LNO Thin Films Research Articles

Flexible LaNiO3 film with both high electrical conductivity and mechanical robustness

Lanthanum nickel oxide (LaNiO3, LNO) films exhibit excellent electrical conductivity but poor mechanical properties, considerably limiting their further development in the field of flexible electronics. In this study, flexible LNO thin films of different thicknesses were fabricated on a unique two-dimensional (2D) mica platform using a simple metal organic deposition technique. The obtained LNO films exhibited a pseudocubic phase without impurities. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterisations proved that the films were well-crystallised, dense, and flat, with controllable thickness. In addition, the flexible LNO/mica element possesses low resistivity (5 × 10−4 Ω cm), translucency, and good bending resistance. The electrical resistivity can remain stable under various bending radii (r = 10∼2 mm), thousands of bending cycles, and a wide temperature range (28–200 °C), demonstrating good durability, mechanical stability and temperature resistance. Furthermore, a ferroelectric BiFeO3 film was constructed based on the obtained conductive LNO electrode, which exhibited typical ferroelectric characteristics. This excellent performance suggests that the flexible LNO electrode is promising for flexible electronic applications.

In Situ Electrochemical Cobalt Doping in Perovskite-Structured Lanthanum Nickelate Thin Film Toward Energy Conversion Enhancement of Polymer Solar Cells.

This study demonstrates that the electrochemical doping of lanthanum nickelate (LNO) with cobalt ions is a promising strategy for enhancing its physical and electrochemical properties, which are critical for energy storage and conversion devices. LNO emerges as a promising hole transport layer (HTL) in solar cells due to its stability, large band gap, and high transparency. Nevertheless, its low conductivity and improperly aligned band positions are persistent problems. Here, in a pioneering endeavor, Co-doped LNO thin films were synthesized electrochemically and applied as the HTL in polymer solar cells (PSCs). Characterization revealed the impact of Co doping on the electrochemical, structural, morphological, and optical properties of LNO thin films. Depending on the Co doping level, PSCs based on 10 mol % Co-doped LNO outperformed pure LNO, achieving a champion efficiency of 6.11% with enhanced short-circuit current density (12.84 mA cm-2), fill factor (68%), open-circuit voltage (0.70 V), and external quantum efficiency (82.6%). This enhancement resulted from decreased series resistance, refined surface morphology, minimized trap-assisted recombination, enhanced conductivity, increased charge carrier production, favorable energy level alignment, and improved current extraction facilitated by LNC0.10O HTL. Moreover, the unencapsulated PSC-LNC0.10O long-term stability notably improved and retained 86% of its initial PCE after 450 h storage in ambient air, 82% after being continuously heated to 85 °C for 300 h, and 80% after operating at maximum power point for 300 h. These findings offer a straightforward approach to enhancing PSC performance through Co doping of LNO, supported by density functional theory (DFT) calculations that validate the experimental results and confirm the improvement in optical properties and stability of PSCs as an HTL.

Rapid Fabrication of Chemical Solution-Deposited Lanthanum Nickelate Thin Films via Intense Pulsed-Light Process

In this paper, we demonstrate the practicality and feasibility of the flash light-sintering method to fabricate the ceramic material perovskite structure for lanthanum nickel oxide (LaNiO3; LNO) thin films using flash light irradiation equipment. LNO thin films are deposited on an Si wafer and Al2O3 substrate via the chemical solution deposition (CSD) method and sintered by a thermal and flash light-irradiation process with a bottom heater. The properties of flash light-sintered LNO thin films are compared with those of thermally sintered films. The surface morphology, crystal development, and electric conductivity of the LNO thin films are measured by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and a four-point probe, respectively. Flash light sintering was accomplished in milliseconds. Through the comparison of thermal sintering and flash light-sintering results, it was confirmed that perovskite LNO thin films deposited by the CSD method can be fabricated by flash light sintering. We show that the flash light sintering method can solve several inherent issues of the conventional thermal sintering method.

