Mitsunori Kokubo

Seamless Pattern Fabrication of Large-Area Nanostructures Using Ultraviolet Nanoimprint Lithography

The seamless pattern fabrication of large-area nanostructures using ultraviolet nanoimprint lithography (UV-NIL) was studied. Large-area nanopatterning is required in the actual mass production of optical devices and biological microchips. We applied the double lithography method of litho-etch-litho-etch for UV-NIL process. The proposed multiple UV-NIL process realized 66 ?45 mm2 pattern area, which has 50 nm width and 150 nm space line patterns on a quartz wafer.

High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer

We increased the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) by introducing a highly reflective photonic crystal (HR-PhC) into the surface of the p-AlGaN contact layer, thereby achieving a high external quantum efficiency (EQE). A low-damage HR-PhC with a lattice period of approximately 250 nm was fabricated using nanoimprinting and dry etching. A reflective Ni/Mg p-type electrode was deposited on the HR-PhC layer using a tilted-evaporation method. The EQE of a conventional DUV LED with emission around 283 nm was increased from 4.8 to 10% by introducing the HR-PhC and the reflective Ni/Mg electrode. A simple estimation of the effective reflectance of the HR-PhC p-AlGaN contact layer with the Ni/Mg electrode indicated a value exceeding 90%.

Soft patterning on cylindrical surface of plastic optical fiber

The authors have developed a novel thermal imprinting method to fabricate microstructures on the surface of plastic optical fibers (POFs) without causing any damage to them. In conventional thermal nanoimprinting using a planar mold, the shape of the molding material is in the form of a film spread on a planar substrate, or the molding material is used in its bulk form. In the case of any 3-dimensional shaped molding material such as in the case of a fiber, the shape becomes susceptible to a certain degree of damage caused by the planar mold. In order to address this problem, we have designed a thermal imprinting method using sliding planar molds. A fiber tightly stretched between two reel stations (for sending and winding of the fiber) is sandwiched between two planar molds facing each other. The fiber is then rolled against the pattern sides of the two planar molds while the rolling motion of the fiber remains synchronized with the sliding motion of the planar molds. The problem of twists in the fiber c...

Fast and continuous patterning on the surface of plastic fiber by using thermal roller imprint

The authors succeeded in producing high-speed continuous patterning on the surface of plastic fiber at a feeding speed of 20 m/min by using a system they developed employing thermal roller imprint methodology. In this method, a cylindrical mold with seamless microstructures formed on its surface was used, wherein a plastic fiber is pressed between the cylindrical mold and a backup roller and is then run for imprinting. Here, the movement of the cylindrical mold in the direction of space-change between the mold and the backup roller can be precisely controlled, and the press force during the imprinting can be measured by a load cell located beneath the backup roller. The cylindrical mold and the backup roller are heated up to 250 °C and are rotated synchronously, imparting a forward-linear motion to the plastic fiber and thereby making continuous patterning of microstructures possible. Since the press force feedback system during high-speed imprinting cannot be adequately controlled, the authors devised a ...

Film tomography as a tool for three-dimensional image construction and gene expression studies

In order to observe three‐dimensional (3D) expression patterns of genes in whole animals, whole organs, or whole tissues, in situ hybridization (ISH) of many sections must be carried out and then used to construct a 3D image. For this purpose, we have developed an automatic microtome to prepare tissue sections with an adhesive film. We used commercially available film suitable for sectioning and ISH. We constructed a microtome and, after adherence of the film to a paraffin‐embedded tissue block, cut the block with a blade to prepare sections on film. Then, the sections‐on‐film were automatically set in a plastic frame that was the same size as a conventional glass slide. With this automatic microtome, tissue sections can be made for ISH or immunohistochemistry in addition to conventional hematoxylin and eosin staining without specific training. We demonstrate that we can construct 3D images of gene expression patterns obtained by ISH on sections prepared with this automatic microtome. We have designated this method as ‘Film Tomography (FITO)’.