M. Sataka

Toward Online Nanoscale Diffusion Measurements Using Radioactive 8Li Tracer

We have examined the feasibility of a new online nanoscale diffusion measurement method using a radioactive 8Li tracer by computer simulations. We have found that the detection limit of the lithium diffusion coefficient can be improved to a low value of 1×10-12 cm2/s by detecting α particles emitted at a small angle relative to a sample surface that is irradiated with a low-energy 8Li beam of about 8 keV.

Simulation of radiotracer method for diffusion studies using short-lived radioactive nuclear beams

Abstract We have studied, by a computer simulation, the feasibility of the radiotracer method for diffusion studies using short-lived radioactive nuclear beams as tracers. We have considered two typical examples of radiotracers that will be available in KEK-JAERI RNB facility, 18F (half-life: 1.8 h, β+-emitter) and 8Li (half-life: 0.83 s, α-emitter). The sample is set on a given temperature and irradiated by the tracer beams for a time-duration. In the case of 18F, the serial sectioning technique by the ion-beam-sputtering device is assumed to obtain the concentration-depth profile of the tracer diffused during the irradiation time. In the case of 8Li, the simulation reveals that the time-dependent yields of α particles can be used as a measure of the diffusivity of the tracer in a non-destructive way. The present method could be applied to measure rather large diffusion coefficients of various radiotracers with a short measuring time.

Tracing temperature in a nanometer size region in a picosecond time period.

Irradiation of materials with either swift heavy ions or slow highly charged ions leads to ultrafast heating on a timescale of several picosecond in a region of several nanometer. This ultrafast local heating result in formation of nanostructures, which provide a number of potential applications in nanotechnologies. These nanostructures are believed to be formed when the local temperature rises beyond the melting or boiling point of the material. Conventional techniques, however, are not applicable to measure temperature in such a localized region in a short time period. Here, we propose a novel method for tracing temperature in a nanometer region in a picosecond time period by utilizing desorption of gold nanoparticles around the ion impact position. The feasibility is examined by comparing with the temperature evolution predicted by a theoretical model.

Diffusion Experiment in Lithium Ionic Conductors with the Radiotracer of 8Li:from Micro‐ to Nano‐diffusion

We have developed a radiotracer method for diffusion studies in lithium ionic conductors, by using, as the tracer, the short‐lived α‐emitting radioisotope of 8Li from TRIAC (Tokai Radioactive Ion Accelerator Complex). In the method, we measured α‐particles coming out of the sample of interest and have found that the time‐dependent yields of α‐particle from the diffusing 8Li primarily implanted is a good measure of the Li diffusion in the sample. The method has been successfully applied to measure the lithium diffusion coefficients in a typical defect‐mediated lithium ionic conductor of LiGa, well demonstrating that the method is very efficient to measure the diffusion in the micro‐meter regime per second. Further development, as an extension of the present method, was proposed to measure the diffusion on the nanoscale in lithium ionic conductors.

Diffusion of 8 Li short-lived radiotracer in Li ionic conductors of NaTl-type intermetallic compounds

Non-destructive and on-line Li diffusion experiments in Li ionic conductors are conducted using the short-lived !-emitting radiotracer of 8Li. The radiotracers produced as an energetic and pulsed ion beam from TRIAC (Tokai Radioactive Ion Accelerator Complex) are implanted into a structural defect mediated Li ionic conductor of NaTl-type intermetallic compounds (-LiGa and -LiIn). The experimental time spectra of the yields of !-particles are compared with simulated results and Li diffusion coefficients in the intermetallic compounds are extracted with an accuracy of ±10%. The diffusion coefficients obtained for -LiGa with Li content of 43-54 at.% are discussed in terms of the interaction between Li-ion and the structural defects in the specimen, compared with the cases of -LiAl and -LiIn. The nonlinear Li-content dependency of Li diffusion coefficients for -LiGa suggests that the Li diffusion with the Li-deficient region is obstructed by the defect complex composed of vacancies at the Li sites.

Reaction of Implanted N Isotope with SiO2 Near Si3N4-Film and SiO2-Substrate Interface

We have investigated 100 keV 15N (90% enriched) implantation effects on Si3N4 films on SiO2-glass-substrate. The Si3N4 films were prepared by using reactive RF-magnetron-sputter-deposition method in N2 (natural isotope abundance) gas at room temperature. The composition and film thickness were measured by Rutherford backscattering spectroscopy (RBS) and optical absorption spectroscopy. The RBS and optical absorption spectroscopy show increase in the film thickness with the stoichiometric composition, by 15N ion implantation. These results and depth distribution of the implanted 15N, which is obtained by nuclear reaction analysis (NRA), lead to formation of Si3 15N4 film (embedded isotope rich nitride film). Enrichment of 15N in the grown silicon-nitride film is estimated to be ∼70%.

On-Line Diffusion Tracing in Li Ionic Conductors by the Short-Lived Radioactive Beam of 8Li

A non-destructive and on-line diffusion tracing in Li ionic conductors has been demonstrated. As the tracer, the pulsed beam of the short-lived α-emitting radioisotope of 8Li was implanted into a typical Li ionic conductor LiGa. By analyzing the time-dependent yields of the α-particles measured in coincident with the repetition cycle of the beam, the tracer diffusion coefficients were extracted with a good accuracy. The ordering of the Li vacancies in the Li-deficient β phase of LiGa was observed for the first time in terms of the Li diffusion by the present method.

Coster-Kronig electrons from Nq+ (q = 1-3) and Oq+ (q = 1,2) Rydberg states produced in high-energy collisions with He

Coster-Kronig (C-K) electrons ejected through autoionization decay of high-Rydberg states in high-energy collisions of Nq+ (q = 1-3) and O q+ (q = 1,2) with He have been measured with high resolution by using zero-degree electron spectroscopy. Autoionizing lines are observed corresponding to decays from 1s22p(2P)nl Rydberg states for 21 MeV N3+ + He, from 1s22s2p(3P)nl Rydberg states for 21 MeV N2+ + He and from 1s22s2p2(4P)nl Rydberg states for 14 MeV N+ + He, respectively. Angular momentum distributions of these three series of C-K decaying Rydberg states for Nq+ (q = 1-3) projectiles are also discussed, where the highly excited states are formed by single-electron excitation. Similarly, series of the autoionizing Rydberg states are observed for two charge states of incident O ions. The C-K spectra observed can be assigned to decays from 1s22s2p2(4P)nl states for 30 MeV O2+ + He and from 1s22s2p3(5S)nl states for 15 MeV O+ + He.