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Non-linear optical properties of PECVD nanocrystal-Si nanosecond excitation
양현훈(Yang, Hyeon-Hun),김한울(Kim, Han-Wool),김주회(Kim, Joo Hoe),김철중(Kim, Chul Joong),이창권(Lee, Chang Gwon) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11
A study of the non-linear optical properties of nanocrystal-Si embedded in SiO2 has been performed by using the z-scan method in the nanosecond and femtosecond ranges. Substoichiometric SiOx films were grown by plasma-enhanced chemical-vapor deposition(PECVD) on silica substrates for Si excesses up to 24 at/%. An annealing at 1250?C for 1 hour was performed in order to precipitate nanocrystal-Si, as shown by EFTEM images. Z-scan results have shown that, by using 5-ns pulses, the non-linear process is ruled by thermal effects and only a negative contribution can be observed in the non-linear refractive index, with typical values around -10-10cm²/W. On the other hand, femtosecond excitation has revealed a pure electronic contribution to the nonlinear refractive index, obtaining values in the order of 10-12 cm2/W. Simulations of heat propagation have shown that the onset of the temperature rise is delayed more than half pulse-width respect to the starting edge of the excitation. A maximum temperature increase of {Delta}T=123.1?C has been found after 3.5ns of the laser pulse maximum. In order to minimize the thermal contribution to the z-scan transmittance and extract the electronic part, the sample response has been analyzed during the first few nanoseconds. By this method we found a reduction of 20% in the thermal effects. So that, shorter pulses have to be used obtain just pure electronic nonlinearities.
A Study on properties of a-Si:H layers by photoelectron spectroscopic
양현훈(Yang, Hyeon-Hun),김한울(Kim, Han-Wool),김주회(Kim, Joo Hoe),김철중(Kim, Chul Joong),이창권(Lee, Chang Gwon),소순열(So, Soon-Youl),박계춘(Park, Gye-Choon),이진(Lee, Jin) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11
We report on a detailed study on gap-state distribution in thin amorphous silicon layers(a-Si:H) with film thickness between 5 nm and 20 nm c-Si wafers performed by UV excited photoelectron spectroscopy(UV-PES). We measured how the work function, the gap state density, the position of the Fermi-level and the Urbch-energy depend on the layer thickness and the doping level of the ultra thin a-Si:H(n) layer. It was found, that for phosphorous doping the position of the Fermi level saturates at E_F-E_V=1.47 eV. This is achieved at a gas phase concentration of 10000 ppm PH₃ in the SiH₄/H₂ mixture which was used for the PECVD deposition process. The variation of the doping level from 0 to 20000 ppm PH₃ addition results in an increase of the Urbach energy from 65 meV to 101 meV and in an increase of the gap state density at midgap(E_i-E_V=0.86eV) from 3{times}10^{18} to 2{times}1019cm^{-3}eV^{-1}.
에너지/환경 : 저급탄의 열분해 및 촤-CO2 가스화 반응의 속도론적 연구
강석환 ( Suk Hwan Kang ),류재홍 ( Jae Hong Ryu ),박수남 ( Soo Nam Park ),변용수 ( Yong Soo Byun ),서석정 ( Seok Jung Seo ),윤용승 ( Yong Seung Yun ),이진욱 ( Jin Wook Lee ),김용전 ( Yong Jeon Kim ),김주회 ( Joo Hoe Kim ),박삼룡 ( 한국화학공학회 2011 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.49 No.1
인도네시아 아역청탄인 ABK탄과 중국 갈탄(lignite)과 같은 저급탄에 대한 열분해와 촤-CO2 가스화반응에 대한 실험을 비등온의 승온 조건에서 열중량분석기(Thermogravimetric analysis, TGA)를 이용하여 수행하였다. 열분해 속도는 2단계, 1차의 열분해 모델(Kissinger 법의 변형)에 의해 잘 모사되었다. 촤의 CO2 가스화반응은 수축 핵 모델에 적용하여 초기의 활성화 에너지가 ABK탄은 189.1 kJ/mol, lignite는 260.5 kJ/mol의 값을 얻었으며, 수축 핵 모델에 의해 잘 모사되었다. 특히, 촤의 CO2 가스화반응에서 활성화 에너지는 무연탄의 결과와 유사하였으며, 다른 모델이나 석탄의 종류에 따라 큰 차이를 보였다. Thermogravimetric analysis(TGA) was carried out for pyrolysis and char-C02 gasification of low rank Indonesian ABK coal and China lignite. The pyrolysis rate was successfully described by a two-step model adopting the modified Kissinger method. The shrinking core model, when applied to char-C02 gasification gave initial activation energy of 189.1 kj/mol and 260.5 kj/mol for the ABK coal and China lignite, respectively. Thus, the char-C02 gasification has been successfully simulated by the shrinking core model. In particular, the activation energy of char-C02 gasification calculated in this work is similar to the results on the anthracite coal, but considerable difference exjsts when other models or coal types are used.