In this study, we investigate the terahertz (THz) characteristics of α-lactose monohydrate powder using a tapered parallel-plate waveguide (TPPWG) technique, which facilitates the analysis of microscopic and sub-milligram quantities. Our results show that the TPPWG method not only minimizes the required sample quantity but also enhances the THz wave interaction with the powder sample, which ensures strong resonance features even with minimal material. The TPPWG technique measured higher-quality resonances using only 0.94% of the lactose powder mass, compared to the traditional pellet measurement method. Despite using only 0.91 mg of lactose powder, the TPPWG technique detected a wide bandwidth and clear resonance peaks with a relatively small base absorption, up to 14 times smaller than the pellet measurement. In addition, it was confirmed that the absorbance characteristics remain consistent regardless of the geometric distribution of the lactose layer as long as the mass or volume of the lactose powder is the same. These findings highlight the TPPWG method's potential for efficient and reliable THz characterization of powdered samples. 

Heteroatom doping is useful for enhancing the electrochemical performance of sodium-based secondary battery (SBB) anodes. However, the complexity of synthesis and safety issues caused by harmful dopant precursors must be overcome. Herein, a one-step plasma-in-liquid process is adopted to synthesize N and S co-doped carbon-based anode material (NS/C) for SBBs. NS/C exhibits a large specific surface area (476.8 m2 g1) and abundant active sites on its surface owing to its void structure. Owing to the advantages of this structure, NS/C evidently caused a co-intercalation reaction in an ether-based electrolyte while avoiding solid electrolyte interface (SEI) layer formation on the anode surface. Transmission electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and the Brunauerno -Emmett- Teller method with a novel analysis method using terahertz waves are employed to prove that no SEI formed on the anode surface. When the anode is applied to a sodium-ion half-cell, NS/C exhibited a remarkable cycling life of 35,000 cycles at an ultrahigh current density of 100 Ag -1 with high reversible capacity of >72 mAh g-1. Furthermore, NS/C shows outstanding electrochemical performance for a seawater battery anode, with a cycling life of more than 1500 at the first attempted current density of 10 Ag-1.

Heteroatom doping is useful for enhancing the electrochemical performance of sodium-based secondary battery (SBB) anodes. However, the complexity of synthesis and safety issues caused by harmful dopant precursors must be overcome. Herein, a one-step plasma-in-liquid process is adopted to synthesize N and S co-doped carbon-based anode material (NS/C) for SBBs. NS/C exhibits a large specific surface area (476.8 m2 g1) and abundant active sites on its surface owing to its void structure. Owing to the advantages of this structure, NS/C evidently caused a co-intercalation reaction in an ether-based electrolyte while avoiding solid electrolyte interface (SEI) layer formation on the anode surface. Transmission electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and the Brunauerno -Emmett- Teller method with a novel analysis method using terahertz waves are employed to prove that no SEI formed on the anode surface. When the anode is applied to a sodium-ion half-cell, NS/C exhibited a remarkable cycling life of 35,000 cycles at an ultrahigh current density of 100 Ag -1 with high reversible capacity of >72 mAh g-1. Furthermore, NS/C shows outstanding electrochemical performance for a seawater battery anode, with a cycling life of more than 1500 at the first attempted current density of 10 Ag-1.

We propose an all-dielectric single-layer guided-mode resonance filter (GMRF) operating in the high-frequency terahertz (THz) region. For the fabrication of thin gratings to achieve strong resonance in the high-frequency region, the refractive index and absorption must be small, while the tensile strength must be high. Cyclic olefin copolymer (COC) films have a lower refractive index and absorption than polyethylene terephthalate (PET) films and a higher tensile yield strength than polytetrafluoroethylene (PTFE) films. Therefore, the COC film was found suitable to fabricate a GMRF operating in the high-frequency THz region. We fabricated COC-based single-layer GMRFs with a thickness of 50 µm and grating periods of 500, 400, 300, 200, and 100 µm; the resonance frequencies of the TE0,1 mode were 0.576, 0.712, 0.939, 1.329, and 2.759 THz, respectively. A shorter grating period caused a greater shift of the resonance to a higher frequency. In particular, the COC film enabled the fabrication of a 100-µm grating period with a ridge width of 32 µm and length of 2 mm, enabling the GMRF to operate up to 2.759 THz, which is very high frequency compared to the previous highest frequency of 0.7 THz. These results were in good agreement with a simulation using rigorous coupled-wave analysis.