Masashi Nagao

Site-specific fragmentation caused by core-level photoionization: Effect of chemisorption

We used the energy-selected-photoelectron photoion coincidence (ESPEPICO) method to study site-specific fragmentation caused by C:1s photoionization of 1,1,1-trifluoro-2-propanol-d1 [CF3CD(OH)CH3, TFIP-d1] on a Si(100) surface. High-resolution electron energy loss spectroscopy showed that TFIP-d1 is dissociatively chemisorbed like (CF3)(CH3)CDO–Si(100), and different chemical shifts at the three carbon sites were observed by photoelectron spectroscopy. The site-specific fragmentation evident in the ESPEPICO spectra of the sub-monolayer at room temperature indicates that the TFIP-d1 there has an O–Si bond oriented in the trans position with respect to the C–CF3 bond. Here we discuss the fragmentation processes in light of the results obtained with the ESPEPICO method and the Auger-electron photoion coincidence method.

High resolution Si 2p photoelectron spectroscopy of unsaturated hydrocarbon molecules adsorbed on Si(100)c(4×2): the interface bonding and charge transfer between the molecule and the Si substrate

Abstract In order to elucidate the nature of the interface bonding between different molecules and a silicon surface, high resolution Si 2p photoelectron spectroscopy measurements were performed. After adsorption of unsaturated hydrocarbon molecules (ethylene, cyclopentene, and 1,4-cyclohexadiene), the peaks corresponding to the up and down atoms of surface asymmetric dimers vanished, while new peaks appeared between 215 and 398 meV relative to the bulk Si peak. These peaks are assigned to the di-σ Si–C bonds at the interface between the molecules and the surface. We can also estimate the amounts of reacted asymmetric dimers and the charge transfers from the peak intensities and the relative binding energies, respectively.

Direct Evidence for Asymmetric Dimer on Si(100) at Low Temperature by Means of High-Resolution Si 2p Photoelectron Spectroscopy.

We have investigated the electronic states of the Si(100) surface at low temperature by means of high-resolution Si 2p photoelectron spectroscopy. The peak intensities of up and down atoms of the asymmetric dimer in Si 2p spectra do not change from 140 K to 55 K, showing that the number of asymmetric dimers is preserved. Therefore, we can conclude that the ground state of the dimer is asymmetric and the symmetric dimer images observed by scanning tunneling microscopy at this temperature range are due to extrinsic or dynamical intrinsic effects on the buckled dimer.

Reaction mechanism and adsorbed states of cyclohexene on Si(100)(2×1)

Abstract We have studied the adsorption states of cyclohexene on Si(100)(2×1) by means of photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). PES results indicate the interaction between π bond of cyclohexene and the dangling bond of the dimer. Two adsorbed state are observed in STM images; one shows a symmetric protrusion, and another one is asymmetric and consists of some small protrusions. The former is assigned to the boat conformation of adsorbed cyclohexene, and the latter is assigned to the twist-boat conformation.

Electronic states and chemical reactivity of Si(1 0 0)c(4 × 2) surface at low temperature studied by high resolution Si 2p core level photoelectron spectroscopy

We have investigated the electronic states of clean and BF 3 adsorbed Si(100) surfaces at low temperature by means of high resolution Si 2p photoelectron spectroscopy. The peak intensities of upper atom and lower atom of the asymmetric dimer in Si 2p spectra do not change even at 30 K compared with those at higher temperature up to 300 K, indicating that the dimer is asymmetric in the ground state. In order to investigate chemical reactivity of asymmetric dimer on Si(100), a typical Lewis acid molecule BF 3 is adsorbed on Si(100). We have found that BF 3 molecules are dissociated into BF 2 and F on Si(100) and dissociated species (BF 2 and F) are adsorbed predominantly on the up dimer atoms of the asymmetric dimers.