The Sr content influence on the positive magnetoresistance in La1-xSrxMnO3/Si heterojunctions

<正>We fabricated La_(1-x)Sr_xMnO_3/Si(LSMO/Si) heterojunctions with different Sr doping concentrations(x = 0.1, 0.2,0.3) in LSMO and studied the Sr content influence on magnetoresistance(MR) ratio.The hetero junctions show positive MR and high sensitivity of MR ratio in a low applied magnetic field.The MR ratio is dependent on Sr content and the low Sr doping in LSMO causes a large positive MR in LSMO/Si junctions.The MR ratio for 0.1 Sr doping in the LSMO/Si heterostructure is 116%in 100 Oe(1 Oe=79.5775 A/m) at 210 K.The mechanism for the positive MR dependence on the doping density is considered to be the competition between the tunneling rate of electrons in e_g~1↑to t_(2g)↓band and that to e_g~2↑band at the interface region of LSMO.The experimental results are in agreement with those observed in La_(0.9)Sr_(0.1)MnO_3/SrNb_(0.01)Ti_(0.99)O_3 p-n junction.The results indicate that choosing low doping concentration to improve the low field sensitivity of the heterojunction devices is a very efficacious method.     

Tunable luminescent properties by adjusting the Sr/Ba ratio in Sr1.97−xBaxMgSi2O7:Eu0.01, Dy0.02 phosphors

The long afterglow phosphors Sr_1.97−xBa_xMgSi₂O₇:Eu²⁺_0.01, Dy³⁺_0.02 (x=0, 0.4, 0.8, 1.2, 1.6 and 1.97) were synthesized via high temperature solid-state reaction. The phase identification reveals that the crystal plane spacing becomes greater with the decrease in the Sr/Ba ratio. Phase transition occurs when x=1.97. A nonlinear relationship between the emission peak and the crystal plane spacing is obtained with the decrease of the Sr/Ba ratio. This ascribes to the splitting of the 5d level of the Eu²⁺ and the change of the crystal field strength. The duration of the afterglow becomes shorter with the decrease of the Sr/Ba ratio. It may ascribe to deeper trap depth, lower trap concentration and the embarrassment of the transfer of carriers.     

External bremsstrahlung spectra of the Sr source in some lead compounds measured using NaI detector

The spectral distributions of external bremsstrahlung (EB) excited by beta particles from a ⁹⁰Sr/⁹⁰Y source in thick target compounds PbCl₂, PbF₂, Pb(NO₃)₂ and CdO were measured using a 3.8 cm × 3.8 cm NaI(Tl) crystal. The spectra, unfolded using the Liden-Starfelt procedure, showed fairly good agreement with theory (Tseng and Pratt) at low energies and some deviation (less than 15%) at higher energies. The discrepancy between theory and experiment increases with modified atomic number of the target compound and photon energy. The application of the measured/theoretical spectrum to estimate the bremsstrahlung dose is also discussed.     

Eu activated M6AlP5O20 (M=Sr/Ba/Mg) novel red phosphors

Eu³⁺ activated M₆AlP₅O₂₀ (where M=Sr/Ba/Mg) phosphors prepared by combustion synthesis and the completion of the synthesis was confirm by XRD (X-ray diffraction) patterns. The surface morphology studied by scanning electron microscopy (SEM) and photoluminescence (PL) properties has been reported in this paper. The Eu³⁺ PL emission spectrum was observed in M₆AlP₅O₂₀ phosphors (where M=Sr/Ba/Mg) at 592 (orange) and 618 nm (red) region, the spectrum due to ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions at mercury free excitation, respectively. Its considerable emission intensity under 350 nm excitations makes it possible candidate materials as red component of tricolor luminescence materials and for near ultra violet light emitting diode (n-UVLED) phosphors.     

A facile synthesis of heteroatom-doped carbon framework anchored with TiO<Subscript>2</Subscript> nanoparticles for high performance lithium ion battery anodes

Titanium dioxide (TiO₂)-based materials have been well studied because of the high safety and excellent cycling performance when employed as anode materials for lithium ion batteries (LIBs), whereas, the relatively low theoretical capacity (only 335 mAh g^?1) and serious kinetic problems such as poor electrical conductivity (~?10^?13S cm^?1) and low lithium diffusion coefficient (~?10^?9 to 10^?13 cm² s^?1) hinder the development of the TiO₂-based anode materials. To overcome these drawbacks, we present a facile strategy to synthesize N/S dual-doping carbon framework anchored with TiO₂ nanoparticles (NSC@TiO₂) as LIBs anode. Typically, TiO₂ nanoparticles are anchored into the porous graphene-based sheets with N, S dual doping feature, which is produced by carbonization and KOH activation process. The as-obtained NSC@TiO₂ electrode exhibits a high specific capacity of 250 mAh g^?1 with a coulombic efficiency of 99% after 500 cycles at 200 mA g^?1 and excellent rate performance, indicating its promising as anode material for LIBs.     

