Tapasztó L, Márk G I, Koós A A, Lambin P, Biró L P
Research Institute for Technical Physics and Materials Science, H-1525 Budapest, PO Box 49, Hungary.
J Phys Condens Matter. 2006 Jul 5;18(26):5793-805. doi: 10.1088/0953-8984/18/26/001. Epub 2006 Jun 16.
Geometric effects influencing scanning tunnelling microscopy (STM) image formation of single wall carbon nanotubes (SWCNTs) were studied within the framework of a simple model potential. We focused on the geometrical effects which may influence the tunnelling probabilities and lead to discrepancies between the apparent height of the nanotubes measured by STM and their real geometrical diameter. We found that there are two main factors responsible for the underestimation of nanotubes diameter by measuring their height in STM images: (1) the curvature of the nanotube affects the cross sectional shape of the tunnelling channel; (2) the decay rate of tunnelling probabilities inside the tunnel gap increases with increasing curvature of the electrodes. For a nanotube with 1 nm diameter an apparent flattening of about 10%, due to these geometry-related effects, is predicted. Furthermore these effects are found to be dependent on the diameter of the tubes and tip-sample distances: an increasing flattening of the tubes is predicted for decreasing tube diameter and increasing tip-sample distance.
在一个简单的模型势框架内，研究了影响单壁碳纳米管（SWCNT）扫描隧道显微镜（STM）成像的几何效应。我们关注的是那些可能影响隧穿概率并导致STM测量的纳米管表观高度与其实际几何直径之间存在差异的几何效应。我们发现，通过在STM图像中测量纳米管高度来低估其直径主要有两个因素：（1）纳米管的曲率会影响隧穿通道的横截面形状；（2）隧道间隙内隧穿概率的衰减率会随着电极曲率的增加而增大。对于直径为1纳米的纳米管，由于这些与几何形状相关的效应，预计会出现约10%的表观扁平化。此外，还发现这些效应取决于纳米管的直径和针尖 - 样品距离：预计随着纳米管直径减小和针尖 - 样品距离增大，纳米管的扁平化程度会增加。
