Browsing by Author "Liu, JR"

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Analysis of size distributions of type IIZnTe/ZnSe quantum dots
(2004-12-01)
Lee, J
;
Yang, CS
;
Chang, CT
;
Liu, JR
;
Chou, WC
The photoluminescence (PL) spectrum of the ZnTe/ZnSe quantum dot (QD) structure which has a type II band alignment. was investigated. A broader structure peaking at 2.180 eV together with the features of the ZnSe buffer layer located at 2.820 eV in the PL spectrum at 10 K were observed. The broadness of the PL attributes to the spatial inhomogeneity of the QD sizes. The PL spectrum was a normal distribution with a variance of 0.002 eV(2). However, the dot size distribution was a deformed Gaussian. Using only one set of data of dot size distribution measured by the Atomic Force Microscopy (AFM), the statistical estimates with standard errors were evaluated using the bootstrap methodology. The probability distribution was inferred by calculating the means, percentiles and correlation coefficients of the base diameter and the height of the QDs. We concluded that the dot distributions were indeed a deformed Gaussian and the correlation coefficient of the diameter and the height of the QDs was 0.49 +/- 0.01. The uniformity of the dot size distribution was poor. To infer the dot size distribution from the PL spectrum, we numerically solved the Schrodinger equation by elaborating on the orthogonal periodic functions (OPF) approximation for the type II lens shaped QDs. The convergence of the probability density was discussed in a great detail. We found that the band edge discontinuities inside the dot acts as a barrier with DeltaE(v) = 315 meV for the conduction band and as a well with DeltaE(v) = 735 meV for the valence band. In the AFM measurement, the offset in dot height is 14 Angstrom and the aspect ratio is 0.04. We employed the Schrodinger equation to correlated the PL spectrum (intensity versus optical energy) to the AFM data (number of QDs versus dot size) and the agreement was excellent. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Effects of aperture wall on the readout signal of erasable thermal phase change super resolution (EPSR) disks
(1999-03-01)
Liu, JR
;
Lu, YS
;
Tien, CH
;
Tang, NY
;
Shieh, HPD
A "below-diffraction-limited" aperture within the readout spot for high-density recording can be achieved on erasable thermal phase change super resolution (EPSR) disks. Compared to the large aperture wall formed by the DC detection method, the small aperture wall formed by pulse readout can not only increase the signal amplitude, but also suppress readout noise when detecting the EPSR disks. The small aperture wall width generated by pulse readout in the EPSR disk resulted in an 8 dB higher in carrier-to-noise (CNR) than that by DC readout in the conventional single-recording-layer phase change disk when reading the below-diffraction-limited marks of 0.4 mu m.
Effects of initialization conditions on erasability of phase change optical disks
(1998-03-01)
Liu, JR
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
Effects of initialization conditions of initialization power and number of initialization cycles on the recording properties of phase change optical disks were studied It is found that initialization conditions affect erasability but have little effect on carrier-to-noise ratio of phase change optical disks. The initialization conditions also affect bias power margin. Erasability of more than 20 dB and carrier-to-noise ratio of 54 do with 4 mW bias power margin were obtained by applying 6 mW of initialization power and 5 initialization cycles.
Erasable phase change disks with super resolution capability by pulse-readout
(1998-05-01)
Liu, JR
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
Erasable thermal phase change super resolution (EPSR) disks composed of mask and recording layers can be Fabricated with a "below-diffraction-limited": aperture within the readout spot to achieve optical super resolution. The formation of the aperture and the readout signal on the EPSR disk were analyzed. The feasibility of the designed EPSR disks was evaluated by thermal simulation. A carrier-to-noise-ratio (CNR) of 32 dB at mark size of 0.4 mu m, 8 dB higher than that in a conventional disk, was obtained by applying pulse-readout to the EPSR disks at a wavelength of 780 nm and numerical aperture of 0.55.
