An intelligent and confident system for automatic surface defect quantification in 3D

Automatic surface defect inspection within mass production of high-precision components is growing in demand and requires better measurement and automated analysis systems. Many manufacturing industries may reject manufactured parts that exhibit even minor defects, because a defect might result in an operational failure at a later stage. Defect quantification (depth, area and volume) is a key element in quality assurance in order to determine the pass or failure criterion of manufactured parts. Existing human visual analysis of surface defects is qualitative and subjective to varying interpretation. Non-contact and three dimensional (3D) analyses should provide a robust and systematic quantitative approach for defect analysis. Various 3D measuring instruments generate point cloud data as an output, although they work on different physical principles. Instrument’s native software processing of point cloud data is often subject to issues of repeatability and may be non-traceable causing significant concern with data confidence. This work reports the development of novel traceable surface defect artefacts produced using the Rockwell hardness test equipment on flat metal plate, and the development of a novel, traceable, repeatable, mathematical solution for automatic defect detection and quantification in 3D. Moreover, in order to build-up the confidence in automatic defect analysis system and generated data, mathematical simulated defect artefacts (soft-artefact) have been created. This is then extended to a surface defect on a piston crown that is measured and quantified using a parallel optical coherence tomography instrument integrated with 6 axis robot. The results show that surface defect quantification using implemented solution is efficient, robust and more repeatable than current alternative approaches

Periodically patterned structures for nanoplasmonic and biomedical applications

Periodically patterned nanostructures have imparted profound impact on diverse scientific disciplines. In physics, chemistry, and materials science, artificially engineered photonic crystals have demonstrated an unprecedented ability to control the propagation of photons through light concentration and diffraction. The field of photonic crystals has led to many technical advances in fabricating periodically patterned nanostructures in dielectric/metallic materials and controlling the light-matter interactions at the nanoscale. In the field of biomaterials, it is of great interest to apply our knowledge base of photonic materials and explore how such periodically patterned structures control diverse biological functions by varying the available surface area, which is a key attribute for surface hydrophobicity, cell growth and drug delivery. Here we describe closely related scientific applications of large-scale periodically patterned polymers and metal nanostructures. The dissertation starts with nanoplasmonics for improving photovoltaic devices, where we design and optimize experimentally realizable light-trapping nanostructures using rigorous scattering matrix simulations for enhancing the performance of organic and perovskite solar cells. The use of periodically patterned plasmonic metal cathode in conjunction with polymer microlens array significantly improves the absorption in solar cells, providing new opportunities for photovoltaic device design. We further show the unprecedented ability of nanoplasmonics to concentrate light at the nanoscale by designing a large-area plasmonic nanocup array with frequency-selective optical transmission. The fabrication of nanostructure is achieved by coating non-uniform gold layer over a submicron periodic nanocup array imprinted on polystyrene using soft lithography. The gold nanocup array shows extraordinary optical transmission at a wavelength close to the structure period. The resonance wavelength for transmission can be tuned by changing the period of the gold nanocup array, which opens up new avenues in subwavelength optics for designing optoelectronic devices and biological sensors. We then demonstrate strong exciton-plasmon coupling between non-toxic CuInS2/ZnS quantum dots in solution and plasmonic gold nanocup array. The photoluminescence decay rate of quantum dots can be enhanced by more than an order of magnitude due to the high electric field intensity enhancement inside the plasmonic nanocup cavity. This solution based metal-nanocrystal coupled system has great promise for biological applications such as biosensing and biolabeling. Moving to the area of biomedical applications, we fabricate nanopatterned biopolymers as templates for controlling the release of therapeutic drugs coated on the polymer surface. From careful drug release experiments performed over extended time periods (e.g. eight days), we find that nanopatterned polymers release the drug slower as compared to the flat polymer surfaces. The slow-down in the drug release from nanopatterned surfaces is attributed to increase in the surface hydrophobicity confirmed by the contact angle measurements and microfluidic simulations. This nanoscale drug release control scheme has great promise for improving the performance of drug-eluting stents in cardiac therapies

Fabrication and Actuation of Hierarchically-Patterned Polymer Substrates for Dynamic Surface and Optical Properties

