Optical properties of GaP photonic crystal nanobeam cavity with WSe2 active monolayer

이호성 KU-KIST Graduate School of Converging Science and 2020 국내석사

인화 갈륨 나노빔 공진기와 이차원 반도체의 광특성 이 호성 고려대학교 KU-KIST 융합대학원 지도교수: 박 홍규 국문 초록 이차원 반도체의 새로운 물리적 특성은 저차원 물리 및 장치 응용분야의 새로운 장을 열었습니다. 이 물질들이 하나의 전이금속 원자가 양쪽에 할로겐 원자에 갇혀있는 X-M-X 구조를 가집니다. 이 물질들은 같은 평면방향으로 강한 결합을 하고 있으며, 매우 얇고, 유연합니다. 그리고 가장 큰 특징은 원자 두께 정도지만, 반도체의 특성인 직접적인 밴드갭을 갖고 있습니다 [38,39]. 또한, 이차원 물질은 강한 여기방출을 하는 것으로 알려져 있습니다. 따라서, 이차원 물질은 광결정 공진기에서 이득 매질로 사용될 수 있습니다 [36,37]. 나노 크기의 높은 품위값을 갖는 나노빔과 텅스텐 디셀레나이드(WSe2) 단층과의 통합은 광 집적 회로에 기여할 수 있습니다. 인화 갈륨은 가시광선 영역에서 가장 높은 굴절률( 555 nm 에서 3.44)을 가지는 물질입니다. 인화 갈륨으로 나노빔 공진기를 만들어 텅스텐 디셀레나이드와 결합시키려고 합니다. 하지만, 인화 갈륨은 박막 형태로 기르기 힘들기 때문에, 베어 웨이퍼에 집속 이온빔 (FIB) 장비를 이용해서 삼각형 형태의 나노빔 공진기를 만들 것입니다. 그리고, 유한 차분 시간 시뮬레이션(FDTD)을 통해 삼각형 나노빔 공진기를 설계하였습니다. 삼각형 형태지만, 인화갈륨의 굴절률이 높기 때문에 〖10〗^6 의 높은 품위값을 가집니다. 희생층이 없기 때문에 두 번의 건조 식각 공정을 거칩니다. 나노빔 공진기의 위, 아래 부분과 구멍들을 일차적으로 식각합니다. 그 다음, 집속 이온 빔으로 기울여서 밀링 공정을 통해 제조될 것입니다. 제작된 나노빔 공진기 위에 텅스텐 디셀레나이드 단층을 옮긴 뒤, 측정을 진행할 것입니다. 이차원 반도체 물질의 광발광의 두께가 얇아지거나, 공동과 결합될 것으로 예상됩니다

Control and analysis of electromagnetic wave transmission of multilayer thin film by transfer matrix method

권지성 KU-KIST Graduate School of Converging Science and 2021 국내석사

We propose and demonstrate that the Transfer matrix method can effectively analyze states of electromagnetic waves scattered from thin material. In this paper, we have studied the electromagnetic waves in metamaterials at a frequency range of X-band electromagnetic wave and infrared light. To analyze the scattered electromagnetic waves for the X-band range, the annealed Ti3CNTx film was modeled as a multilayer structure referring the experimentally measured electrical conductivity and the porous structure. The EMI SE increment of the annealed Ti3CNTx film was measured at a temperature as high as 350 ℃, at the same time, the material’s conductivity was around 1000 to 1800 S∙cm^(-1) and porosity rose from 0 to 16 %. The experimentally measured EMI SE increment of the annealed Ti3CNTx film can be explained theoretically by conductivity and porosity increment calculation of multilayer. For the infrared light range, a perfect anti-reflector was designed and manufactured. The UIM theory provides anisotropic parameter of a layer to eliminate reflection. The theoretical based UIM layer was designed as a sub-wavelength scale multilayer structure and calculated by the transfer matrix method. This UIM layer suppressed reflection under 1% from wavelength of 1.2 to 2.5 μm and incident angle from 0 to 50°. The fundamental UIM theory is applied to the manufacturing process of Si substrates. Furthermore, the reflectivity of the manufactured UIM layer was measured experimentally, and this reflectance was almost identical to that of stimulated. In this research, the transfer matrix method contributes in estimating the state of scattered electromagnetic waves in the thin multilayer structures.

