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

Arizona State University, Scottsdale AZ

Investigators

Abstract

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.