The passivation of InAs(001) surfaces by exposure to sulphur in ultra-high vacuum (UHV), followed by capping with amorphous arsenic, has been studied by high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). Samples grown and passivated at NIMS were transferred to Warwick for analysis, through air and without special precautions. Well ordered and clean InAs surfaces were recovered simply by thermal annealing in UHV. A series of reconstructions were investigated using LEED and XPS by increasing the anneal temperature: a disordered S-rich (1 x 1), ordered S-terminated (2 x 1) and finally a S-free (4 x 2)/c((8/2) In-terininated surface. The evolution of the HREEL spectra with annealing was also measured, and observations of the Surface plasmon mode indicated a very strong surface electron accumulation layer. The downward band bending was largest for the S-rich surfaces with the surface Fermi level as high as 600 meV above the conduction band minimum. (C) 2002 Elsevier Science B.V. All rights reserved.