• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.341-341
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• 2016

The discovery of light emission in nanostructured silicon has opened up new avenues of research in nano-silicon based devices. One such pathway is the application of silicon quantum dots in advanced photovoltaic and light emitting devices. Recently, there is increasing interest on the silicon quantum dots (c-Si QDs) films embedded in amorphous hydrogenated silicon-nitride dielectric matrix (a-SiNx: H), which are familiar as c-Si/a-SiNx:H QDs thin films. However, due to the limitation of the requirement of a very high deposition temperature along with post annealing and a low growth rate, extensive research are being undertaken to elevate these issues, for the point of view of applications, using plasma assisted deposition methods by using different plasma concepts. This work addresses about rapid growth and single step development of c-Si/a-SiNx:H QDs thin films deposited by RF (13.56 MHz) and ultra-high frequency (UHF ~ 320 MHz) low-pressure plasma processing of a mixture of silane (SiH4) and ammonia (NH3) gases diluted in hydrogen (H2) at a low growth temperature ($230^{\circ}C$). In the films the c-Si QDs of varying size, with an overall crystallinity of 60-80 %, are embedded in an a-SiNx: H matrix. The important result includes the formation of the tunable QD size of ~ 5-20 nm, having a thermodynamically favorable <220> crystallographic orientation, along with distinct signatures of the growth of ${\alpha}$-Si3N4 and ${\beta}$-Si3N4 components. Also, the roles of different plasma characteristics on the film properties are investigated using various plasma diagnostics and film analysis tools.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.65-65
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• 2015

In this talk, I will introduce two topics. The first topic is the polymer light emitting diodes (PLEDs) using graphene oxide quantum dots as emissive center. More specifically, the energy transfer mechanism as well as the origin of white electroluminescence in the PLED were investigated. The second topic is the facile synthesis of eco-friendly III-V colloidal quantum dots and their application to light emitting diodes. Polymer (organic) light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nanomaterial without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence (EL) from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions. (Sci Rep., 5, 11032, 2015). New III-V colloidal quantum dots (CQDs) were synthesized using the hot-injection method and the QD-light emitting diodes (QLEDs) using these CQDs as emissive layer were demonstrated for the first time. The band gaps of the III-V CQDs were varied by varying the metal fraction and by particle size control. The X-ray absorption fine structure (XAFS) results show that the crystal states of the III-V CQDs consist of multi-phase states; multi-peak photoluminescence (PL) resulted from these multi-phase states. Inverted structured QLED shows green EL emission and a maximum luminance of ~45 cd/m2. This result shows that III-V CQDs can be a good substitute for conventional cadmium-containing CQDs in various opto-electronic applications, e.g., eco-friendly displays. (Un-published results).

• 한국재료학회지
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• 제20권6호
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• pp.289-293
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• 2010

Silicon quantum dots (Si QDs) in a superlattice for high efficiency tandem solar cells were fabricated by magnetron rf sputtering and their characteristics were investigated. SiC/$Si_{1-x}C_x$ superlattices were deposited by co-sputtering of Si and C targets and annealed at $1000^{\circ}C$ for 20 minutes in a nitrogen atmosphere. The Si QDs in Si-rich layers were verified by transmission electron microscopy (TEM) and X-ray diffraction. The size of the QDs was observed to be 3-6 nm through high resolution TEM. Some crystal Si and -SiC peaks were clearly observed in the grazing incident X-ray diffractogram. Raman spectroscopy in the annealed sample showed a sharp peak at $516\;cm^{-1}$ which is an indication of Si QDs. Based on the Raman shift the size of the QD was estimated to be 4-6 nm. The volume fraction of Si crystals was calculated to be about 33%. The change of the FT-IR absorption spectrum from a Gaussian shape to a Lorentzian shape also confirmed the phase transition from an amorphous phase before annealing to a crystalline phase after annealing. The optical absorption coefficient also decreased, but the optical band gap increased from 1.5 eV to 2.1 eV after annealing. Therefore, it is expected that the optical energy gap of the QDs can be controlled with growth and annealing conditions.

