Origin of the highest occupied band position in pentacene films from ultraviolet photoelectron spectroscopy: Hole stabilization versus band dispersion
Origin of the highest occupied band position in pentacene films from ultraviolet photoelectron spectroscopy: Hole stabilization versus band dispersion
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DOI：
10.1103/physrevb.73.245310
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发表时间：
2006-06-01
影响因子：
3.7
通讯作者：
Ueno, N.
中科院分区：
文献类型：
--
作者：
Fukagawa, H.;Yamane, H.;Ueno, N.
用紫外光电子能谱研究了并五苯/石墨、并五烯/铜酞菁(CuPc)/石墨、并五苯/SiO_2/Si(100)的电子结构随并五苯薄膜厚度的变化。我们观察到并五苯在CuPc和SiO_2表面上的最高占据分子轨道(HOMO)的结合能位置明显低于在石墨表面上的结合能位置。此外，只有在CuPc和SiO_2表面上较厚的结晶薄膜的HOMO才观察到UPS带的分裂，其中分子的长轴几乎垂直于衬底表面。CuPc和SiO_2表面的阈值电离能的降低是由于分子间的能带弥散引起的，而CuPc和SiO_2表面的阈值电离能的降低源于同位能弥散和驰豫/极化能的增加，这可能是由于较好的分子堆积结构和接近稳定的分子取向所致。
The electronic structure of pentacene/graphite, pentacene/Cu-phthalocyanine (CuPc)/graphite, and pentacene/SiO2/Si(100) was studied by ultraviolet photoelectron spectroscopy as a function of the thickness of the pentacene film. We observed that the binding energy position of the highest occupied molecular orbital (HOMO) of pentacene becomes significantly lower on CuPc and SiO2 surfaces than that on graphite. Furthermore, a splitting of the UPS band was observed only for the HOMO of thicker crystalline films on CuPc and SiO2 surfaces, where the molecules are oriented with their long axis nearly perpendicular to the substrate surface. The splitting is ascribed to the intermolecular band dispersion, and the decrease in the threshold ionization energy on CuPc and SiO2 surfaces originates from the HOMO-band dispersion as well as the increase in the relaxation/polarization energies, which may be caused by the better molecular packing structure with a nearly standing molecular orientation.