87Strontium NMR studies

With a Fourier transform NMR spectrometer, especially developed for nuclei with weak signals, the ratio of the Larmorfrequencies of⁸⁷Sr in an aqueous solution of SrCl₂ and⁷³Ge in GeCl₄ has been measured with high accuracy. The concentration dependence of the⁸⁷Sr Larmorfrequency in aqueous solutions of SrCl₂, SrBr₂, Sr(ClO₄)₂, and Sr(NO₃)₂, has been determined. Using this dependence, the ratio of the Larmorfrequencies of the⁸⁷Sr²⁺ ion, for infinite dilution, and⁷³Ge in GeCl₄, isν(⁸⁷Sr²⁺)/ν(⁷³Ge)=1.242 344 6 (15). The magnetic moment of the⁸⁷Sr nucleus, in the Sr²⁺ ion merely surrounded by water molecules, isμ(⁸⁷Sr²⁺)=^?1.089 273 (9)μ _N, without correction for the ionic diamagnetism. Comparing this result with that of an optical pumping experiment, an upper limit for the shielding of the⁸⁷Sr²⁺ ions by the water molecules around the ions, is given.     

Structure of the highly deformed nucleus101Sr63 and evidence for identical K=3/2 bands

The low-energy level scheme of theN=63 nucleus¹⁰¹Sr has been obtained from a β-decay study of¹⁰¹Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ? 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours⁹⁹Sr₆₁ and¹⁰¹Sr₆₃ are very similar. More generally, the identical bands at low spin in^98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region.     

Particle coupling to the octupole state in 89Sr from 88Sr(p,p')88Sr analog resonances and 88Sr(d,p)89Sr

A study has been made of the six most pronounced isobaric analog resonances in the ⁸⁸Sr(p, p')⁸⁸Sr (3^?) excitation function at E_p = 7.65, 7.80, 7.92, 8.78, 9.75, and 9.90 MeV. They are believed to have a simple structure in the parent nucleus ⁸⁹Sr consisting of the lowlying positive-parity, single-neutron spectrum of ⁸⁹Sr weakly coupled to the collective 3^? state in ⁸⁸Sr. A high-resolution ⁸⁸Sr(d, p)⁸⁹Sr experiment was performed to locate small 2f and 3p admixed fragments in ⁸⁹Sr which would allow these analog resonances their entrance widths. In addition, on-resonance ⁸⁸Sr(p, p')⁸⁸Sr (3^?) angular distributions were measured in order to determine the partial waves involved in the exit channel. Results are compared to a particlephonon coupling model, and overall selectivity, strengths, and angular distributions of the (p, p') analog resonances are consistent with the above interpretation.     

3D 1H-13C-14N correlation solid-state NMR spectrum

Nitrogen-14 (spin I = 1) has always been a nucleus difficult to observe in solid-state NMR and until recently its observation was restricted to one-dimensional (1D) spectra. We present here the first 3D ¹H–¹³C–¹⁴N NMR correlation spectrum. This spectrum was acquired on a test sample l-histidine·HCl·H₂O using a recently developed technique, which consists in indirectly observing ¹⁴N nuclei via dipolar recoupling with an HMQC-type experiment.     

In-beam study of 63 143 Eu80

An in-beam γ-ray study with the¹⁴⁴Sm (α, p4n) reaction has established the high-spin states up to 5 MeV excitation and I=35/2 in the N=80 nucleus¹⁴³Eu. The observed yrast states show the typical irregular pattern of a spherical nucleus, with frequent decay branchings and often dominant dipole de-excitation. The level spectrum is in qualitative accord with the coupling of the h_11/2 proton particle to the known yrast levels of the¹⁴²Sm core nucleus. Only in a few cases specific configuration assignments are made.     

