Mutsuo Takenaga

Preparation and characteristics of Li2B4O7 : Cu phosphor

Abstract Li 2 B 4 O 7 : Cu crystal phosphor prepared by a sintering method was found to have the most promising characteristics for use as TLD, i.e., a TL emission band at 368 nm and a moisture resistant property.

TeOx thin films for an optical disc memory

Tellurium suboxide thin films TeOx were found to change in refractive index and extinction coefficient on thermal or optical heating, with accompanying changes in the reflectivity and transmission. The preparation method and thermal or optical properties of the TeOx thin films were investigated to obtain a stable and highly sensitive optical disc memory. A two‐source evaporation method using Te and TeO2 provided uniform and any desired composition. The properties of the film depended on the x value; increasing x to as large as x=1.2, which represents a Te‐poor composition, produced an excellent humidity and heat stability, and decreasing x to 0.8 made the film more sensitive to a laser diode, but susceptible to humidity. The TeO1.1 thin film was found to sufficiently satisfy all requirements for practical disc applications. A reflective optical disc was prepared using the TeO1.1 thin film deposited on a polymethylmethacrylate substrate with grooves for optical tracking. This disc is capable of recording v...

Thermal changes of optical properties observed in some suboxide thin films

Suboxide thin films of SbOx, TeOx, MoOx, and GeOx (x is smaller than the stoichiometric value for each component) were found to have the property of showing a critical change in their absorption coefficients and refractive indices at elevated temperatures. The thin‐film samples were prepared by evaporating a mixture of the stoichiometric oxide powder and a deoxidization metal powder such as tungsten. The critical temperatures of these thin films are 150, 120, 150, and 280 °C, respectively. The absorption coefficients before and after the heat treatment are 2.5×104 (before) and 6.1×104 (after), 8×104 and 1.0×105, 5.6×103 and 1.1×104, and 4.9×104 and 1.8×105 cm−1, respectively. Their refractive indices are 1.8 (before) and 1.9 (after), 3.1 and 3.5, 1.8 and 2.1, and 2.5 and 2.8, respectively. As determined by x‐ray diffraction analysis, these thin films are composed of very small metal grains and stoichiometric oxide grains. The thermal changes accompanied by the optical constant changes are mainly due to st...

An ESR study of thermoluminescent processes in CaSO4 phosphors

Abstract The mechanism of TL of CaSO 4 : Tm is discussed through the investigation of thermal decay of radical ions which were detected by single crystal ESR measurements.

Te-Ge-Sn-Au Phase Change Recording Film For Optical Disk

Te-Ge-Sn-Au thin films were studied for phase change type rewritable disk media, in order to obtain the fast crystallization speed and the thermal stability. Films were prepared by co-evaporation method. It was found that through static record/erase measurements the threshold crystallizing pulse duration of Te60Ge4SnllAu25 film was only 1 usec at 2 mW of laser power; that is less than one tenth compared with that of Te80Ge5Sn15 film, while the threshold amorphizing laser power of them were almost the same, 6 mW at 0.2 psec of pulse duration regardless of Au concentration. Its crystallizaton temperature of about 130°C was enough to maintain the good thermal stability. Through DSC, X-ray and electron diffraction studies, the first appeared crystalline state in crystallization process, corresponding to the drastic change in optical property, showed only one phase of metastable simple cubic(SC) structure. It was concluded that the appearance of the SC structure made the crystallization speed higher. The obtained thin film was a candidate for the simultaneously erasable and recordable material.

