The writing mechanism for discontinuous metal films

Abstract

Discontinuous metal films have been recently proposed as a potential archival optical storage material. This class of materials exhibits a unique writing mechanism that yields relatively low writing energies even when materials with high melting points are used. Here, the physics of this writing mechanism are examined. Transmission electron micrographs of exposed areas clearly indicate that the writing mechanism is laser induced coalescence of the metal particles resulting in a dramatic change in optical properties. It is shown that the observed coalescence mechanism is consistent with a theoretical analysis for the sintering of small particles. Calculations based on this mechanism indicate that writing can occur at temperatures well below the melting point of the bulk material. However, detailed thermal modeling of the writing process coupled with measured threshold energies, indicates that melting almost certainly occurs. Furthermore, experimental results indicate a sharp threshold to the writing process. This is inconsistent with the theory of particle coalescence, but a necessary characteristic for a practical optical storage material. This threshold can be attributed to the necessity of bringing the metal particles into physical contact before coalescence can proceed. © 1983 SPIE.