Switchable optical materials, which possess reversible color and transparency change in response to external stimuli, are of wide interest for potential applications such as windows and skylights in architectural and vehicular settings or optical sensors for environmental monitoring. This thesis considers the tuning of optical properties by tailoring and actuating responsive materials. Specifically, we demonstrate the design and fabrication of tilted pillar arrays on wrinkled elastomeric polydimethylsiloxane (PDMS) as a reversibly switchable optical window. While the original PDMS film exhibits angle-dependent colorful reflection due to Bragg diffraction of light from the periodic pillar array, the tilted pillar film appears opaque due to random scattering. Upon re-stretching the film to the original pre-strain, the grating color is restored due to the straightened pillars and transmittance is recovered. Then, we develop a composite film, consisting of a thin layer of quasi-amorphous array of silica nanoparticles (NPs) embedded in bulk elastomeric PDMS, with initial high transparency and angle-independent coloring upon mechanical stretching. The color can be tuned by the silica NP size. The switch between transparency and colored states could be reversibly cycled at least 1000 times without losing the film’s structural and optical integrity. We then consider the micropatterning of nematic liquid crystal elastomers (NLCEs) as micro-actuator materials. Planar surface anchoring of liquid crystal (LC) monomers is achieved with a poly(2-hydroxyethyl methacrylate)-coated PDMS mold, leading to monodomains of vertically aligned LC monomers within the mold. After cross-linking, the resulting NLCE micropillars show a relatively large radial strain when heated above nematic to isotropic transition temperature, which can be recovered upon cooling. Finally, the understanding of liquid crystal surface anchoring under confined boundary conditions is applied to the self-assembly of gold nanorods (AuNRs) driven by LC defect structures and to dynamically tune the surface plasmon resonance (SPR) properties. By exploiting the confinement of the smectic liquid crystal, 4-octyl-4’-cyanobiphenyl (8CB), to patterned pillars treated with homeotropic surface anchoring, topological defects are formed at precise locations around each pillar and can be tuned by varying the aspect ratio of the pillars and the temperature of the system. As a result, the AuNR assemblies and SPR properties can be altered reversibly by heating and cooling between smectic, nematic and isotropic phases

A Review on Mechanics and Mechanical Properties of 2D Materials - Graphene and Beyond

Since the first successful synthesis of graphene just over a decade ago, a variety of two-dimensional (2D) materials (e.g., transition metal-dichalcogenides, hexagonal boron-nitride, etc.) have been discovered. Among the many unique and attractive properties of 2D materials, mechanical properties play important roles in manufacturing, integration and performance for their potential applications. Mechanics is indispensable in the study of mechanical properties, both experimentally and theoretically. The coupling between the mechanical and other physical properties (thermal, electronic, optical) is also of great interest in exploring novel applications, where mechanics has to be combined with condensed matter physics to establish a scalable theoretical framework. Moreover, mechanical interactions between 2D materials and various substrate materials are essential for integrated device applications of 2D materials, for which the mechanics of interfaces (adhesion and friction) has to be developed for the 2D materials. Here we review recent theoretical and experimental works related to mechanics and mechanical properties of 2D materials. While graphene is the most studied 2D material to date, we expect continual growth of interest in the mechanics of other 2D materials beyond graphene

Designing topographically textured microparticles for induction and modulation of osteogenesis in mesenchymal stem cell engineering

Mesenchymal stem cells are the focus of intense research in bone development and regeneration. The potential of microparticles as modulating moieties of osteogenic response by utilizing their architectural features is demonstrated herein. Topographically textured microparticles of varying microscale features are produced by exploiting phase-separation of a readily soluble sacrificial component from polylactic acid. The influence of varying topographical features on primary human mesenchymal stem cell attachment, proliferation and markers of osteogenesis is investigated. In the absence of osteoinductive supplements, cells cultured on textured microparticles exhibit notably increased expression of osteogenic markers relative to conventional smooth microparticles. They also exhibit varying morphological, attachment and proliferation responses. Significantly altered gene expression and metabolic profiles are observed, with varying histological characteristics in vivo. This study highlights how tailoring topographical design offers cell-instructive 3D microenvironments which allow manipulation of stem cell fate by eliciting the desired downstream response without use of exogenous osteoinductive factors

