Probing the nature of developed silver in photothermographic media

The fundamental imaging element in photothermographic media is nanosized silver particles, formed from the thermally induced reduction of silver ions. In these films, such as the Kodak DryView laser imaging system media, the developed silver imaging elements contain a mixture of dendritic and filamentary silver. Using a temperature series (105-140°C) arrested development study, the latter was found to be ribbon-like, crystalline, and dispersed with microtwins. Dendritic silver, however, was seen to develop at a higher temperature and reached its maximum size at 122°C, the condition normally used in the thermal processing of Kodak DryView films. Its morphology resembled a cluster containing numerous loosely packed silver nanoparticles. At higher temperatures, it gradually collapsed and condensed into a smaller polycrystalline aggregate. With increasing temperature, its degree of structural order gradually increased and was the highest at 140°C. From these results we show how the dendritic silver contributes to the light absorption properties of the image area, and we lay the groundwork for providing better understanding of the silver particle formation that will lead to new and improved imaging materials.