Seung Hyun Shim

Variation of ZnO shell thickness and its effects on the characteristics of coaxial nanowires

We have changed the thickness of the ZnO shell layers in SiO(x)/ZnO core-shell nanowires by increasing the atomic layer deposition (ALD) cycle, using diethylzinc (DEZn) and H(2)O as precursors of Zn and O, respectively. The samples were characterized by means of x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectroscopy. While the thickness of the ZnO shell layers increased almost linearly with increase of the ALD cycle, their tubular morphologies were maintained. The variation in the thickness of the ZnO shell layers was accompanied by changes in the relative intensities of the characteristic ultraviolet (UV) and visible emission bands and by a shift of the UV peak position. On the basis of the observed relationship between the XRD shell grain size and the PL shift, we suggest that the PL shift is attributable to an exciton confinement effect. The findings in this study can be applied to a wide range of materials, and are expected to contribute to the development of potential applications of coaxial nanowires.

Synthesis and Characteristics of SnO2 Nanorods on Pd-Coated Substrates

We have fabricated tin oxide (SnO2) nanorods on palladium-coated substrates by carrying out the thermal evaporation of solid Sn powders. We have employed X-ray diffraction, scanning electron microscope, transmission electron microscope and photoluminescence (PL) spectroscopy to characterize the synthesized products. The obtained 1D nanomaterials with a jagged surface were SnO2 with rutile structure. PL spectra exhibited visible light emission.

Temperature-controlled synthesis of In2Ge2O7 nanowires and their photoluminescence properties

By controlling the heating temperature of a mixture of In and Ge powders, we have obtained monoclinic In2Ge2O7 nanowires at 600?700??C, whereas we have produced cubic In2O3 nanowires at 900??C. The In2Ge2O7 nanowires grown at 600??C were terminated by Au-containing nanoparticles, giving evidence that the vapour?liquid?solid model is the major growth mechanism. With the growth process at 700?900??C being dominated by a vapour?solid process, we have discussed the temperature-induced change in growth mechanisms. Photoluminescence measurements at 10?300?K revealed a broad visible emission centred at around 2.5?eV.

Characteristics of Indium Oxide Rod-Like Structures Synthesized on Sapphire Substrates

In2O3 materials consisting of dense arrays of vertically aligned rod-like structures were deposited on sapphire substrates by thermal chemical vapor deposition (CVD) using triethylindium (TEI) and oxygen as precursors at a substrate temperature of 350 oC. The rod-like structure with a triangular cross section had a cubic structure, exhibiting preferred crystallographic orientation in the [111] direction. The photoluminescence spectra of In2O3 structures under excitation at 325 nm revealed a visible emission.

Fabrication of MgO whiskers on metal-coated substrates by heating MgB2 powders: Effects of Ag layer thickness

A thermal evaporation approach was developed to synthesize single-crystalline MgO whiskers on silver (Ag) layer-coated Si substrates. Magnesium diboride (MgB2) and oxygen (O2) were used as Mg and, O precursors, respectively. The synthetic process using a thinner Ag layer facilitated the growth of 1D whiskers, and the product mainly comprises film-like structures with thicker Ag layer thickness. X-ray diffraction and selected area electron diffraction pattern revealed that the whiskers were of a single-crystalline cubic structure of MgO. We also discuss the possible mechanism by which the thickness of the underlying Ag layer affects the resultant morphology of the MgO structures.

Characteristics of Gallium Oxide Nanowires Synthesized by the Metalorganic Chemical Vapor Deposition

We have synthesized the high-density Ga2O3 nanowires on gold (Au)-coated silicon substrates using metalorganic chemical vapor deposition. The nanowires exhibited one-dimensional structures having circular cross sections with diameters in the range of 30-200 nm. The energy dispersive x-ray spectroscopy revealed that the nanowires contained elements of Ga and O, without Au-related impurities. X-ray diffraction analysis and high-resolution transmission electron microscopy showed that the Ga2O3 nanowires were crystalline.

A Study of Ga2O3 Nanomaterials Synthesized by the Thermal Evaporation of GaN Powders

We have synthesized gallium oxide (Ga2O3) nanomaterials at two different growth temperatures on iridium (Ir)-coated substrates by thermal evaporation of GaN powders. The products consist mainly of nanobelts, with some additional nanosheets. The nanobelts were of a single-crystalline monoclinic Ga2O3 structure. The broad emission photoluminescence band of 900°C-products had a different peak position from that of the 970°C-products.

Appearance of Indium Oxide Nanorods in MOCVD Growth

We report on the first synthesis of nanosized In2O3 rods using the TEI as a precursor in the presence of oxygen. The samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy. XRD analysis revealed that the products are In2O3 phase with a tetragonal cubic structure. SEM analysis indicated that the obtained nanorods have a circular cross section and a diameter in the range of 50-150 nm.

Synthesis of SiOx Nanowires through the Thermal Heating of Au-Coated Si Substrates

We have demonstrated the growth of SiOx nanowires by the simple heating of the Au-coated Si substrates. We used X-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy to characterize the samples. The as-synthesized SiOx nanowires had amorphous structures with diameters in the range of 10-70 nm. We have discussed the possible growth mechanism.

SnO2 Nanostructures Synthesized on Co Substrates

This study reported the fabrication of tin oxide (SnO2) nanostructures on Co-coated Si substrates by the thermal heating of Sn powders. The microstructures and morphologies of the resultant nanostructures were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM). The product mainly comprised the tangled nanowires with average diameters in the range of 50-180 nm. The nanostructures were single-crystalline rutile structure of SnO2. The PL measurement with the Gaussian fitting exhibited visible light emission bands centered at 576 nm and 638 nm, respectively. We have discussed the possible growth mechanism of the nanostructures.