Counter-thermal flow of holes in high-mobility LaNiO3 thin films

Measurements of electronic structure and theoretical models indicate that the Fermi surface of ${\mathrm{LaNiO}}_{3}$ (LNO) is predominantly holelike, with a small electron pocket. However, measurements of the Hall and Seebeck effects yield nominally opposite signs for the dominant charge carrier type, making charge transport in LNO puzzling. Here, we combine measurements of the Hall, Seebeck, and Nernst coefficients in high-mobility epitaxial LNO thin films, and resolve this puzzle by demonstrating that the negative Seebeck coefficient is generated by the diffusion of holes from cold to hot regions of LNO. We further examine this counter-thermal flow of holes by measuring the evolution of the Nernst coefficient from the diffusive to the ballistic regime, where the suppression of energy-dependent scattering leads to a reversal of the flow of holes.

Strain Influence on the Oxygen Electrocatalysis of the (100)-Oriented Epitaxial La2NiO4+δ Thin Films at Elevated Temperatures

Ruddlesden–Popper materials such as La2NiO4+δ (LNO) have high activities for surface oxygen exchange kinetics promising for solid oxide fuel cells and oxygen permeation membranes. Here we report the synthesis of the (100)tetragonal-oriented epitaxial LNO thin films prepared by pulsed laser deposition. The surface oxygen exchange kinetics determined from electrochemical impedance spectroscopy (EIS) were found to increase with decreasing film thickness from 390 to 14 nm. No significant change of the surface chemistry with different film thicknesses was observed using ex situ auger electron spectroscopy (AES). Increasing volumetric strains in the LNO films at elevated temperatures determined from in situ high-resolution X-ray diffraction (HRXRD) were correlated with increasing surface exchange kinetics and decreasing film thickness. Volumetric strains may alter the formation energy of interstitial oxygen and influence on the surface oxygen exchange kinetics of the LNO films.

TEM and FESEM investigation of Lanthanum nickelate thin films obtained by chemical solution deposition

Lanthanum nickelate (LNO) is a perovskite oxide material with metallic conductivity in a wide temperature range which makes it suitable for application as electrode material for thin films. In this paper LNO thin films were prepared by polymerizable complex method from the diluted citrate solutions. Precursor solutions were spin coated onto Si-substrates with amorphous layer of SiO2. Deposited layers were thermally treated from the substrate side with low heating rate (1?/min) up to 700?C and finally annealed for 10 hours. Results of AFM and FESEM showed that films are very smooth (Ra = 4 nm), dense, crack-free and with large square-shaped grains (170 nm). According to FESEM and TEM results the obtained four-layered film was only 65 nm thin. EBSD and XRD analyses confirmed polycrystalline microstructure of the films without preferential orientation. It was concluded that the presence of SiO2 layer on Si substrate prevents epitaxial or oriented growth of LNO.

The role of oxygen pressure and thickness on structure and pyroelectric properties of Ba(Ti0.85Sn0.15)O3 thin films grown by pulsed laser deposition

The roles of oxygen pressure and thickness on the microstructure, electrical, and pyroelectric properties of Ba(Ti0.85Sn0.15)O3 (BTS) thin films have been studied. The highly (h00)-oriented BTS thin films were deposited on the SiO2/Si substrates with a LaNiO3 layer as the bottom electrode by pulsed laser deposition. It was found that the texture and the microstructures of the as-deposited thin films are strongly dependent on the oxygen pressure, and that the BTS thin films deposited at higher oxygen pressures possess better electrical properties. The study on the thickness dependence of the dielectric and pyroelectric properties showed that the tensile stresses on the LNO and BTS thin films decreased as the thickness of the BTS film was increased. With the high textured thin film, a larger dielectric constant and pyroelectric coefficient were therefore achieved.

Effects of LaNiO 3 buffer layers on preferential orientation growth and properties of PbTiO 3 thin films

(1 0 0)- and (1 0 1)-oriented PbTiO 3 (PT) thin films on conductive LaNiO 3 (LNO)-coated Si(1 1 1) substrates were prepared by a metal-organic decomposition method. It is found that the crystallization states of LNO thin films used as buffer layers have significantly effects on preferential orientation of PT thin films. PT thin films with (1 0 0) orientation could be obtained not only on the crystalline LNO (1 0 0) film, but also on the amorphous LNO thin film. The highly (1 0 0)-oriented PT films show high dielectric constant of 189.4 on LNO (1 0 0) films and 183.1 on amorphous LNO films. The PT capacitors fabricated on the LNO buffer layers display good P– E hysteresis loops. The remnant polarization ( P r) and coercive field ( E c) of PT films on amorphous, (1 0 0)- and (1 1 0)-oriented LNO films are 9.35 μC/cm 2 and 162.8 kV/cm, 10.03 μC/cm 2 and 163.3 kV/cm, 11.23 μC/cm 2 and 166.2 kV/cm, respectively.

