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ASEAN Journal on Science and Technology for Development

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Published by Universitas Gadjah Mada

ISSN : 22249028 EISSN : 22249028 DOI : -

Core Subject : Science, Education, Engineering,

Biochemistry, Genetics & Molecular Biology Chemical Engineering, Chemistry & Bioengineering Computer Science & IT Mathematics

The coverage is focused on, but not limited to, the main areas of activity of ASEAN COST, namely: Biotechnology, Non-Conventional Energy Research, Materials Science and Technology, Marine Sciences, Meteorology and Geophysics, Food Science and Technology, Microelectronics and Information Technology, Space Applications, and Science and Technology Policy, Infrastructure and Resources Development.

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Articles 16 Documents

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Search results for , issue "Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)" : 16 Documents clear

PECULIAR OPTICAL PROPERTIES OF Co2MnGa ALLOYS Joo Yull Rhee; Y.V. Kudryavtsev; K.W. Kim; Y.P. Lee
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

Co2MnGa alloy was prepared by the conventional arc-melting method. The optical conductivity (OC) spectrum of the alloy was measured by a rotating-analyzer spectroscopic ellipsometer. The OC spectrum was also calculated based on the electronic structure by using the full-potential linearized-augmented-plane-wave method within the local-spin-density approximation to the density-functional theory. The calculated OC spectrum does not agree well with the experimental one. Since the Co2MnGa alloy could be a strongly-correlated material, the so-called 'LDA+U' method was applied with U = 5.4 eV. The calculated OC spectrum using the 'LDA+U' method agrees very well with the experimental one. The inclusion of the onsite Coulombpotential during the self-consistent calculation significantly modifies the minorityspin Co and Mn 3d bands, resulting in a contraction of the energy gaps between states which are strongly involved in interband absorption peaks.

SPIN-POLARIZED PHOTOCURRENT THROUGH QUANTUM DOT PHOTODETECTOR Hieu, Nguyen Van; Ha, Nguyen Bich
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

The theory of the photocurrent through the photodetector based on a two-level semiconductor quantum dot (QD) is presented. The analytical expressions of the matrix elements of the electronic transitions generated by the absorption of the circularly polarized photons are derived in the lowest order of the perturbation theory with respect to the electron tunneling interaction as well as the electron-photon interaction. From these expressions the mechanism of the generation of the spin-polarized of electrons in the photocurrent is evident. It follows that the photodetector based on the two-level semiconductor QD can be used as the model of a source of highly spinpolarized electrons.

PREPARATION OF THE SINGLE MODE PLANAR OPTICAL SPLITTER MODULES AND THEIR CHARACTERIZATIONS Mien, Vu Doan; Nghiem, Vu Thi; Truong, Pham Van
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

Optical splitter modules have been prepared based on 1x8 single mode silica planar waveguide optical splitter chips with 250 µm spacing and v-groove fiber arrays for applications in fiber optic communications. We report the technology of precise optical coupling and packaging of the splitter modules and the measurements of the insertion loss (< 11 dB), uniformity (< 0.80 dB) and polarization dependence loss (PLD < 0.10 dB) as well as the lateral profile and the image of the input and output lights for the wavelengths of 1310 nm and 1550 nm. The main characteristics of the prepared splitter modules are about the same for the commercial available products. The prepared modules have been tested for operation in the conditions of wide temperature range (5–80°C) and humidity range (50–98%) and no changes in the main characteristics were observed.

MAGNETO-OPTIC PROPERTIES AND OXIDATION/REDUCTION OF ULTRATHIN MAGNETIC FILMS: FE FILMS ON Pt(111) T.-U. Nahm
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

We have investigated magneto-optic properties of ultrathin Fe films grown on Pt(111) surfaces by using the in situ surface magneto-optic Kerr effect (SMOKE) and X-ray photoelectron spectroscopy (XPS). SMOKE measurements show that the Fe layers are not ferromagnetic when the film is thinner than approximately 4.5 MLs (monolayers), but the in-plane magnetization is present for a 4.1 ML Fe film on Pt(111) annealed at 550 K. Upon post-annealing at 770 K, a 9.2 ML Fe film does not show any Kerr signal, while a 6.3 ML Fe film has the in-plane Kerr signal with increased coercivity. The oxidation and reduction of ultrathin Fe films have also been studied by using XPS. Upon an oxygen exposure of 300 Langmuir at a film temperature of 873 K, the Fe layers were mostly oxidized as Fe3O4. When the Fe films were exposed to the same amount of oxygen at room temperature, a partial oxidation as Fe3O4 was observed for a 3 ML Fe film, while there was no oxidation for a 2 ML Fe film. On heating the 873 K oxidized films, Fe3O4O was reduced to FeO, and even the decomposition was observed. Underlying reasons for these chemical changes of Fe and iron-oxide films are discussed.

WHISPERING GALLERY MODE LASERS IN ERBIUM/YTTERBIUM CODOPED PHOSPHATE GLASSES Tran Thi Tam; Dang Quoc Trung; Le Huu Minh; Tran Anh Vu; Do Ngoc Chung; Patrice Feron
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

The study of whispering gallery mode laser in Er3+/Yb3+ co-doped phosphate glass microsphere has been reported. The coupling was carried out by fiber half taper technique. The microsphere lasers have been studied under pumping at 980 nm, to take full advantage of energy transfer effect from ion Ytterbium to ion Erbium. The observed lasing range extends from 1533 nm to 1612 nm.

