Kazuo Nagata

Electronic Property of Thin Single-Crystal Films of α-Al2O3 on Ru(0001)

High-quality single-crystal films of α-Al 2 O 3 with various thicknesses below 35 A have been fabricated on the Ru(0001) surface. The phase transtion from γ- to α-Al 2 O 3 has been used for fabrication. The thickness dependence of the band gap for the oxide layer has been measured by the interband transition using electron energy loss spectroscopy. The band gap has been found to decrease with decreasing oxide thickness. The same tendency of this extraordinary result has been observed in scanning tunneling spectroscopy. These results can be interpreted by the many-body effect.

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.

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.

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.