Epidermal electronics system for physiological monitoring in patients with skin wound

최종찬 KU-KIST Graduate School of Converging Science and 2021 국내석사

While conventional wound assessments need to visit clinicians or help from nurse, there might be potential opportunities to develop an electronic system that can diagnose wound conditions by itself in a real time format, and can ultimately be managed unattended in medical systems. Here, we report a skin-interfaced wireless medical device that can diagnose wound status of patients in a real-time, personalized approach. This epidermal electronics system is systemically composed of two sub modules; a disposable sensor-integrated dressing (unit 1) and a reusable secondary wound enclosure incorporated with wireless communication electronics (unit 2). A mechanically soft, disposable unit 1 that consist of conventional medical dressings integrated with epidermal electronics sensor arrays (EESA) is capable of conformally attaching to the human skin and comprehensive, continuous monitoring of wound-status-related physiological parameters, including pH, temperature, and humidity. A reusable wireless modular unit 2 that utilizes electronic systems constructed on a flexible printed circuit board (FPCB) is contained within a soft, elastomeric housing and offers capabilities in analyzing bio-signals collected from EESA, diagnosing a patient’s status on healing phases, and transmitting data via wireless communications. This new platform illustrates their potential abilities for clinical uses through in vitro and in vivo investigations, and an example mobile application presents further applicability in a patient’s care.

Exosome-based immune checkpoint blockade targeting CD47

고은이 KU-KIST Graduate School of Converging Science and 2017 국내석사

Localized synergistic PLGA nanomedicines triggering effective anti-tumor immunity

최용환 KU-KIST Graduate School of Converging Science and 2021 국내박사

Over the past half century, cancer therapy has developed by presenting alternatives to the deficiencies of the previous generation. Actually, the paradigm of cancer treatment has changed until immunotherapy, the 3rd generation of cancer therapy, leading safe and powerful customized treatments. Ultimately, the core technology to treat cancer is using immune system of our body in a direct or indirect way. This approach provides us safety from the side effects, including unwanted toxicity, of the cancer treatment process. Unfortunately, there are still several obstacles originating from the tumor and its environment. Since the microenvironment of each tumor also has distinct characteristics from an immunological point of view, there is a clear limitation in that the responsiveness and efficacy of cancer immunotherapy can vary greatly from situation to situation. The point of this study is that application of nanomedicine-driven chemo-immunotherapy with a combination of several immunological drugs would overcome the problems of previous generation of cancer therapy, and they also expand the scope of application of cancer immunotherapy. In the point that nanomedicine technology is absolutely necessary to control the tumor environment advantageously for immunotherapy, DOX-loaded PLGA NPs, for controlled ICD, were prepared. Subsequently, several combinations of immunotherapy using anti-PD-L1 Ab and ROCK inhibitor were attempted with this base nanomedicine technology. DOX-PLGA nanomedicine is administrated by intratumoral injection, resulting in sustained release of DOX, leading to continuous ICD, sequentially. It came to appear as a result of induced anti-tumor immunity. Additionally, normalizing adaptive immunity by combination of DOX-PLGA nanomedicine and anti-PD-L1 Ab boosted T cell-mediated immunity. It successfully triggered systemic immune responses in tumor rechallenge model by inhibiting its growth. Similarly, enhancing innate immunity by combination of DOX-PLGA nanomedicine and Y27632, a type of ROCK inhibitor, also showed therapeutic efficacy in tumor growth and elicited anti-tumor immune responses. Unlike conventional mono-immunotherapy, modulating immune responses in tumor and its environment and inducing systemic anti-tumor immunity were made possible by DOX-PLGA nanomedicine-based cancer chemo-immunotherapy. And it is thought that this can enhance the accessibility of treatment as a platform technology for numerous other cancer immunotherapies.

Multi-functional cancer vaccine based on ROS-responsive photoswitching nanocomposites

조유리 KU-KIST Graduate School of Converging Science and 2021 국내석사

Cancer treatment techniques have significantly been advanced in recent decades, but they have a disadvantage of remarkably lowering the immune system in the body. To overcome this issue, immunotherapy is suggested to stimulate the immune system of humans to increase the effectiveness of cancer treatment. Strategies of cancer immunotherapy include immune checkpoint therapy, adoptive cell transfer, and cancer vaccine therapy. Recently, Uric acid (UA), the metabolic end-product of purine metabolism in humans, has been used as an adjuvant in immunotherapy. The crystalline Uric acid (MSU), the leading cause of gout, is known as damage-associated molecular patterns (DAMPs), which are the starting point for triggering the immune effector including dendritic cells and macrophages. In this paper, I devised a photo-switching Nanogel cancer vaccine based on the crystallization of UA, which can be triggered by photodynamic therapy (PDT) via an on-off system for enhancing immune responses. MSU produced after PDT was confirmed using TEM, suggesting that crystallization of UA can be controlled through an on-off system by PDT. The cell penetration efficiency, intracellular distribution, and photo-induced cytotoxicity of the Nanogel were evaluated by in vitro studies on a cancer cell line. Further, the immunogenic efficacy was evaluated by quantitative analysis of DAMPs expression on a cancer cell line.

