Although both thiols and disulfides form excellent quality self-assembled monolayers on Au and other metals (Ag, Pd, Pt, Hg), the latter offer several distinct advantages you might want to consider when planning your experiments. Disulfides are more stable than thiols, significantly less prone to oxidation, and avoid problems associated with intramolecular or intermolecular reactivity of the thiol group (Langmuir, 2003, 19, 1522-1531). In addition, asymmetric disulfides give monolayers of well-defined surface compositions, avoid phase separation (J. Phys. Chem. B 2001, 105, 2975-2980), and eliminate cooperative effects associated with co-adsorption of binary solutions of corresponding thiols (Langmuir 2001, 17, 7735-7741).