Vladimír Slugeň

Czochralski-grown nitrogen-doped silicon : Electrical properties of MOS structures; A positron annihilation study

Abstract Czochralski-grown nitrogen-doped (NCZ) silicon was studied using different methods. Measurements of interface traps density, effective generation lifetime and effective surface generation velocity were performed on selected Metal-Oxide-Semiconductor (MOS) structures. Application of the positron annihilation technique (PAS)—pulsed low energy positron system (PLEPS)—was focused on the detection of nitrogen-related defects in NCZ silicon in the near surface region. PAS—PLEPS technique gave relevant results on p-type NCZ silicon. Low sensitivity in the application to n-type NCZ silicon discriminates the PAS—PLEPS technique and should be alternated by other experimental technique. On the other hand, more pertinent measurement of generation lifetime was performed on MOS structures with n-type Si. Although the generation lifetime decreases in NCZ silicon, considerable lateral homogenization of the relaxation time was observed on the wafer.

JRQ and JPA irradiated and annealed reactor pressure vessel steels studied by positron annihilation

ABSTRACT The paper is focused on a comprehensive study of JRQ and JPA reactor pressure vessel steels from the positron annihilation lifetime spectroscopy (PALS) point of view. Based on our more than 20 years’ experience with characterization of irradiated reactor steels, we confirmed that defects after irradiation start to grow and/or merge into bigger clusters. Experimental results shown that JPA steel is more sensitive to the creation of irradiation-induced defects than JRQ steel. It is most probably due to high copper content (0.29 wt.% in JPA) and copper precipitation has a major impact on neutron-induced defect creation at the beginning of the irradiation. Based on current PALS results, no large vacancy clusters were formed during irradiation, which could cause dangerous embrittlement concerning operation safety of nuclear power plant. The combined PALS, small angle neutron scattering and atomic probe tomography studies support the model for JRQ and JPA steels describing the structure of irradiation-induced clusters as agglomerations of vacancy clusters (consisting of 2–6 vacancies each) and are separated from each other by a distribution of atoms.

Defect Detection in Fe-Cr Alloys with Positron Annihilation Doppler Broadening Spectroscopy

Positron annihilation Doppler broadening spectroscopy (DBS) has been used for the detection of structural defects in Fe-9wt%Cr (Fe-9Cr) alloy in the as-prepared and implanted states. Defects were created by He and H ion implantation with a kinetic energy of 250 keV. DBS is a non-destructive method and is a unique tool for the observation of open volume defects like vacancies and vacancy clusters in solids. A positron beam with variable positron energy was used for the measurement of defect depth profiles up to 1.5 µm. The obtained results provide qualitative and semi-quantitative information about radiation induced defects and their chemical environment. Although the collision damage from helium implantation was one order of magnitude higher than for the case of hydrogen, the changes in S and W parameters are much less significant, probably due to considerably lower mobility of helium in the implanted materials, which results in helium capture by the created open volume defects.

Positron annihilation techniques applied to reactor steels

Different positron annihilation spectroscopy (PAS) techniques were applied in investigations of nuclear reactor steels. Summary of previous applications and evaluation of PAS potential contributions in the area of microstructural study of materials foreseen for fusion and fission technologies are discussed in detail.

Investigation of Defects in Copper Alloys Selected for Nuclear Fusion Technology

Abstract. Positron lifetime measurements using a Pulsed Low Energy Positron System (PLEPS) were applied to the investigation of defects in hydrogen implanted and subsequently thermally treated copper alloys which are designated for the use in the International Thermonuclear Experimental Reactor (ITER). PLEPS results showed that the changes in the microstructure of selected copper-alloys (CuCrZr, CuAl25) depend strongly on the preparing technology of alloys and on the implantation dose. The full recovery of the structure after isochronal annealing in vacuum in a region of 100-600 ”C was observed in all implanted specimens at a level of about 450 ”C. With the PLEPS technique, for the first time, depth profiling of the near-surface region (20-500 nm) of hydrogen implanted copper alloys was performed and compared with the transmission electron microscopy (TEM) studies. Introduction The precipitation hardened alloy (CuCrZr) and the dispersion strengthened alloy (CuAl25) are studied here by positron annihilation spectroscopy (PAS). These Cu-alloys should be applied in the ITER as a cooler and should diffuse the heat [1]. Due to the particle bombardment of ITER first-wall materials (selected copper alloys) various changes in mechanical properties can be induced. Investigation of defects created in this way is an interesting issue for solid-state science as well as for applied research. For the simulation of the radiation damage due to a neutron flux, the ion implantation of protons has been applied. The protons were chosen because they have approximately the same mass as that of neutrons. Although the ballistic influence of protons on the primary-knock-on atom (PKA) production is different from that of D-T fusion reactor conditions, nevertheless it is instructive to investigate fundamental displacement damage effects using proton irradiation.

