• Journal of Powder Materials
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• v.12 no.6 s.53
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• pp.399-405
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• 2005

Nanopowders of titanium dioxide $(TiO_2)$ incorporating the transition metal element(s) were synthesized by flame synthesis method. Single element among Fe(III), Cr(III), and Zn(II) was doped into the interior of $TiO_2$ crystal; bimetal doping of Fe and Zn was also made. The characteristics of transition-metal-doped $TiO_2$ nanopowders in the particle feature, crystallography and electronic structures were determined with various analytical tools. The chemical bond of Fe-O-Zn was confirmed to exist in the bimetal-doped $TiO_2$ nanopowders incorporating Fe-Zn. The transition element incorporated in the $TiO_2$ was attributed to affect both Ti 3d orbital and O 2p orbital by NEXAFS measurement. The bimetal-doped $TiO_2$ nanopowder showed light absorption over more wide wavelength range than the single-doped $TiO_2$ nanopowders.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.6
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• pp.639-646
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• 2015

A treatment for improving the characteristics of a surface is very important in increasing the life of machine parts. Many studies have been carried out on the surface characteristics after such treatments. For enhanced eco-technology, an alternative to a conventional chemical surface treatment process is essential. Ultrasonic nano-crystal surface modification (UNSM) technology is a physical environmentally friendly surface treatment method. This technology was developed in domestic and currently being used. As the mechanism of UNSM technology, a ball tip attached to an ultrasonic vibration device strikes the metal surface at nearly 20,000 times per second. The resulting modified surface layer improves the surface characteristics. This paper describes a self-developed fast tool servo system applied to the UNSM process as a vibration module within a high-frequency bandwidth. After describing the surface modification process based on the material and process changes, the surface characteristics are compared.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.147-147
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• 2011

High crystalline nonpolar a-plane (11-20) nitride light emitting diodes (LEDs) have been fabricated on r-plane (1-102) sapphire substrates by metalorganic chemical-vapor deposition (MOCVD). The multi-quantum wells (MQWs) active region is consists of 4 periods the nonpolar a-plane InGaN/GaN(a-InGaN/GaN) on a high quality a-plane GaN (a-GaN) template grown by using the multibuffer layer technique. The full widths at half maximum (FWHMs) of x-ray rocking curve (XRC) obtained from phiscan of the specimen that was grown up to nonpolar a-plane GaN LED layers with double crystal x-ray diffraction. The FWHM values were decreased down to 477 arc sec for $0^{\circ}$ and 505 arc sec for $-90^{\circ}$, respectively. After fabricating a conventional lateral LED chip which size was $300{\times}600{\mu}m^2$, we measured the optical output power by on-wafer measurements. N-electrode was made with Cr/Au contact, and ITO on p-GaN was formed with Ohmic contact using Ni/Au followed by inductively coupled plasma etching for mesa isolation. The optical output power of 1.08 mW was obtained at drive current of 20 mA with the peak emission wavelength of 502 nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.469-470
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• 2008

We have studied electro-optic characteristics as a function of splay elastic constants ($K_{11}$) in the fringe-field switching (FFS) mode using the LC with positive dielectric anisotropy. When $K_{11}$ is increased from 7.7pN to 11.7pN, a maximum transmittance is slightly increased and rising time become a little bit fast. However, operating voltage and threshold voltage is independent. In opposition to rising time, decay time is not affected by $K_{11}$. We already know that $K_{11}$ affects tilt angle of liquid crystals. Therefore, on the occasion of high $K_{11}$, liquid crystals are mainly affected by twist deformation because the higher $K_{11}$, the less tilt angle. In the FFS device, high $K_{11}$ is favorable to reduce tilt angle in on state and thus improve rising response time.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.142-147
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• 2010

Nano-sized $BaNd_2Ti_5O_{14}$ powders were prepared by the spray pyrolysis process. Sucrose used as the organic additive enabled the formation of nano-sized $BaNd_2Ti_5O_{14}$ powders. The powders prepared from the spray solution without sucrose had a spherical shape, dense structure and micron size before and after calcination. However, the precursor powders prepared from the spray solution with sucrose had a large size, and hollow and porous morphology. The precursor powders had an amorphous crystal structure because of the short residence time of the powders inside the hot wall reactor. The complete decomposition of sucrose did not occur inside the hot wall reactor. Therefore, the precursor powders obtained from the spray solution with sucrose of 0.5M had a carbon content of 39.2wt.%. The powders obtained from the spray solution with sucrose of 0.5M had a slightly aggregated structure of nano-sized primary powders of $BaNd_2Ti_5O_{14}$ crystalline phase after calcination at $1000^{\circ}C$. The calcined powders turned into nano-sized $BaNd_2Ti_5O_{14}$ powders after milling. The mean size of the $BaNd_2Ti_5O_{14}$ powders was 125 nm.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.40-45
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• 2008

We present the effect of Ga-doping on the electrical, structural and optical properties of ZnO layers with a thickness of ${\sim}500nm$ deposited on glass substrates. Polycrystalline ZnO and Ga-doped ZnO (GZO) layers were deposited by radio frequency (rf) magnetron sputtering at room temperature. Based on the X-ray diffraction (XRD) and transmission electron microscopy (TEM) data, the crystalline quality of Ga-doped ZnO film was improved and GZO film has a preferred orientation along with the (002) crystal direction. The transmittance of the GZO film was enhanced by 10% in the visible region from that of the ZnO film. From photoluminescence (PL) data, the ratio of intensity of near band edge (NBE) emission to deep level (DL) emission was as high as 2.65:1 and 1.27:1 in the GZO and ZnO films, respectively. The res istivities of GZO and ZnO films were measured to be 1.27 and 1.61 $\Omega{\cdot}cm$, respectively. The carrier concentrations of ZnO and GZO film were approximately 1018 and 1020 $cm^2$/Vs, respectively. Based on our experimental results, the Ga-doping improves the electrical, structural and optical properties of ZnO film with potential application.

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.519-520
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.521-522
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• 2010

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.181-182
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• 2010

• Proceedings of the Korean Vacuum Society Conference
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• 2009.02a
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• pp.237.1-237.1
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• 2009