2019 저널 커버를 장식한 DGIST 논문: DGIST Journal Cover Images 2019

▶ 관련 뉴스 바로보기 : 가이드와이어 부착형 마이크로로봇으로 심혈관 질환 정복한다('19.2.27) 

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Magnetically actuated soft robots may improve the treatment of disseminated intravascular coagulation. Significant progress has been made in the development of soft robotic systems that steer catheters. A more challenging task, however, is the development of systems that steer sub-millimeter-diameter guidewires during intravascular treatments; a novel microrobotic approach is required for steering. In this article, we develop a novel, magnetically actuated, soft microrobotic system, increasing the steerability of a conventional guidewire. The soft microrobot is attached to the tip of the guidewire, and it is magnetically steered by changing the direction and intensity of an external magnetic field. The microrobot is fabricated via replica molding and features a soft body made of polydimethylsiloxane, two permanent magnets, and a microspring. We developed a mathematical model mapping deformation of the soft microrobot using a feed-forward approach toward steering. Then, we used the model to steer a guidewire. The angulation of the microrobot can be controlled from 21.1° to 132.7° by using a magnetic field of an intensity of 15 mT. Steerability was confirmed by two-dimensional in vitro tracking. Finally, a guidewire with the soft microrobot was tested by using a three-dimensional (3D) phantom of the coronary artery to verify steerability in 3D space.

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Graphene has been gradually studied as a high‐frequency transmission line material owing to high carrier mobility with frequency independence up to a few THz. However, the graphene‐based transmission lines have poor conductivity due to their low carrier concentration. Here, it is observed that the radio frequency (RF) transmission performance could be severely hampered by the defect‐induced scattering, even though the carrier concentration is increased. As a possible solution, the deposition of the amorphous carbon on the graphene is studied in the high‐frequency region up to 110 GHz. The DC resistance is reduced by as much as 60%, and the RF transmission property is also enhanced by 3 dB. Also, the amorphous carbon covered graphene shows stable performance under a harsh environment. These results prove that the carrier concentration control is an effective and a facile method to improve the transmission performance of graphene. It opens up the possibilities of using graphene as interconnects in the ultrahigh‐frequency region.

▶관련 뉴스 바로보기: 초미세먼지를 더 강력하게 걸러낼 물질의 새로운 생성법 개발('19.6.12) 

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Enhancement of hydrolytic stability of metal–organic frameworks (MOFs) is a challenging issue in MOF chemistry because most MOFs have shown limitations in their applications under a humid environment. Meanwhile, inner sphere electron transfer has constituted one of the most intensively studied subjects in contemporary chemistry. In this report, we show, for the first time, a new conceptual coordinative reduction of Cu2+ ion, which is realized in a paddlewheel MOF, HKUST-1, with a postsynthetic manner via inner sphere “single” electron transfer from hydroquinone (H2Q) to Cu2+ through its coordination bond. H2Q treatment of HKUST-1 under anhydrous conditions leads to the single charge (1+) reduction of approximately 30% of Cu2+ ions. Thus, this coordinative reduction is an excellent reduction process to be self-controlled in both oxidation state and quantity. As described below, once Cu2+ ions are reduced to Cu+, the reduction reaction does not proceed further, in terms of their oxidation state as well as their amount. Also, we demonstrate that a half of the Cu+ ions (about 15%) remains in paddlewheel framework with pseudo square planar geometry and the other half of the Cu+ ions (about 15%) forms [Cu(MeCN)4]+ complex in a small cage in the fashion of a ship-in-a-bottle after dissociation from the framework. Furthermore, we show that the coordinative reduction results in substantial enhancement of the hydrolytic stability of HKUST-1 to the extent that its structure remains intact even after exposure to humid air for two years.

▶ 관련 뉴스 바로보기: DGIST 연구팀, 이산화탄소를 에너지로 전환하는 고효율 광촉매 개발('19.5.26)

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If we wish to sustain our terrestrial ecosphere as we know it, then reducing the concentration of atmospheric CO2 is of critical importance. An ideal pathway for achieving this would be the use of sunlight to recycle CO2, in combination with water, into hydrocarbon fuels compatible with our current energy infrastructure. However, while the concept is intriguing such a technology has not been viable due to the vanishingly small CO2-to-fuel photoconversion efficiencies achieved. Herein we report a photocatalyst, reduced blue-titania sensitized with bimetallic Cu–Pt nanoparticles that generates a substantial amount of both methane and ethane by CO2 photoreduction under artificial sunlight (AM1.5): over a 6 h period 3.0 mmol g−1 methane and 0.15 mmol g−1 ethane are obtained (on an area normalized basis 0.244 mol m−2 methane and 0.012 mol m−2 ethane), while no H2 nor CO is detected. This activity (6 h) translates into a sustained Joule (sunlight) to Joule (fuel) photoconversion efficiency of 1%, with an apparent quantum efficiency of φ = 86%. The time-dependent photoconversion efficiency over 0.5 h intervals yields a maximum value of 3.3% (φ = 92%). Isotopic tracer experiments confirm the hydrocarbon products originate from CO2 and water.

▶관련 뉴스 바로보기: 연구뉴스 3D 구조 디바이스를 풍선 불 듯 제작하는 원천기술 개발('19.10.7)

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We fabricated CZTSSe thin films using optimized SLG-Mo/Zn/Cu/Sn (MZCT) as a stacked structure and described the phenomenon of Zn elemental volatilization using the MZCT stacked structure. We introduced H2S gas to effectively control the S/(S + Se) ratio of the film in the sulfo-selenization process and to suppress Zn volatilization. Unlike during the selenization process, a stable ZnSSe thin film was formed on the precursor surface during the sulfo-selenization process. The formation of the ZnSSe thin film inhibited Zn volatilization, which facilitated control of the thin film stoichiometry and played an important role in crystal growth. In addition, the sulfo-selenization process using H2S forms a grading of the S/(S + Se) ratio in the depth direction in the ZnSSe layer. The ZnSSe layer with this property causes the band gap grading in the CZTSSe absorption layer. Finally, through our optimized annealing process, we realized a world record CZTSSe solar cell with a certified power conversion efficiency of 12.62% and a centimetre-scale (1.1761 cm2) efficiency of 11.28%.