Kazuhiro Kanda

We searched for the bound state of the neutron-rich Λ-hypernucleus HΛ6, using the Li6(π-,K+)X double charge-exchange reaction at a π- beam momentum of 1.2GeV/c at J-PARC. A total of 1.4×1012π- was driven onto a Li6 target of 3.5-g/cm2 thickness. No event was observed below the bound threshold, i.e., the mass of HΛ4+2n, in the missing-mass spectrum of the Li6(π-,K+)X reaction in the 2<θπK<20 angular range. Furthermore, no event was found up to 2.8MeV/c2 above the bound threshold. We obtained the double-differential cross section spectra of the Li6(π-,K+)X reaction in the angular range of 2<θπK<14. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the HΛ6 hypernucleus bound state. In addition, not only the bound state region, but also the Λ continuum region and part of the Σ- quasifree production region of the Li6(π-,K+) reaction were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the Σ - nucleus optical potential for Σ - He5 through spectrum shape analysis.

The low-temperature formation of nanocrystalline Si (nc-Si) in SiO_x is one of key technologies for the realization of high-quality solar cells. We proposed a low-temperature crystallization method by soft X-ray at BL07A in the synchrotron radiation facility, NewSUBARU. It is known that the crystallization temperature of amorphous Si (a-Si) film on SiO_2 substrate was reduced by about 100℃. The a-Si in SiO_x film was crystallized by atomic migration via electron excitation by soft X-ray irradiation at the photon energy near the core level of Si2p. The size of nc-Si prepared at 660℃ by soft X-ray irradiation was estimated to 16.8 nm from the peak position of Raman spectra. The nc-Si can be formed by soft X-ray irradiation at low temperature.

To realize a ultrathin junction with 10 nm depth, a novel activation method of B dopant using soft X-ray undulator was examined. In this study, B ion cluster (B_<10>H_<14>^+) was used as B source. The sheet resistance of Si treated soft X-ray irradiation was low compared with a conventional thermal annealing. The effect of soft X-ray irradiation on B activation was remarkable below 500℃. The atomic movement of Si atoms was enhanced by ionization and local phonon composition. The crystallinity of Si was recovered and the substitution of B atom into Si lattice site is occurred via knock-on effect. The low sheet resistance can be achieved by using B_<10>H_<14>^+ instead of B^+.

[in Japanese]

To realize a ultrathin junction with lOnm depth, a novel activation method of B dopant using soft X-ray undulator was examined. As the photon energy of the irradiated soft X-ray closed to the energy of core level of Si 2p, the activation ratio increased. The effect of soft X-ray irradiation on B activation was remarkable at temperature lower than 400℃. The activation energy of B activation by soft X-ray irradiation (0.06 eV) was lower than that of B activation by thermal annealing (0.18 eV). The activation of B dopant confirmed at low temperature, although the activation ratio shows small values of 6.2x 10^<-3> at 110℃. Furthermore the sheet resistance was slightly reduced by using a cooled holder even at 35℃. At first, the electron at Si2p level was excited by soft X-ray. Next, the Si atoms were ionized and Coulomb repulsion was generated between the ionized Si atoms. The atomic movement of Si atoms was enhanced by ionization and local phonon composition. The crystallinity of Si was recovered. In addition, the substitution of B atom into Si lattice site is occurred via knock-on effect.

We examined dependence of the crystallization for a-Ge and a-SiGe on the photon energy. In the storage-ring current of 75 mA, the a-Ge films were crystallized in the photon energy of 100 eV at the sample temperature of 380℃, while they were not crystallized in the photon energy of 130eV at higher temperature of 410℃. Thus, the crystallization of a-Ge films by soft X-ray irradiation depends on the photon energy in comparison with thermal effect. TEM observation was carried out for the a-SiGe multilayer film with gradual change in composition after soft X-ray irradiation. A crystalline SiGe grain formed in the a-SiGe multilayer film. The interface positions and compositions of each layer in the crystalline grain were similar to those of amorphous matrix. The multi layers in the crystalline grain had crystallographic orientation relationship.

