Yiyong Wu

Influence of boric acid on the electrodepositing process and structures of Ni-W alloy coating

Abstract Effects of boric acid introduced into an ammonia-citric plating bath were studied both on the plating process and on the deposit characteristics. It was found that boric acid increased not only current efficiency but also tungsten content of the deposits, implying that boric acid may act as a surfactant to impede the proton reduction and also form some complex with tungstate to be beneficial for tungsten co-deposition. The deposit hardness increased firstly with increasing tungsten content but then decreased as tungsten content was beyond 42 wt.%. The reasons lie mainly in both the Hall–Petch and the reverse Hall–Petch effects rather than solid–solution strengthening when the grain (or domain) size of the Ni–W alloy was in the nanometer scale.

Effects of 2-butyne-1,4-diol on structures and morphologies of electroplating Ni–W alloy

Abstract Effects of brightener 2-butyne-1,4-diol on plating process and structures of Ni–W electro-deposit were investigated by means of cyclic voltammetric measurement, SEM and atomic force microscopy (AFM). A full-bright and smooth Ni–W alloy can be electrodeposited as 2-butyne-1,4-diol is added in the plating bath, but 2-butyne-1,4-diol decreases W content gradually in the deposit and current efficiency rapidly with its concentration. 2-Butyne-1,4-diol in the solution is in favor of hydrogen evolution reaction to decrease current efficiency. Bright Ni–W deposit has much lower root mean square (RMS) surface roughness than corresponding dim one and the RMS difference reduces with W content of the deposit. However, when measured area is 0.1×0.1 μm 2 , RMS roughness of bright Ni–W alloy is higher than that of corresponding dim one. It may result from the more micro-defects in the bright deposit. Grain size of bright deposit is much smaller than corresponding dim one and the grain size difference decreases with increasing W content in the deposit. When W content is more than 42 wt.% (near to the eutectic point in Ni–W equilibrium diagraph), one could not observe grain with AFM.

Pyrolytic carbon free-radical evolution and irradiation damage of polyimide under low-energy proton irradiation

Ionization and displacement effects are basic phenomena in damage processes of materials under space-particle irradiation. In this paper, the damage behaviors were investigated on the polyimide under proton irradiation using electron paramagnetic resonance (EPR) spectra analysis and optical absorbance valuation. The results indicate that the proton irradiation induces the formation of pyrolytic carbon free-radical with a g value of 2.0025, and the population of free radicals increases with the irradiation fluence. The most important finding is that the irradiation-induced free-radical population increases linearly with the displacement damage dose, as does the optical degradation, whereas the ionization effect alone, during the irradiation, cannot induce the formation of pyrolytic carbon free radical. Furthermore, during the post storage, after irradiation, the free-radical population decreases following a sum of an exponential and a linear mode with the storage time. It is interesting that, during the po...

Study on evolution of deep charge traps in polyimide irradiated by low-energy protons using photo-stimulated discharge technique

In this paper, low-energy proton irradiation effects on the evolution of deep charge traps in proton pre-irradiated polyimide are investigated using the photo-stimulated discharge (PSD) technique. The results indicate that in the PSD spectrum there appear three discharge bands with some sub-peaks in the wavelength range from 250 to 300 nm, 300 to 325 nm and 325 to 350 nm, respectively. After proton irradiation, the positions of the PSD bands show almost no change, while the integral intensity of the main PSD band (300–325 nm) decreases drastically from the original 175 pC in the pristine polyimide to the lowest one at about 10 pC in the irradiated sample, when 60 keV proton fluence is 1 × 1014 p cm−2. However, the intensity shows a certain recovery to about 50 pC as 60 keV proton fluence increases further to 1 × 1016 p cm−2. Further analyses indicate that the evolution of the PSD intensity is dependent on the displacement effect induced by proton irradiation. Structural analyses show that the degradation of carbonyl group in polyimide is the main reason for the decrease in PSD intensity due to proton pre-irradiation.

Time resolved photoluminescence studies of degradation in GaInP/GaAs/Ge solar cells after 1MeV electron irradiation

Time resolved photoluminescence (TRPL) is a powerful method to character the behaviors of carriers as it has high time resolution that could reflect the reactions of carriers within nanoseconds. For solar cells, minority carrier lifetime is the most important parameter. TRPL has been used to measure the lifetime for uniform materials. However, for homojunction solar cells, doping distribution and carrier drift make the spectroscopy analysis much difficult. Thus one dimension numerical calculations are used to study the time-dependent photoluminescence (TRPL) decay of GaAs sub-cell in GaInP/GaAs/Ge solar cells. Calculation shows that both lifetime of minorities and light intensities could determine the line shape of TRPL. The bimolecular recombination under high injection modifies the curve from single-exponential to non-single-exponential one. For TRPL of homojunction solar cell, the photoluminescence decay process is not synchronized in all parts, and the decay is fast in emitter but slower in base regions. To get the lifetimes of minority carriers after 1MeV electron irradiation, carrier generation parameter G0 should be fitted by numerical method firstly. The damage factor Kτ=4.8×10-15 cm2/ns is fitted from TRPL results. Photoluminescence spectra (PL) are also used to get Kτ=5.5×10-15 cm2/ns which is similar with the value obtained from TRPL.Time resolved photoluminescence (TRPL) is a powerful method to character the behaviors of carriers as it has high time resolution that could reflect the reactions of carriers within nanoseconds. For solar cells, minority carrier lifetime is the most important parameter. TRPL has been used to measure the lifetime for uniform materials. However, for homojunction solar cells, doping distribution and carrier drift make the spectroscopy analysis much difficult. Thus one dimension numerical calculations are used to study the time-dependent photoluminescence (TRPL) decay of GaAs sub-cell in GaInP/GaAs/Ge solar cells. Calculation shows that both lifetime of minorities and light intensities could determine the line shape of TRPL. The bimolecular recombination under high injection modifies the curve from single-exponential to non-single-exponential one. For TRPL of homojunction solar cell, the photoluminescence decay process is not synchronized in all parts, and the decay is fast in emitter but slower in base regio...

Formation of E’γ Centers Under Electron Irradiation in Ultrapure Glass and Structural Relaxation

The processes of defect formation and evolution in ultrapure glass under 1 MeV electron irradiation were investigated by the measurement of electron paramagnetic resonance (EPR) spectra and optical absorbance. The results show that the 1 MeV electron irradiation of the ultrapure glass can induce the formation of E’γ centers, and the structure of the E’γ center transform from E’γ(1) center to E’γ(2) center with the increasing irradiation fluence, and this variation also affects the defect optical absorption property in the material. During the room temperature aging process, the defects anneal process induces the recovery of the optical property of the ultrapure glass. It is worth to note that the defect structure varied during the ageing process, namely, the E’γ(2) center transform to E’γ(1) center, and the variation of the defect structure induced the no synchronous property between the defect anneal and the optical absorption recovery.

A Study of Electric Properties of Single‐junction GaAs Solar Cells Irradiated by Low‐energy Protons

The effects of low‐energy proton irradiation on the electrical property of GaAs/Ge solar cells used in space applications are studied. The protons energy in the experiment was selected in the range of 70∼170 keV with a fluence of up to 3×1012 cm−2. The results indicate that under the experimental conditions, the electrical properties such as the short circuit current (Isc), the open circuit voltage (Voc) and the maximum power (Pmax) of the GaAs/Ge solar cells decrease with increasing proton fluence. Increasing the proton energy can result in more serious damage to the solar cell. The proton irradiation can also reduce the filling factor (Ff) of the I‐V curves of the cells. A mechanism of the irradiation damage of GaAs solar cell is discussed.