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The Effect of the RF-Sputtering Condition on the ZrO2 Thin Film's Characteristics
Honglae Sohn,B. J. Lee,조영태 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.3
ZrO2 thin films were prepared by RF reactive magnetron sputtering at different sputtering powers and different O2 concentrations. These thin films were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). With a sputtering power above 400 W, diffraction peaks appeared not only on the (002) plane but also on the (102), (111) and (122) planes, indicating that thin-film crystals had grown into a polyphase to give randomly oriented structures. No diffraction peak for the tetragonal structure was found. The ZrO2 thin films prepared with O2 concentrations above 5.0 % had a preferred orientation along the (002) plane monoclinic structure of ZrO2.
Preparation of water-soluble silicon quantum dots and their optical property
Sohn Honglae 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.10
New water-soluble silicon quantum dots (Si QDs) with substantial photoluminescence (PL) in the visible region are simply prepared in one-pot synthesis at room temperature for biomedical applications. Hydroxide-capped Si QDs are water-soluble and their PL characteristics were investigated by PL spectroscopy. The water-soluble Si QDs emit the PL at 470 nm with a full width at half maximum height (FWHM) of 90 nm. Absolute quantum yields were measured and were 6%. The integrated PL as a function of time for the water-soluble Si QDs indicates that the PL of water-soluble Si QDs are stable.
Enhanced explosive sensing based on silole-modified luminescent porous silicon
Sohn Honglae 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.1
A porous silicon sensor capable of rapidly detecting explosive vapors has been developed based on quenching fluorescence of silole-modified porous silicon (PSi). The silole-modified PSi sensor for the detecting explosives is based on FRET between silole molecule and PSi. The silole molecules and fresh PSi emit fluorescence at the wavelength of 506 and 717 nm. Surface morphologies of fresh PSi and surface-modified PSi were obtained with a cold FE-SEM. The quenching of PL is observed with increasing time of exposure to dinitrotoluene (DNT), picric acid (PA), and trinitrotoluene (TNT). The quenching efficiency as a function of time for TNT is more significant than for DNT or PA. The sensing efficiency of silole-modified PSi is much higher than that of fresh PSi for the corresponding analyte. The silole-modified PSi provides a new sensing system with high sensitivity and good selectivity for TNT.
Fabrication and Characterization of Optically Encoded Porous Silicon Smart Particles
Sohn, Honglae The Basic Science Institute Chosun University 2014 조선자연과학논문집 Vol.7 No.4
Optically encoded porous silicon smart particles were successfully fabricated from the free-standing porous silicon thin films using ultrasono-method. DBR PSi was prepared by an electrochemical etch of heavily doped $p^{{+}{+}}$-type silicon wafer. DBR PSi was prepared by using a periodic pseudo-square wave current. The surface-modified DBR PSi was prepared by either thermal oxidation or thermal hydrosilylation. Free-standing DBR PSi films were generated by lift-off from the silicon wafer substrate using an electropolishing current. Free-standing DBR PSi films were ultrasonicated to create DBR-structured porous smart particles. Optical characteristics of porous smart particles were measured by FT-IR spectroscopy. The surface morphology of porous smart particles was determined by FE-SEM.
Chemical Sensors Based on Distributed Bragg Reflector Porous Silicon Smart Particles
Sohn, Honglae The Basic Science Institute Chosun University 2015 조선자연과학논문집 Vol.8 No.1
Sensing characteristics for porous smart particle based on DBR smart particles were reported. Optically encoded porous silicon smart particles were successfully fabricated from the free-standing porous silicon thin films using ultrasono-method. DBR PSi was prepared by an electrochemical etch of heavily doped $p^{++}$-type silicon wafer. DBR PSi was prepared by using a periodic pseudo-square wave current. The surface-modified DBR PSi was prepared by either thermal oxidation or thermal hydrosilylation. Free-standing DBR PSi films were generated by lift-off from the silicon wafer substrate using an electropolishing current. Free-standing DBR PSi films were ultrasonicated to create DBR-structured porous smart particles. Three different surface-modified DBR smart particles have been prepared and used for sensing volatile organic vapors. For different types of surface-modified DBR smart particles, the shift of reflectivity mainly depends on the vapor pressure of analyte even though the surfaces of DBR smart particles are different. However huge difference in the shift of reflectivity depending on the different types of surface-modified DBR smart particles was obtained when the vapor pressures are quite similar which demonstrate a possible sensing application to specify the volatile organic vapors.
Sungyong Um, Honglae Sohn 조선대학교 기초과학연구원 2013 조선자연과학논문집 Vol.6 No.4
Three types of functionalized flexible optical composite films based on Bragg structure porous silicon interferometer have been successfully fabricated by casting a toluene solution of polystyrene onto the free-standing porous silicon. The optical properties of composite films are measured. Surface functionalization of porous silicon is determined by FT-IR measurement. Reflectance and transparence properties of composite films are measured for the possible application of tunable optical filter and indicate that the transmission peak occurred at the identical location where the reflection peak appeared.
Fabrication and Characterization of Free-Standing DBR Porous Silicon Film
Sungyong Um, Honglae Sohn 조선대학교 기초과학연구원 2014 조선자연과학논문집 Vol.7 No.1
Distributed Bragg reflector porous silicon of different characteristics were formed to determine their optical constants in the visible wavelength range using a periodic square wave current between low and high current densities. The surface and cross-sectional SEM images of distributed Bragg reflector porous silicon were obtained using a cold field emission scanning electron microscope. The surface image of distributed Bragg reflector porous silicon indicates that the distributions of pores are even. The cross-sectional image illustrates that the multilayer of distributed Bragg reflector porous silicon exhibits a depth of few microns and applying of square current density during the etching process results two distinct refractive indices in the contrast. Distributed Bragg reflector porous silicon exhibited a porosity depth profile that related directly to the current-time profile used in etch. Its free-standing film was obtained by applying an electropolishing current.
Growth of Silicon Nanowire Arrays Based on Metal-Assisted Etching
Donghee Sihn, Honglae Sohn 조선대학교 기초과학연구원 2012 조선자연과학논문집 Vol.5 No.4
Single-crystalline silicon nanowire arrays (SiNWAs) using electroless metal-assisted etchings of p-type silicon were successfully fabricated. Ag nanoparticle deposition on silicon wafers in HF solution acted as a localized microelectrochemical redox reaction process in which both anodic and cathodic process took place simultaneously at the silicon surface to give SiNWAs. The growth effect of SiNWs was investigated by changing of etching times. The morphologies of SiNWAs were obtained by SEM observation. Well-aligned nanowire arrays perpendicular to the surface of the silicon substrate were produced. Optical characteristics of SiNWs were measured by FT-IR spectroscopy and indicated that the surface of SiNWs are terminated with hydrogen. The thicknesses and lengths of SiNWs are typically 150-250 nm and 2 to 5 microns, respectively.