Dative and Di−σ Binding States of Pyridine on Si(100) and Their Thermal Stability

Abstract

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.

Selective Adsorption of Pyridine at Isolated Reactive Sites on Si(100)

“…It is interesting to note that we do not observe a cyclohexadienyl-like ("butterfly") bonding configuration on a single dimer, even though such a configuration has been calculated to be thermodynamically stable (with binding energies similar to the dative species). 15,16,27 These DFT calculations agree that a 2,5 butterfly configuration (involving formation of two Si-C bonds) is slightly more stable than the 1,4 species (involving a Si-C and Si-N bond). 15,16 However, the 2,5 species cannot be formed directly from the dative species, suggesting that there is likely a significant kinetic barrier for this type of conversion.…”

Thermodynamic factors limiting the preservation of aromaticity of adsorbed organic compounds on Si(100): Example of the pyridine

“…8,13 Among the di-σ compounds, we find the mode IV-C as being the most stable. This result is interesting as this structure had not been considered up to now.…”

“…2 (configurations IV-C and V-C). Henceforth, the configurations IV described by Tao et al 8 will be named IV-A. In fact for a single molecule, the adsorption energies are very similar for p(2 × 2) and c(4 × 2) reconstructions.…”

“…This is the case if we have formation of a dative bond generated via a Lewis acid-base reaction between the lone pair of electrons and the down dimer atom. Examples are heterocycles with an N atom such as pyridine 8,9 and pyrazine 10 or a S atom such as thiophene. 11 Dative-bonded adducts are frequently observed only at low gas exposure and at low temperatures.…”

“…11 Dative-bonded adducts are frequently observed only at low gas exposure and at low temperatures. It is generally believed that the adsorption occurs in a first step through a dative bond followed by the apparition of other structures 8,10,12,13 leading to the vanishing of dative bonds. It is not clear if this transformation is due to a thermodynamic constraint or to a kinetic mechanism.…”