Preparation and passivation of GaAs(001) surfaces for growing organic molecules

Growth of ordered organic films of 3, 4, 9, 10-perylene-tetracarboxylic-dianhydride (PTCDA), on inorganic substrates of GaAs(001) is investigated by means of low-energy electron diffraction, scanning tunnelling microscopy and atomic force microscopy. The passivation of the sample can be achieved by exposing the substrate to sulphur (the SnS2 compound) or wet-chemical etching using an S-containing etchant (S2Cl2). The sulphur-treated surfaces are less reactive and are suitable as substrates for the growth of epitaxial films. In this work we have compared the growth of organic molecules on substrates prepared by two different methods. The samples prepared by molecular beam epitaxy (MBE) present smoother surfaces compared with chemically treated samples. Therefore, an improvement of the PTCDA molecular order is observed for the MBE samples, which exhibit the formation of crystals. (Some figures in this article are in colour only in the electronic version)