Tomofumi Arai

Characteristics of nanostructured Ag films by the reduction of sputtered AgOx thin films

The fabrication process and the optical properties of nanostructured silver?(Ag) films made from silver oxide (AgOx) thin films have been studied in detail. The formation of Ag nanoparticles with a diameter of about 50?nm during the reduction of AgOx films was clearly demonstrated by scanning electron microscopy?(SEM) and cross-sectional transmission electron microscopy?(TEM) observations. The reflectance spectra of the nanostructured Ag films exhibited an intensive localized surface plasmon resonance (LSPR). The transformation in the reflectance spectra with reduction time was in good agreement with computer simulations based on Mie theory. The composition ratio of AgOx films during the reduction was analysed by the Ag LIII edge x-ray absorption near-edge structure?(XANES) measurements.

The size control of silver nano-particles in SiO2 matrix film

We provide a fabrication method for silver nano-particles with a uniform particle size using vacuum deposition. The size uniformity was controlled by a small amount of neodymium?copper (Nd?Cu) as a co-sputtered material. Particles with a size of 20 ? 7?nm dispersed in a SiO2 matrix have been obtained. The full width at half maximum of the plasmon resonance in the optical spectrum by the silver?neodymium?copper (Ag?Nd?Cu) nano-particles was only half of the size compared with the spectral width of a pure Ag nano-particle system. The effect is attributed to an increased uniformity in the particle size.

Toward Biological Diagnosis System Based on Digital Versatile Disc Technology

A novel biosensor utilizing an interference of light reflected at the interfaces of a multilayer structure is proposed. This biosensor detects analytes by monitoring the changes in reflection intensity due to their adsorption to the sensor surface, on which functional biomolecules are immobilized to specifically bind to the analytes. The proposed biosensing instrument is based on a commercial digital versatile disc (DVD) system, which allows the instrument to be small and inexpensive. For the preliminary examination, SiO2 thin films with a well-defined thickness were deposited on the sensor surface. The reflection intensity varied almost linearly depending on the thickness of the SiO2 films in a thickness range of 2–10 nm. Subsequently, it was demonstrated that biotin–streptavidin binding events were clearly detectable on a rotating disc substrate at a constant linear velocity of 4.0 m/s. We named this interference-based biosensor BioDVD, which is expected to be useful for high-throughput multi-analyte bioassays.

Carrier-to-noise ratio enhancement of super-resolution near-field structure disks by Ag nanostructure

The recording and retrieval characteristics of super-resolution near-field structure disks have been evaluated before and after the fabrication of a Ag-nanostructured film on the top dielectric layer, using a 405nm wavelength laser and a 0.65 numerical aperture lens system. The carrier-to-noise ratio for 100nm mark signals is significantly improved by applying the Ag-nanostructured film. The underlying mechanism for the enhancement depends on the top dielectric layer thickness. A simulation based on Mie theory shows good agreement with the measured reflectance spectrum for the Ag-nanostructured film.

Developing Platform for Detecting Biomolecules

Using optical interference of reflected lights from interfaces, a multilayer structure was designed to make a label-free biosensor. This optical system is quite similar to the commercial digital versatile disc (DVD) drive, and reflection intensity was determined by an optimized polycarbonate disc consisting of five layers of Au (5 nm)/(ZnS)85(SiO2)15 (85 nm)/Ag6.0In4.4Sb61.0Te28.6 (15 nm)/(ZnS)85(SiO2)15 (45 nm)/Au (50 nm). Using this multilayered structure, we monitored a DNA hybrid as an application to the field of biology. Considering various issues for developing a suitable platform for detecting biomolecular interactions on this BioDVD, phase shifting alloys used in this system will facilitate the addressing biomolecules. Furthermore, for high-throughput analysis, we proposed the spotting method to attach several molecules to different tracks of BioDVD.

Signal Enhancement of Super Resolution Enhanced Near-Field Structure Disc by Silver Nano-Particles

We propose a carrier-to-noise ratio (CNR) increment method for a super resolution enhanced near-field structure (super-RENS) with silver nanoparticles. The silver nanoparticles were fabricated by the RF magnetron sputtering method. The mean diameters of the particles under as-deposited and 600°C annealed conditions were evaluated as 5 nm and 15 nm, respectively. The light absorption peak of the silver nanoparticles was adjusted to a laser wavelength of 405 nm for an optical disc system. The silver nanoparticles showed a higher absorption characteristic when they were annealed at above 500°C. In the case of a recording mark size of 50 nm, the CNR enhancement of the super-RENS with the silver nanoparticles was evaluated as 11 dB. This method using the silver nanoparticles provided a higher CNR increment in recording marks below the optical resolution limit.