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The lattice constant and the magnetic state of CeO2 are modified by the irradiation with 200 MeV Xe ions. Under the assumption that these modifications are induced in the narrow one-dimensional region (the ion track) along the ion beam path, the dependence of the lattice constant and the saturation magnetization of CeO2 on the Xe ion fluence was analyzed by using the Poisson distribution function. The analysis reveals that the lattice constant inside the ion track, which is larger than that outside the ion track, is not affected by the overlapping of the ion track. On the other hand, the ferromagnetic state is induced inside the ion track, but the analysis shows that this ferromagnetic state is gradually destroyed due to the overlapping of the ion track. The present result implies that the Poisson distribution function is useful for describing the effect of the ion track overlapping on the ion irradiation-induced ferromagnetic state in CeO2.

NiTi bulk intermetallic compound with the B19′ structure was irradiated with 1 MeV He, 5 MeV Al, 16 MeV Au and 200 MeV Xe ions, and the change in lattice structure near the surface by the ion bombardment was investigated by using the grazing incidence X-ray diffraction (GIXD) and the extended X-ray absorption fine structure (EXAFS). The lattice structure transformation by the irradiation strongly depends on ion species and/or energies. For the 1 MeV He irradiation, the lattice structure changed from B19′ to the A2 structure, but did not show an amorphization even after the high fluence irradiation. For the 5 MeV Al irradiation, the samples are partially amorphized. For the 16 MeV Au irradiation, the lattice structure of the NiTi samples changed nearly completely from the B19′ structure to the amorphous state via the A2 structure. The value of dpa (displacement per atom) which is needed for the amorphization is, however, much smaller than the case of the Al ion irradiation. For the 200 MeV Xe ion irradiation, the lattice structure completely changed to the A2 structure even by a small ion fluence. The dependence of the lattice structure transformation on elastic collisions (dpa), the spectrum of the primary knock-on (PKA) atoms and the density of energy deposited through electronic excitation was discussed.

We developed a one-pot preparation method of Pd nanoparticles (NPs) supported on graphene (Pd/G) by using Pd electrode plasma treatment of aqueous KCl solution containing graphene. It was found that Pd NPs were formed from the Pd electrodes during the plasma treatment and they were supported on graphene. The number of Pd NPs on graphene increased with increasing plasma treatment time, but the size of the Pd NPs was almost the same among different plasma treatment time. From the results of FT-IR and Raman spectra of the products, the formation of C O and defect on graphene were confirmed. The prepared Pd/G showed a superior catalytic activity for the hydrogenation of nitrobenzene to aniline to Pd NPs on α-Al 2 O 3 , which was prepared by the same plasma method in the presence α -Al 2 O 3 instead of graphene.

Structural relaxation behavior of various composition for Zr-Cu-Al ternary bulk amorphous alloys (hyper-eutectic: Zr 45 Cu 45 Al 10 and Zr 49 Cu 41 Al 10 , eutectic: Zr 50 Cu 40 Al 10 , hypo-eutectic: Zr 55 Cu 35 Al 10 and Zr 60 Cu 30 Al 10 ) during isothermal annealing below glass transition temperature ( T g ) has been investigated by positron annihilation techniques (positron lifetime and coincidence Doppler broadening (CDB)), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and bulk density measurements. The annealing makes the positron lifetime decrease owing to the relaxation. However, maximum decreasing of positron lifetime after 10 ks annealing for eutectic alloy was observed. And different composition dependence of positron change between hypo- and hyper-eutectic alloys was confirmed. Especially, open-volume in hyper-eutectic alloys is hard to change by the annealing. We found that the trend of positron lifetime change Δτ with Zr concentration is not necessarily correlated with the change in bulk density consistently. On the other hand, the positron lifetime during annealing obeys a stretched exponential relaxation function. Also we found the relaxation parameter β , which indicates the distribution activation energy for open-volume relaxation, varies in Zr concentration.

