Nobuo Yoshiyasu

Self-Induced Vibration of a Water Drop Placed on an Oscillating Plate

Vibration of a water drop placed on a vertically oscillating plate was observed, and the amplitudes and frequencies of the plate were measured with which the drop showed large amplitude vibrations. A special cloth was used so that the drop did not wet the plate. The results are compared with a simple theoretical prediction based on the Mathieu equation. The experimental data are shown to lie within the unstable growing region derived from the theory.

Coulomb explosion potential sputtering induced by slow highly charged ion impact

We have observed secondary ion emission from a hydrogen-terminated Si(111) 1×1 surface and a native SiO2 thin film on the Si substrate (SiO2∕Si) irradiated with slow (vion<vBohr) iodine highly charged ions (HCIs) in a wide range of charge state q from q=15 up to 50. The yields of secondary ions evaluated from time-of-flight mass spectra showed rapid increases with q of the projectile. The relation of the yields to the potential energy of HCIs is discussed in terms of the Coulomb explosion model. It was found that the simultaneous emission of multiple Si+ ions occurs in an event of a single high-q HCI impact onto the SiO2∕Si.

Observation of HCI-induced nanostructures with a scanning probe microscope

We present scanning tunneling microscope (STM) images, atomically resolved, of the nanostructures on various kinds of surfaces bombarded with highly charged ions (HCIs). In the STM image of a highly oriented pyrolytic graphite surface (Xe29+-impact), a protrusion structure was observed with √3 × √3 R30° surface reconstruction around the impact site. A crater-like structure was formed on a Si(111)-(7×7) surface by an I50+-HCI impact. An atomic image of ~0.1 nm in height was also observed around the missing topmost layers of the crater. In the case of a TiO2(110) surface, a typical nanostructure induced by a single I51+-HCI impact, relatively larger crater structure than that on the Si surface was observed; the height (~1 nm) was higher than the atomic step of the TiO2(110)-(1×1) surface (~0.3 nm) and the depth reached at least 1.5 nm. This implies that the degree of the HCI-radiation effect on the TiO2 surface is higher than that of the Si(111) case.

Demonstrative Experiment for Single-Ion Implantation Technique Using Highly Charged Ions

When highly charged ions were implanted on a graphite surface with monitoring of secondary electrons emitted at the point of incidence, dot structures on the surface, as the imprint of ion incidence, were observed by a scanning tunneling microscope (STM). The number of events of secondary electron emission and the number of imprints coincided, which indicates that a method of detecting incident events of ion implantation of almost 100% efficiency has been established by using highly charged ions.

Toward over unity proton sputtering yields from a hydrogen-terminated Si(111) 1×1 surface irradiated by slow highly charged Xe ions

The emission of sputtered ions from a hydrogen-terminated Si(111) 1×1 surface has been measured for impact of slow (v<0.25vBohr) highly charged Xe ions. Proton sputtering yields increase strongly with projectile charge q (qγ;γ∼4) and reach to the value greater than one for Xeq+ impact (q≧44). Yields of Si+ remain constant (∼0.1) for lower q (14≦q≦29) but increase with q for higher q region which shows that the apparent Coulomb explosion-like potential sputtering might set in and enhances the sputtering yield drastically over q=29.

Injection of metallic elements into an electron-beam ion trap using a Knudsen cell

A method of injecting metallic elements into an electron-beam ion trap (EBIT) is described. The method is advantageous over the conventional coaxial and pulsed injection methods in two ways: (a) complicated switching of injection and extraction beams can be avoided when extracting beams of highly charged ions from the EBIT and (b) a beam of stable intensity can be achieved. This method may be applicable to any metallic elements or metallic compounds that have vapor pressures of ∼0.1Pa at a temperature lower than 1900°C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, and Ho.

Effect of Ambient Temperature on the Self-Induced Vibration of Boiling Drop

Self-induced vibration of a drop of liquid N 2 placed on a horizontal plate was observed, where the temperature T a of the plate and the surrounding gas was kept constant at a value within -100°C∼200°C. The drop showed several modes of vibration with polygonal shapes in plane view and made transitions to other modes as its size decreased through boiling. It was found that the process of mode selection did not depend on T a , if it was within -100°C∼150°C. Above 150°C, the drop selected modes rather randomly. Vibrational frequency was measured. It agreed with theory, but showed a small deviation for T a <-69°C. A theoretical estimation of the temperature of boiling liquid surface is made to explain this deviation, and its result is discussed. An aspect of dynamical pattern formation is suggested in relation to the degree of thermal inequilibrium.

Injection of refractory metals into EBIT using a Knudsen cell

A new method for injection of metallic elements into an electron-beam ion trap (EBIT) is described. Injection of metallic elements into an EBIT has so far been mainly achieved by MEVVA (metal vapor vacuum arc) ion sources. However, continuous injection, as is the case of rare gases, is sometimes desirable, especially for stable extraction of highly charged ions. In the course of DR (dielectronic recombination) study, we have developed a method of such a stable injection of metallic elements. This method is applicable to any metallic elements or metallic compounds that have vapor pressures of ~0.1 Pa at a temperature lower than 1900°C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, Ho and W.

Recent activities at the Tokyo EBIT 2006

The electron beam ion trap (EBIT) in Tokyo was constructed about 10 years after the first EBIT at Lawrence Livermore National Laboratory was built, and has been being stably operated since then. In this paper, we present recent experimental activities at the Tokyo EBIT. In particular, experiments utilizing slow, very highly charged ion beams extracted from the EBIT are reported. PACS Nos.: 39.10.+j, 32.30.Rj, 34.50.Dy, 34.80.Kw

X-ray emission in slow highly charged ion-surface collisions

X-rays emitted in the collisions of highly charged ions with a surface have been measured to investigate dissipation schemes of their potential energies. While 8.1% of the potential energy was dissipated in the collisions of He-like I ions with a W surface, 29.1% has been dissipated in the case of He-like Bi ions. The x-ray emissions play significant roles in the dissipation of the potential energies in the interaction of highly charged heavy ions with the surface.