Flakes of CVD grown BxC1-x, (x<0.2) films were exposed to intense electron irradiation (flux density up to ∼100 A/cm2) in a 300 kV high resolution electron microscope equipped with a field emission gun. The starting flakes revealed a turbostratic BxC1-x structure. The composition of the starting materials and irradiated products was determined by using electron energy loss spectroscopy (EELS). Depending on the electron dose applied, irradiation of the turbostratic material led to formation of soap-bubble-like irregularly-shaped objects (linear dimensions of ∼2–5 nm), onion- and semi-onion-like structures (d∼10nm), nested fullerenes (3–14 shells) and elementary fullerene-type cages (d∼0.7 nm). It is thought that these curled and closed nanostructures arise from a continuous bending of the hexagonal Bx C1-x sheets under electron irradiation. Finally, some possible structural models of BxC1-x fullerenes are considered.

We use a new broadband spectroscopic technique to measure ultrafast changes in the dielectric function of a material over the spectral range 1.5–3.5 eV following intense 70-fs laser excitation. The results reveal the nature of the phase transformations which occur in the material following excitation. We studied the response of GaAs and Si. For GaAs, there are three distinct regimes of behavior as the pump fluence is increased — lattice heating, lattice disordering, and a semiconductor-to-metal transition.

Several perovskite-structure oxide compounds, including CaTiO3, SrTiO3, BaTiO3, KNbO3, and KTaO3 were irradiated by 800 keV Kr+ ions in order to investigate and compare their response to heavy-ion irradiation. The critical amorphization temperature Tc, above which amorphization could not be induced, was found to increase in the order SrTiO3 → CaTiO3 → BaTiO3 → KNbO3 → KTaO3. No single physical parameter explains the observed sequence, although Tc correlates well with the melting temperatures. The well-known solid state phase transformations in these materials did not have a significant effect on the dose required for amorphization. Domain boundaries were observed in the pristine samples; however, after only a low dose, the boundaries became poorly defined and, with increasing dose, eventually disappeared. Dislocation loops were observed to aggregate at the domain boundaries.

Buried SiC layers were synthesized by carbon implantation into silicon with a metal vapor vacuum arc ion source under various implantation and annealing conditions. The infrared absorption spectra of these samples were deconvoluted into two or three gaussian components depending on the preparation conditions. One component peaked at around 700 cm-1was assigned to amorphous SiC (a-SiC). The other two components, both peaked at 795 cm-1 but with different values of full width at half maximum (FWHM), were attributed to β-SiC. The one with a larger (smaller) FWHM corresponds to β-SiC of smaller (larger) grains. With this deconvolution scheme, the fraction of various SiC phases in these samples were determined. It was found that for the as-implanted samples there are critical energies and doses at which the crystalline SiC fraction increases abruptly. This was attributed to the ion beam induced crystallization (IBIC) effect. It was also shown that the IBIC effect leads to strong dependence of the β-SiC fraction on the order of implantation for samples synthesized by double-energy implantation. Analysis of the evolution of the β-SiC fraction with annealing time indicated that the crystallization process in these SiC layers could well be described by the classical random nucleation and growth theory.

Glass-bonded zeolite is being considered as a candidate ceramic waste form for storing radioactive isotopes separated from spent nuclear fuel in the electrorefming process. To determine the stability of glass-bonded zeolite under irradiation, transmission electron microscope samples were irradiated using high energy helium, lead, and krypton. The major crystalline phase of the waste form, which retains alkaline and alkaline earth fission products, loses its long range order under both helium and krypton irradiation. The dose at which the long range crystalline structure is lost is about 0.8 dpa for helium and 0.1 dpa for krypton. Because the damage from lead is localized in such a small region of the sample, damage could not be recognized even at a peak damage of 50 dpa. Because the crystalline phase loses its long range structure due to irradiation, the effect on retention capacity needs to be further evaluated.

Zircon (ZrSiO4) is an actinide host phase in vitreous ceramic nuclear waste forms and a potential host phase for the disposition of excess weapons plutonium. In the present work, the effects of 800 and 900 keV electron, and 1 MeV Ne+ irradiations on the structure of single crystals of ZrSiO4 have been investigated. The microstructural evolution during the irradiations was studied in situ using a high-voltage electron microscope interfaced to an ion accelerator at Argonne National Laboratory. The results indicate that electron irradiation at 15 K cannot amorphize ZrSiO4 even at fluences an order of magnitude higher than that required for amorphization by 1.5 MeV Kr + ions. However, the material is readily amorphized by I MeV Ne+ irradiation at 15 K. The temperature dependence of this amorphization is discussed in light of previous studies of radiation Zdamage in ZrSiO4.

