The formation of layers of porous crystalline tin dioxide from a composite on the basis of multiwalled carbon-nanotube arrays

A new method for the synthesis of porous crystalline tin-dioxide (SnO$_2$) layers from composites on the basis of multiwalled carbon nanotubes (MWCNTs) and nonstoichiometric amorphous tin oxide (MWCNT/SnO$_{x}$) is proposed. An MWCN/SnO$_{x}$ composite layer produced by magnetron sputtering is annealed in air atmosphere at 500$^\circ$C for 30 min. A homogeneous porous layer comprised of crystalline SnO$_2$ spherical particles with a size of about 0.1 $\mu$m is obtained as a result. In the process of annealing, nearly all the amount of carbon is removed in the form of gaseous oxides (only a small amount remains in the upper part of the porous SnO$_2$ layer). The structural defectiveness of nanotube walls, which increases because of the magnetron deposition of tin, plays a crucial role in the carbon oxidation and destruction of MWCNTs.