The properties of Terahertz Wave Propagation in Parallel-Plate Waveguides

테라헤르츠(이하, THz) 파는 전자기파 스펙트럼 영역에서 마이크로웨이브 영역과 적외선 영역의 사이로, 일반적으로 0.1~10THz (파장:3mm~30μm)에 해당하는 파를 말하며, 적외선이 가지는 직진성과 마이크로웨이브가 가지는 투과성을 동시에 가지는 독특한 특성을 가지는 영역대의 전자기파이다. 따라서, 비금속성을 띄는 대부분의 물질의(옷, 나무, 플라스틱, 종이 등) 투과가 가능하여 이와 같은 재질로 내부에 숨겨져 있는 물질의 확인이 가능하며(이미징), 인체와 같은 바이오 물질의 경우, 기존에 사용되어 오던 X-ray에(106THz=4.13keV) 비하여 에너지가(1THz=4.13meV) 현저히 낮기 때문에 물질의 원자나 분자를 이온화 시키지 않는 비파괴 특성을 가진다. 또한, 많은 물질의 분자들이 THz 영역에서 공진 특성을 가지고 있어 물질의 연구(분광학)에도 많이 사용되고 있다. 게다가, 앞으로 기존의 무선 통신 및 정보 처리 등에 있어 더 넓은 대역폭과 더 빠른 속도를 필요로 함에 따라 THz 파가 사용되게 될 것이다. 이렇듯, 앞으로 그 응용은 기존의 다른 영역의 기술과 결합하여 계속해서 확대 되게 될 것이다. 최근, THz 파의 단일 횡전자계(TEM) 모드의 전파가 가능한 평행금속판도파로의 특성을 이용하여, 분광학(spectroscopy), 포토닉 도파로(photonic waveguide), 이미징, 필터, 센서 등의 여러 분야에서 활발한 응용이 진행되고 있다. 이 중에서 THz 파의 다양한 응용 및 집적 회로의 구현 등, 모든 시스템에 기본적으로 필요한 수동 소자, 즉 여러 기능의 필터 개발은 반드시 필요하다. 이에 본 저자는 스펙트럼 영역에서 강한 차단 영역, 즉 밴드 갭의 형성이 가능한 포토닉 결정 구조를 평행금속판도파로 구조와 결합하여 다양한 기초 연구 및 그 응용 연구를 실시하였다. 먼저, (Chapter II) 평행금속판도파로의 기본 단일, 다중 모드 전파 특성에 관한 기초 연구를 이론 및 실험을 통하여 실시하였으며, (Chapter III) 이 중, 저주파 영역을 차단하는 스펙트럼 전파 특성을 가진 TE1 모드를 이용하여 THz 고주파 대역 통과 필터를 구현하였다. 그리고, (Chapter IV) 파장 이하의 좁은 공간에 THz 파를 집속, 전파가 가능한 평행금속판도파로의 특성을 이용하여 THz 파가 평행금속판도파로로부터 빠져 나오는 출구 근처에(THz 표면파) 슬릿 배열의 포토닉 결정 구조를 위치시켜, THz 표면파와 포토닉 결정 구조 간의 강한 Bragg 반사 현상과 이에 대한 각 슬릿의 반사 계수를 성공적으로 측정하였다. (Chapter V) 그리고, 기존까지 자유 공간을 전파하는 THz 파를 파장 이하의 평행금속판도파로 갭 사이로 결합시키기 위해 준광학 기법인 실리콘 렌즈가 사용되었다. 하지만, 이는 실리콘 렌즈의 높은 굴절률(n=3.417)에 따른 반사 손실이 두 실리콘 렌즈의 의해 약 50%가 발생하며 또한, 실리콘 내부 전반사로 인하여 시간 영역에서 긴 측정을 불가능하게 만드는 다중 반사 신호가 측정된다. 따라서, 실리콘 렌즈를 경사각 3o를 가지는 경사진 도파로 구조로 대체하여 기존 실리콘 렌즈의 사용에 비해 약 2배 이상의 결합 효율 향상 및 내부 전반사를 제거하였다. (Chapter VI) 이 장에서는 Chapter V에서 연구 된 포토닉 결정 구조, 즉 슬릿 배열을 평행금속판도파로 내의 갭 중앙에 위치시켜, 집속된 THz 파와 슬릿 배열 간의 여러 강한 밴드 갭을 구현하였고, 발생한 여러 밴드 갭에 대한 그 형성 메카니즘을 C언어를 이용하여 직접 구현한 Finite-Difference Time-Domain 시뮬레이션을 이용하여 완벽히 분석하였다. (Chapter VII) 그리고, photonic band anti-crossing 모델을 이용하여 앞서 형성된 밴드 갭 중, 평행금속판과 슬릿 사이의 간격에 따라 밴드 갭의 위치가 변화는 현상을 다른 접근에서 분석하였으며, (Chapter VIII) Chapter VI에서 형성된 밴드 갭 내에 결함 구조의 슬릿 배열을 이용, 강한 결함 모드를 발생시켜 이에 대한 연구를 실시하였다. (Chapter IX) 그리고, 앞서 분석한 밴드 갭 형성 메카니즘의 이해를 바탕으로, 저주파, 특정 주파수 대역 통과 필터 및 특정 주파수 가변 차단 필터를 개발하였고, 이를 미량의 가스 검출이 가능한 센서로의 적용을 실시하였다. (Chapter X) Chatper VI에서 연구된 슬릿 배열과 유사한 홈(groove) 배열을 평행금속판도파로의 갭 중앙이 아닌 한쪽 금속판 내에 구조화하여 앞서 슬릿 배열의 경우보다 더 많은 여러 밴드 갭의 구현 및 그 형성 메카니즘을 분석하였다. (Chapter XI) 그리고, 앞서 Chapter X에서의 여러 밴드 갭을 이용하여 여러 필터 및 미량의 가스 및 유동 액체 센서로의 응용을 실시하였다. (Chapter XII) 이 장에서는 새로운 형태의 평행금속판도파로를 제안한다. 