Materials World Network: Growth, Kinetics, and Morphology of Multi-Layered Organic Thin Films via Low-Energy Secondary Ion Mass Spectrometry

该项目基于三个研究小组之间的合作，一个是卢森堡G.Lippmann研究中心材料科学与分析(SAM)系的一个，另两个是密歇根大学(UM)材料科学系的两个。这种合作关系合并了不能单独提供给每个参与者的资源。本研究的目的是研究由UM基团之一制备的气相沉积多层有机半导体薄膜和器件中的界面的形状、成分定义和能量学。随着光电子器件的日益复杂，在制造具有特殊设计界面的多层结构时，需要分子水平的尺寸控制。然而，由于缺乏适当的表征技术，为实现所需的器件结构而设计的生长和掺杂策略的有效性往往仍未得到验证。尤其是基于共轭有机化合物的器件，它们在能源应用中的应用越来越多(例如有机发光二极管和有机光伏电池等)。当使用传统的表征技术时，埋藏的界面根本无法接触到或遭受损坏。低能二次离子质谱仪(LE-SIMS)是SAM小组的一项专业技术，它为有机薄膜层状结构的分析提供了一条很有前途的途径，因为一次离子的亚keV撞击能减少了样品表面分子物种的碎裂。碰撞级联的物理和导致二次离子在低能下抛射的过程仍然知之甚少，识别被抛射物质的统一形式还不存在。追求这一知识的另一个UM小组将大规模分子动力学(MD)模拟与第一性原理密度泛函理论(DFT)计算相结合，研究碰撞级联中详细的原子轨迹，并预测抛出的分子碎片的性质。该计算框架用于解释LISMS获得的实验数据，从而提高了该技术的深度分辨率和可靠识别有机分子物种的能力，从而进一步确立了LSIMS作为一种深度剖析有机薄膜材料的技术。本项目的目标是以前所未有的精度建立多层薄膜有机半导体的生长条件、结构和性能之间的关系。展望了对有机电子器件设计和制造技术进步的基本见解。该项目是三篇博士论文的基础。学生通过互访伙伴机构、研究人员之间的远程互动、共享数据以及使用网络基础设施传播研究成果，从多样化的教育体验中受益。本科生直接参与到学术层面，而K-12年级的学生则通过密歇根大学新的外展计划参与其中。

This project is based on a partnership between three research groups, one at the Science and Analysis of Materials (SAM) Department at the G. Lippmann Research Center in Luxembourg and two at the Materials Science Department of the University of Michigan (UM). This partnership merges resources that are not available to each participant individually. The purpose of this research is to investigate the shape, compositional definition, and energetics of interfaces in vapor-deposited multi-layer organic semiconductor thin films and devices fabricated by one of the UM groups. The increasing sophistication of optoelectronic devices requires molecular-level dimensional control in the fabrication of multi-layered structures with specifically engineered interfaces. However, the effectiveness of growth and doping strategies devised to achieve the desired device structures oftentimes remains unverified due to the lack adequate characterization techniques. This is particularly true for devices based on conjugated organic compounds, which find increasing use in energy applications (e.g. organic light-emitting diodes and organic photovoltaic cells, etc.). The buried interfaces are simply inaccessible or suffer damage when using conventional characterization techniques. Low-energy secondary ion mass spectrometry (LE-SIMS), a specialty of the SAM group, provides a promising avenue for the analysis of organic-based thin-film layered structures, because sub-keV impact energies of the primary ions result in reduced fragmentation of molecular species at the specimen surface. The physics of the collision cascades and the processes that lead to the ejection of secondary ions at low energies is still poorly understood, and a unified formalism for the identification of ejected species does not yet exist. Pursuing this knowledge, the other UM group combines large-scale molecular dynamics (MD) simulations with first-principles density functional theory (DFT) calculations to study the detailed atomic trajectories in collision cascades and predict the nature of ejected molecular fragments. This computational framework serves to interpret experimental data obtained from LE-SIMS, thereby improving the depth resolution of the technique and its ability to reliably identify organic molecular species, thus further establishing LE-SIMS as a technique for depth-profiling organic thin film materials.The goal of this project is to establish the relationship between growth conditions, structure, and properties of multi-layer thin film organic semiconductors with unprecedented precision. Fundamental insights for the advancement of organic electronic device design and fabrication techniques are anticipated. The project serves as the basis for three Ph.D. theses. Students benefit from a diverse educational experience through exchange visits to partner institutions, remote interactions between researchers, sharing of data, and the use of cyber infrastructure for the dissemination of findings through. Undergraduate students are involved directly at an academic level, and K-12 students through new outreach initiatives at UM.