μ+ shift study inCdMgx (x=1%, 2%, 2.5%)shift study inCdMgx (x=1%, 2%, 2.5%)

In continuation of our earlier studies of the anomalous temperature dependence of the μ⁺ Knight shift K_μ in Cd,CdHg (1.2 at %) andCdMg (3.38 at %) — interpreted as due to Van Hove-type singularities in the local density of electron states /1/ — we have studied the temperature dependence of the μ⁺ Knight shift in polycrystallineCdMg (1.04 at %, 2.05 at %) and in a single crystal ofCdMg (2.5 at %). In contrast to pure Cd no anisotropies in K_μ could be detected. The temperature dependence of K_μ in aCdMg (2.05 at %) sample and in the monocrystallineCdMg (2.5 at %) sample essentially reproduces the one previously observed in polycrystallineCdMg (3.38 at %), showing a steplike discontinuity and a logarithmic singularity. A complete different behaviour is observed inCdMg (1.04 at %), where no logarithmic singularity seems to show up and where a steplike discontinuity of opposite sign at around 90 K is clearly seen. If these singularities are still to be interpreted in terms of Van Hove singularities, the question arises why there is such a nonlinear dependence on the Mg concentration.     

A 3% efficiency N2 laser

A 3% efficiency, crossed-field type, N₂ laser (337.1 nm) has been developed, based on very low inductance circuits (coaxial configuration) and a careful selection of their resonance frequencies.     

10% Yb3+-Lu2O3 ceramic laser with 74% efficiency

We demonstrate laser oscillation at 1080 nm with more than 16 W of output power and with an optical-to-optical slope efficiency of up to 74% using a 10% Yb3+ doped Lu2O3 ceramic made by hot pressing. This represents the highest output power and efficiency obtained for a Yb3+ doped Lu2O3 ceramic and demonstrates the feasibility for power scaling.     

151Eu mössbauer studies in Eu(Cu1−x Au x )2Si2 (x=10%, 15%, 20%)

¹⁵¹Eu-Mössbauer investigations have been made on Eu(Cu_1–xAu_x)₂Si₂ (x=0, 0.1, 0.15, 0.20) as a function of temperature. Intr⤩uction of gold in the matrix not only pr⤩uces significant variations in the isomer shift but also leads to a slowing down of valence fluctuations.     

CuGaSe2 solar cells with 9.7% power conversion efficiency

Heterojunctions, such as ZnO/CdS/CuGaSe₂, were fabricated for photovoltaic applications. Optimization of device structures based on monocrystalline CuGaSe₂ led to the highest-to-date power conversion efficiencies for CuGaSe₂ solar cells. At room temperature under 100 mW/cm² AM1.5 illumination a maximum cell efficiency of 9.7% was achieved, given by an open-circuit voltage of 946 mV, a short circuit current density of 15.5 mA/cm², and a fill factor of 66.5%. Preparation and performance of the optimum device are described. Current voltage characteristics dependent on illumination intensity and temperature, spectral response and electron-beam-induced current measurements were performed to determine the device parameters as well as to analyse the current transport and loss mechanisms. Tunneling, assisted by defect levels in the CdS layer, seems to play a major role. High injection effects are observed at forward bias ofV > 0.5 V or an illumination level ofP > 10 mW/cm². Under such conditions, as well as at low temperatures, the non-zero series resistance comes into play. Effects of the shunt resistance, however, are negligible in all cases.     

Distribution of magnetic moment in an alloy of nickel and 2% titanium

The magnetic form factor of nickel alloyed with 2% of titanium has been measured at room temperature for the first 32 Bragg reflections, using polarized neutrons. The spin density map obtained by Fourier inversion showed significant qualitative differences from that of pure nickel. A least squares fit of the results was used to determine the distribution of the magnetic electrons in the t_2g orbitals, and the moments associated with the nickel and the titanium atoms.     

