Ilan Boaz, Florio Gina M, Hybertsen Mark S, Berne B J, Flynn George W
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Nano Lett. 2008 Oct;8(10):3160-5. doi: 10.1021/nl8014186. Epub 2008 Sep 18.
Scanning tunneling microscopy (STM) images of self-assembled monolayers of close-packed alkane chains on highly oriented pyrolitic graphite often display an alternating bright and dark spot pattern. Classical simulations suggest that a tilt of the alkane backbone is unstable and, therefore, unlikely to account for the contrast variation. First principles calculations based on density functional theory show that an electronic effect can explain the observed alternation. Furthermore, the asymmetric spot pattern associated with the minimum energy alignment is modulated depending on the registry of the alkane adsorbate relative to the graphite surface, explaining the characteristic moiré pattern that is often observed in STM images with close packed alkyl assemblies.
在高度取向的热解石墨上，紧密堆积的烷烃链自组装单分子层的扫描隧道显微镜（STM）图像通常显示出明暗相间的斑点图案。经典模拟表明，烷烃主链的倾斜是不稳定的，因此不太可能解释对比度变化。基于密度泛函理论的第一性原理计算表明，电子效应可以解释观察到的交替现象。此外，与最低能量排列相关的不对称斑点图案会根据烷烃吸附质相对于石墨表面的配准情况而受到调制，这解释了在具有紧密堆积烷基组装体的STM图像中经常观察到的特征性莫尔条纹图案。
