Formation of hydrogen donors in proton-implanted epitaxial silicon

The formation of shallow hydrogen donors in epitaxial silicon implanted with 300-keV hydrogen ions has been studied at implant doses from 10¹³ to 6 × 10¹⁵ cm⁻², using commercial Mo-Si Schottky diodes with the active base region made of epitaxial phosphorus-doped silicon 5 μ m in thickness (ρ = 1.05 and 1.8 Ω cm). The results demonstrate that, at sufficiently high implant doses (F ∼ 10¹⁵ cm⁻²) and temperatures from 350 to 475 °C, there are at least two types of donors, one of which exhibits bistable behavior due to the negative correlation energy of a singly ionized doubly charged donor. At ∼475°C, the bistable H donor is fully annealed, whereas the concentration of stable donors remains unchanged at temperatures from 350 to 475°C. Under fixed post-implantation heat-treatment conditions (350°, 20 min), it is the implant dose that determines which type of H donor will form: at doses in the range 10¹³ to 10¹⁴ cm ⁻², H donors of the former type are formed, and the maximum in their profile coincides with the projected ion range; implant doses from 10¹⁴ to 10¹⁵ cm⁻² produce H donors of the latter type, and the peak in their profile is located closer to the irradiated surface, in the region of the highest radiation damage.     

New hydrogen donors in germanium

The electrical properties of n-type germanium single crystals irradiated with protons were studied by measuring capacitance-voltage characteristics. The thermal treatment of irradiated samples at 200–300°C leads to the formation of highly mobile shallow donor centers. The coefficient of diffusion of these donors is equal to that of atomic hydrogen with allowance for capture on traps. It is concluded that atomic hydrogen plays the role of a shallow donor in germanium.     

Bistability and response to hydrogen adsorption in nanostructured films based on mixed tin and titanium oxides

It is shown that the strong response to hydrogen adsorption exhibited by the electrical conductivity of thin nanostructured films based on mixed tin and titanium oxides and its rapid relaxation to the initial value in an adsorption-desorption cycle are caused by the “trigger” properties of this system relative to changes in the composition of the gaseous atmosphere. Pis’ma Zh. Tekh. Fiz. 24, 11–16 (March 12, 1998)     

Recent progress in GeSi electro-absorption modulators

Electro-absorption from GeSi heterostructures is receiving growing attention as a high performance optical modulator for short distance optical interconnects. Ge incorporation with Si allows strong modulation mechanism using the Franz–Keldysh effect and the quantum-confined Stark effect from bulk and quantum well structures at telecommunication wavelengths. In this review, we discuss the current state of knowledge and the on-going challenges concerning the development of high performance GeSi electro-absorption modulators. We also provide feasible future prospects concerning this research topic.     

Bistability in radiative heat exchange

The possibility of a bistable regime in systems with radiative heat exchange is theoretically demonstrated for the first time. The transfer characteristics of a radiation-closed stationary system have been calculated, in which the radiator is a blackbody and the absorber is made of a material with the absorptivity sharply increasing in a certain temperature interval. The radiator and absorber are separated by a vacuum gap. The heat exchange between the system and the environment is controlled by varying the flow rate of a heat-transfer agent cooling the absorber. The output parameter of a bistable system is the absorber temperature, while the input parameter can be either the radiator temperature or the heat-transfer agent flow rate. Depending on the choice of the input parameter, the transfer characteristic of the system is either represented by a usual S-like curve or has an inverted shape.     

NdFeB氢爆过程中充氢量的定量控制

在实际NdFeB氢爆的温度和压力范围内,对NdFeB氢爆时的吸氢量进行了理论计算.计算表明Mkg成分为NdxFeyBz(质量分数,%)的NdFeB合金在温度为TK,体积为Vm3的容器内氢爆时,其完全氢爆时的吸氢量为△p=1.06×10-2(x-82y-293z+7274)MT/VPa.氢爆实验过程中的吸氢量与此理论计算结果能很好地符合.因此,NdFeB在氢爆过程中完全可以预先通过理论计算对充入的H2量进行定量控制.     

Ternary alloy nanocatalysts for hydrogen evolution reaction

Cu–Fe–Ni ternary alloys (size ～55–80 nm) with varying compositions viz. CuFeNi (A1), CuFe ₂ Ni (A2) and CuFeNi ₂ (A3) were successfully synthesized using microemulsion. It is to be noted that synthesis of nanocrystalline ternary alloys with precise composition is a big challenge which can be overcome by choosing an appropriate microemulsion system. High electrocatalytic activity towards HER in alkaline medium was achieved by the formation of alloys of metals with low and high binding energies. A high value of current density (228 mA cm ² ) at an overpotential of 545 mV was obtained for CuFeNi (A1), which is significantly high as compared to the previously reported Ni _{5 9} Cu _{4 1} alloy catalyst.     

Surface properties of CaNi5 hydrogen storage alloy

The Ca 2p, Ni 2p and O 1s emissions of the air-exposed sample of CaNi₅ indicate that all the calcium and most of the nickel are present in the oxidized state. Interestingly, it is observed that all the peaks are shifted by 3 to 4 eV towards higher binding energy values. This observation has been attributed to the presence of insulating oxide phases leading to partial charging of the sample during the experiment. Depth profiling by argon-ion sputtering removes the insulating oxide species and the sample etched for 7300 sec shows the presence of metallic nickel and mostly metallic calcium. XPS analysis indicates that preferential segregation of calcium in the CaNi₅ alloy is mainly due to induced surface reaction with oxygen.     

