Dissociation and [2+2]-like Cycloaddition of Unsaturated Chain Amines on Si(111)-7×7

Abstract

The covalent attachment of N-methylallylamine (MAA) and N,N-dimethylallylamine (DMAA) on Si(111)-7×7 was investigated with high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). Experimental results showed that MAA chemisorbs dissociatively on Si(111)-7×7 through the cleavage of its N−H bond, while DMAA is covalently bonded to the silicon surface via a [2+2]-like cycloaddition between its CC group and the adjacent adatom−rest atom pair. This study demonstrates that the selective organic functionalization of silicon surfaces can be achieved by fine-tuning molecular structures.

Chemical manipulation of multifunctional hydrocarbons on silicon surfaces

“…[301]. c 2007, The American Chemical Society groups is substituted for hydrogen, amine dissociation prevails forming stable Si-H and Si-N linkers [376].…”

Competing Pathways in N-Allylurea Adsorption on Si(111)-(7 × 7)

“…The highest intensity modes in the N -allylurea/Au­(111) spectrum are observed in the region below 1000 cm –1 and can be attributed to a band of out-of-plane molecular bending modes. In particular, the peak at 742 cm –1 is attributed to the NH out-of-plane deformation, while the peak at 920 cm –1 is due to CH 2 out of plane deformation. ,, As the spectra are taken in dipole-scattering conditions, the higher intensity of these out-of-plane modes relative to the corresponding in-plane modes is a clear indication that N -allylurea adsorbs in an almost flat geometry, as qualitatively sketched in Figure a . The region above 1000 cm –1 is characterized by three main features, at 1274, 1429, and 1686 cm –1 , attributed to in-plane deformations of the −NH and −CH 2 groups and to the ureic-group stretching mode, respectively.…”

“…The binding energy of component H (397.8 eV) corresponds to a downshift of –2.0 eV relative to the unreacted amine. In fact, Si–NH bond formation (with single bond cleavage) typically corresponds to a N 1s binding energy downshift of –1.5 eV, ,, while larger downshifts are attributed in the literature to double bond cleavage, as for instance in the case of acetonitrile adsorption on the Si(111)-(7 × 7) surface, where the −NC group bonds to a Si adatom . Our data therefore indicate that bonding through nitrogen occurs upon cleavage of both NH bonds at the terminal amine and formation of a Si–NC– bonding.…”

“…Besides vinyl-based attachment, the interaction of Si(111)-(7 × 7) surface with the urea functional groups (i.e., the two amines and the carbonyl) could also be envisaged. Reaction of amines with silicon surfaces, through cleavage of NH bonds and formation of Si–N bond, has been reported for instance in the case of N -methylallylamine and of glycine and cysteine on Si(111)-(7 × 7) . Such reaction has also been proposed in the case of UV-assisted allylamine deposition on the Si(111):H surface .…”

“…In the case of N -allylurea, the presence of the vinyl group should in principle allow a simple attachment strategy on silicon surfaces, with formation of covalent Si–C bonds through a [2 + 2]-like cycloaddition or through hydrosilylation. , Both attachment strategies guarantee the availability of the amine and/or the carbonyl as terminal groups. On the (7 × 7) surface, a cycloaddition-like mechanism, where cleavage of the CC bond is followed by the formation of two Si–C bonds at neighboring rest atom–adatom sites, has been observed for instance for ethylene adsorption − and proposed also in the case of N,N -dimethylallylamine, cyclohexene, and N -methylpyrrole . On the other hand, the hydrosilylation mechanism typically takes place at hydrogenated surfaces. − Indeed, for hydrosilylation to take place on the Si(111)-(7 × 7) surface, a proper amount of hydrogen atoms, possibly derived from other concomitant reactions, is required.…”