Effect of Catalyst Size in Heterogeneous Nucleation

Light scattering and optical absorption have been used to study a photosensitive glass in which a gold colloid nucleates further crystallization. The depolarized component of the scattered light at 90° begins to increase abruptly after an elapsed time interval in the precipitation. This increase is attributed to a rapid increase in the nucleation catalysis by the gold colloid. The elapsed interval represents the time necessary for the gold colloid to grow to a size that is effective. In agreement with this, very high exposures, which produce very small colloid particles, result in little crystallization. The colloid size necessary for nucleation catalysis appears to be of the order of 80 angstroms. While this size may be connected with the critical size of the crystals that form on the gold colloid, an alternative explanation based on the curvature of small particles is also proposed.