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

该项目是基于三个研究小组之间的合作，一个在卢森堡G. Lippmann研究中心的材料科学与分析（SAM）部门，两个在密歇根大学（UM）的材料科学系。这种伙伴关系合并了每个参与者单独无法获得的资源。本研究的目的是研究气相沉积多层有机半导体薄膜和器件中界面的形状、组成定义和能量学。光电子器件的日益复杂化要求在制造具有特殊工程界面的多层结构时进行分子水平的尺寸控制。然而，由于缺乏足够的表征技术，为实现所需器件结构而设计的生长和掺杂策略的有效性通常仍未得到验证。这对于基于共轭有机化合物的器件尤其如此，共轭有机化合物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）。当使用常规表征技术时，隐藏的界面根本无法访问或遭受损坏。低能次级离子质谱（LE-SIMS）是SAM小组的一项专长，为分析有机薄膜层状结构提供了一条有前途的途径，因为初级离子的亚kev冲击能量导致样品表面分子物种的碎片减少。碰撞级联的物理学和导致低能次级离子抛射的过程仍然知之甚少，而且还不存在一个统一的确定抛射物质的形式。追求这些知识，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，研究碰撞级联中的详细原子轨迹，并预测喷射分子碎片的性质。该计算框架用于解释从LE-SIMS获得的实验数据，从而提高该技术的深度分辨率及其可靠识别有机分子物种的能力，从而进一步建立LE-SIMS作为深度剖析有机薄膜材料的技术。该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。展望有机电子器件设计和制造技术的发展。该项目是三篇博士论文的基础。通过访问合作机构、研究人员之间的远程互动、数据共享以及利用网络基础设施通过网络传播研究结果，学生可以从多样化的教育体验中受益。本科生直接参与学术水平，K-12学生通过UM的新推广活动参与。

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.