Publications (11)15.78 Total impact
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Article: Effects of Mg doping concentration on the band gap of ZnO/MgxZn1−xO multilayer thin films prepared using pulsed laser deposition method
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ABSTRACT: Epitaxial ZnO/Mg x Zn1-x O multilayer thin films (x = 0~0.15) were prepared on c-Al2O3 substrates by pulsed laser deposition and their crystallinity and optical properties were investigated using X-ray diffraction, TEM, and UV-Vis spectroscopy. ZnO/Mg x Zn1-x O multilayer thin films were grown by stacking alternate layers of ZnO and Mg x Zn1−x O with laser fluence of 3J/cm2, repetition rate of 5Hz, substrate temperature of 600°C, and oxygen partial pressure of 5 × 10–4Torr. The thickness of individual ZnO and Mg x Zn1−x O layers was maintained at 3 and 6nm, respectively, and the total thickness of the films was kept in 300nm. X-ray diffraction results showed that the multilayer thin films were grown epitaxially on c-Al2O3 substrates with an epitaxial orientation relationship of ( 0001 )[ 10[`1]1 ]\textmultilayer ||( 0001 )[ 10[`1]1 ]\textAl\text2 \textO\text3 \left. {\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{multilayer}}} } \right\|\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} } . Cross-sectional TEM micrographs showed alternating layers of bright and dark contrast, indicating the formation of ZnO/Mg x Zn1−x O multilayer thin films. The 2θ value of Mg x Zn1−x O (0002) peak increased from 34.30° at x = 0 to 34.67° at x = 0.15 with increasing Mg doping concentration in the multilayer thin films. The absorption edge in the UV-Vis spectra shifted to shorter wavelength from 360 at x = 0 to 342nm at x = 0.15 and the band gap energy increased from 3.27eV at x = 0 to 3.54eV at x = 0.15.Journal of Electroceramics 04/2012; 23(2):442-446. · 1.19 Impact Factor -
Article: Creation of Nanoscale Two-Dimensional Patterns of ZnO Nanorods using Laser Interference Lithography Followed by Hydrothermal Synthesis at 90 °C
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ABSTRACT: Arrayed ZnO nanorods were fabricated on photoresist coated ZnO/Si(100) substrates. Five different two-dimensional (2D) periodic nanopatterns, including a square lattice, rectangular lattice, centered rectangular lattice, oblique lattice, and hexagonal lattice, of opening windows in photoresist were fabricated by laser interference lithography using a two-step exposure process. The ZnO nanorods were grown through the patterned area by a hydrothermal method. The morphology of 2D nanopatterns and ZnO nanorods was investigated by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The optical property of ZnO nanorods was explored by room temperature photoluminescence. The height and diameter of ZnO nanorods were approximately 500 nm and 150 nm, respectively. The crystallinity, microstructure, and optical property of ZnO nanorods array could be controlled by the proper use of a surfactant chemical, that is, Na-citrate in this report.08/2010; -
Article: Effect of complexing agent and annealing atmosphere on properties of nanocrystalline ZnS thin films.
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ABSTRACT: The nanocrystalline Zinc Sulfide (ZnS) thin films were prepared on glass substrates by chemical bath deposition (CBD) method using aqueous solutions of zinc acetate, thiourea and tri-sodium citrate in alkaline medium at 80 degrees C. The tri-sodium citrate acts as a complexing agent. The effects of complexing agent and annealing atmosphere (95%N2 + 5%H2S) on structural, morphological and optical properties of ZnS thin films were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and optical absorption. XRD study revealed that single phase ZnS powder was formed in the solution with tri-sodium citrate, however, ZnS and ZnO mixed phase powder was formed in the solution without tri-sodium citrate. The films deposited with trisodium citrate showed ZnS with hexagonal wurtzite phase. However, annealed film in (N2 + H2S) atmosphere showed cubic (zincblende) phase. FE-SEM images show that grain size of as-deposited and annealed ZnS films are about 20 nm and 50 nm, respectively. Optical absorption study showed that the films have moderate optical transmission from 65% to 75% in the visible region and the optical band gap energy of as-deposited ZnS film is 3.91 eV and it decreases to 3.73 eV after annealing.Journal of Nanoscience and Nanotechnology 05/2010; 10(5):3686-90. · 1.56 Impact Factor -
Article: Controlling the surface morphology of ZnO films grown on glass substrates by hydrothermal method at 90 degrees C: effects of Na-citrate on the shape of ZnO nano-crystallites.
