La Layer Research Articles

Coupled Compositional and Displacive Modulations in KLaMnWO6 Revealed by Atomic Resolution Imaging.

Complex compositional and displacive modulations of the crystal structure of KLaMnWO6 are imaged with atomic resolution by means of scanning transmission electron microscopy (STEM). This oxide is stabilized by cation vacancies leading to a La1+x/3K1-xMnWO6 stoichiometry. Compositional modulation on both the K and La layers are revealed in the high-angle annular dark-field STEM (HAADF-STEM) images. The compositional modulation within the La layer is coupled with the modulation of the octahedral tilting, which is exposed by imaging of the anion sublattice in annular bright-field STEM (ABF-STEM) images. These complex modulations are accommodated in a 5√2ap × 5√2ap × 2ap perovskite-type structure.

Mo-La2O3 Multilayer Metallization Systems for High Temperature Surface Acoustic Wave Sensor Devices.

Developing advanced thin film materials is the key challenge in high-temperature applications of surface acoustic wave sensor devices. One hundred nanometer thick (Mo-LaO) multilayer systems were fabricated at room temperature on thermally oxidized (100) Si substrates (SiO/Si) to study the effect of lanthanum oxide on the electrical resistivity of molybdenum thin films and their high-temperature stability. The multilayer systems were deposited by the magnetron sputter deposition of extremely thin (≤1 nm) La interlayers in between adjacent Mo layers. After deposition of each La layer the process was interrupted for 25 to 60 min to oxidize the La using the residual oxygen in the high vacuum of the deposition chamber. The samples were annealed at 800 C in high vacuum for up to 120 h. In case of a 1 nm thick La interlayer in-between the Mo a continuous layer of LaO is formed. For thinner La layers an interlayer between adjacent Mo layers is observed consisting of a (LaO-Mo) mixed structure of molybdenum and nm-sized lanthanum oxide particles. Measurements show that the (Mo-LaO) multilayer systems on SiO/Si substrates are stable at least up to 800 C for 120 h in high vacuum conditions.

Multiple strategies to decrease ignition temperature for soot combustion on ultrathin MnO2-x nanosheet array

Diesel soot combustion suffers from ignition temperatures (T10) as high as > 450 °C in the absence of catalysts, which are unavailable in diesel exhaust during normal driving cycles (normally 200–400 °C). A catalytic diesel particulate filter (CDPF) could decrease T10 greatly, but it is often inadequate due to the poor contact associated with the solid (catalyst)-solid (soot) interactions. Herein, a highly significant T10, as low as ˜200 °C, was achieved on noble metal-free ultrathin MnO2-x nanosheet array fabricated by in situ etching of a La layer from LaMnO3 under loose contact conditions in a NO-containing atmosphere. A number of advantages were found with such a system including the improved reducibility. Then, the nanosheet array ensures high dispersion of soot on the catalyst. Finally, high NO-to-NO2 oxidation activity further facilitates contact between catalyst and soot via NO2, a stronger oxidant than O2.

Enhanced multiferroic properties and magneto-dielectric effect analysis of La/Co modified BiFeO3

Multiferroic BiFeO3 (BFO), La/Co modified BiFeO3 (BLFO/BLCFO) ceramics prepared by solid state reaction route were characterised and their magneto-dielectric properties were investigated. The phase purity of La/Co modified BFO ceramics was confirmed from powder X-ray diffraction studies and distortion observed in the lattice due to compression was found to be associated with polarization switching on La/Co co-substitution into BFO. An enhancement and stability in saturation magnetization with low coercive field (Hc ≈ 400 Oe) has been achieved at room temperature in La/Co modified BFO samples. Dielectric and impedance measurements reveal the enhanced values of dielectric constant, real and imaginary part of impedance and modulus on account of modification by La/Co in BFO. The modulus studies confirm the presence of ionic polarization due to the co-substitution of La2+/Co3+ ions and dominant grain effects in BLFO and BLCFO samples. The magneto-dielectric effect (% MDE) is found to be maximum value of 1.8 in magnitude at 8 kOe for BLFO-10%Co, and increases with increase in Co content in to BLFO. The substitution of Co into BLFO generates polarization at La and Fe layer, which provides the enhanced value of %MDE and stability in purity of BFO ceramic.

