Dyson line and modified Dyson line in the EPR measurements

The difficulty in determining the electron paramagnetic resonance (EPR) line parameters of ferromagnetic semiconductors has been addressed. For these materials, the resonance line is very broad and lies at low resonance field, so that only a part of the line can be detected experimentally. Moreover, the line is of asymmetric (Dysonian) shape as described by the line shape parameter α. We have compared values of line parameters derived by computer fitting of the whole experimental EPR line to the Dyson function (or modified Dyson function) with the values obtained by applying this procedure to the left and the right half of the line.

Investigation of defects and nanoparticles with martensitic phase transformation in surface nanostructured 316L stainless steel by slow-positron beam

In this article, we investigated the defects introduced by surface mechanical attrition treatment by Doppler-broadening spectroscopy of positron annihilation radiation in surface-nanostructured 316L stainless steel. Through the measurement of different thinning layers in the samples treated for 15 min, the slope of line shape parameter S versus wing parameter W curves showed three different values with depth responding to the change of defect configuration. An unusual change of S and W parameters near the surface was mainly from the effect of quantum-dot-like state caused by the formation of nanoparticles. Based on the change of S ˜ W with depth, the martensite phase transformation induced by strain could be estimated to occur within a depth of 35 μm.

Slow Positron Annihilation in Ion-Implanted Silicon

The mechanism of slow positron annihilation in ion-implanted Si has been discussed in terms of the Diffusion-Trapping model (DTM). The trapping of positron has been considered in native vacancies (monovacancies) and ion induced vacancies i.e. vacancy clusters. The model has been used to calculate the Doppler broadening line shape parameter (S-parameter) as a function of incident positron energy for different ion-implanted Si. It has been found that at lower energies the monovacancies and vacancy clusters both contribute to the S-parameter while, with the increase in positron energy the vacancy clusters are reduced. The S-parameter is found to be dependent on the fluency of the implanted ions.

Effect of Irradiation Doses on AlCu6.5 Alloy Using Positron Annihilation Doppler Broadening Technique

Positron Annihilation Spectroscopy (PAS) is a powerful and versatile tool for the study of the microscopic structure of materials. Doppler Broadening Positron Annihilation Technique (DBPAT) is the fastest technique used among positron annihilation techniques. The dose effect in Al-6.5at. % Cu alloy was investigated by means of DBPAT. An abrupt change in both the S and W line-shape parameter values occurred at 70 kGy of irradiation. The S- and W-Parameters of the trapped positrons at 70 kGy of γ−irradiation dose are about 48 % and 14 % respectively. The S- versus W-parameter reveals a linear relationship indicating the presence of only one type of defect. The S- and W-parameters have been used in the determination of the positron trapping rate and the grain size of the AlCu6.5 alloy.

Slow Positron Studies of Defects in Si-Doped GaAs

The mechanism of slow positron annihilation in Si-doped GaAs has been discussed in terms of the diffusion trapping model (DTM). The trapping of positrons has been considered in SiAs acceptors i.e. shallow defects and in VGa-SiGa vacancy complexes. The model has been used to obtain the Doppler broadening line shape parameter (S-parameter) and average positron lifetime in Si-doped GaAs, for a temperature range 20K to 290K and for different doping concentrations. Observations are made regarding the effect of doping on the nature and concentration of point defects. The change in point defect concentration due to Si- doping has been found to be proportional to the doping concentration. The effect of detrapping from the shallow defects has been found to be important at higher temperatures.

Point defects in thin HfAlOx films probed by monoenergetic positron beams

ABSTRACTThin HfAlOx films grown on SiON(0.9 nm)/Si by atomic layer deposition technique were characterized by using monoenergetic positron beams. The lifetimes of positrons in the HfAlOx film after post-deposition annealing (PDA) ranged between 412–403 ps. Since these lifetimes were longer than the lifetime of positrons trapped by point defects in metal oxides, such as LaCoO3, PbTiO3, and BaTiO3, the positrons in HfAlOx films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. The line-shape parameter S of the Doppler broadening spectrum corresponding to the annihilation of positrons in HfAlOx films decreased by PDA, and the S value decreased with increasing an O2-content in an atmosphere during PDA (0.004–1%). The observed behavior of the S value was attributed to the shrinkage of the open spaces due to the change in the matrix structure of HfAlOx. After P+- and B+-implantation into poly-Si films grown on the HfAlOx films, the diffusion of positrons in the Si substrates toward the HfAlOx film was suppressed. This fact was attributed to positive charges introduced near the HfAlOx films.

Molecular Resonances Observed in the Predissociation of Cs2

Very cold molecular beam of Cs2 is generated by a high temperature supersonic jet source. State-specific photofragment yield spectrum is obtained in the orange band of Cs2. Asymmetric line shapes are observed. The Fano line shape parameter, q, shows a gradual sign change, which is called “q-reversal”. A very broad absorption band which has about 50 cm-1 width is observed and explained to occur through the perturbation by the D1∑u+ state. The complex resonance line shapes are attributed to the interfering resonances.