In the present study, the thermal conductivity of a silicon nitride(Si3N4) thin-film is evaluated using the dualwavelength pump-probe technique. A 100-nm thick Si3N4 film is deposited on a silicon (100) wafer using the radio frequency plasma enhanced chemical vapor deposition technique and film structural characteristics are observed using the X-ray reflectivity technique. The film’s thermal conductivity is measured using a pump-probe setup powered by a femtosecond laser system of which pump-beam wavelength is frequency-doubled using a beta barium borate crystal. A multilayer transient heat conduction equation is numerically solved to quantify the film property. A finite difference method based on the Crank-Nicolson scheme is employed for the computation so that the experimental data can be curve-fitted. Results show that the thermal conductivity value of the film is lower than that of its bulk status by an order of magnitude. This investigation offers an effective way to evaluate thermophysical properties of nanoscale ceramic and dielectric materials with high temporal and spatial resolutions.

목적 : 소다-라임-실리카 유리(soda-lime-silica glass,SG) 기판위에 Ti, Ba-naphthenates를 출발원료로 사용하고 졸겔법으로 나노 결정질 TiO2, BaTiO3 박막을 제조하였다. 박막의 특성을 분석하기 위하여 X-선 회절 분석, 전자현미경, UV스펙트럼을 이용하여 연구하였다. 방법 : 코팅용액을 soda-lime-silica glass 기판 위에 스핀코팅하고 공기분위기에서 500℃에서 열분해시켜 박막을 제조하였다. 제조된 TiO2, BaTiO3 박막의 결정화도는 고분해능 X-선 회절분석법으로 그리고 표면미세구조와 거칠기는 전계 방출 현미경과 원자간력 현미경으로 또 자외선(200〜380 nm), 가시광선(380〜750 nm), 적외선(750〜900 nm) 영역의 투과율은 UV-Visible-NIR 분광광도계로 측정되었다. 결과 : TiO2박막은 아나타제 상이 존재하였으며, BaTiO3 박막은 최고 피크가 확인되지 않았다. 열처리한 TiO2, BaTiO3 박막의 가시광선 투과율은 80% 이상의 투과율을 나타냈으며, BaTiO3 박막은 TiO2 박막보다 자외선 및 청광 차단율이 높았다. 결론 : BaTiO3 박막은 TiO2 보다 자외선 및 청광에 대해 더 높은 차단율이 나타냈으며, 가시광선 투과율은 제조된 모든 박막에서 80% 이상의 투과율이 측정되었다.

A triple-layered PMMA/Ni64Zr36/PDMS hydrogen gas sensor using hydrogen permeable alloy and flexible polymer layers is fabricated through spin coating and DC-magnetron sputtering. PDMS(polydimethylsiloxane) is used as a flexible substrate and PMMA(polymethylmethacrylate) thin film is deposited onto the Ni64Zr36 alloy layer to give a high hydrogenselectivity to the sensor. The measured hydrogen sensing ability and response time of the fabricated sensor at high hydrogen concentration of 99.9 % show a 20 % change in electrical resistance, which is superior to conventional Pd-based hydrogen sensors, which are difficult to use in high hydrogen concentration environments. At a hydrogen concentration of 5 %, the resistance of electricity is about 1.4 %, which is an electrical resistance similar to that of the Pd77Ag23 sensor. Despite using low cost Ni64Zr36 alloy as the main sensing element, performance similar to that of existing Pd sensors is obtained in a highly concentrated hydrogen atmosphere. By improving the sensitivity of the hydrogen detection through optimization including of the thickness of each layer and the composition of Ni-Zr alloy thin film, the proposed Ni-Zr-based hydrogen sensor can replace Pd-based hydrogen sensors.

We investigated the characteristics of nano crystalline silicon(nc-Si) thin-film solar cells on graphite substrates. Amorphous silicon(a-Si) thin-film solar cells on graphite plates show low conversion efficiency due to high surface roughness, and many recombination by dangling bonds. In previous studies, we deposited barrier films by plasma enhanced chemical vapor deposition(PECVD) on graphite plate to reduce surface roughness and achieved ~7.8 % cell efficiency. In this study, we fabricated nc-Si thin film solar cell on graphite in order to increase the efficiency of solar cells. We achieved 8.45 % efficiency on graphite plate and applied this to nc-Si on graphite sheet for flexible solar cell applications. The characterization of the cell is performed with external quantum efficiency(EQE) and current density-voltage measurements(J-V). As a result, we obtain ~8.42 % cell efficiency in a flexible solar cell fabricated on a graphite sheet, which performance is similar to that of cells fabricated on graphite plates.

