Coincidence Doppler Broadening Research Articles

Coincidence Broadening Doppler spectroscopy applied to elemental oxides

Abstract Coincidence Doppler Broadening Spectroscopy (CDBS) was employed to analyze ten simple oxides and compare them to their corresponding non-oxidized pure elements to identify the spectral signature attributable to oxygen. Despite variations among the oxidized elements, the resulting spectra exhibited consistent features—when referenced against the oxidized elements—that can be attributed to oxygen. Furthermore, CDBS spectra referenced against pure aluminum, a widely used independent standard, also revealed a prominent characteristic signal indicative of oxygen that can serve as a fingerprint for its presence. Comparisons with CDBS spectra of Group XVIa elements (Te, Se, and S) were also conducted to further validate the oxygen-related features. This methodology offers a valuable approach for discerning oxygen contributions in complex materials, even when the CDBS spectra are intricate and involve diverse compositions.

Electrochemical characterization and structural analysis of (In2O3)/(Fe2O3) nanocomposites for high-performance supercapacitors

This study presents a comprehensive investigation of the electrochemical characteristics and structural properties of novel nanocomposites with varying compositions of (In2O3)x/(Fe2O3)1-x, where x ranges from 1 to 0. These nanocomposites were synthesized using a versatile and cost-effective co-precipitation method. The crystallographic structure and morphology of the synthesized samples were thoroughly analyzed using Powder X-ray diffraction (PXRD) and Tunneling Electron Microscopy (TEM). Advanced analytical techniques were employed including Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) to uncover critical insights into the structural and molecular properties of these nanocomposites. PALS analysis revealed valuable insights into the pore characteristics of the nanocomposites, while CDBS identified crucial molecular interactions within the materials. Electrochemical characterization of the nanocomposites is carried out using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical-impedance-spectroscopy (EIS) measurements. The (In2O3)0.3/(Fe2O3)0.7 nanocomposite exhibits a remarkable specific capacitance of 945 F g-1 at 1 A g-1 and exceptional rate performance, retaining 93.6% of its specific capacitance at a six-fold higher current density. Moreover, this nanocomposite electrode demonstrates outstanding cyclic stability, maintaining 92.1% of its specific capacitance even after 3000 GCD cycles at 8 A g-1. These findings suggest that the novel composition and integrated electrochemical properties of the (In2O3)0.3/(Fe2O3)0.7 nanocomposite hold great promise for enhancing the performance of next-generation electrochemical capacitors. This research contributes valuable insights into the design and development of advanced energy storage materials with applications in various high-performance energy storage devices.

A fully digital coincidence Doppler broadening spectrometer based on FPGA

In this article, we implemented a fully digital Coincidence Doppler Broadening (CDB) spectrometer consisting of two HPGe detectors, a fully digital processing and acquisition board, and a dedicated software system. The Field Programmable Gate Array (FPGA) on the board extracts energy and time stamp of digitized pulses from HPGe detectors, and communicates with the dedicated software by which the single channel spectrums and 2D coincidence spectrum were produced. We designed an instruction set dedicated to the CDB Spectrometer and the controller module in FPGA so that the FPGA subsystem is fully controllable and configurable. The trapezoidal pulse shaping algorithm was implemented in FPGA whose arguments are all configurable through the dedicated software by the instruction set. We examined the long-term stability of the spectrometer by 511 keV peak position of both channels. The 2D Gaussian fitting is performed on coincidence spectrum by the software to correct the peak drift of both channels. The results show that this method effectively improves the Doppler-broadened spectrum, by which the peak-to-background ratio increases from 7.0 × 105 to 1.9 × 106.

Novel data analysis tool for the evaluation of Coincidence Doppler Broadening Spectra of the positron–electron annihilation line

Coincidence Doppler Broadening Spectroscopy (CDBS) of the 511keV annihilation line reveals the elemental signature at the annihilation site in matter. For this reason, CDBS enables the analysis of foreign atoms in the host matrix, vacancy-solute complexes and precipitates in solids. Due to the lack of a comprehensive program for the analysis of CDBS data we developed a modular python-based open source software solution for the reliable extraction of the annihilation line to provide so-called ratio curves highlighting the elemental signature in the spectra. In particular, the new program allows the readout and spectra averaging of multiple detector pairs. Moreover, we implemented an improved algorithm to further reduce the background by about one order of magnitude at high Doppler shifts.