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ABSTRACT: The effects of Na-citrate on the morphology change of ZnO films, grown on ZnO buffered glass substrates by hydrothermal synthesis at 90 degrees C and at pH 10.9, have been investigated. Dense and smooth ZnO film consists of ZnO nano-rods that have flat ends was grown with Na citrate. However, very rough ZnO film consists of ZnO nano-rods that have sharp ends were grown without Na citrate. X-ray diffraction analysis shows that all the ZnO films were grown with strong c-axis out-of-plane orientation. Optical transmission spectroscopy of the ZnO films grown with and without Na-citrate shows band gap energy values of 3.36 eV and 3.28 eV, respectively. Photoluminescence results showed strong defect related emission peak centered near 545 nm in the ZnO film grown without Na citrate and strong band-edge emission peak centered near 378 nm in the ZnO film grown with Na citrate.Journal of Nanoscience and Nanotechnology 11/2008; 8(10):5485-8. · 1.56 Impact Factor -
Article: Electronic structure of P-doped ZnO films with p-type conductivity.
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ABSTRACT: The electronic structure of laser-deposited P-doped ZnO films was investigated by X-ray absorption near-edge structure spectroscopy (XANES) at the O K-, Zn K-, and Zn L3-edges. While the O K-edge XANES spectrum of the n-type P-doped ZnO demonstrates that the density of unoccupied states, primarily O 2p-P 3sp hybridized states, is significantly high, the O K-edge XANES spectrum of the p-type P-doped ZnO shows a sharp decrease in intensity of the corresponding feature indicating that P replaces O sites in the ZnO lattice, and thereby generating P(O). This produces holes to maintain charge neutrality that are responsible for the p-type behavior of P-doped ZnO. Both the Zn K-, and Zn L3-edge XANES spectra of the P-doped ZnO reveal that Zn plays no significant role in the p-type behavior of ZnO:P.Journal of Nanoscience and Nanotechnology 12/2006; 6(11):3422-5. · 1.56 Impact Factor -
Article: Dependence of photoluminescence and electrical properties with rapid thermal annealing in nitrogen-implanted ZnO films
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ABSTRACT: Undoped (as-grown) ZnO films grown by pulsed laser deposition on Al2O3 (0001) substrates were doped with nitrogen by means of an ion implantation process. Post-implantation annealing behavior in the temperature range between 500 and 700 °C has been studied by photoluminescence and Hall effect measurements. The implanted films show no peak other than the excitonic recombination emission in the as-implanted state, however, after rapid thermal annealing at 700 °C they reveal a nitrogen acceptor related emission at 3.273 eV. The as-implanted ZnO films show more electron concentrations than the as-grown, unimplanted ZnO film. In contrast, after annealing, the electron concentration in the implanted films is significantly reduced, indicating that the incorporated nitrogen becomes activated after the thermal annealing, then produces holes and eventually compensates for certain amount of electrons. The results imply that a proper nitrogen implantation and subsequent annealing may be a way to produce p-type ZnO films.Thin Solid Films. -
Article: A study on the epitaxy nature and properties of 3wt% Ga-doped epitaxial ZnO thin film on Al2O3 (0001) substrates
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ABSTRACT: 3 wt% Ga-doped ZnO (GZO) thin films were deposited on Al2O3 (0 0 0 1) substrates by RF magnetron sputtering at different growth temperatures ranging from 350 to 750 °C. The crystallinity, microstructure, epitaxial nature, and optical and electrical properties of the GZO thin films were examined by X-ray diffraction (XRD), transmission-electron microscopy (TEM), UV–visible spectroscopy and Hall measurements. XRD and TEM showed that the GZO thin films deposited below a growth temperature of 450 °C grew epitaxially with an orientation relationship of . However, the GZO thin films deposited above 550 °C were in polycrystalline hexagonal wurtzite phase with c-axis preferred. The crystallinity of the GZO thin films deteriorated with increasing growth temperature. The GZO thin film deposited at 350 °C showed the lowest electrical resistivity of 1.13×10−4 Ω cm. The electrical properties of the GZO thin films also deteriorated with increasing growth temperature. UV–visible spectroscopy showed that the GZO thin films are highly transparent (from 75% to 90%) in the visible region. In addition, the band gap of the deposited thin films decreased from 3.5 to 3.2 eV with increasing growth temperature.Journal of Crystal Growth 322(1):51-56. · 1.73 Impact Factor -
Article: Effect of different annealing conditions on the properties of chemically deposited ZnS thin films on ITO coated glass substrates
