Victor Burr Jipson

Phase transformation kinetics—the role of laser power and pulse width in the phase change cycling of Te alloys

The effect of laser pulse width and amplitude on the kinetics of laser‐induced phase transformations of thin films of Te alloys has been mapped. This map, called a phase transformation kinetics diagram, shows distinct regions of crystallization and amorphization and allows important material parameters to be determined. The observed regions were correlated with results from temperature modeling. The minimum crystallization time was measured to be 50 ns for pure Te and increases to 550 ns for Te80Sn20 and 80 μs for Te90Ge10. A boundary, determined by the critical quench rate, separates the region of melt followed by amorphous quench, from melt followed by crystallization. Three methods of reversible cycling are demonstrated.

The Writing Mechanism For Discontinuous Metal Films

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.

Fabrication and testing of trilayers with a high deposition rate plasma-polymerized spacer☆

Abstract A great deal of effort has recently been directed toward the development of digital optical storage systems using Ga-Al-As lasers for both reading and writing. The relatively low output power of these devices necessitates sensitive optical storage media if reasonable data rates are to be achieved. At the same time, it is desirable that the material exhibit archival properties. One method of reducing the writing energy for a wide variety of materials is to incorporate them within an optical structure that improves the optical efficiency. In particular, trilayer structures consisting of an aluminum layer 30 nm thick, a spacer layer about 100 nm thick and a thin storage layer offer the potential of improved sensitivity for a wide range of active materials, but their use requires the fabrication of a low thermal conductivity optically clear spacer layer approximately one-quarter wave thick. Because of manufacturing considerations, it is desirable that this layer be deposited at relatively high rates in an inexpensive process. Here we describe the investigation of the plasma polymerization of various monomers for this purpose. It has been found that stable films of perfluoro-2-butene can be deposited at rates greater than 1 nm s-1. Trilayer structures using this material as the spacer layer are compared with more conventional materials.

Directions in optical storage

This talk will focus on the key technical and functional advantages of optical storage, and how they must evolve over time for optical recording to continue its penetration into the data storage hierarchy.

Drive technologies for the future

Optical storage currently is the fastest growing segment of the data-storage hierarchy. In this presentation, we will review the technology improvements required to continue this growth.