• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.6
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• pp.253-256
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• 2004

Growth of ZnO epitaxial films have been carried out on (0001) sapphire substrates by RF magnetron sputtering. The single crystalline ZnO films of the thickness about 400-500 mm were grown successfully. At the various substrate temperatures of 200～$600^{\circ}C$, the growth behavior and optical properties of the epitaxial films have been characterized. As-grown ZnO films were annealed at the temperatures of 400, 600 and $800^{\circ}C$ respectively in order to characterize the optical properties. The carrier concentration of ZnO films annealed at the temperature of $600^{\circ}C$ was measured $2.6${\times}$10^{16}\textrm{cm}^{-3}$ by Hall measurements.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.21.1-21.1
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• 2011

Vertically aligned single-crystal ZnO nanowires have been successfully grown on c-plane sapphire substrate using chemical vapor deposition (CVD) without catalyst. According to growth temperatures, it was changed ZnO growth characteristic. We investigated the effect of substrate temperatures on the growth ZnO films or nanowires on c-plane (0001) sapphire substrates. The ZnO films were acquired at $500^{\circ}C$, whereas the ZnO nanowires were obtained at $600^{\circ}C$, $700^{\circ}C$, and $800^{\circ}C$. The growth behavior diameter and growth rate of ZnO were changed due to different temperature. As a result of analyzing in-plane residual stress by X-ray diffraction, the optimized condition of ZnO nanowires were at $600^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.505-513
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• 1989

The sintering behavior and grain growth of ZnO in 99.0mol% ZnO-1.0mol% Bi2O3 which are the basic compositions of ZnO varistor were studied. The microstructrual observation confirmed that the final sintered density was mainly determined at the initial stage of sintering, i.e. grain rearrangement and grain growth which were induced by the penetration of eutectic melts formed at eutectic temperature(74$0^{\circ}C$). But when the liquid penetration was terminated, the grain growth did not promote further densification. Activation energy of the grain growth of ZnO in the system of 99.0mol% ZnO-1.0mol% Bi2O3 was 44.8$\pm$1.8Kcal/mol.

• Journal of the Korean Ceramic Society
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• v.30 no.11
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• pp.955-961
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• 1993

Sintering behavior and microstructure development in the system ZnO-Bi2O3-CoO-Zn7Sb2O12 with Zn7Sb2O12 content(0.1mol%~2mol%) were studied. The pyrochlore phase was formed by the reaction of the Zn7Sb2O12 with Bi2O3 phase during heating (below 90$0^{\circ}C$). The formation temperature of the liquid phase (Bi2O3) was dependent on the Zn7Sb2O12 contents (about 74$0^{\circ}C$ for Bi2O3/Zn7Sb2O12>1 by the eutectic melting in the ZnOBi2O3 system, and about 110$0^{\circ}C$ for Bi2O3/Zn7Sb2O12 1 by the decomposition of pyrochlore phase). Hence, sintering behavior and microstructure development were determined virtually by the Bi2O3/Zn7Sb2O12 ratio, which were promoted by liquid (Bi2O3) phase and retarded by the pyrochlore (or spinel) phase. The grain growth of ZnO during sintering was sluggish with increasing Zn7Sb2O12 contents.

• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.404-410
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• 1993

The characterization and sintering behavior of ZnO powders prepared by precipitation method were investigated. ZnO powders were synthesized using the aqueous solutions of ZnCl2 and NH4OH as a precipitation agent, which were crystallized in the shape of plate-like. The grain growth of ZnO(0.68${\mu}{\textrm}{m}$, 1.3${\mu}{\textrm}{m}$ and 3.4${\mu}{\textrm}{m}$) has been studied for temepratures from 100$0^{\circ}C$ to 130$0^{\circ}C$, and the rate of densification was inversely proportional to the ZnO particle size. Densification proceeded slowly by diffusion mechanisms above at 100$0^{\circ}C$. In this work, the grain growth kinetic exponent(n) was 3. The temperature dependence of ZnO grain growth was plotted, and the activation energy of grain growth was 75~85Kcal/mol.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.11
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• pp.875-879
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• 2010

In this study, we have characterized the roles of $Cr_2O_3$ on the sintering and electrical properties of ZnO. The densification and grain growth of Cr-doped ZnO (ZCr) system was mainly influenced by Cr contents. In the beginning of sintering, the densification of ZnO was retarded as reducing the Zni concentration in ZnO lattice with Cr doping. And the densification and grain growth of ZnO was more retarded due to a formation of spinel phase with increasing the Cr contents. ZCr system revealed varistor behavior with nonlinear coefficient $\alpha$ of 3~23 depending on the sintering temperature, implying double Schottky barrier formation on the grain boundary of ZnO. Especially the best varistor characteristics should be developed with 0.1~0.5 at% Cr contents and under $1100^{\circ}C$ in ZCr systems.

