超低加速・超高分解能電界放出型走査型電子顕微鏡の拓くナノ表面分析の新たな世界：ステンレス鋼中のナノ介在物の観察と分析

概要

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For successful application of low-voltage, ultra-high resolution scanning electron microscopy for nano-surface analysis, sample surface preparation is of key importance. Here, this is demonstrated through the examination of fine inclusions in a type 304 stainless steel. Inclusions are mostly MnS, TiO2, Al2O3 and TiN; they are present either in isolation or forming clusters of two, three, or four features. With the use of mirror-finished surfaces, prepared by mechanical polishing using a suspension of colloidal silica, these inclusions were not revealed clearly due to the presence, at the surface, of thin contaminant layers. After removal of such contaminant layers by radio-frequency-powered glow discharge sputtering, however, inclusions were revealed at the clarity never seen before. By sputtering, thin contaminant layers are removed successfully, without formation of new altered surface layers. Simultaneously, sputtering generates fine textures over the surface of inclusions that are directly related to their compositions. Through the use of such sputter-induced textures, compositional variations in mixed inclusions of sizes even below 50 nm can be revealed clearly and at a high lateral resolution of ∼1 nm.