The cross-sectional structure of vanadium oxide nanotubes studied by transmission electron microscopy and electron spectroscopic imaging

Vanadium oxide nanotubes (VOx-NTs) are easily accessible in pure form from vanadium(V) alkoxides and amines by a sol-gel reaction and a subsequent hydrothermal treatment. The wall structure of VOx-NTs containing hexadecylamine or dodecylamine as the structure-directing template has been characterised by transmission electron microscopy (TEM). A standard method for preparing TEM specimens was modified in order to investigate the cross-sectional structure of the tubes. The elemental distribution in the layered structure inside the tube wails has been visualised by electron spectroscopic imaging: vanadium oxide builds up the layers that appear with dark contrast in the TEM images while carbon, i.e., the organic template, is present in between. The bent VOx layers inside the tube walls are preferentially scrolls rather than concentric cylinders. Moreover, some tubes are formed by a combination of both types. The layer structure inside the tube walls is frequently disordered, and several types of defects appear.