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홍승휘,Suk-Ho Choi,Dae Won Moon,Hosun Lee,Kang Ju Lee,Kyung Joong Kim,Sung Kim 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
Si-rich SiOx single-layer and SiOx/SiO2 multilayer (ML) lms have been prepared by ion beam sputtering under various conditions of stoichiometry of the SiOx layer and deposition temperature (TS). Annealing at 1100 C leads to the formation of Si nanocrystals in the SiOx layers. The phase separation between SiO2 matrix and Si nanocrystals is more clearly seen at higher TS. High-resolution transmission electron microscopy images clearly demonstrate the existence of Si nanocrystals, which exhibit photoluminescence (PL) in the visible range. The PL intensity of the MLs decreases with increasing x or TS, which turns out to be caused by the reduction of the nanocrystalline Si fraction. The PL spectra are blue-shifted by increasing the oxygen content (x) or decreasing the layer thickness, which is consistent with the quantum connement eect.
이온빔 스퍼터링과 열처리에 의해 SiOx/SiO_(2) 다층구조에 형성한 Si 나노결정의 광루미네센스 특성 연구
홍승휘,최석호 경희대학교 자연과학종합연구원 2003 자연과학논문집 Vol.9 No.1
The effects of stoichiometry(x) and substrate temperature(T_(s)) on SiOx/S_(1)O_(2) multilayers(MLs) have been systematically investigated during their growth by reactive ion beam sputter deposition, The photoluminescence(PL) spectra of the post-annealed samples are strongly correlated with the formation of S_(1) nanocrystals in the MLs, which is confirmed by high resolution transmission electron microscopy. These results suggest that T_(s) and x play an important role for the visible PL attributed to the quantum confinement effect of S_(1) nanocrystals.
Nonvolatile Memories of Ge Nanodots within ZrO2
홍승휘,김민철,HyeRyong Kim,Suk-Ho Choi,KyungJoong Kim 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6
Trilayer structures of ZrO2/Ge nanodots (NDs)/ZrO2 were fabricated by using ion-beam-sputtering deposition and annealing. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy demonstrated that Ge NDs of 3 ~ 4 nm size were formed between the stoichiometric ZrO2 layers. The memory window, which was estimated by using the capacitance-voltage hysteresis, increased to ~V with increasing annealing temperature (TA) to 500℃ and was almost invariant by further increase of TA to 900℃. These results suggest that the Ge NDs within ZrO2 are promising for thermally-stable nonvolatile memory devices.
황성원,김창오,홍승휘,신동희,최석호 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.6
We report a synthesis approach using a Si-nanocrystal (NC) layer that is formed by annealing a Si-rich oxide with different oxygen contents (stoichiometry, x) for growing vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs). VA-MWCNTs with a largest length and diameter of about 190 µm and 20 nm, respectively, were grown at x = 1.6. The atomic-resolved transmission electron microscopy image of the tube wall at x = 1.6 revealed almost-straight and well-separated graphitic sheets without defects, possibly resulting from the highest-quality Si NCs at x = 1.6. Active iron catalyst particles were formed on the Si-NC layer, resulting in the formation of highlyaligned MWCNTs. Possible mechanisms are described to explain the experimental results.
Microscopic Characterization of Silicon Nanocrystals Formed by In-situ Annealing
황성원,신동희,홍승휘,최석호 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
Scanning tunneling microscopy (STM) and atomic force microscopy were used for characterizing Si nanocrystals (NCs) embedded in SiO2. The Si NCs were formed by in-situ annealing of Si-rich oxide (SiOx) films grown by ion beam sputtering. The thickness of the SiOx layers was 200 nm, and the annealing was done at 1165℃ for 3 min. The sizes and the densities of the Si NCs were estimated as 4 ~ 2.5 nm and 6.2 × 1011 ~ 3.4 × 1012 cm−2, respectively, for x = 1.2 to 1.8, almost consistent with the high-resolution transmission electron microscopy (HRTEM) results. The photoluminescence peak of the Si NCs blueshifts from 1.44 to 1.63 eV as x increases from 1.0 to 1.8, as expected by the quantum confinement effect based the NC-size variation measured by using STM and HRTEM. These results demonstrate that STM is an accurate tool for characterizing the distributions of sizes and densities for Si NCs.