기존의 두껍고 평평한 평행금속판 구조에서 30 μm의 얇은 금속판에 슬릿 배열을 가공하여 도파로의 내외부가 슬릿을 통하여 연결이 되도록 하였다. 따라서, 도파로 내부를 전파해 나가던 THz 파가 전자기파의 회절 현상으로 인하여 공기 슬릿 배열을 통하여 도파로 내에서 외부로 빠져나가게 되는 반면, 도파로의 공기 갭의 두 배에 해당하는 길이의 파장에서 강한 투과 공진 현상이 일어나게 되어, 마치 특정 밴드 패스 필터의 특성을 가지게 되었다. 이는 횡전자계 모드를 이용한 저주파 차단은 처음이며, 공기 갭의 조절에 의하여 특정 밴드의 주파수 가변이 가능하다. 또한, 외부로 드러나는 특이한 구조로 인하여 앞으로 다양한 응용의 가능성이 기대된다.Chapter I Introduction 1 1.1 Metal parallel-plate waveguides 1 1.2 Photonic crystals 2 1.3 Outline of Thesis 3 1.4 Broadband THz setup 5 Chapter II THz propagation through PPWGs 7 2.1 Waveguide Specimen 7 2.2 Fundamental theory of PPWG 9 2.2.1 General Wave Characteristics in a PPWG structure 10 2.2.2 TMm mode (TM0 = TEM) 11 2.2.3 TE modes 12 2.2.4 Cutoff frequencies for TM and TE modes 13 2.2.5 Waveguide Group velocity and Phase velocity 15 2.2.6 Attenuation in Waveguide 18 2.3 Single TEM and TE1 mode 19 2.3.1 Experimental Results : Reference and single TEM mode 21 2.3.2 Experimental Results : TE mode 23 2.4 Multi-TM and TE modes 25 2.4.1 Experimental Results : multi-TM modes 26 2.4.2 Experimental Results : multi-TE modes 28 2.5 Mode analysis 30 2.5.1 Spectrocronography 30 2.5.2 Fitting 32 Chapter III THz Filter Using the TE1 Mode of PPWG 34 3.1 Experimental setup 35 3.2 Experiment results : TM modes 36 3.3 Experiment results : TE1 mode 38 3.4 Analysis : High pass filter using TE1 mode 40 Chapter IV Bragg resonance of THz surface waves in photonic crystals 44 4.1 THz surface wave propagation on rectangular aperture arrays 45 4.1.1 Analysis of the propagated THz waves through samples 46 4.1.2 Analysis of the resonance phenomenon 48 4.2 Bragg reflection of THz surface wave propagation on slit aperture arrays 49 4.2.1 Measurements and analysis : Numerical fitting 50 4.2.2 Measurements and analysis : Interference phenomenon 52 4.2.3 Theoretical calculations of the reflection coefficient 54 Chapter V Improvement of THz coupling using a tapered parallel-plate waveguide 56 5.1 Experiment setup : Tapered waveguide specimen 57 5.2 Experiment results : One-sided TPPWG with the different angles 58 5.3 FDTD simulations and measurements : Round and non-round TPPWG 59 5.4 FDTD simulations : Output tapered