Azobenzene Derivatives for Near-Field Recording

Near-field optics is another promising way to achieve high-density optical memory. Since near-field techniques overcome the diffraction limit of light by the contribution of evanescent wave, it is possible to store a bit datum in a nanometric region. The nanometric resolution is achieved by the contribution of evanescent fields. 

Various materials have been examined for the media of near-field recording, Martin el al and Betzig et used optomagnetic material, and Irie used diarylethene derivatives.  

25b show the near-field recording results on a urethane-urea copolymer thin film. These images show the results of recording bit sizes of 500 nm and 50 nm, respectively. They showed the topographical change of the film surface detected with an atomic force microscope (AFM). 

The film was illuminated with a laser light of 488 nm wavelength and 30 mW power. Note that the laser light is near a resonant absorption peak of the urtthane-urea film. After illumination of the laser light, the film was 

Because the light intensity under the particles was much stronger than that in the area between the particles caused by the multiscattering between the particles and the substrate, the holes were produced by the light intensity at the areas under the particles. This was the same mechanism used to produce surface-relief grating with light illumination.  

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