Nobufumi Atoda

An approach for recording and readout beyond the diffraction limit with an Sb thin film

A technique for recording and retrieving small marks beyond the optical diffraction limit was proposed. The basic experiment with this technique was also carried out at a constant linear velocity of 2.0 m/s, rotating a disk with a multi-layered structure of Sb and GeSbTe, which were separated by a thin film of SiN. By use of the optically nonlinear property of the Sb thin film, carrier to noise ratio of more than 10 dB was obtained from recorded marks of 90 nm, using an optical system with the laser wavelength of 686 nm and a numerical aperture of 0.6.

Local plasmon photonic transistor

A proposal for a photonic transistor is made and some basic proving experiments are described. These experiments show that by focusing two laser beams (405 and 635 nm) in one small spot on a high-speed rotating optical disk, a large signal enhancement is observed. It was found that a plasmon interaction generated between a silver light-scattering center and recorded small marks in the optical disk with a super-resolution near-field structure produced the large signal amplification in the spot (<1 μm). A modulated signal of the blue laser was enhanced by 60 times by controlling the red laser power from 1.5 to 3.5 mW. It has been shown that the system has the potential to realize all-thin-films photonic transistors by using local plasmon amplification.

Sputtered silver oxide layers for surface-enhanced Raman spectroscopy

We present results of reactively sputtered silver oxide thin films as a substrate material for surface-enhanced Raman spectroscopy (SERS). Herein, we show that deposited layers develop an increasingly strong SERS activity upon photoactivation at 488 nm. A benzoic acid/2-propanol solution was used to demonstrate that the bonding of molecules to SERS active sites at the surface can be followed by investigating temporal changes of the corresponding Raman intensities. Furthermore, the laser-induced structural changes in the silver oxide layers lead to a fluctuating SERS activity at high laser intensities which also affects the spectral features of amorphous carbon impurities.

Thermal lithography for 0.1 μm pattern fabrication

Abstract We have succeeded in patterning narrow lines and dots with 100 nm dimensions in a photoresist film by a ‘thermal lithography’ technique using a semiconductor laser with 635 nm wavelength. The demonstrated resolution of the patterns produced is far beyond the diffraction limit of 530 nm given by our optical set-up. We utilized a focused laser spot, which approximately has a Gaussian profile in its light intensity distribution, to produce a spatially confined hot area in a phase change recording layer on a conventional polycarbonate optical disk. This hot area induced a thermal cross-linking reaction in an adjacent photoresist film. By optimizing the sample rotation speed and the laser power, we were able to confine the area where the thermal cross-linking reaction in the photoresist occurred and patterned extremely fine structures.

Micro-optical nonlinearity of a silver oxide layer

We studied the near-field formation mechanism of a silver oxide thin film sandwiched between protective layers using a pump probe with nanosecond laser pulse irradiation and tapping-mode tuning-fork near-field scanning optical microscopy. A multilayer composed of ZnS–SiO2/Ag2O/ZnS–SiO2 showed abnormal optical nonlinear properties compared to ordinary third-order nonlinear materials. The Ag2O layer played a role in generating a strong light scattering center in a reversible chemical reaction in only a small area of the multilayer, and the optical near field produced about the scattering center was 40 times stronger than that produced by an antimony layer instead of Ag2O.

Magneto-optical disk properties enhanced by a nonmagnetic mask layer

Magneto-optical (MO) recording signals were enhanced by a nonmagnetic mask layer combining a silver oxide (AgOx) thin film and near-field coupled super-resolution. The signal intensity of 300 nm marks recorded by a 680 nm laser and a lens numerical aperture of 0.55 with light-intensity modulation was amplified 100 times in comparison with conventional MO media. Resolution of less than 200 nm was achieved by near-field coupling between a light-scattering center generated in the AgOx film and light polarization of MO marks. To identify near-field enhancement, we simulated electrical field components, finding that near-field coupling between the light-scattering center and a MO layer enhances MO signals about 20 times due to the surface plasmon effect.

Reactive recording with rare-earth transition metal

Reactive recording was achieved with typical rare-earth transition metal (RE-TM) for magneto-optical recording. Almost the same carrier-to-noise ratio (CNR) and much higher modulation were obtained by the reactive recording, compared with conventional phase change (PC) recording. By applying this recording material to a super-resolution near-field structure for terabyte recording, CNR below 100-nm-mark length signal, readout durability, and power margin were greatly improved. To identify the recording mechanism, we examined the magnetic and thermo-optical properties, finding that the film properties of amorphous RE-TM are steeply changed at ∼773 K by crystallization and thermal-activated reaction with dielectric layers.

An alignment system for synchrotron radiation x‐ray lithography

We have developed an alignment exposure system for synchrotron radiation (SR) x‐ray lithography. The present system consists of vertical mask and wafer stages, optics for mask‐to‐wafer displacement detection, a feedback control system, and an aluminum chamber containing them. The chamber is filled with He gas in atmospheric pressure and separated by a 25‐μm‐thick Be window from the SR beam line in ultrahigh vacuum. The alignment method is based on an optical‐heterodyne displacement detection using three diffraction gratings. With 1.0‐μm‐period gratings and a He–Ne transverse‐mode Zeeman laser (wavelength=0.6328 μm), alignment precision better than 0.01 μm was achieved. Features and performance of the system are described.

A new lithography technique using super-resolution near-field structure

We have succeeded in fabricating narrow grooves in a photoresist film by a new lithography technique using an optical near-field with 365nm and 440nm light sources. This technique makes use of super-resolution near-field structure (Super-RENS) which is composed of multilayres to convert a focused laser beam to optical near-field. By this technique, grooves with linewidth of 100-nm-order could be produced beyond diffraction limit at high speed.

Nanoelectronic devices with reactively fabricated semiconductor

The economic fabrication of complete circuits at the nanometer level remains challenging because of the difficulty of connecting nanodevices to one another. Here, we report the electronic nanodevices fabrication method based on the Hall effect including the connection through a thermally activated reaction. By combining incident current and external perpendicular magnetic field in the reactively fabricated memory cell, electronic signal is put in storage. It is suggested that 2.5×109–2.5×1011 (2.5 G–250 G) bits/in.2 capacity flash memory or dynamic random access memory can be fabricated by means of the nanosecond pulse laser or electron-beam-induced reaction.