Using Physical Vapor Deposition to Prepare Unusual Liquids and Unusual Glasses

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Mark Ediger of the University of Wisconsin-Madison and Professor Ranko Richert of Arizona State University are using sophisticated analysis tools to study glasses of organic molecules prepared inside a vacuum chamber. Glasses are common in everyday life with applications ranging from pharmaceuticals to engineering materials to cell phone displays. Even so, glasses have many properties that are not well understood. Professors Ediger and Richert are studying glasses made of simple molecules to serve as model systems to answer fundamental questions about glasses. Answering these questions can have an impact on glassy materials used in technology. In this project, glasses are prepared directly from the vapor phase. This project investigates unusual molecular systems that have two distinct liquid states to understand how this is possible and how it might be used to produce new materials. A second goal of this project is to understand how the method of preparing a glass can impact the mobility of molecules in the glass. There are advanced technologies such as quantum computing that can benefit from decreased mobility in glass. The students involved in this project are being trained in a wide variety of chemical and physical analysis tools which are used to characterize thin glassy films. The skills and tools learned are valuable in many areas of science and technology beyond the specific molecules studied in this project. In addition, Professor Ediger and his group participate in a Pre-college Enrichment Opportunity Program for Learning Excellence (PEOPLE)program at University of Wisconsin that encourages careers in science and engineering of high school students from underrepresented backgrounds. The project focuses on glasses prepared by physical vapor deposition, a process known to create glasses with unusual properties. It is likely that physical vapor deposition may serve as a shortcut to the second liquid phase of triphenyl phosphite (TPP) and other systems. AC nanocalorimetry and spectroscopic ellipsometry are used to study the stability and density of the liquids prepared by this route. X-ray scattering is used to assess the structure of the liquids. This project also seeks to understand how physical vapor deposition affects intramolecular motions in the glassy state. Dielectric spectroscopy is used to study glasses of decahydroisoquinoline (DHIQ). DHIQ displays intramolecular degrees of freedom which can alter the dipole orientation even while the molecule is trapped in a glassy solid. Measurements of DHIQ and molecules with similar intramolecular degrees of freedom provide understanding about suppression of molecular motion in vapor-deposited glasses. This project may have a broad impact on the improvement of amorphous materials used in organic electronics, since the molecules studied here serve as model systems for those materials. In addition to the aforementioned training in advanced measurement techniques and glassy organic systems, the students funded by this project also lead a summer chemistry education program in broadening participation of under-represented groups in STEM disciplines. 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.