Formation of molecular templates containing cumulative double bonds (C=C=C) at organic/silicon hybrid interfaces.

The cumulative double bond (C=C=C), an important intermediate in synthetic organic chemistry, was successfully prepared via the selective attachment of acetylethyne to Si(111)-7 x 7. The experimental observation of the characteristic vibrational modes and electronic structures of the C=C=C group in the surface species demonstrates the [4 + 2]-like cycloaddition occurring between the terminal O and C atoms of acetylethyne and the neighboring Si adatom-rest atom pair, consistent with the prediction of density functional theory calculations. Scanning tunneling microscopy images further reveal that the molecules selectively bind to the adjacent adatom-rest atom pairs on Si(111)-7 x 7.

Binding mechanisms of methacrylic acid and methyl methacrylate on si(111)-7 x 7 -- effect of substitution groups.

The interaction of methacrylic acid and methyl methacrylate with Si(111)-7 x 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). While methacrylic acid chemisorbs dissociatively through O-H bond cleavage, methyl methacrylate is covalently attached to the silicon surface via a [4+2] cycloaddition. The different reaction pathways of these two compounds on Si(111)-7 x 7 demonstrate that the substitution groups play an important role in determining the reaction channels for multifunctional molecules, leading to the desired flexibility in the organic modification of silicon surfaces.

Dry synthesis of triple cumulative double bonds (C=C=C=N) on Si(111)-7 x 7 surfaces.

The interactions of cyanoacetylene and diacetylene with a Si(111)-7 x 7 surface have been studied as model systems to mechanistically understand the chemical binding of unsaturated organic molecules to diradical-like silicon dangling bonds. Vibrational studies show that cyanoacetylene mainly binds to the surface through a diradical reaction involving both cyano and C[triple bond]C groups with an adjacent adatom-rest atom pair at 110 K, resulting in an intermediate containing triple cumulative double bonds (C=C=C=N). On the other hand, diacetylene was shown to the covalently attached to Si(111)-7 x 7 only through one of its C[triple bond]C groups, forming an enynic-like structure with a C=C-C[triple bond]C skeleton.

A [4+2]-like cycloaddition of methyl methacrylate on Si(100)-2 x 1.

The attachment of methyl methacrylate (MMA) on Si(100)-2x1 was investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. The HREELS spectra of chemisorbed MMA show the disappearance of characteristic vibrations of C=O (1725 cm(-1)) and C(sp(2))-H (3110, 1400, and 962 cm(-1)) coupled with the blue shift of the C=C stretching mode by 34 cm(-1) compared to those of physisorbed molecules. These results clearly demonstrate that both C=C and C=O in MMA directly participate in the interaction with the surface to form a SiCH(2)C(CH(3))=C(OCH(3))OSi species via a [4+2]-like cycloaddition.

Selective attachment of benzaldehyde on Si(100)-2 x 1: structure, selectivity, and mechanism.

The interaction of benzaldehyde with the Si(100) surface has been investigated as a model system for understanding the interaction of conjugated pi-electron systems with semiconductor surfaces. Vibrational features of chemisorbed benzaldehyde unambiguously demonstrate that the carbonyl group directly interacts with the Si surface dangling bonds, evidenced in the disappearance of the C=O stretching mode around 1713 cm(-1) coupled with the retention of all vibrational signatures of its phenyl ring. X-ray photoemission spectroscopy shows that both C 1s and O 1s binding energies of the carbonyl group display large downshifts by 1.

Formation of a tetra-sigma-bonded intermediate in acetylethyne binding on Si(100)-2 x 1.

The covalent binding of acetylethyne on Si(100)-2 x 1 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The HREELS spectra of chemisorbed monolayers show the absence of the C=O, C[triple bond]C, and C(sp)-H stretching modes coupled with the appearance of C=C (at 1580 cm(-1)) and C(sp2)-H (at 3067 cm(-1)) stretching modes. This demonstrates that both of the C=O and CC groups of acetylethyne directly participate in binding with silicon surfaces to form C-O and C=C bonds, respectively, which is further confirmed by the XPS studies.

Selective bonding of pyrazine to silicon(100)-2x1 surfaces: the role of nitrogen atoms.

The covalent binding of pyrazine on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS) and x-ray photoelectron spectroscopy. Experimental results clearly suggest that the attachment occurs exclusively through the bonding of the two para-nitrogen atoms with the surface without the involvement of the carbon atoms, as evidenced from the retention of the (sp2) C-H stretching mode in HREELS and a significant down shift of 1.6 eV in the binding energy of N 1s.