Rümmeli et al. Nanoscale Research Letters 2011, 6:303 http://www.nanoscalereslett.com/content/6/1/303 Page 4 of 9 Figure 4 Energy filtered TEM images of carbon nanotubes produced from phenylboronic acid in a MgO matrix. The images show a carbon outer shell and a core (nanowire) comprised B, O and Mg. Top image-zero loss image. The C, B, O and MgO energy filtered TEM images are presented in false colour. Reprinted with kind permission from Bachmatiuk et al. [34]. formation when using zirconia as the catalyst. However, it should be noted that Bachmatiuk et al. [37] also found no carbide formation when using XPS despite other techniques clearly demonstrating the presence of carbides. This suggests XPS, which is a surface sensitive technique, may not be best suited to determine if oxides used as catalysts for CNT growth reduce to carbides or not during synthesis. Various other oxides, outside of those mentioned, including TiO2 and lanthanide oxides can also be used to grow carbon nanotubes [36]. Tem- plated CNT grown in porous alumina without catalyst particles have also been demonstrated [39]. Further