Depth profiling analysis of solar wind helium collected in diamond-like carbon film from Genesis

The distribution of solar-wind ions in Genesis mission collectors, as determined by depth profiling analysis, constrains the physics of ion-solid interactions involving the solar wind. Thus, they provide an experimental basis for revealing ancient solar activities represented by solar-wind implants in natural samples. We measured the first depth profile of ^4He in a Genesis collector; the shallow implantation (peaking at <20 nm) required us to use sputtered neutral mass spectrometry with post-photoionization by a strong field. The solar wind He fluence calculated using depth profiling is ~8.5 × 10^(14) cm^(–2). The shape of the solar wind 4He depth profile is consistent with TRIM simulations using the observed ^4He velocity distribution during the Genesis mission. It is therefore likely that all solar-wind elements heavier than H are completely intact in this Genesis collector and, consequently, the solar particle energy distributions for each element can be calculated from their depth profiles. Ancient solar activities and space weathering of solar system objects could be quantitatively reproduced by solar particle implantation profiles

Aberration-corrected focused ion beam for time-of-flight secondary neutral mass spectrometry

A chromatic and spherical aberration corrector with liquid Ga ion metal source was developed. The aberration corrector reduced the ion probe diameter to similar to 1.5 times smaller for the Ga-69(+) beam in aberration correction mode compared with the corrector in non-aberration correction mode. The probe current at a given probe size is approximately two times larger in aberration correction mode than in non-aberration correction mode. The aberration-corrected focused ion beam yields higher lateral resolutions and higher sensitivities with lower acceleration voltage for the same acquisition time down to 10 nm with a current of 1 pA. (C) 2019 The Japan Society of Applied Physic

Quantitative analysis of helium by post-ionization method using femtosecond laser technique

Helium has the largest ionization potential of all elements; thus, it is difficult to ionize for measurement by mass spectrometry. In order to analyze He, a tunnel-ionization time-of-flight sputtered neutral mass spectrometry system (called LIMAS) has recently been developed. LIMAS uses a femtosecond laser technique and can ionize He. We quantified the effectiveness of this method for He analysis from a 2.5x4 mu m(2) area of He-implanted silicon. The amount of He in an implant was quantified by measuring the ion current, giving a nominal implant fluence per unit area. Thus, the fraction of total He measured by LIMAS during depth profiling could be quantified by comparison with the He concentration of the reference implant. The He+ intensities normalized by host ions of Si linearly correlated with the known He concentrations with a reproducibility of 10% at concentrations less than 10(21)cm(-3). The detection limit was down to 10(18) He cm(-3) (20ppm). For concentrations exceeding 10(21)cm(-3), the He intensities are smaller than those expected from the lower concentration range. This non-linearity may reflect the limit of retention of He in the Si lattice, because He is chemically inert. Copyright (c) 2016 John Wiley & Sons, Ltd