Hyperfine Fields of 181Ta in UFe4Al8

The γ–γ Perturbed Angular Correlation technique was used to study the hyperfine interaction of ¹⁸¹Ta at the Hf site(s) in UFe₄Al₈ at room temperature and 12 K. The data at room temperature are well described by two electric field gradients, while at low temperature two combined hyperfine interactions have to be considered, one with the magnetic hyperfine field collinear with the c-axis and another with the magnetic hyperfine field in the basal plane. The results are compared with previous Mössbauer and neutron diffraction experiments and the lattice site of Hf is discussed.

     

强流电子束加载下Ta,Al,Cu的温度测量

利用六波长瞬态光学高温计测量了"神龙一号"加速器发射的高能电子束与靶材作用后靶受作用区的温度变化过程。获得了厚度为0.1~0.25mm的Ta,Al和Cu片靶与强流电子束作用后的温度变化过程,最高温度接近9000K,达到了温密物质区域。实验结果表明,利用"神龙一号"加速器发射的强流电子束与特定靶材作用可以获得可供观测的温密物质,而多波长瞬态光学高温计是测量这种温密物质的温度变化的有效手段。     

强流电子束加载下Ta，Al，Cu的温度测量

利用六波长瞬态光学高温计测量了神龙一号加速器发射的高能电子束与靶材作用后靶受作用区的温度变化过程。获得了厚度为0.1~0.25 mm的Ta,Al和Cu片靶与强流电子束作用后的温度变化过程,最高温度接近9000 K,达到了温密物质区域。实验结果表明,利用神龙一号加速器发射的强流电子束与特定靶材作用可以获得可供观测的温密物质,而多波长瞬态光学高温计是测量这种温密物质的温度变化的有效手段。     

An els study of the oxidation of polycrystalline Ta and Nb at room temperature

ELS has been used to characterize the initial steps in the oxidation of polycrystalline Ta and Nb in an oxygen atmosphere at low pressures (~1.3 × 10^?6 Pa) and room temperature. The results are interpreted in terms of transitions to unoccupied states above E_F and plasmon losses, and are discussed in the light of previous studies. The results show important changes in the valence band. The O 2s and O 2p bands increase in intensity during oxidation.     

各向同性多晶Al、Cu、Ta的超声物态方程

 利用“超声脉冲重合法”测量了多晶Al、Cu、Ta的弹性模量及其压力的偏导数。由Birch-Murnaghan物态方程得到的三种金属的等温线与冲击波等温线作了比较。     

通过Ta，Al的添加改进纳米晶FeXN薄膜的结构和磁性

在本次工作中，制备了纳米晶FeAlN和FeTaN薄膜。虽然两种膜都展示了软磁性，但是观察到了不同的单轴各向异性。微结构的测量揭示了Ta的添加导致了N的更高溶解度，并且导致了更大的晶格膨胀和更大的压缩应力。单轴各向异性来源于N原子在a－Fe点阵中的各向异性分布。Al更容易与N发生反应，所以FeAlN膜中的a－Fe比FeTaN中的要纯，并且其应力是张应力。两种薄膜不同的各向异性可以由它们不同的微结构来解释。     

Hf3Al2 and Zr3Al2 Isostructural Aluminides Studied by PAC with 181Ta and 111Cd Probes

The electric quadrupole hyperfine interactions for ¹⁸¹Hf/¹⁸¹Ta and for ¹¹¹In/¹¹¹Cd probes in polycrystalline Zr₃Al₂ and Hf₃Al₂ compounds were measured in the temperature range 24–1100 K. The hyperfine quadrupole interaction parameters were determined after different doping techniques and heat treatments of the samples.¹⁸¹Hf/¹⁸¹Ta was found to substitute the Hf/Zr sites and the ¹¹¹In/¹¹¹Cd impurities appear to substitute both the 8(j) Al sites and the three nonequivalent Hf/Zr sites.     

Al、Cu、Ta高压熔化曲线的理论计算

由位错熔化理论和不同的静高压实验数据优化的体模量(B0)、剪切模量(G0)及它们对压力的一阶偏导数(B′0、G′0)值计算了Al、Cu、Ta的高压熔化曲线.理论计算的Al、Cu高压熔化曲线与静、动高压实验值较为吻合,Ta的理论高压熔化曲线与动高压实验结果一致,但与静高压实验结果相差较大.     

Enhanced rate of carbon deposition during fischer-tropsch synthesis on K promoted Fe

The synthesis of hydrocarbons from CO and H₂ at 1 bar pressure was measured on a Fe foil which was previously covered with a monolayer of K₂CO₃. The surface composition of the K promoted Fe was monitored repetitively by interrupting the reaction and transfering the sample into the UHV chamber for X-ray photo-emission spectroscopy. The results show that K causes a decrease in the rate of methane formation, an increase, in the rate of carbon deposition, and a shift in selectivity towards the formation of longer chain molecules. The XPS measurements on the K 2p levels show furthermore that the K compound is apparently not being covered by the deposited carbon but rather sitting on top of the carbon layer.     

Positron decays of 25Al, 37K, 38K and 39Ca

Allowed β⁺ decay branches from ²⁵AI, ³⁷K, ³⁸K and ³⁹Ca have been sought by observation of delayed γ-radiation. The precision of previously known branches has been increased and improved limits obtained for unobserved branches.     