It is well known that intermetallic compound alloys possibly include more than two types of vacancies basically, that is A-vacancy and B-vacancy in A-B compound alloy. Although MeV ordered electron irradiation produces vacancies and interstitials, the threshold energy of displacement for each elemental atom in intermetallic alloys is not necessarily same. Then the defect type introduced by the irradiation depends on electron energy. In this study, we performed positron annihilation lifetime and Doppler broadening measurements for different energy of electron irradiated B2 type Fe50%Al alloy. The values of positron annihilation lifetime for this alloy after 2 and 9 MeV electron irradiation were 200 and 172 psec, respectively. Also, the Doppler broadening parameters S and W show difference for this alloy with different energy of electron irradiation. These results suggest that different types of vacancy were induced into Fe-Al compound alloy by electron irradiation with different energies.

The Zr-Cu-Al bulk amorphous (BA) alloys, which have no long-range ordered structure, possess various properties such as high strength and toughness with compositional dependence. In the present study, in order to estimate the natures of local structure change and relaxation behavior of hyper-eutectic BA alloys during annealing, positron annihilation measurements and density measurement have been performed for hyper-eutectic Zr-Cu-Al BA alloys with annealing. The enthalpy relaxation and structural relaxation was also measured by differential scanning calorimetry (DSC) measurement. These results show that the relaxation process of free volume containing in hyper-eutectic BA alloys is different from that in hypo-eutectic alloys.

Electrical resistivity measurement is a useful experimental method for investigating the recovery of defects that are induced by irradiation in metals and alloys. In this study, an Fe-0.6%Cu alloy, used to model steel from old commercial reactor pressure vessels, was irradiated by neutrons at a low temperature range of 14–19 K with a dose of about 1.3 × 1020 neutrons/m2 (E > 0.1 MeV) in the Kyoto University Reactor (KUR); electrical resistivity measurement was performed during irradiation and after annealing of the irradiated sample from 20 K to 300 K to investigate the migration of point defects in the Fe-0.6%Cu alloy. The electrical resistivity was measured at 14–19 K. With the increase in the irradiation dose, the electrical resistivity increased linearly. Four peaks appeared at 70 K, 100 K, 150 K, and 260 K, in the change of electrical resistivity during annealing of the irradiated sample up to 300 K. The former two peaks were caused by the recombination of interstitials and vacancies, and the latter two peaks were caused by the formation of interstitial clusters and the migration of vacancies. Compared with previous electron irradiation results, the former two peaks represent new data, as does the ratio of recombination caused by close-pair and correlation to that caused by migrations of mixed-interstitials Fe–Cu and vacancies decreased in neutron irradiation.

We developed a one-step gamma-ray irradiation method to synthesize nanocomposites composed of graphene and Pt nanoparticles from aqueous solution containing graphene and Pt(IV) complex ions in the presence of 2-propanol (IPA) or sodium dodecyl sulfate (SDS). It was confirmed that gamma-ray irradiation provided carbonyl groups on graphene and Pt nanoparticles formed from the radiolytic reduction of Pt(IV) complex ions were deposited onto the carbonyl modified graphene. In the presence of IPA, small Pt nanoparticles were deposited on graphene, but large Pt nanoparticles were deposited in the presence of SDS: the size of Pt nanoparticles formed was larger in the presence of SDS than IPA. Based on the results, formation and deposition mechanisms of Pt nanoparticles were proposed.

