In situ Investigations of Physical Vapor Deposition of Organic Glass Formers

在化学系化学结构、动力学和机理A （CSDM-A）项目的支持下，威斯康星大学麦迪逊分校的Mark Ediger教授和亚利桑那州立大学的Ranko Richert教授正在研究低温分子玻璃。当液体冷却到低温时，就会形成固体。这种固体通常是晶体，其中分子排列成有序的结构。然而，有时液体冻结成无定形玻璃，在这种情况下，固体的性质很大程度上取决于它是如何制成的。Ediger教授和Richert教授与他们的学生合作，通过在冷表面上蒸汽沉积分子来制造玻璃杯，并使用复杂的实验方法来了解形成的不寻常的玻璃杯。他们的发现可能会对基于有机电子学的先进技术产生影响，比如有机发光二极管（oled）。该项目通过为研究生提供先进实验方法的研究机会，有助于国家科学劳动力的发展。该团队还通过与威斯康辛大学麦迪逊分校的“卓越学习大学预科充实机会计划”（PEOPLE）合作，为来自代表性不足群体的高中生做好上大学的准备。与结晶相反，关于玻璃形成的基本问题仍未得到解答，包括潜在相变和发散时间尺度的可能存在。Ediger和Richert教授正在通过物理气相沉积（PVD）在冷表面上制备低分子量有机分子的非晶分子膜。然后通过原位介电弛豫测量、纳米量热法和光谱椭偏法对所得薄膜进行表征。在（或接近）玻璃化转变温度（Tg）下进行的实验旨在确定单一组分系统是否可以拥有多个长寿命的液态。在气相沉积过程中进行的介电弛豫测量直接表征了表面迁移率，并测试了基于表面平衡的气相沉积玻璃的拟议模型。最后，研究了由两种不同的有机玻璃成形剂制成的共沉积PVD玻璃的动力学稳定性，在这种情况下，每一种成分都形成了高度稳定的纯材料玻璃。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support from Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Mark Ediger of the University of Wisconsin-Madison and Professor Ranko Richert of Arizona State University are studying low-temperature molecular glasses. When liquids are cooled to low temperature, they form solids. Often that solid is a crystal in which molecules are arranged in an ordered structure. However, sometimes the liquid freezes into an amorphous glass and in this case the properties of the solid depend strongly upon how it is made. Working with their students, Professors Ediger and Richert are creating glasses by vapor-depositing molecules onto cold surfaces and using sophisticated experimental methods to understand the unusual glasses that form. Their discoveries could have implications for advancing technologies based on organic electronics, such as organic light emitting diodes (OLEDs). The project contributes to the development of the Nation's scientific workforce by providing research opportunities for graduate students in advanced experimental methods. The team is also working to prepare high school students from under-represented groups for college, through partnership with the University of Wisconsin-Madison’s Pre-college Enrichment Opportunity Program for Learning Excellence (PEOPLE). In contrast to crystallization, fundamental questions about glass formation remain unanswered, including the possible existence of underlying phase transitions and diverging time scales. Professors Ediger and Richert are creating amorphous molecular films through physical vapor deposition (PVD) of low molecular weight organic molecules onto cold surfaces. The resulting films are then characterized by in situ dielectric relaxation measurements, nanocalorimetry, and spectroscopic ellipsometry. Experiments performed at (or near) the glass transition temperature (Tg) aim to determine if a single component system can possess multiple long-lived liquid states. Dielectric relaxation measurements performed during vapor deposition directly characterize surface mobility and test a proposed model for vapor-deposited glasses based upon surface equilibration. Finally, the kinetic stability of co-deposited PVD glasses made from two different organic glass formers are investigated for cases where each component forms a highly stable glass as a pure material.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.