• 한국진공학회지
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• 제15권2호
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• pp.194-200
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• 2006

분자선증착기 (Molecular beam epitaxy. MBE)를 이용하여 InP (001) 기판에 자발형성 (Self-assembled) InAs/InAlAs, InAs/InAlGaAs 양자점 (quantum dots, QDs)을 형성하고 구조 및 광학적 특성을 원자력간현미경(Atomic force microscopy, AFM), 투과전자현미경 (Transmission electron microscopy, TEM), 상온 포토루미네슨스 (Photoluminescence, PL) 실험을 통하여 분석하였다. AFM 측정을 통해 표면 형태를 분석한 결과 InAs 양자구조는 기저물질의 표면상태에 따라 양자대쉬, 비대칭적인 형태를 갖는 양자점, 대칭적인 형태를 갖는 양자점과 같이 다양하게 성장되었다. InAlGaAs 물질을 장벽층으로 하는 InAs 양자점의 평균크기는 폭이 대략 23 nm, 높이가 약 2 nm 이었다. 성장조건을 다양하게 변화시켜 광통신시스템에 중요한 파장중의 하나인 $1.55{\mu}m$ 발광파장을 갖는 InAs 양자점을 형성하였다.

• 한국진공학회지
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• 제15권2호
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• pp.223-230
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• 2006

분자선 에피택시 (MBE)법으로 성장된 양자점 원적외선 수광소자(Quantum Dot Infrared Photodetector: QDIP)구조의 $In_{0.5}Ga_{0.5}As/GaAs$ 자발형성 양자점에 대하여, 수소화 처리(Hydrogen Plasma treatment) 전후의 각각의 특성을 광학적인 방법으로 분석하였다. 광학적 특성은 광루미네센스(photoluminescence: PL) 그리고 광전류(Photocurrent: PC)방법으로 각각 15K 300K 10K 130k 범위에서 측정되었으며, 수소화 처리 전후의 $In_{0.5}Ga_{0.5}As$ 자발형성 양자점의 광학적 특성을 비교 분석해보면, 원시료(as-grown)의 하나의 봉우리가 수소화 처리를 통하여 두개의 봉우리로 나뉘지만 PL의 전체 세기(intensity)에는 큰 변화가 없었으며, 광전류는 수소화 처리 후에 감소함을 알 수 있다. 수소화 처리 전후의 샘플에 대해 PL의 결과로부터 활성화 에너지를 계산하여 비교해보면, 수소화 처리 전후의 활성화 에너지가 다름을 알 수 있고, 이 변화된 활성화 에너지 값은 측정된 광전류의 봉우리에 해당하는 에너지 값과 거의 일치함을 알 수 있다. 수소화 처리된 샘플은 역 수소화 처리를 통하여 PL 그래프의 모양이 원시료의 모양으로 되돌아가야 함에도 불구하고, 수소화 처리된 시료의 PL의 그래프와 동일한 모습을 보였다. 이러한 현상은 자발형성 양자점의 수소화 처리에 따른 양자점 내부의 양자점 조성의 변동에 그 원인이 있는 것으로 보인다.

• 한국산학기술학회논문지
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• 제19권3호
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• pp.584-593
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• 2018

유도전동기를 고효율로 제어하기 위한 다양한 연구가 진행되어 왔다. 그 중에서 단위전류당 최대토크 제어기는 최소한의 고정자 전류로 원하는 토크를 제공하기 때문에 유도전동기 드라이브에서 고효율의 동작을 제공한다. 이는 유도전동기를 수학적으로 정밀하게 표현하는 대안모델을 기반으로 제어기가 설계되었기 때문이다. 그러나, 온도 변화에 따른 회전자 저항의 변이는 대안모델의 파라미터와 실제의 유도전동기의 파라미터의 불일치가 발생하여 단위전류당 최대토크 성능을 심각하게 저해하고 단위전류당 최대토크 제어 조건을 만족하지 못하게 하게 있다. 이러한 유도전동기의 운전시에 발생하는 열적 상승으로 인한 파라미터 값의 변화를 고려하는 단위전류당 최대토크적응 제어기가 제안되었다. 본 논문에서는 단위전류당 최대토크적응 제어기가 다수의 운전영역에서도 최소의 고정자 전류로 원하는 토크를 성취하는지를 검토하였다. 실험을 통한 연구에서 회전자의 온도가 증가하더라도 다수의 운전영역에서 25Nm의 토크 명령에서 5%의 차이가 존재하더라도 토크 명령을 정확하게 추구하고 또한, 원하는 토크를 최소한의 고정자 전류로 얻어짐을 확인함으로써 단위전류당 최대토크적응 제어기의 우수성을 검증하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.334-334
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• 2013

