FIGURE 11.63 TEM images of an NaCl crystal (A) before reaction and (B) after reaction with gaseous HN03 (1.2 X 1015 cm-' for 15 min) and then (C) exposure to water vapor (<15 Torr) followed by drying (adapted from Allen et al., 1996).

spectra with large contributions from Na, O, and S, and the SAED patterns were similar to that of Na2S04.

It should be noted that as with all analytical techniques that involve subjecting the sample to vacuum conditions before and/or during the analysis, separation of components via selective crystallization is expected (e.g., Ge et al., 1998a). Hence these particles may not have actually existed in these crystalline forms at relative humidities above their deliquescence points in the atmosphere, although the various constituents observed were clearly present.

(2) Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) These methodologies for probing the morphological details of a surface down to

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