• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.240-240
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• 2016

반도체 양자점은 불연속적인 에너지준위의 특성 때문에 고전적인 빛과는 다른 단일광자를 방출하여 양자정보 처리과정에 기본 요소로써 사용 될 수 있다. III-Nitride (III-N) 반도체 물질은 III족 원소의 구성비를 조절하였을 때 밴드갭 에너지차이가 크므로 깊은 양자 우물을 만들 수 있으며 최근에는 기존에 연구되던 III-Arsenide 기반의 반도체 양자점과 다르게 상온 (300 K) 동작 가능한 단일광자 방출원이 개발되었다.[1] 또한 약한 split-off 에너지 때문에 양자점 모양에 작은 비대칭성만 존재해도 큰 선형편광도를 가질 수 있다. 하지만 III-N 반도체 양자점의 이러한 특성에도 불구하고 이종기판과의 격자상수 불일치에 따른 많은 threading dislocation, 압전효과에 의한 큰 내부전기장에 의해 발광 효율이 떨어지는 등의 문제가 있다. 이를 해결하기 위해 반도체 양자점을 3차원 구조체와 결합하여 threading dislocation 및 내부전기장을 줄이는 연구들이 진행되고 있다.[2] 본 연구에서는 선택적 영역 성장 방식을 통해 마이크로미터 크기를 가지는 피라미드 형태의 3차원 구조체를 이용, 피라미드의 꼭지점에 형성된 InGaN/GaN 양자점의 광학적 특성에 대해 분석하였다. 저온(9 K)에서 마이크로 photoluminescence 측정을 통해 양자점의 발광파장이 피라미드의 옆면의 파장과는 다름을 확인하였다. 여기광의 세기에 따른 양자점의 발광 세기 측정하여 여기광에 선형 비례함을 보이고, 양자점의 편광도를 측정하여 선형 편광임을 확인하였다. 마지막으로, 광량에 대해 시간에 따른 상관관계를 측정함으로써 양자점이 양자 발광체의 특성을 보이는 지 확인하였다.

• Journal of KSNVE
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• v.8 no.6
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• pp.1093-1102
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• 1998

The success of controllability of smart structures depends on the quality of the bonding along the interface between the main structure and the attached sensing and acuating elements. Generally, the analysis procedures neglect the effect of the interfacial bond layer or assume that this bond layer behaves like viscoelastic material. Three different bond layers. two modified epoxy adhesives, and one isocyanate adhesive were prepared for their toughness and moduli. Bond layer of the chosen adhesive provides an almost perfect bonding condition between the composite structure and the PZT while bended significantly like arrow-shape. The perfect bonding condition is tested by considering various material properties of the bond layers. and based on this perfect bonding condition, the effects of the interfacial bond layer on the dynamic behavior and controllability of the test structure is experimentally studied. Once the perfect bonding condition is achieved. dynamic effects of the bond layer itself on the dynamic characteristics of the main structure is negligible. but the contribution of the attached PZT elements on the stiffness of the multi-layered structure becomes significant when the thickness of the bond layer increased.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.6
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• pp.285-289
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• 2001

We investigated that each site was substituted by new chemical components in Langasite ($La_3Ga_5/SiO_{14}$)-type structure with superior piezoelectric characteristics than $La_3Ga_5/SiO_{14}$. In this study $Ca_3TaGa_5Si_{2}O_{14}$ was synthesized by soilid-state reaction and grown by the $\mu$-PD(micro-pilling-down)and Cz technique. Lattice parameter and chemical composition was investigated by XRD and EPMA respectively.

• Composites Research
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• v.33 no.2
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• pp.81-89
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• 2020

In this review paper, we introduce recent research studied effective physical properties of the reinforced composite using mean-field homogenization. We address homogenization for effective stiffness and expand it to effective thermal/electrical conductivity and dielectric constant. Multiphysics problems like piezoelectricity and thermoelectricity are considered by simplifying the constitutive equation into the linear equations like Hooke's law. We present a generalized theoretical formula for predicting effective physical properties of composite and validation by against finite element analysis.

• Electrical & Electronic Materials
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• v.10 no.5
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• pp.434-439
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• 1997

It this paper, the piezoelectric and electro-induced strain properties of (P $b_{1-}$2x/3/B $i_{x}$ )[N $i_{1}$3/N $b_{2}$3/)$_{0.4}$( $Ti_{0.6}$Z $r_{0.4}$)$_{0.6}$] $O_3$ceramics (x=0, 0.005, 0.02) were investigated with the substitution of B $i^{3+}$, and the feasibility of the application for bimorph actuator was evaluated by measuring the dynamic properties of the piezoelectric bimorph fabricated with above ceramics. Dielectric constant was enhanced with the increase of B $i^{3+}$ substitution, and appeared the maximum value of 5032 at x=0.01 composition. Increasing the substitution of B $i^{3+}$, the electromechanical coefficient( $k_{p}$ , $k_{31}$ ) was increased up to the substitution of 0.5 mol% B $i^{3+}$, showed the value of 0.656, 0.439, respectively. The piezoelectric constant( $d_{33}$ $d_{31}$ ) had the highest value of 344, 825 with the substitution of 0.5 mol% B $i^{3+}$. The strain, generated by 60 Hz AC electric field, had the largest value of 1200($\times$10$^{-6}$ $\Delta$1/1) in the composition with the substitution of 0.5 mol% B $i^{3+}$. The dynamic properties of the bimorph actuator, fabricated with the composition substitution of 0.5 mol% B $i^{3+}$, showed the largest value of 325 $\mu$m at $\pm$150 V square pulse. square pulse.are pulse..