In the past decade, the infrared detectors based on intersubband transition in quantum dots (QDs) have attracted much attention due to lower dark currents and increased lifetimes, which are in turn due a three-dimensional confinement and a reduction of scattering, respectively. In parallel, focal plane array development for infrared imaging has proceeded from the first to third generations (linear arrays, 2D arrays for staring systems, and large format with enhanced capabilities, respectively). For a step further towards the next generation of FPAs, it is envisioned that a two-dimensional metal hole array (2D-MHA) structures will improve the FPA structure by enhancing the coupling to photodetectors via local field engineering, and will enable wavelength filtering. In regard to the improved performance at certain wavelengths, it is worth pointing out the structural difference between previous 2D-MHA integrated front-illuminated single pixel devices and back-illuminated devices. Apart from the pixel linear dimension, it is a distinct difference that there is a metal cladding (composed of a number of metals for ohmic contact and the read-out integrated circuit hybridization) in the FPA between the heavily doped gallium arsenide used as the contact layer and the ROIC; on the contrary, the front-illuminated single pixel device consists of two heavily doped contact layers separated by the QD-absorber on a semi-infinite GaAs substrate. This paper is focused on analyzing the impact of a two dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2DAu-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show the enhanced electric fields (thereby increasing the absorption in the active layer) resulting from a surface plasmon, a guided mode, and Fabry-Perot resonances. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors.

• Asian Pacific Journal of Cancer Prevention
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• 제16권9호
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• pp.4013-4018
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• 2015

Objective: To explore the clinical application of recombinant human endostatin (Endostar) in the treatment of patients with non-small cell lung cancer (NSCLC) in Chinese mainland. Materials and Methods: A total of 75 patients diagnosed as NSCLC were randomly divided into control group (37 cases) and treatment group (38 cases). Control group was treated with postoperative complementary chemotherapy containing two-agent platinum protocol on postoperative d21, 3 weeks as a cycle, for totally 4~6 cycles. On this basis, treatment group was added with Endostar $7.5mg/m^2$ on postoperative d8~9, 3~4 h/time, qd, 14 weeks as a cycle, for totally 4 cycles. The interval between every two cycles was 7 d. The 5-year progression-free survival (PFS), 5-year survival time and complications in both groups were observed. Results: Compared with control group, the average PFS increased evidently in treatment group by 9.8 months (41.6 months vs. 31.8 months), and there was significant difference (P<0.05). And the median PFS was 42.5 months in treatment group, obviously longer than that in control group (33.7 months) by 8.8 months (P<0.05). Additionally, the 5-year overall survival rate (OS), average survival time and median survival time (MST) were 47.4%, 50.1 months and 59.3 months in treatment group, significantly higher than the 29.7%, 42.1 months and 43.5 months in control group (P<0.05). Only 1 patient showed poor healing of surgical wound in treatment group, but no surgery-associated complication was found in control group. Moreover, the postoperative complementary therapy-connected complication rates were 63.2% (24/38) and 59.5% (22/37) in treatment group and control group respectively, but there was no significant difference (P>0.05). Conclusions: The application of Endostar combined with sensitive platinum-contained chemotherapeutic agents in the postoperative complementary chemotherapy can be widely used in clinic because it can significantly prolong the long-term survival time of patients with NSCLC.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.297-297
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• 2010