• Korean Journal of Materials Research
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• v.27 no.11
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• pp.609-616
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• 2017

We investigated a Leidenfrost effect in the growth of ZnO nanostructures on silicon substrates by ultrasonic-assisted spray pyrolysis deposition(SPD). Structural and optical properties of the ZnO nanostructures grown by varying the growth parameters, such as substrate temperature, source concentration, and suction rate of the mist in the chambers, were investigated using field-emission scanning electron microscopy, X-ray diffraction, and photoluminescence spectrum analysis. Structural investigations of the ZnO nanostructures showed abnormal evolution of the morphologies with variation of the substrate temperatures. The shape of the ZnO nanostructures transformed from nanoplate, nanorod, nanopencil, and nanoprism shapes with increasing of the substrate temperature from 250 to $450^{\circ}C$; these shapes were significantly different from those seen for the conventional growth mechanisms in SPD. The observed growth behavior showed that a Leidenfrost effect dominantly affected the growth mechanism of the ZnO nanostructures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.9-9
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• 2009

1 wt % Ga-dope ZnO (ZnO:Ga) thin films with n-type semiconducting behavior were grown on c-sapphire substrates by radio frequency magnetron sputtering at various growth temperatures. The room temperature grown ZnO:Ga film showed the faint preferred orientation behavior along the c-axis with small domain size and high density of stacking faults, despite limited surface diffusion of the deposited atoms. The increase in the growth temperature in the range between $300\sim550^{\circ}C$ led to the granular shape of epitaxial ZnO:Ga films due to not enough thermal energy and large lattice mismatch. The growth temperature above $550^{\circ}C$ induced the quite flat surface and the simultaneous improvement of electrical carrier concentration and carrier mobility, $6.3\;\times\;10^{18}/cm^3$ and $27\;cm^2/Vs$, respectively. In addition, the increase in the grain size and the decrease in the dislocation density were observed in the high temperature grown films. The low-temperature photoluminescence of the ZnO:Ga films grown below $450^{\circ}C$ showed the redshift of deep-level emission, which was due to the transition from $Zn_j$ to $O_i$ level.

• Journal of the Korean Ceramic Society
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• v.35 no.5
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• pp.499-504
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• 1998

ZnO varistors having a composition of 98.0 mol% ZnO 1.0 mol% $Bi_2O_3$ 0.5 mol% $MnO_2$ were prepared by the Pechini process and the sintering behavior and electrical characteristics were studied. ZnO varis-색 powder with $1.5\mu\textrm{m}$ mean diameter and narow particle size distribution was obtained using the Pechni pro-cess. Typical intermediate stage grain growth of liquid phase sintering was observed by sintering at $1100^{\circ}C$ At this temperature ZnO varistors having uniform grain size and Bi-rich liquid phase distributed uniformly along grain boundaries were prepared. The nonlinear coefficients of the ZnO varistors were in the range of 40-60 The breakdown voltages of the varistors were nearly inversely propeortional to the grain size which reflects that ZnO varistors prepared by the Pechini process have uniform distribution of Bi-rich liquid phase along grain boundaries It is believed that the microstructures of ZnO varistors can be controlled effectively by using the Pechini process which makes the control of the electrical properties of ZnO varistors possible.

• Journal of Powder Materials
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• v.12 no.4 s.51
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• pp.284-290
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• 2005

ZnO nanostructures with various shapes were synthesized under ambient pressure condition by a wet chemical reaction method. Nanorods of ZnO with hexagonal cross-section and their aggregates with radiate shape were synthesized. Precursor concentration affected considerably the shape evolution of ZnO nanorods. Low precursor concentration was proved to be more preferable to the growth of ZnO nanorods, which is attributed to the intrinsic characteristics of chemical reaction in the synthesis of ZnO from zinc compounds.