Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
梁建
,
王晓宁
,
张华
,
刘海瑞
,
王晓斌
,
许并社
人工晶体学报
本文以氧化镓、氧化锌和氨气为原料,通过常压化学气相沉积法(APCVD)在Au/Si( 100)衬底上成功生长出了Zn掺杂的”Z”形GaN纳米线.利用场发射扫描电镜(FESEM)、X-射线衍射仪(XRD)、透射电子显微镜(TEM)、光致发光谱(PL)等测试方法对样品的形貌、晶体结构及光学性质进行了表征.结果表明:在温度为950℃,氧化镓和氧化锌的质量比为8∶1的条件下,制备出的Zn掺杂Z形GaN单晶纳米线直径为70 nm、长度为数十个微米,生长机理遵循VLS机制.Zn元素的掺杂使GaN纳米线在420nm处出现了光致发光峰,发光性能有所改善.
关键词:
氮化镓
,
纳米线
,
Zn掺杂
,
化学气相沉积
,
发光性能
Journal of Superconductivity and Novel Magnetism
The local structure and the g factors (g(x), g(y), and g(z)) of the Cu(2+) site in Y(2)BaCuO(5) are theoretically studied using the perturbation formulas of the g factors for a 3d(9) ion in orthorhombically elongated octahedra. The orthorhombic field parameters in these formulas are determined from the superposition model and the local geometry of the system. From the calculations, the oxygen octahedron is found to undergo the local elongation Delta Z (approximate to 0.05 angstrom) along c-axis and the relative bond length variation Delta X (approximate to 0.1 angstrom) along a- and b-axes, respectively. The calculated g factors based on the above local structure are in good agreement with the experimental data. The relationships between the anisotropies of the g factors and the low symmetrical (orthorhombic) distortions of the Cu(2+) site in Y(2)BaCuO(5) are discussed.
关键词:
Crystal fields and spin Hamiltonians;Electron paramagnetic resonance;Cu(2+);Y(2)BaCuO(5);crystal
International Journal of Modern Physics B
The perturbation formulae of EPR parameters g factors g(x), g(y) and g(z) for the lowest Kramers doublet of 4f(1) ion in orthorhombic symmetry are established. In these formulae, the contributions of the covalency effects, the admixture between J = 7/2 and J = 5/2 states as well as the second-order perturbation (which is not considered in the previous works) via crystal-field and orbital angular momentum interactions are all included. According to these formulae, and by using the superposition model, the g-factors g., g(y) and g(z) for Ce3+ center in YBa2CU3O6+x superconductor are calculated. The results are discussed.
关键词:
YBa2Cu3O6+x;EPR;superposition model;Ce3+;crystal-field
Journal of Physics-Condensed Matter
The assignment of the 1.193 eV zero-phonon line of the 3d(2) ion in GaN crystal to the internal luminescence of Cr4+ on the Ga3+ site is analysed. Based on this assignment, the g-shift Ag (=g - g(s)) of the groundstate of this luminescence is calculated by considering not only the conventional contribution due to the crystal-field mechanism, but also the contribution due to charge-transfer mechanism. The calculated result shows good agreement with the observed value, suggesting that the assignment is reasonable. The calculated Ag due to the charge-transfer mechanism is opposite in sign and 62% in magnitude, compared with that due to the crystal-field mechanism, and so it cannot be neglected. It appears that for the 3d(2) (or 3d(n)) ion with a high valence state in crystals (particularly, in the case of the ligand having small optical electronegativity), the reasonable explanation of the g-shift should consider the contributions from both the crystal-field and charge-transfer mechanisms.
关键词:
transition-metal impurities;paramagnetic-resonance;epitaxial layers;identification;luminescence;nitride;defects;gaas
Z.M. Zhang
,
*
,
C.J. Xu
,
J.C. Wang
金属学报(英文版)
Ultrafine-grained pure aluminum L2 with a mean grain size of 1.0μm was produced by equal channel angular pressing (ECAP) and annealing at 150℃ for 2h. Damping behavior of the alloy was measured using a dynamic mechanical thermal analyzer. The alloy had an excellent damping capacity Q-1 with the ambient value being 9.8×l0-3 at 1.0Hz when the strain amplitude was 2.0×l0-5. The damping behavior of the alloy showed a non-linear damping variation tendency, that is, with an increase in temperature and a decrease of frequency, the damping capacity of the alloy increased. The damping capacity increased with the strain amplitude when the strain amplitude was less than 4.6×l0-5. When the strain amplitude was higher than 4.6×10-5, the damping capacity became a constant and independent of strain amplitude. The high damping capacity was attributed to dislocation unpinning and a drag of dislocation on pinning points.
关键词:
ECAP
,
超细晶
,
阻尼
,
铝合金
Optical Materials
The perturbation formulas of the EPR g factors g,, g and g. for a 4f(11) 1 ion in orthorhombic symmetry are established. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various states are taken into account. The above formulas are applied to the orthorhombic Er3+ centers in YAG, YGG and LuGG garnets. By analyzing their g factors, we find that the polar angles theta(j)(') of the impurity-ligand bonds related to the Z axis of the crystals in these Er3+ centers are smaller than the host angles theta(j) in pure crystals, whereas the azimuthal angles, related to the X axis in the impurity centers are larger than the corresponding phi(j) in the hosts. The g factors and their anisotropies Delta g [= g(z) - (g(x) + g(y))/2] and delta g (= g(x) - g(y)) for Er3+ in the garnets based on the above local structural parameters are in good agreement with the observed values. In addition, the angular distortions Delta theta (= theta(j)(') - theta(j)) or Delta phi (= phi(j)(') - phi(j)) obtained by analyzing the EPR data in this work are different from Delta theta(2), or Delta phi(2) (for only the second set of ligands, i.e., j = 2) based on the superposition model crystal-field analysis in the previous work. The validity of the results is discussed. (c) 2004 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance (EPR);defect structure;crystal-field;and spin hamiltonians;Er3+;garnets
