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Principles of Instrumental Analysis, 6th ed. Chapter 21
 
 4
21-9. Surface photon techniques have the major advantage that the surface been examined does 
not have to be in an ultra high vacuum environment and can be in contact with liquids. 
Thus, the environment in the surface photon techniques can be more like that found in 
actual use (catalyst, sensor, biological material, etc.) The major disadvantage is that 
surface composition can be altered by adsorption of gases or by attraction of molecules to 
the surface. 
21-10. A buried interface is an interface found not at the surface, but below the surface in 
layered structures. Most surface characterization methods probe only the surface or a few 
nanometers into the surface. However, semiconductors, sensors, and many other 
materials contain interfaces that are buried below the surface and important to 
characterize. Another example is the interface between two immisicible liquids. Sum-
frequency generation (and second harmonic) can provide access to buried interfaces. 
21.11. Sources of signals in SEM can be backscattered electrons, secondary electrons, and X-ray 
photons. In elastic scattering of electrons, the electrons interact with a solid in such a 
way that their direction is altered, but no energy is lost in the process. In inelastic 
scattering, part of the energy of the incoming electron is lost during the scattering 
process. 
21-12. The two types of scanning probe microscopes are the scanning tunneling microscope 
(STM) and the atomic force microscope (AFM). 
 (a) In the STM, the surface being studied is scanned with a sharp metallic tip whose 
position above the surface is controlled by a tunneling current between the tip and 
surface. In the AFM, the surface is scanned by a fine stylus mounted on a force-sensitive