Ryohei Sumii

Selective chemical bond breaking characteristically induced by resonant core excitation of ester compounds on a surface

Inner-shell excitation possesses an attractive potential to induce selective chemical bond breaking due to its special localization and atomic selectivity. This paper reviews our recent works about site-selective (or site-specific) photon stimulated desorption (PSD) of core-excited ester compounds, poly(methyl methacrylate) (PMMA) thin films, condensed methyl isobutyrate (MIB) multilayers, methyl ester terminated self-assembled monolayers (SAMs), partially deuterided SAMs and ethyl ester terminated SAMs. Exact selective bond breaking was observed for all molecular systems except for MIB multilayers: COO–R (R = CH3, C2H5) breaking in the , O 1s(OR) excitations and CO–OR in the excitation. Such resonant excitations take place within the functional group locally and the initial memory of the excited site and its localization character is effectively conserved during the PSD process even after subsequent Auger decays and ionic dissociation/desorption. Variation of selectivity observed here indicates the importance of the molecular environment and the contribution of the indirect dissociation process due to statistical energy relaxation and x-ray-induced electron stimulated desorption. The obvious polarization dependence measured only for selectively desorbing ions also supports the above characteristics. Neutral fragments desorbing from core-excited PMMA follow the profile of the total electron yield spectrum but not the partial ion yield of corresponding ions. This result indicates that ionic dissociation locally promoted by Coulomb repulsion plays an important role to reveal site-selectivity in chemical reactions induced by core-level excitation.

Active control of site specificity in ion desorption by core excitation

Abstract Active control of site-specific photon stimulated ion desorption (PSID) following core excitation was examined by changing the molecular environment and the direction of the electric field vector of the incidence light in the three different molecular systems, poly-methylmethacrylate (PMMA) thin film, methyl ester terminated self-assembled monolayer (MHDA-SAM), and condensed methyl isobutyrate (MIB) molecule. In PMMA and MHDA-SAM, the site-selective resonant excitation causes site-specific PSID, and the site specificity of MHDA-SAM is more enhanced than that of PMMA, while there is no specific desorption in MIB. These variations were explained with the change of molecular environment. Moreover, PSID of CH n + ( n =1–3) ions observed at the σ * (O–CH 3 )←C1s(OCH 3 ) excitation of MHDA-SAM exhibits significant dependence on the incidence angle of the light.

The Electronic Structure and the Energy Level Alignment at the Interface Between Organic Molecules and Metals

We investigated the electronic structure and the energy level alignment at the interfaces between perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and metals (Au, Cu and Co) by ultraviolet photoelectron spectroscopy (UPS). In the case of PTCDA/Au interface, the apparent interface states and charge transfer (CT) states were not observed in its UPS spectra. In the case of PTCDA/Cu and Co interfaces, however, we found that the CT from metal to PTCDA occurred, and that the apparent CT states were observed at PTCDA/Cu interface.