WHAT: The polarization dependence (linear dichroism) of the C 1s X-ray absorption spectrum of individual multi-walled carbon nanotubes (MWCNTs) has been measured using scanning transmission X-ray microscopy for the first time. A very strong dichroic effect is found in the C 1s ->* transition, with almost complete disappearance of this transition when the E-vector is aligned parallel to high quality (low defect) MWCNTs and maximum intensity when the E-vector is orthogonal to the tube axis. The magnitude of the polarization dependence is much higher in arc discharge than chemical vapor deposition MW-CNTs. This is ascribed to differences in densities of sp2 type defects. This signal can be used to map defect distributions in single carbon nanotube devices.

The image displays the ratio of images recorded from a CVD MWCNT at the C 1s -> p* transition with the E-vector oriented as indicated (purple - vertical (90 deg), yellow - tilted (+45 deg). This is a composite of two images taken from a sequence of images recorded with the E-vector systematically rotated relative to the sample - the set of images are displayed in the movie. The ability of the EPU which feeds the CLS spectromicroscopy (SM) beamline to rotate the E-vector has greatly facilitates the dichroic mapping.

OTHER INFORMATION: E. Najafi, D. Hernández Cruz, M. Obst, A.P. Hitchcock, B. Douhard, J.-J. Pireaux and A. Felten, Polarization dependence of the C 1s X-ray absorption spectra of individual multi-walled carbon nanotubes, Small 4 (2008) 2279-2285.