© Springer-Verlag Berlin Heidelberg 2013. Stability of hydrogen in diamond-like carbon (DLC) film under simulated space environment, i.e., hyperthermal atomic oxygen, vacuum ultraviolet (VUV) and soft X-ray exposures has been studied. Hydrogen in DLC was released by exposure to low-energy atomic oxygen beam, whereas the gasification reaction of carbon atom needed collision energy above 3 eV. The desorption process in the deep region required a higher collision energy. The density of hydrogen decreased 11% by atomic oxygen exposure, and was independent of the collision energy. Photon exposure also releases hydrogen from DLC. High-energy photons in soft x-ray promote the hydrogen desorption even from deeper region with high efficiency. It was considered that soft x-ray could release bonded hydrogen which is not released by VUV or atomic oxygen exposures.

We developed a new low-temperature crystallization method, SXC (Soft X-ray Crystallization), of amorphous (a-) Si, Ge and Si_xGe_<1-x> film deposited on a glass substrate by soft x-ray irradiation using short undulator as a light source at NewSUBARU SR facility. Quasi-nucleation followed by grain growth at low temperature proceeds under a solid phase. The fundamental process of the SXC-method is a local excitation of core electrons to vacuum level by photons followed by atom movement due to coulomb repulsion, which results in quasi-nucleation. Therefore, the grain growth occurs lower temperature than the conventional (conv.) thermal crystallization. The SXC-method realizes the threshold temperature of crystallization for a-Si, Ge and Si_xGe_<1-x> film by approximately 100 degree C under the present conditions than conv. Method.

We developed a new low-temperature crystallization method, SXC (Soft X-ray Crystallization), of amorphous (a-) Si, Ge and Si_xGe_<1-x> film deposited on a glass substrate by soft x-ray irradiation using short undulator as a light source at NewSUBARU SR facility. Quasi-nucleation followed by grain growth at low temperature proceeds under a solid phase. The fundamental process of the SXC-method is a local excitation of core electrons to vacuum level by photons followed by atom movement due to coulomb repulsion, which results in quasi-nucleation. Therefore, the grain growth occurs lower temperature than the conventional (conv.) thermal crystallization. The SXC-method realizes the threshold temperature of crystallization for a-Si, Ge and Si_xGe_<1-x> film by approximately 100 degree C under the present conditions than conv. Method.

We investigated the characteristics of a-Si film with thicknesses of 1 and 50nm those were irradiated by soft X-ray from the undulator source. The average roughness Ra of 1nm-thick-Si film were changed from 0.63 to 1.7nm by soft X-ray irradiation. The cohesion of Si atoms were observed. The electric resistivity of it also increased corresponding to the change of the surface roughness. The X-ray absorption rate of thin Si film becomes larger than the thick film. Because the phonon excitation of Si atoms by X-ray absorption becomes remarkable, the perpendicular force worked to Si atoms increases. This causes the cohesion of Si atoms at the surface.

Our investigation of diamond-like carbon (DLC) nanosprings with a 130nm spring-section diameter, which were fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD), showed for the first time that nanosprings can be stretched. We observed large displacements of the FIB-CVD nanosprings using in situ optical microscopy; in other words, the nanosprings showed behavior similar to that of macroscale springs. In addition, we investigated the dependence of the spring constant of DLC nanosprings on spring diameter. The spring constants, measured using commercially available cantilevers, ranged from 0.47 to 0.07N/m. The diameter dependence of spring constant can be accurately expressed by the conventional formula for a coil spring. The estimated shear modulus of the DLC nano-springs was about 70GPa. This value is very close to the value of conventional coil springs made of steel. Furthermore, we measured the stiffness of a DLC nanospring annealed at 1000℃ in vacuum. The stiffness was decreased to approximately half of the stiffness of the nanospring without annealing.