Colorimetric Plasmonic Gas Sensor

학위논문(석사)--서울대학교 대학원 :공과대학 재료공학부,2019. 8. 장호원.Plasmonics 분야는 지난 수십 년 동안 많은 관심을 받았으며 다양한 응용 분야에 적용 가능성을 보여주었습니다. 다양한 응용 분야 중 특히 가스 감지를 목적으로 하는 플라즈몬 (plasmonics)에 대한 연구가 활발히 진행되고 있다. 가스 센서의 감도, 선택도 및 내구성을 향상시키기 위해 가스 센서의 광 센서로서 플라즈몬을 사용하는 것에 대한 많은 연구가 이루어졌습니다. 광학 센서는 전압을 가할 필요가 없으며 전자기적으로 노이즈에 영향을 받지 않으며 가열 메커니즘을 필요로 하지 않으므로 반도체식 센서에 비해 더 높은 신뢰도를 보인다. 본 연구에서, 플라즈몬 공명의 전자기 강화와 결합 된 광학 간섭의 개념을 기반으로 가스 검출을 위한 센서를 설계하였다. 센서의 플라즈몬 층과 빛의 상호 작용에 의해 야기 된 국부적 인 표면 플라즈몬 공명 (LSPR)과 표면 플라즈몬 분극 (SPP)은 다양한 색의 센서를 제조하는데 이용되었다. 색상은 Lumerical software Finite Difference Time Domain (FDTD) 솔루션을 통해 시뮬레이션 하였다. Reflectance 를 위해 Si 기판 위에 Al layer를 thermal evaporator로 증착 하였다. 이후 e-beam evaporator를 이용해 WO3 박막 또는 WO3 nanorods 구조체를 제작하였다. 최종적으로 Au 필름을 증착하여 plasmonic 효과를 분석하였다. 센서의 플라즈몬 층에서 발생하는 공진은 환경 변화에 매우 민감하다. 따라서, 촉매로서 귀금속으로 장식 된 나노 구조 금속 산화물은 기체의 흡착 및 탈착을 위한 유전체 매체로 사용되었다. 가스의 흡착으로 인해 센서의 광학적 특성에 변화가 생길 것으로 예상하였으며, 그 결과 산란, 흡수 및 투과 스펙트럼에서 피크 시프트가 발생할 것으로 기대한다. 이러한 피크 시프트와 색 변화가 플라즈몬 센서의 가스 감지 능력을 판별하는 파라미터로 사용된다.The field of plasmonics has been of much interest over the past few decades, showing potential for use in various applications. Of these applications, the use of plasmonics in gas sensing is currently being investigated. In order to enhance the sensitivity, selectivity, and durability of gas sensors, many studies have focused on the use of plasmonics as optical sensors for gas sensing. Because optical sensors require no contact measurements, are electromagnetically noise independent, and do not require a heating mechanism they can be more reliable compared to electrical sensors. In this study, the concept of optical interference coupled with the electromagnetic enhancement of plasmon resonances is used to design a sensor for the colorimetric detection of gases. The localized surface plasmon resonance (LSPR) and surface plasmon polariton (SPP) caused by the interaction of light with the plasmonic layer of the sensor is utilized in fabricating sensors of various structural colors. The structural colors were simulated through Lumerical software Finite Difference Time Domain (FDTD) Solutions then fabricated for comparison. The resonances that occur at the plasmonic layers of the sensors are extremely sensitive to changes in its environment. Therefore, nanostructured metal oxides decorated with noble metals as catalysts were used as the dielectric medium for the adsorption and desorption of gases. The adsorption of gas is expected to bring about a change in the sensors optical properties, which in turn causes a peak shift in the scattering, absorption, and transmission spectra. These peak shifts and the possible color change associated with these shifts are used as the response for our plasmonic sensor.Table of Contents Abstract i Contents iii List of tables vi List of figures vii Chapter 1. Introduction 1.1 Background 2 1.2 Objectives of this study 5 Chapter 2. Literature review 2.1 Classification of gas sensing methods 9 2.2 Fundamentals of optical gas sensors 12 2.2.1 Types of optical gas sensors 12 2.2.2 Plasmonic gas sensors 14 2.3 Optical Interference 16 2.3.1 Thin film optical interference theory 16 2.3.2 Structural colors 17 Chapter 3. WO3 thin film with Au plasmonic layer on Al mirror layer for the detection of NO2 3.1 Introduction 19 3.2 Sensor fabrication 21 3.2.1 Thin film plasmonic sensor 21 3.3 Characterization 22 3.4 Finite Difference Time Domain (FDTD) simulation 24 3.5 Gas sensing measurement 25 3.5.1 Optical response 25 3.6 Conclusion 28 Chapter 4. Au/Pd decorated WO3 Nanorods on Al mirror layer for the detection of H2 and NO2 4.1 Introduction 30 4.2 Sensor fabrication 34 4.2.1 Resistive sensor with nanorods 34 4.2.2 Plasmonic sensor with nanorods 35 4.3 Characterization 36 4.4 Gas sensing measurement 38 4.4.1 Resistive response 38 4.4.2 Optical response 42 4.5 Conclusion 45 Chapter 5. Summary 5.1 Summary 47 References 48 Abstract (in Korean) 58Maste