Silica glass samples were implanted with 50-380 keV Ag ions. After ion implantation, some samples were subsequently irradiated with 16 MeV Au ions. The effects of the implantation and the subsequent Au ion irradiation on the optical absorption spectra and morphologies of the Ag nanoparticles produced in the samples were studied by using an ultraviolet-visible scanning spectrophotometer and a transmission electron microscope, respectively. For the samples implanted with 200 keV or 380 keV Ag ions to high fluence, optical absorption peaks appeared around 600 nm, as well as the well-known surface plasmon resonance peaks around 400 nm, and Ag spherical nanoparticles with a high spatial density were observed. The absorption peaks around 600 nm are explained as being due to interactions between the Ag nanoparticles (inter-particle interaction). Under the subsequent irradiation with 16 MeV Au ions, the optical absorption around 400 and 600 nm showed a blue shift and the peak intensity markedly decreased. Transmission electron microscopy observation revealed an elongation of the Ag nanoparticles along the direction of the 16 MeV Au irradiation, and a resulting enlargement of the distances between the nanoparticles. The change in the peak wavelength and peak intensity of the optical absorption by the 16 MeV Au irradiation can, therefore, be explained as originating from a decrease in inter-particle interaction.

The Ni 3 Al bulk intermetallic compound was irradiated with 5.4-MeV Al, 10-MeV I and 16-MeV Au ions at room temperature. The effect of irradiation on the lattice structure was observed by X-ray diffraction (XRD). The change in Vickers hardness by irradiation was estimated. A crystal structure analysis showed that, the Ni 3 Al lattice structure transforms from an ordered L1 2 lattice structure to a disordered A1 (fcc) lattice structure by energetic ion irradiation. The relative degree of order correlates well with the density of energy that was elastically deposited by irradiation. The Vickers hardness tends to decrease with an increase in ion fluence. The hardness is not correlated with the elastically deposited energy. The effect of annealing at elevated temperatures on the irradiation induced crystal phase transformation and the Vickers hardness is also discussed.

The extended X-ray absorption fine structure (EXAFS) measurement is a useful tool for the observation of local atomic arrangements around selected atoms. We performed EXAFS measurements for the electron-irradiated and the thermally-aged Fe–0.6 wt.% Cu alloy and compared the experimental result with that of the simulation by the FEFF simulation code in order to investigate the local atomic structure around Cu atoms. Cu precipitates which were produced by the thermal aging at 773 K transformed from the bcc structure to the fcc structure as the precipitates grow large enough. However, for electron-irradiated specimens, although the hardness greatly increased, the transformation of Cu precipitates from the bcc to the fcc structure was not clearly confirmed. This result indicates that small sized Cu precipitates which had the bcc structure were produced by the electron irradiation and they could hardly coarsen during the irradiation.

So far, we have irradiated Al–Mg–Si alloy with 5.4–16 MeV several ions at room temperature, and have found that ion irradiation is a useful tool for controlling the surface hardness for Al–Mg–Si alloys. In the present study, we tried several experiments as some applications of ion beam irradiation for hardness modifications of Al–Mg–Si alloy. Main results are as follows; (1) the combination of ion beam irradiation and the subsequent thermal aging can be used as an effective tool for the hardness modification of Al–Mg–Si alloy, and (2) designated regions and areas of the specimen can be hardened by changing the energy of ion beam and producing the irradiated area and unirradiated area of the surface. Then, we can expand the possibility of the ion beam irradiation as a new process for the three-dimensional hardness modification of Al–Mg–Si alloy.

Cu–Ti alloys were irradiated with 5.4 MeV Al ions, 7.3 MeV Fe ions, 10 MeV I ions, and 16 MeV Au ions at room temperature and the Vickers microhardness was measured. The hardness once increases by the irradiation with a low fluence, and then it remains almost constant even with increasing the ion fluence. The change in hardness was well correlated with the density of energy deposited through the elastic collisions and not the electronic excitation. The observation of atom probe tomography (APT) did not show any Ti clusters in the irradiated specimens. This result suggests that not Ti clusters but lattic defects (interstitial atoms, vacancies and/or their aggregates) contributed to the increase in hardness of Cu–Ti alloys.

We studied the change in crystal structure of 200 MeV Xe and 10 MeV I ion irradiated CeO2 thin films by means of X-ray diffraction (XRD). The experimental result showed that the average lattice parameter of CeO2 decreased and the full width at half maximum increased by the ion irradiation. Their changes are well correlated with the electronic stopping powers for I and Xe ions. The dependence of lattice parameter on the electronic energy loss was analyzed by using the Poisson’s law, and the radii of the regions affected by the irradiation were determined.

