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전기화학적 식각된 텅스텐 와이어를 이용한 원자현미경 탐침 몰드 제작
고주희(Juhee Ko),이동혁(Donghyuk Lee),김석범(Seokbeom Kim),김광석(Kwangseok Kim),이정철(Jungchul Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Since it demands extensive efforts to fabricate atomic force microscope (AFM) cantilevers with a sharp tip, it is necessary to develop a simple and cost-effective fabrication method. Recently, our group has employed replica molding and subsequent UV curing for hydrogels inside polydimethylsiloxane (PDMS) molds to make all-hydrogel AFM cantilevers where the PDMS tip mold was replicated from an anisotropically wet-etched silicon wafer. Although the PDMS tip mold was bi-axially compressed to vary the aspect ratio of the replicated hydrogel AFM tip, the achievable aspect ratio was limited below ~2.5. Here, we propose a new idea to use an electrochemically etched tungsten wire as a positive tip mold from which the negative PDMS mold can be directly replicated. To reproduce similar sharpness of the etched tungsten, a high speed comparator along with a feedback circuit was employed. With the PDMS tip mold replicated from the tungsten wire etched at 3 V in 3 M NaOH solution, the hydrogel tip radius of 50 nm was able to be attached to a tipless hydrogel cantilever.
마이크로채널 공진기를 이용한 100 피코리터 이하 액상 이원 혼합물의 질량 밀도와 몰분율 동시 측정
고주희(Juhee Ko),이봉재(Bong Jae Lee),이정철(Jungchul Lee) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Microchannel resonators have been widely used in density measurement of liquids due to its high sensitivity and small sample consumption. Since there are many liquid samples with the same density, studies with additional measurements such as Raman analysis have been introduced. However, sequential iterations for each system make difficult to verify the result equivalence due to sample and environmental changes over time. In this paper, we propose a new approach to improve the detection accuracy of unknown liquid samples using chemical fingerprint along with mass by integrating Raman and resonance analysis. While Raman laser is focused on the sample inside microchannel through nearly transparent silicon nitride channel lid, resonance laser with different wavelength is illuminated from the opposite side, focused on the polysilicon layer embedded inside the channel. To demonstrate the simultaneous measurement with the integrated system, Raman spectrum and density are measured and analyzed with water and ethanol mixture.
습도 측정 응용을 위한 석영 튜닝 포크 위 하이드로젤 마이크로 패터닝
고주희(Juhee Ko),윤여원(Yeowon Yoon),이보라(Bora Lee),이정철(Jungchul Lee) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
This paper reports a new humidity sensing platform based on quartz tuning forks (QTFs) with hydrogel printed. Commercial quartz tuning forks are placed into a polydimethylsiloxane (PDMS) mold to make a flat plane between two prongs where hydrogel prepolymer is dispensed and cured as specific shapes and sizes by digital micromirror device (DMD)-based dynamic mask lithography. To control the thickness of hydrogel structures, a PDMS cover with 10-μm deep recess is also placed on top of the QTF-PDMS mold assembly. Once polyethyleneglycol diacrylate (PEG-DA, MW 575) mixed with a photoinitiator is introduced into the empty space between the PDMS cover and the QTF-PDMS mold assembly, the dynamic mask is projected. Each QTF with printed PEG-DA structures is characterized and used for humidity sensing experiments. To maximize the responsivity to the ambient humidity, optimized shape, size, and placement of hydrogel patterns are experimentally explored. In addition, the humidity sensing resolution is investigated by the Allan deviation analysis.