본 논문에서는 비평형 분자동역학 시뮬레이션 기법을 사용하여 알루미늄 박막과 실리콘 웨이퍼 간 열경계저항을 예측하였다. 실리콘의 끝 단 고온부에 열을 공급하고, 같은 양의 열을 알루미늄 끝 단 저온부에서 제거하여 경계면을 통한 열전달이 일어나도록 하였으며, 실리콘 내부와 알루미늄 내부의 선형 온도 변화를 계산함으로써 경계면에서의 온도 차이에 따른 열저항 값을 구하였다. 300K 온도에서 5.13±0.17m2·K/GW의 결과를 얻었으며, 이는 열유속 조건의 변화와 무관함을 확인하였다. 아울러, 펨토초 레이저 기반의 시간영역 열반사율 기법을 사용하여 열경계저항 값을 실험적으로 구하였으며, 시뮬레이션 결과와 비교·검증하였다. 전자빔 증착기를 사용하여 90nm 두께의 알루미늄 박막을 실리콘(100) 웨이퍼 표면에 증착하였으며, 유한차분법을 이용한 수치해석을 통해 열전도 방정식의 해를 구해 실험결과와 곡선맞춤 함으로써 열경계저항을 정량적으로 평가하고 나노스케일에서의 열전달 현상에 관한 특징을 살펴보았다.

We report on the fabrication and characterization of an oxide photoanode with a zinc oxide (ZnO) nanorod array embedded in cuprous oxide (Cu2O) thin film, namely a ZnO/Cu2O oxide p-n heterostructure photoanode, for enhanced efficiency of visible light driven photoelectrochemical (PEC) water splitting. A vertically oriented n-type ZnO nanorod array is first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type Cu2O thin film is directly electrodeposited onto the vertically oriented ZnO nanorod array to form an oxide p-n heterostructure. The introduction of Cu2O layer produces a noticeable enhancement in the visible light absorption. From the observed PEC current density versus voltage (J-V) behavior under visible light illumination, the photoconversion efficiency of this ZnO/Cu2O p-n heterostructure photoanode is found to reach 0.39 %, which is seven times that of a pristine ZnO nanorod photoanode. In particular, a significant PEC performance is observed even at an applied bias of 0 V vs Hg/Hg2Cl2, which makes the device self-powered. The observed improvement in the PEC performance is attributed to some synergistic effect of the pn bilayer heterostructure on the formation of a built-in potential including the light absorption and separation processes of photoinduced charge carriers, which provides a new avenue for preparing efficient photoanodes for PEC water splitting.

본 연구에서는 강유전성 고분자를 이용하여 제작된 100 nm 이하 두께를 가지는 박막형 커페시터의 측정 주파수에 따른 분극 반전 특성을 측정, 분석하였다. 고정된 박막 두께에 대해, 인가되는 최고 전기장의 세기가 증가할수록 더 높은 항전계에서 분극 반전이 발생되었다. 고정된 최고 전기장에 대해, 박막의 두께에 무관하게 같은 항전계에서 분극 반전이 발생되었다. 모든 측정에서 로그스케일 전기장 및 로그스케일 주파수의 관계에서 약 0.12 ± 0.01의 비례 상수를 보였다. 결과적으로, 강유전체 고분자 커페시터가 40 nm 두께까지는 size effect 없이 일정한 분극 반전 특성을 보였다. 본 연구는 저전압 동작 고분자 메모리 소자의 동작 예측에 유용할 것이므로 저전압에서 동작 가능한 고분자 메모리 소자의 가능성을 보여준다.

The transfer characteristics of zinc tin oxide(ZTO) on silicon dioxide(SiO2) thin film transistor generally depend on the electrical properties of gate insulators. SiO2 thin films are prepared with argon gas flow rates of 25 sccm and 30 sccm. The rate of ionization of SiO2(25 sccm) decreases more than that of SiO2(30 sccm), and then the generation of electrons decreases and the conductivity of SiO2(25 sccm) is low. Relatively, the conductivity of SiO2(30 sccm) increases because of the high rate of ionization of argon gases. Therefore, the insulating performance of SiO2(25 sccm) is superior to that of SiO2(30 sccm) because of the high potential barrier of SiO2(25 sccm). The ZTO/SiO2 transistors are prepared to research the CO2 gas sensitivity. The stability of the transistor of ZTO/SiO2(25 sccm) as a high insulator is superior owing to the high potential barrier. It is confirmed that the electrical properties of the insulator in transistor devices is an important factor to detect gases.

Anti-reflection thin films are fabricated on glass substrates using the screen printing method. Tetra ethyl silicate(TEOS) and methyl tri methoxy silane(MTMS) are used as starting materials and buthyl carbitol acetate(BCA) and buthyl cellusolve(BC) are mixed to improve the viscosity of the solution. Anti-reflection thin films are fabricated according to the number of the screen mesh and the characteristics improve as the mesh size increases. The transmittance and reflectance of the coated thin film using 325 mesh are about 94 % and 0.43 % in the visible wavelength. The thickness and refractive index of the AR thin film are 107 nm and n = 1.26, respectively.

