Stonewall model

Skeptics of the cratering spike hypothesis have argued that the clustering of ages near 3.9 Ga may be a stonewall effect (Hartmann, 1975 Wetherill, 1981 Chapman et al., 2002). The stonewall model invokes a saturation of the... 

Stonewall Model. In the Stonewall Model, Hanabata etal (9) showed using gel permeation chromatography (GPC) that multifunctional DNQ can crosslink the novolac via a base catalyzed azo-coupling reaction (Figure 1). They explained that this reaction increases the polymer molecular weight, which results in a decrease in the dissolution rate in the unexposed areas of the resist film. 

Several limitations of this model show that it is not the main mechanism for dissolution inhibition in DNQ/novolac systems. First, the reaction does not occur with all inhibitors. Diazodiones such as Meldrum s Diazo do not undergo base-catalyzed azo-coupling, but they are effective inhibitors (77). Also, Murata et al (72) showed that efficient dissolution inhibition can be observed with inhibitors that do not have diazo functionality. For example, phenyl naphthyl sulfonate is a better dissolution inhibitor than the corresponding phenyl DNQ sulfonate indicating that the dissolution inhibition ability can be attributed to the sulfonate ester of the DNQ, not the DNQ chromophore itself (Figure 2). Despite the shortcomings of the Stonewall Model, it was an important contribution to the understanding of dissolution inhibition, because it was the first microscopic, molecular-interaction model for inhibition. 

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