Metal-organic chemical liquid deposited (1 1 0)-preferred LaNiO 3 buffer layer for Pb 0.97La 0.02(Zr 0.85Sn 0.13Ti 0.02)O 3 antiferroelectric films

Conductive perovskite lanthanum nickelate LaNiO 3 (LNO) thin films were fabricated on SiO 2/Si substrates through metal-organic chemical liquid deposition method. The effect of annealing temperature on the orientation and sheet resistance of the LNO films were investigated. XRD patterns showed that the LNO films deposited on SiO 2/Si substrates exhibited preferred-(1 1 0) orientation. The lowest sheet resistance of the LNO thin films, 250 Ω/□ was obtained after being annealed at 650 °C for 1 h. Subsequently, Pb 0.97La 0.02(Zr 0.85Sn 0.13Ti 0.02)O 3 (PLZST) antiferroelectric thin films were prepared on the LaNiO 3 buffered SiO 2/Si substrates via sol–gel process. And the crystallinity, microstructure and electric properties of the PLZST thin films were studied in details.

FABRICATION AND CONDUCTIVE CHARACTERISTIC OF HIGHLY ORIENTED LANIO3 THIN FILMS

ABSTRACT LaNiO3 thin films were fabricated on Si substrates by sol-gel method under different annealing temperatures. The XRD pattern showed that the films annealed at 700°C were single perovskite phase and highly (200) oriented. Dense and homogeneously distributed surface was observed using AFM, the average grain size and the root mean square roughness (RMS) of the sample are 83.67 nm and 5.06 nm, respectively. It was also revealed that the electrical property of the films mainly depended on the crystallite size of LNO, the resistivity and sheet resistance of the LNO thin films annealed at 700°C are 0.0037 Ω · cm and 76 Ω /□, respectively.

Preparation of LaNiO 3 thin films with very low room-temperature electrical resistivity by room temperature sputtering and high oxygen-pressure processing

LaNiO 3 (LNO) thin films were deposited by radio frequency magnetron sputtering on n-type Si (100) wafers at room temperature (RT). The as-sputtered LNO thin films were amorphous and had very high RT electrical resistivity even after post-annealing at 800 °C. The amorphous as-sputtered LNO films could be transformed to polycrystalline LNO films in rhombohedral phase by heating at 400 °C in an O 2 atmosphere at pressure ranging from 1.5 to 8.0 MPa. Very low RT resistivity of LNO films were obtained by this high oxygen-pressure processing. The lowest value was as low as 1.09 × 10 − 4 Ω cm by processing at oxygen pressure of 8 MPa. Such preparation of LNO thin films is compatible with the Si-based readout integrated circuits. Highly (100)-oriented perovskite structure of Pb(Zr 0.52Ti 0.48)O 3 thin films was formed on this rhombohedral phase LNO, and good ferroelectricity could also be obtained on these HOPP-processed rhombohedral phase LNO films.

Etching characteristics of LaNiO3 thin films in BCl3∕Ar gas chemistry

La Ni O 3 (LNO) electrode was intensively studied as electrodes because LNO has a pseudocubic perovskite crystal structure with a lattice parameter of 3.84Å. But the etching process of LNO thin films must be developed in order to realize highly integrated ferroelectric random access memories. In this work, we investigated etching characteristics and mechanisms of LNO thin films using inductively coupled BCl3∕Ar plasma (ICP) system. The maximum etch rate of LNO thin films was 41.1nm∕min at a BCl3(20)∕Ar(80) gas mixing ratio. The positive ions and the ion energy distributions were measured with a quadrupole mass spectrometer (QMS). As rf power and dc bias voltage increased and working pressure decreased, the ion energy and etch rates of LNO thin films were increased. A chemically assisted physical etch of LNO was experimentally confirmed by ICP system and QMS measurements.

