Theoretical Study of Toluene Chemisorption on Si(100)

A HREELS and DFT study of the adsorption of aromatic hydrocarbons on diamond (111)

Ultrathin layers of organic molecules can be assembled on group IV (e.g., silicon, germanium, diamond) semiconductor surfaces using surface analogues of cycloaddition reactions. We present a study of the chemisorption of benzene, toluene, and styrene on the Pandey chain of C(111) using high resolution electron energy loss spectroscopy and density functional theory calculations. Two cycloaddition reactions, namely, the [4 + 2] and [2 + 2], were examined. The [4 + 2] reaction is found to be thermodynamically unfavorable on C(111), while the [2 + 2] reaction involving the ring is slightly exothermic. In the case of aromatic molecules with an external unsaturated functional group, the reaction can proceed via the external functionality, thereby preserving the aromatic ring and providing further stability. Different reactivity patterns to the C(100) surface are rationalized on the basis of steric effects imposed by the geometrical structure of the Pandey chain. Our study demonstrates the potential of employing the Pandey chain as a template for assembling one-dimensional molecular structures on the diamond surface.

Resonant electron transfer and luminescent enhancement in a toluene suspension of Si nanocrystals

Efficient resonant electron transfer from the surface bonding structure to the conduction band of quantum confined Si nanocrystals is observed by Si nanocrystals in a toluene suspension. Based on the electron transfer mechanism, the enhancement of photoluminescence originates from the band-to-band recombination in the p-type Si nanocrystals suspended in a toluene solution. The energy levels of the electrons in the Si nanocrystals chemisorbed with toluene molecules are calculated using the method of linear combination of atomic orbitals, and the characteristics of the obtained density of states is in good agreement with the observed photoluminescence properties.

Adsorption of 3-pyrroline on Si(100) from first principles

The chemisorption of 3-pyrroline (C(4)H(7)N) on Si(100) is studied from first principles. Three different structures can be realized for which, depending on the temperature, the chemisorption process is facile (for two of them it is essentially barrierless); among these configurations the most favored one, from a thermodynamical point of view, is a dissociated structure obtained through an exothermic reaction characterized by the formation of a N-Si bond and a H-Si bond in which the H atom is detached from the molecule. Several other chemisorption structures are possible which, however, require overcoming a significant energy barrier and often breaking multiple bonds. A number of reaction paths going from one stable structure to another have been investigated. We have also generated, for the two basic adsorption structures, theoretical scanning tunneling microscopy images which could facilitate the interpretation of experimental measurements, and we propose a possible reaction mechanism for nitrogen incorporation.