• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.3
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• pp.141-145
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• 2014

Tubular-shaped ZnO crystals were synthesized by thermal evaporation technique under air atmosphere. Mixture of Zn and Mg powder was used as the source material. The thermal evaporation and oxidation of Zn/Mg mixture were carried out for 1 hr at $1,000^{\circ}C$ and $1,200^{\circ}C$ under in air under atmospheric pressure. When only Zn powder was used as a source material, tetrapod-shaped ZnO crystals were synthesized. This provides that Mg played a key role in the formation of the tubular-shaped crystals. SEM images showed that the tubular-shaped ZnO crystals grew along [0001] direction. XRD spectrum revealed that the ZnO tubes had hexagonal wurtzite structure. Two emission peaks at 380 nm and 510 nm were observed in the room temperature cathodoluminescence spectrum.

• Transactions on Electrical and Electronic Materials
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• v.12 no.4
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• pp.169-173
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• 2011

In this study, Al-N codoped p-type zinc oxide (ZnO) thin films were deposited on Si and homo-buffer layer templates in a mixture of $N_2$ and $O_2$ gas with ceramic ZnO:(2 wt% $Al_2O_3$) as a sputtering target using DC- magnetron sputtering. X-ray diffraction spectra of two-theta diffraction showed that all films have a predominant (002) peak of ZnO Wurtzite structure. As the $N_2$ fraction in the mixed $N_2$ and $O_2$ gases increased, field emission secondary electron microscopy revealed that the surface appearance of codoped films on Si varied from smooth to textured structure. The p-type ZnO thin films showed carrier concentration in the range of $1.5{\times}10^{15}-2.93{\times}10^{17}\;cm^{-3}$, resistivity in the range of 131.2-2.864 ${\Omega}cm$, and mobility in the range of $3.99-31.6\;cm^2V^{-1}s^{-1}$ respectively.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2333-2337
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• 2012

We report the synthesis and thermal annealing of Si-core/ZnO-shell nanorods using a two-step process comprising the metal-assisted electroless etching of Si and the sputter deposition of ZnO. Transmission electron microscopy and X-ray diffraction analysis showed that the cores of the annealed core-shell nanorods were single crystal diamond cubic-type Si, whereas the shells of the annealed core-shell nanorods were single crystal wurtzite-type ZnO. The PL spectra of Si nanorods consisted of a broad red emission band and a weaker blue emission band. The major emission band of Si nanorods was shifted from 700 nm (in the red region) to 440 nm (in the violet region) by ZnO coating. The violet emission of the core-shell nanorods was enhanced in intensity considerably by annealing in an oxidizing atmosphere. The origin of the PL enhancement by annealing is also discussed.

• Particle and aerosol research
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• v.6 no.1
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• pp.29-35
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• 2010

Transition metals such as V, Fe, and Ni were used to synthesize doped zinc oxide nanoparticles from mixed liquid precursors by using the flame spray pyrolysis (FSP). The effects of dopants on the powder properties such as morphology, specific surface area, crystal structure, and light adsorption were analyzed by TEM, BET, XRD, and UV-Vis diffuse reflection spectrum (DRS), respectively. The results showed that hexagonal wurtzite structured ZnO:M (M = V, Fe, Ni) nanoparticles were successfully synthesized by the FSP. The transition metal-doping resulted in the decrease in its particle size and crystallite size. The UV-vis absorption spectra of ZnO:M nanoparticles were also red-shifted. ZnO:V showed the highest MB degradation of 99.4% under the UV irradiation after 3 hrs.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.4
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• pp.502-506
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• 2012

In order to find the structural characteristics of the thin films of group II-VI semiconductor compounds compared with those of powder materials, films were made of 4 powders of ZnS, CdS, CdSe, and CdTe(Aldrich), each with 99.99 % purity. For the ZnS/CdS multi-layers, the ZnS layer was coated over the CdS layer on an $AlO_x$ membrane, which served as a protective layer within a vacuum at the average speed of 1 ${\AA}$/sec. After studying the structures of the group II-VI semiconductor thin films by using X-ray spectroscopy, we found that the ZnS, ZnS/CdS, CdS, and CdSe films were hexagonal and exhibited some degree of preferred orientation. Also, the particles of the thin films of II-VI semiconductor compounds proved to be more homogeneous in size compared to those of the powder materials. These results were further verified through scanning electron microscopy(SEM), EDX analysis, and powder and thin film X-ray diffraction.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.525-531
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• 1996