Frequency dependent conductivity in As2Se3 and As2Se3 + 15% Sb

Dc and ac measurements were performed on bulk samples of undoped and 15% Sb doped As₂Se₃ as a function of temperature (90–400 K) and frequency (10³–10⁶ Hz). The dc results show an activated conductivity dependence on temperature with an activation energy of 0.8 eV above room temperature. The ac results give a temperature dependent frequency exponent s. The temperature dependence of G _ac is discussed in terms of the mechanisms involved. Results are compared with the predictions of the Quantum Mechanical Tunnelling and Correlated Barrier Hopping models. It is found that doping increases the dc conductivity but has no effect on the ac conductivity.     

Phase composition and low-frequency internal friction of ZrO2 + 4 mol % Y2O3 ceramics

Low-frequency internal friction was studied at a torsional-vibration frequency of 24 Hz in polycrystalline samples of ZrO₂ + 4 mol % Y₂O₃ ceramics. The samples were prepared using cold isostatic pressing of a powder followed by sintering in air, hot isostatic pressing of the sample in an argon atmosphere, subsequent mechanical deformation of the surface, and further calcination in air. The x-ray phase analysis method is used to study the variation in the phase composition after mechanical deformation of the sample surface followed by calcination in air. The internal friction was measured in the temperature range 280–380 K on a sample subjected to calcination in air. At 315 K, an internal-friction peak was revealed, which is explained by stress relaxation at the boundaries of the T’-phase domains.     

Hyperfine interactions in ZrO2–5 wt.% Al2O3 ceramics

Two powder samples of ZrO₂-5 wt.% Al₂O₃ derived from precursor solutions of different pH – 2 for sample (C) and 4 for sample (D) – were prepared by the precipitation method. They were studied using PAC between RT and 1150oC and XRD after heating at increasing temperatures. According to XRD, the addition of Al₂O₃ causes the complete stabilization of tetragonal zirconia in both samples. At a nanoscopic level, however, they present different interactions and thermal evolutions. Sample (C) exhibits predominantly the t₁- and dynamic t₂-forms already reported for pure and yttria-doped stabilized tetragonal zirconias. On the other hand, sample (D) exhibits a novel nanoconfiguration depicted by a totally asymmetric and dynamic EFG whose population achieves 86% at 1150oC and which has been associated to aluminium solubility in zirconia. Upon cooling gradually to RT from the highest temperature, (C) transforms completely to m-ZrO₂ and (D) remains 65% in the metastable tetragonal phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diffuse scattering of polarized neutrons from a Ni 2% Ti alloy

The diffuse scattering of long wavelength polarized neutrons from a polycrystalline alloy of nickel containing 2% of titanium has been measured at 2, 70 K and at room temperature. The results show that the moment on the titanium atom is nearly zero and the magnetic effects around an impurity are limited to the second nearest neighbours at 2 K. The disturbance is more widespread at higher temperatures.     

A1 and A2 transitions in superfluid 3He in 98% porosity aerogel

Superfluid 3He in high porosity aerogel is the system in which the effects of static impurities on a p-wave superfluid can be investigated in a systematic manner. We performed shear acoustic impedance measurements on this system (98% porosity aerogel) in the presence of magnetic fields up to 15 T at the sample pressures of 28.4 and 33.5 bars. We observed the splitting of the superfluid transition into two transitions in high fields in both bulk and liquid in aerogel. The field dependence of the splitting in aerogel resembles that of the bulk superfluid 3He caused by the presence and growth of the A1 phase. Our results provide the first evidence of the A1 phase in superfluid (3)He/aerogel.     

Femtosecond pulsed laser damage characteristics of 7% Y2O3-ZrO2 thermal barrier coating

Ablation characteristics of 7% yttria stabilized zirconia thermal barrier coating, deposited by the electron beam physical vapor deposition method, was studied using a femtosecond pulsed laser. The single-pulse damage threshold fluence for the coating was determined to be 1.64 J cm^-2. The threshold fluence was not appreciably dependent on the initial roughness of the coating surface. An incubation effect, i.e., a decrease in the damage threshold fluence with an increase in number of pulses incident at a given location, was observed for this coating. Based on the damage morphology generated by single and multi-pulse interactions, a mechanism for the incubation effect was proposed. PACS 70.20.Ds; 42.62.Cf; 52.38.Mf; 42.62.Cf; 42.55.Px     

