• Korean Journal of Materials Research
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• v.18 no.7
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• pp.367-372
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• 2008

ZnO nanorod gas sensors were prepared by an ultrasound radiation method and their gas sensing properties were investigated for NO gas. For this procedure, 0.01, 0.005 and 0.001M of zinc nitrate hydrate [$Zn(NO_3)_2\;{\cdot}\;6H_2O$] and hexamethyleneteramine [$C_6H_{12}N_4$] aqueous solutions were prepared and then the solution was irradiated with high intensity ultrasound for 1 h. The lengths of ZnO nanorods ranged from 200 nm to 500 nm with diameters ranging from 40 nm to 80 nm. The size of the ZnO nanorods could be controlled by the concentration of solution. The sensing characteristics of these nanostructures were investigated for three kinds of sensor. The properties of the sensors were influenced by the morphology of the nanorods.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.23.1-23.1
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• 2009

ZnO is of great interest for various technological applications ranging from optoelectronics to chemical sensors because of its superior emission, electronic, and chemical properties. In addition, vertically well-aligned ZnO nanorods on large areas with good optical and structural properties are of special interest for the fabrication of electronic and optical nanodevices. To date, several approaches have been proposed for the growth of one-dimensional (1D) ZnO nanostructunres. Several groups have been reported the MOCVD growth of ZnO nanorods with no metal catalysts at $400^{\circ}C$, and fabricated a well-aligned ZnO nanorod array on a PLD prepared ZnO film by using a catalyst-free method. It has been suggested that the synthesis of ZnO nanowires using a template-less/surfactant-free aqueous method. However, despite being a well-established and cost-effective method of thin film deposition, the use of magnetrons puttering to grow ZnO nanorods has not been reported yet. Additionally,magnetron sputtering has the dvantage of producing highly oriented ZnO film sat a relatively low process temperature. Currently, more effort has been concentrated on the synthesis of 1D ZnO nanostructures doped with various metal elements (Al, In, Ga, etc.) to obtain nanostructures with high quality,improved emission properties, and high conductance in functional oxide semiconductors. Among these dopants, Ga-doped ZnO has demonstrated substantial advantages over Al-doped ZnO, including greater resistant to oxidation. Since the covalent bond length of Ga-O ($1.92\;{\AA}$) is nearly equal to that of Zn-O ($1.97\;{\AA}$), high electron mobility and low electrical resistivity are also expected in the Ga-doped ZnO. In this article, we report the successful growth of Ga-doped ZnO nanorods on c-Sapphire substrate without metal catalysts by magnetrons puttering and our investigations of their structural, optical, and field emission properties.

• Proceedings of the Korean Ceranic Society Conference
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• 2004.10a
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• pp.80.3-80.3
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• 2004

• Proceedings of the Korean Vacuum Society Conference
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• 2004.08a
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• pp.252-252
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• 2004

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.664-668
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• 2012

ZnO nanorods were successfully fabricated on Zn foil by chemical bath deposition (CBD) method. The ZnO precursor concentration and immersion time affected the surface morphologies, structure, and electrical properties of the ZnO nanorods. As the precursor concentration increased, the diameter of the ZnO nanorods increased from ca. 50 nm to ca. 150 nm. The thicknesses of the ZnO nanorods were from ca. $1.98{\mu}m$ to ca. $2.08{\mu}m$. ZnO crystalline phases of (100), (002), and (101) planes of hexagonal wurtzite structure were confirmed by XRD measurement. The fabricated ZnO nanorods showed a photoluminescene property at 380 nm. Especially, the ZnO nanorods deposited for 6 h in solution with a concentration of 0.005M showed a stronger (101) peak than they did (100) or (002) peaks. In addition, these ZnO nanorods showed a good electrical property, with the lowest resistance among the four samples, because the nanorods were densely in contact and relatively without pores. Therefore, a ZnO nanorod substrate is useful as a highly sensitive biochip substrate to detect biomolecules using an electrochemical method.

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.596-601
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• 2009

Double-layered ZnO nanostructures have been synthesized by aqueous solution method on (001) plane of ZnO nanorod. A stepwise changing of aqueous solution concentration gave rise to a new nano-structured layer consisting of either multiple of nanorods or nanowires with much smaller radii than that of the ZnO nanorod on which the new layer was grown. As the first step the ZnO nanorods have been grown to have the (001) preferential orientation in the aqueous solution consisting of 0.1M zinc nitrate and 0.1 M HMT. This preferentially aligned ZnO nanorods have been regrown in either a less diluted solution of 0.01M zinc nitrate and 0.01 M HMT or a more diluted solution of 0.005M zinc nitrate and 0.01 M HMT. A new nano-layer consisting of numerous aligned nanorods or nanowires has been produced on the (001) planes of ZnO nanorods. The growth mechanism for this double layered ZnO nanostructure is ascribed to the (001) polar surface energy instability and inhibition of (001) plane growth due to the step-wise change of aqueous solution concentration; ZnO nuclei formed on the (001) plane grow preferentially in (010) plane instead of (001) plane to reduce the total surface energy. Surface area of ZnO nanostructure can be increased in orders of magnitudes by forming a new layer consisting of smaller nanorods/nanowires on (001) plane of ZnO nanorods.

