AEAPS

AEAPS, SXAPS Auger electron APS, Soft x-ray APS Same as APS Same as APS... 

AEAPS Auger electron appearance potential spectroscopy... 

Auger Electron Appearance Potential Spectroscopy (AEAPS)... 

Crossing an ionization threshold means that electrons are lost from the primary beam as a result of ionization of a core hole. Thus if the reflected current of electrons at the primary energy, more usually termed the elastically reflected current, is monitored as a function of energy, a sharp decrease should be observed as a threshold is crossed. This is the principle of operation of DAPS. It is, in a sense, the inverse of AEAPS, and, indeed, if spectra from the two techniques from the same surface are compared, they can be seen to be mirror images. Background problems occur in DAPS also. 

The principal advantages of AEAPS and DAPS over SXAPS is that they can be operated at much lower primary electron currents, thus causing less disturbance to any adsorbed species. 

AEap is the energy is the energy required to allow an electron transfer from an orbital a of molecule A towards a virtual 3 orbital on molecule B. It can be expressed as ... 

Figure 16. Conceptual model for biological redox cycling in a hot spring environment. Influx of external aqueous Fe(II) [Aeap-Ext] may reflect hydrothermal fluids or other sources of Fe(II),q. Oxidation of Fe(II),qis envisioned to occur by Fe(II)-oxidizing phototrophs in anaerobic conditions, but could also occur through interaction of Fe(II), with an oxygen-rich atmosphere. Oxidation of Fe(II) produces a flux of ferric oxide/hydroxide precipitates [Aeanjppt] that settle to the lower, anaerobic sections of the pool. These ferric precipitates are in turn partially reduced by DIR bacteria, returning a flux of Fe(II), to the pool [Aem-Bio] ...

Consequently, the bond is fully saturated for A sp = 0 with a bond order of 1, but it is only partially saturated by the time the gap closes for AEap/2 h = 1 (cf eqn (7.92)) when the bond order equals 0.76. This simple second moment model has been extended to include the compound semiconductors. The resultant values of the bond order are given in Table 7.2. We see that the bonds in tetrahedral carbon and silicon are almost fully saturated, but those in zinc selenide and cadmium telluride are only about 75% saturated due partly to the mismatch in the sp orbitals between chemically distinct atoms. 

Appearance potential auger electron spectroscopy. See AEAPS. 

AEAPS Auger Electron Appearance Potential Spectroscopy The EAPFS cross-section is monitored by Auger electron intensity. Also known as APAES. 

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. 

Appearance potential spectroscopies (SXAPS, AEAPS, DAPS, TCS, XEAPS, EAPFS, lETS)... 

In the case of AEAPS, it is not necessary to detect individual Auger peaks, as the total secondary electron yield can be measured instead. The electron cascade within the material can act as an electron multiplier increasing the AEAPS signal. Hence an REA could be used or an electron detector of a type used in a scanning electron microscope. 

The change in the elastically scattered yield when the primary beam energy passes through an ionisation threshold is typically 0.1%. Hence, electronic differentiation is used to enhance the weak signal. AEAPS is approximately 10 times more sensitive than DAPS. SXAPS is approximately 10,000 times less sensitive than DAPS and hence is the least used despite its simple instrumentation. 

AEAPS Auger Electron Appearance Potential Spectroscopy, 2 AEES Nuclear Auger Electron (Emission) Spectroscopy ... 

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