Metallic and insulating oxide interfaces controlled by electronic correlations

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO(3)) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO(3) matrix. Such correlation effects can lead to new functionalities in designed heterostructures.     

Spontaneous superlattice formation in nanorods through partial cation exchange

Lattice-mismatch strains are widely known to control nanoscale pattern formation in heteroepitaxy, but such effects have not been exploited in colloidal nanocrystal growth. We demonstrate a colloidal route to synthesizing CdS-Ag(2)S nanorod superlattices through partial cation exchange. Strain induces the spontaneous formation of periodic structures. Ab initio calculations of the interfacial energy and modeling of strain energies show that these forces drive the self-organization of the superlattices. The nanorod superlattices exhibit high stability against ripening and phase mixing. These materials are tunable near-infrared emitters with potential applications as nanometer-scale optoelectronic devices.     

Probing nanoscale ferroelectricity by ultraviolet Raman spectroscopy

We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature (Tc) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO3 layers in BaTiO3/SrTiO3 superlattices are not only ferroelectric (with Tc as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. Tc was tuned by approximately 500 kelvin by varying the thicknesses of the BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.     

Electrodeposited defect chemistry superlattices

Nanometer-scale layered structures based on thallium(III) oxide were electrodeposited in a beaker at room temperature by pulsing the applied potential during deposition. The conducting metal oxide samples were superlattices, with layers as thin as 6.7 nanometers. The defect chemistry was a function of the applied overpotential: High overpotentials favored oxygen vacancies, whereas low overpotentials favored cation interstitials. The transition from one defect chemistry to another in this nonequilibrium process occurred in the same potential range (100 to 120 millivolts) in which the rate of the back electron transfer reaction became significant. The epitaxial structures have the high carrier density and low electronic dimensionality of high transition temperature superconductors.     

Rare-Earth manganites: surface-segregated platinum increases catalytic activity

Crushed and etched lanthanum lead manganite (La(0.7)Pb(0.3)MnO(3)) crystals containing as little as 0.005 atomic percent platinum have significantly higher catalytic activity than free platinum crystals. This higher activity is due to an almost 100-fold segregation of platinum on the surface. The surface platinum concentration found, 0.5 atomic percent, is sufficient to account for the enhanced activity provided that the platinum has the same activity as platinum supported on alumina.     

Magnetic properties of the lunar crystalline rock and fines

Magnetic measurements have shown that nondiamagnetic minerals in a lunar crystalline rock of type B are (free Fe(2)+ in paramagnetic pyroxenes) : (antiferromagnetic FeSiO(3)) : (antiferromagnetic FeTiO(3)) : (ferromagnetic iron) = 4.3 : 7 : 20 : 0.08 in weight percentage. The abundance of ferromagnetic Fe in the lunar fines is about 7.5 times its abundance in the crystalline rock. The natural remanent magnetization of the crystalline rock of 7.5 x 10(-6) emu/ g in intensity may not be attributable to its thermoremanent magnetization.     

Superlattices of iron nanocubes synthesized from Fe[N(SiMe3)2]2

The reaction of the metal-organic precursor Fe[N(SiMe3)2]2 with H2 in the presence of a long-chain acid and a long-chain amine in various proportions produces monodisperse zerovalent iron nanoparticles. These Fe particles display magnetic properties that match those of bulk iron as evidenced by magnetic and M?ssbauer measurements. The nanoparticles adopt a cubic shape with edges of 7 nanometers and are incorporated into extended crystalline superlattices containing nanocubes in close proximity and with their crystallographic axes aligned. These superlattices are formed in solution, precipitate in high yield, and may be redissolved and redeposited as two-dimensional arrays.     

