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The use of aluminum-based coagulants in water pretreatment is being carefully considered because aluminum exposure is a risk factor for the onset of Alzheimer’s disease. Lightly burned-dolomite kiln dust (LB-DKD) was evaluated as an alternative coagulant because it contains high levels of the healthful minerals calcium and magnesium. An organic pore forming agent (OPFA) was incorporated to prepare porous granules after OPFA removal through a thermal decomposition process. A spray drying method was used to produce uniform and reproducible spherical granules with low density, since fine dolomite particles have irregular agglomeration behavior in the hydration reaction. The use of fine dolomite powder and different porosity granules led to a visible color change in raw algae (RA) containing water, from dark green to transparent colorlessness. Also, dolomite powders and granules exhibited a mean removal efficiency of 48.3% in total nitrogen (T-N), a gradual increase in the removal efficiency of total phosphorus (T-P) as granule porosity increased. We demonstrate that porous dolomite granules can improve the settling time and water quality in summer seasons for the emergent treatment of excessive algal blooms in eutrophic water.

One of the most threatening consequences of eutrophic freshwater reservoirs is algal blooming which typically occur after the long a mega drought or/and irregular rainfall under influence of climate change. The long-term experiences of chemical treatment are known as a most practical effort to reduce health concerns from human exposure of harmful cyanobacteria as well as to preserve ultimate freshwater resources. Even though these conventional chemical treatment methods do not completely solve the algal residue problem in water treatment plant or directly in the water bodies, they still have big advantages as fast and efficient removal process of cyanobacteria due to cheaper, easier to manage. This review summarizes their chemical treatment scenarios of the representative coagulants, pre-oxidants and algaecides composed to chemical compounds which immediately may help to manage severe cyanobacteria blooms in the summer seasons.

Here, we introduce a means of utilizing waste oyster shells which were obtained from temporary storage near coastal workplaces as CO₂ adsorbents. The calcined CaO can be easily dissociated to Ca 2+ cation and CO₃ 2− anion by hydrolysis and gas-liquid carbonation reaction and converted to precipitated calcium carbonate (PCC) in algae-containing water. The calcium hydroxide and carbonation combination in algae-containing water significantly contributed to improving water quality which is very dependent on the addition amount of calcined powders.

The synthesis of pure calcium carbonate nanocrystals was achieved using a simultaneous injection method to produce nano particles of uniform size. These were characterized using scanning electron microscopy and powder X-ray diffraction. The nano particles were needle-shaped aragonite polymorphs, approximately 100–200 nm in length. The aragonite polymorph of calcium carbonate was prepared using aqueous solutions of CaCl₂ and Na₂CO₃, which were injected simultaneously into double distilled water at 50°C and then allowed to react for 1.5 h. The resulting whisker-type nano aragonite with high aspect ratio (30) is biocompatible and potentially suitable for applications in light weight plastics, as well as in the medical, pharmaceutical, cosmetic and paint industries

In this year, Koreans have a shortage in agricultural and drinking water due to severe algal blooms generated in major lakes. Waste oyster shells were obtained from temporary storage near the workplace at which oysters were separated from their shells. Heating (1000oC for 1 h in air) was employed to convert raw oyster shell powders into calcium oxide powders that reacted efficiently with phosphorus and nitrogen to remove algal blooms from eutrophicated wastewater. As the dispersed amount of heated oyster shell powders was increased, water clarity and visual light penetration were improved. Coagulation, precipitation and carbonation process of the heated oyster shell powders in a water purifier facilitated removal of eutrophication nutrient such as phosphorus and nitrogen, which is both beneficial and economically viable. CO2 implantation by carbonation treatment not only produced thermodynamically stable CaO in oyster shells to derive precipitated calcium carbonate (PCC) but also accelerated algal removal by activation of coagulation and precipitation process. The use of oyster shell powders led to a mean reduction of 97% in total phosphate (T-P), a mean reduction of 91% in total nitrogen (T-N) and a maximum reduction of 51% in chemical oxygen demand (COD), compared with the total pollutant load of raw algal solution. Remarkable water quality improvement of algal removal by heated oyster shell powders and PCC carbonation treatment will allow utilization as water resources to agricultural or industrial use.

