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206   5 Near Field
                             Table 5.7. Parameters of materials for super-RENS disk using AgO mask layer
                                                                                    x
                             layer          material  thickness (nm)phase      optical constant
                                                                                n       k
                             substrate      PC       0.6 × 10 6     –          1.56    0
                             protective layer  ZnSiO 2  170         –          2.25    0.01
                             mask layer     AgOx     15             AgO 2      28      0.08
                                                                    Ag particle  0.04  6.99
                             protective layer  ZnSiO 2  30          –          2.25    0.01
                             recording layer  GeSbTe  15            crystal    4.29    2.09
                                                                    amorphous  3.97    4.41
                             protective layer  ZnSiO 2  20          –          2.25    0.01


                                     (a)                       (b)





                                                  P  = 2.5 mW             P  = 3.5 mW
                                                   i                       i
                                     (c)                       (d)





                                                  P  = 4.0 mW             P i  = 5.5 mW
                                                   i
                                 Fig. 5.50. Effect of initialization laser power P i on reproduced signals


                               Figure 5.50 shows the reproduced signals (normalized with as-depo level
                            V i ) at different initializations of laser power P i for an as-depo medium. The
                            reproduced signal V i (mark) at the read power P r = 1 mW changes in ways
                            such as the following: becomes small negative at P i =2.5 mW (a), becomes
                            maximum positive at P i =3.5mW (b), becomes nearly zero at P i = 4mW
                            (c), and gradually increases to negative as P i increases (d). This variation
                            generated by the written mark is shown in greater detail by the curve “mark”
                            in Fig. 5.51. This figure shows the effect of initiallization on an as-depo medium
                            of the super-RENS disk. The mark reflectivity V 2 , normalized with as-depo
                            reflectivity V i , changes from (a) a small negative to zero to (b) positive to
                            (c) zero to (d) increases to negative and then becomes saturated as the laser
                            power increases.
                               This phenomenon corresponds to (a) the little decrease in reflectivity due
                            to the little amorphous process in GeSbTe and then cancellation due to the
                            increase in refrectivity with the AgOx decomposition (Ag particle), (b) fully
                            decomposed Agparticles, (c) cancellation due tothe half amorphous process
                            of GeSbTe, (d) the decrease in reflectivity due to the completely amorphous
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