structure for two-sided TPPWG 62 5.5 Measurements and analysis : Two-sided TPPWG 63 Chapter VI THz band gap properties by using metal slits in TPPWG 65 6.1 Experiment setup 66 6.2 Experiment results 67 6.3 FDTD simulations : A1, A2 - Bragg stop band 70 6.4 FDTD simulations : B, C – non-Bragg stop band 72 6.5 FDTD simulations : 3-D THz power transmission 74 Chapter VII Photonic band anti-crossing in a coupled system of a THz plasmonic crystal film and a metal air-gap waveguide 75 7.1 Experiment setup 76 7.2 FDTD simulations and experiment results 76 7.3 Analysis : Anti-crossing model 78 Chapter VIII Properties of defected one-dimensional THz plasmonic crystal films in a metal air-gap waveguide 81 8.1 Experiment setup 82 8.2 FDTD simulations : Defect modes 82 8.3 FDTD simulations and experimental results 83 Chapter IX Application for THz filters and Sensing based on band gaps properties by using metal slits in TPPWG 87 9.1 Experimental setup : Notch Filter 88 9.2 Experimental results : Notch Filter 89 9.3 FDTD simulations : Notch Filter 91 9.4 FDTD simulations : Notch Filter Sensor 93 9.5 FDTD simulations : Low-Pass Filter 95 9.6 Experimental results : Low-Pass Filter 97 Chapter X THz band gaps induced by metal grooves inside TPPWG 99 10.1 Experiment setup 100 10.2 Experiment results 101 10.3 FDTD simulations : Multiple Grooves vs Single Groove 103 10.4 FDTD simulations : Band gaps A~C and I~IV 104 Chapter XI Application for THz filters and Sensing based on band gaps properties by using metal grooves in TPPWG 109 11.1 Experimental setup : Notch filter 110 11.2 Experimental results : Notch filter 112 11.3 FDTD simulations : Tunable Notch filter 116 11.4 Application for tunable Notch filter using Piezo-actuator 117 11.5 FDTD simulations : Application for THz microfluidic sensor 118 11.6 FDTD simulations : Low-Pass Filter and Band-pass filter 119 11.7 Experimental results : Low-Pass Filter and Band-pass filter 121 Chapter XII Resonant transmission through slit arrays patterned parallel-plate waveguide 122 12.1 Experimental setup : Photonic PPWG 124 12.2 Experimental results and FDTD simulation : Photonic PPWG 125 12.3 FDTD simulations : Single slit and multiple slits 127 12.4 FDTD simulations : Misaligned photonic PPWG 130 12.5 FDTD simulations : Photonic PPWG 131 Chapter XIII Conclusion 132 Reference 13

