Near-edge X-ray absorption fine structure (NEXAFS) Studies of Nanomaterials

We have recently used synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, surface molecular orientation, degree of order, and electronic structure of carbon nanotubes and related nanomaterials. This work is summarized in an invited contribution, namely Small(Concepts Article), v.2, 26 (2006). That is, we employed NEXAFS as an exciting, complementary tool to microscopy and spectroscopy for providing localized information about single-walled carbon nanotube and multi-walled carbon nanotube (MWNT) powders, films, and arrays as well as of boron nitride nanotubes. Specifically, for SWNTs, we analyzed their structure as a function of oxygenation/oxidation (e.g. comparison of wet-air oxidized, ozonized, and pristine tubes).

In additional experiments, we compared the degree of order and alignment in nanotube powder, film, and aligned samples with those of graphite. Specifically, we analyzed the surface order of vertically-aligned single-walled and multi-walled carbon nanotube arrays of varying length and composition by means of NEXAFS. Both NEXAFS and scanning electron microscopy (SEM) studies concluded that the nanotubes in these samples were oriented vertically to the plane of the surface. However, NEXAFS polarization analysis provided for a more quantitative and nuanced description of the surface structure, indicative of far less localized surface order, an observation partially attributed to misalignment and bending of the tubes. Moreover, it was demonstrated by NEXAFS that the surface order of the arrays was imperfect and relatively independent of the height of the nanotube arrays. Furthermore, we have shown that NEXAFS can be used to correlate the extent of chemical functionalization and oxygenation with disruption of the electronic and physical structure of nanotubes embedded in array motifs.