Write-once Optical Recording Research Articles

Preparation and Characterization of Tin Tungstate Thin Films

Tin tungstate thin films were prepared by dc magnetron sputtering method and studied by x-ray diffraction, confocal microscopy and Raman spectroscopy. It is shown that the films are composed mainly of nanocrystalline α-SnWO4 phase. The possibility to use these films as write-once optical recording media is demonstrated.

Electrical Resistivity and Application of Cu<sub>3</sub>N Thin Films

The paper mainly reviewed the electrical resistivity and application of Cu3N thin films. The electrical resistivity increases from 2×10-5Ω•cm to 2×102Ω•cm. The application of Cu3N thin films as write-once optical recording materials and anode material for Li-ion rechargeable batteries was also presented.

Write-Once Optical Recording Property of Amorphous WO<sub>3</sub> Thin Film and its Relative Mechanism

Write-once optical recording property of the amorphous WO3 (a-WO3) thin film prepared on the glass substrate by thermal evaporation deposition, has been demonstrated by focusing the laser of 514.5 nm with a variable power to a spot with a size of 1-2μm in diameter on the surface of thin film. The mechanisms responsible for the refractive index change of thin film after the laser recording, has also been studied by monitoring the Raman signal change with the increase of the incident laser power, and by characterizing the micro-structures of the pits induced by laser irradiation. As a result, two mechanisms, the laser-induced phase transition and the laser-induced micro-explosion, are proposed to be responsible for the write-once optical recording.

Phase-Change Kinetics of Bi–Fe–(N) Layer for High-Speed Write-Once Optical Recording

In this work, we present the phase-change kinetics of Bi–Fe–(N) layers for write-once optical recording. In situ reflectivity measurement indicated that the phase-change temperature (Tx) of the Bi–Fe–(N) layers is strongly related to the heating rate. The Tx's were about 170 °C at low heating rates and approached the melting point of the Bi phase (i.e., 271.4 °C) at high rate of heating provided by laser heating. For a 100-nm-thick Bi–Fe–(N) layer, Kissinger's analysis showed that the activation energy of phase transition (Ea) = 1.24 eV, while the analysis of isothermal phase transition in terms of the Johnson–Mehl–Avrami (JMA) theory showed that the average Avrami exponent (m) = 2.2 and the appropriate activation energy (ΔH) = 5.15 eV. With the aid of X-ray diffraction (XRD) analysis, a two-dimensional phase transition behavior in the Bi–Fe–(N) layers initiated by the melting of the Bi-rich phase was confirmed. For optical disk samples with optimized disk structure and write strategy, the signal properties far exceeding the write-once disk test specifications were achieved. Satisfactory signal properties indicated that the Bi–Fe–(N) system is a promising alternative for high-speed write-once recording in the Blu-ray era.

Phase-Change Kinetics of Bi–Fe–(N) Layer for High-Speed Write-Once Optical Recording

Phase-Change Kinetics of Bi–Fe–(N) Layer for High-Speed Write-Once Optical Recording

Confocal spectromicroscopy of amorphous and nanocrystalline tungsten oxide films

A Raman confocal spectromicroscopic system was used to study in situ phase composition and surface morphology in amorphous and nanocrystalline tungsten oxide and tungstate thin films, prepared on silicon and glass substrates by dc magnetron co-sputtering technique. The possible use of these films for the phase-change optical recording was demonstrated using 442 nm He–Cd laser with a variable power of up to 50 mW. The formation of nanocrystalline tungsten trioxide or tungstate phases was observed under the laser irradiation. These nanocrystalline phases show relatively strong Raman activity, which can be used for information reading purposes. A multilayer structure composed of several tungstate films with different chemical composition is proposed as potential write-once optical recording media.

