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Nanometer-scale pattern formation on the surface of a photochromic crystal by optical near-field induced photoisomerization

 National Institute of Information and Communications Technology (NICT), University of Yamanashi and Ryukoku University announced on 4 October 2018, that nanomater-scale pattern of alphabet characters are successfully generated on the surface of the diarylethene photochromic crystal by using optical near-field induced local photoisomerization. This work was supported in part by a JST CREST project, and details were published in Scientific Reports as Professor Hirokazu Hori at University of Yamanashi as senior author*.

 Unique interactions between light and matter are expected to be utilized in a novel intelligent system like decision making and solution searching. The researchers are interested in the molecular distortion caused by photoisomerization to realize innovative intelligent functions on the nanometer scale. In this study, they used diarylethene crystal as the reversible photoisomeric material and observed nanometer-scale optical near-field induced photoisomerization on the surface of the crystal. The optical near-field was generated at the probe tip of a light-assisted atomic force microscope (AFM) by irradiating the laser light (wavelength 670 nm) and this AFM was also used for the observation of the local distortion induced by the photoisomerization. On the photoisomerization, nanometer-scale concavity with diameter of about 30 nm, ie. 1/20 of the wavelength and with depth of about 1.5 nm was found to form on the surface of diarylethene. In addition, they succeeded in drawing nanomater-scale alphabet characters 'UY' with arranged several concavities by sequential optical near-field excitation on the surface. Erasure of generated characters was confirmed with a procedure depending on the local spatial characteristics of the crystal. These findings show the possibility of dynamic memorization in nanometer-scale using photochromic materials.

*R.Nakagomi, K.Uchiyama, H.Suzui, E.Hatano, K.Uchida, M.Naruse, and H.Hori, "Nanometre-scale pattern formation on the surface of a photochromic crystal by optical near-field induced photoisomerization", Scientific Reports Vol. 8, Article number: 14468 (2018), doi: 10.1038/s41598-018-32862-9; Published 27 September 2018