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ABSTRACT: The effects of different annealing conditions such as atmospheres, temperatures and times on the structural, morphological and optical properties of ZnS thin films prepared on ITO coated glass substrates by chemical bath deposition were studied. Aqueous solutions of zinc acetate and thiourea were used as precursors along with stable complexing agents, such as Na2EDTA and Na3-citrate, in an alkaline medium. X-ray diffraction patterns showed that the as-deposited and as-annealed ZnS films had an amorphous structure or poor crystallinity below the optimized annealing conditions of 500 °C and 60 min with the exception of the films annealed in N2+H2S annealing atmosphere. The ZnS thin films annealed in N2+H2S atmosphere for 1 h at 500 °C showed three sharp peaks for the (1 1 1), (2 2 0) and (1 1 3) planes of polycrystalline cubic ZnS without any unwanted secondary ZnO phases. X-ray photoelectron spectroscopy revealed Zn–OH and Zn–S bonding in the as-deposited ZnS thin film. However, the ZnS thin films annealed at 500 °C showed Zn–S bonding regardless of the annealing atmosphere. The sharp absorption edge and band gap energy of the as-deposited and as-annealed ZnS thin films varied from 295 to 310 nm and 3.5 to 3.89 eV, respectively.Solar Energy Materials and Solar Cells 95(3):856-863. · 4.54 Impact Factor -
Article: Effect of pH on the characteristics of nanocrystalline ZnS thin films prepared by CBD method in acidic medium
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ABSTRACT: The structural, morphological, and optical properties of zinc sulfide (ZnS) thin films deposited using chemical bath deposition method are reported. These films were deposited on soda lime glass substrates using Na2EDTA as a complexing agent, in acidic medium at 80 °C. The effect of the pH ranging from 5 to 6.5 on quality of ZnS thin films is investigated. Irrespective of the pH values used for the deposition all films are polycrystalline with a wurtzite (hexagonal) structure. Field emission scanning electron microscopy (FE-SEM) characterization shows that the surface of the sample deposited with pH 5 and 5.5 is compact and uniform. However, agglomerated clusters (∼100 nm) are observed in ZnS thin films grown with pH above 6. X-ray photoelectron spectroscopy results shows the presence of only Zn–S bonding for the ZnS thin film grown at pH = 5 while those films deposited with pH > 5.5, Zn–OH as well as Zn–S bonding have been observed. The composition is almost stoichiometric for a wide range of pH values of the solution (5–6.5). The transmission spectrum of ZnS thin films having thickness from 30 to 220 nm indicates a good transmission characteristic with an average transmittance of 70–85%. The absorption coefficient depends on the pH values of the solution used and are responsible to the changes observed in absorption edges. The band gap energy values of ZnS thin films decreased from 3.91 to 3.78 eV with increasing pH values of the solution.Current Applied Physics 10(3). · 1.90 Impact Factor -
Article: Effect of a ZnO buffer layer on the properties of Ga-doped ZnO thin films grown on Al2O3 (0001) substrates at a low growth temperature of 250°C
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ABSTRACT: 4 wt% Ga-doped ZnO (GZO) thin films have been prepared on the buffered and non-buffered Al2O3 (0 0 0 1) substrates by RF magnetron sputtering technique at a low growth temperature (250 °C). The effect of a ZnO buffer layer on the crystallinity, optical, and electrical properties of the GZO thin films is investigated. X-ray diffraction and transmission electron microscopy studies showed that the GZO thin film on a buffered substrate was epitaxially grown at a low growth temperature of 250 °C with an orientation relationship of . However, the GZO thin film on a non-buffered substrate was grown as a polycrystalline hexagonal wurtzite phase with c-axis preferred, out-of-plane orientation, and random in-plane orientation. The optical transmittance in the visible region and the electrical resistivity of the GZO thin film was improved by introducing a ZnO buffer layer from 70% to 80% and from 4.69×10−3 to 1.01×10−3 Ω cm, respectively.Journal of Crystal Growth 312(9):1551-1556. · 1.73 Impact Factor -
Article: Heteroepitaxial growth of Pb(Mg1/3Ta2/3)O3 thin films on SrTiO3 substrates using chemical solution deposition method: microstructural evolution
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ABSTRACT: Epitaxial Pb(Mg1/3Ta2/3)O3 (PMT) thin films were grown on (001) SrTiO3 (STO) substrates using a chemical solution deposition method. Microstructural evolution as a function of annealing temperatures (600∼900 °C/1 h) has been studied using transmission electron microscopy, scanning electron microscopy, and four-circle X-ray diffractometry. A thin layer of epitaxial perovskite phase was formed first at the film/substrate interface in a sample annealed at 650 °C/1 h and then it grew upward to the film surface by consuming the pyrochlore phase in the upper region of the film. No further microstructural evolution was observed in the sample annealed at above 750 °C/1 h. An epitaxial orientation relationship of [100](001)PMT||[100](001)STO was found by selected area diffraction pattern.Microelectronic Engineering.
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Institutions
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2008–2012
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Chonnam National University
- Department of Material Science and Engineering
Yeoju, Gyeonggi, South Korea
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