Reactive DC magnetron deposition of copper nitride films for write-once optical recording

Copper nitride (Cu x N) films were prepared on glass slides by reactive direct current (DC) magnetron sputtering under different nitrogen flow rates and substrate temperature, respectively. X-ray diffraction and reflectance spectra were employed to characterize the films. The Cu x N films can completely decompose through heat treatment at temperature as low as 160 °C. The reflectance spectra of the as-deposited films are quite different from that of the decomposed films in a wide wavelength range from UV to infrared. Its relatively low decomposition temperature and large reflectance change before and after decomposition makes it a potential write-once optical recording medium.

Write-once optical recording using WO 2 films prepared by pulsed laser deposition

WO 2 films were deposited onto the glass substrates (Corning #7059 with an area of 26 × 38 mm) by the pulsed laser deposition method using an ArF excimer laser. It was found that after annealing at 500 °C for 10 min, the film thickness became 1.9 times compared with that (approximately 40 nm) in the as-deposited state. At that time, the difference in the transmittance, ΔT, between the annealed state and the as-deposited state was about 70% at the wavelength of 405 nm. From the XRD and XPS spectra, it was considered that oxygen was absorbed into the tungsten oxide films through the annealing process, accelerating the formation of WO 2 or WO 3 structure which caused the incremental effect in the transmittance and the expansion effect in the film thickness. For the revolution-test of the sample without the protection layer in which the WO 2 films were deposited upon the digital versatile disk (DVD-R) substrate, a write peak power dependence of CNR (at λ = 405 nm, NA = 0.65) of 3T signal (58.5 MHz) was measured at a linear velocity of 5 m/s and a read power of 0.6 mW. The values of CNR of 35 ∼ 40 dB were obtained at the peak power of 5 ∼ 7 mW, and increased largely up to 60 dB at 8 mW, and then reached a maximum of 62 dB at 8.5 mW. After that, the values of the CNR suffered some deterioration at more than 9 mW because of too much expansion of the written dot by which the portion between the dot and neighbor dots became to be invaded. For the dots formed in the writing performance on the DVD-R disk, the expansion effect in direction along the groove or over the neighboring lands was recognized by SEM images. It was found that bits of 0.18 ∼ 0.30 μm size, corresponding to the maximal storage capacity of 25 GB in the ‘Blu-ray disk’ specification, were made.

Spinel oxides thin films for write-once optical recording with blue laser sources

Spinel oxides thin films for write-once optical recording with blue laser sources

Optical Recording Properties of a Novel Subphthalocyanine Thin Film

A novel bromoboron trinitro-subphthalocyanine (BTN-SubPc) thin film has been developed for write-once optical recording by vacuum evaporation. The spectral and optical properties of the film are studied. Some information may be useful when dealing with recording applications, such as uniformity and anisotropy of this film are given. The optical recording performance of the BTN-SubPc thin film shows that high reflectivity contrast (>30%) can be obtained at low writing power (10 mW) and short writing pulse width (300 ns) using He–Ne laser (632.8 nm) irradiation. For this kind of thin film, lower recording energy is needed to get higher or equivalent reflectivity contrast when compared with some MPc and cyanine (for commercial use) films studied previously. These results indicate the great potential of SubPc in short-wavelength optical recording applications, especially as recording medium of DVD-R.

Metal and metal oxide thin films for write-once optical recording media

Metal and metal oxide thin films for write-once optical recording media

Thermal and optical characterization of push–pull azo dye-doped poly(methylmethacrylate) thin film as short wavelength optical recording media

A new push–pull azo dye-doped polymer material has been developed for short wavelength write-once optical recording by means of a spin-coating process. The absorption spectrum of the spin-coated thin film shows a strong and broad absorption region at 400–550 nm, which matches well with the wavelength of the Ar + laser. Thermal properties indicate that the rapid decomposition of the azo dye is in the narrow temperature range. The optical recording performance of the azo dye-doped polymer thin film shows that higher reflectivity contrast (>25) can be obtained at lower writing power and writing pulse-width using Ar +-laser (514.5 nm) irradiation. These results show that the single-layer thin film of azo dye-doped poly(methylmethacrylate) is a promising candidate for short wavelength optical recording.