Al–Mg–Si alloys were irradiated with 5.4 MeV Al ions, 7.3 MeV Fe ions, 10 MeV I ions, and 16 MeV Au ions at room temperature and the Vickers microhardness was measured. The hardness of Al–Mg–Si alloys increases with increasing the ion fluence. In a viewpoint of ion fluence, hardness change of the Al alloys is different by the kind of irradiating ions. But, in a viewpoint of the density of elastically deposited energy, the effect of the four kinds of them on hardness is almost the same. This result means that the effect of irradiation on hardness of Al–Mg–Si alloys is dominated by the elastically deposited energy. The microstructure of the ion-irradiated specimens were investigated by means of three-dimensional atom probe (3DAP). The experimental result was compared with the microstructure and the hardness for thermally aged specimens. We also discuss the difference in ion-irradiation induced change in hardness between Al–Mg–Si alloys and Al–Cu–Mg alloys (duralumin).

We have studied the magnetic properties of pure CeO 2 irradiated with swift heavy ions. Experimental results showed that the ferromagnetism was induced even at room temperature by 200 MeV Xe ion irradiation. The value of saturation magnetization, M s , systematically changes as a function of ion-fluence. The value of M s increases with increasing the ion-fluence and reaches a maximum value at about the fluence of 2.0 × 10 13 /cm 2 , and then decreases. The X-ray diffraction (XRD) spectra show that the lattice constant of CeO 2 increases with increasing ion-fluence. This result and our previous XPS result show that the ion-irradiation produced oxygen vacancies. The present study implies that the ferromagnetic behavior of the ion-irradiated CeO 2 is attributed to the magnetic moments of localized 4f electrons on Ce 3+ atoms, which are related to oxygen vacancies.

To study the effects of Gd 2 O 3 -doping and the irradiation with high energy fission products in the nuclear fuels (UO 2 ), Gd 2 O 3 -doped CeO 2 pellets, which are simulation materials of UO 2 , were irradiated with 200 MeV Xe 14+ ions. Effects of Gd 2 O 3 -doping and the ion irradiation were estimated by using Extended X-ray Absorption Fine Structure (EXAFS) measurement. The interatomic distances between each Ce and the first nearest O atoms, and Ce and the second nearest Ce atoms increase by the irradiation and the effect of the ion irradiation on the atomic distances is more pronounced for higher amounts of dopant. The Debye–Waller factors for Ce–O and Ce–Ce pairs increase with increasing the amount of Gd 2 O 3 dopant. These results suggest that the lattice binding energy is weakened by Gd 2 O 3 -doping. The Debye–Waller factors increase also by the irradiation. The effect of ion irradiation on the Debye–Waller factors, however, becomes smaller for higher amounts of dopant.

So far, we have found that the hardness of Al–Cu–Mg alloy (JIS2017, Duralumin) increases by energetic heavy ion irradiation at room temperature. Observations by using the three-dimensional atom probe (3DAP) have revealed that nano-meter sized precipitates are homogeneously distributed in the irradiated specimens, which are produced through the irradiation enhanced diffusion of solute atoms. The small precipitates contribute to the increase in hardness. In this report, we show the results for the hardness modification of Al–Cu–Mg alloy by the combination of energetic ion irradiation and thermal aging treatment. The hardness of the specimens pre-irradiated and thermally aged at 423 K is much larger than that without the pre-irradiation. The present result indicates that the combination of energetic ion irradiation and subsequent thermal aging can be used as an effective tool for the hardness modification of Al–Cu–Mg alloy.

Fe48-at.%Al alloy were implanted with 50 keV H+ ions to the fluence of 3×1016 and 1×1018/cm2 at room temperature. Positron annihilation Doppler broadening and lifetime measurements for these alloys have been carried out using slow positron beam apparatus with an energy range of 0.2 to 30.2 keV. The positron annihilation S-parameter decreased by H+ ion irradiation. Also the positron lifetimes for hydrogen deposited region in the alloy decreased by the irradiation. These results show that implanted H atoms were trapped by vacancy type defects.