It is highlighted that increasing the adsorbent surface area on volumetric basis is very important in providing an easy access for gas molecules. Fine particles around 3 μm of soft-burned dolomite kiln dust (SB-DKD) were hydrated to wet slurry samples by ball mill process and then placed in a chamber to use spray dryer method. Spherical granules with particle size distribution of 50~60 ㎛ were prepared under the experimental condition with or without addition of a pore-forming agent. The relationship between bead size of the pore-forming agent and size of SB-DKD particles is the most significant factor in preparation of spherical granules with a high porosity. Whereas addition of smaller beads than SB-DKD resulted in almost no change in the surface porosity of spherical granules, addition of larger beads than SB-DKD contributed to obtaining of the particles with both 15 times larger average pore volume and 1 order of magnitude larger porosity. It is considered that spherical granules with improved N₂ gas adsorption ability may also be utilized for other atmospheric gas adsorption.

In this paper, we have developed a simple, new and economical carbonation method to synthesize a pure form of aragonite needles using dolomite raw materials. The obtained aragonite Precipitated Calcium Carbonate (PCC) was characterized by XRD and SEM, for the measurement of morphology, particle size, and aspect ratio (ratio of length to diameter of the particles). The synthesis of aragonite PCC involves two steps. At first, after calcinated dolomite fine powder was dissolved in water for hydration, the hydrated solution was mixed with aqueous solution of magnesium chloride at 80℃, and then CO₂ was bubbled into the suspension for 3 h to produce aragonite PCC. Finally, aragonite type precipitated calcium carbonate can be synthesized from natural dolomite via a simple carbonation process, yielding product with average particle size of 30-40 ㎛.

폴리아닐린 분말과 고분자 계면활성제, cyclohexanone용매를 micro-milling장치내에서 분산시켜 (m입자 크기를 갖는 가공용이한 분산액을 제조하였다. 분산액을 백금 전극 위에 코팅하여 얻은 분산박막의 전기화학적 특성들은 순환전압전류법(CV)을 이용하여 조사하였다. CV의 결과에 의하면 폴리아닐린 분산박막이 순수한 폴리아닐린 박막과 유사한 전기화학적 특성을 갖는 것으로 나타났다. $3wt.\%$ NaCl용액에서 수행한 분극실험과 열린회로전위 측정 실험에서는 PANI분산액을 철표면에 코팅하면 부식전위가 증가하였다. 분산박막/철 전극의 열린회로전위값(OCP, Voc)이 분산액의 제조 조건에 따라 변화가 있음을 관찰하였다. 이러한 결과들은 본 연구에서 사용한 전도성 고분자 분산액이 철의 부식방지코팅물질로서 유용성을 갖고 있다는 것을 보여주고 있다. 【Processible polyaniline (PAM) dispersions consisting of polyaniline micro-particles, cyclohexanone, and a polymeric surfactant were prepared in a micro-milling machine with various mixing conditions. The electrochemical properties of the dispersion film coated on Pt electrode were investigated by cyclic voltammetry (CV). The electrochemistry of the PAM dispersion coatings was basically similar to a pure PAM coating based on the results of CV. The results of polarization measurements and open circuit potential measurements carried out in $3\;wt.\%$ NaCI solution showed increase in corrosion potential when the PANI dispersion coatings applied on steel surface. Variation of open circuit potential $(OCP,\;V_{OC})$ of the dispersion coating/steel electrodes was observed, which differed with milling conditions. The results demonstrated practical use of the conducting polymer dispersion as a coating material for corrosion prevention of steel.】

