The chemical binding of pyridine on Si(100) has been studied using thermal desorption spectroscopy (TDS), X-ray phototelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and DFT theoretical calculations. XPS results show two chemisorption states of pyridine with N 1s binding energies at 398.8 and 401.8 eV, attributable to the [4+2]-like cycloadduct with two σ-linkages of Si-N 1 and Si-C 4 , and the dative-bonded pyridine through the lone pair electrons of its N atom, respectively. These observations were further confirmed in our vibrational studies. The formation of a dative bond between pyridine and Si(100) demonstrates a new approach for the chemical attachment of unsaturated organic molecules on the Si surface. The 1,4-dihydropyridine-like cycloadduct formed at 350 K can be considered as a template for further modification and functionalization of Si surfaces or as an intermediate for syntheses in a vacuum.

Articles you may be interested inAdsorption and thermal decomposition of acetic acid on Si ( 111 ) 7 × 7 studied by vibrational electron energy loss spectroscopy J. Chem. Phys. 132, 174702 (2010) Pyrrole adsorption on Si(111)-(7ϫ7) has been investigated using high-resolution electron energy loss spectroscopy ͑HREELS͒, thermal desorption spectroscopy, scanning tunneling microscopy ͑STM͒, and theoretical calculations. Compared to physisorbed pyrrole, chemisorption leads to the appearance of N-Si and Si-H vibrational features, together with the absence of N-H stretching mode. This clearly demonstrates the dissociative nature of pyrrole chemically binding on Si(111)-(7ϫ7) through the breakage of N-H bond. Based on STM results, the resulting fragments of pyrrolyl and H atom are proposed to bind with an adatom and an adjacent rest atom, respectively. The STM images further reveal that the adsorption is site selective. The faulted center adatoms are most favored, followed by unfaulted center adatoms, faulted corner adatoms, and unfaulted corner adatoms. In addition, the chainlike pattern of reacted adatoms was observed, implying the possible existence of attractive interaction between adsorbed pyrrolyl and the precursor state. Theoretical calculation confirms that the dissociative adsorption with pyrrolyl bonded to an adatom and H atom to an adjacent rest atom is energetically favored compared to the associative cycloaddition involving the two ␣-carbon atoms of pyrrole and an adatom-rest atom pair.

The covalent binding and structure of acetonitrile on Si(111)-7 × 7 have been investigated to provide information on the interaction of π electrons of the CtN group with the dangling bonds of Si(111)-7 × 7. Vibrational features of chemisorbed acetonitrile and acetonitrile-d 3 unambiguously show the absence of Ct N stretching mode around 2232 cm -1 coupled with the appearance of CdN stretching mode at 1663 cm -1 . Both C 1s and N 1s core levels of chemisorbed acetonitrile display large chemical shifts of 2.2 and 1.3 eV, respectively, compared with those of physisorbed molecules. In addition, the photoemission from π CN was observed to be weakened upon chemisorption. These results clearly suggest that the cyano group directly participates in the interaction with Si surface dangling bonds. Scanning tunneling microscopy images reveal that the cyano groups selectively bind to adatom-rest atom pairs on Si(111)-7 × 7. Density functional theory calculations indicate that the C and N atoms of the cyano group favorably link with the adatom and rest atom, respectively, forming C-Si and N-Si bonds.

The cumulative double bond (C[double bond]C[double bond]N), an important intermediate in synthetic organic chemistry, was successfully prepared via the selective attachment of acrylonitrile to Si(111)-7 x 7. The covalent binding of acrylonitrile on Si(111)-7 x 7 was studied using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM) and DFT calculations. The observation of the characteristic vibrational modes and electronic structures of the C[double bond]C[double bond]N group in the surface species demonstrates the [4 + 2]-like cycloaddition occurring between the terminal C and N atoms of acrylonitrile and the neighboring adatom-rest atom pair, consistent with the prediction of DFT calculations. STM studies further show the preferential binding of acrylonitrile on the center adatom sites of faulted halves of Si(111)-7 x 7 unit cells.