LaNiO3 Films Research Articles

Effect of interface structure on the chemical composition and electrical properties of sol–gel-derived LaNiO3 films

In the present work, lanthanum nickel oxide (LNO) thin films are prepared with the sol–gel multilayer coating method. Lattice-matched SrTiO3 (STO) buffer layer is introduced to tailor the film–substrate interface. The effect of interface structure on the electrical properties, microstructure and chemical composition of LNO films is investigated. The results show that the improvement in the interface structure minimizes the effect of interface on the electrical properties of LNO films and leads to a sharp decrease in room-temperature resistivity of LNO films to 570 μΩ cm, comparable to that of the LNO films on single-crystal STO substrate. This is ascribed to the decrease in structural disorder and the concentration of oxygen vacancies in the LNO films.

Synthesis and characterisations of sol-gel-derived LaNiO<SUB align="right">3 thin-film electrodes on Si substrates

We present the fabrication and characterisation of conductive LaNiO3 (LNO) thin films, deposited on different substrates including Si(100), SiO2/Si(100) and Pt/Ti/SiO2/Si(100) by the sol–gel spin–coating technique. Deposition parameters, such as the sol concentration and annealing temperature as well as the number of coating layers, were optimised to obtain the desired film quality. X–ray diffraction analysis showed that crystalline and highly (110) oriented LNO thin films were obtained after annealing at 750C. Scanning electron microscopy images revealed that LNO films show a dense and smooth surface. Moreover, the crystallites' size increased with increasing film thickness, which resulted in the enhancement of electrical conductivity. The well–controlled crystallinity and low resistivity of 3.73 10–4Ω.cm, measured on a film thickness of 200 nm, indicate that LNO thin films can be used as the template and electrode for the fabrication of integrated piezoelectric thin–films on Si substrates.

Fabrication and characterization of compositionally graded PbxSr1−xTiO3 thin films by the Sol–gel method

Different compositionally graded PbxSr1−xTiO3 (x = 0.2, 0.3, 0.4, 0.5 and 0.6; PST) thin films were deposited on LaNiO3(LNO)-buffered stainless steel (SS) substrates. Both LNO and PST thin films were prepared by the sol–gel method. X-ray diffraction and scanning electron microscopy analysis were used to investigate the crystallinity and surface morphology of PST thin films. It showed that the crack-free PST thin films presented pure perovskite phase. The dielectric permittivity was measured in the frequency range of 103–106Hz. The tunable value of compositionally graded PST films can be as high as about 30 % (measured at E = 300 kV/cm, 105Hz). The LNO-buffered layers can effectively reduce the dissipation constant of PST films on SS, which was about 3 % and in the same level with the PST films deposited on traditional Si substrates. The temperature and frequency stability of tunability has been improved. The value of (Δnr/nrTo) % (rate of tunability change) could be less than 5 % in the most range of temperature, which demonstrated that PST could be a promising candidate material for tunable devices applications.

Raman light scattering on ultra-thin films of LaNiO3 under compressive strain

In order to investigate the lattice dynamics of very thin films, we have carried out a series of depth-resolved Raman scattering measurements. Combining the narrow depth-of-field of confocal Raman spectroscopy with vertical scans of the sample, we have obtained high quality phonon spectra of fully strained LaNiO3 films with thickness as low as 4 pseudocubic unit cells. With increasing film thickness a large softening of a LaNiO3Eg-bending mode is observed, indicating the relaxation of biaxial compressive strain imposed by the LaAlO3 substrate.

Effect of Surface Termination on the Electronic Properties ofLaNiO3Films

The electronic and structural properties of thin LaNiO₃ films grown by using molecular beam epitaxy are studied as a function of the net ionic charge of the surface terminating layer. We demonstrate that electronic transport in nickelate heterostructures can be manipulated through changes in the surface termination due to a strong coupling of the surface electrostatic properties to the structural properties of the Ni—O bonds that govern electronic conduction. We observe experimentally and from first-principles theory an asymmetric response of the structural properties of the films to the sign of the surface charge, which results from a strong interplay between electrostatic and mechanical boundary conditions governing the system. The structural response results in ionic buckling in the near-surface NiO₂ planes for films terminated with negatively charged NiO₂ and bulklike NiO₂ planes for films terminated with positively charged LaO planes. The ability to modify transport properties by the deposition of a single atomic layer can be used as a guiding principle for nanoscale device fabrication.

Polarity compensation in ultra-thin films of complex oxides: the case of a perovskite nickelate.

We address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO3 on the band insulator SrTiO3 along the pseudo cubic [111] direction. While in general the metallic LaNiO3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, and synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La2Ni2O5 (Ni2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO3/SrTiO3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.