Precise control of the position and density of doping elements at the nanoscale is becoming a central issue for realizing state-of-the-art silicon-based optoelectronic devices. As dimensions are scaled down to take benefits from the quantum confinement effect, however, the presence of interfaces and the nature of materials adjacent to silicon turn out to be important and govern the physical properties. Utilization of visible light is a promising method to overcome the efficiency limit of the crystalline Si solar cells. Si quantum dots (QDs) have been proposed as an emission source of visible light, which is based on the quantum confinement effect. Light emission in the visible wavelength has been reported by controlling the size and density of Si QDs embedded within various types of insulating matrix. For the realization of all-Si QD solar cells with homojunctions, it is prerequisite not only to optimize the impurity doping for both p- and n-type Si QDs, but also to construct p-n homojunctions between them. In this study, XPS and SIMS were used for the development of p-type and n-type Si quantum dot solar cells. The stoichiometry of SiOx layers were controlled by in-situ XPS analysis and the concentration of B and P by SIMS for the activated doping in Si nano structures. Especially, it has been experimentally evidenced that boron atoms in silicon nanostructures confined in SiO2 matrix can segregate into the Si/$SiO_2$ interfaces and the Si bulk forming a distinct bimodal spatial distribution. By performing quantitative analysis and theoretical modelling, it has been found that boron incorporated into the four-fold Si crystal lattice can have electrical activity. Based on these findings, p-type Si quantum dot solar cell with the energy-conversion efficiency of 10.2% was realized from a [B-doped $SiO_{1.2}$(2 nm)/$SiO_2(2\;nm)]^{25}$ superlattice film with a B doping level of $4.0{\times}10^{20}\;atoms/cm^2$.

• 한국농공학회지
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• 제29권4호
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• pp.59-72
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• 1987

Although long-term runoff analysis is important as much as flood analysis in the design of water works, the technological level of the former is relatively lower than that of the latter. In this respect, the precise estimation model for the volume of successive runoff should he developed as soon as possible. Up to now, in Korea, Gajiyama's formula has been widely used in long-term runoff analysis, which has many problems in applying in real situation. On the other hand, in flood analysis, unit hydrograph method has been exclusively used. Therefore, this study aims at trying to apply unit hydrograph method in long-term runoff analysis for the betterment of its estimation. Four test catchment areas were selected ; Maesan area in Namlum river as a representative area of Han river system, Cheongju area in Musim river as one of Geum river system, Hwasun area in Hwasun river as one of Yongsan river system, and Supyung area in Geum river as one of Nakdong river system. In the analysis of unit hydrograph, seperation of effective rainfall was carried out firstly. Considering that effective rainfall and moisture condition of catchrnent area are inside and outside of a phenomenon respectively and the latter is not considered in the analysis, Initial base flow(qb)was selected as an index of moisture condition. At the same time, basic equation(Eq.7) was established, in which qb can take a role as a parameter in relating between cumulative rainfall(P) and cumulative loss of rainfall(Ld). Based on the above equation, computer program for estimation model of qbwas seperately developed according to the range of qb, Developed model was applied to measured hydrographs and hyetographs for total 10 years in 4 test areas and effective rainfall was estimated. Estimation precision of model was checked as shown in Tab- 6 and Fig.8. In the next stage, based on the estimated effective rainfall(R) and runoff(Qd), a runoff distribution ratio was calculated for each teat area using by computerised least square method and used in making unit hydrographs in each test area. Significance of induced hydrographs was tested by checking the relative errors between estimated and measured runoff volume(Tab-9, 10). According to the results, runoff estimation error by unit hydrograph itself was merely 2 or 3 %, but other 2 or 3 % of error proved to be transferred error in the seperation of effective rainfall. In this study, special attentioning point is that, in spite of different river systems and forest conditions of test areas, standardized unit hydrographs for them have very similar curve shape, which can be explained by having similar catchinent characteristics such as stream length, catchinent area, slope, and vegetation intensity. That fact should be treated as important factor ingeneralization of unit hydrograph method.