New Optical Erasable Medium Using Tellurium Suboxide Thin Film

A suboxide thin film of TeOx ( x is smaller than the stoich.Lometric value ) containing a small amount of additives of such metals and semimetals as Sn and Ge has been found to have the property of showing a reversible change in its optical constants when the film was exposed in turn to two diode laser spots with different sizes, and this property can be utilized for an erasable disc. For recording, a TeOx thin film deposited on a PMMA substrate is irradiated by a diffraction limited laser spot, 0.8 pm in dia., modulated in response to an input electrical signal. This causes a micro-sized area of the film to be suddenly heated and rapidly quenched, resulting in a decrease in optical reflectivity. This recorded bit can be erased at real time by the irradiation of a diffused laser spot to an elliptical shape, 1 x 10 pm, by which the bit recovers its optical properties. An optical head having the two laser beams, one for recording/playback and one for erasing, has been developed. Real time erasing and recording at the same time has been achieved for a video signal. In excess of a million record/erase cycles have been demonstrated with no significant degradation in playback signal quality or erasability. Carrier-to-noise ratio, C/N, was more than 55 dB at 5 MHz, 30 kHz bandwidth.

Sub-Oxide Thin Films For An Optical Recording Disk

Thin films of SbOx, GeOx, TeOx, MoOx, InOx and PbOx ( x is smaller than the stoichiometric value for each component ) were found to have a feasibility to be applied to an optical recording disc. Upon heating, these thin films are critically changed in their optical constants at 150°, 280°, 120°, 150°, 120° and 100°C, respectively. The contrast ratios before to after heat treatment of the GeOx, TeOx and MoOx films of 1000 - 2000 Å thick are very high, they are 50, 20 and 15, respectively. Among them, the TeOx (x ≈1.1) film was excellent in both the sensitivity and the contrast ratio, and an optical recording disc was prepared by depositing the TeOx on a PMMA disc, substrate. Video-signals can be recorded and played back using a laser diode (λ =8300 Å, N.A.= 0.5) at the laser power of 6 - 8 mW incident. The carrier to noise ratio at 5 MHz was in excess of 55 dB.

Laser diode beam exposure instrument for rapid quenching of thin-film materials

An extremely rapid heating and quenching instrument for thin‐film materials was prepared, which established a quenching speed of 1011 K/s for a 20‐nm GeSbTe film. It contains a thin‐film device part and a laser diode/electro‐optical section; the former is composed of the thin film which absorbs 830‐nm laser light sandwiched between a transparent and highly heat‐conductive ZnS‐SiO2 mixture layer. It is designed to produce a high‐temperature gradient between the two layers at the moment of laser exposure. In the latter, the laser beam is designed to be automatically focused with a half‐value width of 1 μm at the thin‐film surface to be heated. The beam exposure condition is variable: the pulse width 10 ns–10 μs, and the beam power amplitude, 0.5–30 mW. The reflectivity of the beam exposure part can be monitored in situ during the exposure as well as before and after the exposure using the same laser diode.

New Write-Once Media Based On Te-Te02 For Optical Disks

Thin film media composed of Te-Te02 (TeOx) containing Pd additive was found to have a feasibility of being applied to high reliability data file optical disks. The carrier to noise ratio (C.N.R.) exceeds 56 dB at 1,200 r.p.m. disk rotation. The response time of saturation amplitude after a pulsed laser power irradiation was less than 300 nsec and is able to apply to high speed read verify systems. From acceleration environmental stress test results, no defect variation was observed. By the Arrhenius plot method, the disk life has been estimated to be more than 10 years at the storage environment 32 degree C, 80 %RH. The recording and degradation mechanism will be also discussed.

Lithium Borate Activated with Copper and Silver for TLD

Lithium borate (Li2B4O7) is known as one of the most promising thermoluminescence materials because of its low dependence on photon energy. A new phosphor, Li2B4O7 activated with copper and silver (0.02_??_Cu, 0.02_??_Ag), has been developed and found to have the following thermoluminescence characteristics.(1) Its thermoluminescence emission bands lie in the near ultraviolet region; a dominant peak appears at 368 mμ (by Cu) and another smaller one at 268 mμ.(2) The main thermoluminescence glow peak appears at 185°C (by Ag), and another smaller one at 110°C.(3) The thermoluminescence output detected by a widely used photomultiplier (1P21) is about 3 times larger than that of Li2B4O7: Mn, and the expoure response is linear in an exposure range from 10 mR to 300R.(4) Fading is less than 9% in 2 months.