High-reflectance La/B-based multilayer mirror for 6.x nm wavelength.

We report a hybrid thin-film deposition procedure to significantly enhance the reflectivity of La/B-based multilayer structures. This is of relevance for applications of multilayer optics at 6.7-nm wavelength and beyond. Such multilayers showed a reflectance of 64.1% at 6.65nm measured at 1.5-degrees off-normal incidence at PTB (BESSY-II). This was achieved by a special scheme of La passivation. The La layer was nitridated to avoid formation of the optically unfavorable LaBx compound at the B-on-La interface. To avoid the also undesired BN formation at the La-on-B interface, a time-dosed nitridation at the initial stage was applied. This research revealed a good potential for further increase in the reflectivity of multilayer structures at 6.7nm.

Coercivity Enhancement in La Coated Nd-Fe-B Thin Films

The Nd-Fe-B/La thin films were deposited on the Al2O3(0001) substrate in order to investigate the effect of rare earth overlayer on the coercivity Hc. Highly textured Nd2Fe14B grains were grown by inserting the Mo(111) single crystal buffer layer. By depositing the La overlayer onto Nd2Fe14B thin films and subsequently post-annealing at 470 ̊C, the Hc value increased from about 10.5 kOe to 15.0 kOe. The amount of Hc increase by the combination of the La coating and post-annealing was about 4.5 kOe. After the post annealing, La oxide (hcp La2O3) was formed in the La layer, which was confirmed by means of XRD and SIMS depth profile measurements.

Domain boundaries and their influence on Li migration in solid-state electrolyte (La,Li)TiO3

The influence of 90° domain boundaries in (La,Li)TiO3 (LLTO) on the Li conduction mechanism has been examined by a combination of state-of-the-art electron microscopy techniques and first-principles calculations. The atomistic structure of 90° domain boundaries in LLTO was determined from aberration-corrected scanning transmission electron microscopy images. At 90° domain boundaries, each perovskite unit of one domain is connected by an La-rich layer to units of the neighboring domain. First-principles calculations of a model domain boundary show that Li migration through the La layer has a very high activation energy, Ea, of 3.58 eV, indicating that La layers serve to block Li migration. However, if La vacancies are present within La layers, the migration energy decreases significantly to 0.58 eV, a value more in line with experimental observation. The results show that Li conduction in LLTO is strongly influenced by 90° domain boundaries. The activation energy in a single crystal (Ea = 0.19 eV) is much lower, suggesting that if 90° domain boundaries could be eliminated, an increase in conductivity of approximately three orders of magnitude compared with conventional LLTO could be achieved.

90° Domain Structure of (La,Li)TiO3 and Its Influence on Li Conduction Properties

The influence of 90° domain boundaries in (La,Li)TiO3 (LLTO) on the Li conduction mechanism has been examined by a combination of state-of-the-art experiments and first-principles calculations. The atomistic structure of 90° domain boundaries in LLTO has been determined using HAADF-STEM observations. Using HAADF-STEM observations, we can obtain Z-contrast image. As shown in Fig.1, bright spots correspond to heavier La column. Important finding is that at 90° domain boundary, each cells connected by La layer. Based on this structural information, first-principles calculations were carried out. In this study, we use projector augmented wave (PAW) method based on the density functional theory (DFT). Li conduction path and its activation energy were determined using nudged elastic band (NEB) method. Phonon dispersion relations were determined by frozen phonon method. Firstly we performed bulk crystal calculations using tetragonal (SG: P4/mmm) (La0.5,Li0.5)TiO3 assuming alternative stacking La layer and Li layer along c-direction. The calculated phonon dispersion for bulk crystal shows soft-mode in the entire wave vector space. This indicate lattice instability mainly TiO6-octahedoron rotation. Because of this TiO6-octahedoron rotation instability, calculated Li conduction activation energy for LLTO bulk shows exceptionally small value (E a = 0.2 eV). However, this theoretical E a was quite small to compare with experimentally reported value (E a = 0.4 eV). To reveal the origin of this E a discrepancy between theory and experiments, secondary, we examined Li-conduction energies at 90° domain boundary. We assumed two type of Li conduction: a) Li conduction through La layer, b)Li conduction through La vacancy at La layer. a) Li conduction through La layer shows very high E a of 3 eV. This indicate La layer acting blocking layer for Li conduction. However, if we assume the La vacancy at La layer, conduction energy significantly decreased to 0.6 eV. This conduction energy well corresponds to experimental value. Our calculations reveal that Li conduction in LLTO should be strongly influenced by 90° domain boundaries in this system.