Initialization characteristics and their effects on the erasability of phase change optical disks using transmission electron microscopy
(1999-03-01)
Chen, HW
;
Hsieh, TE
;
Liu, JR
;
Shieh, HPD
;
材料科學與工程學系
We investigated the microstructure of phase change optical disks subjected to various initialization conditions using transmission electron microscopy (TEM). The effects of initialization powers on the erase ratio of phase change optical disks and corresponding microstructure changes were also studied. It was found that the increase of initialization power enlarged the width of the recrystallization band formed in the recording media of the disk. A wide recrystallization band was effective for decreasing the residual signal level hence the erase ratio increased. Disk dynamic test and TEM study results also revealed the deterioration of carrier-to-noice ratio (CNR) characteristic and the increasing trend of erase ratio was reduced when a substantial amount of coarse grains appeared in the crystalline region. This elucidates the necessity for phase change optical disks to have good heat dissipation property in order to suppress the formation of coarse granular structures.
Interface wall energy in exchange-coupled magneto-optical recording films
(1997-05-01)
Hwang, WK
;
Liu, JR
;
Shieh, HPD
;
交大名義發表
;
光電工程學系
Exchange-coupled double-layered (ECDL) films were adopted to increase density of magnetically induced superresolution (MSR) media by using center aperture detection scheme, and to improve sensitivity of switching field simultaneously. A carrier to noise ratio of 40 dB was obtained at 0.5 mu m recording marks produced by a switching field of 75 Oe. Temperature dependence of interface wall energy affects recording/playback characteristics of ECDL MSR disks considerably.
Interface wall energy in exchange-coupled magneto-optical recording films
(1997-05-01)
Hwang, WK
;
Liu, JR
;
Shieh, HPD
;
光電工程研究所
;
Institute of EO Enginerring
Exchange-coupled double-layered (ECDL) films were adopted to increase density of magnetically induced superresolution (MSR) media by using center aperture detection scheme, and to improve sensitivity of switching field simultaneously. A carrier to noise ratio of 40 dB was obtained at 0.5 mu m recording marks produced by a switching field of 75 Oe. Temperature dependence of interface wall energy affects recording/playback characteristics of ECDL MSR disks considerably.
Magneto-optic imaging of proton-irradiated high T-c superconducting thin films: A revisit of J(c)(T) functional and flux pinning enhancement
(2001-10-10)
Wang, C
;
Seo, HW
;
Su, CJ
;
Wang, YH
;
Chen, QY
We have performed systematic quantitative measurements of the critical current density J(c)(B,T) for YBCO thin films proton-irradiated to various dosages using the MOI technique. Results for external magnetic fields up to 400Oe and temperature ranging from 5 to 80 K are T resented for a 600 nm thick YBCO film irradiated by proton up to a dosage of 10(16) cm(-2) at 500 keV. While no significant differences were observed for T > 50K, the J(c) values consistently increased with the increasing external field for T < 50 K.
Mask films for thermally induced superresolution readout in rewritable phase-change optical disks
(2001-03-01)
Lu, YH
;
Dimitrov, D
;
Liu, JR
;
Hsieh, TE
;
Shieh, HPD
Tellurium was studied as a mask film in a thermally induced superresolution rewritable optical disk for detecting below-diffraction-limit marks. Mark trains of 0.15 mum could be retrieved with 9 dB in carrier-to-noise (CNR) using an optical system with the laser wavelength of 780 nm and an objective lens of 0.55 numerical aperture. Readout cyclability was examined and methods to further improve readout cyclability were proposed.
Pulse-read on erasable thermal phase-change superresolution disks
(1998-12-10)
Liu, JR
;
Liu, PY
;
Tang, NY
;
Shieh, HPD
;
光電工程學系
New erasable thermal phase-change superresolution (EPSR) disks composed of mask and recording layers can increase recording density by the detection of the below-diffraction-limited marks within the readout spot. The formation of the aperture and the readout signal on the EPSR disk were analyzed. The feasibility of optically designed EPSR disks was evaluated by thermal simulation. A carrier-to-noise ratio of 32 dB at a mark size of 0.4 mu m, 8 dB higher than that of a conventional disk, was obtained by application of a pulse-read method to the EPSR disks at a wavelength of 780 nm and a numerical aperture of 0.55. (C) 1998 Optical Society of America.