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External infrared reflection absorption spectroscopy of methanol on an epitaxially grown Si(100) 2 × 1 surface
A237 measured under random incidence conditions is approximately constant for electron energies E extending from the Auger transition energy E A at 1620 eV down to 1500 eV. It falls off approximately as 1 / ~ A - E for lower electron energies. This result is qualitatively in agreement with theoretical models. However, the transport elastic mean free path that follows from the analysis of the spectra is much lower than theoretically expected.
Surface ScJo~-e 248 (1991) 183-192 North-Holland
183
Analyses of the adsorption of oxygen and hydrogen on PtxNil_ x alloys using ion scattering spectroscopy P. Novacek and P. Varga lnstitut fi~r Allgemeine Physik, TU Wien, Wiedner Haupstrasse 8-10, A-1040 Wien, Austria Received 4 July 1990; accepted for publication 29 October 1990 The ISS-signals of Pt and Ni were used to detect the surface composition of three polycrystalline PtxNi I _~, alloys after adsorbing various amounts of oxygen and hydrogen. Oxygen was adsorbed in the range from 0-20 langmuir at room temperature on PtgNi91, Pta4Ni ~ , PtssNil2, pure NI and pure Pt. Below 2 L the adsorption process was found to be quite the same on the pure metals as well as on the respective metals in the alloys. At exposures above 2 L there are distinct differences between the reaction of the alloys and the pure metals. They are interpreted as an enrichment of Ni atoms in the topmost layer due to oxygen induced segregation. The adsorption of hydrogen at T = 80 K does not show any significant differences in the adsorption process between the pure metals and the alloys, which implies that there is no hydrogen induced segregation.
Surface Science 248 (1991) 193-200 North-Holland
193
External infrared reflection absorption spectroscopy of methanol on an epitaxially grown Si(100)2 x 1 surface W. Ehrley Institut far Grenzfliichenforschung und Vakuum physik, Forschungszentrum Ji~lich GmbH, PO Box 1913, 5170 Jiilich, Germany
R. Butz and S. Mantl lnstitut fro" Schicht- und lonentechnik, Forschungszentrum Jiiflch GmbH, PO Box 1913, 5170 Ji~lich, Germany Received 24 September 1990; accepted for publication 3 December 1990 Infrared spectra of thin layers of hydrocarbons adsorbed on a Si single-crystal surface (monolayer or less) using a single reflection are difficult to obtain as this material is highly transparent in the infrared region, resulting in a relatively poor signal-to-noise ratio of the spectra. To overcome this problem, in a first step a highly reflecting CoSi 2 layer was imbedded into a Si single crystal using ion bombardment and subsequent annealing. In a second step, a well-ordered and impurity-free Si layer of 600 ~k thickness was grown onto the surface, using molecular beam epitaxy. This peculiarly prepared sample was then used to study the adsorption of methanol at 100 K and its subsequent decomposition upon heating. At 100 K, the initial adsorption in the first layer at low methanol exposure and the following multilayer formation after high methanol exposure could be clearly distinguished by the observation of specific bands. The condensed phase is completely desorbed after heating the sample to 150 K, leaving a spectrum which is identical to the spectrum obtained at 100 K for low methanol exposures and which is attributed to a surface methoxy species adsorbed on Si(100). No decomposition of this surface intermediate is observed below 500 K, indicating a relatively high stability of the methoxy species.
Surface ScJo~-e 248 (1991) 183-192 North-Holland
183
Analyses of the adsorption of oxygen and hydrogen on PtxNil_ x alloys using ion scattering spectroscopy P. Novacek and P. Varga lnstitut fi~r Allgemeine Physik, TU Wien, Wiedner Haupstrasse 8-10, A-1040 Wien, Austria Received 4 July 1990; accepted for publication 29 October 1990 The ISS-signals of Pt and Ni were used to detect the surface composition of three polycrystalline PtxNi I _~, alloys after adsorbing various amounts of oxygen and hydrogen. Oxygen was adsorbed in the range from 0-20 langmuir at room temperature on PtgNi91, Pta4Ni ~ , PtssNil2, pure NI and pure Pt. Below 2 L the adsorption process was found to be quite the same on the pure metals as well as on the respective metals in the alloys. At exposures above 2 L there are distinct differences between the reaction of the alloys and the pure metals. They are interpreted as an enrichment of Ni atoms in the topmost layer due to oxygen induced segregation. The adsorption of hydrogen at T = 80 K does not show any significant differences in the adsorption process between the pure metals and the alloys, which implies that there is no hydrogen induced segregation.
Surface Science 248 (1991) 193-200 North-Holland
193
External infrared reflection absorption spectroscopy of methanol on an epitaxially grown Si(100)2 x 1 surface W. Ehrley Institut far Grenzfliichenforschung und Vakuum physik, Forschungszentrum Ji~lich GmbH, PO Box 1913, 5170 Jiilich, Germany
R. Butz and S. Mantl lnstitut fro" Schicht- und lonentechnik, Forschungszentrum Jiiflch GmbH, PO Box 1913, 5170 Ji~lich, Germany Received 24 September 1990; accepted for publication 3 December 1990 Infrared spectra of thin layers of hydrocarbons adsorbed on a Si single-crystal surface (monolayer or less) using a single reflection are difficult to obtain as this material is highly transparent in the infrared region, resulting in a relatively poor signal-to-noise ratio of the spectra. To overcome this problem, in a first step a highly reflecting CoSi 2 layer was imbedded into a Si single crystal using ion bombardment and subsequent annealing. In a second step, a well-ordered and impurity-free Si layer of 600 ~k thickness was grown onto the surface, using molecular beam epitaxy. This peculiarly prepared sample was then used to study the adsorption of methanol at 100 K and its subsequent decomposition upon heating. At 100 K, the initial adsorption in the first layer at low methanol exposure and the following multilayer formation after high methanol exposure could be clearly distinguished by the observation of specific bands. The condensed phase is completely desorbed after heating the sample to 150 K, leaving a spectrum which is identical to the spectrum obtained at 100 K for low methanol exposures and which is attributed to a surface methoxy species adsorbed on Si(100). No decomposition of this surface intermediate is observed below 500 K, indicating a relatively high stability of the methoxy species.