Sheet resistance of laser-irradiated Ge2Sb2Te5 films prepared by magnetron sputtering was measured by the four-point
probe method. With increasing laser power the sheet resistance underwent an abrupt change of four orders of magnitude
(107→103 Ω/sq) at about 580mW , x-ray diffraction studies of the three samples before, at and after the abrupt point
revealed the phase change process of the Ge2Sb2Te5 thin films from amorphous to crystal states. Optical constants of the
three samples were measured by ellipsometry. Based on the experimental results, the relationship between the electrical /
optical properties and the structure of the Ge2Sb2Te5 thin films is discussed and it is shown that optical-electrical hybrid
data storage may be realized using optical writing and electrical reading.
ASM method is an effective method for disk-type photopolymer high-density holographic storage that has a limited medium thickness. In this paper, the effects of recording angles of ASM method disk-type photopolymer high-density holographic storage on the recording capacity and density are studied theoretically. The calculation and analysis show that the recording density and capacity depend on the recording angles critically whether the spherical wave beam or plane wave beam is used as the reference beam. The results show that no matter spherical wave or plane wave is used as the reference beam the recording density and capacity increases monotonously with the increase of θs when θR is fixed. When the recording angle between two recording beams is large, it has an optimal incidence angle of reference beam to get the maximum recording density and capacity. By using this optimal recording angle we can get 3 - 4 times improvmeent of recording density and capacity.
Green light sensitive acrylamide-based photopolymer system has been prepared. The photosensitive medium was composed of monomer, photoinitiator, charge transfer agents and polymeric film-forming binder. The best Eosin Y, TEA, BAA and AA's concentration were got by optimization of acrylamide-based photopolymers composition. And diffraction efficiency as high as 55% with energetic sensitivity of 60 mJ/cm2 has been obtained in the photosensitive films of 150 μm thickness. The principle of photopolymerization reaction was investigated in the paper, especially the function of charge transfer agents TEA and DPI were studied and we found that there existed a compensation effect between TEA and DPI in the polymerization process of photopolymer.
KEYWORDS: Optical discs, Digital video discs, Optical storage, Data storage, Video, Digital holography, Holography, Compact discs, Image storage, Digital video recorders
Great progress in optical storage has taken place in the last decade. The development of optical discs is always towards higher and higher storage density and data transfer rate in order to meet the ever-increasing requirements of applications in audio, video and image areas. It has been proved a logical and effective approach to employ laser light of shorter wavelength and lenses of higher numerical aperture for increasing storage density, as is shown by the evolution of optical disc from CD family to DVD family. At present, research and development of high density DVD (HD-DVD), blu-ray disc and advanced storage magneto-optical (AS-MO) disc are carried out very extensively. Meanwhile, miniaturization of disc size and use of multiplication techniques to increase the storage density and capacity have already given rise to new formats such as iD Photo disc and Data Play disc as well as multi-layer discs. Digital holographic storage (DHS) disc is also one of the research and development subjects of many companies and research institutions. Some new concept optical storage such as fluorescent multiplayer disc (FMD) is also under intensive development. All these have greatly promoted applications of optical discs in audio, video and image devices.
Ge-Sb-Te phase change thin films are widely used as the recording media in rewritable optical storage. Doping of certain elements into Ge-Sb-Te films is an effective way to enhance their recording performance. In the present work effect of oxygen-doping on the optical constants of Ge-Sb-Te phase change thin films prepared by RF-sputtering were studied in the region of 400 to approximately 800 nm. The results show that the optical constants of the Ge-Sb-Te films change considerably with the doped oxygen content. With the increase in oxygen concentration, the extinction coefficients decrease monotonically. The calculated reflection spectra at normal incidence showed a good agreement with the measured values. With the optimal oxygen-doping, the reflectivity contrast between the crystalline and amorphous states of the Ge-Sb-Te films exceeds 30% throughout the whole visible region. The effect of the strain field induced by oxygen-doping on the optical properties is discussed.
The relationship of Bragg-mismatch and recording angles of holographic photopolymer was deduced, the calculated and experimental results were compared. It showed that the theory tallied with the experiment well. The result indicates that the Bragg-mismatch depends on the recording angles strongly, this result is important to the design of high-density photopolymer holographic memory system.
The use of Ge-Sb-Te films for rewritable optical storage is based on the reversible phase change between their amorphous and crystalline states. Study of the crystallization behavior of the films is very necessary to the optimization of film composition and dopants. This work dedicates our experimental investigation on the crystallization behavior of oxygen-doped Ge-Sb-Te phase change films, which were prepared by RF-sputtering. The crystallization behavior of the thin films was investigated using differential scanning calorimeter (DSC). XRD spectra of the films in the as-deposited and heat-treated states show that the films changed from amorphous to crystalline states due to heat-treatment. By measuring the peak temperature of crystallization at different heating rates we calculated the crystallization activation energies and frequency factors. It was found that the oxygen-doped Ge-Sb-Te sample has a higher value of crystallization activation energy than that without oxygen-doping, it is clear that oxygen-doping can improve the crystallization rate of Ge-Sb-Te phase-change material.
