氟化并五苯分子在金屬表面的吸附行為

Abstract

我們使用掃描穿隧顯微術以及光電子能譜來研究氟化并五苯在金屬表面的吸附行為。首先，我們比較并五苯和氟化并五苯在金(111)表面的吸附行為。可以發現如果樣品正偏壓提高，掃描探針會拖動并五苯分子在金(111)的表面移動，而并五苯分子的移動同時還會改變金(111)上面的表面重構。然而，氟化并五苯在金(111)的表面會由於強烈的自身內聚力而形成島嶼結構。再者，光電子能譜研究可以證明單層氟化并五苯有很強的分子間作用力以及分子內作用力。除此之外，我們比較了氟化并五苯在金(111)、銀(111)和銅(111)表面上吸附行為的不同。我們發現氟化并五苯在三種金屬上的排列情形不同，而在銅(111)結構最堅硬。而較強的吸附物與基板的作用力將會幫助氟化并五苯的內聚。最後，我們使用兩種不同的方法，包括紫外光電子能譜以及高階的昆拉赫震盪來量測有機材料在金屬上的工函數改變。我們發現，昆拉赫震盪量測出來的結果與相同厚度的紫外光電子能譜量測的結果不同。原因是紫外光電子能譜量測的是全域的平均結果，而昆拉赫震盪量測的結果是局域性的，比較接近高層數的薄膜層的真空階改變，再加上表層分子結構的影響。

We use scanning tunneling microscopy (STM) and X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) to study the adsorption behaviors of perfluoropentacene (PFP) on metallic surfaces. At first, the comparison study of different adsorption behaviors of pentacene (PEN) and PFP molecules on Au(111) surfaces is presented. PEN molecules are mobile underneath the scanning probe tip at elevated positive sample bias and the surface reconstruction of Au(111) is changed by the moving PEN molecules as well. However, PFP molecules are self-assembled and form compact islands on Au(111). Furthermore, strong intermolecular and intramolecular interactions of monolayer PFP are verified by UPS and XPS. Additionally, we compare the different adsorption behaviors of PFP on Au(111), Ag(111) and Cu(111) surfaces. The arrangements of PFP islands on these three surfaces are different and the islands are firmest on Cu(111). The adsorbate-substrate interaction is verified to aid the assembly process. Finally, two different methods, UPS and high order Gundlach oscillation are demonstrated for measuring the work function difference of PFP islands and metallic surfaces. The work function shift measured by high order Gundlach oscillation is not consistent with that measured by UPS at low coverage but is close to that measured by UPS at high coverage. The reason could be UPS reflects the surface dipole but high order Gundlach oscillation reflects the local vacuum level shift and the shift is similar to the vacuum level shift at high coverage with the influence by the arrangement at monolayers.