To simulate the effects of Gd 2 O 3 -doping and high-energy fission products in UO 2 , Gd 2 O 3 -doped CeO 2 pellets were irradiated with 200-MeV Xe 14+ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO 2 decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd 2 O 3 -dopant levels. Our results are compared with those of a study involving Er 2 O 3 -doped CeO 2 .

Effects of thermal annealing on ion-irradiation induced ferromagnetism of Fe–50at.%Rh bulk alloy and the related structural change were investigated by means of superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS), respectively. Depending on the annealing temperature from 100 to 500 °C, the magnetization induced by 10 MeV iodine ion irradiation and the lattice structure of the alloy were remarkably changed. After 500 °C annealing, the magnetization and the lattice ordering of the alloy become similar to the states before the irradiation. The experimental result indicates that the thermal relaxation of irradiation-induced atomic disordering dominates the magnetic state of ion-irradiated Fe–50at.% Rh alloy.

We irradiated Al–Cu–Mg alloy with 10 MeV iodine ions at room temperature and measured the surface microhardness. We analyzed the microstructure using a three-dimensional atom probe. Irradiation for 3.5 h led to an increase in hardness comparable to that obtained after 4 days of aging at 423 K. Precipitates of about 2.9 nm in diameter were distributed homogeneously over the irradiated region. The nanometer-sized precipitates produced by the irradiation caused a remarkable increase in hardness.

To simulate the effects of burnable poison doping in nuclear fuel UO 2 , Er 2 O 3 (or Gd 2 O 3 )-doped CeO 2 pellets were prepared. Changes in lattice constant and atomic disordering for CeO 2 due to the Er 2 O 3 and Gd 2 O 3 doping were measured by means of XRD and XAFS. By the Er 2 O 3 doping, the lattice constant decreased, and a disordering of lattice structure was induced in the samples. The doping with Er 2 O 3 also induced the disordering of atomic arrangement around Er atoms, which was observed through the change in XAFS spectra. In contrast, the effect of Gd 2 O 3 doping was smaller than that of Er 2 O 3 doping. The result was discussed in terms of ionic size of dopants in CeO 2 crystal.

In order to simulate the effects of burnable poison doping on the fission fragment damage of UO2 nuclear fuels, Er2O3-doped CeO2 pellets were irradiated with 200 MeV Xe14+ ions. The irradiation effect was measured by means of X-ray diffraction (XRD). The expansion of lattice and the disordering of atomic arrangement due to the irradiation become more remarkable with increasing the concentration of the Er2O3 dopant.

The relaxation and crystallization behaviors of the ternary Zr 50 Cu 40 Al 10 bulk metallic glass were investigated by the positron annihilation measurements and the extended X-ray absorption fine structure (EXAFS) analysis at the Zr K-edge. The result of positron annihilation coincidence Doppler broadening (CDB) for as-prepared specimen suggests that the fraction of Zr atom around free volume is greater than that of composition for alloy system. According to the results of CDB spectrum and Fourier transformed EXAFS spectrum, the isothermal annealing below the glass transition temperature ( T g ) (structural relaxation) decreases the size of free volume, but it causes little change in the distribution of atoms, either around free volume or around Zr atoms. For the isothermal annealing above crystallization temperature ( T x ), the XRD and EXAFS spectra clearly show the crystallization of specimens. The CDB result also suggests the crystallization. These results demonstrate that the chemical order around free volume is dissociated, and crystallized order is newly formed during the thermal annealing above T x .

