Jieun Koo

Influence of growth mode on the structural, optical, and electrical properties of In-doped ZnO nanorods

The growth mechanism of In-doped ZnO (ZnO:In) nanorods grown on AuGe/Si(111) substrates has been investigated. Unlike to general vapor-liquid-solid mechanism, the adatom kinetics on the surface determines the length-diameter relationship [L(D)], initial nuclei size (D∗), and spatial distribution of impurity atoms. The incorporated In-concentration was estimated to be within solid solubility limit of ZnO in terms of x-ray diffraction analysis, but the evolution of photoluminescence peak position and intensity revealed an evidence of extrinsic carrier increment. Hall-effect measurement was used to evaluate the carrier concentration of ZnO:In nanorods.

Development of waterborne oil spill sensor based on printed ITO nanocrystals.

Oil spill accidents occasionally occur in coastal and ocean environments, and cause critical environmental damage, spoiling the marine habitats and ecosystems. To mitigate the damages, the species and amount of spilled oil should be monitored. In this study, we developed a waterborne oil spill sensor using a printed ITO layer. ITO is a compatible material for salty environments such as oceans because ITO is strong against corrosion. The fabricated sensor was tested using three oils, gasoline, lubricant and diesel, and different oil thicknesses of 0, 5, 10, and 15mm. The results showed that the resistance of the sensor clearly increased with the oil thickness and its electrical resistance. For sustainable sensing applications in marine environments, XRD patterns confirmed that the crystal structure of the ITO sensor did not change and FE-SEM images showed that the surface was clearly maintained after tests.

Fabrication of printed ITO sensor for the ammonia hydroxide detection

Monitoring the hazardous and noxious substances (HNS) is a very important issue for mitigating the influence of catastrophic accidents in ocean and coastal areas. However, research on the HNS sensor is just in the beginning stage. In this study, we proposed a new HNS sensor using a printed ITO layer. We carried out a series of experiments of detecting the NH4OH and seawater solution to investigate the feasibility as a HNS sensor. The resistance of ITO layer dropped abruptly when it soaked into the solutions. The resistance change (δR) was linearly correlated with the NH4OH concentration of the solution, also it can be classified into two states; one is the transition stage, the other is the stabilized stage. The former is considered to be caused by the large capacitance of the electrical double layer (EDL) on the ITO surface. Also, the ITO layer showed considerable chemical stability within our experimental condition. In this paper, we have investigated the feasibility of printed ITO layer as a sensitive and cheap HNS sensor.

High Performance Printed Ultraviolet-Sensors Based on Indium-Tin-Oxide Nanocrystals

A UV sensor was fabricated by screen printing indium–tin-oxide (ITO) nanocrystals on to quart glass. The initial printed ITO layer showed a resistivity too high for sensing applications, but considerable improvements were achieved through annealing under external pressure. The effects of this pressurized annealing were investigated using a commercial ITO film. The annealing aided the development of low-resistivity ITO through the repression of complex defects. The feasibility of the ITO sensor was confirmed through annealing coil-shaped ITO sensors under different conditions. Pressurized annealing greatly enhanced the output signal intensity under similar UV illumination conditions.

Fabrication of LED Solar Simulator for the Evaluation of Large Solar Panel

We developed a new solar simulator to evaluate a large-scale solar cell using seven kinds of LEDs (Infrared, Red, Yellow, Green, Blue, White and Ultra Violet LED). LED solar simulator can be displaced the existing solar simulator which has several demerits such as high power consumption and short lifetime. We have tried to fabricate LED solar simulator which fulfills the spectrum for AM 1.5G condition, and to verify the feasibility of LED solar simulator.

Effect of anion-to-cation supplying ratio on the surface morphology of AlN films grown on ZnO substrates at low temperature

The authors investigated the evolution of surface morphology of AlN films grown on ZnO substrates at low temperature (LT) (400°C) as a function of anion/cation supplying ratio (V/III ratio). Unlike the well-known favorable growth conditions for high-temperature growth, smooth-surface LT-AlN layers were obtained under the O-polar surface, stoichiometric, and N-rich conditions. LT-AlN layers revealed smooth surface (roughness in root mean square=0.20nm for AlN on O-polar ZnO and 0.44nm for AlN on Zn-polar ZnO) and quite low etch-pit density (∼2×106cm−2 for AlN∕Zn-polar ZnO).