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

Benzenethiol (C6H5SH) and diphenyl disulfide (C6H5S-SC6H5) were used as mod el systems to compare the interaction of chemically similar pi -conjugated molecules with the Si(001)-2x1 surface. The bonding behavior of these subst ituted aromatic hydrocarbons on the Si(001) surface was investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectro scopy (XPS), and scanning tunneling microscopy (STM). Both FTIR and XPS ind icate that benzenethiol molecules chemisorb on the Si(001) surface predomin antly through the sulfur atom via deprotonation-of the thiol substituent gr oup. There also is evidence that a small minority of benzenethiol molecules may adsorb on the surface through the phenyl ring or undergo further fragm entation. Diphenyl disulfide appears to bond to the Si(001) surface in one primary configuration in which the S-S bond of diphenyl disulfide is cleave d and the two sulfur-phenyl moieties are bonded to the silicon surface thro ugh the sulfur atoms. Thermal studies indicate that the sulfur-tethered aro matic rings of benzenethiol and diphenyl disulfide are stable to temperatur es above 520 K. Furthermore, STM studies show that these molecules chemisor b to the silicon surface within a single dimer row and, in the case of diph enyl disulfide, appear to form ordered rows of sulfur-tethered aromatic rin gs. This new chemistry demonstrates remarkable potential as a means of sele ctively attaching pi -conjugated systems to technologically useful semicond uctor surfaces.