Solares Santiago D, Esplandiu Maria J, Goddard William A, Collier C Patrick
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
J Phys Chem B. 2005 Jun 16;109(23):11493-500. doi: 10.1021/jp051363u.
When using single-walled carbon nanotube (SWNT) probes to create AFM images of SWNT samples in tapping mode, elastic deformations of the probe and sample result in a decrease in the apparent width of the sample. Here we show that there are two major mechanisms for this effect, smooth gliding and snapping, and compare their dynamics to the case when a conventional silicon tip is used to image a bare silicon surface. Using atomistic and continuum simulations, we analyze in detail the shape of the tip-sample interaction potential for three model cases and show that in the absence of adhesion and friction forces, more than two discrete, physically meaningful solutions of the oscillation amplitude are possible when snapping occurs (in contrast to the existence of one attractive and one repulsive solution for conventional silicon AFM tips). We present experimental results indicating that a continuum of amplitude solutions is possible when using SWNT tips and explain this phenomenon with dynamic simulations that explicitly include tip-sample adhesion and friction forces. We also provide simulation results of SWNT tips imaging Si(111)-CH3 surface step edges and Au nanocrystals, which indicate that SWNT probe multistability may be a general phenomenon, not limited to SWNT samples.
当使用单壁碳纳米管（SWNT）探针在轻敲模式下对SWNT样品进行原子力显微镜（AFM）成像时，探针和样品的弹性变形会导致样品表观宽度减小。在此我们表明，这种效应存在两种主要机制，即平滑滑动和突然咬合，并将它们的动力学与使用传统硅尖端对裸硅表面成像的情况进行比较。通过原子和连续介质模拟，我们详细分析了三种模型情况下尖端 - 样品相互作用势的形状，并表明在没有粘附力和摩擦力的情况下，当发生突然咬合时，可能存在不止两个离散的、具有物理意义的振荡幅度解（与传统硅AFM尖端存在一个吸引解和一个排斥解形成对比）。我们给出的实验结果表明，使用SWNT尖端时可能存在连续的幅度解，并通过明确包含尖端 - 样品粘附力和摩擦力的动态模拟来解释这一现象。我们还提供了SWNT尖端对Si(111)-CH3表面台阶边缘和金纳米晶体成像的模拟结果，这表明SWNT探针的多稳定性可能是一种普遍现象，不限于SWNT样品。