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1146-1151
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• 1998

The crystallization behaviour of perovskite $PbTiO_3$ for the samples heat- treated at various temperatures for various times in the $PbO-TiO_2-A1_2O_3-SiO_2$, glass system has been investigated by the means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. Higher crystallinity obtained in the sample heat-treated at higher temperature for longer time. With increasing heat-treatment time, dielectric constant of the samples heat-treated at $610^{\circ}C$ and $650^{\circ}C$ increased, but that of the sample heat- treated at $800^{\circ}C$ decreased. Loss tangent of the heat-treated samples was not much influenced by heat-treatment conditions. Piezodielectric charge constant was approximately $1.0\times10^{-12}~8.0$\times$10^{-12}C/N$ in the samples heat-treated at $800^{\circ}C$ for 1h, 2h, and 8h.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.30-35
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• 2004

PMW-PZT thick films of about $30{\mu}m$ thickness were fabricated on Pt/$TiO_2$/$SiN_x$Si substrate by the hybrid method of screen printing and PZT sol application. With the increase of the number of the sol application times, the sintered density and electrical properties of PMW-PZT thick films were evidently increased. For the PMW-PZT thick film with PZT sol application of 10-times, the dielectric constant ($\varepsilon_r$) was 745 at the frequency of 100 KHz and thepiezoelectric coefficient ($d_33$) was 155 pC/N at the applied pressure of 1 atm.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.52-58
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• 2005

To establish low-cost and high efficiency water treatment process, feasibility of applying ultrasonic spray nozzle for chemical injection was evaluated. Ultrasonic spray nozzle was manufactured using piezoelectric ceramics. Treatment efficiencies of contaminants by ultrasonic spray nozzle were compared with conventional chemical mixing such as back-mixing. It was found out that the rate of chemical diffusion rate by ultrasonic spray nozzle was faster than by back-mixing method. Removal efficiencies of various contaminants, such as turbidity, organics and microorganism by ultrasonic spray nozzle were also higher than by back-mixing method. By adapting ultrasonic spray nozzle in coagulant injection process, it can be prevented that the decline of treatment efficiency by coagulant overdose. The amount of coagulant can be reduced by applying ultrasonic spray nozzle in water treatment. Along with these advantages chemical mixing chamber is not required if ultrasonic spray nozzle is adapted. From these results, it can be concluded that chemical injection by ultrasonic spray nozzle is an economical and highly efficient device for coagulant mixing.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.589-598
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• 1997

The effects of PT/PZ ratio variations in a modified PZT system on crystal structure and electrical properties were studied. $0.05Pb(Sn_{0.5}Sb_{0.5})O_3＋xPbTiO_3＋yPbZrO_3$＋0.4Wt% $MnO_2$(＝0.55PSS＋0.11PT＋0.84PZ＋0.4wt%$MnO_2$ ; x＋y=0.95) systems with variations of PT/PZ from 0.50/0.45 to 0.l1/0.84 were sintered at $1250^{\circ}C$ for 2 hr, and then sintering density, crystal structure, dielctric, piezoelectric, pyroelectic and voltage responsity to infrared were investigated. Sintering density was increased from 7.52g/$\textrm {cm}^3$ to 7.82g/$\textrm {cm}^3$ with increasing PZ content. Dielectric constants at 1 KHz were decreased from 1147 to 193 with variation of PT/PZ from 0.50/0.45 to 0.l1/0.84 after poling of $4 KV_{DC}$/mm at $140^{\circ}C$ for 20 minutes. All Dielectric losses at 1 KHz were less than 1 % in all specimens. $K_{p}$ was increased near to 1 of PT/PZ, and maximun value of 48.2 % was .at 0.45/0.50. Pyroelectric coefficient of PT/PZ with 0.l1/0.84 was maximun value, 0.0541 C/$\m^2$K, and voltage responsity to infrared was 1.5 V.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.34-40
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• 2000

The $Pb_{0.94}Y_{0.04}[(Zr_{0.6}Sn_{0.4})_{0.915}Ti_{0.085}]O_3$ ceramics which corresponded to the antiferroelectric-ferroelectric phase boundary composition were prepared for digital-type-piezoelectric/electrostrictive device application. Their dielectric, field-induced polarization (P) and strain (X) behaviors were studied with variations in sintering condition and excess PbO content. The orthorhombic structure of specimens was hardly affected either by excess PbO addition or sintering temperature. With increasing excess PbO content, grains tended to be smaller and rounded ones, and the optimum sintering temperature was lowered. Excess PbO addition stabilized the antiferroelectric phase of the specimen effectively, which was confirmed by P-E and X-E analyses. Also the digital-type-strain character was found to be enhanced despite of slight increase in phase transition (AFE-FE) field and electrical resistivity, and decrease in maximum strain. These results were explained in terms of possible lattice defects and domain wall motion.