Papers by Author: Hong Lae Sohn

Abstract: The efficient detection method based on nanostructured photonic DBR PSi has been developed for DMMP, which is a simulant for G-type nerve agents. The manufactured DBR PSi chip exhibits a sharp photonic band gap at 520 nm. The detection method involves the shift of DBR peak in reflectivity spectra under the exposure of vapors of analyte. Rapid detection has been achieved in few seconds, in situ, and observed by the red-shift of DBR peak resulted from the increase of refractive indices in DBR PSi. When DBR PSi chip is exposed to DMMP, TEP, and DEEP-saturated air, DBR peak in reflectivity is red shifted by 10 nm, 25 nm, and 10 nm, respectively. Real-time detection for the nerve gases indicates that the measurement is reversible. Detection limit of DMMP (1.5 ppm) using DBR PSi is 8.8 mg/m3 for 1 min.

Abstract: We developed a device that makes possible the normal generation of low-temperature plasma under atmospheric pressure. For plasma generation, a radio frequency of rf (13.56 MHz) was used, for plasma gas, helium (He), and for material gases, acetylene (C2H2) and toluene (C6H5CH3) were used. As a result of measuring Fourier transform infrared (FT-IR) after adding the CO2 gas to the generated plasma, the absorption of C=O (carboxyl group) was observed around 1715 cm-1. When the flow rates of the added CO2 increased, the absorption peak increased at the same time, and we knew that this originated from the CO2 molecules.

Abstract: Distributed Bragg reflector (DBR) porous silicons exhibiting unique reflectivity were successfully obtained by an electrochemical etching of silicon wafer using square wave currents. Optically encoded smart dust which retained optical reflectivity was obtained from DBR porous silicon film in organic solution by using ultra-sono method. The size of optically encoded smart dust was measured by field emission scanning electron micrograph (FESEM) and was about 500 nm to few microns depending on the duration of sonication. Investigation for the optical characteristics of smart dust revealed that smart dust could be useful for application such as chemical sensor for detecting organic vapors.