Wurtzite GaN films irradiated at room temperature with 308 MeV 129Xe35+ or 230 MeV 208Pb27+ ions have been studied by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The three-dimensional AFM images showed that swellings of the GaN films were caused by the ion irradiations at very low fluences. In comparison with the Xe ions, the Pb ions led to a much more pronounced swelling. The XPS results indicated that after the Xe and Pb irradiations, the contents of Ga and N dangling bonds in the GaN increased, and the contents of Ga-O and N-O bonds in the surface layer also increased. In the case of the Pb irradiation, a peak associated with the defect of interstitial N was detected in the N 1s core-level spectrum, implying the formation of N2 bubbles close to the GaN surface. However, no homonuclear Ga-Ga bond was found according to the related Ga 3d spectrum. The dramatic experimental results are discussed and the distinct difference of irradiation damages in GaN induced individually by the Xe and Pb ions is analyzed.

The effects of laser incidence angle on lateral fast electron transport at front target surface, when a plasma is preformed, irradiated by intense (>1018 W/cm2) laser pulses, are studied by Kα imaging technique and electron spectrometer. A horizontally asymmetric Kα halo, resulting from directional lateral electron transport and energy deposition, is observed for a large incidence angle (70°). Moreover, a group of MeV high energy electrons is emitted along target surface. It is believed that the deformed preplasma and the asymmetrical distribution of self-generated magnetic field, at large incidence angle, play an important role in the directional lateral electron transport.

The Ti-6Al-4V sheet alloys were welded by using a common gas tungsten arc welding process. In this work, we study the correlation of corrosion resistance and oxide layer structure produced after commonly used industrial heat treatments. We also study the oxide scales that were formed as a result of the heat-related treatment/aging process. The results indicate that better corrosion resistance of the Ti-6Al-4V alloy weldment can be obtained and significantly improved by a solution treatment plus an artificial aging (ST+AA) treatment, owing to the enhanced intensity of TiO2, V2O5, and Al2O3 oxides that compacted and grew on the surface of fusion zone. The newly found γ-TiAl and α2-Ti3Al particles that nucleated in the fusion zone due to different heat treatments do affect the composition of the oxide layer. The possible mechanism for this oxide layer formation in the fusion zone is discussed.

Ceramics with III-IV pyrochlore compositions, A3+2B4+2O7 (A = Y and rare earth elements; B = Ti, Zr, Sn, or Hf), show a wide range of responses to ion-beam irradiation. To evaluate the role of the B-site cations on the radiation stability ofthe pyrochlore structure-type, Gd2Sn2O7 and Gd2Hf2O7 have been irradiated by1 MeV Kr+. The results are discussed in terms of the ionic size and type ofbonding of Sn4+ and Hf4+ and compared to previous results for titanate andzirconate pyrochlores. Gd2Sn2O7 is sensitive to ion beam–induced amorphizationwith a critical amorphization dose of approximately 3.4 displacements per atom(dpa) (2.62 × 1015 ions/cm2) at room temperature and a critical amorphization temperature of approximately 350 K. Gd2Hf2O7 does not become amorphous at adose of approximately 4.54 displacement per [lattice] atom (3.13 × 1015 ions/cm2) at room temperature, but instead is transformed to a disordered fluorite structure upon ion-beam irradiation. Although the radius ratio of the A- to B-site cations provides a general indication of the type of radiation response of different pyrochlore compositions, the results for Gd2Sn2O7 emphasize the importance of bond type, particularly the covalency of the 〈Sn–O〉 bond in determining the radiation response.

The formation of Au nanoclusters in MgO using ion implantation and subsequent annealing was investigated. Approximately 1200 and 1400 Au2+ ions/nm2 were implanted in MgO(100) substrates at 300 and 975 K, respectively. Subsequent annealing in air for 10 h at 1275 K promoted the formation of Au nanostructures in MgO. The sample implanted at 300 K showed severe radiation damage. In addition, two-dimensional plateletlike structures with possible composition of Au and MgO were formed during implantation in the sample that was implanted at 300 K. In contrast, Au implantation at 975 K promoted the nucleation of Au nanostructures during implantation. Subsequent annealing of both samples show three-dimensional clusters in MgO. However, the 975 K implanted sample shows clean, high-quality, single-crystal Au clusters that have an epitaxial relationship to MgO(100).

