• Bulletin of the Korean Chemical Society
• /
• 제33권5호
• /
• pp.1491-1504
• /
• 2012

InP quantum dot (QD)-organosilicon nanocomposites were synthesized and their photoluminescence quenching was mainly investigated because of their applicability to white LEDs (light emitting diodes). The as-synthesized InP QDs are capped with myristic acid (MA), which are incompatible with typical silicone encapsulants. We have introduced a new ligand, 3-aminopropyldimethylsilane (APDMS), which enables embedding the QDs into vinyl-functionalized silicones through direct chemical bonding. The exchange of ligand from MA to APDMS does not significantly affect the UV absorbance of the InP QDs, but quenches the PL to about 10% of its original value with the relative increase in surface related emission intensities, which is explained by stronger coordination of the APDMS ligands to the surface indium atoms. InP QD-organosilicon nanocomposites were synthesized by connecting the QDs using a short cross-linker such as 1,4-divinyltetramethylsilylethane (DVMSE) by the hydrosilylation reaction. The formation and changes in the optical properties of the InP QD-organosilicon nanocomposite were monitored by ultraviolet visible (UV-vis) absorbance and steady state photoluminescence (PL) spectroscopies. As the hydrosilylation reaction proceeds, the QD-organosilicon nanocomposite is formed and grows in size, causing an increase in the UV-vis absorbance due to the scattering effect. At the same time, the PL spectrum is red-shifted and, very interestingly, the PL is quenched gradually. Three PL quenching mechanisms are regarded as strong candidates for the PL quenching of the QD nanocomposites, namely the scattering effect, F$\ddot{o}$rster resonance energy transfer (FRET) and cross-linker tension preventing the QD's surface relaxation.

• 한국분말재료학회지
• /
• 제23권5호
• /
• pp.348-352
• /
• 2016

Quantum dots (QDs) are capable of controlling the typical emission and absorption wavelengths because of the bandgap widening effect of nanometer-sized particles. These phosphor particles have been used in optical devices, photovoltaic devices, advanced display devices, and several biomedical complexes. In this study, we synthesize ZnSe QDs with controlled surface defects by a heating-up method. The optical properties of the synthesized particles are analyzed using UV-visible and photoluminescence (PL) measurements. Calculations indicate nearly monodisperse particles with a size of about 5.1 nm at $260^{\circ}C$ (full width at half maximum = 27.7 nm). Furthermore, the study results confirm that successful doping is achieved by adding $Eu^{3+}$ preparing the growth phase of the ZnSe:Eu QDs when heating-up method. Further, we investigate the correlation between the surface defects and the luminescent properties of the QDs.

• 전자공학회논문지D
• /
• 제36D권7호
• /
• pp.66-79
• /
• 1999

본 논문에서는 얕은 양자 우물(extremely shaliow quantum wells, ESQWs)을 사용한 광 쌍안정 대칭형 자기 전광 소자(symmetric self elctrooptic effect device, S-SEED)의 성능에 있어서 높은 입사 광전력의 영향을 조사한다 . 다음과 같은 네 가지 ESQWs S-SEED 구조를 고려하였다. 무 반사 입힘(AR-coated) ESQWs S-SEED, back-to-back ARcoated ESQWs S-SEED, 비대칭 공명구조(AFP) ESQWs S-SEED, back-toback AFP ESQWs S-SEED. 입사 광 전력이 증가함에 따라 On/Off 대조비, On/Off 반사율 차이와 같은 소자성능은 ohmic heating 과 여기자 포화(exciton saturation)의 영향으로 심각하지 않게 저하된다. 한편 소자의 스위칭 속도는 지속적으로 증가하다가 특정 입사 광 전력 하에서 점차 감소하기 시작한다. 직렬 광 연결 시스템(cascading optical interconnection system)에 있어서 소자의 최대 속도 스위칭 동작을 위한 최대 입사 광 전력의 최적화를 바탕으로 0 V와 5 V의 외부 전압 조건에서 양자우물의 수를 변화시키면서 $5{\times}5{\mu}m^2$의 mesa 영역에 대하여 네 가지 ESQWs S-SEED의 시스템 비트 레이트를 모의 실험하고 그 결과를 분석하였다.

• 한국세라믹학회지
• /
• 제35권5호
• /
• pp.493-498
• /
• 1998

ZnS doped borosilicate glass for nonlinear optical application was prepared by melting and precipitation process. The optical band gap of the precipitated ZnS particles ranged from 3.83 to 3.96 eV compared with the bulk ZnS energy gap of 3.53 eV. This result was interpreted in terms of a quantum confinement effect due to small crystal size. ZnS partilcle size estimated by effective mass approximation ranged from about 39 to 83 $\AA$ It increased wtih the increase of heat tratment time and temperature.

• Journal of Magnetics
• /
• 제18권1호
• /
• pp.1-4
• /
• 2013

Structural and magnetic properties of $Fe_{50}Mn_{50}$ nanocrystalline alloys prepared by the mechanical alloying technique (using commercial Fe and Mn powders as the precursors) are studied as a function of milling time, 1 hr to 48 hrs. The nano-crystallite size and shape are examined by using scanning electron microscopy (SEM). The effect of milling time on structural characterization was investigated using X-ray diffractometer (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS). Both XRD and EXAFS studies showed that the alloying process should be completed after 36 hrs milling. Concerning the magnetic behavior, the data obtained from superconducting quantum interference devices (SQUID) exhibited both magnetic saturation ($M_s$) and coercivity ($H_c$) depend strongly on the milling time, which are related to the changes in the crystallite size and magnetic dilution.