Superior hydrogen storage and electrochemical properties of Mg–La–Pd trilayer films at room temperature

A series of Mg–La–Pd trilayer films (La = 0.5–9 nm) have been prepared by magnetron sputtering method. When the thickness of La layer is larger than 3 nm, the distribution of La element becomes homogeneous. The hydrogen storage properties of the films under 0.1 MPa H2 and at 298 K are investigated by measuring their resistance and optical transmittance during the hydrogenation. The hydrogenation of the La 3 nm film saturates within 14 s and possesses the fastest absorption kinetics compared with other Mg–La–Pd films. The further increase of La thickness decreases the hydrogenation rate due to the decreased hydrogen diffusion rate through this layer. The La 3 nm film also exhibits the fast hydrogen desorption rate in air at room temperature. It releases 80% of hydrogen within 60 min. The electrochemical properties of the Mg–La–Pd films have been carried out in 6 M KOH with a three-electrode cell. Among these films, the La 3 nm film possesses the largest anodic area and anodic peak current, as well as the highest maximum discharge capacity of 377.8 mAh g−1.

Inelastic background analysis of HAXPES spectra: towards enhanced bulk sensitivity in photoemission

We report on quantitative inelastic background analysis in hard X‐ray photoelectron spectroscopy at high excitation energy (12–18 keV) using the Tougaard method implemented with careful optimisation of the inelastic scattering cross section. Such a method enables the determination of the in‐depth elemental distribution over depths up to70 nm. We studied three parameters and investigate their influence on the results: the depth of the layer increases the uncertainty, the thickness and composition of the layer has an influence on statistics, and the excitation energy that must be chosen as a trade‐off between high probing depth and low photoionization cross section. We show how this promising method can be used to follow diffusion of a 1‐ML La layer after annealing a technologically relevant sample. Copyright © 2014 John Wiley & Sons, Ltd.

Short period La/B and LaN/B multilayer mirrors for ~68 nm wavelength

In the first part of this article we experimentally show that contrast between the very thin layers of La and B enables close to theoretical reflectance. The reflectivity at 6.8 nm wavelength was measured from La/B multilayer mirrors with period thicknesses ranging from 3.5 to 7.2 nm at the appropriate angle for constructive interference. The difference between the measured reflectance and the reflectance calculated for a perfect multilayer structure decreases with increasing multilayer period. The reflectance of the multilayer with the largest period approaches the theoretical value, showing that the optical contrast between the very thin layers of these structures allows to experimentally access close to theoretical reflectance. In the second part of the article we discuss the structure of La/B and LaN/B multilayers. This set of multilayers is probed by hard X-rays (λ = 0.154 nm) and EUV radiation (λ = 6.8 nm). The structure is reconstructed based on a simultaneous fit of the grazing incidence hard X-ray reflectivity and the EUV reflectivity curves. The reflectivity analysis of the La/B and LaN/B multilayer mirrors shows that the lower reflectance of La/B mirrors compared to LaN/B mirrors can be explained by the presence of 5% of La atoms in the B layer and 63% of B in La layer. After multi-parametrical optimization of the LaN/B system, including the nitridation of La, the highest near normal incidence reflectivity of 57.3% at 6.6 nm wavelength has been measured from a multilayer mirror, containing 175 bi-layers. This is the highest value reported so far.

The superconducting phase transitions for the asymmetrical FS superlattices with interelectronic interaction in ferromagnet layers