Investigation of room temperature electrical resistivities of LaNiO3−δ thin films deposited by rf magnetron sputtering and high oxygen-pressure processing

Highly (100)-oriented electrically conductive LaNiO3−δ (LNO) thin film with perovskite-type structure was deposited on Si(100) substrates by rf magnetron sputtering at substrate temperatures of 200, 300, 450, and 600°C with a series of 0%, 20%, 40%, and 60% oxygen partial pressures, respectively. The room temperature (RT) resistivity of LNO films decreases with decreasing substrate temperature at a fixed oxygen partial pressure and with increasing oxygen partial pressure at a fixed substrate temperature. The lowest RT resistivity of as-sputtered LNO thin films was about 5.3×10−4Ωcm. This value could be as low as ∼1.55×10−4Ωcm by postprocessing called high oxygen-pressure processing at 8MPa and is comparable to the lowest one, 1.5×10−4Ωcm, of epitaxial LNO thin film deposited on lattice-matched SrTiO3, LaAlO3, or sapphire single-crystal substrates.

Magnetic field effect on quantum corrections to the low-temperature conductivity in metallic perovskite oxides

The transport and magnetotransport properties of the metallic and ferromagnetic $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ (SRO) and the metallic and paramagnetic $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ (LNO) epitaxial thin films have been investigated in fields up to $55\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ at temperatures down to $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At low temperatures both samples display a well-defined resistivity minimum. We argue that this behavior is due to the increasing relevance of quantum corrections to the conductivity (QCC) as temperature is lowered; this effect being particularly relevant in these oxides due to their short mean free path. However, it is not straightforward to discriminate between contributions of weak localization and renormalization of electron-electron interactions to the QCC through temperature dependence alone. We have taken advantage of the distinct effect of a magnetic field on both mechanisms to demonstrate that in ferromagnetic SRO the weak-localization contribution is suppressed by the large internal field leaving only renormalized electron-electron interactions, whereas in the nonmagnetic LNO thin films the weak-localization term is relevant.

Orientation control of chemical solution deposited LaNiO 3 thin films

High quality LaNiO 3 (LNO) thin films with preferred orientation could be synthesized on Pt/Ti/SiO 2/Si substrates at 700 °C using the chemical solution deposition method. The homogeneous and stable LNO precursor solutions were prepared using lanthanum isopropoxide and nickel (II) acetylacetonate in a mixed solvent of absolute ethanol and 2-methoxyethanol. The oriented LNO thin films exhibit metallic electro-conduction, and their resistivity at room temperature is sufficiently low for making them an alternative electrode material for functional ceramic thin films.

Preparation of highly (1 0 0)-oriented LaNiO 3 nanocrystalline films by metalorganic chemical liquid deposition

Lanthanum nickelate LaNiO 3 (LNO) nanocrystalline films have been grown by the metalorganic chemical liquid deposition (MOCLD) technique using lanthanum acetate and nickel acetate as the starting materials. The technique simplified the process of preparation for LNO thin films by chemical solution routes. XRD measurements showed that the LNO films deposited on Si, SiO 2/Si and Pt/Ti/SiO 2/Si substrates exhibit preferential (1 0 0) orientation. The effects of pyrolysis temperature and thickness on (1 0 0)-orientation parameters of LNO films were investigated. The lowest resistivity film was obtained by annealing at 750 °C. The effects of thickness and annealing temperature on resistivity of the LNO films have been discussed. PbZr 0.4Ti 0.6O 3 (PZT) films deposited onto LNO films displayed a good P–E hysteresis characteristic and fatigue free to 10 8 fatigue cycles.

