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Origin of the bimodal island size distribution in ultrathin films of para-hexaphenyl on mica

机译：云母对六苯基超薄膜双峰岛尺寸分布的起源

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摘要

Ultrathin films of para-hexaphenyl (6P) were prepared on freshly cleaved and sputter-amorphized mica(001) by physical vapor deposition. Ex situ atomic force microscopy (AFM) revealed a bimodal island size distribution for the films on both surfaces. On freshly cleaved mica long needlelike islands exist, which are surrounded by small crystallites. On the sputter-amorphized substrates, large dendritic islands exist which are again surrounded by small, compact islands. We could prove by thermal desorption spectroscopy that the small islands are the result of adsorbate-induced subsequent nucleation, when the films were exposed to air. In case of the freshly cleaved mica, islands grow on a wetting layer in vacuum. This layer dewets and forms the small islands upon venting, due to the adsorption of water. In the case of the amorphous mica substrate an equilibrium exists between the islands and a two-dimensional gas phase in the sub-monolayer regime. Again, the latter phase nucleates after venting. In a particular coverage range, islands due to nucleation during deposition and subsequent nucleation coexist on the substrate, leading to the bimodal island size distribution. Kinetic Monte Carlo (KMC) simulations were performed to model the nucleation process after venting on the sputter-modified mica substrate. The density of the subsequently nucleated islands just depends on the initial coverage and the critical island size. A critical cluster size of i = 7 molecules was determined for 6P on amorphized mica, by comparing the KMC results with the AFM images in case of adsorbate-induced nucleation. Furthermore, the experimentally obtained island size distributions could be well reproduced by KMC simulations.
机译：通过物理气相沉积法，在新近裂解和溅射非晶的云母（001）上制备了对六苯基（6P）的超薄膜。异位原子力显微镜（AFM）揭示了两个表面上薄膜的双峰岛尺寸分布。在新近切割的云母上，长针状岛存在，周围环绕着小晶粒。在溅射非晶化的衬底上，存在大的树枝状岛，它们又被小的紧凑岛包围。我们可以通过热解吸光谱法证明，当这些膜暴露在空气中时，这些小岛是被吸附物诱导的随后成核作用的结果。如果是新鲜切割的云母，则在真空中在润湿层上生长岛。由于水的吸附，该层在排气时会润湿并形成小岛。在无定形云母基底的情况下，在亚单层态中，岛与二维气相之间存在平衡。同样，后一相在排气后成核。在特定的覆盖范围内，由于沉积过程中成核和随后成核的岛共存于基底上，从而导致双峰岛尺寸分布。进行动力学蒙特卡洛（KMC）模拟以对在溅射改性的云母基板上排气后的成核过程进行建模。随后成核岛的密度仅取决于初始覆盖率和临界岛的大小。通过比较KMC结果与AFM图像（在吸附剂诱导的成核情况下），在非晶云母上确定6P的i = 7分子的临界簇大小。此外，通过KMC模拟可以很好地再现实验获得的岛屿尺寸分布。

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  • 来源
    《Physical review》 |2012年第8期|085402.1-085402.11|共11页
  • 作者

    L. Tumbek; C. Gleichweit; K. Zojer; A. Winkler;

  • 作者单位

    Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria;

    Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria;

    Institute of Theoretical Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria;

    Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria;

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  • 正文语种 eng
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  • 关键词

    theory and models of film growth; atomic force microscopy (AFM); thermal desorption;

    机译：电影生长的理论和模型;原子力显微镜（AFM）;热脱附;

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