Near-field terahertz (THz) spectroscopic imaging, which enables sub-wavelength analysis, is a powerful method for investigating nano- and micro-scale objects such as nanomaterials, polymers, cells, and biomolecules. However, near-field imaging in the THz region remains to be fully explored, compared to other frequency regions. This review explains our chip-type near-field THz spectroscopic imaging technology. We develop a collection-mode near-field THz imager, which is based on an evanescently coupled THz sensor with a two-dimensional electron gas. The utilization of frequency-selective THz detection makes it possible to obtain near-field THz images in separate frequency bands. With this technology, we perform cryogenic near-field THz-emission imaging without external THz sources, and visualize the spatial distribution of THz radiation associated with electron injection from a source electrode in a semiconductor device. Finally, a graphene-based THz detector with wide-band frequency-tunability is presented, in which the detection mechanism is based on Landau-level formation of Dirac fermions of the graphene. This device is promising as a wide-band near-field THz spectroscopic imager.
Recent development of matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS) is summarized. Comparing about ten years ago when study of imaging mass spectrometry was started, sample preparation methodology is dramatically improved as well as instruments performance. Our group performs MALDI-IMS under microscope using iMScope TRIO (Shimadzu, Kyoto, Japan). In microscopic MALDI-IMS, special sample preparations are required to improve detection sensitivity and spacial definition. We consider “one-size-fits-all” sample preparation method cannot be available to date, therefore sample preparation methods should be selected for different sample types or target molecules.
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been recognized gradually as a powerful analytical tool for plant materials. The availability of TOF-SIMS measurements in a research field of plant science is briefly introduced. Main polymer components of plant cell wall, cellulose, hemicellulose, and lignin are detected as fragment ions. Inorganics and low molecular-weight extractives are detectable as elemental and molecular ions. In living plant materials, there are various water-soluble organic/inorganic chemicals. There is a strong apprehension that such water-soluble chemicals can be moved by the sample preparation process of trimming, sectioning, and drying. Recently, the author and co-workers have analyzed freeze-fixed plant samples by cryo-TOF-SIMS. The latest topics of cryo-TOF-SIMS dealing with frozen-hydrated samples are introduced.
The high sensitivity of secondary ion mass spectrometry (SIMS) allows isotope imaging and the high spatial precision has a potential for the localization of isotopes corresponding to the ultrastructure of cell components. This paper reviews a study in which transfers of carbon and nitrogen from the fungus in a symbiotic orchid protocorm were analyzed, combining an isotope tracer experiment, sample preparation for transmission electron microscopy, and SIMS cellular imaging. The results showed that, 13C and15N transferred from young and senescent hyphae, and in the plant cells, they were localized differently in individual cells and organelles, depending on the colonization status (the presence or absence of fungal structures and the early or late developmental stage of the fungal structure). Stable isotope imaging at the cellular level provides new insights into cellular functions of the endosymbiosis.
Recent development of digitized and automated measurement systems has inevitably accelerated applications of data mining techniques based on statistical/information processing. In the present article we outlined the recent progress in our chemical imaging techniques based on the statistical analysis of ‘spectral image’ datasets, obtained by a suite of scanning transmission electron microscopy and associated spectroscopy. Finally, we discuss the future prospects of the field to extend the present bilinear model to multi-way analysis for more robust modeling of low signal-to-noise ratio data.
Using near-field microscope, one can realize optical nano-imaging beyond the diffraction limit of incident light. The characteristic of this microscope is to combine variety of spectroscopic technique e. g. linear and non-linear vibrational spectroscopy, IR absorption, light scattering spectroscopy, fluorescence and photoluminescence. In this article, we will provide the basics of near-field microscope as well as reviewing recent 2-3 yearʼs publications related to this technique.
Briefly summarized are our present activities on how to utilize ion beams for bio imaging. We have been trying to extend the analysis scope of bio-SIMS from lipids and metabolites to proteins to make SIMS an omni-molecular imaging tool. To overcome the sample preparation requirement of mass spectrometry for vacuum compatibility, an ambient imaging mass spectrometer has been developed. A TOF-MEIS system developed for nano thin film interface analysis were used for liquid interface analysis, which can be extended further to cell membrane analysis. Ultimate spatial resolution of 0.5 nm with ion beams is provided by HIM. Complementary multimodal approaches are necessary for better understanding of nano and bio systems.
Recent developments in the research field of Dirac and Weyl semimetals are reviewed. We introduce Weyl semimetal which has linear energy dispersion and nontrivial topology in the band structure. One of characteristic phenomena is negative magnetoresistance, which stems from three-dimensional linear dispersion. Another characteristic phenomenon is the anomalous Hall effect which occurs in Weyl semimetals with magnetic order. Fermi arc states appear as surface states localized at the boundary. Type II Weyl semimetals are also argued.