• Journal of the Korean institute of surface engineering
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• v.54 no.5
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• pp.260-266
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• 2021

Synthesizing low-dimensional structures of oxide semiconductors is a promising approach to fabricate highly efficient gas sensors by means of possible enhancement in surface-to-volume ratios of their sensing materials. In this work, vertically aligned zinc oxide (ZnO) nanorods are successfully synthesized on a transparent glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Zn metal film. Structural and optical characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy reveals the successful preparation of the ZnO nanorods array of the single hexagonal wurtzite crystalline phase. From gas sensing measurements for the nitrogen dioxide (NO₂) gas, the vertically aligned ZnO nanorod array is observed to have a highly responsive sensitivity to NO₂ gas at relatively low concentrations and operating temperatures, especially showing a high maximum sensitivity to NO₂ at 250 ℃ and a low NO₂ detection limit of 5 ppm in dry air. These results along with a facile fabrication process demonstrate that the ZnO nanorods synthesized on a transparent glass substrate are very promising for low-cost and high-performance NO₂ gas sensors.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.446-446
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• 2011

One dimensional (1-D) structures of ZnO nanorods are promising elements for future optoelectronic devices. However there are still many obstacles in fabricating high-quality p-type ZnO up to now. In addition, it is limited to measure the degree of the doping concentration and carrier transport of the doped 1-D ZnO with conventional methods such as Hall measurement. Here we demonstrate the measurement of the electronic properties of p- and n-doped ZnO nanorods by the Kelvin probe force microscopy (KPFM). Vertically aligned ZnO nanorods with intrinsic n-doped, As-doped p-type, and p-n junction were grown by vapor phase epitaxy (VPE). Individual nanowires were then transferred onto Au films deposited on Si substrates. The morphology and surface potentials were measured simultaneously by the KPFM. The work function of the individual nanorods was estimated by comparing with that of gold film as a reference, and the doping concentration of each ZnO nanorods was deduced. Our KPFM results show that the average work function difference between the p-type and n-type regions of p-n junction ZnO nanorod is about ~85meV. This value is in good agreement with the difference in the work function between As-doped p- and n-type ZnO nanorods (96meV) measured with the same conditions. This value is smaller than the expected values estimated from the energy band diagram. However it is explained in terms of surface state and surface band bending.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.3
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• pp.178-183
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• 2014

Recently, various type of nanomaterials such as nanorod, nanowire, nanotube and their core/shell nanostructures have attracted much attention in photocatalyst due to their unique properties. Among them, Type-II core/shell heterostructures have extensively studied because it has exhibited improved electrical and optical properties against their single-component nanostructure. Such structures are expected to offer high absorption efficiency and fast charge transport due to their stepwised energetic combination and large internal surface area. Thus, it has been considered as potential candidates for high efficient photocatalytic activity. In this work, we introduce a novel chemical conversion process to synthesize Type-II ZnO/ZnSe core/shell heterostructures. A plausible conversion mechanism to ZnO/ZnSe core/shell heterostructres was proposed based on SEM, XRD, TEM and XPS analysis. The ZnO/ZnSe heterostructures exhibited excellent photocatalytic activity toward the decomposition of RhB dye compared to the ZnO nanorod arrays due to enhanced light absorption and the type-II cascade band structure.

• Korean Journal of Materials Research
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• v.28 no.4
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• pp.214-220
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• 2018

We report on the fabrication and photoelectrochemical(PEC) properties of a $Cu_2O$ thin film/ZnO nanorod array oxide p-n heterojunction structure with ZnO nanorods embedded in $Cu_2O$ thin film as an efficient photoelectrode for solar-driven water splitting. A vertically oriented n-type ZnO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type $Cu_2O$ thin film was directly electrodeposited onto the vertically oriented ZnO nanorods array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were characterized using X-ray diffraction and scanning electron microscopy as well as Raman scattering. The PEC properties of the fabricated $Cu_2O/ZnO$ p-n heterojunction photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the $Cu_2O/ZnO$ photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., $0.77mA/cm^2$ at 0.5 V vs $Hg/HgCl_2$ in a $1mM\;Na_2SO_4$ electrolyte, revealing an effective operation of the oxide heterostructure. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs $Hg/HgCl_2$, which made the device self-powered. The observed PEC performance was attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential, including the light absorption and separation processes of photoinduced charge carriers.