Templated self-assembly of siloxane block copolymers for nanofabrication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references.Monolayer patterns of block copolymer (BCP) microdomains have been pursued for applications in below sub-30 nm nanolithography. BCP selfassembly processing is scalable and low cost, and is well-suited for integration with existing semiconductor fabrication techniques. The two critical issues are how to obtain reliable long-range ordering of features with minimum defect densities and how to successfully transfer the patterns into other functional materials. Exceptionally well-ordered and robust nanoscale patterns can be made from poly(styrene-b-dimethylsiloxane) (PS-PDMS) BCPs, which have a very large Flory-Huggins interaction parameter between the blocks compared to other commonly used BCPs. Cylinder- or sphere-forming BCP films were spincoated over silicon substrates patterned with shallow steps using optical lithography or nanoscale posts made by electron-beam lithography, and solvent-annealed to induce ordering. This generates patterns with a correlation length of at least several micrometers. The annealed film was treated with plasma to obtain oxidized PDMS patterns with a lateral dimension of 14 - 18 nm. These can be used as an etch mask or an easily removable template for patterning functional materials. Solvent vapor treatments can tune the pattern dimension and morphology. Different degrees of solvent uptake in BCP films during solvent-annealing can manipulate the interfacial interaction between the two blocks, and a mixed solvent vapor can change the effective volume fraction of each block. The self-assembled patterns can be transferred into various kinds of functional materials.(cont.) For example, arrays of parallel lines were used as a mask to pattern poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) conducting polymer thin films. The resulting PEDOT:PSS nanowire array was used as an chemiresistive-type ethanol-sensing device. Metallic films such as Ti, Pt, Ta, W, and magnetic Co and Ni were structured using a pattern-reversal process. Coercivity enhancements were observed for the fabricated ferromagnetic nanostructures such as wires, rings, and antidots. These functional nanostructures can be utilized for a variety of devices such as high-density and high performance sensor or memory devices.by Yeon Sik Jung.Ph.D

Parametric Optimization of Visible Wavelength Gold Lattice Geometries for Improved Plasmon-Enhanced Fluorescence Spectroscopy

The exploitation of spectro-plasmonics will allow for innovations in optical instrumentation development and the realization of more efficient optical biodetection components. Biosensors have been shown to improve the overall quality of life through real-time detection of various antibody-antigen reactions, biomarkers, infectious diseases, pathogens, toxins, viruses, etc. has led to increased interest in the research and development of these devices. Further advancements in modern biosensor development will be realized through novel electrochemical, electromechanical, bioelectrical, and/or optical transduction methods aimed at reducing the size, cost, and limit of detection (LOD) of these sensor systems. One such method of optical transduction involves the exploitation of the plasmonic resonance of noble metal nanostructures. This thesis presents the optimization of the electric (E) field enhancement granted from localized surface plasmon resonance (LSPR) via parametric variation of periodic gold lattice geometries using finite difference time domain (FDTD) software. Comprehensive analyses of cylindrical, square, star, and triangular lattice feature geometries were performed to determine the largest surface E-field enhancement resulting from LSPR for reducing the LOD of plasmon-enhanced fluorescence (PEF). The design of an optical transducer engineered to yield peak E-field enhancement and, therefore, peak excitation enhancement of fluorescent labels would enable for improved emission enhancement of these labels. The methodology presented in this thesis details the optimization of plasmonic lattice geometries for improving current visible wavelength fluorescence spectroscopy

