Donghong Gu

Optical recording performance of thin films of phthalocyanine compounds

Abstract As organic dyes with excellent thermal and light stability, phthalocyanine compounds have been investigated as write-once read-many optical recording materials. By selecting different substituents and metallic ions, the absorption bands of thin film of phthalocyanine compounds were matched with the wavelengths of semiconductor lasers. It was found that the absorption regions of vacuum sublimated thin films of vanadyl phthalocyanine (VOPc), tetra-pentyloxy phthalocyanine vanadyl (TPPcVO) and tetra-nonyloxy phthalocyanine vanadyl (TNPcVO) were between 580 and 850 nm. In the near-IR region, the absorbance and reflectivity of thin films of VOPc were greater than 50% and 20% respectively. The static optical recording test of the VOPc thin film showed that the write power was less than 10 mW with the write pulse width of 200 ns using an He-Ne laser as light source. The dynamic optical recording test of VOPc as a write-once read-many recording material on a 5.25 in optical disk indicated that the carrier-to-noise ratio (CNR) was greater than 45 dB.

Optical and recording properties of copper phthalocyanine films

Abstract Vacuum-sublimed films of copper phthalocyanine (CuPc) were prepared. The absorption spectrum and optical constants of the film were studied. It was found that there is a comparatively large absorption region at wavelength of 550 – 750 nm. A static optical recording test on a CuPc film on a glass substrate indicated that low power HeNe laser irradiation could initiate a relatively large reflectivity change. It has been observed that the introduction of a metallic reflective layer on the recording layer will raise the writing threshold energy and the maximum reflectivity contrast.

Synthesis and optical properties of an azo metal chelate compound for optical recording medium

Abstract An azo nickel chelate compound has been synthesized. Smooth thin films have been prepared by spin-coating. The absorption, transmission and reflection spectra of the films were measured. The optical constant (complex refractive index N = n + ik ) of the film on single-crystal silicon has been determined using scanning ellipsometer, and the complex dielectric function ( e ) as well as absorption coefficient ( α ) were then calculated. The optical recording medium was prepared by spin-coating on a PC substrate with aluminium as reflective layer. Dynamic optical recording test of the disc showed that the carrier-to-noise (CNR) of 45dB was obtained.

Metallized thiazolylazo dyes as optical recording materials

Abstract A series of metallized thiazolylazo dyes have been designed and synthesized. Smooth films on optical glass and single-crystal silicon were prepared using the spin-coated method. The UV-Vis absorption spectra of the dyes were measured in solution and in films. The optical constant (complex refractive index N = n + ik ) of the films on single-crystal silicon has been determined using a scanning ellipsometer. The variation of the complex refractive index, N , with wavelength, λ , was obtained. From the value of n , k and the thickness of the dye films, the variation of the reflectance vs dye film thickness was then calculated. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the nickel thiazolylazo dye showed a clear threshold of thermal decomposition with a sharp exothermic park. Static optical recording tests were carried out. The results show that the nickel thiazolylazo dye is more suitable for use in short-wavelength diode-laser optical recording.

Synthesis and optical properties of axially bromo-substituted subphthalocyanines

Subphthalocyanines (SubPc) are composed of three iso-indole units containing boron inside, which defines a molecular axis and forms a cone-shaped structure. Despite being non-planar, they show a delocalized 14π-electron system similar to that present in phthalocyanines. The attractive characteristics of SubPc are their chemical stability and thermal stability. In this paper, we report here the synthesis of five SubPc compounds, in which the axial substituent is a bromide. The peripheral substituent in the compounds leads to an improved solubility in common organic solvents such as ethanol and chloroform etc. The spectral and optical properties of these compounds were studied. The spectra and optical constants (refractive index, extinction coefficient) of the sublimed films of these SubPcs were measured by a spectrophotometer and an ellipsometer respectively. We also measured the static optical recording performance of these films with a thin Al (or Ag) reflective layer on them. These results demonstrated that SubPc showed a strong and broad absorption region near 600 nm and it will be a promising candidate for short-wavelength optical recording (such as DVD-R), if high-quality films can be got.

Ellipsometric spectra of cobalt phthalocyanine films

Abstract The ellipsometric spectra of vacuum sublimed cobalt phthalocyanine (CoPc) thin films on single-crystal silicon were studied on a new type of scanning photometric ellipsometer in which the analyser and polarizer rotate synchronously. The complex dielectric function and optical constants of the film have been obtained in the wavelength range 550–800 nm. It has been found that there is a comparatively large absorption region at 600–750 nm for the vacuum sublimed CoPc film and the exciton coupling greatly influences its absorption spectrum.

Spectroscopic and optical properties of an azo-metal chelate dye as optical recording medium

Abstract The spectroscopic, optical and thermal properties of an azo-nickel chelate dye have been studied in solution and in thin films. Complex formation constant of the compound was evaluated spectroscopically in methanol. The optical constant (complex refractive index N = n + ik ) of the film on single-crystal silicon has been determined using scanning ellipsometer and the complex dielectric function e as well as absorption coefficient α were then calculated. Thermal decomposition with a sharp exothermic peak was observed. The optical recording medium was prepared by spin-coating on a PC substrate with aluminum as reflective layer. Dynamic optical recording test of the disc gave a value of carrier-to-noise (CNR) of 45 dB, indicating that the azo-metal chelate dye is a promising candidate for use as optical recording medium.

Comparison of two types of phthalocyanine thin films

Thin films of TNPPcZn (tetra-neopentoxy phthalocyanine zinc) were prepared by methods of spin-coating and vacuum evaporation. The absorption spectra and X-ray diffraction of both types of thin films were measured at various temperature or after annealing at various temperature. Phase changes were found in the TNPPcZn spin-coating film while the evaporating thin film hardly showed any changes.

Scanning tunneling microscopy observations of recorded organic thin films

Scanning tunneling microscopy (STM) was used to observe recorded areas of an organic optical recording medium. Microarea morphology images show that bubbles emerge after laser irradiation of phthalocyanine films. It is demonstrated that STM is a very useful tool to understand the performance of an optical disc.

Write-once medium with BiOx thin films for blue laser recording

BiOx films are prepared by reactive direct current (DC) magnetron sputtering from a metallic bismuth target in Ar + O2 with different O2/Ar ratios. It is found that the optical property of BiOx films is sensitive to O2/Ar ratios and the films deposited at O2/Ar ratio of 0.5 have the best reflectivity contrast under the same conditions. The structure and optical characteristics of the films are studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectrophotometer. As revealed by investigations, the phase transition is mainly responsible for the change of optical properties. The static test results indicate that the BiOx films have good writing sensitivity for blue laser beams. A high reflectivity contrast of about 52% at a writing power of 11 mW and writing pulse width of 800 ns is obtained. In addition, the films demonstrate good stability after being read for 10000 times.