Rewrite Characteristics of a Scattered-Type Superresolution Near-Field Structure Optical Disk with a Ag_2O Mask Layer

摘要

On the basis of the working mechanism of a silver-oxide-type superresolution near-field structure (super-RENS) disk, we realized excellent rewriting by performing the following steps: (1) initialize the disk at a continuous power of P_i = 8.0mW for 3 s, (2) write at a pulsed power of P_w = 8.0-9.0mW, (3) read (reinitialize only the mask layer) at a superresolution power of P_(sr) ＝ 5.5 mW, which lies between the powers under reversible conditions of P_i~l = 4.5 mW and P_i~u = 6.0 mW for the mask layer, (4) erase at a continuous power of P_e = 7.5 mW for 3 s, and (4) rewrite at a pulsed power of P_w = 8.0-9.0 mW. The carrier-to-noise ratio (CNR) difference between writing and erasing slightly varies for successive rewritings, resulting in CNR = 23 dB after 20 rewrite operations for a mark length of 400 nm, which is less than the resolution limit λ/4NA = 413 nm. The Ag_2O mask layer is decomposed into Ag nanoparticles at 160 ℃ that aggregate to form nanoclusters dispersed in the mask layer after the initialization operation at P_i = 8.0 mW (3 s), and the recording layer made of Ge_2Sb_2Te_5 (GST) is transformed by a second phase transition from a rocksalt crystal structure of fcc to a hexagonal crystal structure (the phase transition temperature range is estimated to be 250-450 ℃) at a pulsed power of P_w = 8.0-9.0 mW, and vice versa at a continuous power of P_e = 7.5 mW for a disk velocity of 2 m/s.