Soft X-ray Appearance Potential Spectroscopy SXAPS

In SXAPS the X-ray photons emitted by the sample are detected, normally by letting them strike a photosensitive surface from which photoelectrons are collected, but also - with the advent of X-ray detectors of increased sensitivity - by direct detection. Above the X-ray emission threshold from a particular core level the excitation probability is a function of the densities of unoccupied electronic states. Because two electrons are involved, incident and the excited, the shape of the spectral structure is proportional to the self convolution of the unoccupied state densities. 

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Soft X-ray appearance potential spectroscopy (SXAPS) studies of radiant coil alloys were carried out to determine surface compositions resulting from exposure to a range of environments. 

SXAPS Soft X-ray Appearance Potential Spectroscopy Another name for APXPS. 

Figure 1 A schematic diagram showing energy levels involved in techniques used to probe unoccupied density of states of a metai. XAS, X-ray absorption spectroscopy BIS, Bremsstrahlung isochromat spectroscopy I PE, inverse photoemission DAPS, disappearance potentiai spectroscopy SXAPS, soft X-ray appearance potentiai spectroscopy and AEAPS, Auger electron appearance potential spectroscopy.

There are three main detection modes for EAPFS within the appearance potential spectroscopy (APS) technique./31/ First, one may monitor soft-x-ray emission due to the decay of the core hole left by the primary process. This is called SXAPS-EAPFS (Figure le). Second, it is also possible to monitor Auger electrons due to the same core-hole decay, as in AEAPS-EAPFS and AMEFS-EAPFS, cf. Figure If. Third, one may measure the remaining total intensity of... 

Appearance potential spectroscopy involves detection of electronic transitions not of the backscattered electrons as in ELS, but of secondary processes. The latter include increase in soft X-ray (SXAPS) or Auger electron (AEAPS) emission or decrease in elastically scattered primary electrons (DAPS) (382). SXAPS is not as sensitive as AES for surface chemical analysis. However, SXAPS and IS spectra are easier to analyze than AES, since only one core transition is involved. This makes SXAPS and IS quite convenient for detecting heavy elements on catalyst surfaces. 

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