Sandwich molecular nanowires: on-surface synthesis, structure and magnetism

该项目的重点是以环辛四烯(C8H8，简称Cot)分子为配体，由4f个稀土金属阳离子组成的周期性序列的夹心分子纳米线，这些阳离子与离子结合，并与平面芳香族阴离子配位八次。这些一维实体在概念上不同于二维有机金属配位网络，也不同于零维有机金属分子磁体，这是由于金属原子态和CoT分子的扩展pi轨道的杂化，金属离子在导线上是磁性耦合的。因此，这些体系可能是比单分子磁体更稳定的磁性单元，并且可以表现出更大的磁各向异性和相应的更高的阻塞温度。本研究的第一个目标是探索一种新的表面合成方法的通用性，使我们能够在清洁的条件下在衬底上制备这些一维有机金属纳米线，从而使它们首次能够被详细研究。从典型的EU-Cot案例开始，我们将(I)测试不同的稀土、稀土碱和3D金属，(Ii)改变配体分子，或将官能团连接到其上，以及(Iii)使用不同的底物和掺杂方法。对于有趣的情况，我们将超越探索性实验，仔细分析结构和生长机制，以优化生长，从而优化线材产品的纯度和质量。第二个目标是了解金属4f(或3d)电子与分子pi系统相互作用的物理。为此，对于选定的体系，我们将对夹心分子线的电子和磁性进行详细的实验表征，包括能带结构、带隙、磁矩、磁各向异性以及磁耦合，并将这些结果与专用的从头计算进行比较。我们相信，这种将实验和理论相互作用的过程将为合成提供更好的概念。第三个目标将在从属于前两个目标的活动中作为指导方针，即创造可能用于自旋电子应用的稳定的磁性单元。这意味着要关注导线中金属中心的磁各向异性和磁耦合强度，注意绝缘衬底上的生长，最后尝试操纵和接触导线以测量自旋极化输运。

In focus of the project are sandwich molecular nanowires consisting of a periodic sequence of 4f rare earth metal cations, ionically bound and eightfold coordinated to planar aromatic anions, based on the cyclooctatetraene (C8H8, briefly Cot) molecule as ligand. These one dimensional entities are conceptually distinct from the two dimensional organometallic coordination networks as well as from zero dimensional organometallic molecular magnets Due to the hybridization of the metal atomic states and the extended pi-orbitals of the Cot molecule, the metal ions in the wire couple magnetically. Therefore, these systems could be more stable magnetic units than single molecule magnets, and could display larger magnetic anisotropy with correspondingly higher blocking temperatures.The first objective of the proposed research is to explore the versatility of a new on-surface synthesis method enabling us to create these one dimensional organometallic nanowires under clean conditions on a substrate and thereby making them accessible to detailed investigation for the first time. Starting from the paradigmatic Eu-Cot case we will (i) test different rare earth, earth alkali, and 3d metals, (ii) vary the ligand molecule, or attach functional groups to it, and (iii) use different substrates and doping methods. For the interesting cases, where we go beyond explorative experiments, structure and growth mechanism will be carefully analyzed to optimize the growth and thus the purity and quality of the wire product.The second objective is to understand the physics of metal 4f (or 3d) electrons interacting with molecular pi-systems. To this end, and for selected systems, we will experimentally characterize the electronic and magnetic properties of the sandwich molecular wires in detail, including band structure, band gaps, magnetic moments, magnetic anisotropy, as well as magnetic coupling and compare these results to dedicated ab initio calculations. We are convinced that this process of bringing experiment and theory to interaction will provide improved concepts for the synthesis. The third objective will serve as a guideline within the activities subordinated to the first two objectives, namely to create stable magnetic units with a potential use for spintronic applications. This implies to keep in focus magnetic anisotropy as well as the magnetic coupling strength of the metal centers in the wires, to pay attention to growth on insulating substrates, and finally to try to manipulate and contact wires in order to measure spin-polarized transport.