Yuichi Saitoh

Micrometer-Sized Magnetic Patterning of FeRh Films Using an Energetic Ion Microbeam

FeRh thin films were irradiated with a focused 10 MeV I 2 ×2 µm2 ion microbeam at intervals of several µm. Following irradiation, the magnetic state at the surface was observed via magnetic force microscopy. The micrometer-sized regions irradiated with the microbeam show a ferromagnetic state while unirradiated regions remain in an anti-ferromagnetic state. Results indicate that an energetic ion microbeam can be used as a tool to produce micrometer-sized modulations of lateral magnetic states of FeRh films.

Effect of high temperature annealing on non-thermal equilibrium phases induced by energetic ion irradiation in FeRh and Ni3V intermetallic compounds

FeRh and Ni3V intermetallic compounds were irradiated with 16 MeV Au5+ ions and were subsequently annealed at elevated temperatures from 100 to 500 °C. The non-thermal equilibrium A1 and L10 phases of FeRh, which were caused by the ion irradiation, disappeared by 300 °C–100 min annealing. The non-thermal equilibrium A1 phase of Ni3V caused by the ion irradiation disappeared by 500 °C–100 min annealing. The Vickers hardness for these two intermetallic compounds changes during the thermal annealing in a direction opposite to its change by the irradiation. The present experimental result shows that the combination of energetic ion irradiation and subsequent thermal annealing can be used as a useful tool for the modification of the mechanical properties of FeRh and Ni3V intermetallic compounds.

Transmission of cluster ions through a tandem accelerator of several stripper gases

The transmissions of carbon cluster ion beams through a tandem accelerator using several stripper gases (He, N2, CO2, and SF6) with a terminal voltage of 2.5 MV were measured as a function of the gas pressure in investigating the most suitable gas for cluster ion acceleration. This resulted in it being demonstrated that the highest transmission could be obtained using the smaller size gas, i.e., helium displayed the best performance of the four gases used. In addition, the ratio of transmissions of C(n) with helium and nitrogen increased with increases in the n, thus revealing that helium gas should prove the most effective in larger cluster ion acceleration using the same energy.

Organic Contaminant Detection of Silicon Wafers Using Negative Secondary Ions Induced by Cluster Ion Impacts

Emission yields of carbon and hydrogenated carbon cluster secondary ions CpHq± (p≥1, q≥0) originating from organic contaminants on a silicon wafer are compared between monoatomic (0.5-MeV/atom C1+) and cluster ion (0.5-MeV/atom C8+) impacts using time-of-flight (TOF) secondary ion mass spectrometry. CpHq- for the cluster ion impact exhibits the highest emission yield per incident atom among CpHq± with the same p number. The highest relative CpHq- emission yield for the cluster ion impact reaches ~20 and ~60 times higher in comparison with those of CpHq- and CpHq+ with the same p number for the impact of the monoatomic ion with the same velocity, respectively. Combination of negative secondary ion TOF measurements with cluster impact ionization is a promising tool for highly sensitive detection of organic-contaminants on silicon wafers.

Magnetic patterning of FeRh thin films by energetic light ion microbeam irradiation

Magnetic patterning of FeRh thin films of various shapes and dimensions by 2 MeV H and He ion microbeam irradiation was examined by X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) at the photon energy of the Fe L3 absorption edge. The XMCD-PEEM images clearly show that the various magnetic patterns whose sizes are about 1–2 µm, can be successfully produced by controlling the scan condition and the size of the ion beam probe. Furthermore, the quantitative analysis of the XMCD-PEEM images reveals that the localized magnetization in the micrometer-sized magnetic patterns significantly depends on the irradiation ion fluence. In addition, the annealing condition is also found to be one of the predominant factors that determine the magnetic state even for the micrometer-sized magnetic patterns.