(A) study of enhancing the therapeutic efficacy of adoptive T cell therapy in cancer treatment

김우준 KU-KIST Graduate School of Converging Science and 2021 국내박사

In recent years, immunotherapy has emerged as a fourth pillar of cancer treatment other than conventional three pillars of cancer therapy: chemotherapy, and radiotherapy, and surgery. There has been increasing interest in optimizing this immunotherapy due to a unique approach for cancer treatment, using the patient’s immune system to recognize and kill tumor cells. Among many modalities in immunotherapy, adoptive T cell transfer (ACT) is the primary modality that uses tumor specific cytotoxic T lymphocytes to recognize and destroy tumor cells. ACT including chimeric antigen receptor (CAR) T cell therapy and T cell receptor (TCR) T cell therapy, have achieved significant improvements but the therapeutic result is varying among patients with same treatment. To minimize the therapeutic gap between the patients, it important to track the adoptively transferred T cells to understand the transfer route, in vivo biodistribution and tumor-targeting ability. Moreover, the ACT has been showed potent therapeutic in liquid tumor and melanomas, however therapeutic outcome of patients with solid tumor is relatively poor due to immunosuppressive tumor microenvironment (TME). TME possess variety of factors that influence the therapeutic result of ACT such as think layer extracellular membrane that impedes the T cell infiltration, immune checkpoint receptors on tumor cells, and low-oxygen and acidic environment that causes T cell exhaustion or senescence of T cell. In order to resolve the issues that hamper the outcome of ACT, we need to develop 1) noninvasive and stable cell tracing strategy for understanding the T cell biodistribution and evaluating the efficacy of T cell therapy, 2) remodeling of thick ECM surrounding tumor tissue to enhance the T cell accumulation in tumor region, 3) combinational therapy with other conventional therapy to establish synergetic effect for complete tumor eradication.

Theory of spin-torque ferrimagnetic resonance

김석종 KU-KIST Graduate School of Converging Science and 2021 국내석사

스핀 토크 강자성 공명실험(Spin-Torque Ferromagnetic Resonance, ST-FMR)은 강자성체/비자성 금속 이중층에서 강자성체에 가해지는 스핀 궤도 토크(Spin-Orbit Torque)를 측정하는 데 사용되는 실험 중 하나로, ST-FMR 그래프 분석을 통해 두 형태로 나타나는 스핀 궤도 토크의 효율을 각각 계산할 수 있다. 최근 스핀 전류를 이용한 페리자성체(Ferrimagnets)의 자화 거동 연구가 진행되면서, 페리자성체/비자성 금속 이중층에서 나타나는 스핀궤도토크를 ST-FMR로 분석한 연구들이 발표된 바 있다. 그러나 이 방법이 페리자성체의 스핀 궤도 토크를 계산하는 데 타당성이 있는지 확인된 연구가 없는 상태이다. 본 논문에서는 스핀궤도토크에 의한 페리자성체의 공명현상(Spin-Torque Ferrimagnetic Resonance, ST-FiMR)을 분석하였다. 이론과 수치 모사를 통해 ST-FMR에서는 나타나지 않는 몇 가지 특성을 확인하였다. 먼저, ST-FiMR 값은 알짜 스핀 각운동량 값에 비례하여, 각운동량 보상점 조건 부근에서 부호가 변함을 확인하였다. 또한 각운동량 보상점 부근에서 반강자성체 거동의 기여로 인해, 감쇠 형태의 SOT만으로도 공명 시그널 값이 비대칭적으로 나타날 수 있음을 확인하였다. 마지막으로, 페리자성체에서는 구성원자들의 Zeeman 에너지가 서로 상쇄되어, 자기장 형태의 SOT가 기여하는 공명 시그널 값은 매우 작음을 확인하였다. 해당 연구 결과는, 기존의 ST-FMR 분석법은 페리자성체에 작용하는 SOT의 크기와 부호를 정확히 계산하는 데 한계가 있음을 시사한다. In this thesis, we report a theory of spin-torque-induced magnetic resonance in collinear ferrimagnets, i.e., spin-torque ferrimagnetic resonance (ST-FiMR). In Chapter 1, we introduce theoretical background for spin-torque ferromagnetic resonance (ST-FMR). Then in Chapter 2, we derive rectified dc voltage signal in ferrimagnet / heavy metal bilayer structure with staggered Landau-Lifshitz-Gilbert equation, describing the dynamics of collinear antiferromagnetic system. We find that rectified DC voltages of ST-FiMR have several distinct features as compared to spin-torque ferromagnetic resonance (ST-FMR) signals. (i) The magnitude of ST-FiMR signal due to damping-like spin-orbit torque is almost linearly proportional to the net spin density and its sign changes near the angular momentum compensation condition. (ii) Because of antiferromagnetic dynamics, field dependence of ST-FiMR signal is asymmetric near the angular momentum compensation condition even when only damping-like spin-orbit torque is applied. (iii) Contribution of field-like spin-orbit torque to ST-FiMR signal is much smaller than that of damping-like spin-orbit torque, because of reduced Zeeman coupling. Our result suggests that the traditional ST-FMR line-shape analysis is unable to correctly estimate the spin-orbit torque magnitude and sign of ferrimagnets so that an analysis based on the ST-FiMR theory must be applied.

