Wei Chih Lin

Probing the near fields of the super-resolution near-field optical structure

Super-resolution near-field structure, glass/SiN (170 nm)/Sb (15 nm)/SiN (20 nm), a promising structure for near-field ultrahigh-density optical data storage, has been studied by a tapping-mode tuning-fork near-field scanning optical microscope in transmission mode. Both propagating and evanescent field intensities were found at the focused spots of the surface of the super-resolution near-field structure. Images of the near-field intensity gradients at different excited laser powers (0.42–2.43 μW) showed that the area of the static evanescent intensity could be stably controlled. The enhancement of the near-field intensity, and the reduction of the focused spot through the super-resolution near-field structure, glass/SiN (170 nm)/Sb (15 nm)/SiN (20 nm) have been observed.

Near-field images of the AgOx-type super-resolution near-field structure

As a promising disk structure for ultrahigh density optical data storage, super-resolution near-field structure of AgOx type has been studied by the tapping-mode tuning-fork near-field scanning optical microscope as well as the transmission electron microscope. This structure presents strong near-field intensity enhancement and nonlinear optical effect, compared with the ordinary material. Numerical calculations confirm that the localized surface plasmon and the nonuniform material structures are the main causes for these unusual characteristics.

Fabrication of phase-change chalcogenide Ge2Sb2Te5 patterns by laser-induced forward transfer.

Femtosecond laser pulses are focused on a thin film of Ge2Sb2Te5 phase-change material, and the transfer of the illuminated material to a nearby substrate is investigated. The size, shape, and phase-state of the fabricated pattern can be effectively controlled by the laser fluence and by the thickness of the Ge2Sb2Te5 film. Results show multi-level electrical and optical reflection states of the fabricated patterns, which may provide a simple and efficient foundation for patterning future phase-change devices.

Study of a Super-Resolution Optical Structure: Polycarbonate/ZnS–SiO2/ZnO/ZnS–SiO2/Ge2Sb2Te5/ZnS–SiO2

A new super-resolution near-field optical structure was demonstrated. The structure, polycarbonate/ZnS–SiO2(130 nm)/ZnO(15 nm)/ZnS–SiO2(30 nm)/Ge2Sb2Te5(15 nm)/ZnS–SiO2(20 nm), has the ability in recording the small marks beyond the diffraction limit. At a readout power of 5 mW, the carrier to noise ratio (CNR) of more than 33 dB was measured for the recorded marks with the size of 100 nm by a digital versatile disc (DVD) tester. Transmission electron microscope (TEM) images of such structure displayed local orderly nanograins in 15 nm ZnO thin film. Ensemble effects of these ZnO nanostructures of the active layer are the key of the near-field super-resolution.

Fast fabrication of a Ag nanostructure substrate using the femtosecond laser for broad-band and tunable plasmonic enhancement.

Using a femtosecond laser, we have transformed the laser-direct-writing technique into a highly efficient method that can process AgO(x) thin films into Ag nanostructures at a fast scanning rate of 2000 μm(2)/min. The processed AgO(x) thin films exhibit broad-band enhancement of optical absorption and effectively function as active SERS substrates. Probing of the plasmonic hotspots with dyed polymer beads indicates that these hotspots are uniformly distributed over the treated area.

Dynamic Aperture of Near-Field Super Resolution Structures

Direct experimental observation of the near-field aperture formed in the super resolution near-field structure of glass/SiN(170 nm)/Sb(15 nm)/SiN(20 nm) has been achieved using a tapping-mode tuning-fork near-field scanning optical microscope. Both propagating and evanescent field intensities were found at the focused spots of the surface of the super resolution structure. Images of the near-field intensity gradients at different excited laser powers (0.45–2.33 µW) demonstrated that the area of the static evanescent intensity could be stably controlled.

Implementation of Practical Super-Resolution Near-Field Structure System Using Commercial Drive

The implementation of a practical super-resolution near-field structure (Super-RENS) system using an existing commercialdrive is achieved. Using ZnO-type Super-RENS discs as storage media, the commercial drive can perform mark positionrecording at a mark size of 220nm and correctly retrieve the recorded signal. [DOI: 10.1143/JJAP.45.1383]

Study of optical recording bits by scanning surface potential microscopy

We demonstrate a convenient method for the determination of recording bits in phase-change media based on scanning surface potential microscopy using a conductive tip. Commercially available digital versatile disks(DVD)±rewritable(RW) with initialization process are measured in experiments. The minimum size of the recording bits of DVD+RW, written by a commercial recorder, is around 425.22 nm. The mean work function (WF) value of the recording layer is found to be 4.27 eV from the contact potential difference images. After writing by a read∕write disk tester, the mean WF value of the amorphous bits has a drop of 15.46 meV. The results indicate that surface electronic energy of recorded regions is raised due to the writing process.

Calculation of Surface Plasmon Effect on Optical Discs

We calculated the conditions of surface plasmon resonance for various optical discs to evaluate the role of periodic lands and grooves or recording mark trains as grating couplers. With the typical parameters of structure used in the discs, it is shown that surface plasmons have a weak influence on ordinary optical discs. These results differ from the situation with super-resolution near-field optical structures where surface plasmons or localized surface plasmons have a considerable influence on such discs.

The size effect in the AgOx-type super-resolution near-field structure

Abstract To understand the mechanism of AgOx-type super-resolution near-field structure (Super-RENS), the size effect is studied by using the photoacoustic measurement. The absorption spectra for AgOx-type Super-RENS with different thickness are obtained, and the blue shift of the peak position of absorption spectra is successfully observed as the size of the silver particles or clusters in the AgOx layer is decreased.