CVD PREPARED Mn-DOPED ZnO NANOWIRES T.L. Phan; R. Vincent; D. Cherns; N.X. Nghia
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

Mn-doped ZnO nanowires prepared by chemical vapor deposition (CVD) were obtained in the temperature range of 450–500°C. X-ray diffraction patterns, SEM and TEM images indicate that crystals with a hexagonal structure grow along the c axis. At low Mn-doped concentrations, photoluminescence (PL) and Raman scattering (RS) spectra are almost independent of the Mn doping. However, the increase in concentration of Mn above 1.6 at% weakens significantly the PL signal and the RS-lines intensity in the low wavenumber range of 300–480 cm-1, and concurrently increases the RS-lines intensity in the higher wavenumber range of 480-700 cm-1.. Magnetic measurements determined the Curie temperature of Mn-doped ZnO nanowire to be about 37 K.

PHOTOLUMINESCENCE OF ZnO NANOSTRUCTURE PREPARED BY CATALYST - ASSISTED VAPOR - LIQUID - SOLID TECHNIQUE Tran Thi Quynh Hoa; Ta Dinh Canh; Nguyen Ngoc Long; Nguyen Viet Tuyen; Nguyen Duy Phuong
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

ZnO semiconductor nanostructures have been synthesized by thermal evaporation of mixture of ZnO and graphite powders. The thin layer of gold coated on Si substrates was used as a catalyst. The structure analysis shows high crystallinity of ZnO, their preferred orientation along the (0 02) plane of the wurtzite phase and their chemical purity. The scanning electron microscopy (SEM) images of products indicate that ZnO nanowires have a diameter of about 40 - 150 nm and a length of up to tens of micrometers. The morphology and structure of ZnO nanowires and nanorods depend on the thicknesses of the Au layers. The fact that Au nanoparticles are located at the tips of the nanowires represents a strong evidence for a growth process dominated by the vapor - liquid - solid mechanism. The low temperature photoluminescence spectra of the ZnO nanowires indicate a group of the ultraviolet narrow peaks and a blue - green very broad peak at 500 nm.

RESEARCH AND DEVELOPMENT OF DIODE-PUMPED PASSIVELY Q-SWITCHED Nd:YVO4 LASERS USING Cr4+:YAG CRYSTAL AS SATURABLE ABSORBER Nguyen Trong Nghia; Trinh Dinh Huy; Le Thi Thanh Nga; Nguyen Dai Hung
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

The results in research and development of diode-pumped passively Q-switched Nd:YVO4 lasers are presented with Cr4+:YAG crystal used as an intra-cavity saturable absorber. Using a-cut Nd:YVO4 laser crystals, the passively Q-switched lasers have been successfully developed and provided stable single shortest pulses of 40 ns at the repetition rate of 18.5 kHz, the maximal average output power of 180 mW was achieved corresponding to the optical efficiency of 9% and the slope efficiency of 16%. The dependences of average output power, repetition rate, pulse width and peak power on pump diode power for different transmissions of output mirror are also investigated.

EUROPIUM SILICATE THIN FILMS FABRICATED BY RF MAGNETRON SPUTTERING AND THERMAL TREATMENT Young Chul Shin; Eun Hong Kim; Tae Geun Kim
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

We report the fabrication and optical characteristics of europium silicate thin films. Layer structures of Eu2O3/SiOX/Si (100) were deposited by an rf-sputtering method and annealed at 1100°C by rapid thermal annealing (RTA). Two methods were used for the deposition of SiOX layer: One was deposited by sputtering using SiO2 target (Ar gas at a rate of 50 sccm) and the other was deposited by reactive sputtering using Si target (Ar gas at a rate of 45 sccm, with an O2 gas at a rate of 5 sccm). Photoluminescence peak at 430 nm was observed in the sample composed of SiOx interlayer sputtered from SiO2 target. In comparison, PL peak at 570 nm was observed in the other sample, the SiOx layer of which was deposited by reactive sputtering from Si target. The compositional distributions of these samples were analyzed by X-ray photoelectron spectroscopy (XPS).

OPTICAL AND STRUCTURAL PROPERTIES OF OPTICAL THIN FILMS WITH VARIOUS COLUMNAR MICROSTRUCTURES Seouk-Hoon Woo; Yong Jun Park; Chang Kwon Hwangbo
ASEAN Journal on Science and Technology for Development Vol. 24 No. 1-2 (2007): ASEAN Journal on Science and Technology for Development (AJSTD)
Publisher : Universitas Gadjah Mada

In this study, optical and structural properties of the thin films prepared using glancing angle deposition (GLAD) are investigated. Various glancing angles and substrate rotations are employed to control the columnar microstructure of the films. The results show that as the glancing angle increases, the column angle and the porosity of TiO2 films increase and the refractive index decreases, due to shadow effects. The optical anisotropy of tilted and zigzag microstructure TiO2 films have a large anisotropy and reaches a maximum at a glancing angle of 60°, while that of helical microstructure TiO2 film deposited at 60° with substrate rotation shows a very small anisotropy due to the symmetric structure. It is found that the optical anisotropy of TiO2 films deposited by GLAD can be controlled by modification of microstructure.

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