Optical Storage Properties of Novel Azo Dye-in-Polymer (PMMA) Thin Films

A new write-once optical recording medium (azo dye-in-poly(methylmethacrylate) film) is reported. Optical and thermal properties of the azo dye and its films are studied. The azo dye prepared has a strong absorption band at 461 nm. The azo dye-in-polymer film made by the spin coating process has a strong and broad absorption band, and the reflectivity is greater than 10% in the visible region, which matches well with the wavelength of the argon-ion laser. The aggregate state of the azo dye molecules greatly influences its absorption spectra. The electronic structure of the film has been explained. The reflectivity contrast of the film is more than 30% at writing power (13.3 mW) and writing pulse width (600 ns) using an argon-ion laser operating at 514.5 nm, and the film has sharp thresholds for optical recording.

Copper nitride and tin nitride thin films for write-once optical recording media

The feasibility of using copper nitride and tin nitride thin films as write-once optical recording media was explored. The Cu3N and SnNx films were obtained by the reactive sputtering method. They were thermally decomposed into Cu and Sn films at 470 and 550 °C, respectively. The Cu film obtained by the thermal decomposition showed a large difference in reflectance which is applicable to the optical recording media. The Sn film obtained by the thermal decomposition included SnO, and consequently it showed a small difference in reflectance from that of SnNx film.

Mixing kinetics and write-once optical recording characteristics of Sb/Se bilayer films

Bilayer Sb/Se films are irradiated with 12 ns pulses from an ArF laser (extended areas) and from a focused Ar+ laser (micron-sized areas). Real-time reflectivity measurements are used to determine if the process occurs within the solid or liquid phase and the transformation time, in addition to measure the optical contrast and the medium sensitivity. Transmission electron microscopy is used to analyze the structure of the transformed areas and the medium resolution. The results show that mixing is initiated by preferential melting at the grain boundaries and an amorphous phase is produced upon irradiation at high energy densities. Finally, the characteristics of the mixing process in Sb/Se films as a write-once optical recording mechanism are discussed in terms of the sensitivity and resolution of the recorded spots and the time required for recording.

Mixing kinetics and write-once optical recording characteristics of Sb/Se bilayer films

Mixing kinetics and write-once optical recording characteristics of Sb/Se bilayer films

Cu3N Thin Film for a New Light Recording Media

Copper nitride thin films were prepared by using the ion-assisted deposition in which accelerated nitrogen ions were irradiated during the deposition of copper metal. The degree of nitrification of the film was controlled by changing the ion current density. The reflection coefficient of the prepared copper nitride films decreased with the increase of the ion current density. The reflection coefficient was about 30% at 780 nm wavelength, and it recovered to 70% after the film was heated at 300°C. The preliminary experiment of write-once optical recording of this film was carried out, and the viability of its practical use in new media was confirmed.

Stability of Te–Cu amorphous alloy thin films for optical recording

We have studied the structure and optical stability of Te–Cu thin film alloy candidates for write-once optical recording. Films prepared by rf diode sputtering with 20–50 at. % Cu are amorphous, as-sputtered. One of these, Te65 Cu35 , has a relatively high crystallization temperature (150 °C), as determined by x-ray diffraction. Near the eutectic composition (∼29 at .% Cu), alloy films have stable optical properties after accelerated aging at 60 °C and 85% relative humidity. The mechanism for film stability near the eutectic was studied by x-ray photoelectron spectroscopy and depth profiling using ion scattering spectroscopy. We found that a Cu-enriched surface oxide, formed at ambient conditions, passivates the film and is responsible for its subsequent stability after accelerated aging. We also demonstrated that a 14 in. diam, multilayer optical disk with a Te65 Cu35 recording medium exhibits excellent linearity for 3 and 8 MHz pulses, good written pulse length stability, and high signal-to-noise ratio. Thus, a Te–Cu recording medium can effectively use run-length-limited codes, which allow very high data storage capacity and data transfer rates.