Electrical Conductivity Measurement Through the Loaded Q Factor of a Resonant Cavity

We present a method for measuring the electrical conductivity of metallic materials that relies on the ratio of two loaded Q factors, Q_R/Q_X, with Q_R corresponding to a TE₀₁₁-mode reference cavity made of aluminum, and Q_X the Q that results upon replacing the aluminum plate with the one fabricated from the material to be examined. Electrical conductivity is mathematically inferred from the ratio Q_R/Q_X where the loaded Q factors are measured by using the transmission-type method. Within a 3.0 percent accuracy, conductivities determined at 8.7 GHz for electrolytic copper (5.6 times 10⁷ S/m) and brass (1.6 times 10⁷ S/m) show to be in good agreement with those reported in the literature.     

Accuracy and Precision for Measurements of the Mass Ratio 30/28 in Dinitrogen from Air Samples and its Application to the Investigation of N Losses from Soil by Denitrification

Abstract

In the 1950s Hauck introduced a special version of the ¹⁵N dilution technique (¹⁵N flux method) for the determination of N losses from the soil by denitrification. Although this method is very useful and reliable its application has been rather infrequent up to now. This is mainly due to the need to measure the m/z 30 in addition to the usually measured m/z 28 and 29 for dinitrogen, because the ¹⁵N in the enriched air sample taken from an enclosure (cover box) at the soil surface is nonrandom. The signal from the m/z 30 is very low and difficult to measure with sufficient precision because other species (e.g. NO) also having the m/z 30 often interfere with its measurement. In this study the accuracy and precision of an easy to use CF-IRMS with sample batch operation to measure the ratio 30/28 was investigated. The relative standard deviation (RSD = precision) from natural abundance up to 2 at.% was always <1%. After correction of the mass ratio 30/28 (R30), by means of a formula obtained by linear regression of theoretical R30 against measured R30, the accuracy of the abundance calculated from this corrected R30 was very high. From the achieved precision and assuming a cover box height of 10 cm (headspace volume of 7 1), and a collection time of 2 h, a limit of detection for N₂ losses by denitrification equivalent to 16 g N/ha*d or 6 kg N/ha*a can be estimated. The performance of the ¹⁵N dilution method using the equipment and procedure described is demonstrated by means of results from an incubation experiment with [¹⁵N]nitrate-amended soils.     

Synthesis and luminescence properties of red-emitting M2Si5N8:Eu2+-based (M=Ca,Sr, Ba) phosphors by a simple nitrate reduction

M2Si5N8:Eu2+-based(M=Ca,Sr,Ba)red-emitting phosphors are fabricated at relatively low temperature(1200°C)and atmospheric pressure using a simple solid-state reaction process.Several processing parameters are systematically investigated to optimize the phosphors structural characterization and photoluminescence performance,including the amount of europium and the properties of the precursor materials.The as-prepared M2Si5N8:Eu2+-based(M=Ca,Sr,Ba)phosphors are orange in color and are intensively emitted in the red region of 580–670 nm under 465 nm excitation.     

Synthesis and studies of trisubstituted biphthalonitrile/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic hybrid microspheres

New trisubstituted biphthalonitrile/magnetite (TSB/Fe₃O₄) magnetic hybrid microspheres were synthesized from TSB and FeCl₃ · 6H₂O using the method of one-stage thermal temperature crystallization of solvents. The morphology and structure of magnetic hybrid microspheres were inspected using a scanning electron microscope, IR Fourier spectroscopy, and X-ray diffraction. It was found that the grown TSB/Fe₃O₄ magnetic hybrid microspheres represent spherical particles with an average size of ~137 nm and a small size spread. The size and size distribution of magnetic hybrid microspheres can be controlled by a small change in the ratio of TSB and Fe³⁺ ion contents in the microsphere. TSB/Fe₃O₄ hybrid microspheres exhibit a rather high saturation magnetization (58.16 emu g^–1) and new microwave electromagnetic properties, i.e., lower (in comparison with published) dielectric losses at low frequencies; magnetic losses are increased obviously due to an increase in the TSB content. Furthermore, it is detected that magnetic hybrid microspheres absorb microwaves, and strong reflection losses in a wide frequency range are established. The effective reflection loss of–31 dB is obtained in the microwave range from 2 to 16 GHz due to TSB content variations. Wide absorption properties of microwaves along with regular spherical shape and excellent magnetic properties offer wide opportunities for various applications of TSB/Fe₃O₄ magnetic hybrid microspheres as functional materials.     

