In situ Investigations of Physical Vapor Deposition of Organic Glass Formers

美国威斯康辛大学麦迪逊分校的Mark Ediger教授和亚利桑那州立大学的Ranko里切特教授在化学系化学结构、动力学和机制A（CSDM-A）项目的支持下，正在研究低温分子玻璃。 当液体冷却到低温时，它们就形成固体。通常，固体是一种晶体，其中分子以有序结构排列。然而，有时液体会冻结成无定形玻璃，在这种情况下，固体的性质很大程度上取决于它是如何制造的。Ediger教授和里切特教授正在与他们的学生一起工作，通过将分子气相沉积到冷表面上来制造玻璃，并使用复杂的实验方法来理解形成的不寻常的玻璃。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，例如有机发光二极管（OLED）。 该项目通过为研究生提供先进实验方法的研究机会，为国家科学劳动力的发展做出了贡献。 该团队还致力于通过与威斯康星大学麦迪逊分校的大学预科学习机会计划（PEOPLE）合作，为来自代表性不足群体的高中生上大学做好准备。与结晶相反，关于玻璃形成的基本问题仍然没有答案，包括可能存在的潜在相变和不同的时间尺度。Ediger教授和里切特教授正在通过物理气相沉积（PVD）将低分子量有机分子沉积到冷表面上来制造无定形分子膜。所得的薄膜，其特征在于在原位介电弛豫测量，nanocalorimetry，和光谱椭圆偏振。在玻璃化转变温度（Tg）下（或接近玻璃化转变温度）进行的实验旨在确定单组分系统是否可以具有多个长寿命液态。在气相沉积过程中进行的介电弛豫测量直接表征表面迁移率和测试的基础上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形成剂制成的共沉积PVD玻璃的动力学稳定性，其中每种成分作为纯材料形成高度稳定的玻璃。该奖项反映了NSF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.