Te Zhu

Helium/hydrogen synergistic effect in reduced activation ferritic/martensitic steel investigated by slow positron beam

Abstract Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He2+ irradiation, (ii) H+ irradiation and (iii) He2+ irradiation followed by H+ irradiation, at temperature 450 °C. The presences of vacancy defects, represented by ∆SHe+H parameter, induced by sequential irradiations was larger than the sum of defects, ∆SHe parameter + ∆SH parameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy.

Tuning perpendicular magnetic anisotropy in the MgO/CoFeB/Ta thin films

The characteristic of magnetic anisotropy is one of the keys to determine the applications of the ferromagnetic thin films for decades. The perpendicular magnetic anisotropy (PMA) in the ferromagnetic thin film has been found in the conventional ferromagnetic metal/non-magnetic metal (FM/NM) multilayers, such as Co/Pd multilayers [1], and in the annealed ferromagnetic metal/ oxide thin films, such as Pt/Co/AlOx and Ta/CoFeB/MgO thin films [2,3]. The strength of PMA can be tuned not only by varying the thickness of FM layer, but also by changing the oxidation status at the interface of FM/MOx. Since it is of great interest in both experimental and theoretical views to investigate the mechanism of PMA, the MgO/CoFeB interface have received continuous attentions due to their potential use in highly sensitive magnetic field sensors or in spin-transfer-torque magnetic random access memories. In this paper, we propose a new approach to manipulate the strength of PMA at the MgO/CoFeB interface. It is found that the strength of PMA dramatically decreases with the increasing of MgO thickness in the MgO/CoFeB/Ta thin films, due to the onset of crystalline MgO forming.

Helium irradiation-induced defects in deformed 316L stainless steel

Abstract Well-annealed 316L stainless steel was first cold rolled to 10% and 20% reductions in thickness and then irradiated by 50 keV He+ to a dose of 1 × 1020 He+/m2 at room temperature. Thermal desorption spectroscopy was used to investigate the helium desorption behaviour at different helium trapping states. The results showed that high-density dislocations had stronger inhibitory effect for helium desorption at temperatures from 800 to 1200 K. Positron annihilation Doppler broadening spectroscopy measurements were used to investigate the distribution of helium irradiation-induced defects. The S–E and ΔS–E plots clearly demonstrated that the helium irradiation-induced defects were trapped and restricted in motion by dislocations. The interaction between dislocations and helium irradiation-induced defects in deformed 316L stainless steel was investigated.

Irradiation Induced Defects by Fe-Ion in 316L Stainless Steel Studied by Positron Annihilation Spectroscopy

Solution annealed type 316L austenitic stainless steels were irradiated using 2 MeV Fe ions at room temperature. The implanted fluences were 2×1012 ions/cm2 and 1×1013 ions/cm2, respectively. Variable mono-energetic positron beam was performed to characterize the evolution of microstructure and irradiation induced defects. Results show that large amount of vacancy defects formed after heavy ion irradiation. In which, some of mono-vacancies might migrate to form small-sized clusters at room temperature. After irradiation, implanted Fe atoms mainly be interstitials atoms, but some Fe atoms might recombine with vacancies due to their high mobility, which could decrease the defect concentration, effectively.