No abstract

Phase imaging during tapping mode atomic force microscopy (TMAFM) has revealed that an optical near field caused a change in the viscoelastic property on the surface of an urethane-urea copolymer film containing donor-acceptor substituted azobenzenes. Monolayers of polystyrene microspheres with 100 nm diameter and 19 nm diameter were fabricated on the surface of the copolymer film and exposed to a 488 nm wavelength laser beam coincident with the absorption band of the azobenzene derivatives. After removal of the monolayer, the phase image of the film's surface was obtained by TMAFM. The phase shift of a cantilever oscillation (the shift was induced by a tip-sample interaction) indicated that the area affected by the optical near field of the microsphere became relatively softer (the phase shift was smaller) and the vicinal area became harder (the phase shift was larger). These results suggested that the optical near field produced a change in the density on the surface of the copolymer in nanometric dimensions. The copolymer was capable of transcribing the optical near field within the resolution of 20 nm on the basis of the viscoelastic feature.

We report a recording medium in which a three-dimensional nanoscale structure can be photofabricated for multilayered optical memory using a two-photon process. By fabricating the structures in the medium, we can control the shape of recorded bits and, in effect, their spatial frequency distribution. We succeeded in recording bits with a 0.5μm interval in any particular plane and 2.0μm interval between successive layers. Thus, storage density of 2.0Tbits∕cm3 is achieved.

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We present a multilayered optical memory for use in reading data with a confocal reflection microscope system. We use a recording medium in which photosensitive thin films and nonphotosensitive transparent films are stacked alternately. Since the photosensitive films are thinner than the depth of focus of the recording beam, the spatial frequency distribution of the recorded bit data is extended in the axial direction. The extended distribution overlaps the coherent optical transfer function of the reflection-type confocal microscope. Urethane-urea copolymer film is used as a photosensitive material. The recording and reading of two layers are demonstrated.