Light control by nanostructured metal surfaces and photonic crystals in nanobeams and freestanding membranes

The work presented in this thesis aims at studying the properties of photonic crystals (PhCs) and developing their applications, such as slow light waveguide, superlens, modulator and sensor. PhCs are periodic nanostructures, which affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons. In this thesis, both simulation and experimental studies are presented. For the simulations, the plane wave expansion and finite difference time domain methods are used to calculate the band structures of PhCs and obtain the field distribution of a finite PhC, respectively. The fabrication is done in the clean room with the state of the art technology. Exploiting the incorporated quantum dots, the optical characterization was performed with a micro-photoluminescence (µPL) experiment. At terahertz frequencies, tailoring the topography of metal surface allows to localize the evanescent parts of surface waves to a distance significantly smaller than the wavelength. The propagation loss is discussed, when the metal is used as a waveguide. Normally, the loss is large when the group velocity is small. A new type of metal waveguide is designed for slow light with a small propagation loss and small group velocity dispersion by applying two thin metal slabs with subwavelength periodic corrugations on their inner boundaries. Several dielectric PhC configurations are designed and analyzed for different applications. A PhC superlens is designed with a resolution of 0.164¿ which beats the diffraction limit. The effect of disorder in the PhC on the extraction efficiency of a Light Emitting Diode is also studied by modelling the disordered PhC. A PhC waveguide is designed to make a fast modulator as an optical circuit component. A liquid crystal is used to tune the degeneracy of cavity modes of a PhC cavity. The latter design was verified experimentally. A major part of the thesis is concerned with sensing. Miniaturization of label-free optical sensors is of particular interest for realizing ultracompact lab-on-a-chip applications with dense arrays of functionalized spots for multiplexed sensing, which may lead to portable, low cost and low power devices. A PhC is very promising as a sensing element. A record high sensitivity PhC nanobeam is realized experimentally with a sensitivity of about 900 nm per refractive index unit. Simulations show that the quality factor can be substantially increased by tapering the two ends. Spectrally encoded PhC nanocavities by independent lithographic mode tuning are experimentally demonstrated for identification. The PhC nanocavities are taken from the chip to serve as autonomous devices for (bio)sensing. The properties of these free PhC nanocavities are studied by nano-manipulation and µPL experiments. The possibility of attaching one PhC nanocavity to the end of a fibre to make a fibre sensor is shown. The feasibility of an alignment procedure by precise nano-manipulation is demonstrated, which will enable to make three dimensional nanophotonic structures

Polarity inverted gallium nitride for photonic crystal biosensors.

Photonic crystals are periodic nanostructures used to control the propagation of electromagnetic waves. Depending on geometry and refractive index contrast between adjacent regions, periodic variation of the refractive index can result in a photonic band gap or non-allowed set of frequencies that cannot propagate through the crystal. Defects can be introduced at photonic crystal lattice sites, resulting in localized modes that lie within the photonic gap. Such defect cavities can be tuned to resonant frequencies of a defect mode and whole planes or lines of defects can be fabricated in photonic crystals resulting in optical confinement of defect modes. These properties of photonic crystals make them useful in a wide variety of applications such as chemical and biological sensors, high Q lasers, and optical wave guiding. With its transparency in the visible wavelength regime of the electromagnetic spectrum, GaN is a candidate for photonic crystal structures with photonic band gaps corresponding to visible wavelengths. GaN is a wide, direct band gap semiconductor which exists primarily in the wurtzite crystal structure. The wurtzite crystal structure lacks inversion symmetry, resulting in two distinct crystal polarities or crystal growth directions, the Ga-polar or [0001] and N-polar or [0001¯]. Through choice of substrate or growth conditions, GaN can be grown with either polarity. An unusual, but potentially useful, result is that by generation of near-monolayer surface coverage of Mg, the crystal polarity can be inverted during growth from gallium polar to nitrogen polar without introducing any additional defects at the domain boundary. Subsequent patterning and etching of the inversion layer, followed by re-growth, results in periodically poled GaN. This changes the nonlinear optical response of the material and such a structure can be used in a variety of applications. This study uses a subsequent highly anisotropic wet etch of polarity inverted GaN to selectively etch N-polar regions, where Ga-polar regions remain unaffected without introducing any additional structural damage. This wet etching technique for fabricating nanostructures has potential advantages over other dry etching techniques, such as inductively coupled plasma and reactive ion etching. The specific aim of this work is to develop the knowledge and techniques to allow fabrication of GaN photonic crystals via wet etching of periodically poled GaN. Growth conditions for polarity inversion by Mg doping during Molecular Beam Epitaxy growth of GaN, as well as process development for fabrication of photonic crystal structures on both the micron and nanometer scales are investigated. This study also involves theoretical modeling using MIT photonic bands software to determine photonic crystal geometries for the fabrication of GaN photonic crystals with photonic band gaps in the visible as well as the infrared wavelength regimes for future optical characterization. This work is part of a larger collaborative effort at West Virginia University for the design, fabrication, and testing of a flow-though, resonant florescence based GaN photonic crystal biosensor