The superconducting and magnetic states coexistence in the FS superlattice, where F is ferromagnetic metal and S is superconductor, is investigated on base of microscopically derived boundary value problem for the Eilenberger function. The asymmetrical four-layered structure FSF' S' is considered as elementary cell. The second order phase transitions are explored for case of ideal boundary transparencies and clean Cooper limit. Each layer is characterized by its own thickness and electronic structure. Materials are also differed by electron-electron interaction constants (note these constants for ferromagnets are nonzero!). It is shown, that 0- and π-phase superconducting states of clean thin superlattices FS are defined by value and sign of electronic correlations in all four layers of elementary cell. The competition between uniform BCS pairing and non-uniform Fulde-Ferrell-Larkin-Ovchinnikov pairing are also taken into account. We predict that the complex system under consideration may have up to 8 different states which are characterized by phase shifts between superconducting order parameters in S(F) and S'(F') and mutual orientation of magnetizations in the F and F' layers. The states with π-phase magnetism can fully explain surprising experimental behavior of short-range Gd/La superlattice, i.e the coincidence of superlattice critical temperature Tc with Tc(La) = 5 K for different thickness of the Gd layers exceeding the La layer thickness.

Electrospark alloying of Mg–La electrode on ZM5 Mg alloy under distilled water or kerosene

The electrospark alloying (ESA) technique has been successfully applied to deposit an Mg–La layer on a ZM5 Mg–Al–Zn type Mg alloy at room temperature. The effect of Mg–La magnesium alloy on the coating layer formation with varying processing parameters was investigated. The effect of kerosene and distilled water as dielectrics on ESA of ZM5 alloy was studied. Optical microscopy and scanning electron microscopy equipped with energy dispersive X-ray analysis were used to study the microstructure and element distribution of the alloying layers. The distribution of the rare earth La in the coating layer was determined. It has been possible to obtain a fully dense and strongly adherent coating layer. The typical ‘splash’ appearance of the coating surface can be observed and is related to the mechanism of the consumable Mg–La electrode alloying technique.

Soil C, N and P stoichiometry of Deyeuxia angustifolia and Carex lasiocarpa wetlands in Sanjiang Plain, Northeast China

The theory of ecological stoichiometry has improved understanding of nutrient circulation processes in ecosystems. The purpose of this work was to study ecological stoichiometric characteristics of carbon, nitrogen and phosphorus in wetland soils of Sanjiang Plain, northeast China. A Deyeuxia angustifolia wetland (swamp meadow) and a Carex lasiocarpa wetland (marsh) were chosen for collection of soil cores (0–30 cm depth). Soil organic carbon, total nitrogen and phosphorus were analyzed to study patterns of C/N (R CN), C/P (R CP), N/P (R NP), and C/N/P (R CNP) in wetland soils. Soil carbon, nitrogen and phosphorus stoichiometry differed between the two wetlands. Soil RCN (0–30 cm depth) in the D. angustifolia wetland was close to that in C. lasiocarpa wetland (12.97 and 12.80, respectively), but R CP and R NP in C. lasiocarpa soils were significantly higher than those in D. angustifolia soils. R CN changed little within soil profile, without obvious trends in both wetlands. Both R CP and R NP decreased with depth from the surface, and both R CP and R NP were higher at every depth interval in C. lasiocarpa soils compared to D. angustifolia soils. R CN in surface soil (0–10 cm, organic-rich “Lo” layer) was not significantly different from R CN in the entire profile (0–30 cm, “La layer”) of D. angustifolia wetland, while R CP and R NP were both significantly different between the Lo and La layers. In Carex lasiocarpa wetland, R CN, R CP and R NP in Lo layer were significant higher than those in La layer. R CNP in La layer of D. angustifolia and C. lasiocarpa wetlands were 65:5:1 and 163:13:1, respectively. Soil R CN was relatively consistent, while R CP and R NP reflected P limitation in wetlands of Sanjiang Plain. Further research is needed to determine whether these ratios hold among other wetland ecosystems.

Spectral properties of La/B - based multilayer mirrors near the boron K absorption edge

The spectral properties of La/B, La/B(4)C, and LaN/B, LaN/B(4)C multilayer mirrors have been investigated in the 6.5-6.9 nm wavelength range based on measured B and B(4)C optical constants. Experimentally it is verified to what extent measured and tabulated optical constants are applicable for simulations of the reflectivity of these short period multilayer mirrors. The measured maximum reflectance at various wavelength values around the boron-K absorption edge is compared to calculated values from model systems. The measured reflectance profiles of La/B and La/B(4)C show a maximum at a slightly larger wavelength than calculations would predict based on the measured B and B(4)C optical constants. This is explained by the influence of a formed boron-lanthanum compound on the wavelength where the multilayer shows maximum reflectance. The maximum reflectance profiles of LaN/B and LaN/B(4)C multilayers can be described accurately by using the same boron atomic scattering factors, indicating boron in the LaN/B(4)C multilayer to be in a similar chemical state as boron in the LaN/B multilayer. It also indicates that nitridation of the La layer in the multilayer prevents the formation of La-B compounds. We show that the optimal wavelength for boron based optics is about 6.65 nm and depends on the B chemical state. Finally, using the measured B optical constants we are able to calculate the spectral response of the multilayers, enabling the prediction of the optimal parameters for the above mentioned multilayers.