We show that acetone-derived graphene coating can effectively enhance the corrosion efficiency of copper (Cu) in a seawater environment (0.5-0.6 M (∼3.0-3.5%) sodium chloride). By applying a drop of acetone (∼20 μl cm(-2)) on Cu surfaces, rapid thermal annealing allows the facile and rapid synthesis of graphene films on Cu surfaces with a monolayer coverage of almost close to ∼100%. Under optimal growth conditions, acetone-derived graphene is found to have a relatively high crystallinity, comparable to common graphene grown by chemical vapor deposition. The resulting graphene-coated Cu surface exhibits 37.5 times higher corrosion resistance as compared to that of mechanically polished Cu. Further, investigation on the role of graphene coating on Cu surfaces suggests that the outstanding corrosion inhibition efficiency (IE) of 97.4% is obtained by protecting the underlying Cu against the penetration of both dissolved oxygen and chlorine ions, thanks to the closely spaced atomic structure of the graphene sheets. The increase of graphene coating thickness results in the enhancement of the overall corrosion IE up to ∼99%, which can be attributed to the effective blocking of the ionic diffusion process via grain boundaries. Overall, our results suggest that the acetone-derived graphene film can effectively serve as a corrosion-inhibiting coating in the seawater level and that it may have a promising role to play for potential offshore coating.

We have realized metal-coated semiconductor nanostructures for a stable and efficient single-photon source (SPS) and demonstrated improved single-photon extraction efficiency by the selection of metals and nanostructures. We demonstrate with finite-difference time-domain (FDTD) simulations that inclination of a pillar sidewall, which changes the structure to a nanocone, is effective in improving the photon extraction efficiency. We demonstrate how such nanocone structures with inclined sidewalls are fabricated with reactive ion etching. With the optimized design, a photon extraction efficiency to outer airside as high as similar to 97% generated from a quantum dot in a nanocone structure is simulated, which is the important step in realizing SPS on-demand operations. We have also examined the direct contact of such a metal-embedded nanocone structure with a single-mode fiber facet as a simple and practical method for preparing fiber-coupled SPS and demonstrated practical coupling efficiencies of similar to 16% with FDTD simulation.

피롤 단량체는 균일하고 접착력 있는 폴리피롤 고분자로 알루미늄 합금 전극 위에 성공적으로 전착되었다. 다양한 농도의 질산으로 산성화된 전해질 용액 안에서 전하보상 상대이온이면서 메트릭스의 역할을 하는 폴리스티렌설포네이트 고분자를 첨가하면 첨가량에 따라 폴리피롤 고분자의 표면 모폴로지와 전기적 특성이 변화됨을 보고한다. 일정한 전하 밀도(1 mAcm -2 )에서 수행된 전압-시간 중합 곡선은 폴리피롤이 초기 핵 생성 단계에서 2차원적인 성장으로 전이하는 전압 거동을 나타내었다. SEM-EDS 분석을 이용한 이 필름들의 특성은 전압-시간 곡선에서 예상되었던 것과 같이 폴리피롤의 성장 메커니즘과 일치함을 보였다. 더 나아가, C-AFM 관찰을 통해 Al alloy 위에 형성된 폴리피롤 고분자막의 전류 이미지와 모폴로지가 질산 산성화 농도와 피롤을 포함한 PSS의 첨가 농도에 의존하여 변화됨을 서술할 것이다.

Interband optical transition probability (usually given as the B coefficient) is normally fixed for a given semiconductor structure. Here we will show the B coefficient can be drastically enhanced effectively with electron injection in paired states.

We introduce a novel three-step procedure for precise niobium (Nb)-etching on the nanometer-scale, including the design of high contrast resist patterning and sacrifice layer formation under high radio frequency (RF) power. We present the results of precise slit fabrication using this technique and discuss its application for the production of superconducting devices, such as superconductor-semiconductor-superconductor (S-Sm-S) Josephson junctions. For the reactive ion etching (RIE) of Nb, we selected CF(4) as etchant gas and a positive tone resist to form the etching mask. We found that the combination of resist usage and RIE process allows for etching of thicker Nb layers when utilizing the opposite dependence of the etching rate (ER) on the CF(4) pressure in the case of Nb as compared to the resist. Precise slit-width control of 80 and 200 nm thick Nb apertures was performed with three kinds of ER control, for the resist, the Nb, and the underlying layer. S-Sm-S Josephson junctions were fabricated with lengths as small as 80 nm, which can be considered clean and short and thus exhibit critical currents as high as 50 µA. Moreover, possible further applications, such as for apertures of superconducting light emitting diodes (SC LEDs), are addressed.