微波等离子体化学汽相沉积法沉积CNx膜的研究

对用微波等离子体化学汽相沉积法沉积在Si基片上的CN_x膜分别进行Raman散射、X射线光电子能谱、X射线衍射和扫描电子显微镜等技术的分析与测试. Raman散射的研究结果表明在CH₄与N₂的流量比低于1∶8时，CN_x膜的散射谱中以非晶石墨峰的形式出现.当流量比为1∶8时，则表现为较尖锐的C≡N键(2190cm^-1)的特征峰；从X射线光电子能谱的分析结果可以看出C，N成键的方式主要是C≡N键和C—N 关键词：     

Single-phased silicate-hosted phosphor with 660 nm-featured band emission for biological light-emitting diodes

A single-phased (Ba,Sr)₃MgSi₂O₈:Eu²⁺, Mn²⁺ phosphor with 660 nm-featured dual band-emission is investigated upon optimizing composition to simulate the artificial photosynthetic action spectrum (PAS) for near-ultraviolet (NUV) biological light-emitting diodes (bio-LEDs). A specific composition range in Ba–Sr binary solid solution of (Ba,Sr)₃MgSi₂O₈ is found to be capable of obtaining single-phased host in the absence of an easily formed orthosilicate impurity, leading to a 660 nm-featured red band emission of Mn²⁺ induced by an efficient energy transfer from a co-doped blue-emitting Eu²⁺ sensitizer. This dual broad band emission phosphor has a 72 nm full width at half maximum (FWHM) for red band that covers fairly well to the absorption spectrum of chlorophyll and PAS for most plants, enabling a flexible option in the application of bio-illumination for artificial photosynthesis.     

The structure of83Sr excited states

The -decay of⁸³Y isomers (7.06 min and 2.85 min) have been studied by means of Ge (Li) detectors. The proposed level scheme of the⁸³Sr nucleus is based on the coincidence measurement and the analysis of energy sums. The intensity balance requirement leads to _T (35·5 keV)=3.2 which is consistent with M1 multipolarity of this transition. A probable structure of some of the excited states in the⁸³Sr nucleus is discussed in the framework of Alaga's model and Kuriyama's model.     

Analysis of n(87Sr)/n(86Sr), δ88Sr/86SrSRM987 and elemental pattern to characterise groundwater and recharge of saline ponds in a clastic aquifer in East Austria

Elemental and isotopic pattern of n(⁸⁷Sr)/n(⁸⁶Sr) and δ⁸⁸Sr/⁸⁶Sr_SRM987 were used to characterise groundwater and recharge of saline ponds in a clastic aquifer in East Austria. Therefore, shallow, artesian and thermal groundwaters of the investigated aquifer along with rainfall and rivers were analysed using (MC) ICP-MS. The n(⁸⁷Sr)/n(⁸⁶Sr) ratio and elemental pattern changed with aquifer depth as a result of progressing bedrock leaching and dissolution with increasing groundwater residence time. The n(⁸⁷Sr)/n(⁸⁶Sr) ratio of shallow groundwater below saline ponds of 0.71019?±?0.00044 was significantly different from thermal groundwater of 0.71205?±?0.00035 (U, k?=?2). In contrast to previous theories, this result suggested no recharge of saline ponds by upwelling paleo-seawater. Isotope pattern deconvolution revealed that rainfall accounted to about 60% of the n(⁸⁷Sr)/n(⁸⁶Sr) ratio of shallow groundwater below saline ponds. The δ⁸⁸Sr/⁸⁶Sr_SRM987 values of groundwater decreased from about 0.25 ‰ in most shallow, to predominantly negative values of about –0.24 ‰ in artesian groundwater. This result indicated leaching and dissolution of weathered minerals. In turn, the δ⁸⁸Sr/⁸⁶Sr_SRM987 of deep thermal groundwater showed positive values of about 0.12 ‰, which suggested removal of ⁸⁶Sr from solution by carbonate precipitation. These results highlight the potential of δ⁸⁸Sr/⁸⁶Sr_SRM987 signature as an additional geochemical tracer.     

Fully quantitative description of hybrid TiO2 nanoparticles by means of solid state 31P NMR

For the first time, an absolute quantification of hybrid materials obtained from the reaction of phenylphosphonic acid (PPA) with TiO₂ nanoparticles under different reaction conditions is reported. Next to the amount of PPA involved in grafting to the TiO₂ nanoparticles, also the PPA included in titaniumphenylphosphonate crystallites is described quantitatively. The quantitative analysis is based on solid state ³¹P MAS NMR and is further applied to evaluate the stability of the resulting hybrid materials towards hydrolysis and organic solvent exposure.