Lerch A, Zimmermann J E, Namgalies A, Stallberg K, Höfer U
Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, 35032 Marburg, Germany.
J Phys Condens Matter. 2018 Dec 12;30(49):494001. doi: 10.1088/1361-648X/aaec53. Epub 2018 Nov 19.
The unoccupied electronic structure of stacked layers of copper(II)phthalocyanine (CuPc) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on Ag(1 1 1) has been investigated by means of two-photon photoemission (2PPE). We find a rich electronic structure comprising at least five unoccupied electronic states which we identify based on their energetic position and their dispersion in momentum space. More specifically, we observe the first and the second image-potential states of the modified Ag(1 1 1) surface, as well as the metal-organic interface state (IS) inherent to the PTCDA/Ag(1 1 1) interface. Moreover, two additional molecular features are observed for the CuPc/PTCDA/Ag(1 1 1) system which we attribute to an unoccupied molecular orbital (LUMO + 2) of CuPc. The 2PPE intensity of the IS exhibits a pronounced dependence on the pump photon energy, which closely follows the optical absorption of the outer molecular layer. This strongly points to charge transfer from the optically excited molecules to the interface state.
利用双光子光电子能谱（2PPE）研究了银（111）表面上铜（II）酞菁（CuPc）和苝-3,4,9,10-四羧酸二酐（PTCDA）堆叠层的未占据电子结构。我们发现了一个丰富的电子结构，其中包含至少五个未占据的电子态，我们根据它们在能量上的位置及其在动量空间中的色散来识别这些态。更具体地说，我们观察到了修饰后的银（111）表面的第一和第二镜像势态，以及PTCDA/银（111）界面固有的金属有机界面态（IS）。此外，对于CuPc/PTCDA/银（111）体系，还观察到另外两个分子特征，我们将其归因于CuPc的一个未占据分子轨道（LUMO + 2）。界面态的2PPE强度对泵浦光子能量表现出明显的依赖性，这与外层分子层的光吸收密切相关。这强烈表明电荷从光激发分子转移到界面态。