SIMS investigation of the Si(111) oxidation promoted by potassium overlayers

The removal of the potassium is a critical issue in the Si oxidation promoted by potassium overlayers. The effects of the morphology of the potassium and SiO₂ overlayers on the potassium desorption process have been investigated using a very sensitive technique: SIMS. For a uniform potassium overlayer (monolayer, simultaneous oxygen/potassium adsorption or multilayers exposed to low O₂ pressure) there is no evidence of a significant amount of potassium left after its desorption. However, under specific conditions: potassium multilayers exposed to high O₂ pressure (in which SiO₂ islands were observed using SEM), there is a significant amount of potassium left under the surface after the desorption attempt. These effects of the overlayer morphologies allow us to explain some reported contradictory results.     

On-line separation of163Ta and162Ta

A new 12s activity has been produced via the³⁵C1+¹¹²Sn reaction at 191 MeV and ascribed to the¹⁴³Tb EC/β⁺ decay. A decay scheme is derived from γ-γ and γ-X-ray coincidence measurements.     

Mechanisms of K Mixing: the Role of Octupole Vibrations in 180Ta

K-mixing mechanisms are reviewed, with reference to isomers in the A≈180 region of well deformed nuclei. The strong E1 photoactivation of ¹⁸⁰Ta ^m , through states at 1.1, 1.3 and 1.5 MeV, provides evidence for the role of octupole vibrations in the conversion of the K = 9 isomer to the K = 1 ground state. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrostatic field enhancement of Al(111) oxidation

We show that the electrostatic charging of an aluminum oxide film by electron-bombardment produces a greatly enhanced rate of Al(111) oxidation by O2(g) at 90 K, compared to a film which has not been bombarded by electrons. This novel memory effect for prior electron irradiation is caused by the negative electrostatic potential created and stored on the outer oxide film surface as a result of electron bombardment. The high electrostatic field ( approximately 10(7) V/cm) produced across the depth of the film is postulated to cause an enhancement of ion migration through the film, leading to rapid oxide film growth, as predicted by the Cabrera-Mott theory of low temperature metal oxidation.     

Dielectric response of K(Ta,Nb)O3 thin films

The dielectric response of K(Nb,Ta)O₃ films grown on (001) MgAl₂O₄ (100) by pulsed laser deposition from a mosaic target of KTa_0.63Nb_0.37O₃ and KNO₃ has been examined. In particular, the effects of growth temperature (650–800 °C), growth pressure (1–100 mTorr O₂), and annealing conditions on the tunability, dielectric constant, and dielectric losses in interdigitated capacitor device structures fabricated with these films are described. Annealing treatments lead to a reduction in the loss tangents for most of the films considered. Figure of merit calculations indicate that the best dielectric response (tunability=37%, tan =0.022) is achieved for films grown at 750 °C in an oxygen pressure of 100 mTorr and then annealing at 1000 °C for 2 h in air.     

NMR-on of182Ta and183Ta in Fe

Nuclear magnetic resonance has been observed on radioactive¹⁸²Ta and¹⁸³Ta oriented at low temperature in an Fe host, by detection of the change in spatial anisotropy of γ-rays emitted during nuclear decay. By measuring the resonant frequencies of¹⁸³Ta in four different applied magnetic fields the nuclear magnetic moment and hyperfine field have been deduced. These are: $$|\mu \left( {{}^{183}Ta; I = \tfrac{\user2{7}}{\user2{2}}} \right)| = 2.28(3)\mu _{\rm N} and B_{hf} \left( {Ta\underline {Fe} at 0 K} \right) = - 67.2(1.3)T$$ . The spin of the ground state of¹⁸²Ta has been determined asI=3 by comparing resonance results with those obtained in a thermal equilibrium nuclear orientation study. The ratio of the resonant frequencies observed for¹⁸²Ta and¹⁸³Ta at one applied field value yields a magnetic moment for the former of $$|\mu \left( {{}^{182}Ta; I = \user2{3}} \right)| = 2.91(3)\mu _{\rm N} $$ . The spin lattice relaxation time for¹⁸³TaFe (0.12 at% Ta) at 18 mK in an applied field of 0.5 T has been found to be 40(10) s.     

Matrix of rectangular pores obtained by AFM nanoindentation and electrolytic oxidation of Al

AFM nanoindentation is used for pretexturing of Al sample intended for anodic oxidation in porous film-forming electrolytes. The rectangular quadratic and non-quadratic matrices of nanoindents were made by means of an AFM with diamond tip. The period of the 2D array of nanoindented concaves ranged from ∼50 to ∼370 nm. The pitch of the holes ranged from 13 to 170 nm. After anodization in water solutions of three different acids (0.3 M sulfuric, 0.3 M oxalic and 0.3 M phosphoric) at voltages chosen according to matrix period (20, 30 and 160 V), the well-arranged matrices of rectangular pores were obtained. The rectangular symmetry of the pretextured Al surface almost ideally transferred on porous alumina matrix, maintaining the highly ordered arrangement of the pores and rectangular cross section trough the whole film thickness with high pore depth to aperture size aspect ratio. During prolonged anodization in phosphoric acid, standard cells on the boundary of nanoindented area disturbed the arrangement and shape of quadratic cells.