A paramagnetic bonding mechanism for diatomics in strong magnetic fields

Elementary chemistry distinguishes two kinds of strong bonds between atoms in molecules: the covalent bond, where bonding arises from valence electron pairs shared between neighboring atoms, and the ionic bond, where transfer of electrons from one atom to another leads to Coulombic attraction between the resulting ions. We present a third, distinct bonding mechanism: perpendicular paramagnetic bonding, generated by the stabilization of antibonding orbitals in their perpendicular orientation relative to an external magnetic field. In strong fields such as those present in the atmospheres of white dwarfs (on the order of 10(5) teslas) and other stellar objects, our calculations suggest that this mechanism underlies the strong bonding of H(2) in the (3)Σ(u)(+)(1σ(g)1σ(u)*) triplet state and of He(2) in the (1)Σ(g)(+)(1σ(g)(2)1σ(u)(*2)) singlet state, as well as their preferred perpendicular orientation in the external field.     

Transient electronic structure and melting of a charge density wave in TbTe3

Obtaining insight into microscopic cooperative effects is a fascinating topic in condensed matter research because, through self-coordination and collectivity, they can lead to instabilities with macroscopic impacts like phase transitions. We used femtosecond time- and angle-resolved photoelectron spectroscopy (trARPES) to optically pump and probe TbTe3, an excellent model system with which to study these effects. We drove a transient charge density wave melting, excited collective vibrations in TbTe3, and observed them through their time-, frequency-, and momentum-dependent influence on the electronic structure. We were able to identify the role of the observed collective vibration in the transition and to document the transition in real time. The information that we demonstrate as being accessible with trARPES will greatly enhance the understanding of all materials exhibiting collective phenomena.     

Structural and electronic properties of la@c82

The structural and electronic properties of the La@C(82) fullerene have been investigated by means of the Car-Parrinello method, which is based on the local density approximation of the density functional theory. The topological arrangement of the C(82) cage was assumed to be a C(3v) symmetry isomer. Three configurations were considered, one with the lanthanum atom at the center of the cluster, one with it along the threefold axis, and one with it at a low-symmetry, highly coordinated site. The structure was fully relaxed and it was found that the last of these configurations is energetically preferred. In this position, the lanthanum atom is nearly in a La(3+) state and the unpaired electron is somewhat delocalized on the cage, in agreement with available experimental data. This arrangement suggests that the chemical shifts of the 5s and 5p lanthanum states can be used as a structural probe and as a way of further validating this picture. It is argued that this conclusion is not affected by the assumed fullerene structure.     

不同浓度镧对茶树根系抗氧化酶活性及根细胞超微结构的影响

【目的】探究不同浓度镧（La）对铁观音和水仙茶树根系抗氧化酶活性和根细胞超微结构的影响,为选育镧低吸收茶树品种提供数据参考。【方法】以茶树品种水仙和铁观音为试材,测定分析不同浓度La3+溶液（0.08、0.40和1.20 mmol/L）处理下根系的抗氧化酶活性和根细胞超微结构的变化以及镧在茶树根组织部位的定位分布。【结果】La3+浓度为1.20 mmol/L时,铁观音根系的超氧化物歧化酶（SOD）活性比水仙高73.9%,过氧化物酶（POD）活性及过氧化氢酶（CAT）活性与水仙根系相比无显著差异（P>0.05）。扫描电镜观察发现,高浓度La3+处理下根系细胞排列疏松,无规则,蜡质增多;品种间相比,水仙较铁观音根细胞蜡质覆盖量多,受害程度较重。透射电镜观察发现,高浓度La3+处理下2个茶树品种根系细胞排列散乱,细胞壁膨大,细胞壁、细胞质膜上分布较多黑色沉积物,进一步结合能谱分析,发现黑色沉积物中含有镧元素,且主要分布于铁观音根细胞中的原生质体,而在水仙根细胞的细胞壁及原生质体中均有积累。【结论】镧处理后铁观音根系较水仙抗氧化酶活性增高,根细胞超微结构受害较轻,综合表现受镧影响较小,可作为选育镧低吸收茶树品种材料加以深入研究和开发。     

