AlN layers were formed on (1 1 1)Al substrates at a temperature below the melting point of Al using preheated ammonia in vacuum. The effect of the removal of the surface oxides on the substrate in the process was investigated. It was found that treatment using a buffered HF solution and subsequent annealing in vacuum was effective for obtaining a clean Al substrate surface. It was clarified that the removal of the surface oxides is required for the nitridation of Al substrates at a low temperature below the melting point of Al. (C) 2009 Elsevier B.V. All rights reserved.