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Determination of attenuation lengths of photoelectrons in aluminium and aluminium oxide by angle‐dependent x‐ray photoelectron spectroscopy
Author(s) -
Marcus P.,
Hinnen C.,
Olefjord I.
Publication year - 1993
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740201108
Subject(s) - x ray photoelectron spectroscopy , photoelectric effect , aluminium , oxide , attenuation , analytical chemistry (journal) , attenuation length , materials science , aluminium oxide , range (aeronautics) , chemistry , atomic physics , optics , nuclear magnetic resonance , physics , optoelectronics , chromatography , metallurgy , composite material
Angle‐dependent x‐ray photoelectron spectroscopy (AD‐XPS) measurements have been carried out on thin aluminium oxide layers formed on pure aluminium by oxidation in oxygen at 25°C and at 250°C. The amounts of oxygen of the oxide overlayers were measured by nuclear reaction analysis (NRA). The equipment thicknesses of the oxide layers were 14 Å and 21.5 Å for the oxides formed at 25°C and at 250°C, respectively. The AD‐XPS measurements were carried out in the range of take‐off angles 12–122°. The signals emitted by Al 3+ in the oxide and by Al m in the metal versus take‐off angle can be, within experimental error, fittex by an exponential function in the range of take‐off angles ∼30–120°. This confirms the applicability of an exponential law for the attenuation of photoelectrons for the studied system in the range of take‐off angles ∼30–120°. The AD‐XPS measurements were used to determine the attenuation lengths of the electrons emitted by aluminium (kinetic energy ∼1180 eV) in the oxide (λ ox ) and in the metal (λ m ). The attenuation lengths derived from the experiments are: λ ox = 20 Å and λ m = 18 Å. These values are lower than the theoretical inelastic mean free paths owing to the contribution of elastic scattering. For the lowest investigated take‐off angles (<30°) the measurements deviate from the exponential law. The deviation is attributed to the effects of elastic scattering and of the angle of acceptance of the photoelectrons. As a complement to this work, an intercomparison of AD‐XPS measurements was performed in four laboratories on the two reference samples. In the range of take‐off angles 40–120°, the results can be fitted by the exponential law for the attenuation of the photoelectrons. However, differences of 10–20% were observed in the apparent overlayer thickness. Careful analysis of the data revealed that this was primarily caused by a systematic error introduced in the peak fitting when a symmetrical peak is used, instead of an asymmetrical peak, for the Al m signal.