Construction of a three dimensional atom probe and its applications to materials research

我们研制了一种三维原子探针，并应用该仪器对各种金属材料的显微组织进行了表征。这种新型原子探针由反射式飞行时间原子探针（ToFAP）和位置敏感原子探针（PoSAP）组成，它们由基于CAMAC的控制系统与Macintosh计算机接口控制。在评价了反射式原子探针和位置灵敏原子探针的基本性能后，我们用该仪器对几种纳米磁性材料的微结构进行了研究。Co-Cr薄膜的三维原子探针分析表明，Co-22 at.%铬薄膜的高温化学沉积。层状铁磁相和顺磁相共存于同一晶粒内。这些纳米级相直接在具有原子空间分辨率的三维空间中可视化。应用该仪器对某些纳米晶磁性材料的显微组织演变进行了表征，揭示了合金初晶化过程中纳米晶组织演变的机理。我们还展示了铁磁颗粒如何通过退火Cr-Fe合金演变，并将微观结构与在该合金系统中观察到的磁电阻行为相关联。

We have constructed a three dimensional atom probe and applied this instrument for characterizing microstructures of various metallic materials. The new atom probe consists of both a reflectron type time-of-flight atom probe (ToFAP) and a position sensitive atom probe (PoSAP) , which are controlled with a CAMAC based controlling system interfaced with a Macintosh computer. After the evaluation of the basic performances of the reflectron atom probe and the position sensitive atom probe, we have employed this instrument for studing microstructures of some selected nanostructured magnetic materials. Three diemensional atom probe analysis of Co-Cr thin films revealed that nanoscale compositional fluctuations were present in the Co-22at.%Cr thin films sputter-deposited at elevated temperatures. The lammer-like ferromagnetic and paramagnetic phases were found to coexist within a crystal grain. These nanoscale phases were directly visualized in a three dimensional space with atomic spatial resolution. Application of this instrument to charactrizing the microstructural evoluiton in some nanocrystalline magnetic materials revealed mechanisms how nanocrystalline microstructure evolved by primary crystallization of alloys. We have also shown how ferromagnetic particles evolve by annealing Cr-Fe alloys, and correlated the microstructure with the magnetoresistance behovior observed in this alloy system.