K. Tanaka, E. O. Sako,
E. Ikenaga, K. Isari, S. A. Sardar, S. Wada, T. Sekitani, K. Mase, N. Ueno
[J. Electron Spectrosc. Relat. Phenom., 119, 255-266 (2001)]
Recent progress in synchrotron radiation techniques in a soft X-ray region has developed a new field in chemistry. Using tunable synchrotron radiation in a soft X-ray region, site selective core excitation can be achieved. The site-specificity of the consequent chemical reactions is one of the attractive issues and has been studied for various kinds of molecules. During these studies, a remarkable site-specific reaction has been found in the case of photon stimulated ion desorption (PSID) of polymethylmethacrylate (PMMA) thin films. The PSID of PMMA has been examined in order to elucidate the reaction mechanism using total electron yield, total and partial ion yield, Auger electron, and Auger electron-photoion coincidence spectroscopies. In this paper we discuss the possibility of controlling chemical bond scission by using the site-specific photochemical surface reactions mainly based on the recent experimental results.
E. Ikenaga, K. Kudara, K. Kusaba, K. Isari, S.
A. Sardar, S. Wada, K. Mase, T. Sekitani, K. Tanaka
[J. Electron Spectrosc. Relat. Phenom., 114-116, 585-590 (2001)]
Auger electron-photoion coincidence (AEPICO) measurements have been performed for poly-methylmethacrylate (PMMA) thin films induced by oxygen core excitation. The dominant productions of
CHn+(n=1-3) ions were observed at resonant excitation to O-CH3 anti-bonding state, and OCH+ ion was observed at resonant excitation to C-OCH3 anti-bonding state. Their AEPICO yields were strongly dependent on Auger
electron kinetic energy and shows enhancement around 505 eV Auger electron
energy for each ion. This seems to be related to the spectator resonant
Auger-stimulated ion desorption. The correlation between ion desorption
and Auger final state for PMMA thin films in the oxygen K-edge region is
discussed.
Shin-ichi Nagaoka, Shin-ichiro Tanaka, Kazuhiko Mase
[J. Phys. Chem. B, 105, 1554-1561 (2001)]
We used photoelectron spectroscopy, the energy-selected-photoelectron photoion coincidence (ESPEPICO) method, the Auger electron photoion coincidence (AEPICO) method, and the ab initio method to study sitespecific phenomena in the C:1s photoionization of 1,1,1-trifluoroethane (CF3CH3, TFEt) condensed on a Au surface. Site-specific excitation and occurrence of different chemical shifts at two carbon sites were evident in the total electron-yield spectrum and the photoelectron spectrum, and site-specific fragmentation was evident in the ESPEPICO spectrum. The fragmentation processes inferred from the ESPEPICO and AEPICO results were very different from those occurring in the vapor phase. We also studied the effect of the surface on the site-specific phenomena observed in a 2,2,2-trifluoroethanol (TFEtOH) monolayer chemisorbed on a Si(100) surface (CF3CH2OSi {substrate} ). The molecular structure of TFEtOH is the same as that of TFEt except that it has a hydroxyl group substituted for one of the hydrogen atoms. Although site-specific phenomena were also observed in TFEtOH, the fragmentation process was very different from that of TFEt because of the chemisorption structure of TFEtOH on Si(100).
E. Ikenaga, K. Isari, K. Kudara, Y. Yasui, S. A. Sardar, S. Wada, T. Sekitani, K. Tanaka, K.
Mase, S. Tanaka
[ J. Chem. Phys., 114, 2751-2759 (2001)]
We have developed a new electron-ion coincidence apparatus combined with synchrotron radiation in order to examine the various ion desorption mechanisms related to the Auger process induced by core excitation. Photon stimulated ion desorption (PSID) of a poly-methylmethacrylate (PMMA) thin film has been investigated by this apparatus. The PSID of PMMA induced by carbon core excitation has been examined using Auger electron yield, total ion yield, resonant Auger electron, and Auger electron-photoion coincidence (AEPICO) spectra. The spectrum of the total ion yield divided by the Auger electron yield shows that the desorption efficiency is largely increased at the resonant excitation of carbon 1s electron in the O-CH3 side chain to ƒÐ*(O-CH3) orbital. In AEPICO measurement, H+ and CH‚Ž+ (n=1- 3) ions are observed at various resonant excitations. The AEPICO signal intensity depends on the Auger electron energy. Particularly, the CH3+ ion desorption in coincidence with Auger electron at 270 eV shows strong enhancement with ƒÐ*(O-CH3) resonant excitation. The results of the resonant Auger spectra and AEPICO yield spectra demonstrate the relation of the ion desorption mechanism to the bonding/antibonding character and localized character of the excited ƒÐ*(O-CH3) orbital and the Auger final state.