GOALI: Fluctuation Electron Microscopy Studies of Ultra-Low Expansion Glasses and Ceramics

非技术描述：高精度的仪器和工具，如空间望远镜反射镜和芯片制造室内的工作台，往往会受到很大的温度变化，因此它们需要用不随温度改变大小或形状的材料制成。康宁研究开发公司生产的一系列超低膨胀材料(ULE)满足了这些苛刻的要求。它们是二氧化钛和二氧化硅的玻璃混合物，但其精确结构和零膨胀机制尚不清楚。这项研究是利用一种名为涨落电子显微镜的特殊显微镜技术在原子水平上研究ULE结构。有限元是一种统计技术，它探索在其他无序材料中原子有序的微妙痕迹。这项研究有两个广泛的目标。第一是确定超低膨胀材料的结构如何随二氧化钛含量和工艺条件的变化而变化，并解释其低膨胀机理。第二是将有限元技术发展成为研究所有无序材料，特别是玻璃和非晶态陶瓷的完全定量的工具。康宁公司的Aram Rezikyan是该项目的工业合作伙伴；PI和共同PI由另一名正在进行模拟的工业研究人员加入。一名研究生正在与康宁密切互动，正在学习仪器和分析技能，这些技能对未来在材料科学领域的职业生涯很有价值。高中生在这一年中通过亚利桑那州立大学运行的科学指导计划(场景计划)参与这项研究。技术细节：一种超低膨胀材料(ULE)是由康宁研究开发公司制造的，它是二氧化钛(二氧化钛)和二氧化硅(二氧化硅)的固溶体。可以调整成分和工艺条件，使其在指定温度下的热膨胀系数(CTE)为零。开发在很宽的温度范围内具有零或接近零的CTE变化率的材料是非常理想的。为了实现这些性能，必须确定ULE微晶玻璃材料的详细结构，并需要详细了解导致零膨胀的机理。由于这种材料是一种无序玻璃，标准的衍射和成像方法不能给出结构的清晰图像。在这个项目中，涨落电子显微镜被用来检测和探索这些原本是长程无序的材料中存在的1到2 nm长度尺度上的中程有序。这项研究有两个广泛的目标。首先，应用有限元方法研究了超细二氧化钛-二氧化硅微晶玻璃的结构-性能关系。正在研究小于2 nm的长度尺度上的组成和中程有序对性能的影响方式。第二，通过改进研究电子束敏感材料的实验和建模方案，推动有限元作为一种定量技术来研究无序材料，如陶瓷和玻璃。一名研究生正在发展透射式电子显微镜的许多方面的高级技能，以及开发有限元作为研究玻璃材料的定量工具。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: High precision instruments and tools, such as space-telescope mirrors and stages in chip-fabrication chambers, are often subjected to large temperature changes and so they need to be made from materials that do not change size or shape with temperature. A family of ultra-low expansion materials (ULE) are produced by Corning Research and Development Corporation that meet these demanding requirements. They are a glassy mixture of titania and silica, but their precise structure and zero-expansion mechanism are not well understood. This research is investigating the ULE structures at the atomic level using a specialized microscope technique called fluctuation electron microscopy (FEM). FEM is a statistical technique that explores subtle traces of atomic ordering in otherwise disordered materials. There are two broad goals to the research. The first is to determine how the structure of the ULE materials change as a function of titania content and processing conditions, and to explain their low-expansion mechanism. The second is to develop the FEM technique into a fully quantitative tool for the study of all disordered materials, particularly glasses and amorphous ceramics. Aram Rezikyan of Corning Inc. is the industrial partner in this project; the PI and co-PI are joined by an additional industrial researcher who is conducting simulations. A graduate student is interacting closely with Corning and is learning instrumental and analytical skills that are valuable for a future career in materials science. High School students participate in this research during the year via a science-mentoring program (the SCENE program) run at Arizona State University. TECHNICAL DETAILS: An ultra-low expansion material (ULE) is made by Corning Research and Development Corporation as a solid solution of titania (TiO2) and silica (SiO2). The composition and processing conditions can be adjusted to give it a zero coefficient of thermal expansion (CTE) at a specified temperature. It is highly desirable to develop materials with a zero, or close to zero, rate of change of CTE over a wide range of temperatures. To achieve these properties, the detailed structure of the ULE glass-ceramic material must be determined, and the mechanism responsible for the zero expansion needs to be understood in detail. Because the material is a disordered glass, standard diffraction and imaging methods do not give a clear picture of the structure. In this project, fluctuation electron microscopy (FEM) is being used to detect and explore the medium-range order that is present at the 1- to 2-nm length scales in these otherwise long-range-disordered materials. There are two broad goals of this research. The first is to apply the FEM method to study the structure-property relationships of ULE TiO2 - SiO2 glass ceramics. The manner in which composition and medium-range order at length scales less than 2 nm affect properties is being examined. The second is to advance FEM as a quantitative technique for studying disordered materials, such as ceramics and glasses, by improving experimental and modeling protocols for investigating electron-beam-sensitive materials. A graduate student is developing high-level skills in many aspects of transmission electron microscopy, as well as developing FEM as a quantitative tool for studying glassy materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.