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Explosive phenomenon during the interaction of NO with Ag

par Baer, Thomas;Visart de Bocarmé, Thierry ;Kruse, Norbert
Référence Ultramicroscopy, 79, page (245-249)
Publication Publié, 1999-01-22

Article révisé par les pairs

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Résumé :

The adsorption and reaction of NO on silver-field emitter tips was studied using FEM at low temperatures. Exposing an either [1 1 1] or [0 0 1] oriented clean tip to a single dose of NO gas (50 L whereby 1 L = 1.3x10-4 Pa.s) at sample temperatures between 50 and 61 K under zero-field conditions was found to strongly increase the work function of the Ag specimen. Upon heating to 66 K a wave-like pattern of high brightness could be observed starting at the shank and moving toward the center of the tip apex. The pattern occurred in an explosive manner by spreading over the whole surface during ~2 s and was associated with an exponential increase of the FEM brightness. The phenomenon is not reversible, i.e. on recooling to 50 K neither the explosive pattern formation nor the initial darkness of the FEM image as obtained after NO adsorption were observed. We suggest that the occurrence of a surface explosion during heating is associated with the desorption of multilayer (NO)2 dimers. The model is advanced that the self-accelerating pattern evolution is associated with the thermal dissolution of a "eld-oriented dipole structure, starting at the low-field outskirts of the tip and propagating toward the apex.