Development of laser ionization mass nanoscope (LIMAS)

Abstract

We have developed a new nano-beam time-of-flight secondary neutral mass spectrometry system: laser ionization mass nanoscope or LIMAS. The primary ion beam column was equipped with a Ga liquid metal ion source and aberration correction optics. The primary ion beam was down to 40 nm in diameter under a current of 100 pA with an energy of 20 keV. The sputtered particles were post-ionized under non-resonance mode by a femtosecond laser. The post-ionized ions were introduced into a multi-turn mass spectrometer. A mass resolution of up to 40 000 was achieved. The vacuum of the sample chamber was maintained under an ultrahigh vacuum of 2 Â 10 À8 Pa. This instrument would be effective for ultrahigh sensitive analysis of nanosized particles such as return samples from asteroids, comets, and planets.

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

“…The absolute concentration at a given depth, however, is variable for each measurement because calibration factors from ion intensities to 4 He concentrations may vary with the measurement area. That is, because He has a much lower ionization efficiency by laser (~10%) than all other elements (~100%) (Ebata et al, 2012), the ionization efficiency of 4 He strongly depends on the laser photon density, i.e., the focusing conditions at the postionization position. Therefore, the extraction efficiency of each post-ionized ion for LIMAS would vary from spot to spot because the geometric relationship between the sputtering and the laser focusing changes slightly each time the sample moves.…”

“…An SNMS instrument called LIMAS (Ebata et al, 2012) was used for our measurements. A pulsed primary beam of 69 Ga (30 keV and 38 nA) was focused to a spot 800 nm in diameter on the sample surface of the DOS.…”

“…In this study, we used a novel technique-sputtered neutral mass spectrometry (SNMS) using strong-field ionization* (Ebata et al, 2012)-to measure He profiles in Genesis collectors, thus revealing the nanoscale depth distribution of solar wind He. We can obtain depth profiles because our instrument can quantify 4 He present at tens of parts per millions atomic by analyzing an area of a solid surface only a few microns in size.…”

New mass spectrometry techniques for studying physical chemistry of atmospheric heterogeneous processes

“…Imaging of smaller particles may become possible using recent instrument development efforts reported by Ebata et al [128]. Their study described the development of a new laser ionisation mass nanoscope, in which the primary 20 keV Ga + ion beam can be focused to a diameter of 40 nm.…”

Nucleosynthetic Signatures in Presolar SiC and Graphite Grains

“…The other instrument, LIMAS (Laser Ionization Mass Nanoscope), has been installed at Hokkaido University, Japan [50]. This is a non-resonant, post-ionization mass spectrometer.…”