Elemental Zr-Al-Ni-Cu foils of bulk glass forming composition were cold rolled at ambient temperature. The phase transformations during the cold deformation process were monitored with electron and X-ray diffraction and thermal analysis. After 120 deformation cycles a fully amorphous sample was obtained, as indicated by a distinct endothermic glass transition and a large exothermic crystallization reaction. The characteristics of the amorphous phase are compared with a liquid quenched metallic glass and mechanically alloyed elemental powder mixtures of similar composition. The amorphization reaction during cold rolling is similar to mechanical alloying and proceeds by the formation of a fine layered structure of the constituents, a rapid reduction of the layer thickness and of the average grain size to a nanometer scale and dissolution reactions in the hcp Zr lattice. While in the beginning of the cold rolling process the elemental foils were ductile, after several rolling passes the multilayered sample became brittle and, finally, displayed large elastic flexure in the amorphous state. Several thermal treatments of the multilayered and amorphous samples were performed in order to study thermally activated solid-state amorphization reaction as well as phase formation during crystallization.

Zr100−xAlx powder blends have been subjected to ball milling at different temperatures to investigate the amorphization process. At low temperatures the Zr-Al solid solutions amorphized under the polymorphous constraints, whereas at higher temperatures there was an obvious twophase coexistence region. The Al concentration for the complete amorphization of Zr-Al increased with increasing temperature, suggesting a re-entrant melting behavior. Both of the temperature- and composition-dependent amorphization mechanisms are analyzed in terms of the thermodynamic properties of the phases involved, as well as the dynamic effects brought in by the non-equilibrium milling process.

Phase evolution during ball milling of Si in NH3 gas and during subsequent annealing has been studied and compared with nitride formation during ion bombardment of Si. X-ray diffraction, differential thermal analysis, Rutherford backscattering and channeling, combustion analysis and transmission electron microscopy have been used as analytical techniques. Results have shown that an amorphous SixNy(Fe) phase forms during milling which transforms into α-Si3N4 and FeSi2 on annealing. During ion bombardment, slightly N-rich Si3N4 is formed but it is mostly crystalline at temperatures between 150 and 450°C.

Changes in transverse phonon sound velocity were measured during low temperature irradiation of amorphous Pd80Si20 with 3.5 MeV krypton ions. The sound velocity decreases as a function of the ion fluence and shows a tendency to saturate at large fluences at a relative change of −4.7%. The changes in sound velocity were used to determine the changes in shear elastic constant and in Debye temperature both of which were in reasonable agreement with the value reported in the literature.

A molecular-dynamics simulation with an n-body potential was performed to study solid-state amorphization in the Ni-Zr system upon annealing at medium temperatures ranging from 300 to 600 °C. The models for simulation were a Zr-Ni-Zr sandwich consisting of both hcp Zr and fcc Ni (001) atomic planes and a bilayer with a thin preset disordered interfacial layer, respectively, for revealing the detailed amorphization process and the growing kinetics of an amorphous layer upon solid-state reaction. Our simulation results demonstrated, for the first time, that the atomic process proceeded through first diffusion, then alloying and eventually amorphization. In other words, amorphization was controlled by a diffusion-limited reaction and the growth kinetics of the amorphous layer followed exactly a t1/2 law. Another interesting finding was that the growing speeds of the amorphous layer exhibited an asymmetric behavior, i.e. the amorphous layer extended faster towards Ni lattice than that directed to Zr side. Besides, it was also found that an initiation of amorphization upon annealing was dependent to the interfacial textures, i.e. amorphization could take place when the interfaces were composed of the more open atomic planes, whereas it was suppressed if the interfaces were constructed with the close-packed planes of both lattices.

The objective of this work is to study the crystallization process of the amorphous ribbon of NiTi-Cu based shape memory alloys. An amorphous material with a composition of Ti50Ni25Cu25 was used to conduct this study. First, a study was conducted to understand the crystallization kinetics of this amorphous material at the isothermal model and continuous heating mode, respectively. The characteristic parameters associated with the crystallization process, such as the start and finish time for isothermal crystallization, the peak temperature for continuous heating crystallization, and activation energy, are obtained. Based on the study of experimental data of crystallization kinetics, a series of isothermal annealing experiments was conducted to study the crystallization process and microstructure of fully crystallized materials. The TEM micrograph shows the crystal phase growths in the amorphous matrix as a perfect geometric sphere. A system analysis was conducted to explain the crystallization micro-mechanism.

Conventional and high-resolution cross-sectional TEM observations have been carried out on Si-, As- and BF2-implanted, bonded 100-nm-thick (001) SOI layers having polycrystalline Si (poly-Si) masks followed by annealing at 600°C. Amorphized SOI layers by these ion implantations are recrystallized through lateral solid-phase seeding epitaxy (L-SPE) by single crystal SOI under the poly-Si mask as a seed. The recrystallization of these SOI layers is completed in the order of BF2-, Si- and As-implanted layers by <110>-directed L-SPE, although the recrystallized layers have a high-density of {111}twins due to {111} facet formation at the growth front occurring during the first 30 s of annealing, independent of implanted ions. On the other hand, in the case of <100>-directed L-SPE, the growth of {110} faceted regions progresses after annealing for a few tens of minutes before folded {111} facets are formed, resulting in a good crystal quality region of 0.1∼0.2μm remaining, measured from the mask edge.

