This commentary explains the origin, principles, practical applications, and future perspectives of mass-selected ion beams generated using two rotating electric-field mass (REF-MS) filters as a formation of primary ion beams. Our team has been investigating the underlying principles of REF-MS separation and assessing the feasibility of developing suitable systems to realize mass separation and ion beam convergence using rotating electric fields as well as the practicability of this method. This commentary focuses on the mechanism observed cycloid trajectories followed by REF-MS-selected ions as a formation of primary ion beams. A focused ion beam column with Ga and AuGe liquid metal ion sources was introduced to REF-MS optics to assess the mass-selection performance as the filter. The column was then replaced with a vacuum electrospray ionization source, and the resulting mass-selected and/or cluster size-selected ion beam was used to create a microscale crater and Co elemental ring.

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Automatic estimation methods (1/n-Power Plot and Shift-Log-Log Plot methods) are proposed to estimate the power exponent of a spectrum following a power law and the threshold at which the power begins to increase. The 1/n-Power Plot method is used when there is prior information on the power exponent and the inverse of the power exponent is applied to the spectrum to linearise the increasing region and obtain the threshold. The shift-log-log plot method is used when there is no a priori information and estimates the power exponent by a log-log plot taking into account the threshold. These methods were used to automatically estimate the threshold and power exponent from the photoelectron emission spectrum and the voltage-current spectrum.

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Li metal have been attracting attention as the next generation anode material for all-solid-state batteries (ASSBs) with high energy density. However, since severe side reactions occur at the interface between Li metal anode and solid electrolytes, Li metal anodes have not yet been commercialized. In this study, the authors examined the side reactions at the interface between the Li metal anode and oxide solid electrolyte using surface analysis technique. As a result, it was found that some of the components of the solid electrolyte diffused to the Li metal anode side. It was clear that suppressing this diffusion is essential for stable battery operation.

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Focused ion beam (FIB) is widely used in sample processing for failure analysis of intricate electronic devices. In general, a Ga ion beam is used for this purpose. Recently, the combination of time-of-flight secondary ion mass spectrometry (TOF-SIMS) and FIB, so called FIB-TOF, has gained attention for enabling three-dimensional imaging of materials with complex chemical distributions and/or structures. However, a challenge of Ga-FIB is its slow processing speed. To address this issue, Bi-FIB has been investigated. Bi, the heaviest non-radioactive element on the periodic table, has the potential not only to enhance the processing speed but also to minimize the influence of FIB residues on TOF-SIMS spectra. In this paper, we present a comparison between Ga-FIB and Bi-FIB, and demonstrate the results of Bi-FIB for cross-sectional observations of all-solid-state battery materials.

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