Zr-based bulk glassy (BG) alloys show high tensile strength and a high Charpy impact value. In this study, the free volume changes for the hypoeutectic Zr60Cu30Al10 BG alloy during isothermal annealing below glass transition temperature (Tg) have been investigated by positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements. The positron lifetime of hypoeutectic and eutectic BG alloys is almost the same, although the atomic volume ratio, estimated by the density for the eutectic BG alloy is different from that for the hypoeutectic BG alloy. The CDB spectra show a marked difference between eutectic and hypoeutectic BG alloys; that is, the spectrum of the hypoeutectic BG alloy is closes to that of Zr metal than that of the eutectic BG alloy. This result exhibits that the elemental fraction of Zr atoms around free volume in hypoeutectic BG alloy is greater than that in eutectic BG alloy. The CDB ratio profiles for the hypoeutectic BG alloy during annealing shows no appreciable change. The same trend was observed in the eutectic BG alloy.

We performed first-principles calculations of stable atomic structure and partial density of states (PDOS) analysis of Ethylene (C2H4) adsorption on Pd(100) surface stacked on fcc-Au using the projector augmented-wave (PAW) method. In case of Pd overlayers on the Au(100) substrate, from the analysis of PDOS around surface, highest occupied states become sharpen compared with the case of C2H4 adsorption on Pd monometallic slab surface in both di- and  adsorption model.

It has been reported that heavy ion irradiation causes softening in some cases of Zr-based bulk metallic glass alloys. However, the fundamental mechanisms of such softening have not been clarified yet. In this study, Zr50Cu40Al10 bulk glassy alloys were irradiated with heavy ions of 10 MeV I at room temperature. The maximum fluence was 3 × 1014 ions/cm2. The positron annihilation measurements have performed before and after irradiation to investigate changes in free volume. We discuss the relationship between the energy loss and local open volume change after 10 MeV I irradiation compared with those obtained for 200 MeV Xe and 5 MeV Al. The energy loss analysis in ion irradiation for the positron lifetime has revealed that the decreasing trend of positron lifetime is well expressed as a function of total electronic energy deposition rather than total elastic energy deposition. It means that the positron lifetime change by the irradiation has a relationship with the inelastic collisions with electrons during heavy ion irradiation.

Bimetallic Au–Pd nanoparticles were synthesized under high-energy irradiation fields (1.17 and 1.33 MeV γ-rays, 9 MeV electrons, and 1.6 GeV C ions) from solutions containing Au 3+ and Pd 2+ and cationic surfactant (sodium dodecyl sulfate). Particles synthesized by the irradiation were observed using conventional transmission electron microscope (TEM) and annular dark-field scanning transmission electron microscopy (ADF-STEM). The particles synthesized by γ-rays and C ion irradiation exhibit core–shell structure with a Au-core and a Pd-shell. The dependence of the size distribution of nanoparticles on the dose rate is discussed.

In this review, reductive nanoparticle preparation using plasma generated in aqueous solutions is described. The reduction mechanism of Au(III) ions and the plasma reaction sites are characterized in comparison with the sonochemical reaction sites generated by ultrasound irradiation to aqueous solutions. The contribution of organic additives such as surfactants, water-soluble polymers, and alcohols to the reduction is also addressed.

Thermal vacancy formation was studied for the Heusler-type ferromagnetic alloys Co 2 MnZ (Z = Si, Ge, Sn) as a function of temperature (773–1273 K) by the density, electrical resistivity and positron annihilation measurements. The vacancy concentration increased with increase in quenching temperature and particularly, a high vacancy concentration exceeding 2% was observed in Co 2 MnGe and Co 2 MnSn. Estimated vacancy formation and migration energies were comparable with those for B2-type FeAl and CoGa alloys with high vacancy concentration. Further, the vacancy type and the vacancy site were examined for alloys quenched from 773 K. As a result, it was suggested that the mono-vacancies are randomly distributed over the lattice sites.

Atomic and electronic structures of H-adsorbed Pd overlayers on Au(100) substrates have been studied by first-principles calculations. The geometric strain effects change the electronic structure and local reactivity of the surface. The lattice strained Pd overlayers on Au surfaces have larger adsorption energies for atomic hydrogen than the unstrained Pd slabs. Adsorption energies for several adsorption sites on the models with different numbers of Pd overlayers have been analyzed from the viewpoints of strains and H-Pd and H-substrate interactions.