Positron annihilation studies of methylammonium lead bromide perovskite

Methylammonium lead halide-based perovskite has shown excellent optoelectronic properties. But their performances and stability are critically affected by the ionic defects present in the crystal lattice. In this article, we have investigated the presence of ionic vacancy mediated defects formation in ball mill ground methylammonium lead bromide (MAPbBr3) which has applications in tandem solar cell, light emitting diodes and laser devices. The evaluation of those point defects with temperature was analysed by employing the positron annihilation spectroscopic (PAS) studies. The phase transition from tetragonal to cubic phases around 260 K was exactly correlated with the temperature-dependent ‘S parameter’ determination from PAS analysis and with dc conductivity measurement. From coincidence Doppler broadening (CDB) spectroscopy significant proportion of defects arising from lead vacancy was observed whose magnitude reduces from the low-temperature tetragonal phase to higher temperature cubic phases.

On the Sc-rich core of Al3(Sc,Er,Zr) precipitates

The development of microstructure in an Al–Sc–Er–Zr alloy during aging at 600 °C was investigated utilizing microhardness measurements, positron annihilation spectroscopy (PAS) and (scanning) transmission electron microscopy ((S)TEM). The results of positron lifetime (LT) spectroscopy and coincidence Doppler broadening (CBD) indicate that Sc atoms segregate at dislocations. Two major groups of precipitates were observed after 4 h of aging at 600 °C, one having the usual Er-rich core, Sc-rich inner shell and Zr rich outer shell structure and the other having a core rich in Sc.

Characterization of Lattice Defects in Refractory Metal High‐Entropy Alloy HfNbTaTiZr by Means of Positron Annihilation Spectroscopy

Lattice defects in refractory metal high‐entropy alloy HfNbTaTiZr are investigated using positron lifetime spectroscopy combined with coincidence Doppler broadening (CDB) spectroscopy. Annealing of HfNbTaTiZr alloy at 1000 °C results in full recovery of defects and formation of single‐phase random solid solution characterized by the bulk positron lifetime of 141 ps. This value is in accordance with the theoretical estimation. Quenching of the alloy from high temperature prevents recovery of thermally equilibrium vacancies and enables to retain a high concentration of vacancies in the sample at ambient temperature. For single vacancies in the HfNbTaTiZr alloy, a characteristic positron lifetime of 212 ps is measured, which is significantly shorter than the value estimated by theoretical calculations. It indicates that there is considerable ion relaxation around vacancies. The CDB spectroscopy investigations reveal that vacancies in HfNbTaTiZr alloy are not distributed randomly but are preferentially coupled with Hf solutes.

Ion beam-based coincidence Doppler broadening spectroscopy of positron annihilation radiation: The experiences of Tehran Van de Graaff lab

Coincidence Doppler Broadening Spectroscopy of positron annihilation radiation is developed using high energy gamma-rays instead of standard positron source for defect assessment in thick samples. A 2.5 MeV proton beam of a Van de Graaff accelerator is used to generate high-energy gamma-ray through 19Fp,αγ16O nuclear reaction. The collimated gamma-ray is used to generate positron inside the sample. The performance of the technique to support the positron annihilation spectroscopy experiment is evaluated by investigation of the defect evolution of five low-carbon steel samples preloaded during the uniaxial tension test. The variation of the S-parameter versus strain is investigated and discussed considering the engineering stress-strain curve of the samples. Moreover, the advantages and limitations of the technique over the conventional CDBS are discussed. The developed spectrometer provides a systematic approach for the defect assessment in thick high-Z elements samples.

Positron annihilation investigation of thermal cycling induced martensitic transformation in NiTi shape memory alloy

Thermal cycling of a Ni-excess NiTi alloy was conducted between 50 °C and liquid nitrogen temperature to induce martensitic transformations and to reverse them after. The starting point was an annealed and slowly cooled state, the end point a sample thermally cycled 1500 times. Positron annihilation lifetime spectra and Coincidence Doppler Broadening profiles were obtained in various states and at various temperatures. It was found that the initial state was low in defects with positron lifetimes close to that of bulk NiTi. Cycling lead to a continuous build-up of a defect structure up to 200−500 cycles after which saturation was reached. Two types of defects created during cycling were identified, namely pure dislocations and vacancies attached to dislocations.

The influence of rhenium addition on the distribution of vacancy-type defects in tungsten

To investigate the influence of transmutation rhenium on the irradiation-induced defects in tungsten , H + and He + irradiation of 50 keV with a fixed fluence of 1 × 10 16 atoms·cm −2 were conducted on W x Re ( x =0, 3, 5 and 25 wt.%) alloys, respectively. Doppler Broadening Spectroscopy and Coincidence Doppler Broadening Spectroscopy both based on slow positron beam were employed in the current work to characterize the depth distribution and the chemical surroundings of the irradiation-induced defects. The results showed that under 723K irradiation, Re addition suppressed the accumulation of vacancy-type defects compared with pure W. This suppression was enhanced by increasing Re content in W. An obvious Re-related peak from (7-28) × 10 −3 m 0 c was observed in CDB spectra of well-annealed W-Re alloys. The irradiation effect led to the height deviation of Re-related peak. The decrease of the Re-related peak could be attributed to the formation of irradiation-induced defects in irradiated samples, and the reduction of positron annihilation fraction with core electrons of Re.