Nanostructured polymeric surfaces by different patterning techniques

322 p.En esta tesis se recoge el trabajo que se ha llevado a cabo en el campo del estructurado de superficies poliméricas centrado en el uso de técnicas que usan como proceso de impresión del motivo el fotocurado de resinas basadas en el polihidroxiestireno, la infiltración o la ablación sobre sustratos capas y films de Poliestireno y derivados nativos, así como de mezclas de estos con copolímeros en bloque derivados del Poliestireno como, el copolímero en bloque de Poliestireno con poliácido acrílico (PS-b-PAA) con grupos químicos carboxilos, lo que aporta a la matriz de Poliestireno un carácter polar o de Poliestireno con 2,3,4,5,6-pentafluoroestireno (PS-b-P5FS) con los protones del anillos bencílicos sustituidos por flúor y así darle un mayor carácter no polar que el del Poliestireno.Con este trabajo se ha buscado imprimir motivos con detalles comprendido en el rango de los nanómetros a los micrómetros. Estas técnicas se han aplicado sobre sustratos de fotoresina o de PS nativas así como mezcladas con PS-b-PAA y P5FS-b-PS, con el fin de comparar el comportamiento de los sustratos ante estas técnicas. Además, como condición, se ha buscado que las técnicas se puedan aplicar de modo complementario con el fin, ya en proyectos futuros, conseguir estructuras jerarquizadas. Con esto se desea desarrollar superficies con motivos de un tamaño que por asociación formen el motivo para la siguiente escala.ICTP : Instituto de Ciencia y Tecnología de Polímeros CSIC : Consejo Superior de Investigaciones Científica

Modification of n-type and p-type metal oxide semiconductor systems for gas sensing applications

This thesis investigates the modification of three metal oxide semiconductor gas sensors with zeolite materials for the purposes of detecting trace concentrations of gases that have an effect on health, security, safety and the environment. SnO2, Cr2O3 and Fe2O3 were chosen as the base materials of interest. Zeolites HZSM- 5, Na-A and H-Y were incorporated into the sensing system either as admixtures with the base material or as coatings on top of it. The aim of introducing zeolites into the sensing system was to improve the performance of the otherwise unmodified sensors. Twenty-two novel zeolite-modified sensor systems are presented for the detection of a range of hydrocarbons and inorganic gases. Whilst sensors based on SnO2 systems were more responsive to gases, some sensors were also found to provide a greater degree of variability among repeat tests, particularly at lower operating temperatures i.e. 300 °C. Cr2O3 sensors modified by admixture with zeolite H-ZSM- 5 were seen to be poorly sensitive to most analytes. Cr2O3 sensors modified by admixture with zeolite Na-A and by overlayer of zeolite H-Y provided very promising sensitive and selective results towards toluene gas. Sensors based on the zeolite modification of Fe2O3 were not found to be promising candidates as gas sensors at this stage. Sensors were purposely exposed to gases that had similar molecular structures or kinetic diameters to assess the true capability of the sensors to discriminate among analytes. An array of four sensors based on n-type and p-type systems was subsequently chosen to see whether machine learning classifiers could be used to accurately discriminate among nine analytes. Using an SVM SMO classifier with a polykernel function, the model was 94.1% accurate in correctly classifying nine analytes of interest just after five seconds into the gas injection. Using an RBF kernel function, the model was 90.2% accurate in correctly classifying the data into gas type. These are very encouraging results, which highlight the importance of furthering research in this field; a sensing array based on zeolite-modified metal oxide semiconductor sensors may benefit a number of research domains by providing accurate results in a very fast and inexpensive manner

Design of Polymeric Sensing Materials for Volatile Organic Compounds: Optimized Material Selection for Ethanol with Mechanistic Explanations