Au-ions were implanted at RT conventionally and through a mask into TiO2- and SrTiO3-single crystals with doses in the range from 1×1015Au+/cm2 to 1×1017Au+/cm2, and dose rates of ∼1011ions/sec and ∼3×1013ions/sec, at an energy of 260keV; some samples subsequently were annealed at temperatures up to 1100K. The Au-atoms precipitated to nanocrystals during implantation with an average particle size of 1.5nm. HRTEM investigations revealed that the Au-nanocrystals, embedded in amorphous TiO2-regions, have a broad size distribution varying from large sizes in the near surface region to smaller sizes at larger depths. In the annealing process a coarsening and a reorientation of the Au-nanocrystals is observed. At 1000K the particle size of the textured Au-implant was evaluated to be ∼6nm. Implantation with a high dose rate performed through a metal mask with holes of 120μm diameter and without annealing resulted in an almost equidistant arrangement of the Au-nanocrystals with a narrow size distribution of 2–6nm in TiO2 and 3–5nm in SrTiO3 in the near surface region. Au-ion implantation through an e-beam resist mask (50nm × 50nm holes), with doses ranging from 1×1015Au+/cm2 to 4×1015Au+/cm2 at the low dose rate and annealed at 1000K, lead to a periodic structure of the Au-nanocrystals. The nanocrystal size, evaluated from TEM analysis, in the as-implanted state was ∼5nm and after annealing at 1000K sizes of several nanometers to several tens of nanometers were observed.

Electron and ion irradiation-induced nanostructures in an iron phosphate glass with a composition of 45 mol%Fe2O3-55 mol%P2O5 have been characterized by advanced electron microbeam techniques. Analysis by energy-filtered transmission electron microscopy indicated that Fe-rich and P-rich nanophases were formed when the glass was irradiated under a broad (with a diameter of 1.2μm) electron beam [give the dose range]. Phase separation developed with the increase in electron dose (from 1.0×1026e/m2 to 4.8×1026e/m2) as a result of the formation of an Fe-rich phase and pure P-phase. The formation of the Fe-rich and the P-phases are thought to be due to mainly ionization process. Under a low energy ion beam irradiation, Fe/FeO nanoparticles were formed, as confirmed by selected-area electron diffraction analysis. However, no nanoparticles were observed under a high-energy high-dose ion irradiation. The ion beam-irradiation results suggest that the formation of the Fe/FeO nanoparticles was due to preferential sputtering during ion irradiation and that the nanoparticles lie within the surface layers of the glass.

64-keV Ni ion implantation was performed at room temperature up to a dose of 1×1017 cm-2 in α-Al2O3 single crystals. The charge states, structure and optical properties of metallic embedded Ni nanoparticles were studied by using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and optical spectroscopy, respectively. XPS analysis showed that implanted Ni ions are mainly in charge state of metallic Ni0. Nanoparticles distributed from the surface to 30 nm below the surface were observed in a bright-field cross-sectional image. The size of nanoparticles ranges from 1 to 5 nm in diameter. A selected area electron diffraction (SAED) pattern shows Ni nanoparticles with lattice parameter a = 0.352 nm. A high-resolution electron microscopy (HREM) image indicated the Ni-implanted area had been entirely amorphized. A new broad absorption band centered at 400 nm appeared in the optical absorption spectrum of the as-implanted crystal, due to surface plasma resonance (SPR) of Ni nanoparticles.

