Jeong Sook Ha

Origin of the slow photoresponse in an individual sol-gel synthesized ZnO nanowire

Photocurrent of a single ZnO nanowire synthesized by a sol-gel route was investigated. In vacuum, the dark current was bigger but the photoresponse was slower than that in air, attributed to the release of the available charge carriers by the desorption of water molecules and the decrease of the exchange rates of molecular ions. Under the steady radiation of the ultraviolet light (λ=325nm), a gradual decrease of the photocurrent was noticeable, which can be explained in terms of the annihilation of the carriers by the replacement of hydroxyl groups (OH−) by O2−, resulting in the decrease of charge carriers.

Effect of Ultrasound on Surfactant-Aided Soil Washing

The use of ultrasound as an enhancement mechanism in the surfactant-aided soil-washing process was examined by conducting desoption tests of soils contaminated with naphthalene or diesel-oil. The experiments were conducted to elucidate the effect of ultrasound on the mass transfer from soil to the aqueous phase using naphthalene-contaminated soil. In addition, the use of ultrasound for the diesel-oil-contaminated soil was investigated under a range of conditions of surfactant concentration, sonication power, duration, soil/liquid ratio, particle size and initial diesel-oil concentration. The ultrasound used in the soil-washing process significantly enhanced the mass transfer rate from the solid phase to the aqueous phase. The removal efficiency of diesel-oil from the soil phase generally increased with longer sonication time, higher power intensity, and large particle size.

Controlling orientation of V2O5 nanowires within micropatterns via microcontact printing combined with the gluing Langmuir?Blodgett technique

Previously, we suggested a facile method to transfer dioctadecyldimethylammonium bromide (DODAB)/V(2)O(5) nanowire hybrid patterns onto both hydrophobic and hydrophilic substrates via microcontact printing combined with the Langmuir-Blodgett (LB) technique (Park et al 2007 Nanotechnology 18 405301). Herein, we report on the delicate control of the orientation of V(2)O(5) nanowires within the micropatterns transferred via the gluing LB technique using a patterned polydimethylsilicate (PDMS) stamp. According to the orientation of the PDMS line patterns relative to the air-water interface, the aligned orientation of the nanowires, either parallel or perpendicular to the patterns, could be obtained and attributed to the moving direction of the water menisci formed between the PDMS stamp and water. In particular, addition of a small amount of ethanol in the subphase enhanced the dispersion of the DODAB at the air-water interface as well as the aggregation of V(2)O(5) nanowires, resulting in alignment of the V(2)O(5) nanowires via compression of the hybrid LB film by a barrier. Directional alignment of nanowires has potentially broad applications in the fabrication of aligned nanowire devices.

Control of adsorption and alignment of V2O5 nanowires via chemically functionalized patterns

We developed a method to precisely control the locations and orientations of deposited divanadium pentoxide (V2O5) nanowires on SiO2 surfaces using chemically functionalized patterns. The nanowires were deposited onto the substrates either from solution or via the edge transfer mechanism of micro-contact printing. In both cases, negatively charged V2O5 nanowires showed a strong adsorption selectivity onto 3-aminopropyltriethoxysilane (APS) self-assembled monolayers (SAMs) with positively charged functional groups, whereas the SAMs with non-polar and neutral terminal groups of octadecyltrichlorosilane (OTS) worked as perfect passivation layers. In particular, directional alignment of nanowires inside the chemically patterned area, depending upon the shapes of the patterns, was observed. The wires were aligned along the long axis of the pattern when the width of the APS pattern was as small as 1xa0µm. This strategy allows us to control the adsorption and alignment of V2O5 nanowires on the substrates, which could be used for various nano-device applications such as interconnection of electronic circuits.

Array of ultraviolet luminescent ZnO nanodots fabricated by pulsed laser deposition using an anodic aluminium oxide template

Ordered arrays of ZnO nanodots were fabricated by pulsed laser deposition (PLD) using an anodic aluminium oxide (AAO) nanopore membrane. Hexagonal-shaped ZnO nanodots with an average diameter of 60xa0nm and a periodicity of 100xa0nm were uniformly assembled into hexagonally ordered nanopores of the AAO membrane. Control of the oxygen pressure used in PLD resulted in a preferential photoluminescence (PL) at 380xa0nm from the ZnO nanodots: keeping the higher O2 pressure gave a dominant PL peak in the UV range over the visible range, which is attributed to the reduction of the number of oxygen vacancies.

