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impacts北山 巧*; 中嶋 薫*; 鈴木 基史*; 鳴海 一雅; 齋藤 勇一; 松田 誠; 左高 正雄*; 辻本 将彦*; 磯田 正二*; 木村 健二*
Nuclear Instruments and Methods in Physics Research B, 354, p.183 - 186, 2015/07
被引用回数：2 パーセンタイル：17.57(Instruments & Instrumentation)According to an inelastic-thermal-spike (i-TS) model, which is regarded as the most promising among several models proposed to explain the formation of an ion track, a part of the energy deposited to electrons in a solid by a swift heavy ion is gradually transferred to target atoms via electron-phonon coupling. The temperature of target atoms rises along the ion path and consequently an ion track is formed when the temperature exceeds the melting point. Therefore, the temperature of target atoms along the ion path is regarded as a key parameter for the i-TS model; however, such a spatiotemporally-localized temperature is difficult to measure because the processes involved occur in a very short period (
10
s) and in a very localized area. In this study, the temperature of target atoms along the ion path is estimated experimentally with transmission-electron-microscope (TEM) observation of desorption of Au nanoclusters (the melting point 
1300 K) on an amorphous Si
N
thin film under 1.1-MeV C-ion irradiation to the fluence of 5
10
ions/cm
. TEM images show that Au nanoclusters, deposited at the areal density of 1.1610
particles/cm, disappear in a surface area with a diameter of 20 nm around each ion track, whose diameter is 4 nm, after irradiation. This indicates that the temperature at the film surface rises locally to at least 1300 K by the ion bombardment.
今井 誠*; 左高 正雄*; 松田 誠; 岡安 悟; 川面 澄*; 高廣 克己*; 小牧 研一郎*; 柴田 裕実*; 西尾 勝久
Nuclear Instruments and Methods in Physics Research B, 354, p.172 - 176, 2015/07
被引用回数：14 パーセンタイル：75.5(Instruments & Instrumentation)炭素薄膜通過後の2.0MeV/uの炭素イオンについて平衡状態および非平衡状態の両方の電荷分布を実験的に調べた。測定された電荷状態分布は、10
g/cmの標的厚さで平衡に達し、これは98g/cmの最大標的厚さまで変化しなかった。平衡電荷分布、平衡平均電荷、および平衡分布の幅と傾きを、ETACHAコードを含むシミュレーション結果だけでなく、既存の半経験式を用いた予測と比較した。C
, C
, C
入射イオンの電荷分布, 平均電荷状態および分布幅は、平衡前の領域で5.7g/cmの標的厚さで準平衡値に合流し、そして同じ速度での硫黄イオンで既に示されているように、C
およびC
イオンを含む全ての初期荷電状態についての真の平衡値に到達している。ETACHAと単一電子移動のみを考慮したレート方程式の2種類のシミュレーションを使用することで、測定された電荷状態の変化を定性的に再現した。準平衡な挙動はETACHAコードで再現できるが、初歩的なレート方程式では再現できない。
齋藤 勇一; 千葉 敦也; 薄井 絢; 山田 圭介; 的場 史朗; 鳴海 一雅
no journal, ,
Intense cluster ion beams are required in research of surface modification, surface analysis and so on. One of the key points in increasing a current of a cluster beam accelerated by a tandem accelerator is enhancement of transmission, a ratio of a beam current of incident negative cluster ions upon the tandem to that of accelerated intact positive cluster ions. The transmission is strongly dependent on a charge-exchange gas pressure. Therefore, the measurement of transmission as a function of the gas pressure is important to obtain a higher beam current of cluster ions. In this work, the transmission of C
ions was measured as a function of the helium gas pressure in the high voltage terminal at 2.5 MV. The maximum transmission ratios of 2.6% for C
and 1.4% for C were finally obtained.
鳴海 一雅; 千葉 敦也; 山田 圭介; 的場 史朗; 齋藤 勇一
no journal, ,
A vicinage effect on secondary-electron (SE) emissions from a solid induced by swift molecular/cluster ions is one of the open questions of atomic collisions in solids. It cannot be explained by only the production process of the three-step model of SE emissions, which is closely related to the energy deposition by a projectile. We have investigated cluster-size dependence of SE yields emitted in the forward direction from amorphous C foils (2-100 g/cm) bombarded with 62.5-keV/u C
ions (
= 1-4) in order to demonstrate the vicinage effect not originating from the production process in the present study. Suppression of SE emissions (one of the vicinage effects) is observed and does not diminish in all the foils measured. The suppression effect is larger as the cluster size is larger. This dependence is observed for at least 60 g/cm, indicating that the effect originating from some physical mechanism exists even at the thick foils, where the contribution of the production process to the effect could be excluded on the basis of previous studies. This can lead to the conclusion that the vicinage effect not originating from the production process is demonstrated experimentally.
中嶋 薫*; 永野 賢悟*; 鈴木 基史*; 鳴海 一雅; 齋藤 勇一; 平田 浩一*; 木村 健二*
no journal, ,
Secondary-ion mass spectrometry has been much improved in sensitivity to large molecular ions with large clusters as primary ions, such as C ions, Ar cluster ions, water cluster ions and so on in the last two decades. In this study, further enhancement of sensitivity to the intact organic molecular ions is demonstrated with measuring secondary ions emitted in the forward direction by transmission of swift cluster ions through a film target. Thin phenylalanine films (20-100 nm thick) deposited on self-supporting SiN membranes (20 or 50 nm thick) were bombarded with 5-MeV C ions. Mass distributions of positive secondary ions emitted in the forward direction were measured using a time-of-flight technique under the bombardment of the SiN side, as well as those in the backward direction under the bombardment of the phenylalanine side. Measurements with primary 6-MeV Cu ions were also carried out for comparison. The yield of intact phenylalanine molecular ions emitted in the forward direction is significantly enhanced compared to that in the backward direction, while yields of small fragment ions are suppressed. The behaviors of the enhancement and suppression both for 5-MeV C ions and for 6-MeV Cu ions will be discussed in terms of density distribution of energy deposited to the surface of the phenylalanine side.
irradiation北山 巧*; 森田 陽亮*; 中嶋 薫*; 鈴木 基史*; 鳴海 一雅; 齋藤 勇一; 松田 誠; 左高 正雄*; 辻本 将彦*; 磯田 正二*; et al.
no journal, ,
Our previous observation of an ion track by sub-MeV C-ion bombardment of a thin amorphous silicon nitride (a-SiN) film with transmission-electron microscopy has shown a large density reduction in the core region, and it suggests emission of thousands of atoms from the cylindrical region. Sputtering yields of a-SiN films by C ions were evaluated in order to confirm this suggestion. A-SiN films deposited on Si(001) were irradiated with 540-keV C ions at fluences up to 110
ions/cm. The sputtering yields were estimated to be 3900
500 N atoms/ion and 15001000 Si atoms/ion from the compositional depth profiles measured with high-resolution Rutherford-backscattering spectroscopy. The sputtering yield of N was two orders of magnitude larger than the elastic sputtering yield by the SRIM code, indicating that the observed sputtering yield cannot be explained by elastic collisions. The sputtering yield of an a-SiN film by 100-MeV Xe
ions was also measured in order to confirm a possibility of electronic sputtering. Although the electronic stopping power for 100-MeV Xe is more than twice larger than that for 540-keV C, the observed sputtering yield was only 500200 atoms/ion. This indicates that the huge sputtering yield for the impact of C cannot be explained by the simple electronic sputtering, either. A possible explanation might be a synergistic effect of the nuclear and electronic stopping powers.