Effect of heat-treatment on LaNiO3film electrode of PZT thin films derived by a sol–gel method

Lanthanum nickel oxide (LaNiO3 or LNO) conducting thin films that could be used as electrodes for improving fatigue and aging properties of ferroelectric thin films were investigated. In this paper, LNO films were directly spin-coated onto SiO2/Si(1 0 0) substrates followed by thermal treatment in air and in oxygen. It was found that crack-free dense and uniform films with good crystallinity and medium grains were obtained, preferentially (1 0 0)-oriented LNO thin films could be formed at a lower annealing temperature of 550 °C and that with the increase in thermal annealing temperature the LNO thin film possessed better electrical properties especially at 750 °C. However, the LNO film displayed a structure transformation above 850 °C. A phenomenon was found that the first heat-treatment temperature and time played a key role to determine the crystallite size of LNO films. A subsequent deposition of a sol–gel derived Pb(Zr0.53Ti0.47)O3 (PZT53/47) thin film on the LNO-coated SiO2/Si(1 0 0) substrates was also found to have a (1 0 0)-oriented texture. Moreover, the Au/PZT/LNO capacitor was found to significantly improve the fatigue and the effects of the LNO electrodes to the fatigue were discussed.

Microstructure and electrical properties of Pb(Zr 0.52Ti 0.48)O 3 ferroelectric films on different bottom electrodes

The crystalline quality, dielectric and ferroelectricity of the Pb(Zr 0.52Ti 0.48)O 3 (PZT) films deposited on the LaNiO 3 (LNO), LNO/Pt and Pt bottom electrodes were comparatively analyzed to investigate the possibility for their application. LNO thin films were successfully prepared on Si (100) and Pt(111)/Ti/SiO 2/Si substrates by modified metallorganic decomposition (MOD). The PZT thin films were spin-coated onto the LNO, LNO/Pt and Pt bottom electrodes by sol–gel method. The crystallographic orientation and the microstructure of the resulting LNO films and PZT thin films on the different bottom electrodes were characterized by X-ray diffraction analysis. The dielectric and ferroelectric properties of PZT films on the different bottom electrodes are discussed. The PZT films deposited onto Pt/Ti/SiO 2/Si and LNO/Si substrates show strong (110) and (100) preferred orientation, respectively, while the films deposited onto LNO/Pt/Ti/SiO 2/Si substrates show the peaks of mixed orientations. PZT films on LNO and LNO/Pt bottom electrodes have larger dielectric constant and remnant polarizations compared with those grown on the Pt electrode.

Microstructural and transport properties of LaNiO 3− δ films grown on Si (111) by chemical solution deposition

Electrically conductive LaNiO 3− δ (LNO) thin films with typical thickness of 200 nm were deposited on Si (111) substrates by a chemical solution deposition method and heat-treated in air at 700 °C. Structural, morphological, and electrical properties of the LNO thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field-emission scanning electron microscopy (FEG-SEM), and electrical resistivity ρ( T). The thin films have a very flat surface and no droplet was found on their surfaces. The average grain size observed by AFM and FEG-SEM was approximately 100 nm in excellent agreement with XRD data. The ρ( T) data showed that these thin films display a good metallic character in a large range of temperature. These results suggest the use of this conductive layer as electrode in the integration of microelectronic devices.

Comparative analysis for the crystalline and ferroelectric properties of Pb(Zr,Ti)O 3 thin films deposited on metallic LaNiO 3 and Pt electrodes

The crystalline quality and ferroelectricity of the Pb(Zr,Ti)O 3 (PZT) films deposited on the metallic LaNiO 3 (LNO) and Pt electrodes were comparatively analyzed to investigate the possibility for their application to non-volatile memory devices. LNO thin films were successfully deposited on various substrates by using r.f. magnetron sputtering even at a low temperature ranging from 250 to 500 °C, and the ferroelectric PZT thin films were spin-coated onto the LNO and Pt bottom electrodes. Metallic LNO thin films exhibited [100] orientation irrespective of the substrate species and PZT films coated onto LNO films had highly a- and c-axis orientations, while those with Pt bottom electrode were polycrystalline. PZT films with LNO bottom electrode had smaller grain size and larger dielectric constant compared to those grown on the Pt electrode. The ferroelectric thin films fabricated on LNO bottom electrode displayed an asymmetric D–E hysteresis loop, which was explained by the defect effects formed at the interface. Especially, the LNO/PZT/LNO capacitor was found to significantly improve the polarization fatigue and the effects of the LNO electrodes to the fatigue were discussed.