Out Of Plane Lattice Parameter Research Articles

Epitaxial growth of high quality SrFeO3 films on (001) oriented (LaAlO3)0.3(Sr2TaAlO6)0.7

The growth of strontium ferrite SrFeO3 films with a stoichiometry of (1:1:3) is challenging as the unstable Fe4+ oxidation state favors the formation of O vacancies. Here, we report the layer by layer growth of SrFeO3 on (001) oriented (LaAlO3)0.3(Sr2TaAlO6)0.7 using ozone assisted molecular beam epitaxy. Upon cooling from room temperature, the film's resistivity decreased from 750 μΩ cm to 150 μΩ cm, as low as the best single crystals, with two identifiable transition points near 110 K and 60 K in resistivity measurements, being hysteretic between cooling and warming through the 60 K transition. During various annealing steps, the low temperature resistivity changes by orders of magnitude, accompanied by an increase in the c-axis lattice parameter. The hysteresis near 60 K persists for a wide range of annealing conditions. We have identified conditions under which changes due to annealing can be reversed. We attribute changes in resistivity and the out of plane lattice parameter to the reversible movement of oxygen ions in the lattice. SrFeO3 may be a promising material for resistive memory applications based upon the control of oxygen vacancies.

Studies on structural and optical properties of pulsed laser deposited NiO thin films under varying deposition parameters

Lattice parameter of NiO layers deposited using pulsed laser deposition is determined accurately using three parallel Bragg reflections. A small decrease in out of plane lattice parameter is found as O2 partial pressure is increased, which is attributed to the lattice contraction due to Ni vacancies. The NiO layers are found to be oriented along (111) direction on (0001) oriented Al2O3 substrate. The presence of Pendellosung oscillations indicates high crystalline and interfacial qualities of NiO layers, which gradually degrade with increase in O2 partial pressure. The NiO layer thickness determined from both x-ray diffraction and x-ray reflectivity show similar trend with O2 partial pressure. The optical band gap does not vary much due to the presence of very small compressive strain.

Laser fluence and spot size effect on compositional and structural properties of BiFeO3 thin films grown by Pulsed Laser Deposition

We investigated the effect of laser fluence and spot size on the structure and composition of BiFeO3 (BFO) epitaxial thin films grown on SrTiO3 substrates by Pulsed Laser Deposition. X-ray diffraction shows that BFO's out of plane lattice parameter increases with the laser fluence. A coherent epitaxial film growth is observed for all tested laser fluences and spot sizes for thicknesses up to 16nm. The critical thickness at which relaxation occurs depends either on the laser fluence or spot size. The fluence dependence of the out of plane lattice parameter is accompanied with a cationic composition variation. Bi vacancies are evidenced at lower fluences while as Bi/Fe tends towards 1 a higher relaxation critical thickness is observed. An optimum Bi/Fe ratio is obtained for a fluence of 1.72J/cm2. This result was confirmed by wavelength-dispersive x-ray spectroscopy (WDS) scans over a 1cm2 film. An excellent thickness and composition uniformity is attained over the entire sample area.

Effects of Applied Potential and Water Intercalation on the Surface Chemistry of Ti2C and Mo2C MXenes

Two-dimensional transition metal carbides and nitrides, also known as MXenes, represent an attractive class of materials for a multitude of electrochemical and other applications. While single sheets of MXenes have been widely studied theoretically, there have been much fewer studies on layered bulk MXenes, which are more representative of multi- or few-layer MXenes used in actual applications. Herein, we investigate the structural and electronic effects of water intercalation, multiple functional groups and applied potential on layered bulk Ti2C and Mo2C MXenes using density functional theory. The out-of plane lattice parameter, c, was found to vary significantly with the functional group, and is greatly increased upon intercalation of water. Experimental results confirm the change in lattice constant due to addition or removal of intercalated water. Under zero applied potential, both Ti2C and Mo2C were found to be functionalized by one monolayer of O; bare MXenes were never found to be stable, regardles...

Tuning the orbital ordering in La0.7Sr0.3MnO3 thin films in all-oxide hybrids

This work presents a systematic characterization including x-ray diffractometry, SQUID magnetometry and x-ray absorption spectroscopy on all-oxide ferromagnetic/ferroelectric heterosystem BaTiO3/La0.7Sr0.3MnO3/SrTiO3(001) fabricated by pulsed-laser deposition. The key aspect of this study is to provide accurate information about differences in electronic and structural properties in LSMO thin films as a function of the oxygen pressure during BTO growth. X-ray absorption spectroscopy experiments at the Mn L3,2 edge have revealed the conservation of mixed valency configuration of the LSMO films near the interface while tuning the oxygen pressure of overlayer BTO growth. The existing ions favor an in-plane eg orbital ordering, reducing the in-plane strain and promoting room temperature ferromagntism in the LSMO film. Furthermore, diffraction experiments showed that the out-of plane lattice parameter of BTO reduces with increasing oxygen pressure consistent with the x-ray linear dichrosim at Ti edge showing less tetragonal symmetry, although the chemical environment of the Ti ions was not changed notably. We demonstrated a way to control magnetic properties and orbital ordering in LSMO thin films while optimizing the ferroelectric properties of BTO overlayer films, which are promising results in terms of magnetoelectric applications using functional heterosystems.

Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

Highly oriented polycrystalline Sm0.55Sr0.45MnO3 thin films (thickness ∼100 nm) deposited on LaAlO3 (LAO, (001)), SrTiO3 (STO, (001)) and (La0.18Sr0.82) (Al0.59Ta0.41)O3 (LSAT, (001)) single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The out of plane lattice parameter (OPLP) of the film on LAO is slightly larger than that of the corresponding bulk. In contrast, the OPLP of the films on STO and LSAT are slightly smaller than the corresponding bulk value. This suggests that the film on LAO is under compressive strain while LSAT and STO are under tensile strain. The films on LAO and LSAT show simultaneous paramagnetic-ferromagnetic (PM–FM) and insulator-metal transition (IMT) temperature at TC/TIM ∼ 165 K and 130 K, respectively. The PM–FM and IM transition occur at TC ∼ 120 K and TIM ∼ 105 K, respectively in the film on STO substrate. At T < TC, the zero field cooled–field cooled (ZFC–FC) magnetization of all the films shows strong bifurcation. This suggests the presence of a metamagnetic state akin to cluster glass formed due to coexisting FM and antiferromagnetic–charge order (AFM–CO) clusters. All the films show colossal magnetoresistance but its temperature and magnetic field dependence are drastically different. The films on LAO and STO show peak CMR around TC/TIM, while the film on LSAT shows MR > 99 % over a very wide temperature range of ∼40 K centred on TC/TIM. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signature of metamagnetic transitions. The observed results have been explained in terms of the variation of the relative fractions of the coexisting FM and AFM–CO phases as a function of the substrate induced strain and oxygen vacancy induced quenched disorder.

Structural characterization of AlxGa1−xSb grown by LPE

AlxGa1−xSb ternary solid solutions lattice-matched to the GaSb (001) substrate with composition in the range 0.05≤x≤0.2 were grown by liquid phase epitaxy. High resolution X-ray diffraction and Raman scattering techniques were applied to characterize AlxGa1−xSb alloys. The out of plane lattice parameter was estimated directly from the asymmetrical diffractions of planes (115) and (−1−15). The out of plane lattice parameter as a function of Aluminium content is higher than the corresponding bulk lattice parameter of AlxGa1−xSb layers obtained with Vegard's law. These results show that some of the layers are more strained than others. Two peaks are observed in their Raman spectra over this composition range. The assignment of the observed modes to GaSb-like modes is discussed. The studies of the chemical composition of the layers by SIMS exhibit the presence of tellurium, carbon and oxygen like the main residual impurities.

Strain dependent defect mediated ferromagnetism in Mn-doped and undoped ZnO thin films

The structural and magnetic properties of pulsed laser deposited zinc oxide thin films have been investigated. Room temperature ferromagnetism is present in undoped as well as Mn-doped films. The saturation magnetization of the thin films reveals a dependence on both the composition and the out of plane lattice parameter. X-ray magnetic circular dichroism down to 2 K reveals a purely paramagnetic contribution from the Mn in Mn:ZnO films. We conclude that the observed ferromagnetism arises entirely from intrinsic defects in the ZnO which can be varied by manipulation of the lattice parameter.

Substrate-dependent structural and magnetic properties of Sr 2FeMoO 6 nanostructured double perovskite thin films

We report the synthesis of nanostructured Sr 2FeMoO 6 (SFMO) thin films on SrTiO 3 (0 0 1), LaAlO 3 (0 0 1) and MgO (0 0 1) substrates by pulsed laser deposition technique. The influence of substrate nature on structural and magnetic properties of thin films has been systematically investigated. The films deposited on SrTiO 3 and LaAlO 3 were single crystalline with preferred (0 0 4) orientation without any impurity peak, whereas the films deposited on MgO substrate exhibit impurity peaks of SrFeO 3 along with (0 0 4) reflection of SFMO. The out of plane lattice parameter, ‘ c’ and grain size have been shown to be influenced by nature of substrate. Further, the magnetic properties of the films, including the coercive field, remnant magnetization, saturation magnetization and magnetoresistance were also observed to be strongly dependent on the choice of substrate. The investigations reveal an increase in magnetization with decrease in film–substrate lattice mismatch. The films on SrTiO 3 substrate exhibit a saturation magnetic moment of 3.24μ B/f.u. at 5 K, with a Curie temperature larger than 320 K, whereas the films deposited on MgO substrate are observed to have low magnetization, which is related to the high proportion of antisite defects in these films. The magnitude of MR was observed to be smaller in case of films deposited on SrTiO 3 substrate and in addition the variation in MR with applied field was found to be linear in these films, whereas the films on MgO substrate were found to exhibit higher value of MR with two different regimes: the low-field region ( H<20 kOe) with a steeper slope and the high-field behavior with a less pronounced slope. The present study elucidates the effects of substrate nature on magnetization and that the magnetoresistance behavior of SFMO thin films are useful in magnetic sensors and spintronics application.

