On-surface synthesis of higher acenes beyond undecacene: Evolution of conductance and electronic states

丙烯腈是一类多环芳香烃，其苯环呈线性熔合。它们被广泛认为是有机和分子电子学的有前途的材料。它们的电子结构的性质目前正在积极讨论，关于它们基态的电子构型作为环数的函数的基本问题尚未得到回答。目前对环烯的高度兴趣主要是由于期望增加的自由基性质以及减少的光激发势垒对于越来越多的环。建立了polyacene项目，以了解高级芳烃的能隙发展和基态自由基特征作为线性熔合苯环数的函数。本课题的目的是通过实验测定表面合成的低聚丙烯酸酯的电子性质和电导，研究其电子共振的演化和隧穿电流的衰减。采用低温高分辨率扫描隧道显微镜（STM）在单分子水平上验证了化学转化。在polyacene中，我们的目标是继续在表面合成一系列的cenes到12 cenes， 14 cenes，甚至更长。扫描隧道光谱学可以获得电子态的能量位置和空间分布，从而确定电子共振的演化。为了进一步了解新长烃的开壳性质，我们将把间隙和电子共振的研究与横向操纵实验结合起来。我们将使用得到的长烯分子进行电导测量。利用STM的顶端拉住分子的一端，记录非共振状态下的隧穿电流，研究电导随分子长度的变化以及共轭效应。此外，我们将研究衬底在表面合成芳烃中的作用，以及通过钝化h层对Si进行去耦的影响（001）。

Acenes are a class of polycyclic aromatic hydrocarbons with linearly fused benzene rings. They are widely considered as promising materials for organic and molecular electronics. The nature of their electronic structure is presently actively discussed and fundamental questions regarding the electronic configuration of their ground state as a function of the number of rings are not answered yet. The present high interest in acenes is mainly motivated by the expected increasing radical character as well as the reduced optical excitation barrier for an increasing number of rings. The POLYACENES project is established to understand the energy gap development and the radical character of the ground state of higher acenes as a function of the number of linearly fused benzene rings. The goal of the project is to experimentally determine the electronic properties and the conductance of oligoacenes synthetized on surface, studying the evolution of the electronic resonances and the decay of the tunneling current. High-resolution scanning tunneling microscopy (STM) at low temperature is employed to verify the chemical conversion at a single-molecule level.In POLYACENES, we aim to continue the series of acenes synthetized on surface to 12 cene, 14 cene, and longer. Scanning tunneling spectroscopy will give access to the energy position and spatial distribution of the electronic states, determining the evolution of the electronic resonances. To gain further information on the open shell character of the new long acenes, we will combine the study of gap and electronic resonances with lateral manipulation experiments. We will use the obtained long acene molecules for conductance measurements. By pulling one end of the molecule with the apex of the STM, we will record the tunneling current in non-resonant regime studying the evolution of the conductance with the molecular length and the effect of conjugation. Moreover, we will investigate the role of the substrate in the on-surface synthesis of acenes and the effect of decoupling via a passivating H-layer on Si(001).