Secondary ion emission with MeV heavy ions provides a unique opportunity for insight into ion collisions and material analysis. MeV-energy ion beams excite electrons near the surface and enhance the ionization of high-mass molecules, enabling the acquisition of secondary ion mass spectrometry (SIMS) spectra of ionized molecules with suppressed fragments. The SIMS technique with MeV-energy heavy ions (MeV-SIMS) has opened new possibilities for investigating the chemical composition and structure of organic and biological materials, as well as for their imaging. The ambient analysis system is essential for analyzing solid–liquid interfaces, because liquid materials evaporate easily in a vacuum. It is difficult to measure volatile liquid (wet) samples using conventional SIMS. The mean free path of ions with energy in the keV range is very short in low vacuum, and these ions cannot penetrate the surface. By contrast, evaporation of liquid materials in He at atmospheric pressure is suppressed and samples containing liquid can be measured using the MeV-SIMS technique without the need for preparing dry samples. Recently, the authors developed a humidity-controlled ambient MeV-SIMS system because the water evaporation rate strongly depends on humidity. To obtain imaging mass spectra of wet samples, the wet sample surface needs to be maintained under ambient and humid conditions for a prolonged time. At 0.04 MPa, under 100% humidity, a sample of aqueous solution of benzoic acid produced water droplets that remained in the target chamber for more than 30 min, and clusters and compounds of benzoic acid with water were detected with high sensitivity by the humidity-controlled ambient MeV-SIMS system.

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使用 MeV 离子在环境和潮湿条件下进行二次离子质谱测量

带有 MeV 重离子的二次离子发射为深入了解离子碰撞和材料分析提供了独特的机会。MeV 能量离子束激发表面附近的电子并增强高质量分子的电离，从而能够获得具有抑制碎片的电离分子的二次离子质谱 (SIMS) 光谱。具有 MeV 能量重离子的 SIMS 技术 (MeV-SIMS) 为研究有机和生物材料的化学成分和结构以及它们的成像开辟了新的可能性。环境分析系统对于分析固液界面至关重要，因为液体材料在真空中很容易蒸发。使用传统的 SIMS 很难测量挥发性液体（湿）样品。能量在 keV 范围内的离子的平均自由程在低真空中非常短，这些离子无法穿透表面。相比之下，大气压下液体材料在 He 中的蒸发受到抑制，并且可以使用 MeV-SIMS 技术测量含有液体的样品，而无需制备干样品。最近，作者开发了一种湿度控制的环境 MeV-SIMS 系统，因为水蒸发率在很大程度上取决于湿度。为了获得湿样品的成像质谱，湿样品表面需要在环境和潮湿条件下保持较长时间。在 0.04 MPa、100% 湿度下，苯甲酸水溶液样品产生的水滴在目标室中停留了 30 分钟以上，