Zhong Hai Wang

Covalent attachment of acetonitrile on Si(100) through Si–C and Si–N linkages

The covalent binding and adsorption states of acetonitrile on Si(100) have been investigated using temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and density function theory (DFT) calculation. XPS and HREELS results show that acetonitrile chemisorbs on Si(100) in a side-on di-σ binding configuration, forming Si–C and Si–N σ bonds. TPD measurements reveal the presence of two desorption states, β1 and β2 with desorption energies of 29.8 and 24.6 kcal mol−1, respectively. Based on DFT calculations, the β1 state is possibly assigned to di-σ bonded acetonitrile on top of a dimer and/or in an in-row bridging chemisorption, while the β2 state is related to acetonitrile bonded in a cross-row bridging configuration.

Dissociative adsorption of pyrrole on Si(111)-(7×7)

Pyrrole adsorption on Si(111)-(7×7) has been investigated using high-resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy, scanning tunneling microscopy (STM), 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)-(7×7) 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 a...

Cycloaddition chemistry of thiophene on the silicon (111)-7×7 surface

The mechanism of the cycloaddition reaction between thiophene and Si(111)-7×7 has been investigated using thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS), electronic electron energy loss spectroscopy (EELS), scanning tunneling microscopy (STM), and PM3 semiempirical calculations. The results show that thiophene binds on Si(111)-7×7 through a [4+2] cycloaddition reaction between the 2, 5 C-atoms of thiophene and the adjacent adatom-rest atom pairs on Si(111)-7×7. Semiempirical PM3 calculations based on the cluster model further confirm this di-σ bonding configuration. A stepwise surface diradical mechanism has been proposed to account for the regioselective [4+2] cycloaddition reaction.