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Adsorption of oxygen on Pt(111)
A441 Surface Science 123 (1982) 1-17 North-Holland Publishing Company ADSORPTION
OF OXYGEN
H. STEININGER
1 ON
*, S. L E H W A L D
Pt(lll) and H. IBACH
lnstitut fi~r GrenzfliJchenforschung und Vakuumphysik, Kernforschungsanlage Jiilich, D - 5170 Ji~lich, Fed Rep. of Germany Received 5 April 1932; accepted for publication 16 September 1982 Oxygen adsorbed on Pt(111) has been studied by means of temperature programmed thermal desorption spectroscopy (TPDS), high resolution electron energy loss spectroscopy (EELS) and LEED. At about 100 K oxygen is found to be adsorbed in a molecular form with the axis of the molecule parallel to the surface as a peroxo-like species, that is, the OO bond order is about 1. At saturation coverage (0too I = 0.44) a ( 3 / 2 X 3/2)R15 ° diffraction pattern is observed. The sticking probability S at 100 K as a function of coverage passes through a m a x i m u m at 0 = 0.11 with S = 0.68. The shape of the coverage dependence is characteristic for adsorption in islands. Two coexisting types of adsorbed oxygen molecules with different OO stretching vibrations are distinguished. At higher coverages units with u-OO = 875 cm J are dominant. With decreasing oxygen coverages the concentration of a type with u-OO = ~/00 c m - i is increased. The dissociation energy of the OO bond in the speices with u-OO = 875 cm i is estimated from the frequency shift of the first overtone to be - 0.5 eV. When the sample is annealed oxygen partially desorbs at - 160 K, partially dissociates and orders into a p ( 2 x 2 ) overlayer. Below saturation coverage of molecular oxygen, dissociation takes place already at92 K. Atomically adsorbed oxygen occupies threefold hollow sites, with a fundamental stretching frequency of 480 c m - 1. In the non-fundamental spectrum of atomic oxygen the overtone of the E-type vibration is observed, which is "dipole forbidden" as a fundamental in EELS.
18 ROOM
Surface Science 123 (1982) 18-28 North-Holland Publishing C o m p a n y TEMPERATURE
SURFACE LOSS
HYDROGENATION
S T U D I E D BY A N G L E - R E S O L V E D
OF THE
Si(001)2 x 1
ELECTRON
ENERGY
SPECTROSCOPY
Shigemitsu
MARUNO,
Hiroshi
IWASAKI,
Keiji HORIOKA,
Sung-Te
LI and
Shogo NAKAMURA
The Institute of Scientific and lndustrial Research, Osaka University, Mihogaoka, lbaraki-shi, Osaka 567, Japan Received 17 June 1982; accepted for publication 16 September 1982 We observed the hydrogen adsorption on the Si(001)2 x 1 surface achieved at room temperature by angle-resolved electron energy loss spectroscopy (AR-ELS) and elastic low-energy electron diffraction. From measurements of the intensities of elastically diffracted beams, we found a characteristic hydrogen covered surface (called Si(001)2 x I H(RT) surface in this paper), where all the diffracted beam intensities were enhanced drastically and a sharp 2 x I LEED pattern was observed. The angular dependence of the elastically diffracted beams on the 2 x 1H(RT) surface was different from that on the monohydride 2 x I:H surface. On the 2 x IH(RT) surface the S 3 transition from the back bond surface state disappeared in contrary to the 2 x I:H surface and two hydrogen induced transitions were observed at 7.0 and 8.0 eV in AR-ELS spectra. We revealed that the 2 x IH(RT) surface consisted of the monohydride and the dihydride phases with comparable weights. Additionally, we found the new transition S'I ascribed to the newly produced dangling bond surface state due to the rupture of the dimerization bond with hydrogen adsorption.
OF OXYGEN
H. STEININGER
1 ON
*, S. L E H W A L D
Pt(lll) and H. IBACH
lnstitut fi~r GrenzfliJchenforschung und Vakuumphysik, Kernforschungsanlage Jiilich, D - 5170 Ji~lich, Fed Rep. of Germany Received 5 April 1932; accepted for publication 16 September 1982 Oxygen adsorbed on Pt(111) has been studied by means of temperature programmed thermal desorption spectroscopy (TPDS), high resolution electron energy loss spectroscopy (EELS) and LEED. At about 100 K oxygen is found to be adsorbed in a molecular form with the axis of the molecule parallel to the surface as a peroxo-like species, that is, the OO bond order is about 1. At saturation coverage (0too I = 0.44) a ( 3 / 2 X 3/2)R15 ° diffraction pattern is observed. The sticking probability S at 100 K as a function of coverage passes through a m a x i m u m at 0 = 0.11 with S = 0.68. The shape of the coverage dependence is characteristic for adsorption in islands. Two coexisting types of adsorbed oxygen molecules with different OO stretching vibrations are distinguished. At higher coverages units with u-OO = 875 cm J are dominant. With decreasing oxygen coverages the concentration of a type with u-OO = ~/00 c m - i is increased. The dissociation energy of the OO bond in the speices with u-OO = 875 cm i is estimated from the frequency shift of the first overtone to be - 0.5 eV. When the sample is annealed oxygen partially desorbs at - 160 K, partially dissociates and orders into a p ( 2 x 2 ) overlayer. Below saturation coverage of molecular oxygen, dissociation takes place already at92 K. Atomically adsorbed oxygen occupies threefold hollow sites, with a fundamental stretching frequency of 480 c m - 1. In the non-fundamental spectrum of atomic oxygen the overtone of the E-type vibration is observed, which is "dipole forbidden" as a fundamental in EELS.
18 ROOM
Surface Science 123 (1982) 18-28 North-Holland Publishing C o m p a n y TEMPERATURE
SURFACE LOSS
HYDROGENATION
S T U D I E D BY A N G L E - R E S O L V E D
OF THE
Si(001)2 x 1
ELECTRON
ENERGY
SPECTROSCOPY
Shigemitsu
MARUNO,
Hiroshi
IWASAKI,
Keiji HORIOKA,
Sung-Te
LI and
Shogo NAKAMURA
The Institute of Scientific and lndustrial Research, Osaka University, Mihogaoka, lbaraki-shi, Osaka 567, Japan Received 17 June 1982; accepted for publication 16 September 1982 We observed the hydrogen adsorption on the Si(001)2 x 1 surface achieved at room temperature by angle-resolved electron energy loss spectroscopy (AR-ELS) and elastic low-energy electron diffraction. From measurements of the intensities of elastically diffracted beams, we found a characteristic hydrogen covered surface (called Si(001)2 x I H(RT) surface in this paper), where all the diffracted beam intensities were enhanced drastically and a sharp 2 x I LEED pattern was observed. The angular dependence of the elastically diffracted beams on the 2 x 1H(RT) surface was different from that on the monohydride 2 x I:H surface. On the 2 x IH(RT) surface the S 3 transition from the back bond surface state disappeared in contrary to the 2 x I:H surface and two hydrogen induced transitions were observed at 7.0 and 8.0 eV in AR-ELS spectra. We revealed that the 2 x IH(RT) surface consisted of the monohydride and the dihydride phases with comparable weights. Additionally, we found the new transition S'I ascribed to the newly produced dangling bond surface state due to the rupture of the dimerization bond with hydrogen adsorption.