There are many applications in which sensing and monitoring volatile organic compounds (VOCs) and other gas analytes are important. This thesis focusses on finding suitable sensing materials for ethanol to reduce the instances of people driving while intoxicated. To find suitable sensing materials, many constraints must be taken into consideration. For example, a sensing material and sensor must have the appropriate sensitivity and selectivity required. The goal is to create a sensing material or multiple materials capable of detecting ethanol that is emitted from the skin (transdermally). This requires highly sensitive sensing materials and sensors capable of detecting ethanol close to 5 ppm. This limit of 5 ppm was confirmed by measuring transdermal ethanol. In addition, to avoid false positives, the sensor must be able to selectively identify ethanol (i.e. respond preferentially to ethanol). To achieve this goal, polymeric sensing materials were used because of their ability to be tailored towards a target analyte. Multiple polymeric sensing materials were designed, synthesized, and evaluated as a sensing material for ethanol. Both the sensitivity and selectivity of the sensing materials were evaluated using a specially designed experimental test set-up that included a highly sensitive gas chromatograph (GC) capable of detecting down to the ppb range. In total, over thirty potential sensing materials were evaluated for ethanol. These sensing materials, which include polyaniline (PANI) and two of its derivatives, poly (o-anisidine) (PoANI) and poly (2,5-dimethyl aniline) (P25DMA), doped with various concentrations of five different metal oxide nanoparticles (Al2O3, CuO, NiO, TiO2, and ZnO), were synthesized and evaluated for sensitivity and selectivity to ethanol. In addition, specialized siloxane-based polymers and other polymers such as poly (methyl methacrylate) (PMMA) and polypyrrole (PPy) were evaluated. From these thirty plus sensing materials, P25DMA doped with TiO2, NiO, and Al2O3, along with PPy, had the best sensitivity towards ethanol. Most of the materials tested, with the exception of the CuO doped P25DMA, P25DMA doped with 20% ZnO, poly (ethylene imine) (PEI), and the siloxane-based sensing materials, were able to sorb, and therefore detect, 5 ppm of ethanol. Therefore, the sensitivity requirement of 5 ppm was satisfied. In terms of selectivity, P25DMA doped with 5% Al2O3 and P25DMA doped with 10% TiO2 had the best selectivity towards ethanol with respect to five typical interferent gases (acetaldehyde, acetone, benzene, formaldehyde, and methanol). Some of the most promising polymeric sensing materials were then deposited onto two different kinds of sensors: a capacitive radio frequency identification (RFID) sensor and a mass-based microcantilever microelectromechanical systems (MEMS) sensor. These sensors were evaluated for sensitivity, selectivity, and response and recovery times. It was found that P25DMA doped with 20% NiO had a detection limit of 3 ppm on the RFID sensor, whereas P25DMA had a detection limit of 5 ppm on the MEMS sensor. It should be noted that not all sensing materials work well on all sensors. To improve the selectivity of a sensor, a sensor array or electronic nose can be used. These use a pattern-recognition algorithm to separate the responses for different gas analytes. A proof-of-principle study was done using principal component analysis that was capable of distinguishing between six different VOCs using five different polymeric sensing materials. In addition, a three sensor array was evaluated on the RFID platform. Using PCA as the filtering algorithm, four gas analytes (ethanol, methanol, acetone, and benzene) were able to be identified. These four analytes could also be identified even when in gas mixtures of twos and threes and when all four gas analytes were present. After this wide experimentation, and based on the knowledge gained from the sorption responses between various VOCs and polymers, along with what has been reported in the literature, various sensing mechanisms were proposed. These sensing mechanisms explain why certain VOCs sorb more preferentially onto certain polymers. Therefore, identifying the dominant sensing mechanisms for a target analyte can improve sensing material selection. Based on these sensing mechanisms, potential sensing materials can be chosen for a target analyte. By including other constraints from the specific application target and sensor, this list of potential sensing materials can be further narrowed. From here, these sensing materials can be evaluated for sensitivity and selectivity, before the most promising ones are deposited onto sensors for further testing. This has led to prescriptions that can be followed when designing a new sensing material for a target application. These prescriptions take into consideration the chemical nature of the target analyte (and thus, the dominant mechanisms by which it is likely to interact), any constraints of the target application (including operational temperature and type of sensor), and the chemical nature of the common interferents present with the target analyte. These prescriptions allow one to narrow down a list of hundreds or thousands of potential sensing materials to a manageable few, which can then be evaluated