Sangtae Lee

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.

Abnormal variation of the growth rate under high NH3 injected regime in the growth of GaN by NH3-source MBE

Unusual growth-rate variation during GaN formation using gas-source MBE has been discussed with respect to the chemical reactions occurring in the transition layer. A series of samples were prepared to confirm the assumption by verifying the growth regime and the impacts on the crystal quality of the GaN film. We found that the growth rate can be varied along with the amount of NH3 supply even under NH3-rich condition with a fixed Ga flux. Two growth conditions were investigated for their impact on the transition layer. One was the atomic force microscopy result, which revealed that the adatom migration length is closely related to the transition layer formation. The other one is the photoluminescent spectra, which revealed that the luminescence property of GaN is strongly related to the transition layer.

Study on the Crystallinity Change Caused by Heat Treatment of AlN Thin Films Grown by Using Pulsed Sputter Deposition

AlN thin films were grown by using pulsed sputter deposition (PSD), and the cause of the crystallinity change caused by heat treatment was investigated. The AlN thin films were grown on a sapphire substrate and annealed at temperatures of 700 ∼ 1100 ◦C by flowing nitrogen gas through a horizontal furnace. The change in the surface morphology, the crystallinity, and the vibration mode were investigated. The PSD-grown samples showed relatively good crystallinity with a very flat surface. Furthermore, the effect of residual strain, which is commonly observed in thin AlN films deposited by sputtering, was confirmed using X-ray diffraction. When the heat treatment temperature was above 900 ◦C, surface oxidation proceeded rapidly, and the surface morphology and the changes in the crystal phase were confirmed. From the results of Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, the oxidation observed during annealing was found to be related to the interstitial Al defects occurring during film formation.

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.

Growth of O- and Zn-polar ZnO films by DC magnetron sputtering

Department of Nano-semiconductor Engineering, National Korea Maritime University, Busan 606-791, Korea*Department of Offshore Plant Management, National Korea Maritime University, Busan 606-791, Korea**Division of Electrical and Electronics Engineering, National Korea Maritime University, Busan 606-791, Korea***PAN-Xal Co., Ltd., Suwon 443-380, Korea****Center for Interdisciplinary Research, Tohoku University, Sendai 980-8577, Japan