Crystal and electronic structures of pentacene thin films from grazing-incidence x-ray diffraction and first-principles calculations
Crystal and electronic structures of pentacene thin films from grazing-incidence x-ray diffraction and first-principles calculations
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DOI：
10.1103/physrevb.76.235322
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发表时间：
2007-12-01
影响因子：
3.7
通讯作者：
Smilgies, Detlef-M.
中科院分区：
文献类型：
--
作者：
Nabok, Dmitrii;Puschnig, Peter;Smilgies, Detlef-M.
为了确定并五苯薄膜相结构，对并五苯薄膜进行了理论和实验相结合的研究。用掠入射X射线衍射法研究了一种名义厚度为180 nm的并五苯薄膜。晶体结构参数为a=0.592 nm，b=0.754 nm，c=1.563 nm，α=81.5度，β=87.2度，伽马=89.9度。在密度泛函理论框架下，这些晶胞尺寸被用作从头算总能量计算的唯一输入参数，揭示了晶体结构中的分子堆积。此外，我们还计算了薄膜相的电子能带结构，并与体相的能带结构进行了比较。我们发现，与体相结构相比，薄膜相的分子间带宽要大得多，例如，价带宽是体相的两倍。这种显著的效应可以追溯到由于薄膜相中的直立分子而导致的分子间pi-pi重叠的增强。
Combined experimental and theoretical investigations on thin films of pentacene are performed in order to determine the structure of the pentacene thin film phase. Grazing incidence x-ray diffraction is used for studying a pentacene thin film with a nominal thickness of 180 nm. The crystal structure is found to exhibit the lattice parameters a=0.592 nm, b=0.754 nm, c=1.563 nm, alpha=81.5 degrees, beta=87.2 degrees, and gamma=89.9 degrees. These crystallographic unit cell dimensions are used as the only input parameters for ab initio total-energy calculations within the framework of density functional theory revealing the molecular packing within the crystal structure. Moreover, we calculate the electronic band structure of the thin film phase and compare it to that of the bulk phase. We find the intermolecular bandwidths of the thin film phase to be significantly larger compared to the bulk structure, e.g., the valence bandwidth is twice as large. This remarkable effect is traced back to an enhanced intermolecular pi-pi overlap due to the upright standing molecules in the thin film phase.