Application fields of light emitting diodes (LEDs) are expanding in various fields. Development of LED-based single photon sources is expected to open a new possibility to expand the applications to quantum information communication and processing. The authors have proposed a photon-emitting LED combined with superconducting electrodes (SC), which is expected to be an on-demand entangled photon pair source [1]. The main mechanism is based on the coherent spatial extension of Cooper-pairs injected from a superconducting electrode to a semiconducting active layer, which is expected to enhance the oscillator strength of the radiative recombination processes by the Cooper-pair condensation effect [2,3]. The preliminary operation was demonstrated with InGaAs quantum well (QW) LEDs and about 20-times enhancement of the electroluminescence (EL) was observed under the low-injection current regime [4]. This is the demonstration of the improved internal quantum efficiency (QE) under the low internal QE operation of the LED. In this paper, enhancement of radiative recombination processes with the Cooper-pair injection is demonstrated by the lifetime measurements under the operation with high (∼100%) internal QE.

We studied the novel structure for improving the emission properties of semiconductor light sources both theoretically and experimentally. The proposed structure is a semiconductor pillar buried in a metal except for one end surface of the pillar. Photons are extracted only from the air-exposed surface. The structure consists of the GaAs nanopillar structures embedded in metal and is analyzed by the finite-difference-time-domain method. InAs quantum dots buried in a GaAs pillar are assumed to be the photon emitters. Simulations are performed on GaAs pillars with different diameters buried in Niobium. Consequently, the simulation showed 75% light extraction efficiency from the pillar to air with the optimization of the structure. In addition, we experimentally measured photoluminescence intensities of up to 40 times enhancement in embedded structures compared to normal pillar structure. These are promising for future applications to overcome single photon sources.

Semiconductor optical amplifiers (SOAs) having nano-sized quantum dot (QD) particles show attractive features such as the achievement of a steady temperature characteristic, low power consumption, and a high-speed response to the input signal. QD active layers were designed to 15 stacks of InAs QDs, AlGaAs/GaAs double hetero structure. QD-SOAs were fabricated for optical triode that can be used with a 1.3 μm band. Modulation results extracted by input, control and output waveforms support the fact that cross-gain modulation and negative feedback amplification effect can be strongly contributed to obtain essential factors for future application such as dramatical baseline suppression of output signal and satisfying high modulation. Optical triode revealed inverted type characteristics that high output power can readily obtained by be increased quite small amount of input power while output power rarely change though input power increase high. Fulfillment of far more upgraded stable high-speed bit rate was completed by optical triode improved by QD-SOA and it's containing cross-gain modulation effect. 40 Gbps performance optical triode will be the accelerator for realization of the functions of regeneration, reshaping, multiple-wavelength processing, wavelength conversion, and demultiplexing of high-bit rate patterned optical signals.

Semiconductor optical amplifier (SOA) module, RSOA, SOA with mirror has become an essential component to be at the head of negative feedback amplification effect, optimum gain, and cross-gain modulation with demand for longer transmission lengths. The SOA module is expected to have an advantage of exhibiting much faster negative feedback (NF) response because distance of optical signal passing through component to component is shorten than system connected with fibers. Scattered degree and baseline line difference of eye-pattern diagrams demonstrated that NF effect can be compensated compactness and stability from band pass filter in SOA module. Modulation degree (MD) of input and output signals confirmed that SOA module with NF effect can be stabilized gain and waveguide of output signal and reduced a wave distortion as well as consistent with results in eye-pattern waveform and bit error rate (BER). All-optical switching triode with SOA module was realized in about 60 % output modulation degree at control power range of 0.01 to 1 mW. We propose that our manufactured SOA module become strong component candidate to realize all optical switching triode with NF effect for high speed optical processing in next generation.

