Charles R. Davis

New phase change material for optical recording with short erase time

We present data on a new erasable phase change medium, demonstrating for the first time that very short erase times can be obtained without sacrificing room‐temperature stability of the amorphous state. Thin films of the composition Sb2Se underwent 10% relative reflectivity changes when switched with a laser between amorphous and crystalline states. Twenty milliwatt, 50 ns laser pulses were used for writing amorphous spots; 6.9 mW, 200 ns pulses were used for erasing. A playback carrier to noise ratio of 43 dB was observed on a plastic disk. Amorphous spots could be heated in a microscope to 175 °C before they crystallized. Transmission electron microscopy and x‐ray diffraction indicate that the erased state is single phase and polycrystalline. The crystal structure, however, does not correspond to known compounds in the antimony‐selenium system.

Dopant-induced excimer laser ablation of poly(tetrafluoroethylene)

Poly(tetrafluoroethylene) (PTFE) does not exhibit excimer laser etching behavior at conventional, e.g., single photon absorption, emissions of 193, 248, and 308 nm, due to the lack of polymer/photon interaction. This is not surprising since the electronic transitions available to the PTFE molecule are high energy and thus require short wavelength the radiation However, by incorporating a small quantity of material into the non-absorbing fluoropolymer matrix that interacts strongly with the emitted laser energy, e.g., a dopant, successful ablation, both in terms of etch rate and structuring quality occurs. Specifically, excimer laser ablation of PTFE films containing 5, 10, and 15% polyimide (wt/wt) as a dopant was achieved at 308 nm in a fluence range of 1 to 12 J/cm2. Ablation rates for the materials increased with increasing fluence and, at the polyimide levels investigated, varied inversely with dopant concentration. All compositions exhibited excellent structuring quality.