Binding of chemical functionalities onto silicon surfaces

Abstract

The interactions of organic molecules, including acetyl cyanide, methyl methacrylate, methyl propiolate, formic acid, methacrylic acid, N-methylallylamine, N,N-dimethylallylamine, glycine and L-cysteine, with silicon surfaces were investigated using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), high-resolution electron energy loss spectroscopy (HREELS) and density functional theory (DFT) calculations. The results demonstrate that silicon surfaces can be efficiently modified by covalent attachment of chemical functionalities, creating fundamental molecular interface for the fabrication of new organic/silicon hybrid devices. Acetyl cyanide, methyl methacrylate and methyl propiolate were found to undergo different reaction pathways on Si(100)-2??1, determined by the reactivities of various functionalities and the reactive sites on the Si surface. While Methacrylic acid chemisorbs dissociatively on Si(111)-7??7 through the O-H bond cleavage, methyl methacrylate is covalently attached to the silicon surface via a [4+2]-like cycloaddition. Similarly, N-methylallylamine and N,N-dimethylallylamine react with Si(111)-7??7 via a N-H dissociation and a [2+2]-like cycloaddition across C=C, respectively. These results indicate that the substitution groups play an important role in determining the reaction channels for multifunctional molecules, leading to desired flexibility in organic modification of silicon surfaces. Chemisorbed glycine and L-cysteine both dissociate to yield two surface intermediates on Si(111)-7??7 through the breakage of O-H and N-H groups. The information obtained from these two model biological molecules would be helpful for the further studies in more complicated systems including protein/Si and peptide/Si.