Single-Walled Carbon Nanotubes as One-Dimensional Scattering Surfaces for Measuring Point Spread Functions and Performance of Tip-Enhanced Raman Spectroscopy Probes

Abstract

This Article describes a method for the characterization of the imaging performance of tip-enhanced Raman spectroscopy probes. The proposed method identifies single-walled carbon nanotubes that are suitable as one-dimensional Raman scattering objects by using atomic force microscope maps and exciting the radial breathing mode using 785 nm illumination. High-resolution cross sections of the nanotubes are collected, and the point spread functions are calculated along with the optical contrast and spot diameter. The method is used to characterize several probes, which results in a set of imaging recommendations and a summary of limitations for each probe. Elemental analysis and boundary element simulations are used to explain the formation of multiple peaks in the point spread functions as a consequence of random grain formation on the probe surface.

Feasibility of gold nanocones for collocated tip‐enhanced Raman spectroscopy and atomic force microscope imaging

“…We have previously developed a method for characterising the imaging performance of TERS probes 29 . This involves performing high‐resolution cross‐section TERS scans of an isolated single‐walled carbon nanotube (SWCNT) that acts as a 1D scattering object.…”

“…This method was repeated with 638 nm and 785 nm laser excitation using a gold nanocone TERS probe. The results from three commercially available probes previously reported are reproduced in this article for the sake of comparison 29 . The commercially available TERS probes are labelled as follows: A ‐ silver coated silicon with a thin gold passivation layer of unknown thickness B1, B2 ‐ gold coated silicon C1, C2 ‐ gold coated silicon …”

“…We have previously developed a method for characterising the imaging performance of TERS probes. 29 This involves performing high-resolution cross-section TERS scans of an isolated single-walled carbon nanotube (SWCNT) that acts as a 1D scattering object. The radial breathing mode (RBM) of SWCNTs reveals information about the diameter and local distribution of nanotubes.…”

“…The results from three commercially available probes previously reported are reproduced in this article for the sake of comparison. 29 The commercially available TERS probes are labelled as follows: • A -silver coated silicon with a thin gold passivation layer of unknown thickness • B1, B2 -gold coated silicon • C1, C2 -gold coated silicon Probes A and B are both specified by the manufacturer as suitable for use with the TERS setup used in this paper; however, the optimal excitation wavelength is not given. Probe C is not specified as a TERS F I G U R E 4 Data acquired from high-resolution cross-section TERS maps of SWCNTs.…”

“…The results of three commercially available probes are included for comparison. 29 The SWCNT cross-sections with Raman intensity/mW À1 s À1 are plotted in (E1-E6). The PSFs are used to calculate the contrast and spot diameter of each TERS probe, which are summarised in Table 1.…”