Photorefractive response time of proton-implanted KNbO3:Rb crystal

Abstract

The photorefractive response time of Rb-doped KNbO₃ crystal has been measured after proton-implantation. The experimental results show that there is only one detectable photorefractive grating, with a response time of 434.41 s at erasure light intensity of 65.94μ W cm^?2 and 12.787s at 1 W cm^?2. This phenomenon has been analysed.     

氢燃料电池用镁-钛基合金储氢性能研究

采用高能振动球磨法,制备了Mg₃₅Ti₆₅合金,并添加(10%La_0.4Ce_0.1Pr_0.3Nd_0.2Ni_4Co_0.5Mn_0.3Al_0.2)作为改性剂,制备了储氢合金Mg₃₅Ti₆₅/(10%La_0.4Ce_0.1Pr_0.3Nd_0.2Ni_4Co_0.5Mn_0.3Al_0.2),研究了改性剂的添加及球磨时间对合金显微组织、吸放氢性能的影响规律。结果表明:球磨Mg₃₅Ti₆₅时间为20h时,能获得单一的BCC固溶体相,加入质量分数为10%的改性剂球磨0.5h时能明显地改善其储氢性能,8MPa,573K下100s内吸氢质量能达到3%,随着球磨时间的增加,其相结构发生改变,吸氢量及动力学性能逐渐变差。     

Crack propagation of secondary hardened alloy steels in gaseous hydrogen atmosphere

Abstract

The crack propagation behaviour of secondary hardened alloy steels having various Ni contents and a 18%Ni maraging steel was studied using modified compact tension specimens under 98–784 kPa hydrogen gas pressure p_H2 . The effect of Ni content and retained austenite was examined by comparing oil quenched specimens with those cooled to liquid nitrogen temperature. It was estimated from the effect of p_H2 on the crack propagation rate da/dt that the permeation of hydrogen from the crack tip surface decreased with increasing Ni content in the order 6 or 9, 13, then 18%Ni. It was also estimated that the hydrogen induced embrittlement of grain boundaries decreased with increasing Ni content in the order 6, 9, then 13%Ni and that the embrittlement was greater for the steel containing 18%Ni than for the steel containing 13%Ni. The effect of retained austenite was expected to suppress not the permeation of hydrogen, but the embrittlement of grain boundaries.

MST/757     

Growth and mechanical properties of GeSi bulk crystals

Bulk crystals of Ge_1–xSi _x alloys were grown by the Czochralski technique. Full single crystals were obtained for the alloys of composition 0 < x < 0.15 and 0.9 < x < 1, while single crystal parts near the seeds of ingots provided alloys of intermediate composition. The dislocation velocity and mechanical strength of the GeSi alloys were investigated by the etch pit technique and compressive deformation tests, respectively. In the GeSi alloys of the composition range 0.004 < x < 0.080 the dislocation velocity decreases monotonically with increasing Si content in the temperature range 450–700°C and the stress range 3–24 MPa. In contrast, in the composition range 0.94 < x < 1 the dislocation velocity first increases and then decreases with decreasing Si content in the temperature range 750–850°C and the stress range 3–30 MPa. The velocity of dislocations was determined as functions of stress and temperature. The stress–strain behaviour in the yield region of the GeSi alloys of composition 0 < x < 0.4 is similar to that of Ge at temperatures lower than about 600°C. However, the yield stress becomes temperature-insensitive at high temperatures and increases with increasing Si content. The stress–strain curves of the GeSi alloys of composition 0.94 < x < 1 are similar to those of pure Si at temperatures of 800–1000°C and the yield stress increases with decreasing Si content down to x = 0.94. The yield stress of the GeSi alloys is dependent on the composition, being proportional to x(1 – x). The strengthening mechanism in alloy semiconductors is discussed.     

Pd-Ag alloy dendritic nanowires: fabrication and application in hydrogen sensor

Dendritic Pd-Ag alloy nanowires (Pd-Ag DNWs) with different bimetallic composition have been directly self-assembled on the microelectrodes from mixed solutions of palladium and silver ions by applying an alternating current (AC) field. The size and morphology of the final product were controlled via adjusting the electrodeposition parameters and the metal ion concentration ratio. The influence of three factors on the bimetallic composition in alloy nanowires was examined. Structural characterizations suggest that there was a preferential growth along (200) and (111) directions, leading to the formation of Pd-Ag nanodendritic wires with 150-200 nm in stem and branch diameter. The mechanism of forming the DNWs is discussed. The DNWs were studied as sensing materials for the detection of hydrogen, and they were found to exhibit good sensitivity and reproducibility. The Pd-Ag sensing materials with 22.2 wt% Ag content possessed were also found to display a rapid response time of less than 1 min for 4% (V/V) hydrogen concentration.     

Hot extrusion-induced Mg-Ni-Y alloy with enhanced hydrogen storage kinetics

In this work,the influence of the hot-extrusion method on the hydrogen storage kinetics of Mg-Ni-Y alloy was investigated.It was shown that the extruded Mg91.47Ni6.97Y1.56 alloy exhibits improved hydriding and dehydriding(H/D)kinetics,with a capacity of 3.5 wt.％H2 absorption within 60 s and 5.4 wt.％H2 des-orption within 5 min at 573 K.The dehydrogenation activation energy of extruded alloy is 71.4 kJ mol-1,smaller than that of as-cast alloy(140.5 kJ mol1).The enhancement of H/D kinetics is attributed to the microstructural refinement and increased grain/phase boundaries introduced by hot extrusion,as well as the catalytic effects from the in-situ generated and grain-refined Mg2Ni and YH2 particles during the H/D process.Furthermore,the dehydrogenated rate-determining step transforms from hydrogen diffusion in the hydride(as-cast alloy)to the surface penetration of hydrogen atoms(extruded alloy).These findings provide crucial insights for the design of Mg-based hydrogen storage alloys in the future.