Influence of Elastic Deformation on Single-Wall Carbon Nanotube Atomic Force Microscopy Probe Resolution

Abstract

We have previously reported that 4−6 nm diameter single-wall carbon nanotube (SWNT) probes used for tapping-mode atomic force microscopy (AFM) can exhibit lateral resolution that is significantly better than the probe diameter when prone nanotubes are imaged on a flat SiO2 surface. To further investigate this phenomenon, accurate models for use in atomistic molecular dynamics simulations were constructed on the basis of transmission electron microscopy (TEM) and AFM data. Probe−sample interaction potentials were generated by utilization of force fields derived from ab initio quantum mechanics calculations and material bulk and surface properties, and the resulting force curves were integrated numerically with the AFM cantilever equation of motion. The simulations demonstrate that, under the AFM imaging conditions employed, elastic deformations of both the probe and sample nanotubes result in a decrease of the apparent width of the sample. This behavior provides an explanation for the unexpected resolution improvement and illustrates some of the subtleties involved when imaging is performed with SWNT probes in place of conventional silicon probes. However, the generality of this phenomenon for other AFM imaging applications employing SWNT probes remains to be explored.

Scanning Tunneling Microscopy of Ethylated Si(111) Surfaces Prepared by a Chlorination/Alkylation Process

“…These calculations used the Cerius2 software (Accelrys, San Diego, CA) with previously reported force-field parameters for silicon 23 and hydrocarbons 24 but with the H-CSi-Si torsional parameter adjusted to 2.945 kcal/mol based on DFT (SeqQuest) calculations. From those simulations, two predictions were extracted that could then be directly compared with the data of Figure 3.…”

Nanoscale Fluorescence Microscopy Using Carbon Nanotubes

“…First, after pulse shortening, the nanotubes should be open ended, and thus, are very pliable along the radial direction. Atomistic simulations of this system have predicted that this can lead to finer resolution than predicted by the tube diameter, as the tube deforms, and thus, narrows its profile as it scans over an object [68]. On the other hand, there is also evidence that a thin water layer that forms on the surface of all the samples will increase the width of the AFM images under some circumstances [69].…”

“…Furthermore, imaging in a dry environment (e.g., N 2 or Ar) or under vacuum should reduce or eliminate the artifacts caused by the water layer. Other imaging artifacts, such as a narrowing of the AFM image caused by the deformation of the nanotube as it scans over a small object [68], [79], are also possible. Evidently the importance of various artifacts depends on the imaging and/or environmental parameters.…”

Mechanisms of Single-Walled Carbon Nanotube Probe−Sample Multistability in Tapping Mode AFM Imaging

“…4 The additional parameters, required for the simulation of the Si(111)-CH 3 surface step edge and for the Au nanoparticle, were taken from the Dreiding Force Field 3 (with the H-C-Si-Si torsion barrier adjusted to 2.945 kcal/mol based on ab initio QM calculations on the Si(111)-CH 3 surface) and from the work of Jang et al 5 on Au surfaces (using a 6-12 Lennard-Jones function for the Au -C interaction, with R o = 4.5 Angstroms, and D o = 0.175 kcal/mol).…”