Photoemission electron microscopes PEEM

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). 

Fig. 7. Schematic of a photoemission electron microscope (peem). Courtesy of S. Anders, ALS, and B. Tonner, University of Central Florida.

Advancing such innovative, enabling instrumentation has been among the Department s core activities. Other instruments developed by the Department include a photoemission electron microscope (PEEM) with ultimate resolution attained by implementing corrections for both chromatic and spherical aberrations a micro calorimeter whose sensitivity is sufficient to measure temperature-dependent heats of adsorption on nano-particles with aggregate sizes down to about a hundred atoms and a photon STM, which adds chemical sensitivity through local excitation of a fluorescence signal by electrons from the tip. 

Figure 7.23 Ordering of adsorbates on a surface into islands gives rise to regions of different work function, which can be imaged because of the associated differences in photoelectron intensity. The principle forms the basis of photoemission electron microscopy (PEEM). The same principle underlies the imaging of single molecules in the field electron microscope (FEM) (see also Fig. 7.9).

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