Highly efficient CW laser operation in 4 at. % Tm~(3+) and 4 at. % Y~(3+) codoped CaF_2 crystals

Tm:CaF_2 and Tm;Y:CaF_2 single crystals were prepared by the temperature gradient technique. The spectral properties of Tm;Y:CaF_2 single crystals were investigated and compared with those of Tm:CaF_2. It was demonstrated that codoping with Y~(3+) ions could efficiently improve the spectroscopic properties. Tm;Y:CaF_2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections, and much longer fluorescence lifetimes of the upper laser level(Tm~(3+):~3H_4 level) than Tm:CaF_2 crystals. Continuous-wave(CW) lasers around 1.97 μm were demonstrated in 4.0 at. % Tm,4.0 at. % Y:CaF_2 single crystals under 792 nm laser diode(LD) pumping. The best laser performance has been demonstrated with a low threshold of 0.368 W, a high slope efficiency of 54.8%, and a maximum output power of 1.013 W.     

Characterization and comparison of 1% at Yb-doped Lu2O3 and Sc2O3 ceramics as laser gain media

We present the first laser oscillation achieved on Yb-doped Sc₂O₃ and Lu₂O₃ ceramics with a level of doping as low as 1 at %, under quasi-continuous wave pumping at 968 nm. Ceramic samples reached comparable performances in terms of tunability ranges, which exceeds 41 nm, and laser output powers. In particular, with the former sample emitting at 1040.5 nm we measured a maximum output power of 2.2 W with a corresponding slope efficiency of ?? = 59%. The latter medium delivered 1.8 W with a slope of ?? = 45% at 1032.5 nm while at 1078 nm we measured 1.5 W with ?? = 34%. Finally, we report the measured level of the Amplified Spontaneous Emission (ASE) for both samples, which was found to be less than 0.1 mW at the maximum pump power.     

Direct measurement of oxygen extraction with fMRI using 6% CO2 inhalation

The blood-oxygenation-level-dependent (BOLD) signal is an indirect hemodynamic signal that is sensitive to cerebral blood flow (CBF), cerebral blood volume (CBV) and cerebral metabolic rate of oxygen. Therefore, the BOLD signal amplitude and dynamics cannot be interpreted unambiguously without additional physiological measurements, and thus, there remains a need for a functional magnetic resonance imaging (fMRI) signal, which is more closely related to the underlying neuronal activity. In this study, we measured CBF with continuous arterial spin labeling, CBV with an exogenous contrast agent and BOLD combined with intracortical electrophysiological recording in the primary visual cortex of the anesthetized monkey. During inhalation of 6% CO2, it was observed that CBF and CBV are not further increased by a visual stimulus, although baseline CBF for 6% CO2 is below the maximal value of CBF. In contrast, the electrophysiological response to the stimulation was found to be preserved during hypercapnia. As a consequence, the simultaneously measured BOLD signal responds negatively to a visual stimulation for 6% CO2 inhalation in the same voxels responding positively during normocapnia. These observations suggest that the fMRI response to a sensory stimulus for 6% CO2 inhalation occurs in the absence of a hemodynamic response, and it therefore directly reflects oxygen extraction into the tissue.     

941nm2%占空比大功率半导体激光器线阵列

计算了半导体激光器的激射波长与量子阱宽度以及有源层中In组分的关系,确定了941nm波长的量子阱宽度和In组分.并利用金属有机化合物气相淀积(MOCVD)技术生长了InGaAs/GaAs/AlGaAs分别限制应变单量子阱激光器材料.利用该材料制成半导体激光器线阵列的峰值波长为940.5 nm,光谱的FWHM为2.6 nm,在400 μs,50 Hz的输入电流下,输出峰值功率达到114.7 W(165 A),斜率效率高达0.81 W/A,阈值电流密度为103.7 A/cm2;串联电阻5 mΩ,最高转换效率可达36.9%.