{001} Oriented piezoelectric films prepared by chemical solution deposition on Ni foils

Flexible metal foil substrates are useful in some microelectromechanical systems applications including wearable piezoelectric sensors or energy harvesters based on Pb(Zr,Ti)O3 (PZT) thin films. Full utilization of the potential of piezoelectrics on metal foils requires control of the film crystallographic texture. In this study, {001} oriented PZT thin films were grown by chemical solution deposition (CSD) on Ni foil and Si substrates. Ni foils were passivated using HfO2 grown by atomic layer deposition in order to suppress substrate oxidation during subsequent thermal treatment. To obtain the desired orientation of PZT film, strongly (100) oriented LaNiO3 films were integrated by CSD on the HfO2 coated substrates. A high level of {001} LaNiO3 and PZT film orientation were confirmed by X-ray diffraction patterns. Before poling, the low field dielectric permittivity and loss tangents of (001) oriented PZT films on Ni are near 780 and 0.04 at 1 kHz; the permittivity drops significantly on poling due to in-plane to out-of-plane domain switching. (001) oriented PZT film on Ni displayed a well-saturated hysteresis loop with a large remanent polarization ∼36 μC/cm2, while (100) oriented PZT on Si showed slanted P-E hysteresis loops with much lower remanent polarizations. The |e31,f| piezoelectric coefficient was around 10.6 C/m2 for hot-poled (001) oriented PZT film on Ni.

Structural, dielectric, ferroelectric and optical properties of PBCT, PBST and PCST complex thin films on LaNiO3 metallic conductive oxide layer coated Si substrates by the CSD technique

Ferroelectric thin films and LaNiO3 (LNO) metallic conductive oxide thin films were prepared by a chemical solution deposition (CSD) method. PBCT60, PBST60 and PCST60 ferroelectric thin films were grown on different structures such as LNO/Si and single-crystalline quartz SiO2 (X-cut) substrates. The LNO layer acts as the bottom electrode for the electrical measurements. X-ray diffraction (XRD) analysis shows that LNO thin films on Si substrates and PBCT60, PBST60 and PCST60 thin films on LNO/Si structures are polycrystalline with a moderate (110)-texture and a complete perovskite phase. LNO, PBCT60, PBST60 and PCST60 thin films have a continuous, dense and homogenous microstructure with a grain size on the order of 50–80nm. Electrical resistivity-dependence temperature data confirm that LNO thin films display a good metallic character over a wide large range of temperatures. Optical characteristics of PBCT60, PBST60 and PCST60 thin films have also been investigated using ultraviolet–visible (UV–vis) spectroscopy in the wavelength range of 200–1100nm. Ferroelectric thin films show a direct allowed optical transition with optical band gap values on the of order of 3.54, 3.66 and 3.89eV for PBCT60, PCST60 and PBST60 thin films deposited on a SiO2 substrate, respectively. Good dielectric and ferroelectric properties are reported for ferroelectric thin films deposited on the LNO layer as bottom electrodes. Au/PBCT60/LNO/Si, Au/PBST60/LNO/Si and Au/PCST60/LNO/Si multilayer structures show a hysteresis loop with remnant polarization, Pr, of 9.6, 6.6 and 4.2μC/cm2 at an applied voltage of 6V for PBCT60, PBST60 and PCST60 thin films, respectively.

Structural, microstructural, optical and electrical properties of (Pb,Ba,Sr)TiO3 films growth on conductive LaNiO3-coated LaAO3(100) and Pt/Ti/SiO2/Si substrates

The ferroelectric and dielectric properties of lead barium strontium titanate (PBST) thin films are investigated on different bottom electrode and substrate such as Pt, LaNiO3 and Pt/Ti/SiO2/Si, LaAlO3(100), respectively. X-ray diffraction results indicate that the PBST and LaNiO3 films on LaAlO3(100) single crystal substrate are highly (100)-oriented whereas the PBST films on Pt/Ti/SiO2/Si are polycrystalline. The results indicate strong effects of bottom electrode on the dielectric permittivity and tunability of the PBST films. The dielectric permittivity and tunability for the highly (100)-oriented PBST films on LaNiO3/LaAlO3(100) structure were 1238% and 65%, respectively, at 100kHz, while PBST films prepared on Pt/Ti/SiO2/Si substrate, showed a dielectric permittivity of 520 and tunability of 47%, at 100kHz. A slight shift of the phase transition temperature to lower temperatures was observed for highly (100)-oriented films in comparison to the polycrystalline films. Electrical properties should depend strongly on orientation and bottom electrode, which is reflected in our experimental observations.

