No abstract

Gold (Au) line patterns of 0.5 and 1 µm widths were fabricated on a silicon substrate covered with a Au thin film by thermal nanoimprint lithography with poly(methyl methacrylate) (PMMA) and polystyrene (PS), followed by Au electrodeposition with their thin films as resist masks. We described the differences in the fidelity of the deposited Au patterns for linewidth and linewidth roughness and differences in undesired Au deposition in the masked regions between thin PMMA and PS films. The linewidths of the convex deposited Au pattern were larger than those of the concave nanoimprinted polymer pattern, and the deviation from the polymer concave pattern in the case of PS was significantly smaller than that in the case of PMMA. The linewidth roughness of the Au lines deposited with a PMMA mask was markedly high owing to particle-like Au deposition in comparison with that deposited with a PS mask. Undesired Au deposition occurred even on electrode surfaces masked with the thin PMMA and PS films. It was considered from these results that the difference in the size accuracy of Au electrodeposition between PMMA and PS was responsible for the resistance in the oxygen dry-etching step of a residual layer during thermal nanoimprint lithography in addition to polymer water absorbability in Au electrodeposition.

We describe the selective electrodeposition of submicrometer gold (Au) patterns achieved by a thin film resist layer of polystyrene (PS) that was exposed to ultraviolet (UV) light on a photoreactive monolayer of a benzophenone-containing alkylthiol formed on a Au-plated substrate and patterned by thermal nanoimprint lithography. The presence of a PS graft layer caused by the benzophenone monolayer photochemistry at an interface between the PS resist layer and photoreactive monolayer played the important role of suppressing the unfavorable growth of tiny Au grains in regions masked with the PS resist layer, resulting in the selective Au electrodeposition in aperture regions of PS resist patterns. The suppressive effect on selective Au electrodeposition depended on the molecular weight of PS used as a resist material. Among unimodal PSs having weight-average molecular weights (M(w)'s) of 2100, 10,900, and 106,000 g mol(-1), the PS of M(w) = 10,900 g mol(-1) functioned most effectively as the resist layer. Au electrodeposition at a low current density allowed the preparation of Au lines having widths of submicrometers and a uniform height independent of line widths in resist aperture regions. Submicrometer bump structures of Au lines could be fabricated on transparent silica substrates by the subsequent wet etching of a Au electrode layer and then a chromium adhesive layer.

Organized Autotelescopes for Serendipitous Event Survey (OASES) is an optical observation project that aims to detect and investigate stellar occultation events by kilometer-sized trans-Neptunian objects (TNOs). In this project, multiple low-cost observation systems for wide-field and high-speed photometry were developed in order to detect rare and short-timescale stellar occultation events. The observation system consists of commercial off-the-shelf 0.28 m aperture f /1.58 optics providing a 2 • .3 × 1 • .8 field of view. A commercial CMOS camera is coupled to the optics to obtain full-frame imaging with a frame rate greater than 10 Hz. As of September 2016, this project exploits two observation systems, which are installed on Miyako Island, Okinawa, Japan. Recent improvements in CMOS technology in terms of high-speed imaging and low readout noise mean that the observation systems are capable of monitoring ∼ 2000 stars in the Galactic plane simultaneously with magnitudes down to V ∼ 13.0, providing ∼ 20% photometric precision in light curves with a sampling cadence of 15.4 Hz. This number of monitored stars is larger than for any other existing instruments for coordinated occultation surveys. In addition, a precise time synchronization method needed for simultaneous occultation detection is developed using faint meteors. The two OASES observation systems are executing coordinated monitoring observations of a dense stellar field in order to detect occultations by kilometer-sized TNOs for the first time.