Self-assemblies of 2 6-naphthalenedicarboxylic acid (NDC) and 4 4'-biphenyldicarboxylic acid (BDC) molecules on the highly oriented pyrolytic graphite (HOPG) and reconstructed Au(1 1 1) surfaces has been respectively studied by using scanning tunneling microscopy (STM) The NDC molecules form an incommensurate structure while BDC molecules form a commensurate structure on the HOPG surface The aromatic rings take the same orientation with that of the underlying HOPG substrate to gain optimum adsorbate-substrate interactions On the Au(1 1 1) surface both molecules form incommensurate structures The orientations of aromatic ring locate about 20 with respect to the gold rows the (1 1 0) direction On the HOPG surface the whole carboxyl groups are invisible while the carbon atoms of the carboxyl groups may appear bright on the gold surface (C) 2010 Elsevier Ltd All rights reserved