4-Nitrophenyl sulfenyl chloride was used as a new precursor for the formation of densely packed aromatic SAMs on gold. The adsorption involves the reductive dissociation of the S-Cl bond. A well-ordered row structure corresponding to a √3 × 4 phase with a molecular area of 27.8 Å(2) is obtained.

Long-range-ordered aromatic SAMs are formed on Au(111) using 4-nitrophenyl sulfenyl chloride as a precursor. Although the main structure is a √3 × √3 with a molecular density similar to that usually found for aliphatic SAMs, particular spots presenting specific shapes are also observed by STM. These include hexagons, partial hexagons, parallelograms, and zigzags resulting from specific arrangements of adsorbed molecules. These molecular arrangements are reversible as they form and dissociate or "vanish" in various areas on the surface. STM shows that these particular structures provide some order to their surrounding because areas void of these structures look less ordered. More interestingly, STM shows submolecular details of the molecules involved in forming these structures, hence providing direct experimental evidence for the ability of the STM to provide physical structure information of standing up SAMs. This is indeed a heavily debated question, and this work reports the first experimental example where submolecular physical structure is revealed by STM for standing-up SAMs.

The use of triphenylmethane sulfenyl chloride as a new precursor leads to the efficient deposition of sulfur on polycrystalline gold and Au(111) substrates. The modified surfaces are characterized using X-ray photoelectron spectroscopy (XPS), electrochemistry and scanning tunneling microscopy (STM). The XPS data shows the rapid deposition of polymeric sulfur within very short times. Electrochemical stripping cyclic voltammetry (CV) confirms the rapid deposition and shows that high coverage values are achieved. STM imaging shows the formation of a wide range sulfur layer and production of the well-known etch pits. High-resolution STM images confirm the high density of the sulfur layers and show formation of a long-range phase consisting of rhombus structures close to the previously described rectangular structures along with other parallelograms and partial parallelograms. The present results do not show the initial formation of any organic self-assembled monolayer (SAM) indicating that the formation of polymeric sulfur does not result from the decomposition of an initial SAM as previously observed with alkyl and aryl thiolate-based SAMs. The suggested mechanism involves an initial reductive process similar to the one reported for thiocyanates and sulfenyl chlorides. This is followed by the dissociation of the Ph(3)C-S bond, leaving only sulfur on the surface, through a process leading to the recombination of the remaining fragments to yield triphenylmethyl chloride.

The formation of aromatic SAMs on Au(111) using three nitro-substituted arene sulfenyl chlorides (4-nitrophenyl sulfenyl chloride (1), 2-nitrophenyl sulfenyl chloride (2), and 2,4-dinitrophenyl sulfenyl chloride (3)) is studied. The formation of SAMs and their quality are investigated as a function of the position of the nitro substituent(s) on the aromatic ring. The modified surfaces are characterized by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), polarization modulation infrared reflection absorption spectroscopy (PMIRRAS), and cyclic voltammetry (CV). The results show that all three compounds are deposited on Au within very short times. The corresponding coverages are determined using CV. However, only compound 1 forms stable, long-range, well-ordered SAMs. The 4-nitrophenyl thiolate is adsorbed nearly vertically on the Au surface. Compounds 2 and 3 both form lower-quality SAMs where the adsorbed nitro-phenyl thiolates are more tilted. These SAMs are less stable than the ones obtained with the 4-nitrosubsituted precursor and decompose with time, leaving only sulfur on the gold surface.