Molecular self-assembly at bare semiconductor surfaces: characterization of a homologous series of n-alkanethiolate monolayers on GaAs(001).

Structural trends for a homologous series ofn-alkanethiolate self-assembled monolayers (SAMs), CnH2n1S- with 12 16 cases. A 4=-methyl-biphenyl-4-thiolate companion SAM shows evidence for ordered structures but with lattice parameters close to those expected for a structure commensuratewiththeintrinsicGaAs(001)squarelattice.Thesetrendsareexplainedonthebasisofcompetitions between lattice, interfacial, and intermolecular forces controlling the nanoscale structures of the SAMs. Overall these results provide an important aspect of understanding the effects of SAM formation on surface properties such as electronic and chemical passivation.