Array of luminescent Er-doped Si nanodots fabricated by pulsed laser deposition

Ordered arrays of Er-doped Si nanodots were fabricated by pulsed laser deposition using an anodic aluminum oxide (AAO) nanopore membrane. Er-doped Si (Si:Er) nanodots with an average diameter of 60–80nm and a periodicity of 100nm were uniformly assembled into hexagonally ordered nanopores of AAO membrane. Photoluminescence (PL) spectra taken from Si:Er nanodots showed an emission peak at 1.54μm, which is due to intra-4f shell transition (I13∕24→I15∕24) of Er3+ ions. Postannealing of nanodot arrays up to 500°C resulted in the enhancement of PL intensities without enlargement or aggregation of the nanodots.

Fabrication of Nanodot Arrays on Si by Pulsed Laser Deposition Using Anodic Aluminum Oxide Nanopore Membrane as Mask

We demonstrate the fabrication of metal and semiconductor nanodot arrays on Si by pulsed laser deposition using an anodic alumina membrane as a mask. A Hexagonal-close-packed nanopore membrane mask was fabricated by the anodic oxidation of aluminum sheet. Pulsed laser deposition of Ag, Ni, ZnO, and Er-doped Si (Si:Er) nanodots was performed on a Si substrate to which an alumina membrane mask adheres by van der Waals interaction. Highly ordered arrays of Ag, Ni, ZnO, and Si:Er nanodots with average diameters ranging from 55 to 86 nm and a periodicity of ~100 nm were obtained. Also, the time-resolved images of laser-produced plasma plumes were analyzed to examine the dynamical properties of the ejected materials.

Effects of Al content on the electrical properties of LaxAlyOz films grown on TiN substrate by atomic layer deposition

The effects of Al content on the electrical properties of LaxAlyOz films grown on TiN substrate by atomic layer deposition technique were investigated. With increasing Al content, the leakage current characteristics improved, but the dielectric constant became smaller. Postannealing of the films at temperatures up to 500°C reduced the leakage current density due to thermal stabilization by the addition of Al. For the 25-nm-thick La2.4AlO3.3 film, the authors obtained a dielectric constant of 22 and a leakage current density of 10−7A∕cm2 at 1V after postannealing at 450°C, which gives an equivalent oxide thickness of 3.8nm.

Controlled direct patterning of V2O5 nanowires onto SiO2 substrates by a microcontact printing technique

Vanadium pentoxide (V2O5) nanowires were directly transferred to desired patterns on SiO2 substrates using the microcontact printing (MCP) technique. The hydrophilicity of the poly(dimethylsiloxane) (PDMS) stamp exerted a strong influence on the mechanism of transfer of polar V2O5 nanowires onto the substrate. The V2O5 nanowires were transferred from the relief side of the hydrophilic stamp, whereas they were transferred from the recess edges of the hydrophobic one forming agglomerated nanowire patterns on the substrate. When the hydrophobic stamp was used, the width of the agglomerated nanowire patterns could be controlled by the concentration of the nanowire solution as well as by the width of the recess area of the PDMS stamp. This method allows us to generate nanowire patterns with a submicrometre line width, which is much smaller than a the few-micrometre sizes of PDMS stamp patterns. When the hydrophilic stamp with a small-sized (≤ the average length of V2O5 nanowires) pattern was used, alignment of individual nanowires in the direction of the boundary of the line pattern was obtained. These results suggest that the transfer mechanism in the MCP process strongly depends on the wetting interaction between the stamp and the nanowire ink.

Facile Transfer of Thickness Controllable Poly(methyl methacrylate) Patterns on a Nanometer Scale onto SiO2 Substrates via Microcontact Printing Combined with Simplified Langmuir-Schaefer Technique

We report on the facile patterning of poly(methyl methacrylate) (PMMA) layers onto SiO2 substrates via microcontact printing combined with the simplified Langmuir-Schaefer (LS) technique. Langmuir film of PMMA was formed just by dropping a dilute PMMA solution onto the air/water surface in a glass Petri dish via self-assembly, and it was used as an ink for the patterned poly(dimethylsilioxane) (PDMS) stamp. The transferred film properties were systematically investigated with variation of postannealing temperature, molecular weight of PMMA, and the inking number. The patterned PMMA film surface was smooth with no vacancy defect in a few micrometers scale AFM images over the whole film area after post-annealing process. The thickness of the PMMA patterns was controlled on the nanometer scale by the number of inkings of the LS layer of PMMA on the PDMS stamp. By using the PMMA patterns as a barrier and a sacrificial layer against the chemical etching and metal deposition, SiO2 and metal patterns were fabricated, respectively. The PMMA layers also worked as a passivation layer against the patterning of V2O5 nanowires and the selective adsorption of single-walled carbon nanotubes (SWCNTs). We also fabricated thin film transistors using patterned SWCNTs with different percolation states and investigated the electrical properties.