CDBTools - Evaluate Positron Annihilation Coincidence Doppler Broadening Spectrum

CDBTools is a lightweight and easy to use application designed to provide you with an analysis tool for coincidence Doppler broadening (CDB) of the positron annihilation energy spectrum files. This application enables you to analyze the CDB and ratio curves, plots as well as graphs representing the evolution of the orbital electron momentum spectrum. The CDB extraction is provided by selectable filters applied at the diagonal line of the input matrix. To achieve CDB ratio curves with minimal error caused by 511keV peak shift, spectrum curves are recalculated by penalized regression spline.

Investigation of materials for fusion power reactors

The possibility of application of nuclear-physical methods to observe radiation damage to structural materials of nuclear facilities is nowadays a very actual topic. The radiation damage to materials of advanced nuclear facilities, caused by extreme radiation stress, is a process, which significantly limits their operational life as well as their safety. In the centre of our interest is the study of the radiation degradation and activation of the metals and alloys for the new nuclear facilities (Generation IV fission reactors, fusion reactors ITER and DEMO). The observation of the microstructure changes in the reactor steels is based on experimental investigation using the method of positron annihilation spectroscopy (PAS). The experimental part of the work contains measurements focused on model reactor alloys and ODS steels. There were 12 model reactor steels and 3 ODS steels. We were investigating the influence of chemical composition on the production of defects in crystal lattice. With application of the LT 9 program, the spectra of specimen have been evaluated and the most convenient samples have been determined.

Performance of LYSO and BC420 coupled with Ketek and Sensl SiPM for needs of PALS

Material research of structural steels used in extreme conditions is important for the safe and reliable operation of individual components of nuclear installations. One of the effective methods of examining their microstructure is positron annihilation lifetime spectroscopy (PALS). For the needs of PALS, new types of detectors are currently being used compared to conventional photomultipliers. These types of detectors, however, are not sensitive to fast ultraviolent component of emission spectrum of the most commonly used scintillation material in this area - barium fluoride. This paper analyses the effect of the usage of LYSO and plastic scintillators on the properties of the spectrometric apparatus. These scintillation materials were linked to the SiPM detectors Sensl MicroFJ-SMA-30035 and Ketek PE6650-EB-AX as well as to the conventional Photonis XP2020Q photomultiplier.Material research of structural steels used in extreme conditions is important for the safe and reliable operation of individual components of nuclear installations. One of the effective methods of examining their microstructure is positron annihilation lifetime spectroscopy (PALS). For the needs of PALS, new types of detectors are currently being used compared to conventional photomultipliers. These types of detectors, however, are not sensitive to fast ultraviolent component of emission spectrum of the most commonly used scintillation material in this area - barium fluoride. This paper analyses the effect of the usage of LYSO and plastic scintillators on the properties of the spectrometric apparatus. These scintillation materials were linked to the SiPM detectors Sensl MicroFJ-SMA-30035 and Ketek PE6650-EB-AX as well as to the conventional Photonis XP2020Q photomultiplier.

Investigation of laboratory produced ODS alloys

Irradiation, heat and mechanical stresses are factors which influence structural materials of nuclear power plants (NPP), e.g. reactor pressure vessel steels and may reduce lifetime of NPP operation [1-3]. High radiation and thermal loads are expected in the newest generation of nuclear power plants, such as Generation IV (GEN IV) and fusion reactors, which will be operated at temperatures between 550 - 1 000 °C and will be exposed to irradiation over 100 DPA during planned lifetime (more than 60 years) [4]. Consequently, the demands on the structural materials are very high and so the research and development needs to be focus on their improved characteristics. The advanced structural materials, as oxide-dispersion-strengthened (ODS) steels, are developed for application in cooling systems, reactor pressure vessel or fuel cladding of the GEN IV nuclear power plants. The ODS steels fulfill demands on radiation, thermal and mechanical resistance during operation of nuclear reactor. ODS steels have high the...

Simulation of nanostructure evolution under helium implantation in Fe–(2.5–12.5)at% Cr alloys at a temperature of 343 K

Characterization of helium-implanted Fe–(2.5–12.5)at% Cr alloys with the flux of 7 × 10–6 dpa/s at a temperature of 343 K has been performed by means of cluster dynamics simulations. We have suggested a model for simulating an Fe–C–Cr system under helium implantation based on a selection of the latest data from atomistic studies and available experiments. Kinetics of carbon-vacancy and helium-vacancy complexes has been studied. Only one parameter is used to guarantee the best reproduction possible of experimental positron annihilation lifetime spectroscopy data for Fe–Cr alloys on dependences of vacancy cluster size on chromium content and irradiation dose via fitting. This is an effective binding energy of self-interstitial atoms to dislocation loops decorated by chromium atoms. It has a “snaky” dependence of chromium content with a minimum of about 9%Cr.