections and decreasing the tilt of the MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> octahedron, leading to the weakening of the phase separation. On the other hand, the in-plane tensile strain in films prefers to increase the stability of long-range charge/orbital ordering (COO) phase. Under 5 T magnetic field, the 30 nm LPCMO films on NGO and LSAT substrates show an obvious metal-insulator transition, indicating that the COO phase can be melted by the magnetic field at low temperature in the film with small in-plane tensile strain. The LPCMO film on STO substrate keeps insulating in the entire measuring temperature range even under 5 T magnetic field, suggesting that the COO phase in the film with a large tensile strain is more robust.

Impact of symmetry on the ferroelectric properties of CaTiO3 thin films

Epitaxial strain is a powerful tool to induce functional properties such as ferroelectricity in thin films of materials that do not possess ferroelectricity in bulk form. In this work, a ferroelectric state was stabilized in thin films of the incipient ferroelectric, CaTiO3, through the careful control of the biaxial strain state and TiO6 octahedral rotations. Detailed structural characterization was carried out by synchrotron x-ray diffraction and scanning transmission electron microscopy. CaTiO3 films grown on La0.18Sr0.82Al0.59Ta0.41O3 (LSAT) and NdGaO3 (NGO) substrates experienced a 1.1% biaxial strain state but differed in their octahedral tilt structures. A suppression of the out-of-plane rotations of the TiO6 octahedral in films grown on LSAT substrates resulted in a robust ferroelectric I4 mm phase with remnant polarization ∼5 μC/cm2 at 10 K and Tc near 140 K. In contrast, films grown on NGO substrates with significant octahedral tilting showed reduced polarization and Tc. These results highlight the key role played by symmetry in controlling the ferroelectric properties of perovskite oxide thin films.

Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films

Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ∼ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ∼ 120 K and 130 K, respectively. At T &amp;lt; TC, the zero field cooled and field cooled magnetization curves of all the films show huge bifurcation. In case of S_STO and S_LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and above Tp, respectively, for S_STO and S_LSAT films have been observed with maximum value of MCE ∼ 10 J kg−1 K−1. The S_STO film also exhibits a large relative cooling power of 142 J/kg for a magnetic field change of 1 T. Our findings of substrate-induced strain modulated large MCE in epitaxial Sm0.55Sr0.45MnO3 films have been well explained through the substrate induced film lattice strain, and it may be useful for active magnetic refrigerant materials.