ABSTRACT
I. The Paradigm of Heterogeneous Catalysis 370
II. From Dispersed Silica to Reactive Silica 372 A. Pyrolysis 373 B. Fracture 374 c. Strain 375 D. Radiation damage 376
III. Radiation Damage in Dispersed Silica 376 A. The imparted damage 377 B. Silicon-link vacancy 378 c. Oxygen-bridge vacancy 378 D. Environmental stability of radiation defects 380 E. Reactivity of native defects in a controlled atmosphere-
IV . C02 Addition to Ion-Bombarded Si02 381 A. Expectations 382 B. Experimental results 383 c. Theoretical studies 385
v. C2H4 Reactions with Ion-Bombarded Si02 387 A. Expectations 387 B. Experimental results 389 c. Theoretical studies 391 References 396
I. THE PARADIGM OF HETEROGENEOUS CATALYSIS
Surfaces represent a way to impart bulk electronic and vibrational properties to condensed-phase atoms exposed to a gas or liquid atmosphere. As far as nonlocalized electronic states are involved, unexplainable reactivities in atomic or molecular terms are manifested. We simply mention a few examples: For metals in condensed phase the electron affinity and ionization energy coincide and equal the work function of the considered face; the work function on tungsten lowindex faces is higher than the fluorine electron affinity; and atomic cesium ionizes spontaneously when it comes in contact with tungsten surfaces (this phenomenon is practically exploited in spacecraft ion engines). For semiconductors, doping can be used to populate preferentially donor or acceptor states, thus conferring to the surface reducing or oxidizing properties, while bandgap engineering can be used to narrow or widen the gap. The combination of bandgap engineering, doping, and micromachining should eventually allow the integration of controlled chemical reactivity with suitably designed microreactors.
