Characterization of crystalline structure and morphology of Ga2O3 thin film grown by MOCVD technique

Growth of gallium oxide thin film was realized with MOCVD on (0001) sapphire substrate. Structural and compositional properties of thin film were studied employing trimethylgallium and water as precursors, carrier gases were H2 and N2. Obtained film is polycrystalline and predominantly consisted of (201) oriented β-Ga2O3. Sample exhibited blue luminescence which is attributed to oxygen vacancies. H2 gas proved to have beneficial effect on film quality and overall growth process.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Depth profiles of damage creation and hardening in MgO irradiated with GeV heavy ions

This work has been performed within the framework of the EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02 “Advanced experimental and theoretical analysis of defect evolution and structural disordering in optical and dielectric materials for fusion applications”. The views and opinions expressed herein do not necessarily reflect those of the European Commission.The effect of irradiation with GeV heavy ions (U, Au, Bi) on the structure and mechanical properties of MgO single crystals was studied. The methods of nanoindentation, dislocation mobility, optical absorption and photoluminescence (PL) spectroscopy, X-ray diffraction and atomic force microscopy were used for damage characterization. The ion-induced increase of hardness and reduction of dislocation mobility was observed. The depth profiles of hardness, dislocation mobility and PL were investigated, and the contribution of electronic and nuclear loss mechanisms was confirmed. The efficiency of damage vs. average absorbed energy for heavy and light ions was compared. The change in the mechanism of plastic deformation at indentation was observed after severe irradiation due to the immobilization of dislocations by ion-induced extended defects. The results show that MgO single crystals maintain integrity and micro-plasticity at indentation, and exhibit improved hardness after irradiation with swift heavy ions at fluences up to 7 × 1013 ions/cm2.EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Formation of dislocations in LiF irradiated with 3He and 4He ions

Influence of the irradiation with 13.5 MeV 3He and 5 MeV 4He ions on the micro-structure and mechanical properties of LiF single crystals was studied. The depth profiles of nanoindentation, dislocation mobility, selective chemical etching and photoluminescence served for the characterization of damage. Strong ion-induced increase of hardness and decrease in dislocation mobility at the stage of track overlapping due to accumulation of dislocations and other extended defects was observed. At high fluences (1015 ions/cm2) the hardness saturates at about 3.5 GPa (twofold increase in comparison to a virgin crystal) thus confirming high efficiency of light projectiles in modifications of structure and properties. The effects of ion-induced increase of hardness and decrease of dislocation mobility are observed also beyond the ion range and possible mechanisms of such damage are discussed.This work has been supported by the Latvian national program IMIS2; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Formation of dislocations and hardening of LiF under high-dose irradiation with 5–21 MeV 12C ions

R. Zabels, I. Manika, J. Maniks, and R.Grants acknowledge the national project IMIS2, and A. Dauletbekova, M. Baizhumanov, and M. Zdorovets the Ministry of Education and Science of the Republic of Kazakhstan for the financial support.The emergence of dislocations and hardening of LiF crystals irradiated to high doses with 12C ions have been investigated using chemical etching, AFM, nanoindentation, and thermal annealing. At fluences ensuring the overlapping of tracks (Ф ≥6 × 1011 ions/cm2), the formation of dislocation-rich structure and ion-induced hardening is observed. High-fluence (1015 ions/cm2) irradiation with 12C ions causes accumulation of extended defects and induces hardening comparable to that reached by heavy ions despite of large differences in ion mass, energy, energy loss, and track morphology. The depth profiles of hardness indicate on a notable contribution of elastic collision mechanism (nuclear loss) in the damage production and hardening. The effect manifests at the end part of the ion range and becomes significant at high fluences (≥1014 ions/cm2).IMIS2; Ministry of Education and Science of the Republic of Kazakhstan; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Accumulation of radiation defects and modification of micromechanical properties under MgO crystal irradiation with swift 132Xe ions

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. A.A. also acknowledges support via the project GF AP05134257 of Ministry of Education and Science of the Republic of Kazakhstan .Accumulation of F-type defects under irradiation of MgO crystals by 0.23-GeV 132Xe ions with fluence varying by three orders of magnitude has been investigated via the spectra of optical absorption and low-temperature cathodoluminescence. The number of single centers continuously increases with fluence without any marks of saturation. At the highest fluence, a mean volume concentration of 3.1 × 1019 and 3.35 × 1019 cm−3 is reached for F and F+ centers, respectively. The F+ emission strongly dominates in the cathodoluminescence of irradiated MgO and its enhancement with fluence is detected. However, the creation efficiency of the F2 aggregate centers is very low and fluence dependence has a complicated shape. Radiation-induced changes of micro-mechanical properties of the same samples have been analysed; the depth profiles of hardening correlate with the ion energy loss. A joint contribution of ionization and impact mechanisms in the formation of structural defects under MgO irradiation with Xe ions is considered.H2020 Euratom 2019-2020,633053,2014-2018,GF AP05134257; Ministry of Education and Science of the Republic of Kazakhstan GF AP05134257; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Changes of the structure and micromechanical properties in LiF crystals induced by swift xenon ions

Pētīta treku veidošanās LiF kristālos, kas apstaroti ar ātrajiem Xe joniem ar specifisko enerģiju 11,1 MeV uz nuklonu fluenču 107 -1010 joni/cm2 apgabalā, izmantojot dislokāciju kustīguma, atomspēka un optiskās mikroskopijas metodes. Dislokācijas un treki tika vizualizēti selektīvas ķīmiskās kodināšanas ceļā. Fluencei pārsniedzot 107 joni/cm2 tika novērota dislokāciju kustīguma samazināšanās uz apstarotās virsmas. Tika konstatēti pārtraukumi treku serdes struktūrā, kuri samazina treku efektivitāti dislokāciju bremzēšanā. Rezultāti analizēti, izmantojot Orovana modeli dislokāciju mijiedarbībai ar trekiem kā spēcīgiem šķēršļiem. Iegūtie rezultāti parāda dislokāciju kustīguma metodes priekšrocības treka serdes defektu diagnosticēšanai zemo fluenču diapazonā. Atslēgas vārdi: litija fluorīds, ātrie joni, treku kodināšana, dislokācijas.Track damage in LiF crystals irradiated with swift Xe ions with specific energy 11.1 MeV per nucleon at fluences from 107 to 1010 ions/cm2 was studied using dislocation mobility, AFM and optical microscopy methods. The dislocations and ion tracks were revealed by selective chemical etching. Pronounced reduction of the dislocation mobility on irradiated surface was observed above the threshold fluence of 107 ions/cm2. Discontinuities of track structure are observed which reduce the obstacle strength of tracks. The results are analysed using the Orowan’s model of dislocation impeding by tracks as strong barriers. The obtained results demonstrate the advantages of the dislocation mobility method for the diagnostics of track core damage at low-fluence irradiations. Keywords: lithium fluoride, swift ions, track etching, dislocations