Sulfur atoms as tethers for selective attachment of aromatic molecules to silicon(001) surfaces

Benzenethiol (C6H5SH) and diphenyl disulfide (C6H5S-SC6H5) were used as model systems to compare the interaction of chemically similar pi -conjugated molecules with the Si(001)-2x1 surface. The bonding behavior of these substituted aromatic hydrocarbons on the Si(001) surface was investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). Both FTIR and XPS indicate that benzenethiol molecules chemisorb on the Si(001) surface predominantly through the sulfur atom via deprotonation-of the thiol substituent group. There also is evidence that a small minority of benzenethiol molecules may adsorb on the surface through the phenyl ring or undergo further fragmentation. Diphenyl disulfide appears to bond to the Si(001) surface in one primary configuration in which the S-S bond of diphenyl disulfide is cleaved and the two sulfur-phenyl moieties are bonded to the silicon surface through the sulfur atoms. Thermal studies indicate that the sulfur-tethered aromatic rings of benzenethiol and diphenyl disulfide are stable to temperatures above 520 K. Furthermore, STM studies show that these molecules chemisorb to the silicon surface within a single dimer row and, in the case of diphenyl disulfide, appear to form ordered rows of sulfur-tethered aromatic rings. This new chemistry demonstrates remarkable potential as a means of selectively attaching pi -conjugated systems to technologically useful semiconductor surfaces.