Masahide Tona

SEM and ESR measurements on HOPG surfaces irradiated with Ar11+ and Ar1+

Highly oriented pyrolytic graphite (HOPG) samples were irradiated with a highly charged ion (HCI) Ar11+ at a fluence of 1014 cm−2. After irradiation, scanning electron microscopy (SEM) was used to observe the irradiated trace. During SEM measurement, an electron acceleration voltage of 0.5, 1 and 5 kV was applied to measure the samples, respectively. The irradiated contrast can be observed in the Si surface at 0.5 kV, which could not be found at 1 kV or higher. The irradiated area becomes brighter than that of the unirradiated area. When Ar1+ was used to bombard the solid surface, the fluence should become of the order of 1015 cm−2. In this case, the irradiated contrast could be observed. It means HCI is able to enhance more effectively the surface modification. Furthermore, electron spin resonance was used to measure the surface of highly oriented pyrolytic graphite (HOPG). A clear resonant peak appears in the irradiated sample, which cannot be found in the pristine sample. The phenomenon could be related to defects induced by the HCI impact.

Correlation between Electronic Shell Structure and Inertness of Cun+ toward O2 Adsorption at n = 15, 21, 41, and 49

The inertness of metal clusters in air is important for their application to novel materials and catalysts. The adsorption reactivity of copper clusters with O2 has been discussed in connection with the electronic structure of clusters because of its importance in electron transfer from the cluster to O2. Mass spectrometry was used to observe the reaction of Cu n+ + O2 ( n = 13-60) in the gas phase. For O2 adsorption on Cu n+, the relative rate constants of the n = 15, 21, 41, and 49 clusters were clearly lower than those with other n. Theoretical calculations indicated that the inertness of Cu15+ with 14 valence electrons was related to the large HOMO-LUMO gap predicted for the oblate Cu15+ structure. The Clemenger-Nilsson model was used to predict that the electronic subshell of oblate Cu49+ with 48 electrons was closed. This electronic shell closing of Cu49+ corresponds to the inertness for O2 adsorption.

Surface Modification Using Highly Charged ions

In the present experiment, the samples (HOPG) were irradiated with Ar11+ HCIs at the fluence of 1014/cm2. SEM and AFM are used to observe the irradiated area. The different electron acceleration voltage was applied to observe the irradiated surface. In the SEM observation, the contrast of irradiated areas on the Si surface becomes darker than that of unirradiated area at the acceleration voltage of 1.0 kV or higher. For HOPG sample, it was necessary to lower the acceleration voltage down to 0.5 kV in order to obtain good contrast. However, for the samples irradiated by singly charged ions (SCIs), the fluence in the order of 1015∼16/cm2 was necessary to obtain similar contrast as that of HCI irradiation. It means HCI has efficiency of 100 times as much as that of SCI for the production of SEM contrast. These effects were also found under the AFM observation. Therefore, compared to the singly charged ions, the HCIs are able to enhance the surface modification effectively.

Activities at the Tokyo EBIT 2010

In this paper, we present recent activities at the Tokyo EBIT after giving an overview of the present status of the devices. We have been studying dielectronic recombination processes by means of several techniques. In addition to X-ray observations and charge abundance observations, 2-photon observations have been recently used to study DR processes which emit two photons successively (but practically simultaneously). Recent efforts on spectroscopic work are mainly concentrated on Fe and W ions, which are relevant to astrophysical and fusion plasmas. Several spectrometers that can cover a wide range of wavelength, such as visible, EUV, and X-rays, were used for accumulating useful data for plasma diagnostics applications. HCI-surface collision processes were studied using ions extracted through the beam line, that has recently been modified. Very highly charged ions up to Bi81+ were used for studying the effect of huge potential energy.

Development and applications of electron beam ion source for nanoprocesses

An electron beam ion source (EBIS) was developed and applied to create nanostructures. The EBIS uses a commercial superconducting magnet (3T) with vacuum system independent from another vacuum system which comprises all of the ion source constituents except the magnet. The attained parameters of electron beam are emission current of 180mA and acceleration voltage of 20kV. The EBIS creates HCIs in nA region (e.g. 2nA for Ar12+). Higher charge states are suppressed by residual gases. The HCIs were irradiated to HOPG and the structure of irradiated surface was observed by STM, and the image indicates the fluence as much as 1013ion/cm2 is accessible with the present EBIS.