Study of Interaction Mechanism between Positrons and Ag Clusters in Dilute Al-Ag Alloys at Low Temperature.

The microstructural evolution of dilute Al–Ag alloys in its early aging stage and at low temperatures ranging from 15 K to 300 K was studied by the combined use of Positron annihilation lifetime spectroscopy (PALS), high resolution transmission electron microscopy (HRTEM), and positron annihilation Coincidence Doppler broadening (CDB) techniques. It is shown that at low temperatures below 200 K, an Ag–vacancy complex is formed in the quenched alloy, and above 200 K, it decomposes into Ag clusters and monovacancies. Experimental and calculation results indicate that Ag clusters in Al–Ag alloys can act as shallow trapping sites, and the positron trapping rate is considerably enhanced by a decreasing measurement temperature.

Positron Annihilation Spectroscopy of KCl (Zn) crystals

Four samples of nominally pure KCl crystals and doped with Zn2+ impurities are grown by the Czochralski method and characterized by X-ray diffraction and Proton Induced X-ray Emission techniques. Positron Annihilation Lifetime Spectroscopy (PALS) is performed to obtain information on the cation vacancy type defects and their evolution under doping. The results of the PALS experiment indicate that doping KCl by Zn2+ ions, at first increases the concentration of mono vacancies and in the second stage leads the creation of divacancy sites. Coincidence Doppler Broadening Spectroscopy (CDBS) is carried out to obtain the chemical environment of positron annihilation sites. The results of CDBS show that cation vacancies have a significant role in the annihilation process. An interesting observation is the participation of Zn2+ cations in the positron annihilation process which confirms that positrons are not completely localized on the anion sites. The internal consistency between the results of PALS and CDBS experiments is also clarified.

Lattice defects in severely deformed biomedical Ti-6Al-7Nb alloy and thermal stability of its ultra-fine grained microstructure

Biomedical Ti-6Al-7Nb alloy was prepared by a dedicated thermal treatment followed by equal-channel angular pressing (ECAP) and extrusion. Ultra-fine grained duplex microstructure consisting of deformed primary α-grains and fragmented α + β region was achieved. Microstructural changes during heating with the rate of 5 °C/min were studied by in-situ electrical resistance. Microstructure after deformation and also after subsequent heating was thoroughly characterized by scanning electron microscopy, X-ray diffraction, and positron annihilation spectroscopy (PAS). X-ray diffraction and positron annihilation spectroscopy proved a very high dislocation density and the presence of high concentration of vacancy clusters in deformed material.The ultra-fine grained microstructure of Ti-6Al-7Nb alloy is stable up to 440 °C, while upon heating to 550 °C and to 660 °C, the dislocation density decreases and vacancy clusters disappear. Enhanced microhardness can be achieved by ECAP followed by aging at 500 °C. Upon heating to 660 °C, the microhardness decreases due to ongoing recovery and recrystallization. Coincidence Doppler broadening (CDB), a special method of PAS, proved that dislocation cores are preferentially occupied by Al atoms that are known to cause substitutional solid solution strengthening.

Tellurium coincidence Doppler broadening spectroscopy study

Abstract The Coincidence Doppler broadening (CDB) reference curve for pure Tellurium (Te) has been obtained stablishing a point of departure for future Positron Annihilation Spectroscopy (PAS) studies of alloys that include Te among its components to determine the influence of this element in the open volume defects and its environment.

Investigation of X-ray-induced Defects on Metals and Silicon by Using Coincidence Doppler Broadening Positron Annihilation Spectroscopy

The mechanical properties of Al, Ti, Fe, and Cu metals p-type Si, and n-type Si were investigated by using coincidence Doppler broadening (CDB) positron annihilation spectroscopy. The samples in this experiment were irradiated by using X-rays at generating powers for up to 9 kW. The data taken after the irradiation showed all the characteristic features predicted from defects with vacancies. The S parameter values of the metals were generally less than those of semiconductors such as p-type Si and n-type Si. The relationship between n-type Si and p-type Si were more affected when n-type Si rather than p-type Si was irradiated with X-rays.