• ETRI Journal
• /
• 제15권2호
• /
• pp.11-25
• /
• 1993

Interface trap densities at gate oxide/silicon substrate ($SiO_2/Si$) interfaces of metal oxide semiconductor field-effect transistors (MOSFETs) were determined from the substrate bias dependence of the subthreshold slope measurement. This method enables the characterization of interface traps residing in the energy level between the midgap and that corresponding to the strong inversion of small size MOSFET. In consequence of the high accuracy of this method, the energy dependence of the interface trap density can be accurately determined. The application of this technique to a MOSFET showed good agreement with the result obtained through the high-frequency/quasi-static capacitance-voltage (C-V) technique for a MOS capacitor. Furthermore, the effective substrate dopant concentration obtained through this technique also showed good agreement with the result obtained through the body effect measurement.

• 한국경영과학회:학술대회논문집
• /
• 한국경영과학회 2006년도 추계학술대회
• /
• pp.40-54
• /
• 2006

Recently, Kim and Mauborgne [40] has introduced the concept of blue ocean strategy that provides quantum leap in value innovation, thus creating new market space. This study, based on the blue ocean strategy concept, suggests blue ocean new product development strategy (BONPDS), and attempts to examine how much this BONPDS has impact on new product peformance, compared to existing new Product development strategy Perspectives (i.e., competitive strategy-based new product development strategy and resource-based new product development strategy) in an empirical way. The research result shows that the BONPDS has greater impact on new product performance than existing new product development strategies. In addition, it is revealed that such contingency variables as firm size and environmental dynamism have moderating effect on the relationship between the BONPDS and new product performance. The BONPDS is more effective in the small-sized firms than the large-sized ones, and its effect on new product performance is different according to environmental dynamism.

• Applied Science and Convergence Technology
• /
• 제23권3호
• /
• pp.128-133
• /
• 2014

We study the ballistic spin transport properties in a two-dimensional electron gas system in the presence of magnetic barriers using a transfer matrix method. We concentrate on the size-effect of the magnetic barriers parallel to a two-dimensional electron gas plane. We calculate the transmission probability of the ballistic spin transport in the magnetic barrier structure while varying the width of the magnetic barriers. It is shown that resonant tunneling oscillation is affected by the width and height of the magnetic barriers sensitively as well as by the inter-spacing of the barriers. We also consider the effect of additional electrostatic modulation on the top of the magnetic barriers, which could enhance the current spin polarization. Because all-semiconductor-based devices are free from the resistance mismatch problem, a resonant tunneling structure using the two-dimensional electron gas system with electric-magnetic modulation would play an important role in future spintronics applications. From the results here, we provide information on the physical parameters of a device to produce well-defined spin-polarized current.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.85.2-85.2
• /
• 2016

With the advent of ultra-short high-intense XFEL (X-ray Free Electron Laser), time-resolved dynamics has become of great importance in exploring femtosecond real-world phenomena of nanoscience and biology. These include studying the response of materials to femtosecond laser excitation and investigating the interaction of XFEL itself with condensed matter. A variety of dynamic phenomena have been investigated such as radiation damage, ultrafast melting process, non-equilibrium phase transitions caused by orbital-lattice-spin couplings. As far as bulk materials are concerned, the sample size has no effect on the following dynamic process. As a result, imaging information is not required by and large. If the sample size is of tens of nanometers, however, sample starts to experience quantum confinement effect which, in turn, affects the following dynamic process. Therefore, to understand the fundamental dynamic phenomena in nano-science, time-resolved imaging information is essential. In this talk, we will briefly introduce scientific highlights achieved in XFEL-based dynamics. In case of bio-imaging, recent scientific topics will be mentioned as well. Finally, we will aim to present feasible topics in ultrafast time-resolved imaging and to discuss the future plan of CXI beamline at PAL-XFEL.

• Corrosion Science and Technology
• /
• 제10권5호
• /
• pp.180-188
• /
• 2011

In the present study, denting corrosion experiments were performed as a function of crevice gap size (50, 100 and 200 ${\mu}m$) in a solution containing 3,500 ppm NaCl + 0.2 M $CuCl_2$ (pH = 3 adjusted by HCl). The effects of chloride ion concentrations (3, 3,500 and 35,000 ppm as NaCl) were also outlined with two different crevice gap sizes (100, 200 ${\mu}m$). In addition, the effect of NiB on the denting corrosion was also investigated in a solution of 35,000 ppm NaCl + 0.2 M $CuCl_2$ (pH = 3 adjusted by HCl). The results showed that denting rate increased with the increasing crevice gap size at an initial stage and became nearly constant afterwards. As the concentration of chloride ion increased, the denting rate also increased. However, the addition of a NiB powder of 4 g/L in to the acid-chloride solution was observed to suppress the denting rate significantly.