Development and characterization of catalysts based on two-dimensional materials for photoelectrochemical water splitting

이재윤 KU-KIST Graduate School of Converging Science and 2021 국내박사

The development of hydrogen energy as eco-friendly and sustainable energy has become increasingly important toward realizing a low-carbon society. Among various hydrogen production methods, the solar-energy-driven photoelectrochemical (PEC) water splitting technology using photoelectrodes is one of the promising ways to produce clean and carbon-free hydrogen. A semiconductor photocathode, p-type silicon (p-Si), is widely used as a photoactive material of the PEC water splitting cell for hydrogen evolution reaction (HER). However, the semiconductor photocathodes are typically very unstable in acid solutions and have the high kinetic energy barriers required for electrochemical hydrogen reduction occurring on the photocathode/electrolyte interface. To efficiently reduce kinetic energy barriers, an appropriate catalyst is required on the photocathode surface while being inexpensive and stable. Additionally, it is highly demanded to develop a reliable characterization technique that clearly analyzes and correlates the catalytic activity with the properties of the catalyst. Transition metal dichalcogenides (TMDs) with two-dimensional (2D) layered structures, such as molybdenum disulfides (MoS2) and Tungsten disulfides (WS2), have recently received the spotlight as a promising candidate for the HER catalyst because they are cheap and earth-abundant. Although the catalyst activity at the atomic edge sites of TMDs is known to be high, studies have recently been actively conducted on the technology to activate the catalytic activity of the relatively inert basal plane to take advantage of the large surface-to-edge ratio of these 2D layered materials. The studies tried so far include the uses of naturally-existing or intentionally-strained atomic vacancies and grain boundaries, catalytic dopants incorporated on the basal surface, etc. This dissertation mainly focused on the development and characterization of atomically thin heterojunction catalysts using TMDs with different energy band structure without additional surface engineering as an efficient HER catalyst. The heterojunction catalyst using energy-band-engineered semiconductors has been widely used in conventional bulk material systems. The formation of type-II heterojunction can efficiently reduce the kinetic energy barriers that exist at the photocathode/electrolyte interfaces. In this respect, a heterojunction consisting of atomically thin TMD layers is expected to form a physically limited deletions region, enabling the ultrafast transfer of photo-excited charge carriers by the strong built-in electric field, resulting in optimizing the interfacial kinetics of photoelectrolysis. However, in commonly used PEC measurements using large-area photoelectrode under global illumination, it is experimentally very difficult to correlate the PEC performances with specific properties of the catalyst because of the ensemble averaging effects caused by various inhomogeneous factors, such as step edges, vacancies, and grain boundaries, as well as other extrinsic factors in the electrode fabrication processes such as contact resistances, the number of layers, and local strains. To resolve this critical issue, we have developed a new PEC characterization technique, named scanning photoelectrochemical microscopy (SPECM), using a microscale device. This SPECM analysis enables the spatial resolved characterization and imaging of PEC performance of the designed catalytic surfaces, thus visualizing the HER catalytic activity on various catalytic surfaces. The technique uses a focused laser with a diameter less than 1 µm, and its incident power is very low at around 100 nW, excluding the photothermal effects caused by local heating. Using the methodology developed above, the difference in catalytic activity between the TMD heterojunction and the single TMD layer was clearly revealed, while excluding other influential effects. In particular, when the MoS2/WS2 heterojunction is introduced as a catalyst on the photocathode, a significant reduction in both overpotential and charge-transfer resistance is achieved even without intentional generation of catalytic sites. The beneficial effect of atomically thin vertical heterojunction is explained by the built-in potential resulted from the efficient charge transfer of excited carriers in type-II heterojunction with the theoretical support of the first-principles calculation. Based on this, the large-scale atomically thin TMD heterojunction catalyst was demonstrated, and their PEC performances were characterized. The large-area MoS2/WS2 heterojunction catalyst was fabricated on a p-Si photocathode using 2-inch TMD films grown by metal-organic chemical vapor deposition. The fabricated photocathode resulted in a very low onset potential and a high photocurrent density at 0 V versus a reversible hydrogen electrode. Furthermore, the spatially resolved PEC characterization using SPECM clearly revealed the PEC performance of more complex catalytic structures, including the atomic edge sites, different thickness of TMD layer, vertically aligned TMD with nanoparticles. Our demonstration not only provides an unprecedented approach to fundamentally investigating the PEC performances about the tailored properties of catalysts but also proposing a new catalytic architecture, thereby enabling the design of highly efficient energy converging systems, including PEC water splitting cell.

