  The morphological and electronic properties of isolated and monolayer phases
of carboxyl- and amine-functionalized carboranethiols on unreconstructed
Au(111) were determined using density functional theory calculations by
including van der Waals interactions. The groups are effective in the assembly
of pristine adlayers on gold and also offer functionality when exposed at the
SAM-environment interface. Anisotropy brought by both functional groups
increases tilting of carboranethiols relative to the surface normal and
absolute values of the dissociative chemisorption energies. Positional
isomerization and the functional groups modify the molecular dipole moments
which influnce the adsorption characteristics. Even though carboxylic acid and
amine groups have different chemical properties, they have similar effects on
the adsoprtion characteristics of carboranethiols. Dense packing favors
intermolecular interactions which gives a stronger binding relative to isolated
adsorption. The carboranethiols with the functional groups can be arranged in
the same lateral direction or in a dimer conformation with molecues facing each
other. Carboxyl and amine groups offer functionalization of cabranethiol SAMs
and in conjuction with positional isomerization shift tunability ranges of the
work function of gold to higher energies.
