PTCDA/ITO表面和界面的AFM和XPS分析

利用X射线光电子能谱(XPS)对苝四甲酸二酐[3,4,9,10-perylenetetracarboxylic dianhydride(PTCDA)]/铟锡氧化物(ITO)表面和界面进行了研究.用原子力显微镜(AFM)对PTCDA/ITO样品的表面形貌进行了分析.XPS表明,在原始表面的C1s精细谱存在两个主谱峰和一个伴峰,主谱峰分别由结合能为284.6eV的苝环中的C原子和结合能为288.7eV的酸酐基团中的C原子激发;而结合能为290.4eV的伴峰的存在,说明发生了来源于ITO膜中的氧对C原子的氧化现象.O原子在C=O键和C-O-C键的结合能分别为531.5和533.4eV.在界面处,C1s谱中较高结合能峰消失,且峰值向低结合能方向发生0.2eV的化学位移;O1s谱向低结合能方向发生1.5eV的化学位移.由此可以推断,在界面处PTCDA与ITO的结合是PTCDA中的苝环与ITO中的In空位的结合.AFM的结果显示,PTCDA薄膜为岛状结构,岛的直径约为100～300nm,表面起伏约为14nm.相邻两层PTC-DA分子由于存在离域大π键而交叠和PTCDA分子中的苝环与ITO的In空位的紧密结合是最终导致PTCDA岛状结构形成的原因.

Analysis of PTCDA/ITO Surface and Interface Using X-ray Photoelectron Spectroscopy and Atomic Force Microscopy

The electronic states of the surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA)/indium-tin-oxide (ITO) thin film are investigated using X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) is also applied to investigate the pattern of PTCDA/ITO film. XPS results show that there are two main peaks, which are associated with C atoms in the perylene rings and acid anhydride groups,located at 284.6 and 288.7eV, respectively,in the C1s spectrum of the original surface. It can be deduced from the emergence of a small peak at 290.4eV in the C1s spectrum that some C atoms are oxidized by O atoms from ITO.The binding energies of O atoms in C=O bonds and C-O-C bonds are 531.5 and 533.4eV respectively. At the interface,the peak at the high binding energy in the C1s spectrum disappears,and the peak value shifts about 0.2eV to lower binding energy. There is a significant 1.5eV chemical shift to lower binding energy in the O1s spectrum. These observations indicate that perylene rings inside PTCDA molecules are combined with In vacancies in the ITO at the interface. The AFM results show that PTCDA molecules formed an island-like structure a height of about 14nm. The sizes of the crystal grains are about 100～300nm. The island-like pattern comes from the delocalized π bonds of adjacent molecules in PTCDA and the combination of vacancies in ITO with perylene rings at the PTCDA/ITO interface.