TEM Study for Self-Orientated LaNiO3 Film along [100

LaNiO3 (LNO) is known as a candidate for oxide electrodes with perovskite type crystal structure which is suitable for lattice matching with conventional perovskite ferroelectrics, Pb (Zr,Ti)O3 (PZT), BaTiO3 (BTO), etc. We have been investigating thermal expansion effects of the LNO film with PZT/LNO/Si and BTO/LNO/Si structures, where ferroelectric and piezoelectric properties are enhanced by a compressive thermals stress impressed from the LNO layer to the ferrelectric films. The ferroelectric films also shows high [00 orientation owing to [100] orientation of the LNO film. In the present study, further investigation of the LNO films prepared on Si substrates by CSD method is made by transmission electron microscopy (TEM) in order to understand self-orientation along [100] perpendicular to the film plane which effectively leads orientation of PZT films prepared on the LNO film. The results obviously indicates that the 1 layer deposited LNO film has almost no orientation, whereas it shows tendency of orientation of [100] perpendicular to the film plane when the layer number increased.

Discrepancies in the morphology and physical properties of amorphous and crystalline sprayed lanthanum nickel oxide films

Amorphous LaNiO3 (a-LNO) and crystalline LaNiO3 (c-LNO) films were prepared by spraying an aqueous precursor solution of lanthanum and nickel chlorides on hot (450°C) fused silica substrates followed by annealing at high temperatures (550–850°C). Thermal analysis of a dried precursor indicated that a stable oxide phase is formed at 560°C with no distinct crystallization peak. Scanning electron microscopy (SEM) powered with energy-dispersive X-ray spectroscopy (EDX) of as-sprayed films showed rough surfaces with particulate-like deposits and incomplete pyrolysis chloride composition. No chloride contents were detected in annealed films. X-ray diffraction showed that films annealed at 550°C and 650°C were a-LNO and those annealed at 750°C and 850°C were c-LNO. The c-LNO phase was indexed as a single-phase perovskite structure with (110) orientation. SEM/EDX showed that a-LNO films have rough surfaces and c-LNO films have uniform crack-free smooth surfaces. Electrical properties measurements showed that c-LNO films have lower resistivity than a-LNO films and both types of LNO films have semiconductor resistant temperature dependence. The activation energy of electric conduction of a-LNO films was found to be much higher than that of c-LNO films. The optical transmittance and reflectance of the films were studied in the UV–visible–near IR range. The optical constants were obtained by modeling the measured transmission and reflection spectra. Because of the discrepancies in the morphology and in the physical properties of a-LNO and c-LNO films, the best fit modeling of transmission and reflection spectra was obtained by using different theoretical models and different geometrical configurations. While the Drude model accounting for larger carrier density was found to be significant for c-LNO, using the Bruggmann model and a configuration of a rough layer on top of a compact film was found to be significant for a-LNO.

Stress state analysis of stress engineered BaTiO3 thin film by LaNiO3 bottom electrode

Ferroelectric materials with excellent performance without containing lead has been desired for saving human body from a harmful element, lead. The authors have reported BaTiO3 (BTO) thin films with enhanced ferroelectricity by stress engineering by thermal stress assisted by LaNiO3 (LNO) bottom electrodes. In the present study, we investigate the local stress state of the BTO and LNO films using TEM techniques. TEM observation reveals that the LNO film is porous structure whereas the BTO film is dense. Electron diffraction and dark field images of the films also reveal that the BTO and LNO films oriented along [001] and [100] directions perpendicular to the film plane, respectively. Another effect on the stressed BTO films, increased Curie temperature owing to the stabilized tetragonal phase, is also reported.

Oxide loading effect on the electrochemical performance of LaNiO3 coatings in alkaline media

LaNiO3 film electrodes were prepared by brush painting using nickel-foam supports in order to increase its surface area available for electrochemical reactions. Loadings varying between 20 and 140mgcm−2 were tested. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to evaluate the coatings roughness (Rf) and morphology (φ) factors, complemented by optical microscopy observations. The values obtained from the two methods are in excellent agreement. The Rf values, ranging from 848±50 to 4260±60, are within the highest in the open literature.A simulation, of the effect of the oxide loading on the coatings Rf values, was performed using just the experimental values of the roughness factors for oxide free foam and pelleted electrodes. It was found that the increase of oxide loading causes a quasi linear increase of the electrodes active surface area. Simulated values were in excellent agreement with the experimental roughness factors and pore resistances obtained by CV and EIS. The electrodes were tested for oxygen evolution.

Rapid Microwave Annealing of Amorphous Lead Zirconate Titanate Thin Films Deposited by Sol‐Gel Method on LaNiO3/SiO2/Si Substrates

The heating behavior of LaNiO3 (LNO) films on SiO2/Si substrate heated by 2.45 GHz microwave irradiation in the microwave magnetic field was first investigated, and then amorphous Pb(Zr0.52Ti0.48)O3 (PZT) thin films were deposited on LNO‐coated SiO2/Si substrates by a sol‐gel method and crystallized in the microwave magnetic field. The crystalline phases and microstructures as well as the electrical properties of the PZT films were investigated as a function of the elevated temperature generated by microwave irradiation. The perovskite PZT films with a highly (100)‐preferred orientation can be obtained by microwave annealing at 700°C for only 180 s of total processing time, and have good electrical properties. The results demonstrated that conductive metal oxide LNO as a bottom electrode layer is an advantage for the crystallization of PZT thin films by microwave irradiation in the microwave magnetic field.

