Tohru Mitamura

Surface modification of titanium by nitrogen ion implantation

Abstract Nitrogen ions were implanted in high purity titanium at various doses. The nitride phase, TiN, was identified using either grazing incidence X-ray analysis or transmission electron microscopy. AES depth profile of nitrogen was altered from Gaussian-like to a rectangle with increasing nitrogen doses. Both dissolved nitrogen and tendency to form TiN increased precipitates with increasing nitrogen doses. These TiN precipitates that size were several tens of nm were observed at a lower dose. They grew larger as nitrogen dose increased. The dynamic ultra-microhardness rose to a thickness of within 200 nm of the surface owing to TiN formation, resulting in improved wear resistance of titanium. The wear volume was minimum at a dose of 5×10 21 N 2 + m −2 .

Formation of metal–TiN/TiC nanocomposite powders by mechanical alloying and their consolidation

Abstract Fe–TiN, Ni–TiN, and SUS316–TiC nanocomposite powders were prepared by ball-milling Fe–Ti, Ni–Ti, and SUS316–TiC powder mixtures in a nitrogen or argon gas atmosphere. Fe–63vol.% TiN and Ni–44–64vol.% TiN milled powders were dynamically compacted by use of a propellant gun to produce bulk materials of nanocrystalline structure and having grain sizes between about 5 and 400 nm. SUS316–2.8–5.6vol.% TiC milled powders were consolidated by hot isostatic pressing (HIP) to produce bulk materials having grain sizes between about 100 and 400 nm. The possibility of using fine-dispersed TiN/TiC particles to pin grain boundaries and thereby maintain ultra-fine grained structures of grain sizes down to the nanocrystalline scale has been discussed.

Optical Thin Film Formation with O2 Cluster Ion Assisted Deposition

O2 cluster ion assisted deposition was demonstrated to form optical multilayer films for advanced optical communications. With O2 cluster ion assisted deposition, high refractive index 2.20 at 550 nm and very smooth surface (Ra=0.37 nm) of Ta2O5 films were realized. From a scanning electron microscope (SEM) image, dense film structure were observed without porous or columnar structures at the O2 cluster ion assisted layers. The surface and interface of Ta2O5/SiO2 multilayer films were very flat due to surface smoothing effect of cluster ion beams, and it can be realized even though the beneath surface was rough. The shift of a center wavelength of multilayer film was quite small after an environmental test.

High energy resolution PIXE with high efficiency using the heavy ion microbeam

Abstract An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam (E

Identification of B-K near edge x-ray absorption fine structure peaks of boron nitride thin films prepared by sputtering deposition

Four π∗ resonance peaks were observed in the B-K near edge x-ray absorption fine structure spectra of boron nitride thin films prepared by magnetron sputtering. In the past, these peaks have been explained as the K-absorption of boron atoms, which are present in environment containing nitrogen vacancies, the number of which is 1–3 corresponding to the three peaks at higher photon energy. However, the authors found that there was a strong correlation between the intensities of these three peaks and that of O-K absorption after wide range scanning and simultaneous measurement of nitrogen and oxygen K-absorptions of the BN films. Therefore, the authors conclude that these three peaks at the higher energy side correspond to boron atoms bound to one-to-three oxygen atoms instead of three nitrogen atoms surrounding the boron atom in the h-BN structure. The result of the first-principles calculation with a simple cluster model supported the validity of this explanation.

Atomic imaging in EBCO superconductor films by an X-ray holography system using a toroidally bent graphite analyzer

X-ray fluorescence holography (XFH) is a new technique enabling the determination of the three-dimensional local atomic structure around a certain element. This method has been applied to analyze the local structure around Cu in 300 nm thin films of EuBa(2)Cu(3)O(7-delta) (EBCO) epitaxially grown on MgO (100) substrate, using the newest system for XFH measurement and high-brilliance synchrotron radiation at SPring-8. Here, the results of a study on the irradiation effect on the local atomic structure of EBCO superconductor with XFH measurements are presented.

Sputtering due to Coulomb explosion in highly charged ion bombardment

Sputtering processes of silicon in the bombardment of highly charged ions (HCIs) are studied using molecular dynamics simulation. Assuming the potential energy of the HCI transferred to target is stored as the electrostatic energy of Si atoms ionized by the HCI, the Si ions up to 375 are embedded on a Si(1 0 0) surface as an initial condition, resulting in Coulomb explosion. The dynamics of particle ejection (sputtering) from the surface and crater formation on the surface are simulated. The formation and propagation of shock wave and rapid increase of the sputtering yield are seen during relaxation process. Strong dependence of the sputtering yield on the HCIs potential energy is found and discussed in comparison with experiment.

Metal surface swelling by heavy charged particle irradiation

Abstract Austenitic stainless steel specimens of Type 316SS were irradiated with 200 keV He+ or N+ ions, and the irradiated specimen surfaces were observed by atomic force microscopy (AFM). At the ion irradiation in high temperatures the specimens show surface step-up. In case of He+, the surface swelling is remarkable and increases linearly with He ion fluence, which indicates the swelling is due to formation of He bubbles. The irradiated surface is sometimes in irregularity, especially at and near grain boundary, remarkable ridging is observed. In case of N+, the surface step-up is less remarkable compared with He+. The swelling shows a so-called bi-linear behavior, i.e. a threshold of N+ fluence appears and beyond the threshold the swelling increase is almost linearly presumably due to evolution of voids induced by the N+ irradiation in high temperature. Denudation of void formation adjacent to grain boundary is recognized.

AFM study of the surface deformation of austenitic stainless steel irradiated by He+ ions

Abstract Atomic force microscopy (AFM) was employed to confirm the validity for studying the surface deformation by radiation damage. Distinct swelling was noted by AFM observation in austenitic stainless steel SUS316 specimens which were irradiated by 200 keV He + ions in the range of dose from 2.4×10 16 He / cm 2 (0.6 dpa) to 7×10 17 He / cm 2 (17.5 dpa) at 673, 773, 823 and 873 K. The step height due to He ion-induced swelling showed an obvious dependence on irradiation dose and temperature. It was found for the first time that sharp ridging along the grain boundaries occurred, suggesting He atom agglomeration at high doses and temperatures.

Investigation of analyzing depth of N-K absorption spectra measured using TEY and TFY methods

In order to investigate the analyzing depth of N-K absorption spectra measured using the TEY and TFY methods, the spectra of Si3N4 crystals covered with Cr thin films were measured. The thicknesses of Cr films were 1 – 100 nm. The N-K absorption intensity of Si3N4 measured using the TEY method was observed at Cr thickness of less than 3 nm, while that measured with the TFY method was observed for more than 100 nm. The decrease in the TFY peak intensity was explained by the transmittance of Cr film. The results were applied to estimate the damage depth of plasma-etched GaN crystal. The deformation of the crystal structure in n-GaN etched by Ar plasma was restricted in a shallow region of less than 3 nm from the surface.