Pang Lilong

Helium-Implantation-Induced Damage in NHS Steel Investigated by Slow-Positron Annihilation Spectroscopy

Evolutions of defects and helium contained defects produced by atomic displacement and helium deposition with helium implantation at different temperatures in novel high silicon (NHS) steel are investigated by a slow positron beam. Differences of the defect information among samples implanted by helium to a fluence of 1 x 10(17) ions/cm(2) at room temperature, 300 degrees C, 450 degrees C and 750 degrees C are discussed. It is found that the mobility of vacancies and vacancy clusters, a recombination of vacancy-type defects and the formation of the He-V complex lead to the occurrence of these differences. At high temperature irradiations, a change of the diffusion mechanism of He atoms/He bubbles might be one of the reasons for the change of the S-parameter.

Cavity Swelling in Three Ferritic-Martensitic Steels Irradiated by 196 MeV Kr Ions

We report on cavity swelling at peak damage regions of three ferritic-martensitic (FM) steels (NHS, RAFM and T91) irradiated by 196 MeV Kr ions at different temperatures (450/550°C). Cavity configurations of the irradiated specimens are investigated by transmission electron microscopy with cross-section technique. For home-made reduced activation ferritic-martensitic (RAFM) and T91 steels irradiated at 450°C, both large size and bimodal size distribution of the cavity are found in their peak damage regions, whereas novel high silicon (NHS) steel exhibits good swelling resistance at different irradiation temperatures. Temperature relativity of the cavity swelling in NHS, RAFM and T91 steels is discussed briefly.

Cavity swelling of RAFM steel under 792 MeV Ar-ions irradiation at 773 K

China reduced-activation ferritic/martensitic steel is irradiated at 773 K with 792 MeV Ar-ions to fluences of 2.3×1020 and 4.6×1020 ions/m2, respectively. The variation of the microstructures of the Reduced-activation ferritic/martensitic (RAFM) steel samples with the Ar-ion penetration depth is investigated using a transmission electron microscope (TEM). From analyses of the microstructure changes along with the Ar-ions penetrating depth, it is found that high-density cavities form in the peak damage region. The average size and the number density of the cavities depend strongly on the damage level and Ar-atom concentration. Swelling due to the formation of cavities increases significantly with an increased damage level, and the existence of deposited Ar-atoms also enhances the growth of the average size of the cavities. The effect of atom displacements and Ar-atoms on the swelling of the RAFM steel under high energy Ar-ion irradiation is discussed briefly.

The Structural Modification of LiTaO3 Crystal Induced by 100-keV H-ion Implantation

The effects of 100 keV H-ion implantation on the structure of LiTaO3 crystal are investigated by Raman and UV/VIS/NIR spectroscopies. The implantation fluence is in the range from 1.0 × 1013 to 1.0 × 1017 H+/cm2. The experimental results show the dependence of the crystal structure on ion fluence. It is found that the structural modification of the LiTaO3 crystal is due to two processes. One is H-ions occupying lithium vacancies (VLi), which is predominant at a fluence less than 1.0 × 1014 H+/cm2. This process causes the reduction of negative charge centers in the crystal and relaxation of distortion in the local lattice structure. The other is the influence of defects created during implantation, which plays a dominant role gradually in the structural modification at a fluence larger than 1.0 × 1015 H+/cm2.

Modification of Optical Band-Gap of Si Films After Ion Irradiation

Amorphous silicon (a-Si), nanocrystalline silicon (nc-Si) and hydrogenated nanocrystalline silicon (nc-Si:H) films were fabricated by using chemical vapor deposition (CVD) system. The a-Si and nc-Si thin films were irradiated with 94 MeV Xe-ions at fluences of 1.0 × 1011 ions/cm2, 1.0 × 1012 ions/cm2 and 1.0 × 1013 ions/cm2 at room temperature (RT). The nc-Si:H films were irradiated with 9 MeV Xe-ions at 1.0 × 1012 Xe/cm2, 1.0 × 1013 Xe/cm2 and 1.0 × 1014 Xe/cm2 at RT. For comparison, mono-crystalline silicon (c-Si) samples were also irradiated at RT with 94 MeV Xe-ions. All samples were analyzed by using an UV/VIS/NIR spectrometer and an X-ray powder diffractometer. Variations of the optical band-gap (Eg) and grain size (D) versus the irradiation fluence were investigated systematically. The obtained results showed that the optical band-gaps and grain size of the thin films changed dramatically whereas no observable change was found in c-Si samples after Xe-ion irradiation. Possible mechanism underlying the modification of silicon thin films was briefly discussed.