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Adsorption of hydrogen on Ni(110) at 90 K studied by EELS
A61 Surface Science 137 (1984) 595-606 North-Holland, Amsterdam
595
THERMAL DESORPTION FROM HETEROGENEOUS NORMALIZED CURVE TREATMENT
SURFACES;
Pio FORZATTI,
and
Massimo
BORGHESI,
Italo PASQUON
Enrico TRONCONI Dipartimento di Chimica lndustriale ed Ingegneria Chimica del Politecnico, Piazza Leonardo da Vinci 32, 1-20132 Milano, Italy Received 24 May 1983; accepted for publication 28 October 1983 A new method for analyzing thermal desorption traces from heterogeneous surfaces is presented, based on the use of a single normalized desorption curve. The method provides the coverage dependence of the desorption activation energy and of the frequency factor A. It can also iterate to the correct kinetic order of the desorption reaction. Application of the procedure is demonstrated for a number of different normalized desorption energy profiles in the case of constant A, and by the analysis of published experimental data for a coverage dependent A~
Surface Science 137 (1984) 607-617 North-Holland, Amsterdam ADSORPTION
OF HYDROGEN
607 ON Ni(ll0)
AT 90 K STUDIED
BY EELS
L. O L L I ~ a n d A . M . B A R O Departamento de Flsica Fundamental and Instituto de Fisica del Estado S6lido del CS1C, Universidad Aut6noma de Madrid, Cantoblanco, Madrid-34, Spain Received 4 July 1983; accepted for publication 3 November 1983 H 2 adsorption on Ni(ll0) is a complex system showing many interesting phenomena. In this work we present an electron energy loss spectroscopy (EELS) study of hydrogen (and deuterium) adsorption at 90 K on Ni(110). At low temperatures hydrogen adsorption is characterized by two different vibrational spectra. For hydrogen exposures below ~ 0.9 L two bands at 650 and 1060 cm -a appear. For exposures larger than ~ 0.9 L the bands shift to 610 and 940 cm -1. We associate the EEL spectrum at low coverages to the ordered structures on the unreconstructed surface. The high exposure spectrum would then correspond to the 1 × 2 reconstructed surface. Analysis of frequency and intensity of the observed bands leads us to suggest a definite adsorption site model for hydrogen on this surface. For both coverage regimes two adsorption sites are occupied. For the unreconstructed surface these are a low-symmetry short-bridge site (Cs) forming the zig-zag structure and a (Czv) short-bridge site. After reconstruction, the C s short-bridge site remains unchanged and a new site is provided by the second surface layer.
595
THERMAL DESORPTION FROM HETEROGENEOUS NORMALIZED CURVE TREATMENT
SURFACES;
Pio FORZATTI,
and
Massimo
BORGHESI,
Italo PASQUON
Enrico TRONCONI Dipartimento di Chimica lndustriale ed Ingegneria Chimica del Politecnico, Piazza Leonardo da Vinci 32, 1-20132 Milano, Italy Received 24 May 1983; accepted for publication 28 October 1983 A new method for analyzing thermal desorption traces from heterogeneous surfaces is presented, based on the use of a single normalized desorption curve. The method provides the coverage dependence of the desorption activation energy and of the frequency factor A. It can also iterate to the correct kinetic order of the desorption reaction. Application of the procedure is demonstrated for a number of different normalized desorption energy profiles in the case of constant A, and by the analysis of published experimental data for a coverage dependent A~
Surface Science 137 (1984) 607-617 North-Holland, Amsterdam ADSORPTION
OF HYDROGEN
607 ON Ni(ll0)
AT 90 K STUDIED
BY EELS
L. O L L I ~ a n d A . M . B A R O Departamento de Flsica Fundamental and Instituto de Fisica del Estado S6lido del CS1C, Universidad Aut6noma de Madrid, Cantoblanco, Madrid-34, Spain Received 4 July 1983; accepted for publication 3 November 1983 H 2 adsorption on Ni(ll0) is a complex system showing many interesting phenomena. In this work we present an electron energy loss spectroscopy (EELS) study of hydrogen (and deuterium) adsorption at 90 K on Ni(110). At low temperatures hydrogen adsorption is characterized by two different vibrational spectra. For hydrogen exposures below ~ 0.9 L two bands at 650 and 1060 cm -a appear. For exposures larger than ~ 0.9 L the bands shift to 610 and 940 cm -1. We associate the EEL spectrum at low coverages to the ordered structures on the unreconstructed surface. The high exposure spectrum would then correspond to the 1 × 2 reconstructed surface. Analysis of frequency and intensity of the observed bands leads us to suggest a definite adsorption site model for hydrogen on this surface. For both coverage regimes two adsorption sites are occupied. For the unreconstructed surface these are a low-symmetry short-bridge site (Cs) forming the zig-zag structure and a (Czv) short-bridge site. After reconstruction, the C s short-bridge site remains unchanged and a new site is provided by the second surface layer.