Eiichi Nishimura

Bias Annealing of Radiation and Bias Induced Positive Charges in N- and P-Type MOS Capacitors

The radiation-induced positive charges trapped in an n-type MDS capacitor were observed to decrease with the number of C-V measurements. The positive gate bias applied on the capacitor was found to cause the decrease in the trapped charges. Its proposed mechanism was a recombination of the trapped positive charges with electrons injected from the Si substrate into the SiO2 layer due to the bias.

Development of a dual-ion beam accelerator connected with a TEM for in situ observation of radiation-induced defects

A dual-ion beam accelerator connected with a TEM has been developed for in situ observation of radiation-induced defects. The system consists of a 400-kV Cockcroft-Walton accelerator, which can accelerate two different kinds of ions alternatively, and a 200-kV TEM equipped with a high-sensitivity TV camera. The ion beam from the accelerator is fed into the TEM by an electrostatic beam transport system which consists of three deflectors, two quadrupole lenses and a 57° static prism. A copper specimen is bombarded with 150-keV Ar ions. A small cascade of < 5 nm in diameter is observed for an Ar-ion current of about 85 nA/cm2. At a higher current of 1 μA/cm2, recombination, growth, overlap, and collective motions of cascades are observed during irradiation. In situ observation of argon bubbles at a grain boundary of copper gives a diameter growth rate of 2.8 × 10−2 nm/s at a dose rate of 5.3 × 1014 Ar+/cm2 s and a temperature of about 500 K.

Development of a dual ion beam system with single accelerator for materials studies

Abstract The dual ion beam accelerator system has been developed for simulation studies of neutron radiation damage of structural materials for nuclear fusion and fission reactors. One accelerator is used to accelerate two different kinds of ions, which are generated in the ion source simultaneously. One of these ions is selected alternatively by switching the magnetic field of the analyzing magnet, and is then accelerated to the desired energy value. The system is controlled by a microcomputer. The accelerator used in the system is a conventional 400 kV Cockcroft-Walton accelerator. The performance test by the acceleration of He+ and Ar+ shows that the system is capable of accelerating two ions alternatively with a switching time of less than 22 s. The beam current obtained with the microcomputer control is more than 98% of the current obtained by manual operation.

Development of multispecimen holder for ion irradiation experiments

Abstract A specimen holder has been developed for ion irradiation experiments. Nine specimens (diameter: 3 mm, thickness: 0.1–0.3 mm) can be loaded onto the holder. The thermal resistivity between the specimen and the specimen table is reduced by setting a gold disk between them. Temperatures are controlled by a ceramic heater and cooling gas to within 1°C over the range of −50 to 550°C during ion irradiation with beam powers up to 10 W. The temperature differences between specimens are less than 5°C. The specimen assembly is insulated to allow accurate ion beam current measurements. A quartz prism is mounted in front of the specimen assembly to allow viewing of the beam shape and adjustment of the specimen position within the beamline.

Development of a micro FEL irradiation system

Abstract A microscopic Free Electron Laser (FEL) irradiation system has been developed for bio-medical applications. This system has two major functions; irradiation and observation. This irradiation system cannot only focus the FEL from infrared to ultraviolet in wavelength but can also adjust the area, time and intensity of FEL irradiation. Furthermore, experimental cells are incubated and observed in detail during and after FEL irradiation with an integrated microscope.

Delivering dye into cultured cells using infrared free-electron laser

Free electron lasers (FELs) can be used to molecular operation such as the delivery of a number of molecules into cells. Cultured NIH3T3 cells are exposed to high-intensity short pulse FEL. The FEL is tuned to an absorption maximum wavelength, 6.1 micrometers , which was measured by microscopic FTIR. A fluorescence dye in the cell suspension is more absorbed into the cell with the FEL exposure due to the FEL- induced mechanical stress to the cell membrane. A quantitative fluorescence microscopy is used to determine the efficiency of delivery. The result showed that the fluorescence intensity of sample cells were higher than that of control cells, and there was significant difference between the control and the sample group. Blebbing and the colony formation of the cells were observed for cells with mechanical stress.