(Ti1-xAlx)N films were deposited on high speed steel and silicon substrates by reactive sputtering in mixed $Ar-N_2$ discharges. Crystalline phases and microhardness of ($Ti_1_xAl_x$)N films were investigated with variation of the film composition and substrate RF bias voltage. With Al content x of about 0.6, crystalline phase of ( $Ti_1_xAl_x$N films was changed from single-phase NaCl structure to two phase mixture of NaCl and wurtzite structures: Microhardness of ($Ti_1_xAl_x$)N films was largely improved by applying RF bias voltage above 50 V during deposition. Hardness of ($Ti_1_xAl_x$)N films reached a maximum value for Al content x of about 0.4, and 1900 kg/$mm^2$ was obtained for 1$\mu m$-thick ($Ti_{0.6}Al_{0.4}$)N films.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.4
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• pp.659-664
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• 2010

The ZnS/CdS thin films were made using 99.99% ZnS and CdS(Aldrich) powders in $7{\times}10^{-6}torr$. The ZnS layer was coated over the CdS layer on an AlOx membrane within a vacuum, at the average speed of $1{\AA}/sec$. After studying the ZnS/CdS and CdS thin films(both with the dimensions of 2.52nm), using fluorescence spectroscopy and comparing the respective results together, we found that although both of the resulting spectra peaked at 390nm, the ZnS/CdS thin films showed a narrower peak, and a higher intensity of photoluminescence than the CdS thin films. The particles of ZnS/CdS thin films also proved to be more homogeneous in size. In addition, the ZnS layer acted as a protective layer. Also, after studying the spectra of ZnS/CdS thin films taken 30 days after their preparation, we found no signs of aging. These results were verified through the scanning electron microscopy(SEM), EDX analysis, thin film X-ray diffraction, and luminescence spectroscopy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.10
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• pp.884-889
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• 2009

Recently, the control of size, morphology and dimensionality in inorganic materials has been rapidly developed into a promising field in materials chemistry. 3D nanostructured flower-like ZnO architecture with different size and shapes have been simply synthesized by hydrothermal process, using zinc acetate and ammonium hydroxide as reactants. In this study, the ZnO thin-films were deposited by RF magnetron sputtering in other to get high adhesion and uniformity of 3D nanostructured flower-like ZnO architecture on a $SiO_2$ substrate. The XRD patterns identified that the obtained the nanocrystallized ZnO architecture exhibited a wurtzite structure. SEM images illustrated that the flower-like ZnO bundles consisted of flower-like or chestnut bur, which were characterized by polycrystalline and (002) preferential orientation.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.51-51
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• 2010

Group III-nitride semiconductors have been widely studied as the materials for growth of light emitting devices. Currently, GaN devices are predominantly grown in the (0001) c-plane orientation. However, in case of using polar substrate, an important physical problem of nitride semiconductors with the wurtzite crystal structure is their spontaneous electrical polarization. An alternative method of reducing polarization effects is to grow on non-polar planes or semi-polar planes. However, non-polar and semipolar GaN grown onto r-plane and m-plane sapphire, respectively, basically have numerous defects density compared with c-plane GaN. The purpose of our work is to reduce these defects in non-polar and semi-polar GaN and to fabricate high efficiency LED on non/semi-polar substrate. Non-polar and semi-polar GaN layers were grown onto patterned sapphire substrates (PSS) and nano-porous GaN/sapphire substrates, respectively. Using PSS with the hemispherical patterns, we could achieve high luminous intensity. In case of semi-polar GaN, photo-enhanced electrochemical etching (PEC) was applied to make porous GaN substrates, and semi-polar GaN was grown onto nano-porous substrates. Our results showed the improvement of device characteristics as well as micro-structural and optical properties of non-polar and semi-polar GaN. Patterning and nano-porous etching technologies will be promising for the fabrication of high efficiency non-polar and semi-polar InGaN LED on sapphire substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.69-69
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• 2010

The research is the structural and optical characteristics of the Cadmium Sulfide(CdS) film, nanowires and nanobelts grown on the $Al_2O_3$ substrate using the vapor phase epitaxy method. The field-emission scanning electron microscopy(FE-SEM) were used to identify the shape of the surface of the nanostructures and x-ray diffraction(XRD) and transmission electron microscopy (TEM) were used to evaluate the structural characterisitcs. As a result, the XRD was confirmed the CdS peak and the substrate peak and TEM showed single crystals with wurtzite hexagonal structure on the nanostructures. As for the optical characteristic of the nanostructures, photoluminescence(PL) and micro-raman spectrum were measured. The PL measurements confirmed the emission peak related bound exciton to neutral donor($D^0X$) peak and free exciton(FX) peak. The micro-raman spectrum showed that the peak of the nanostructures were similar to the pure crystalline CdS peak and each peak were overtone of LO phonon of the hexagonal CdS of the longitudinal optical(LO) phonon mode. Therefore, it is confirmed that the CdS nanostructures grown in this research have superior crystallinity.