Yuki Matsushita

Photo-induced strain imaging of semiconductors

This paper presents a novel method for high-resolutions imaging of band-gap energies of semiconductors. When electron-hole pairs are generated in a semiconductor irradiated with a laser, they induce electronic strains in the semiconductor. The electronic strains can be detected and imaged by a scanning probe microscope. The electron-hole-pair generation depends on the band-gap and photon energies. When there are variations in band-gap energies in a sample, strains could be detected in regions having narrower gaps than the irradiated photon energy, and so their distributions can be imaged. The threshold of electron-hole-pair generation can be varied by changing the irradiated photon energies. Consequently, we can quantitatively image the band-gap energy distributions of semiconductors.

Strain imaging of a LiCoO2 cathode in a Li-ion battery

Li-ion batteries have been recognized as promising devices for a sustainable society. Layered LiCoO2 and graphite are commonly used as electrode materials for Li-ion batteries. When charging and discharging, Li-ions are extracted or inserted into the interlayers, which causes changes in volume. Scanning probe microscopy (SPM) can allow high resolution imaging of these volume changes, which enables us to investigate Li-ion migration without destruction. We observed volume changes in the LiCoO2 cathode using SPM and successfully imaged the distribution of the volume changes corresponding to the LiCoO2 particles. Volume changes in the interspace were significantly larger than those in the particles. The large volume changes are caused by electrolyte flux induced by changes in concentration of Li ions. The volume changes were greatly reduced when the electrolyte dried out. The dry-out and infiltration of electrolyte between the LiCoO2 particles and the current collector spread out with the procedure of degradation of the batteries. The boundaries between the dry-out and infiltration regions acted as barriers of electrolyte flux.

High-resolution imaging of Li-ion migration at the interface of LixTi5O12 and solid electrolyte in an all-solid-Li-ion battery

The authors investigated Li-ion migration at an interface between a LixTi5O12 (LTO) anode and solid electrolyte in an all-solid Li-ion battery using optical and scanning probe microscopy (SPM). LTO changes from an insulator to a conductor with increasing Li content, which decreases LTO transparency. Therefore, observation of changes in the transparency enables us to image Li-ion migration. LTO was sputtered on an indium tin oxide with a glass substrate in order to observe the transparency using an optical microscope. Variations in Li content by charge/discharge of the battery using the LTO as an anode could be observed during operation. Li-ion migration was confirmed in specific locations at the contact areas between the LTO and solid electrolyte. When electron–hole pairs are generated in a semiconductor by photon injection, electric strains are generated. SPM can detect and image the photo-induced strains with high resolution. Discharged LTO is a semiconductor having a band gap but charged LTO is metalli...