YSZ and MgAl2O4-YSZ composite are two promising materials as in the inert matrix nuclear fuel for the incineration of plutonium. In this study, 400 keV Cs ions were implanted to a fluence of 1×1017 ions/m2 in both materials in order to investigate the retention behavior of fission product at elevated temperature. The implantations were completed at room temperature for the YSZ and 973 K for MgAl2O4-YSZ, respectively. Subsequent annealing at 1273 K was performed after a room temperature implantation of YSZ. After annealing, a high density of gas bubbles formed with diameter from 3 to 40 nm from the surface to a depth of 150 nm in the YSZ matrix. The swelling due to bubbles formation was estimated to be 2.5%. In situ TEM was employed during high temperature ion implantation of the MgAl2O4-YSZ composite. A high density of small bubbles with 5 nm in diameter formed in the MgAl2O4 and YSZ grains after an ion dose of 1×1017 ions/cm2. There was no preferential precipitation along grain boundaries. Electron Paramagnetic resonance (EPR) spectroscopy was used to investigate the type of defects that formed in the YSZ matrix.

Yttria stabilized zirconia (YSZ) is an important oxygen ion conducting solid electrolyte. YSZ is used in oxygen sensors, oxygen pumps, and fuel cells. Perovskite-type oxides of general formula ABO3 are also of fundamental significance due to their electrical and electro-optical properties. SrZrO3 is a promising material- for application as protonic conductor. in this paper, we present electron microscopy analysis of the formation of SrZrO3 nano-particles in the top surface of YSZ single crystal after ion implantation. These results demonstrate a unique process for obtaining mixed-conducting oxides in the surface layer of YSZ. in addition, it is important to study the behavior of strontium in YSZ because of the potential application of YSZ as an inert fuel matrix for “burning“ excess plutonium in nuclear reactors.

400 keV strontium ions have been implanted into YSZ at room temperature to a fluence of lxl021 ions/m2.

Cesium, iodine and strontium ions have been implanted into yttria-stabilized cubic zirconia (YSZ) to determine the effects of fission product incorporation in YSZ that is considered as an inert nuclear fuel matrix. The ion implantation was conducted at room temperature to 1 × 1021ions/m2 for each ion with ion energies ranging from 70 to 400 keV. The peak displacement damage level and the peak ion concentration in YSZ reached 205-330 dpa and 11-26 at%, respectively. The microstructure of the implanted YSZ was studied by in situ and cross-sectional transmission electron microscopy. In the iodine and strontium implanted samples, a damaged layer with a high density of defect clusters was observed, while in the cesium implanted specimen, the damaged layer is amorphous. Nanocrystalline precipitates were observed in the strontium implanted specimen after annealing at 1000°C. The results are discussedin terms of the ionic size, mobility and the solubility of the implanted species in YSZ.

The long-term radiation effects on materials in the near-field of a nuclear waste repository have been evaluated using accelerated laboratory experiments with energetic electron or ion beam irradiation. The materials studied include: zeolites, layered silicates (smectite clay and mica), as well as crystalline silicotitanate (CST) which is an important ion exchange material for the chemical separation of high-level liquid radioactive wastes.

In situ transmission electron microscopy (TEM) during irradiation by energetic electrons and ions has shown that all of the studied materials are susceptible to irradiation-induced amorphization. At room temperature, complete amorphization was observed after ionizing doses of 1010 ∼ 1012 Gy or displacement doses on the order of 0.1 dpa (equivalent to doses received in 400-1,000 years for a high-loading nuclear waste form). Amorphization may be preceded or accompanied by dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layered silicates, radiation effects are significantly enhanced at higher temperatures. Our experiments have shown that amorphization or even partial amorphization will cause a dramatic reduction in ion exchange and sorption/desorption capacities for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g. zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release of sorbed or ion-exchanged radionuclides.

The solubilities of Hf and Gd in sodium alumino-borosilicate glasses based on the target compositions were examined and confirmed by electron microprobe analysis. The measured compositions of essentially crystal-free glasses are generally homogeneous and close to the target compositions. Therefore, the solubilities of Gd and Hf in sodium alumino-borosilicate glasses based on the target glass compositions are valid. However, for glasses containing precipitates (crystals grown from the melt) and undissolved HfO2 with overgrowths, the chemical compositions are often heterogeneous and may be significantly different from the target compositions. Precipitated crystalline phases include a rare earth silicate with the apatite sructure (NaGd9(Si5.25B)O26) in a gadolinium sodium alumino-borosilicate glass and a HfO2 phase in hafnium sodium alumino-borosilicate glasses.

