Transformative Atomic Chemical Resolution Analysis of Modulated Nanostructures

具有调制纳米级结构的合金，其组成元素（例如铜和钛）在其整个体积中以波状模式分布。波的波峰和波谷对应于高铜和高钛浓度。波峰和波谷之间的间距很小，通常为20到70个原子直径。这些调制取决于合金的加工条件，并且在合金投入使用后会发生变化。这些合金的重要性能，如强度、磁性和电学性能，取决于成分调制，因此测量这些特性的能力对于理论理解和实际应用至关重要，例如先进制造和国防应用。现在，使用新开发的高分辨率电子显微镜，首次可以对这些精细尺度的成分调制进行精确的实验测量。本研究的主要目标是高分辨率测量这些调制及其在几种具有实践和理论重要性的合金中的三维分布。研究结果将在科学档案文献、研究会议和专题讨论会中广泛报道，并将纳入我们备受推崇的高分辨率电子显微镜冬季学校的教学以及电子显微镜和材料科学课程。冬季学校每年一月在亚利桑那州立大学开课（从1981年开始）。典型的入学人数是50名学生（包括国内和国际学生），男女比例大致相等。材料相变和综合电子显微镜的研究生课程（包括讲座和实验室）通常每学期招收15至20名学生，性别分布均匀。技术摘要：本项目的主要目的是定量测量具有调制纳米结构的合金的成分波动，并对纳米结构进行层析成像。合金中调制纳米结构的形成通常归因于旋回沉淀反应。调制成分、振幅和波长是测量这些重要合金的力学、磁性和电学性能以及与合金理论相关的最重要的实验变量。x射线和电子衍射以及衍射对比电子成像较早地被用于测量调制波长，但这些方法不能提供非常重要的调制成分和梯度。观察到的波长很小，通常约为20至70个原子直径，因此需要非常高的空间分辨率组成测量。一种新的配有精密EELs和EDX光谱仪的单色场发射STEM电子显微镜已经证明了所需的原子空间和化学分辨率。这些将用于HAADF STEM/EELs/EDX线扫描和光谱成像模式，以确定调制成分的振幅和梯度。早期的常规显微镜也表明，调制可以发生在多个维度上，并且调制周期中发生复杂的故障，但投影复杂性阻碍了这些特征的清晰解释。HAADF STEM和HAADF STEM/EELs层析成像将用于更全面地了解这些特征。在这个项目中展示的新的变革性高分辨率化学成像方法对于推进美国制造业和国防应用以及研究生教育重要的各种合金的研究和开发非常重要。项目结果将在档案期刊和科学会议上报告，并将纳入备受推崇的年度高分辨率电子显微镜冬季学校和材料与固体科学研究生教育计划。

Non-Technical AbstractAlloys with modulated nano-scale structures have their constituent elements (copper and titanium, for example) distributed in wave-like patterns throughout their volume. The peaks and valleys of the waves correspond to high copper and high titanium concentrations. The spacings between the peaks and valleys are small, typically 20 to 70 atom diameters. These modulations depend on alloy processing conditions, and they can change after the alloys are put into service. Important properties of these alloys, such as strength, and magnetic and electrical properties, depend on the composition modulation, so the ability to measure these characteristics is essential for theoretical understanding and practical applications, such as advanced manufacturing and defense applications. Accurate experimental measurements of these fine scale composition modulations are now possible for the first time, using newly developed high-resolution electron microscopes. The primary objectives of this research are high-resolution measurements of these modulations and their three-dimensional distributions in several alloys of practical and theoretical importance. The results will be reported widely in the scientific archival literature and at research conferences and symposia, and they will be incorporated into teaching at our highly regarded Winter School for High Resolution Electron Microscopy and classes on electron microscopy and materials science. The Winter School is taught every January (beginning in 1981) at Arizona State University. Typical enrollment is 50 students (both domestic and international) about equally divided between women and men. Enrollment in graduate courses on materials phase transformations and comprehensive electron microscopy (both lectures and laboratories) is typically fifteen to twenty students per semester, with an even gender distribution. Technical AbstractThe primary objectives of this project are quantitative measurements of composition fluctuations in alloys with modulated nanostructures, and tomographic imaging of the nanostructures. Formation of modulated nanostructures in alloys is most often attributed to spinodal precipitation reactions. Modulation composition amplitude and wavelength are the most important experimental variables to measure to control the mechanical, magnetic and electrical properties of these important alloys, and for correlation with alloy theory. X-ray and electron diffraction and diffraction contrast electron imaging have been used earlier to measure modulation wavelengths, but these methods do not provide the very important modulation compositions and gradients. The wavelengths observed are small, typically about 20 to 70 atom diameters, thus very high spatial resolution composition measurements are required. A new aberration corrected and monochromated field emission STEM EMs fitted with precision EELs and EDX spectrometers have demonstrated the required atomic spatial and chemical resolution. These will be used in HAADF STEM/EELs/EDX line scan and spectrum imaging modes to determine modulation composition amplitudes and gradients. Earlier conventional microscopy also showed that modulations could occur in more than one dimension and that complicated faults occurred in modulation periodicity, but projection complications prevented a clear interpretation of these features. HAADF STEM and HAADF STEM/EELs tomographic imaging will be used to develop a more complete understanding of these features. The new transformative high-resolution chemical imaging methods demonstrated on this project are important for advancing research and development on diverse alloys important for US manufacturing and defense applications and for graduate education. Program results will be reported in archival journals and scientific meetings, and will be incorporated into the highly regarded annual Winter School for High Resolution Electron Microscopy and into the graduate education program for materials and solid state science.