Yuuichi Ishikawa

Development of a scanning atom probe

In order to extend the applicability of the conventional atom probe (AP), a new AP named ‘‘scanning atom probe (SAP)’’ is proposed. The SAP has a microextraction electrode which scans over a flat specimen surface with many microcusps. Then the electrode and a cusp forms a minute field ion microscope. Calculation of field distribution in the confined small space between the cusp apex and the electrode indicates that the field can be high enough to field evaporate the apex atoms and that the atom‐by‐atom mass analysis by the SAP is highly feasible. Accordingly, a trial SAP is under construction modifying a low‐temperature UHV scanning tunneling microscope.

Characterization of the spinodal decomposition of Fe−Cr alloys by Mössbauer spectroscopy

Addition of 5%Ni to an Fe−28%Cr alloy causes a transition of the aging behavior from the nucleation and growth to the spinodal decomposition. Very rapid increase in the average internal magnetic field and a broadening of the internal magnetic field distribution occur in the spinodal decomposition. Mössbauer spectra are synthesized by assuming a rectangular and a sinusoidal wave for the composition fluctuation, and the internal magnetic field distributions obtained from those are compared with the experimental results to estimate a time evolution of the amplitude of the composition wave.

Performance of the trial scanning atom probe: New approach to evaluate the microtip apex

In order to examine the feasibility of realizing the scanning atom probe, a trial instrument was constructed by modifying a low‐temperature ultrahigh vacuum scanning tunneling microscope (STM). A scanning electron microscope was mounted on the trial instrument to inspect the relative position of both the open hole at the end of the funnel‐shaped extraction electrode and a cusp apex on a specimen surface. In the preliminary experiment, a single sharp W tip of the STM and two extraction electrodes with respective open hole diameters of 10 and 20 μm were employed. The tip was brought near the electrode by employing a microscrew and a piezoactuator as with a conventional STM. The variation of the field emission current with the position of the center of the hole relative to the cusp apex was found to be significant enough to bring the apex precisely to the center of the hole. An interesting finding was that the field emission was observed from a tip with a radius of more than 2 μm at a relatively low voltage,...

Field ion microscope with photostimulable phosphor screen — new approach for quantitative analysis of FIM images-

Abstract Adaptability of a photostimulable phosphor screen, called an imaging plate (IP), for field emission and field ion microscopies was examined. The photostimulated luminescence (PSL) of the IP for He+ is strong enough for field ion microscopy, but that for Ne+ is less than one tenth of He+, like an ordinary fluorescent material. The digitized computer-processed images of W, W-Re and Pt-Ir are unexpectedly clear. The image brightness seems to increase with the number of incoming ions and the PSL intensity ratio of a dark atom to a bright atom is found to be as large as 1 to 160, suggesting the possibility of a quantitative analysis of electron tunneling and a field ionization probability over individual surface atoms. However, this ratio is significantly smaller than the expected dynamic range of the IP, 104, possibly due to the charge up of the IPs surface, low ion energies and an IPs high outgassing rate, which deteriorates vacuum and induces high background counting. Accordingly, darkly imaged “invisible atoms” of the alloys are hardly recognizable at present.

A Mössbauer spectrometry study on the phase decomposition of cast duplex stainless steel

Cast CF3M duplex stainless steel having 25% of ferrite in volume fraction was aged at 723 K for time periods up to 10000 h. Phase decomposition of ferrite was investigated by Mössbauer spectroscopy. Ferrite decomposed initially via a spinodal process to finally yield the Fe-rich and the Cr-rich phase. The hyperfine magnetic field distribution obtained from the experimental Mössbauer spectrum was analyzed by assuming trinomial distribution of main constituent atoms Fe, Cr, Ni to determine Cr and Ni content of the Fe-rich phase. Main compositions of the phase were 84 at.% Fe, 11 at.% Cr, 5 at.% Ni.

A trial scanning atom probe and field distribution at a tip apex of a micro-tip array

Summary form only given, as follows. A trial scanning atom probe (SAP) was constructed by modifying a low temperature UHV scanning tunneling microscope (STM). The specimen holder of the conventional STM was replaced with a holder of an extraction electrode made of a 10 micrometer thick Pt foil. The specimen micro-tip array is mounted at one end of a piezo tube which allows one to move the specimen with subnanometer precision. Silver foils connecting the cold end of the cryogenic refrigerator and the holder of the piezo tube cool the specimen and piezo assembly down to 50 K. Field emitted electrons and field ionized gas ions project images of an individual tip apex of a micro-tip array at atomic resolution and field evaporated apex atoms fly into the flight space of a reflectron mass analyzer through the probe hole at the center of the screen. The results of preliminary experiments are reported. While constructing the SAP, the field distributions around the tip apex were computed in order to examine the variation of field emitted current with the relative position of the tip apex and the open hole of the extraction electrode. The calculated field distribution is presented, comparing the observed variation of emitted current with the relative positions.