Hardening induced by energetic electron beam for Cu-Ti alloys

Cu–4.2 at. % Ti alloy sheets with the dimension of 10 × 10 × 0.15 mm3 were irradiated with 2 MeV electrons at 200 and 250 °C, and the Vickers hardness was measured as a function of electron fluence. The hardness increased by the electron irradiation. The increase in hardness depends on the electron fluence and irradiation temperatures. The hardening induced by the electron irradiation was observed not only at the directly irradiated surface but also at the reverse side of irradiated surface. By masking an area of specimen surface with a thick copper sheet, we could modify the hardness only for the unmasked area. The atom probe tomography (APT) and the field-emission scanning microscope (FE-SEM) were used for the observation of the microstructures of the specimens. The image of FE-SEM suggests that Ti-rich small precipitates are produced by the irradiation. The present result shows that the electron beam irradiation at elevated temperatures can be a useful tool for improving the hardness of designated areas in bulk Cu–Ti alloys.

Surface-sensitive Chemical Analysis of Organic Insulating Thin Films Using Negative Secondary Ions Induced by Medium Energy C60 Impacts

We report on the surface-sensitive chemical analysis of organic insulating thin films using negative secondary ions (N-SIs) induced by C60 impacts in the medium energy range from several tens to several hundreds keV. The incident C60 energy dependence of emission yields of characteristic N-SIs for poly(methyl methacrylate) and charging effects on the N-SI mass spectra were investigated using time-of-flight SI mass spectrometry. Our results show that medium energy C60 impacts stably provide considerably high characteristic N-SI yields without charge compensation, and demonstrate that time-of-flight SI mass spectrometry with medium energy C60 impacts is advantageous for the highly-sensitive chemical analysis of organic insulators.

Effect of 10 MeV iodine ion irradiation on the magnetic properties and lattice structure of CeO2

We have studied the magnetic properties and the lattice structure of pure CeO2 irradiated with swift heavy ions. Experimental results showed that the ferromagnetism was induced at room temperature by 10 MeV I ion irradiation. The value of saturation magnetization increases with increasing the ion fluence and reaches a maximum value at about the fluence of 1.2 × 1013/cm2, and then decreases. The X-ray diffraction (XRD) spectra showed that the lattice parameter of CeO2 increases with increasing ion fluence. To examine the origin of the ferromagnetic state in CeO2, we compared the result for 10 MeV I ion irradiation with that for 200 MeV Xe ion irradiation. We also estimated the magnetic properties for CeO2 pellets annealed at 1273 K in a vacuum. From the experimental results, we concluded that oxygen vacancies, which are produced by electronic excitation process due to high energy ion beam, play an important role in the appearance of the ferromagnetic state in CeO2.

Transmission Properties of a 4-MeV C+ Ion Beam Entering a Narrow Gap between Two Cylindrical Glass Surfaces

To investigate the possibility of guiding a fast, heavy-ion beam with tilted curved surfaces, we study the transmission properties of a 4 MeV C+-ion beam passing through a narrow gap between a convex glass lens and concave glass lens. The ion-beam transmission of 42–59% obtained at the tilt angle θ= 3° is 20–30 times greater than that of 2% estimated from the cross section of the narrow gap between the two cylindrical lenses. The results of laser-beam-transmission experiments indicate that, even at θ= 3.4° where almost no ions pass through the gap without interacting with the cylindrical glass surfaces, approximately 10% of the ions are transmitted. The transmission probability is asymmetric with respect to the polarity of θ, indicating that the ion beam impinging on the concave surface is more easily transmitted than when impinging on the convex surface. Furthermore, no significant ion-energy loss occurs upon transmission for the angular range -3≤θ≤+ 3.4°. These results provide evidence that fast heavy-ion beams are guided by curved surfaces.

Optical emission spectroscopy of excited atoms sputtered on a Ti surface under irradiation with multicharged Ar ions

Optical emission spectroscopy of excited atoms was carried out in order to investigate the sputtering processes on solid surfaces under irradiation of slow, multicharged ions. Many atomic lines of Ti I (neutral) and Ti II (single-charged ions) were observed in wavelengths from 250 to 750 nm with irradiation by Ar3+ (30 keV) on a Ti surface which was placed in a low pressure O2 atmosphere. The emission intensity of Ti I (520 nm) decreased monotonically with an increase of O2 partial pressure, whereas that of Ti I / II (670 nm, a 2nd order wavelength of 335 nm) slightly increased. From a semi-logarithmic plot of emission intensity for the 670 nm spectrum as a function of distance from the surface, the mean velocity of the excited Ti atoms and ions in a normal direction parallel to the surface, or