Wang Zhi-Guang

Structural and photoluminescent properties of ZnO films deposited by radio frequency reactive sputtering

Zinc oxide films with c-axis preferred orientation were deposited on silicon (100) substrates by radio frequency (RF) reactive sputtering. The properties of the samples were characterized by X-ray diffractometer, X-ray photoelectron spectroscopy and fluorescent-spectrophotometer. The effect of sputtering power and substrate temperature on the structural and photoluminescent (PL) properties of the ZnO films was investigated. The results indicated that when the sputtering power is 100 W and the substrate temperature is 300–400°C, it is suitable for the growth of high c-axis orientation and small strain ZnO films. A violet peak at about 380 nm and a blue band at about 430 nm were observed in the room temperature photoluminescence spectra, and the origin of blue emission was investigated.

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.

Ne2+ Ion Irradiation Induced Swelling Effects in Pyrochlore Ho2Ti2O7 by Using a GIXRD Technique

We carry out 400 keV Ne2+ ion irradiation damage experiments at cryogenic temperature (about 77 K) on poly-crystalline Ho2Ti2O7 pyrochlore. The irradiation fluences range from 2x10(14) to 1.3x10(15) ions/cm(2), corresponding to the peak ballistic displacement damage of 0.075-0.487 in units of displacement per atom (dpa). The value indicates the statistical average of the fractional number of lattice atoms which have experienced a lattice displacement. Irradiation-induced structural evolution is examined by using grazing incidence x-ray diffraction (GIXRD) at x-ray angles. gamma = 0.25 degrees and 3 degrees. It is found that the irradiated layer is volumetrically swelled as compared with the underlying non-irradiated substrate and the volume increase in the irradiated layer is contributed mainly to the irradiated ion fluence.

Design of the IMP microbeam irradiation system for 100 MeV/u heavy ions

A state-of-the-art high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics of the Chinese Academy of Sciences. This microbeam system operates in both full current intensity mode and single ion mode. It delivers a predefined number of ions to pre-selected targets for research in biology and material science. The characteristic of this microbeam system is high energy and vertical irradiation. A quadrupole focusing system, in combination with a series of slits, has been designed to optimize the spatial resolution. A symmetrically achromatic system leads the beam downwards and serves simultaneously as an energy analyzer. A high gradient quadrupole triplet finally focuses a C6+ ion beam to 1 μm in the vacuum chamber within the energy range from 10 MeV/u to 100 MeV/u. In this paper, the IMP microbeam system is described in detail. A systematic investigation of the ion beam optics of this microbeam system is presented together with the associated aberrations. Comparison is made between the IMP microbeam system and the other existing systems to further discuss the performance of this microbeam. Then the optimized initial beam parameters are given for high resolution and high hitting efficiency. At last, the experiment platform is briefly introduced.

Cu Segregation at Σ5 Symmetrical Grain Boundary in α-Fe: Atomic-Level Simulations

Cu-rich precipitation is regarded as one of the main issues causing embrittlement of ferritic steels. In the present work, the Cu segregation at ?5 {012} symmetrical grain boundary (GB) in BCC iron is investigated by combining Metropolis Monte Carlo and molecular statics approaches. The segregation driven energies of Cu clusters decrease with increasing the distance from GB and also depend on the cluster size. The length scales associated with Cu segregation at GB are determined. All these results indicate that Cu atoms prefer to segregate at S5 GB, which may account for the embrittlement of ferritic steels. The present results provide important knowledge to understand the detailed mechanisms of Cu segregation at GB and also the possible effects on mechanical properties of ?-Fe.Cu-rich precipitation is regarded as one of the main issues causing embrittlement of ferritic steels. In the present work, the Cu segregation at Σ5 {012} symmetrical grain boundary (GB) in BCC iron is investigated by combining Metropolis Monte Carlo and molecular statics approaches. The segregation driven energies of Cu clusters decrease with increasing the distance from GB and also depend on the cluster size. The length scales associated with Cu segregation at GB are determined. All these results indicate that Cu atoms prefer to segregate at S5 GB, which may account for the embrittlement of ferritic steels. The present results provide important knowledge to understand the detailed mechanisms of Cu segregation at GB and also the possible effects on mechanical properties of α-Fe.

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.

Raman scattering investigation of C-doped a-SiO2 after high energy heavy ion irradiations

Thermally grown amorphous SiO2 films were implanted at room temperature with 100 keV C-ions to 5.0×1017 or 1.2×1018 ions/cm2. These samples were irradiated at room temperature with 853 MeV Pb-ions to 5.0×1011, 1.0×1012, 5.0×1012 ions/cm2, or with 308 MeV Xe-ions to 1.0×1012, 1.0×1013, 1.0×1014 ions/cm2, respectively. Then the samples were investigated using micro-Raman spectroscopy. From the obtained Raman spectra, we deduced that Si—C bonds and sp2 carbon sites were created and nano-inclusions may also be produced in the heavy ion irradiated C-doped SiO2. Furthermore, some results show that Pb ion irradiations could produce larger size inclusions than Xe ions and the inclusion size decreased with increasing the irradiation fluence. The possible modification process of C-doped a-SiO2 under swift heavy ion irradiations was briefly discussed.

Corrosion related properties of iron (100) surface in liquid lead and bismuth environments: A first-principles study

The corrosion of steels in liquid metal lead (Pb) and bismuth (Bi) is a critical challenge in the development of accelerator driven systems (ADS). Using a first-principles method with a slab model, we theoretically investigate the interaction between the Pb (Bi) atom and the iron (Fe) (100) surface to assess the fundamental corrosion properties. Our investigation demonstrates that both Pb and Bi atoms favorably adsorb on the (100) surface. Such an adsorption decreases the energy required for the dissociation of an Fe atom from the surface, enhancing the dissolution tendency significantly. The segregation of six common alloying elements (Cr, Al, Mn, Ni, Nb, and Si) to the surface and their impacts on the corrosion properties are also considered. The present results reveal that Si seems to have a relatively good performance to stabilize the surface and alleviate the dissolving trend caused by Pb and Bi.