Point defect structure of La-doped SrTiO3 ceramics with colossal permittivity

Sr1-xLaxTiO3 (SLTO) ceramics with colossal permittivity were fabricated by conventional solid-state reaction method. The point defects of pure STO and SLTO ceramics were analyzed by Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening (CDB). The charge compensation mechanisms and dielectric properties of ceramics were investigated. The results indicated that the intrinsic defects in pure STO ceramics were mainly VTi″″. The charge compensation mechanism of SLTO ceramics was predominantly formation of VSr″. With increasing La content, εr of SLTO ceramics increased up to ∼70000 at room temperature. The results of first-principle calculations indicated that the colossal permittivity came from a sharp polarization increase caused by dipole structure of defects. tanδ of SLTO ceramics showed obvious Debye relaxation at high temperatures and the relaxation showed a multiple relaxation times derived from different kinds of polarization mechanism. The main polarization mechanism of SLTO ceramics gradually changed from ion displacement polarization to defect dipole polarization influenced by the concentration of La dopants.

Momentum distribution of core and 3d electrons in mechanically strained NiO nanoparticles

Nickel oxide (NiO) nanoparticles was prepared using top-down method in the size range 12–70 nm via ball milling of their bulk. Bulk size NiO was prepared by heating of Ni(NO3)2.6H2O in air. This NiO powder was then milled in planetary ball mill keeping a fixed powder to ball ratio. Strain was introduced in the powder during milling process. The structure of milled samples was studied using x-ray diffraction (XRD) while Vibrating Sample Magnetometer (VSM) measurements were carried out to study magnetization in samples. The peaks in the x-ray diffraction (XRD) pattern correspond to pure NiO phase showing no trace of any other phase. Strained particles showed higher magnetization as compared to relaxed NiO nanoparticles. Positron Annihilation Coincidence Doppler Broadening (PACDB) spectroscopy was used to study the 3d and core electron momentum distribution in the vicinity of Ni atom. It is observed that as milling proceeds and the particles become more and more laminar the positrons get annihilated preferentially at the oxygen core. A relation between PACDB quotient ratio and mechanical strain is established in this study.

Formation of D–VZn complex defects and possible p-type conductivity of ZnO nanoparticle via hydrogen adsorption

The hydrogen adsorption on surfaces and on defect sites of ZnO nanoparticles (NPs) has been studied by using Raman and Fourier transform infrared spectroscopic methods. The presence of hydrogen at defect sites bound to zinc vacancy with different coordinations has been confirmed. To further identify the existence of isolated VZn and H–VZn complexes in the ZnO NPs, coincidence Doppler broadening (CDB) spectroscopic studies have been performed with respect to the CDB spectra of a 99.9999% pure Al single crystal. The broad momentum dip ρL showed between 15–17 × 10−3 m0c suggests the trapping of positrons with the core electrons of 3p Zn. However, positron annihilation takes place between ρL 20–25 × 10−3 m0c and this may occur with an electron belonging to OH bonds (VZn–Hi–O). Here the lattice hydrogen H+ ion acts as a compensating centre, and it can bind with the VZn around the dislocation and stacking faults (SFs) core, which may produce the acceptor-type complex defect for p-type conductivity. Finally, the existence of SFs and dislocation defects, including edges and steps, was confirmed by transmission electron microscopy.

Detection of phase separation of neutron-irradiated Fe–Cr binary alloys using positron annihilation spectroscopy

Phase separation in Fe–Cr binary alloys irradiated with neutrons at 473 K and 573 K was investigated using positron annihilation spectroscopy. Using positron annihilation coincidence Doppler broadening (CDB) measurements, the phase separation progress was observed in neutron-irradiated samples at 473 K and 573 K. Vacancy clusters were detected in Fe–xCr (x = 0, 9, 15, 30, 45, 50, and 100) during 473 K irradiation using positron annihilation lifetime measurements, but were not detected in Fe–xCr (x = 70, 85, and 91) irradiated at 473 K or in any samples irradiated at 573 K. Additionally, in Fe–xCr (x = 70, 85, and 91) irradiated at 473 K, all positrons were annihilated with core Fe electrons as determined from CDB ratio curves. Thus, vacancy clusters were not detected in the Fe-rich phase. There was a possibility that vacancy clusters are formed in the Cr-rich phase, but they were not detected by the PAS. Therefore, another method is necessary to investigate this further. Vickers hardness tests indicated that neutron-irradiated samples were harder than unirradiated samples. The contribution of phase separation and neutron-irradiation defects to increased hardness was dependent on the irradiation conditions including temperature and dose.

Chemical Information of Chitosan-Based Complex Extracted from Coincidence Doppler Broadening Spectra

Chemical Information of Chitosan-Based Complex Extracted from Coincidence Doppler Broadening Spectra