The objective of this study was to simulate the aqueous corrosion of the nuclear waste glass over extended periods of time using vapor phase alteration by which reaction progress of glass corrosion is accelerated to form a characteristic suite of secondary alteration phases. In this study, extensive SEM/EDS, AEM, and HRTEM have been performed on the French SON68 waste glasses which were reacted in saturated water vapor at 200 °C for 908, 1013, and 1021 days, respectively. In order to study chemistry and microstructure of surface layers, TEM specimens were prepared in cross-section using the ultramicrotomy slicing technique. In this process, small chunks containing the surface layer and a thin layer of unaltered glass were broken off from the sample surface and each of these chunks was then embedded in resin to form a block. Finally, thin sections, approximately 50-90 nm thick, were microtomed from these blocks and were transferred to holey carbon coated copper grids.

Radiation damage in quartz has been of interest to the semiconductor industry, optical fiber industry, and nuclear industry. Cross-section transmission electron microscopy (TEM) is a powerful tool for investigating the irradiation effects since it provides a direct measurement of the ion and the damage distributions, and can also provide detailed microstructural information such as the presence of amorphous regions and the size, density and chemical nature of defect aggregates. The results reported below are from a systematic cross-section TEM study on 1.5 MeV Kr+ ion irradiated quartz.

3-mm discs of quartz (along 010 face) were prepared with 100 μm in thickness. One side for each discs was well polished using a 0.05 μm diamond paste. The well-polished side was irradiated at room temperature with 1.5 MeV Kr ions in the HVEM-Tandem Facility at Argonne National Laboratory. Following irradiation, cross-section TEM specimens were prepared using the so-called T-tool technique, a modified tripot technique

Ion-irradiation induces amorphization in many intermetallics and ceramics, but spinel (MgAl2O4) is considered a “radiation resistant” ceramic. Spinel was irradiated with 1.5 MeV Kr+ at 20 K and observed in situ by transmission electron microscopy (TEM). The spinel remained crystalline to a high dose of 1 × 1016 ions/cm2, without any evidence of amorphization. Another spinel was preimplanted with Ne (400 keV and 50 keV). The microstructure revealed a still crystalline material with 8 nm interstitial loops. After irradiation with 1.5 MeV Kr+ (20 K), amorphization, a result of cation disordering, initiated at a dose of 1.7 × 1015 ions/cm2. At a dose of 1 × 1016 ions/cm2, the spinel was partially amorphous and the remaining crystalline domains disordered. These results show that spinel can be disordered and that amorphization can be triggered by the introduction of stable defects, followed by ion irradiation at low temperature.

The roles of irradiation temperature and interfaces (free surfaces and grain boundaries) in irradiation- and thermally- induced amorphization of ceramics (coesite, apatite, olivines and spinels) have been studied by transmission electron microscopy (TEM). The irradiations were performed with 1.5 MeV Kr+, 200 keV and 1 MeV electrons over a wide temperature range (20-700 K). The critical amorphization dose at which amorphization is complete, Dc, increased with increasing irradiation temperature for most materials except coesite (a high pressure polymorph of Si02) which showed a decreasing Dc with increasing temperature under 1 MeV electron irradiation. Although amorphization may occur directly within a displacement cascade or by cascade overlap, this study shows that free surfaces and grain boundaries are favorable sites for nucleation of amorphous volumes. Once the amorphous volume is formed at interfaces, it may grow rapidly under continued irradiation. Coesite which has a glass transition temperature higher than its melting temperature underwent spontaneous amorphization during thermal annealing at 1200 K. This thermally-induced amorphization also started at free surface and grain boundaries and propagated into the interior of the crystal. The interface-mediated amorphization is analogous to the process of thermodynamic melting.