We present differential scanning calorimetry (DSC) and in situ Mössbauer spectroscopy results for Metglas ribbons, to which different heat treatments were made. The Curie temperature of the amorphous phase is determined and the evolution of the magnetic field of this phase is studied as a function of temperature.

In-situ TEM investigations during thermal treatment of amorphous Pd81Si19 have been performed. It was found that crystalline nuclei are formed near the perforation edge of the hole produced by electrochemical polishing. After impinging with neighboring crystals, a crystallization front formed which was aligned parallel to the perforation edge. The crystallization front moved in the direction perpendicular to the perforation edge. Crystal growth was found to proceed faster in thinner parts of the specimen than in thicker parts. The results are described qualitatively within a thermodynamic model taking into account volume-, surface- and interfacial free energies and an appropriate specimen geometry.

We report our findings on the sintering kinetics of slip-cast glass-ceramic coatings on rigid substrates at temperatures between 900°C and 1000°C; the glass-ceramic crystallizes into cordierite at sintering temperatures above 900°C. Changes in coating thickness during sintering were monitored in situ using an optical setup, and the crystallization of the coatings was determined by x-ray diffraction. The coatings went through a rapid shrinkage due to initial densification, followed by an expansion stage caused by the transformation of the glass into a crystalline phase with a lower density. The rate and extent of the expansion were more noticeable at sintering temperatures above 900°C. We also found that wetting between the glass-ceramic and the substrate was important to the sintering kinetics and sintered microstructure of the coatings. For coatings formed on silicon substrate, growth of large pores was observed at the glass-ceramic/silicon interface. Using wafer-curvature measurement technique, we found a significant tensile stress build-up in the coatings during the initial stage of sintering. We believe that the combination of poor wetting and the tensile stress build-up led to the observed desintering phenomenon at the glass-ceramic/silicon interface.

The influence of Mo atoms on the solid phase epitaxial crystallization of amorphous silicon layers on (100) and (111) Si substrates has been studied by RBS/channeling and cross-sectional TEM. For this purpose, Mo doped amorphous surface layers were produced by low temperature 180 keV Mo+ ion implantation with different doses. Mo is observed to cause enhanced crystallization rates for both (100) and (111) substrates, compared to literature data on pure amorphous silicon. Similar to pure Si, recrystallization in <100> directions is much faster than in <111> directions, where two different velocities are found. For (111) substrates, the formation of thick, uniformly twinned layers is observed. Annealing for several hours at 550° C does not lead to detectable changes of the Mo depth distribution, but for high doses the formation of hexagonal MoSi2 precipitates is observed.

Mössbauer spectroscopy, coercive field and permeability were used to study the transformations produced by annealing at 375°C as-quenched amorphous ribbons of Metglas® 2605 SC of nominal composition Fe81B13.5Si3.5C2. The coercive field showed a decrease (softening) in the 0-30 min range, followed by an increase (hardening) for annealing times above 30 min. Permeability exhibited the opposite behavior, with a maximum for about 30 min. The Mössbauer magnetic hyperfine spectra showed variations in the intensities ratios, which were related with macroscopic measurements in good agreement with the softening-hardening processes.

We have fabricated Se nanoparticles in silica substrates by ion implantation followed by thermal annealing up to 1000°C, and studied the Se nanoparticle formation by optical absorption spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and transmission electron microscopy. The sample with the highest dose (1 × 1017 ions/cm2 ) showed the naonparticle formation during the ion implantation, while the lower dose samples (1 and 3 × 1016 ions/cm2) required thermal treatment to obtain nano-sized particles. The Se nanoparticles in silica were found to be amorphous. After thermal annealing, the particle sizes became larger than the exciton Bohr radius for bulk Se. Thus, the absorption edges for different doses approached the value of bulk after thermal annealing. The temperature dependent absorption spectra were also measured for this system in a temperature range from 15 to 300 K.

In multiphase materials systems involved in coatings, composites or multilayered structures, diffusion treatments often results in the development of intermediate phases at the reaction interfaces. While diffusional growth of phases has received much attention, the initial phase evolution involves a nucleation stage as well. The development of metastable phases during solid state interdiffusion demonstrates that the nucleation reaction can be controlling in some cases. For alloy systems with extensive solubility, intermediate phase nucleation is proceeded by interdiffusional mixing in order to achieve the required supersaturation. This leads to the identification of a critical concentration gradient for the onset of phase nucleation.The concentration gradient and the relative magnitudes of the component diffusivities provide a basis for a phase selection strategy and the application of a kinetic bias to modify the phase selection. For multicomponent alloy systems, the identification of the operative diffusion pathway is central to the control of phase formation. Experimental access to the nucleation stage of reaction is facilitated in thin film multilayer samples where the results from systems with both extensive and limited solubility offer new insight into the phase formation kinetics.