ZnO nanowires were synthesized on gold-coated glass substrates using the hydrothermal method. The effects of precursor concentration, substrate annealing and seeding on the morphology, dimension, and distribution of resultant nanowires were investigated. We found that the density of nanowires on substrates pre-seeded with ZnO nanoparticles is about two orders of magnitude greater than unseeded ones, while the dimension of ZnO nanowires for pre-seeded samples is much smaller than unseeded samples. In addition, we found that the fraction of substrate area covered by nanowires for unseeded samples is proportional to the precursor concentration, and proposed a simple nucleation model to explain this behavior. For pre-seeded substrates, ZnO nanowire density first increases with concentration and decreases as concentration exceeds 20 mM. We attribute this behavior to the competition for ions among the dense wires of varying length as well as the fusion of neighboring wires into larger ones.

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The reflectivity of an amorphous mark on a first-surface phase-change optical storage disk is shown to vary with the level of ciystallization of the GST layer. A static tester with 680-nm laser diode for writing amorphous marks and a 643-nm laser diode for monitoring the reflectivity changes is used for the experiment. An 8% difference in reflectivity is measured between the amorphous marks formed in the fully crystallized, high reflectivity (R=43%) state and partially crystallized, low reflectivity (R30%) state.

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