富镧稀土对甘蔗的效应研究总结

试验分析表明，富镧稀土在甘蔗分蘖期进行叶面喷施处理后，能使甘蔗旺盛生长期叶片中的水溶性蛋白质含量和硝酸还原酶、ＮＡＤＰ—苹果酸酶和多酚氧化酶活性提高，而使过氧化物酶活性降低，提高蔗株生活力，促进生长；并能使生长中后期的Ｃａ２＋—ＡＴＰ酶、Ｍｇ２＋—ＡＴＰ酶、多酚氧化酶和过氧化物酶活性提高，促进蔗茎中的蔗糖分积累，降低还原糖含量，提高甘蔗品质。用９７％Ｌａ２Ｏ３、８２％Ｌａ２Ｏ３和３８％（Ｌａ２Ｏ３＋ＣｅＯ２）和“常乐”稀土这４种不同产品进行２个年度的试验表明，适当浓度的富镧稀上处理确能使甘蔗增产增糖，且增糖效果优于目前生产上所用的“常乐”稀土，尤以９７％Ｌａ２Ｏ３处理的综合效果最好。     

Monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices

Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.     

Plackett-Burman和Box-Benhnken Design设计优化促进红松多酚合成诱导条件的研究

[目的]优化促进红松多酚合成的诱导条件.[方法]以红松不定芽为试验材料,通过单因素试验、Plackett-Burman设计试验和Box-Benhnken Deign设计试验研究8种诱导子（苯丙氨酸、肉桂酸、茉莉酸甲酯、水杨酸、壳聚糖、酵母提取物、镧、铕）对红松不定芽中多酚合成的影响,并且对促进多酚合成的诱导子组合条件进行优化.[结果]除了肉桂酸外,其他7种诱导子都能不同程度地提高多酚含量.Plackett-Burman试验确定了3种影响多酚合成的关键因素：壳聚糖、镧和茉莉酸甲酯.Box-Benhnken Design试验对3种关键因素（壳聚糖、镧、茉莉酸甲酯）协同作用的诱导条件进行优化,优化得到的最佳诱导条件为：壳聚糖浓度79.58 mg/L、镧浓度42.21 μmol/L、茉莉酸甲酯浓度16.63 μmol/L,预测多酚含量最高可达到14.28 mg/g,实际多酚含量为13.42 mg/g,与对照组相比提高了122.19％.[结论] Plackett-Burman设计结合Box-Benhnken Design响应面分析法可以很好地对促进多酚合成的诱导条件进行优化,3种诱导子（壳聚糖＋镧＋茉莉酸甲酯）协同组合比单一诱导子更有效地提高红松不定芽中多酚含量,更有利于地促进多酚的合成.     

不同类型外源稀土化合物与农业面源磷流失关联性的对比

通过室内人工模拟降雨实验,在稳定雨强条件下,分别观察了LaCl3、La2O3和P随地表径流流失的特征,对比了稀土氧化物和稀土氯化物与土施畜禽肥料P随暴雨径流流失的相关性。结果表明,径流量和沉积物量在产流开始后的短时间内迅速增加,径流中总La和总P均有共同迁移的特征,对于添加不同剂量LaCl3和La2O3的土槽,La和P随地表径流的流失量之间都呈现显著或极显著的相关,稀土元素La的氧化物和氯化物都能较好地示踪总磷随暴雨径流流失的过程。     

Effects of Soaking Seeds with Lanthanum Nitrate on Seed Germination and Seedling Growth of Quinoa Under Salt Stress