The optical constants of phase-change films are assumed to be constant regardless of film thickness in conventional optical design and thermal simulation of multilayer structure optical disks. However this assumption is not valid when the phase- change film thickness in the optical disks becomes very small. In this study, the dependence of the optical properties on the thickness of AgInSbTe phase-change films was investigated. The reflectivity, absorptivity, thickness and optical constant of the films were measured. The change of the extinction coefficient and refractive index become significant when the film is very thin, and become larger at shorter wavelengths such as in the blue and green region. These results are very useful in improving the accuracy of optical design and simulation of AgInSbTe phase-change optical disks, as well as in the study of phase-change optical disks at shorter wavelengths.
Monolayer Ag-In-Te-Sb-O thin films were deposited by reactive RF-sputtering using Ag8In14Te55Sb23 alloy target in a mixed argon-oxygen plasma at different partial pressure ratio of oxygen to argon (P02/PAr). The optical properties of these films were studied. It was found that films deposited at P02/PAr of 2 to approximately 4% had comparatively large absorption in the wavelength range of 400 - 650 nm. After annealing at 300 degrees Celsius for 30 minutes under protection of argon, the reflectivity in the wavelength range of 500 - 700 nm could rise by about 18 - 25%. The optical constants (n,k) also changed much after heat treatment. XRD analyses indicated that the changes were attributed to the crystallization of Sb. The reflectivity contrast can be as high as 20% after being recorded using short-wavelength laser beam (514.4 nm) with low writing power (10 mW) and short pulse width (100 ns). The film also exhibits certain erasability. This kind of films possess the potentially for use in high density optical storage.
AgInSbTe phase-change films were deposited on K9 glass substrates by RF magnetron sputtering technology using a Ag- In-Sb-Te alloy target. The as-deposited films were annealed at 300 degrees Celsius. The influence of background pressure, sputtering gas pressure and sputtering power on the optical properties of the phase-change films were investigated. It was found that the optical properties of the phase change films were synthetically affected by the sputtering parameters. It is disadvantageous to the optical properties of the films when the sputtering gas pressure and power are too high or too low. Lower background pressure, proper sputtering gas pressure and sputtering power are very important to producing the phase- change films with good properties.
Effects of preparation parameters on the optical constants (n,k) of Ge2Sb2Te5 thin films in the wavelength range of 300 - 830 nm were studied. The results show: (1) When the sputtering power is constant, the refractive index (n) first increases and then decreases with increasing Ar gas pressure, whereas the extinction coefficient (k) changes with Ar gas pressure in a contrary way to that of n. (2) When the Ar gas pressure is constant, for the amorphous thin films in the wavelength range of 300 nm - 500 nm, the refractive index (n) first increases and then decreases with increasing power, whereas the extinction coefficient (k) decreases monotonically. In the wavelength range of 500 nm - 830 nm, the refractive index (n) decreases with sputtering power, while the extinction coefficient (k) first decreases and then increases. For the crystalline thin films, in the wavelength range of 300 nm - 830 nm the refractive index (n) first decreases and then increases, whereas the extinction coefficient (k) decreases. (3) The extent of the influence of preparation parameters on n and k also changes with wavelength, it is greater in the long wavelength region than in the short wavelength region. The mechanism by which the optical constants of the Ge2Sb2Te5 thin films are affected by the preparation parameters is analyzed.
The effects of thermal treatment on the dependence of optical constants on wavelength and the changes of optical constants of GeTe, Sb2Te3 and Ge2Sb2Te5 thin films at different annealing temperatures are studied. It can be found that the optical constants of GeTe, Sb2Te3 and Ge2Sb2Te5 thin films change with increasing annealing temperature. The crystallization speed changes with increasing Sb content, i.e.: the crystallization speed of GeTe < the crystallization speed of Ge2Sb2Te5 < the crystallization speed of Sb2Te3. The mechanism of the change of the optical constants of the GeTe, Sb2Te3 and Ge2Sb2Te5 systems due to thermal treatment is also analyzed.
TiO2 thin films were deposited on glass substrates by the sol-gel process using spin-coating technique. Three kinds of sol systems were used to produce the films which were then baked at various temperatures. Water contact angles of the films were measured using the tilting plate method. The initial water contact angle of an as-prepared film was < 5 degree(s), and after a certain period of placement it started to increase gradually up to a maximum of 72 degree(s). Water adsorption was found to accelerate the increase of the contact angle. Appropriate UV light irradiation could make the high (72 degree(s)) water contact angle of the film return to the initial value, i.e., < 5 degree(s). Films prepared with DEA-chelated precursors have higher speed of increase in the water contact angle than those prepared with AcAc-chelated precursors or without any chelating agent. AFM images showed that the surface roughness of these films were different, suggesting that the surface roughness is another factor affecting the wettability of the films.
New azo dye-doped polymer thin films have been made by spin- coating method on single-crystal silicon substrates. The complex dielectric function and optical parameters of the films have been measured with a fixed angle of incidence automatic spectroscopic ellipsometer. The electronic structure of the films has been explained.
The research and development of high density optical data storage technology has become one of the most important objectives of the current data storage research activities.
Polymer materials show their impact on optical storage technology for developing high information density and fast access-type memories. A new push-pull azo dye-doped polymer material has been developed by a spin coating process and used for write-once optical media in this paper. The absorption spectrum of the spin-coated thin film show a strong and broad absorption region at the 400 - 550 nm, which matched with the wavelengths of Ar-laser. The optical recording performance of the azo dye-doped polymer thin film show that higher reflectivity contrast can be obtained at lower writing power and writing pulse width using an Ar- laser (514.5 nm) irradiation.
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