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Choe, Hyeokmin,Nho, Hyun Woo,Park, Jonghoon,Kim, Jin Bae,Yoon, Tae Hyun Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.2
For real-time monitoring of colloidal nanoparticles (NPs) in aqueous media, a light sheet type dark-field microscopy system combined with a microfluidic concentration gradient generator (${\mu}FCGG$-LSDFM) was developed. Various concentrations of colloidal Au NPs were simultaneously generated with the iFCGG and characterized with the LSDFM setup. The number concentrations and hydrodynamic size distributions were measured via particle counting and tracking analysis (PCA and PTA, respectively) approaches. For the 30 nm Au NPs used in this study, the lower detection limit of the LSDFM setup was 3.6 ng/mL, which is about 400 times better than that of optical density measurements under the same ${\mu}FCGG$ system. Additionally, the hydrodynamic diameter distribution of Au NPs was estimated as $39.7{\pm}12.2nm$ with the PTA approach, which agrees well with DLS measurement as well as the manufacturer's specification. We propose this ${\mu}FCGG$-LSDFM setup with features of automatic generation of NP concentration gradient and real-time monitoring of their physicochemical characteristics (e.g., number concentration, and hydrodynamic size distribution) as an important component of future high-throughput screening or high-content analysis platforms of nanotoxicity.
Hyeokmin Choe,Hyun Woo Nho,Jonghoon Park,Jin Bae Kim,Tae Hyun Yoon 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.2
For real-time monitoring of colloidal nanoparticles (NPs) in aqueous media, a light sheet type dark-field microscopy system combined with a microfluidic concentration gradient generator (㎌CGG-LSDFM) was developed. Various concentrations of colloidal Au NPs were simultaneously generated with the ìFCGG and characterized with the LSDFM setup. The number concentrations and hydrodynamic size distributions were measured via particle counting and tracking analysis (PCA and PTA, respectively) approaches. For the 30 nm Au NPs used in this study, the lower detection limit of the LSDFM setup was 3.6 ng/mL, which is about 400 times better than that of optical density measurements under the same ㎌CGG system. Additionally, the hydrodynamic diameter distribution of Au NPs was estimated as 39.7 ± 12.2 nm with the PTA approach, which agrees well with DLS measurement as well as the manufacturer’s specification. We propose this ㎌CGG-LSDFM setup with features of automatic generation of NP concentration gradient and real-time monitoring of their physicochemical characteristics (e.g., number concentration, and hydrodynamic size distribution) as an important component of future high-throughput screening or high-content analysis platforms of nanotoxicity.
Control of nucleation characteristics of GaN nanograins grown by hydride vapor phase epitaxy
Chinkyo Kim,Boa Shin,Hyeokmin Choe,Jaiwon Jeon,이상화,Taegeon Oh,Yuri Sohn 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III
GaN nanograins were grown by hydride vapor phase epitaxy and the nucleation characteristics of the nanograins were investigated by using secondary electron images. It was found that the density and the diameter of the grains could be {\it independently} controlled by changing the substrate temperature and the flow rate of N$_2$ over a Ga boat. In addition to the independent controllability of the diameter and density, the formation of nanofacets on the individual nanograins was observed to become prominent with increased growth temperature. These nanofacets were inferred to act as quasi-substrates for subsequently adsorbing atoms. In fact, randomly oriented nanorods in consistent with the nanofaceted grains were observed to form with similar growth conditions.
수소기상화합물 증착법을 이용한 질화갈륨(GaN) 박막과 나노막대의 선택적 과성장(ELOG)
오태건(Taegeon Oh),이상화(Sanghwa Lee),최혁민(Hyeokmin Choe),손유리(Yuri Sohn),전재원(Jai Weon Jean),김진교(Chinkyo Kim) 한국생산제조학회 2007 한국공작기계학회 춘계학술대회논문집 Vol.2007 No.-
넓은 에너지 띠를 가지고 있는 GaN는 짧은 파장의 광전소자를 제작하는데 쓰일 수 있으며, 격자상수가 맞는 기판이 없기 때문에 보통 다량의 결정성 결함이 박막 내부에 발생한다. 질화갈륨(GaN)의 Epitaxial lateral overgrowth(ELO)는 GaN의 bulk substrate가 없는 상황에서 이종기판과의 격자상수 차이에 인하여 생기는 다량의 결정성 결함을 줄이기 위한 방편으로서, hydride vapor phase epitaxy(HVPE)를 이용하여 성장조건을 다양하게 변화시켜 가며 ELOG 방식에 의해 성장된 GaN의 표면 형상을 연구해 보았다.
이상화,Chinkyo Kim,Boa Shin,Hyeokmin Choe,Jaewon Jeon,Taegeon Oh 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
The effect of NH$_3$ pretreatment at high temperature (above 1000~$^{\circ}$C) on the surface morphologies of GaN films grown on 0.3$^{\circ}$-miscut sapphire substrates by using hydride vapor phase epitaxy (HVPE) was investigated by employing scanning electron microscopy (SEM) and atomic force microscopy (AFM). NH$_3$ pretreatment introduced many hillocks on the surfaces of the GaN films, and the coarsening effect of nucleated grains was clearly observed with the increasing flow rate and exposure time of NH$_3$. Unlike previously reported results on no-miscut substrates by other researchers, high-temperature pretreatment of NH$_3$ did not produce mirror-like flat surface morphologies, but the GaN films grown without NH$_3$ pretreatment showed flat terraces with steps, which were supposedly due to an enhanced nucleation mechanism through the step edges present in miscut sapphire substrates