We performed first-principles calculations using the projector augmented-wave (PAW) method for Au/Pd slab interface models. The calculations of relaxed configurations and energies for the thin Pd layers (3 layers) stacking on Au (111) and Au (100) slabs with an epitaxial relationship represent that Pd overlayers have a lateral expansion in both cases. This trend is in good agreement with experimental results for Pd/Au slabs and Au-Pd core-shell nanoparticles, obtained by electron microscopy, X-ray diffraction, and positron annihilation. In addition, an intermixing configuration near the Au-Pd interface was shown to be more stable than the binary separated one.

The Au–Pd nanoparticles prepared by sonochemical technique were investigated by the analytical transmission electron microscopy. The core (Au)–shell (Pd) structure without apparent mixing layers and with similar thickness of Pd shells was clearly confirmed by the image and intensity profile of annular dark field scanning transmission electron microscopy (ADF-STEM) and also by the line-scan analysis of energy dispersive X-ray spectroscopy (EDS) in STEM mode. Detailed analyses of the ADF-STEM imaging, the electron diffraction pattern and the FFT pattern of HRTEM images complementarily show that the Pd shell epitaxially grows on the Au core expanded with the same lattice constant as Au and with the coherent Pd/Au interface structure.

Relaxation of free volume in Zr 50 Cu 40 Al 10 bulk metallic glass during isothermal annealing below T g (glass transition temperature) has been investigated by using positron annihilation lifetime and coincidence Doppler broadening (CDB) techniques. The mean positron lifetime decreases with increasing annealing time at each annealing temperature. The decrease in lifetime is due to shrinkage and annealing out of the free volume. The relaxation kinetics of free volume obeys the stretched exponential function (KWW: Kohlrausch-Williams-Watts law). An adjustable parameter of the KWW exponent β depending on temperature was determined. The electron momentum distribution around free volume derived from a CDB spectrum during annealing showed no appreciable change at each temperature. These results suggest that long-range atomic diffusion and rearrangement, particularly around the free volume, do not occur essentially during relaxation below Tg.

Recently, we have found that 100–200 MeV heavy ion irradiation induces ferromagnetic state in B2 type Fe-50at.%Rh intermetallic alloy below antiferromagnetic-ferromagnetic transition temperature of unirradiated alloy. In order to characterize the lattice defects induced by swift heavy ion irradiation, we performed Doppler-broadening experiments for unirradiated Fe-Rh alloy and that irradiated with 200 MeV 136Xe ions by using a slow positron beam. The S-parameter increases gradually with increasing the ion-fluence up to 5 x 1012 ions.cm–2. Above 5 x 1012 ions.cm–2, the rate of S-parameter increase is slowly saturated. From the dependence of S-parameter on ion-fluence, we have calculated the concentration of vacancy-type defects surviving in the specimen, which is much smaller than that estimated by TRIM-code. The result implies that anti-site type defects dominantly remain in the irradiated specimen, which stabilize the ferromagnetic state in Fe-50at.%Rh alloy. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Binary AuPd nanoparticles were prepared by sonochemical reduction of solutions containing Au3+, Pd2+ ions and surfactant (SDS: sodium dodecyl sulfate and PEG-MS: polyethylene glycol monostearate). When using SDS as an additive, AuPd nanoparticles became a core-shell structure of Au core and Pd shell. AuPd nanoparticle with core-shell structure has catalytic activity superior to alloyed particle or Pd nanoparticles. In order to study the electronic states of AuPd nanoparticles, positron annihilation Doppler broadening measurements by using slow positron beam (energy range of 0.1 to 10 keV) have been performed for AuPd nanoparticles. The size and shape of the nanoparticles are also examined by using transmission electron microscope (TEM). The differences of Doppler broadening parameters between core-shell, alloyed AuPd, pure Au and Pd particles were found. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)