Although thin-film nanocomposite membranes (TFNs) have paved the way to develop high-performance reverse osmosis (RO) membranes, scale-up production of TFNs is still challenging issue. Herein, we introduced a novel preparation method for TFNs using spray-assisted nanofiller pre-deposition (Spray method) to circumvent the limitations in conventional method. The precise control of nanofiller (ZIF-8) loading was possible by simply varying the spraying ZIF-8 concentration. Most importantly, TFNs prepared by both Spray and conventional method showed similar RO performances, while Spray method only requires ~100 times minimized amount of ZIF-8 with an unprecedentedly short deposition time (< 1 min) ever reported. Our results revealed that Spray method would be promising for the scale-up of TFNs in terms of cost, time, and controllability.

This study investigates the microstructural properties of CoCrFeMnNi high entropy alloy (HEA) oxynitride thin film. The HEA oxynitride thin film is grown by the magnetron sputtering method using nitrogen and oxygen gases. The grown CoCrFeMnNi HEA film shows a microstructure with nanocrystalline regions of 5~20 nm in the amorphous region, which is confirmed by high-resolution transmission electron microscopy (HR-TEM). From the TEM electron diffraction pattern analysis crystal structure is determined to be a face centered cubic (FCC) structure with a lattice constant of 0.491 nm, which is larger than that of CoCrFeMnNi HEA. The HEA oxynitride film shows a single phase in which constituting elements are distributed homogeneously as confirmed by element mapping using a Cs-corrected scanning TEM (STEM). Mechanical properties of the CoCrFeMnNi HEA oxynitride thin film are addressed by a nano indentation method, and a hardness of 8.13 GPa and a Young’s modulus of 157.3 GPa are obtained. The observed high hardness value is thought to be the result of hardening due to the nanocrystalline microstructure.

To remove SO2 from flue gas, a thin film nanocomposite (TFN) hollow fiber membrane was decorated with Nafion/TiO2 nanoparticles. Morphological and structural analyses of the TFN membranes were performed using FTIR, SEM, EDX, TEM, and AFM. The gas permeation experiments were performed with pure gases and a mixed gas within a pressure range of 1-3 bar and feed gas flow rate of 0.03-0.15 L/min. The obtained experimental results suggest that the addition of Nf/TiO2 nanoparticles improved the membrane performance by introducing sulfonate and hydroxyl functional groups to the membrane, and thus increased SO2 permeability and selectivity. The SO2 permeability was found to be 411-1671 GPU, while the ideal selectivities achieved for SO2/N2 and SO2/CO2 were 2928 and 72, respectively. Overall, an SO2 removal efficiency of 93% was achieved by using the Nf/TiO2 incorporated TFN membrane.

Membrane fabrication is a critical area that hampers forward osmosis (FO) technology from industrialization. Herein, electrospun poly(vinyl alcohol) (PVA) nanofiber (NF) was used as a support layer for thin film composite (TFC) FO membrane. The PVA NF was incorporated with sulfonated graphene oxide (sGO). The oxygenous-rich sGO enhanced the hydrophilicity and mechanical strength of PVA NF as revealed by contact angle and tensile strength measurements, and pure water flux. On this support, the active polyamide layer was formed through interfacial polymerization. Meanwhile, FO performance of sGO/PVA TFC membrane is currently being evaluated. This work was supported by NRF of Korea funded by the Ministry of Science and ICT (2016R1A2B1009221 and 2017R1A2B2002109) and Ministry of Education (2009-0093816 and 22A20130012051 (BK21Plus)).

We report on the fabrication of a high performance reverse osmosis membrane based on a hydrophilic polyacrylonitrile support via an aromatic solvent-assisted interfacial polymerization process. The use of aromatic solvent (toluene or xylene) produced the membranes with unprecedentedly high NaCl rejection (~99.9%) and superior water flux, outperforming both the control membrane prepared using a conventional aliphatic solvent (n-hexane) and commercial membranes. The membranes fabricated using toluene or xylene had roof-like structures covering a thin and highly dense polyamide (PA) layer, which was induced by enhanced amine diffusion and the extended miscible layer resulting from the increased miscibility of aromatic solvent with water. The high performance of the membranes is attributed to thin and highly cross-linked basal PA layer.

Growing demands for reducing energy consumption have raised interest to design advanced materials for thin film composite (TFC) desalination membranes with high permselectivity and low fouling. Here, we synthesized a star-shaped polymer as a new building block material, which can be assembled into selective layer of the TFC membrane via a facile interfacial polymerization (IP). Star polymer with compact globular structure and high density amine functional groups enabled to fabricate higher permselectivity and lower fouling propensity membrane compared to commercial membranes. In addition, star polymer assembled TFC membrane can function as either nanofiltration or reverse osmosis membrane by simply adjusting IP process conditions, which cannot feasible in conventional materials, demonstrating remarkable versatility of our star polymer.