Annihilation Spectroscopy Techniques Research Articles

CHARACTERIZATION OF DEFECTS IN TUNGSTEN SAMPLES INTERESTED IN PFM STUDIES USING POSITRON ANNIHILATION AND PHOTOLUMINESCENCE SPECTROSCOPY

The defect structure of four pure tungsten samples is investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL) and positron annihilation spectroscopy (PAS) techniques before and after annealing. The results of the SEM and XRD analyses show that the grain size is increased up to 43.3[Formula: see text][Formula: see text]m, and their growth in the (2 0 0) orientation occurs at 1673[Formula: see text]K. Also, the smooth of the peaks at 1673[Formula: see text]K in the PL test demonstrates the increase of the size of defects of the sample. Moreover, the results of the PAS indicate a decrease in the concentration of defects and an increase in their size at 1673[Formula: see text]K, which confirms the results obtained from the PL measurement. The collected results from the four examination techniques are in close agreement with each other and reveal that w ith the increase in the annealing temperature of tungsten samples, a gradual coalescence of the defects would happen to lead to an increase in their size and hence a reduction in their number as well as preferred grain growth in the (2 0 0) orientation and virtually perfect recrystallization of the samples at higher temperatures.

Investigations of HAVAR<sup>®</sup> Alloy Using Positrons

A study of irradiation-induced damage in HAVAR® foils was initiated in order to extract the highest proton dose the foils can sustain. The lattice structure of HAVAR® foils in different metallurgic conditions is presented, as well as visible internal structure, measured by Transmission Electron Microscopy (TEM). Positron Annihilation Spectroscopy (PAS) techniques were used to investigate these foils, and another foil that had been irradiated to the maximal proton dose limit, set by the manufacturer to a total charge of 1 mAh (= 3.6 C). PAS techniques included Doppler broadening (DB) measurement in the SPONSOR beam and lifetime (LT) measurements, both carried at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Both positron spectroscopy methods show clear differences between the investigated foils, with distinguished characteristics for annealed, cold-rolled and irradiated foils. The advantages of using a slow positron beam to study thin foils and defect profiles, over a table-top LT spectrometer, are discussed and demonstrated by the HAVAR® measurements.

Comparison of residual stress in martensitic alloys by nondestructive techniques

Three martensitic materials, namely Alloys EP-823, HT-9 and 422 were subjected to tensile loading at ambient temperature. The cylindrical specimens tested at different levels of tensile loading were analyzed for characterization of residual stress resulting from plastic deformation corresponding to the applied loads between the yield strength and the ultimate tensile strength. The extent of residual stress developed at these applied stresses was analyzed by nondestructive positron annihilation spectroscopy, activation, and neutron diffraction techniques. The results indicate that the residual stresses characterized by all three techniques exhibited a consistent pattern showing a gradual enhancement in residual stress with increasing applied load.

Evaluation on Defects of Er and Yb Implanted Al070Ga030As by Using Positron Annihilation Spectroscopy

ABSTRACTThe influence on defects of Er implanted Al0.70Ga0.30As was studied, using standard Positron Annihilation Spectroscopy (PAS) and Photoluminescence (PL) technique. The incident energy of mono-energetic positrons was implanted from 0.1 eV to 30 keV. The characterization of un-doped Al0.70Ga0.30As and Al0.70Ga0.30As:Er,Yb as implanted, and Al0.70Ga0.30As:Er,Yb annealed ranging from 500 to 900 °C were successfully studied by using PAS technique. Into the incident energy around 5keV, the shape parameter of Al0.70Ga0.30As:Er,Yb annealed ranging from 500 to 900 °C was decreased and the PL intensity also increased in response to the annealing temperature ranging from 500 to 900 °C.

Preparation and structural characterization of polystyrene-rectorite nanocomposites

The polystyrene/rectorite nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic rectorite. The structures and thermal properties of these hybrids have been investigated by X-ray diffraction (XRD), fourier transform infrared (FT-IR), positron annihilation spectroscopy (PAS) and thermal gravimetric analysis (TGA) techniques. It was found that exfoliation of rectorite in polystyrene (PS) matrix was achieved. The average free-volume radius in the PS/clay nanocomposites is generally same as that in PS. Along with increment of rectorite contents, the interface between rectorite and polystyrene matrix increases, and the free-volume concentration decreases obviously. And the polystyrene nanocomposites have higher thermal decomposition temperature than pure PS.

Physical Characterization of Residual Implant Damage in 4H-SiC Double Implanted Bipolar Technology

ABSTRACTThe effects of post-implant anneal conditions on the level of residual damage resulting from nitrogen and boron implants after different anneal processes are investigated using the Positron Annihilation Spectroscopy (PAS) technique. It is shown that after implantation there is a substantial defect concentration significantly below the range of the implants. However such damage is almost completely recovered after anneal in contrast with the damage close to the implant range point. Such residual damage has a strong effect on the electrical characteristics of double implanted bipolar transistors - principally though reduction in carrier mobility and lifetime. It is shown that the precise implant and anneal conditions play a strong role in the level of such damage and the subsequent electrical performance of bipolar devices.