【Objective】 With the formation of soil salinization, not only causes the resource-wasting, but also restricts the agricultural production. Quinoa has salt-tolerant properties, It can alleviate salt stress. China is the country with the most rare earth content. There is a study that lanthanum may alleviate the effects of salt stress on plants. In this study, quinoa was treated with salt stress, which seed had been soaked with lanthanum nitrate before. The effects of soaking seeds with lanthanum nitrate on seed germination and seedling growth of quinoa under salt stress were examined to find a way to improve salt resistance of the species. 【Method】 In this study, quinoa was used as the research material and greenhouse potted planting method was adopted in order to study the effects of different lanthanum nitrate leaching species (25, 50, 100 mg·L ^-1) on seed germination and seedling growth under different salt stresses (100, 200, 300 mmol·L ^-1 sodium chloride solution). 【Result】(1) When lanthanum nitrate was 50 mg·L ^-1, the effect of quinoa seeds were the optimal, the germination percentage, germination potential, and germination index of quinoa seeds were the highest, and there were significant differences compared with other concentrations. (2) At the same socking concentration, plant height and root length of seedlings decreased with the increase of salt concentrations within 300 mmol·L ^-1 NaCl, while peroxidase (POD), superoxide dismutase (SOD), malondialdehyde (MDA), soluble sugar, proline and other physiological and biochemical indexes increased with the increase of salt concentrations. (3) At the same salt concentration, plant height, root length and other growth indicators of quinoa seedlings showed the tendency of first increasing and then decreasing with the increase of soaking concentrations, as well as POD, SOD, soluble sugar, soluble protein, proline and other physiological and biochemical indexes. For MDA, the trends were reversed. (4) Quinoa seedlings survived and grown in the NaCl solutions less than 300 mmol·L ^-1, but optimal concentration was 300 mmol·L ^-1. At the same time 300 mmol·L ^-1 salt concentration, the growth index were the best when lanthanum nitrate was 50 mg·L ^-1.【Conclusion】 Under salt stress, quinoa seeds socked in low concentration solution of lanthanum nitrate could promote the seed germination and the shoot growth, strengthen the antioxidant enzyme activities of seedlings, and improve the content of the osmotic adjustment material, resulting in increasing resistance to salt stress. However, seedling growth was inhabited by high concentration solution of lanthanum nitrate. This study suggested that the resistance of quinoa to salt stress was enhanced by adding adequate lanthanum nitrate.     

镧/铝改性沸石的磷释放条件及再生能力研究

通过将磷吸收饱和的镧/铝改性沸石分别放入pH为2.0、3.0、4.0、5.0、6.0、7.0、8.0、9.0、10.0、11.0、12.0、13.0的溶液中,研究了镧/铝改性沸石的最佳磷释放条件,并在最佳磷吸附和最佳磷释放条件下研究了镧/铝改性沸石的再生能力。结果表明,当pH变化在2~13时,镧/铝改性沸石的磷释放量和释放百分比随pH的升高先降低后升高,其中：pH为2和12~13时的磷释放率较高,在76%以上,且pH13时的释放率最大,为98.2%;而pH在3~11时,磷释放率较低,在30%以下,且pH6时的释放率最小,为1.7%。表明强酸或强碱环境有利于镧/铝改性沸石中磷的释放。对镧/铝改性沸石再生能力的研究显示,经过4次再生后,镧/铝改性沸石的磷吸附量和再生能力分别为2.367、2.336、2.312、2.253 mg·g-1和96.7%、95.5%、94.5%、92.1%,虽然吸附剂的磷吸附能力随再生次数的增加呈现逐渐降低的趋势,但经过4次再生后,其对磷的吸附能力仍保持在92%以上,表明镧/铝改性沸石具有较好的稳定性和再生能力。     

Giant piezoelectricity on Si for hyperactive MEMS

Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO(3) template layer with superior piezoelectric coefficients (e(31,f) = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.     

Effect of rare earth application on the growth of Trichoderma spp. and several plant pathogenic fungi

Rare earth elements (REEs) enriched fertilisers are currently used in China for soil and foliar applications to crops, but little is known about the effect of REEs applications on the growth of beneficial and detrimental soilborne microorganisms. The growth of biological control agents Trichoderma atroviride strain P1, Trichoderma harzianum strain A6 and strain T22, plant pathogens Botrytis cinerea, Alternaria alternata, Fusarium solani, Rhizoctonia solani and Sclerotinia scleroti…     

Ferromagnetism in LaFeO3-LaCrO3 superlattices

Ferromagnetic spin order has been realized in the LaCrO3-LaFeO3 superlattices. Ferromagnetic coupling between Fe3+ and Cr3+ through oxygen has long been expected on the basis of Anderson, Goodenough, and Kanamori rules. Despite many studies of Fe-O-Cr-based compounds, random positioning of Fe3+ and Cr3+ ions has frustrated the observation of ferromagnetic properties. By creating artificial superlattices of Fe3+ and Cr3+ layer along the [111] direction, ferromagnetic ordering has been achieved.