Determination of the density of ultrathin La films in La/B4C layered structures using X‐ray standing waves

AbstractUsing simultaneous analysis of both the grazing incidence X‐ray reflectivity (GIXR) and the angular dependent fluorescence yield from ultrathin layer structures, the densities of thin La and LaN layers of 2–6 nm thickness enclosed by B4C layers have been determined with approximately 5% precision. The density of the La layer in these systems is found to be reduced to the bulk La value. This is explained by LaB6 interlayers formation. The density of LaN layers were similar to the bulk LaN value, which favors this compound as the most energetically stable in LaN/B4C layered systems.

Lanthanide Sulfate Frameworks: Synthesis, Structure, and Optical Properties

Layered lanthanide sulfate compounds with three different structures have been prepared and characterized. The compounds [C10H10N2][La(SO4)2]·2H2O (I), [C10H10N2][La(SO4)2(H2O)2]2 (IIa), [C10H10N2][Pr(SO4)2(H2O)2]2 (IIb), [C10H10N2][Nd2(SO4)4(H2O)2]2 (IIIa), [C10H10N2][Sm2(SO4)4(H2O)2]2 (IIIb), and [C10H10N2][Eu2(SO4)4(H2O)2]2 (IIIc) have anionic lanthanide sulfate layers separated by protonated bipyridine molecules. The layers are formed by the connectivity between the lanthanide polyhedra and sulfate tetrahedra. The formation of a two-dimensional La−O−La layer (Ia), Pr−O−Pr chains (IIb), and a tetramer cluster (IIIa) is noteworthy. The compounds exhibit honeycomb (I), square (IIa, IIb), and honeycomb (IIIa−IIIc) net arrangements, when the connectivity between the lanthanide ions is considered. Optical studies indicate the observation of characteristic metal-centered emission at room temperature. The Nd compound (IIIa) exhibits a two-photon upconversion behavior.

Spin-Polarized Two-Dimensional Electron Gas at Oxide Interfaces

The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO_3/(LaMnO_3)_1/SrMnO_3 heterostructure is predicted from density-functional calculations. The La(d) electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t_2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.

Positron potential and wave function in LaFeAsO

We report calculations of the positron potential and wave function in LaFeAsO. These calculations show that the positron wave function does sample the entire unit cell, although it is largest in the interstices of the La layer adjacent to As atoms. The implication is that annihilation correlation of annihilation radiation is a viable probe of the Fermi surfaces in this material. The results also apply to positive muons and indicate that these will be localized in the La layer adjacent to As.

Formation of Ni Aluminide Layer Containing La by Molten-Salt Electrodeposition and Cyclic-Oxidation Resistance

In order to improve the cyclic-oxidation resistance of Ni and SUS304 steel, the coating of a Ni aluminide containing La on both samples were carried out by the electrodeposition of Al and La in a molten salt. The electrodepositions of Al and La were conducted using a potentiostatic polarization method at 1023 K in an equimolar NaCl-KCl melt containing 3.5 mol%AlF3, and that containing 4 mol%La2O3-24 mol%NH4Cl, or 3.5 mol%LaF3. Observation and analysis of the cross-section of the specimen after polarization showed that a deposited layer consisting of a thick inner Ni aluminide layer and a thin outer layer containing a large amount of La was formed on both samples. The cyclic-oxidation resistance of the Ni specimen covered with the deposit layer having the La layer as the outer layer was higher than those of the untreated Ni specimen and the Ni specimen coated with the deposit layer without La. The stainless steel covered with the Ni aluminide showed a high cyclic-oxidation resistance in the atmosphere containing water vapor at 1273 K in comparison with untreated stainless steel, without depending on the existence of La in the deposited layer.