Gold surfaces were treated with solutions of 1-iodododecane, 1-iodooctadecane, 1,10-diiododecane, 1-bromododecane, and 1,10-dibromodecane. Thereafter the surfaces were studied with IR spectroscopy at grazing incidence reflection, XPS, ellipsometry, and contact angle measurements. Evidence for the formation of ultrathin layers was found for the compounds containing iodine but not for those containing bromine. The results imply that the iodoalkanes dissociate on the surface, creating Au-C and Au-I bonds. As a consequence, a mixed monolayer of iodide and alkyl species is present on the surface. These layers are hydrophobic; the advancing contact angles of water on these surfaces are 82-93 degrees. The surface-bound species resist desorption in pure solvent at least for 1-2 days.