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Surface-enhanced Raman scattering study on temperature-induced adsorption structure change of acrolein on coldly evaporated silver films
A40 been identified, which for higher coverage exhibits a Iransition to a 2 × 3 structurc. At saturation coverage the tunneling currenl could be stabilized already at vel3' low sample bias voltages in the mV range, which indicates the presence of a lwo-dimcnsionai metallic K layer. The photoemission results do not show a shift of Si surface state emission towards higher binding energy wilh increasing K coverage. Metallic features in the vicinity of the Fermi level could not be identified in the entire coverage range Absence of a visible metallic edge at saturation coverage may be explained by a small photoionization cross section of the K derived states for the used photon energy of 55 eV.
Surface Science 277 (1992) 220-228 North-Holland
Surface-enhanced Raman scattering study on temperature-induced adsorption structure change of acrolein on coldly evaporated silver films Shuji Fujii, Yasuhito Misono and Koichi Itoh Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169, Japan Received 24 April 1992; accepted for publication 24 June 1992 Raman scattering and surface-enhanced Raman scattering (SERS) spectra were measured for acrolein adsorbed on a coldly evaporated silver film under the base pressure of 10 - s Torr in the temperature range of 15-240 K. The SERS spectrum measured at 120 K indicates that the adsorbate exists mainly in a physisorption state. The physisorbed adsorbate desorbs from the silver surface around 150 K. When the substrate temperature was increased further to 180 K, there appeared SERS features which were different from those observed at 120 K. The main adsorbate at 180 K (type A) has the C---Obond attached to the silver surface. On increasing the temperature to 240 K the type A species is converted to another adsorption state (type B), in which aerolein lies flat on the silver surface with both the C---O and C=C bonds coordinated to the silver. When the temperature is reduced to 15 IC the type B species persists as a main adsorbate. During the successive temperature change, the SERS spectra always exhibit a set of bands ascribable to a third adsorption state (type C), which is concluded to be silver(l) acrylate. Thus, under a base pressure of 10 -8 Torr a part of acrolein is oxidized to acrylate. The SERS spectrum was measured also for acetaldehyde adsorbed on the silver film at 180 K. The spectral feature can clearly be ascribed to silver(I) acetate, indicating that an oxidation reaction takes place at the surface. The adsorbate assumes an end-on structure with the symmetry axis of the carboxyl group perpendicular to the surface. When the temperature is increased from 180 to 240 K, the adsorbed acetate ion gives rise to a broad SERS band centered around 1544 cm-1 ascribable to an asymmetric CO 2 stretching vibration. The result indicates that the temperature increase causes tilting of the symmetry axis. This temperature-induced tilting process is reversible because, when the temperature was reduced again to 15 K, the 1544 cm-1 band disappeared. This kind of reversible orientation change was also observed for silver acrylate (type C) adsorbed on the coldly evaporated silver film.
Surface Science 277 (1992) 229-233 North-Holland
Studies on RHEED oscillations at low glancing angles Z. Mitura 1 and A. Daniluk Department of Experimental Physics, Institute of Physics, Marie Curie Sktodowska University,pl. M. Curie-Sktodowskiej 1, 20-031 Lublin, Poland Received 6 April 1992; accepted for publication 9 June 1992 A new approach for interpreting RHEED intensity oscillations is presented. Only low values of the glancing angle of the incident electron beam are considered. The intensity of the specularly reflected beam is calculated by solving the Schr'6dinger equation with a one-dimensional model of a scattering potential of a growing film. For low values of the glancing angle (less than 0.5° for an electron energy of 20 keV) such calculations may be expected to lead to similar results to those obtained assuming a three-dimensional model of the potential. In the present paper numerically determined shapes of the intensity oscillations are shown for different cases of deposition of atoms at surfaces of growing films.
Surface Science 277 (1992) 220-228 North-Holland
Surface-enhanced Raman scattering study on temperature-induced adsorption structure change of acrolein on coldly evaporated silver films Shuji Fujii, Yasuhito Misono and Koichi Itoh Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169, Japan Received 24 April 1992; accepted for publication 24 June 1992 Raman scattering and surface-enhanced Raman scattering (SERS) spectra were measured for acrolein adsorbed on a coldly evaporated silver film under the base pressure of 10 - s Torr in the temperature range of 15-240 K. The SERS spectrum measured at 120 K indicates that the adsorbate exists mainly in a physisorption state. The physisorbed adsorbate desorbs from the silver surface around 150 K. When the substrate temperature was increased further to 180 K, there appeared SERS features which were different from those observed at 120 K. The main adsorbate at 180 K (type A) has the C---Obond attached to the silver surface. On increasing the temperature to 240 K the type A species is converted to another adsorption state (type B), in which aerolein lies flat on the silver surface with both the C---O and C=C bonds coordinated to the silver. When the temperature is reduced to 15 IC the type B species persists as a main adsorbate. During the successive temperature change, the SERS spectra always exhibit a set of bands ascribable to a third adsorption state (type C), which is concluded to be silver(l) acrylate. Thus, under a base pressure of 10 -8 Torr a part of acrolein is oxidized to acrylate. The SERS spectrum was measured also for acetaldehyde adsorbed on the silver film at 180 K. The spectral feature can clearly be ascribed to silver(I) acetate, indicating that an oxidation reaction takes place at the surface. The adsorbate assumes an end-on structure with the symmetry axis of the carboxyl group perpendicular to the surface. When the temperature is increased from 180 to 240 K, the adsorbed acetate ion gives rise to a broad SERS band centered around 1544 cm-1 ascribable to an asymmetric CO 2 stretching vibration. The result indicates that the temperature increase causes tilting of the symmetry axis. This temperature-induced tilting process is reversible because, when the temperature was reduced again to 15 K, the 1544 cm-1 band disappeared. This kind of reversible orientation change was also observed for silver acrylate (type C) adsorbed on the coldly evaporated silver film.
Surface Science 277 (1992) 229-233 North-Holland
Studies on RHEED oscillations at low glancing angles Z. Mitura 1 and A. Daniluk Department of Experimental Physics, Institute of Physics, Marie Curie Sktodowska University,pl. M. Curie-Sktodowskiej 1, 20-031 Lublin, Poland Received 6 April 1992; accepted for publication 9 June 1992 A new approach for interpreting RHEED intensity oscillations is presented. Only low values of the glancing angle of the incident electron beam are considered. The intensity of the specularly reflected beam is calculated by solving the Schr'6dinger equation with a one-dimensional model of a scattering potential of a growing film. For low values of the glancing angle (less than 0.5° for an electron energy of 20 keV) such calculations may be expected to lead to similar results to those obtained assuming a three-dimensional model of the potential. In the present paper numerically determined shapes of the intensity oscillations are shown for different cases of deposition of atoms at surfaces of growing films.