We designed InAs QDs, AlGaAs/GaAs double heterostructure and fabricated QD-SOAs for optical triode. Our results demonstrate input, control and output waveforms, and response time of two optical triodes.

We designed active layer of 15 stacks of InAs quantum dots, AIGaAs/GaAs double heterostructure and fabricated QD-SOAs for optical inverted triode. Our results demonstrate input, control and output waveforms, and input-output characteristics of the optical triode. It was obtained high speed response time at higher bit rate of 40 Gbps.

InAs quantum dots (QDs) grown on InP substrates can be used as light emitters in the telecommunication bands. In this paper, we present optical characterization of high-density circular quantum dots (QDots) grown on InP(311)B substrates and elongated dots (QDashes) grown on InP(001) substrates. We study the charge carrier transfer and luminescence thermal quenching mechanisms of the QDots and QDashes by investigating the temperature dependence of their time-integrated and time-resolved photoluminescence properties. This results in two different contributions of the thermal activation energies. The larger activation energies are attributed to the carrier escape to the barrier layer and the wetting layer (WL) from QDots and QDashes, respectively. The smaller activation energies are found to be originated from inter-dot/dash carrier transfer via coupled excited states. The variation of the average oscillator strength associated with the carrier re-distribution is discussed. The relation of the two activation energies is also quantitatively studied with the measurements of excited-state and ground-state energy separations. Finally, we show an approach to isolate individual quantum dots or dashes in a suitable nanostructure.

Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as ~0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as 'pseudo-substrates' in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.

We use high-density InAs quantum dots, which were grown by molecular beam epitaxy on InP(311)B substrates, as photon sources in the telecommunication C band at approximately 1.55 µm. To select a small numbers of dots, we fabricate sub-micrometer sized mesas by electron beam lithography and reactive ion etching. The benefit of using high-density quantum dot samples is that at least one optically active quantum dot can be expected in every single mesa. We show that the etching rate and resulting mesa shape of the In0.53Al0.22Ga0.25As epitaxial layer can be varied with the chamber pressure during the etching process. Furthermore, under constant pressure and with increasing etching time, the sequential etching of the epitaxial layer and the underneath substrate leads to a significant modification in the mesa shape, too. We demonstrate that the isolation of a small number of quantum dots within one mesa results in the appearance of single quantum dot emission with a narrow line width and minimal spectral overlap between different emission lines. We moreover present significant enhancement of the luminescence collected from single dots in silver-embedded nanomesas when compared with as-etched mesas.

The injection of Cooper pairs into a normal medium such as a semiconductor is known as the proximity effect at the superconductor/normal interface. We confirm this injection as well as the contribution of Cooper pairs to a drastic enhancement of inter-band optical transitions in semiconductor heterostructures. In this paper we investigate and clarify the relation of internal quantum efficiencies and radiative lifetimes in Cooper-pair light emitting diodes (CP-LEDs). A quantitative description of the dynamic photon generation processes is given, and the contribution of the Cooper-pair recombination relative to normal-electron recombination in CP-LEDs is discussed in detail.

High efficiency in the extraction, transmission and detection of single and entangled photons is one of the most significant factors to provide general usage and to suppress the bit-error rate in optical communication networks. We propose and realize metal embedded nanostructures with quantum dots (QDs) as photon sources to meet these challenges on the emitter side. Advantages of the process are the ability of fast nanometer-scale fabrication and the high reproducibility and yield. Mesas with typical taper angles of 20–30° and diameters between 100 nm and 1 µm were produced; these nanostructures are referred to as “cones” in this work. The dependence of the taper angle on the composition of the etched cone material is discussed, focusing on the contribution of indium. The nano-cones used as photon sources were embedded in highly reflective metal and turned upside down to provide efficient and partly directed photon extraction. We present the selection of 1.35 µm photons emitted from a single QD as a result of embedding only a small number of dots in a nanometer sized cone.