NEXAFS spectroscopy measurements using

Having seen the power (and limitation) of nexafs spectroscopy in the preceding sections, one can readily envision the enhanced utility of nexafs spectroscopy as a characterization tool that would result from the addition of high spatial resolution capabilities. Since the spectroscopic sensitivity to specific moieties and functional groups can in many or even most cases be exceeded by ir, nmr, and Raman spectroscopies, nexafs microscopy will have to exceed the spatial resolution of these other spectroscopy techniques in order to be truly useful. To date, nexafs microscopy has surpassed a spatial resolution of 50 nm both in transmission to measure bulk properties (75-77) and in a reflection geometry to study surfaces (78,79). This level of spatial resolution is at least an order of magnitude better than what can be accomplished with complementary compositional analysis techniques. Future developments in nexafs microscopy might achieve a spatial resolution of a few nanometers (80,81). In addition, nexafs microscopy has exceptional surface sensitivity of about 10 nm, a sensitivity that could be improved to about 1 nm with photoemission electron microscopes (peem s) that incorporate a bandpass filter (80-82). 

NEXAFS spectroscopy basically does not require the most sophisticated apparatus to be performed but a source of tunable radiation as that dispensed by a photon factory or synchrotron plant. The experimental station for the study of macromolecular materials requires a UHV system and a detector apparatus for counting the emitted electrons. The primary process in NEXAFS is the core electron excitation into an appropriate final state empty molecular orbital. After excitation, the whole system undergoes relaxation and this can occur through two main decay processes secondary or Auger electron emission and fluorescence emission. Mostly, the detector for NEXAFS uses a simple channeltron tuned for a specific Auger energy or tuned to collect the whole secondary electrons resulting from the relaxation process fluorescence detector are also relatively common alternatively, for sample insulator the measurement of the drain current from the conductor sample holder is often measured examples are displayed in Fig. 4.4. Measurements can be performed on gas, solid and recently liquid state [3]. 

FT-RAIRS measurements of CO have also been used to identity facets of oxide supported Cu particles [78, 82]. The low sensitivity of RAIRS on single crystal ZnO(OOOl) prevented the observation of adsorbed CO or CO2, despite their observation in NEXAFS [78], although the local metallic dielectric allowed CO to be observed on the Cu particles. There appear to be no examples of HREELS being used to carry out vibrational spectroscopy of adsorbates on oxide supported metal particles. A HREELS study of Ag on MgO(lOO) films [95] was used only to characterise the Ag induced attenuation in the substrate Fuchs-Kliewer phonons, and the appearance of the metal/oxide interfacial plasmon at higher energies. HREELS has also been used to characterise the oxide/oxide interface between NiO and thin film MgO(lOO) [96]. Similar measurements of substrate phonon attenuation were made in HREELS studies on Pt films grown on ZnO(OOOl) [97]. 

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