Aluminium nitride (AN) was grown on porous silica by atomic layer chemical vapour deposition (ALCVD) from trimethylaluminium (TMA) and ammonia precursors. The ALCVD growth is based on alternating, separated, saturating reactions of the gaseous precursors with the solid substrate. TMA and ammonia were reacted at 423 and 623 K, respectively, on silica which had been dehydroxylated at 1023 K and pretreated with ammonia at 823 K. The growth in three reaction cycles was investigated quantitatively by elemental analysis, and the surface reaction products were identified by IR and solid state Al-27 and Si-29 NMR measurements. Steady growth of about 2 aluminium and 2 nitrogen atoms/nm(silica)(2)/reaction cycle was obtained. The growth mainly took place through (i) the reaction of TMA which resulted in surface AI-Me and Si-Me groups, and (ii) the reaction of ammonia which replaced the aluminium-bonded methyl groups with amino groups. Ammonia also reacted in part with the silicon-bonded methyl groups formed in the dissociative reaction of TMA with siloxane bridges. TMA reacted with the amino groups, as it did with surface silanol groups and siloxane bridges. In general, the Al-N layer interacted strongly with the silica substrate, but in the third reaction cycle AlN-type sites may have formed.