Dependence on the growth direction of the strain in AlGaSb alloys

High resolution x-ray diffraction profiles were obtained from AlxGa1-xSb layers grown on (001) and (111) GaSb substrates. The out of plane lattice parameter, was estimated directly from the symmetrical diffractions for (001) and (111) alloys. These results show that all the layers are strained, and those grown on (001) GaSb are slightly more strained than the corresponding layers grown on (111) GaSb. This difference is explained by the dependence of the strain ratio on growth direction. The out of plane lattice parameter as a function of Al content is higher than the corresponding bulk lattice parameter of AlxGa1-xSb layers obtained with Vegard's law. Also, the perpendicular and the in-plane lattice parameter expected for pseudomorphic alloys, was estimated from the strain ratios, assuming an elastic deformation and using the EDX alloy composition to interpolate the elastic constants Cij. This estimation also shows that almost all the layers are fully strained.

Influence of thickness on the epitaxial stabilisation of SmNiO 3 thin films

SmNiO 3 thin films have been prepared by liquid injection Metal Organic Chemical Vapour Deposition on SrTiO 3 (100) and LaAlO 3 (100) single crystalline substrates. The influence of the film thickness on the epitaxial stabilisation has been studied for both substrates by X-ray diffraction and Atomic Force Microscopy (AFM). In the case of SmNiO 3 on LaAlO 3, the nickelate is obtained as a single phase up to a thickness of 200 nm; the surface remains smooth in agreement with the small lattice mismatch between film and substrate. In the case of the SrTiO 3 substrate, SmNiO 3 is never stabilised as single phase: NiO and Sm 2O 3 single oxides both appear beside the perovskite. We show that the strain state is driven by the choice of the substrate and the thickness of the film. Two different relaxation mechanisms of the film are evidenced depending on the substrate used. For LaAlO 3, the good in-plane lattice match leads to a relaxation only in the growth direction. On the contrary, in the case of SrTiO 3 which presents a strong lattice mismatch with the film, the out-of plane lattice parameter remains constant and constraints are relaxed through the chemical dissociation of SmNiO 3 into single oxides.

Studies of structural, magnetic, electrical, and photoconducting properties ofBi1−xCaxMnO3epitaxial thin films

The dynamics of the charge ordered (CO) state under non-equilibrium conditions created by strong dc-electric field (~106 V/cm) and photo-illumination with short (~ 6 ns) laser pulses is investigated in Bi1-xCaxMnO3 (x > 0.5) epitaxial films. A pulsed laser deposition method was used to synthesize films on (100) LaAlO3 (LAO) and (100) SrTiO3 (STO) substrates. The crystallographic structure, temperature dependence of electrical resistivity and magnetization of the samples of different composition prepared under different oxygen partial pressure (pO2) and deposition temperature (TD) are studied. For the x = 0.6 sample grown on LAO, a clear signature of charge ordering at ~275 K is seen in the magnetization and at ~ 260 K in the resistivity data. The same sample grown on STO revealed a complex behavior, which entails charge ordering at ~300 K, a Neel order at ~150 K and finally a weak ferromagnetic phase below 50 K. A strong correlation between charge ordering temperature (TCO) and the c-axis lattice parameter (c) of the type (dTCO/dc ~-350 K/A) imerges from measurements on films deposited under different growth conditions. Since the out of plane lattice parameter (c) increases with in plane compressive strain, this effect directly show a compressive strain induced suppression of the TCO. The current (I)- voltage (V) characteristics of the samples at T < TCO show hysteresis due to a compound effect of Joule heating and collapse of the CO state. Transient changes in conductivity of lifetime ranging from nano to microseconds are seen at T < TCO on illumination with pulsed UV (355 nm) radiation. These observations are explained on the basis of the topological and electronic changes in the charge ordered phase.

Strain induced phase separation in La0.67Ca0.33MnO3 ultra thin films

Magnetic and transport properties are investigated in epitaxial La0.67Ca0.33MnO3 thin films grown on SrLaAlO4 under high in plane compressive strain (K3.1%). Films with thickness in the range 2‐6.5 nm show a two dimensional coherent growth mode and are significantly strained as shown by the expansion of the out of plane lattice parameter. We provide evidence for phase separation induced by the inhomogeneous strain field, free of artefacts related to composition changes at grain boundaries or structurally disordered regions characteristic of island growth. q 2005 Elsevier Ltd. All rights reserved.