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The University of Southampton

Research project: Nandhakumar: Characterization of nano-scale materials using carbon nanotubes

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The distinctive properties of mesoporous materials are a function of their high internal surface area; the size, shape, and degree of interconnectedness of the pores; and the chemical nature of the framework. It is therefore not surprising that they hold great promise for a wide range of applications including catalysis, batteries, fuel cells, sensors, supercapacitors and optical devices.

Transmission electron microscopy (TEM) and low-angle X-ray scattering (XRD) have so far been the preferred methods to provide evidence for the presence of pores within mesoporous materials. Whilst TEM can provide useful information on the presence and diameter of nano- and mesopores there are a number of limitations associated with its use. For example TEM sample preparation requires scraping the mesoporous films onto a TEM grid. This results in the destruction of the film at the surface. Important information on the surface topography, which is key to the material’s properties, is thereby lost. In addition TEM can only produce two-dimensional projections of the electron density of a mesoporous material. XRD only provides spatially averaged information of surface structure. Mesoporous materials represent highly corrugated surfaces on the nanometer-scale and the use of conventional SPM imaging techniques for analyzing their pore structure has so far been impossible due to limitations arising from the geometry and size of standard probe tips.

Groundbreaking progress in the structural characterization of mesoporous materials has recently been made by my group and we have demonstrated that single-walled carbon nanotube (SWNT) AFM probe tips enable the nanometer-scale imaging of mesoporous materials as shown below and for the first time the pore structure in such a material has been directly visualized. The development of tips based on carbon nanotube technology heralds a significant breakthrough in this area as this new type of tip has a significantly reduced diameter and generally a more suitable shape for the surface analysis of mesopores.

Figure 1

Left: High resolution AFM tapping mode image of a mesoporous TiO2 film acquired with a carbon nanotube probe tip shown on the right.

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