Low-dielectric-constant fluorinated amorphous carbon films have been prepared from a C6F6 and C5F8 gas mixture by an inductively coupled plasma-enhanced chemical vapor deposition method. The films from 100% C5F8 have volatile nature, and they are vaporized by heating to 400°C. On the other hand, the films prepared with 100% C6F6 have higher thermal stability. After the thermal treatment of the composite films, the dielectric constant of the films is reduced to 1.6, although the residual thickness of the films is not 100%. This result suggests that the tissue from C5F8 is vaporized by thermal treatment and voids are formed in the films. Void concentration in the films is estimated to be 40–60%. The structural change due to the thermal treatment stops after 5–10 min, and no marked structural changes are observed after further thermal treatment at 400°C. The higher thermal stability of the films prepared with C6F6 has been attributed to the incorporation of the aromatic ring structure in the films. The gas-phase diagnostics of the deposition processes and the structural analysis of the films have suggested that C6F6 is highly polymerizable and its ring structure can be incorporated in the films.
A rewritable phase-change optical disk providing a large capacity of 100 Gbyte on a 120 mm disk was first demonstrated using the multilayer Bluray Discä (BD-XL) format. The doubled capacity of this optical disk compared with that of a conventional dual-layer disk was achieved firstly by stacking triple recording layers and secondly by increasing the recording capacity per layer from 25 to 33.4 Gbyte at 33.6%. The high transmittances of 50% (middle layer) and 60% (front layer) were achieved by thinning a Ge-Sb-Te phase-change film to 7.5 and 6 nm and also by thinning a Ag-alloy film to 9 and 7 nm, respectively. An additional TiO 2 -based film formed on the Ag-alloy film was effective in improving the transmittance at 3%, compared with the structure using a conventional TiO 2 film. Furthermore, a transmittance-balanced structure was adopted for these layers in order to stabilize the recording-reading properties. To improve cyclability, ZrO 2 -Cr 2 O 3 -based interface films were provided on both sides of the phase-change film for the middle and front layers. The increase in recording capacity per layer was achieved by reducing the minimum mark length from 0.149 to 0.112 m. Since the optical changes degrade with the reductions in the mark lengths and thicknesses of the Ge-Sb-Te and Ag-alloy films, a phase-change material with a GeTe-rich composition on a GeTe-Sb 2 Te 3 pseudo-binary line was adopted for every layer to compensate it. It was confirmed that the sample disk successfully satisfies all the requirements of the BD-XL format.
A sputtered phase-change material, Ge 10 Sb 90 , processed into dots with a height and diameter of 50 nm, shows rapid crystallization triggered by 300 ps laser excitation. Crystallization takes place with a short time delay of approximately 70 ns for a sample with Sb seed layers. The delay becomes just 15-20 ns when a NiCr layer is provided to control the heating-cooling profi le. The nanodot sample requires less energy for crystallization, with a large optical change equivalent to that of the blanket fi lm. These results demonstrate that the nanodot phase-change material could be a possible candidate for next-generation "green" optical storage.Adv. Optical Mater. 2013, 1, 820-826 821 wileyonlinelibrary.com
We have developed a system of laser-pump and synchrotron radiation probe microdiffraction to investigate the phase-change process on a nanosecond time scale of Ge2Sb2Te5 film embedded in multi-layer structures, which corresponds to real optical recording media. The measurements were achieved by combining (i) the pump-laser system with a pulse width of 300 ps, (ii) a highly brilliant focused microbeam with wide peak-energy width (ΔE∕E ~ 2%) made by focusing helical undulator radiation without monochromatization, and (iii) a precise sample rotation stage to make repetitive measurements. We successfully detected a very weak time-resolved diffraction signal by using this system from 100-nm-thick Ge2Sb2Te5 phase-change layers. This enabled us to find the dependence of the crystal-amorphous phase change process of the Ge2Sb2Te5 layers on laser power.
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