Microstructure and electrical properties of LaNiO3 thin films by RF sputtering for the growth of (Pb,La)(Zr,Ti)O3 films on silicon and nickel substrates

Conductive LaNiO3 (LNO) thin films were deposited on Si substrates by RF sputtering at room temperature to 600 °C. X-ray diffraction of the LNO films showed that preferred orientation varied from (100) below 500 °C to (110) at 600 °C at deposition temperature of 200–600 °C. The room temperature resistivity was 2250–3400 μΩ-cm at the range of 200 °C ∼500 °C. The LNO films, deposited at room temperature, were postannealed in air from 500 to 800 °C, and the resistivity value was 280 μΩ-cm at a postannealing temperature of 600 °C. Subsequently, sol–gel derived (Pb,La)(Zr,Ti)O3 thin films were deposited on LNO-buffered nickel substrates and characterized, the results were compared to those of the same films on silicon substrates. The comparison demonstrated that the performance characteristics of the LNO-buffered nickel foils are similar to those of LNO-buffered silicon substrates. Thus, LNO films prepared by the sputtering method can act as an effective barrier layer on nickel substrates for embedded microelectronic devices.

Characteristics of highly (001) oriented (K,Na)NbO3 films grown on LaNiO3 bottom electrodes by RF magnetron sputtering

(K,Na)NbO3 ferroelectric films were grown on LaNiO3 coated silicon substrates by RF magnetron sputtering. The conductive LaNiO3 films acted as seed layers and induced the highly (001) oriented perovskite (K,Na)NbO3 films. Such films exhibit saturated hysteresis loops and have a remnant polarization (2Pr) of 23μC/cm2, and coercive field (2Ec) of 139kV/cm. The films showed a fatigue-free behavior up to 109 switching cycles. A high tunability of 65.7% (@300kV/cm) was obtained in the films. The leakage current density of the films is about 6.0×10−8A/cm2 at an electric field of 50kV/cm.

Quantifying Octahedral Rotations in Ultrathin LaNiO3 Films Using Position Averaged Convergent Beam Electron Diffraction

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Nanoscale quantification of octahedral tilts in perovskite films

NiO6-octahedral tilts in ultrathin LaNiO3 films were studied using position averaged convergent beam electron diffraction (PACBED) in scanning transmission electron microscopy. Both the type and magnitude of the octahedral tilts were determined by comparing PACBED experiments to frozen phonon multislice simulations. It is shown that the out-of-plane octahedral tilt of an epitaxial film under biaxial tensile stress (0.78% in-plane tensile strain) increases by ∼20%, while the in-plane rotation decreases by ∼80%, compared to the unstrained bulk material.

Electrolytic Production of (CF3)3N from Room-Temperature Molten Fluoride of (CH3)3N•3HF Using LaNiO3 Coated Ni Sheet Anode

The LaNiO3 coated Ni sheet anodes prepared by sol-gel coating method was developed to improve the Ni sheet anode for electrolytic synthesis of perfluorotrimethylamine, (CF3)3N, using the (CH3)3N·3HF melt as the electrolyte. The LaNiO3 films may give the electric conductivity to the Ni sheet anode during electrolysis of the (CH3)3N·3HF melt. (CF3)3N was successfully obtained at a ratio of about 62 and 55% together with other partially fluorinated gaseous products.

Magnetized at the Interface

Applied Physics Magnetism arises when electron spins in a solid align parallel (ferromagnetism) or antiparallel (antiferromagnetism) to each other. Especially useful in today's computer industry is the so-called exchange bias, a somewhat counterintuitive phenomenon whereby an antiferromagnet (AFM) interfaced with a ferromagnet (FM) biases the preferred direction of the magnetization of the FM despite having zero net magnetization of its own. Gibert et al. now demonstrate the exchange bias effect in an artificial lattice consisting of alternating thin layers of the normally nonmagnetic LaNiO3 and the magnetic LaMnO3. When sliced thinly, LaMnO3 is a FM, and the authors show that its magnetization curve is shifted by the presence of LaNiO3, as is typical in exchange bias systems; this suggests that LaNiO3 develops magnetic ordering as well. Previous work has indicated the presence of AFM order in thin films of LaNiO3; the authors' numerical modeling suggests that a modulated spin distribution resembling a spin wave is created in the nickelate. Nat. Mater. 11 , 10.1038/nmat3224 (2012).