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5.4 Future Applications 199
The second is by the aperture formed with the Agnanoparticle ring
in the mask layer (AgO ) and the CNR is increased by 20 dB as that of
x
the transparent-aperture type described earlier [5.54]. The CNR increase is
thought due to the plasmon scattering by Ag particles. This type optical disk
consists of PC-substrate (0.6 mm)/ZnSiO 2 (170 nm)/AgO (15 nm)/ZnSiO 2
x
(15 nm)/GeSbTe (15 nm)/ZnS i O 2 (20 nm). The functional structures of AgO x
thin film for near-field recording has reported [5.55]. The aggregated Ag clus-
ter produced by a lower input energy, high reflectivity, scatters near field
efficiently and the Ag ring produced by a higher input energy, low reflectiv-
ity, not only confines the input light energy for writing but also enhances the
scatteringfields for reading.
Kataja et al. [5.56] studied the AgO super-RENS phenomena numerically
x
usinga 2-D FDTD method. They indicated that a super-RENS structure hav-
ingan AgO active layer can produce beyond the difraction limit resolution
x
when the aperture surrounded by small Agparticles formed and filled with a
low index material such as O 2 . Recently, read/write characteristics have been
studied through systematic experiments and the detaild mechanism to explain
the Agtype super-RENS has been proposed more clearly [5.57].
This mechanism by a deformed gas bubble associated with metallic
nanoparticles was also elucidated for a platinum oxide super-RENS disk.
The CNR of over 47 dB for 100 nm mark length was obtained for the
optical disk with the followingstructure: PC–substrate (0.6 mm)/ZnS–
SiO 2 (170 nm)/PtO 1.6 (4 nm)/ZnS–SiO 2 (40 nm)/AIST (60 nm)/ZnS–SiO 2
(20 nm) [5.58,5.59].
The third is a huge change in the refractive index generated in a focused
laser spot. Tominaga et al. [5.60] have proposed a ring aperture formed by
ferroelectric catastrophe in AgInSbTe recording medium. This superresolution
◦
◦
aperture can be observed between 350 C and 400 C, resultingin a second
phase transition from a hexagonal to a rhombohedral structure. This type
optical disk consists of PC–substrate (0.6 mm)/ZnSiO 2 (130 nm)/AgInSbTe
(40 nm)/ZnSiO 2 (100 nm) [5.61]. Mask layer does not required.

Sb-super-RENS(Aperture Type)

Here, write and read mechanism of super-RENS optical disk of PC–substrate
(0.6 mm)/SiN (170 nm)/Sb (15 nm)/SiN (30 nm)/GeSbTe (15 nm)/SiN (20 nm)
is presented by the results obtained from the experiments in various read/write
conditions and theoretical analyses for a six-layer film reflectivity.

Experimental setup and read/write conditions

Figure 5.39 shows the conventional experimental apparatus consists of an op-
tical disk tester (Pulstec Industrial Co., Ltd) with a wavelength of λ = 826 nm
laser diode and an NA = 0.5 objective lens. Figure 5.40 shows a typical super-
RENS disk usingan Sb mask layer with an objective lens. A near-field aperture