Skin-attachable all-in-one sensor system consisting of a flexible micro-supercapacitor with a strain sensor on a bio-inspired adhesive

박효진 KU-KIST Graduate School of Converging Science and 2021 국내석사

We report on the fabrication of a skin-attachable, all-in-one sensor system (AIOS) consisting of a vertically integrated flexible micro-supercapacitor (MSC) and a stretchable strain sensor on a gecko-inspired micro-structured adhesive (GIA). Combined utilization of the mixed manganese/vanadium (Mn/V) oxide grown on MWCNT and the sulfone-based electrolyte, PC/SL/LiClO4/PMMA, enhances both the capacitance and operation voltage up to 2 V of MSC. Thus, the fabricated MSC exhibits excellent electrochemical performance with an areal capacitance increase of 25 times compared to MWCNT-based electrode supercapacitor. The MSC shows mechanical stability over repetitive bends at a bending radius of 3.7 mm and dynamic bending deformations down to bending radius of 2.9 mm regardless of the bending rate. The strain sensor made of fragmentized graphene foam embedded in PDMS film provides a high gauge factor of 12.6 up to 50% strain to detect strains due to various bio-signals. Our gecko-inspired adhesive is made of PDMS micropillars inked with a mixture of PDMS and silbione to have spatula tips. Such fabricated adhesive exhibits not only high adhesion property but also high durability over repeated cycles of attachment-detachment and negligible skin irritation. With the integrated AIOS attached to the skin, bio-signals such as an arterial pulse, swallowing, and frowning of the brow are successfully detected using energy stored in the MSC. 해당 논문은 게코 도마뱀 모사 접착 기판 (GIA) 상에서, 유연 마이크로 수퍼커패시터 (MSC) 와 신축성 스트레인 센서를 층층이 결합한 형태의 피부 부착형 올인원 센서 시스템(AIOS) 에 대하여 보고한다. MWCNT 위에 성장한 망간/바나듐 (Mn/V) 옥사이드 혼합물과 설폰 기반 전해질 (PC/SL/ LiClO4/PMMA) 을 사용함으로써, MSC의 용량 향상 뿐만 아니라 2 V 의 전압까지 작동 전압을 향상하는 효과를 기대한다. 제작된 MSC는 MWCNT 기반 전극 수퍼커패시터에 비해 면적 당 용량이 25 배 증가한 우수한 전기화학적 성능을 보여준다. 또한, 제작한 MSC는 3.7 mm의 반경으로 반복적으로 구부렸을 때와 2.9 mm의 반경으로 실시간으로 구부렸을 때 모두 기계적으로 안정한 특성을 보인다. 또한, PDMS 필름에 내장된 조각화된 그래핀 폼으로 만들어진 스트레인 센서는 다양한 생체 신호로 인한 스트레인을 감지하기 위해 12.6 의 높은 게이지 계수를 가진다. 게코 도마뱀 모사 접착 기판 (GIA) 은 미세 기둥들로 이루어진 PDMS 기판을 PDMS와 Silbione의 혼합물에 찍어서 제작되어진다. 제작된 접착 기판은 접착력이 우수할 뿐만 아니라, 반복적인 탈부착에 대한 높은 내구성과 피부에 오랜 시간 부착하였을 때에도 경미한 염증 반응을 보인다. 최종적으로, 제작한 MSC와 스트레인 센서, 게코 도마뱀 모사 기판은 PDMS의 접착성을 이용하여 결합할 수 있다. 이렇게 제작된 올인원 센서 시스템 (AIOS)을 피부에 부착한 후, MSC로 구동하여 맥박, 목 삼킴, 미간 찡그림에 대한 생체 신호를 성공적으로 감지할 수 있다.