Zwick Christian, Baby Anu, Gruenewald Marco, Verwüster Elisabeth, Hofmann Oliver T, Forker Roman, Fratesi Guido, Brivio Gian Paolo, Zojer Egbert, Fritz Torsten
Institute of Solid State Physics, Friedrich Schiller University Jena , Helmholtzweg 5, 07743 Jena, Germany.
Institute of Solid State Physics, NAWI Graz, Graz University of Technology , Petersgasse 16, 8010 Graz, Austria.
ACS Nano. 2016 Feb 23;10(2):2365-74. doi: 10.1021/acsnano.5b07145. Epub 2016 Jan 26.
Alkali metal atoms are frequently used for simple yet efficient n-type doping of organic semiconductors and as an ingredient of the recently discovered polycyclic aromatic hydrocarbon superconductors. However, the incorporation of dopants from the gas phase into molecular crystal structures needs to be controlled and well understood in order to optimize the electronic properties (charge carrier density and mobility) of the target material. Here, we report that potassium intercalation into the pristine 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) monolayer domains on a Ag(111) substrate induces distinct stoichiometry-dependent structural reordering processes, resulting in highly ordered and large KxPTCDA domains. The emerging structures are analyzed by low-temperature scanning tunneling microscopy, scanning tunneling hydrogen microscopy (ST[H]M), and low-energy electron diffraction as a function of the stoichiometry. The analysis of the measurements is corroborated by density functional theory calculations. These turn out to be essential for a correct interpretation of the experimental ST[H]M data. The epitaxy types for all intercalated stages are determined as point-on-line. The K atoms adsorb in the vicinity of the oxygen atoms of the PTCDA molecules, and their positions are determined with sub-Ångström precision. This is a crucial prerequisite for the prospective assessment of the electronic properties of such composite films, as they depend rather sensitively on the mutual alignment between donor atoms and acceptor molecules. Our results demonstrate that only the combination of experimental and theoretical approaches allows for an unambiguous explanation of the pronounced reordering of KxPTCDA/Ag(111) upon changing the K content.
碱金属原子经常被用于对有机半导体进行简单而有效的n型掺杂，并且作为最近发现的多环芳烃超导体的一种成分。然而，为了优化目标材料的电子性质（载流子密度和迁移率），需要控制并深入理解从气相中将掺杂剂引入分子晶体结构的过程。在此，我们报道，将钾插入Ag(111)衬底上的原始3,4,9,10-苝四羧酸二酐（PTCDA）单层畴中会引发明显的依赖于化学计量比的结构重排过程，从而产生高度有序且大尺寸的KxPTCDA畴。通过低温扫描隧道显微镜、扫描隧道氢显微镜（ST[H]M）以及作为化学计量比函数的低能电子衍射来分析所形成的结构。密度泛函理论计算证实了对测量结果的分析。这些计算结果对于正确解释实验性的ST[H]M数据至关重要。确定了所有插入阶段的外延类型为点在线上。K原子吸附在PTCDA分子的氧原子附近，并且它们的位置以亚埃精度确定。这是前瞻性评估此类复合薄膜电子性质的关键前提条件，因为它们相当敏感地依赖于供体原子和受体分子之间的相互排列。我们的结果表明，只有实验方法和理论方法相结合，才能对改变K含量时KxPTCDA/Ag(111)中明显的重排给出明确的解释。
