PEEM imaging of the growth of organic thin films and diffusion of molecules on topological surfaces

用亚稳电子发射显微镜（MEEM）和光电子发射显微镜（PEEM）研究了在Si（100）上真空沉积的酞菁铜（CuPc）薄膜。在SiO_2/Si（100）衬底上沉积极少量CuPc后，SiO_2图案边缘的MEEM图像发生了明显变化，而在PEEM图像中没有这种变化。在MEEM和PEEM中不同的对比特征可能是这两种显微镜不同的表面灵敏度的结果。CuPc沉积后图案边缘的MEEM对比特性可能源于PEEM无法观察到的CuPc分子取向的差异。此外，在半外延生长于MoS_2表面的苝-3,4,9,10-四羧基二氢化物（PTCDA）薄膜上沉积方形结构的金属铟，通过PEEM观察到不同寻常的三角形图像。三角形图案的形成证明了铟原子在PTCDA/MoS_2体系上的各向异性表面扩散。形成三角形结构的三持扩散方向与MoS_2衬底的三个等效表面晶轴极好地对应。当In原子直接沉积在MoS_2上时，没有观察到这种扩散现象，这表明这种现象与In原子与取向PTCDA分子之间强烈的化学相互作用有关。

A combined metastable electron emission microscopy (MEEM) and photoelectron emission microscopy (PEEM) study has been performed for copper phthalocyanine (CuPc) thin films vacuum deposited on Si(100) with a lithographic SiO_2 pattern. The MEEM image of SiO_2 pattern edges changed considerably upon deposition of very small amount of CuPc on the SiO_2/Si(100) substrate, whereas no such changes could be seen in PEEM images. The different contrast features in MEEM and PEEM can be the result of different surface sensitivities of these microscopy. The MEEM contrast characteristic for the pattern edge after the CuPc deposition may originate from the difference of the molecular orientation of CuPc which cannot be observed by PEEM. Furthermore, an unusual triangle image was observed by PEEM when a square-shaped microstructure of indium metal was deposited on a thin film of perylene-3,4,9,10-tetracarboxilicdianhydride (PTCDA) grown semi-epitaxially on a cleaved MoS_2 surface. The formation of the triangle pattern demonstrates the anisotropic surface diffusion of indium atoms on the PTCDA/MoS_2 system. The three-hold diffusion directions, which give the triangle structure, correspond excellently with the three equivalent surface crystal axes of the MoS_2 substrate. When In atoms were directly deposited on MoS_2, such diffusion was not observed, suggesting that the phenomenon is related to strong chemical interaction between In atoms and oriented PTCDA molecules.