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Practical algorithm for background subtraction
A330 Surface Science 216 (1989) 343-360 North-Holland, Amsterdam
PRACTICAL
ALGORITHM
343
FOR BACKGROUND
SUBTRACTION
S. TOUGAARD Fysisk Institut,
Odense Universitet,
DK 5230 Odense M, Denmark
Received 9 November 1988; accepted for publication 7 February 1989 This is an investigation of the validity of the previously proposed algorithm F(E)
- j(E)-B,Jm
E’-E E
[C+(E,_E)2]2j(E’)dE’7
for use in background correction of electron spectra. Here j(E) is the measured flux of emitted electrons, F(E) the primary spectrum at the point of excitation in the solid, C = 1643 eV2, while B, is a fitting parameter. For homogeneous solids, the algorithm is shown to be valid for the analysis of entire experimental spectra extending over an energy range of more than 1000 eV. Moreover, through examination of model spectra, the algorithm is found to be a reasonable approximation for the analysis of spectra from most classes of in-depth concentration profiles. For certain profiles, the validity is restricted to energies below - 40 eV from the peak energy.
361
Surface Science 216 (1989) 361-385 North-Holland, Amsterdam
HYDROGEN CHLORIDE ADSORPTION AND COADSORPTION WITH HYDROGEN OR WATER ON PLATINUM (111) Frederick T. WAGNER Physical Chemistry Department, Warren, MI 48090-9055, USA
and Thomas E. MOYLAN General Motors Research Laboratories,
Received 18 August 1988; accepted for publication
10 February 1989
Aqueous chloride ions accelerate the corrosion of all metals, and chloride chemistry is essential to the preparation of noble metal catalysts. To improve the understanding of the interactions of chloride species with metals, the adsorption of anhydrous HCl on Pt(ll1) at 90 K and its coadsorption with hydrogen and water were studied by high resolution electron energy loss spectroscopy (HREELS), temperature programmed desorption (TPD), low energy electron diifraction (LEED), and Auger electron spectroscopy (AES). Low coverages of HCl fully dissociate to form a disordered mixture of adsorbed H and adsorbed Cl. Higher exposures produce first a well-ordered 3 x 3 phase and then an increasingly disordered form which saturates just above the density of one layer of close-packed Cl; no multilayer of HCl ice can be grown. Coadsorption of HCl and water produces adsorbed HsO+. The thermal desorption of water indicates two types of water stabilization by HCl, but there is no evidence for water molecules bound directly to adsorbed Cl. The chemistry of HCl+H,O coadsorption, which is dominated by strong Pt-Cl interactions, is contrasted with that of the previously-studied HF+ H,O system, which is dominated by hydrogen bonding effects.
PRACTICAL
ALGORITHM
343
FOR BACKGROUND
SUBTRACTION
S. TOUGAARD Fysisk Institut,
Odense Universitet,
DK 5230 Odense M, Denmark
Received 9 November 1988; accepted for publication 7 February 1989 This is an investigation of the validity of the previously proposed algorithm F(E)
- j(E)-B,Jm
E’-E E
[C+(E,_E)2]2j(E’)dE’7
for use in background correction of electron spectra. Here j(E) is the measured flux of emitted electrons, F(E) the primary spectrum at the point of excitation in the solid, C = 1643 eV2, while B, is a fitting parameter. For homogeneous solids, the algorithm is shown to be valid for the analysis of entire experimental spectra extending over an energy range of more than 1000 eV. Moreover, through examination of model spectra, the algorithm is found to be a reasonable approximation for the analysis of spectra from most classes of in-depth concentration profiles. For certain profiles, the validity is restricted to energies below - 40 eV from the peak energy.
361
Surface Science 216 (1989) 361-385 North-Holland, Amsterdam
HYDROGEN CHLORIDE ADSORPTION AND COADSORPTION WITH HYDROGEN OR WATER ON PLATINUM (111) Frederick T. WAGNER Physical Chemistry Department, Warren, MI 48090-9055, USA
and Thomas E. MOYLAN General Motors Research Laboratories,
Received 18 August 1988; accepted for publication
10 February 1989
Aqueous chloride ions accelerate the corrosion of all metals, and chloride chemistry is essential to the preparation of noble metal catalysts. To improve the understanding of the interactions of chloride species with metals, the adsorption of anhydrous HCl on Pt(ll1) at 90 K and its coadsorption with hydrogen and water were studied by high resolution electron energy loss spectroscopy (HREELS), temperature programmed desorption (TPD), low energy electron diifraction (LEED), and Auger electron spectroscopy (AES). Low coverages of HCl fully dissociate to form a disordered mixture of adsorbed H and adsorbed Cl. Higher exposures produce first a well-ordered 3 x 3 phase and then an increasingly disordered form which saturates just above the density of one layer of close-packed Cl; no multilayer of HCl ice can be grown. Coadsorption of HCl and water produces adsorbed HsO+. The thermal desorption of water indicates two types of water stabilization by HCl, but there is no evidence for water molecules bound directly to adsorbed Cl. The chemistry of HCl+H,O coadsorption, which is dominated by strong Pt-Cl interactions, is contrasted with that of the previously-studied HF+ H,O system, which is dominated by hydrogen bonding effects.