Mapping and differentiating CNTs
The Nanonics MultiView series (MV 1000, MV 2000, and MV 4000) provide complete hardware and software integration for the full suite of AFM and Raman characterization of all your materials including AFM, Raman, TERS, and NSOM characterization. AFM together with Raman based methods have become the method of choice for characterizing carbonaceous materials. For carbon nanotubes, AFM-Raman imaging is especially useful for differentiating the different kinds of nanotubes.
Below is a 10um x 10um AFM topography image of carbonaceous material on silicon clearly showing the presence of a nanotube on the surface in addition to some round carbonaceous domains at the top and bottom two corners.
Raman spectra were collected both on the nanotube and the circular domains. Below the red spectrum corresponds to the Raman spectrum on the nanotube showing a large peak at 1575cm-1 and a smaller peak at about 1340cm-1. A Raman spectrum from the round domains is shown in green revealing a large peak at 1340cm-1 and a weak, dual peak at about 1600cm-1. These spectra clearly differentiate the carbon nanotube and the surrounding disordered material.
Finally, a Raman intensity map at 1600cm-1 and 1340cm-1 was collected with the resulting image shown below, clearly mapping the carbon nanotube (red) and the regions of disordered materials (Green).
Raman difference spectroscopy
Nanonics has implemented into the Multiview 2000 and 4000 series a set of specialized AFM scanning protocols of Raman difference spectroscopy effectively discriminating between the near-field and far-field contribution of the scattered Raman signals. The upper scanner in the scanning head enables automated vertical tip motion at every pixel during the AFM/Raman mapping. Thus, a Raman map can be collected while the tip is in contact with the sample (near-field signal) and then again when the tip is retracted at a predetermined distance above the sample (far-field signal) and then retraces the substrate. The software then automatically calculates the difference between the intensity of the Raman spectrum when the TERS probe is in contact and when the probe is retracted.
A Multiview 4000 with a TERS probe was used to collect Raman difference spectra of carbon nanotube clusters in the images shown below. A topography map of the clusters is shown in (a) revealing several hundred nanometer round domains of carbon nanotubes.
Next a TERS map with the probe in contact with the sample was collected in (b) showing the Raman intensity at 405cm-1. The Raman map was collected at an array of 1850 points (pixels shown in the topography image) where measurements were separated by 180nm.
The tip is then retracted, and the far-field Raman intensity map at 405cm-1 is again collected as shown in (c). The difference map between (b) and (c) is shown in (d), clearly providing significantly better resolution in the Raman intensity map that can be accurately correlated with the topographic map in (a), revealing important chemical information about the various CNT clusters.