Nanoimprint lithography

We report on the use of nanoimprint lithography at room temperature (RT-NIL) for the direct structuring of polyfluorene and poly (phenylenevinylene) derivatives and of their blends without the degradation of the emissive characteristics of the active molecules. We apply RT-NIL for the fabrication of periodic one-and two-dimensional gratings with feature width that varies from 100 to 500 nm. Moreover, we analysed the effects that a superimposed periodic corrugation induces on the emitted light in terms of spectral properties and luminescence efficiency, thus ruling out any degradation of the emission. In particular, the combination of nanopatterning and active blends opens new perspectives for the control of the emitted colour from conjugated polymer films.

Additive and lithographic manufacturing technologies using photopolymerisation provide a powerful tool for fabricating multiscale structures, which is especially interesting for biomimetic scaffolds and biointerfaces. However, most resins are tailored to one particular fabrication technology, showing drawbacks for versatile use. Hence, we used a resin based on thiol-ene chemistry, leveraging its numerous advantages such as low oxygen inhibition, minimal shrinkage and high monomer conversion. The resin is tailored to applications in additive and lithographic technologies for future biofabrication where fast curing kinetics in the presence of oxygen are required, namely 3D inkjet printing, digital light processing and nanoimprint lithography. These technologies enable us to fabricate scaffolds over a span of six orders of magnitude with a maximum of 10 mm and a minimum of 150 nm in height, including bioinspired porous structures with controlled architecture, holepatterned plates and micro/submicro patterned surfaces. Such versatile properties, combined with noncytotoxicity, degradability and the commercial availability of all the components render the resin as a prototyping material for tissue engineers.

We demonstrate the use of nanoimprint lithography as an alternative low-cost fabrication route for the production of ordered arrays of individual carbon nanotube field emitters. A high emission site density of 4×105cm−2 was observed and is well within the specification of the cathode for a field emission display. The measured field enhancement values from the geometry of the nanotubes were in reasonable agreement with the values obtained through electrical measurements. We also show that the distribution of the field enhancement factor is Gaussian, indicative of the presence of well ordered arrays of carbon nanotube field emitters.

Grayscale structured surfaces with nanometer-scale features are used in a growing number of applications in optics and fluidics. Thermal scanning probe lithography achieves a lateral resolution below 10 nm and a vertical resolution below 1 nm, but its maximum depth in polymers is limited. Here, we present an innovative combination of nanowriting in thermal resist and plasma dry etching with substrate cooling, which achieves up to 10-fold amplification of polymer nanopatterns into SiO2 without additional surface roughness. Sinusoidal nanopatterns in SiO2 with 400 nm pitch and 150 nm depth are fabricated free of shape distortion after dry etching. To exemplify the possible applications of the proposed method, grayscale dielectric nanostructures are used for scalable manufacturing through nanoimprint lithography and for strain nanoengineering of 2D materials. Such method for high aspect ratio and smooth grayscale nanopatterning has the potential to find application in the fabrication o...

We report on the fabrication of diffraction gratings for application as back contact reflectors. The gratings are designed for thin-film solar cells incorporating absorbers with bandgap slightly lower than GaAs, i.e. InAs quantum dot or GaInNAs solar cells. Light trapping in the solar cells enables the increase of the absorption leading to higher short circuit current densities and higher efficiencies. We study metal/polymer back reflectors with halfsphere, blazed, and pyramid gratings, which were fabricated either by photolithography or by nanoimprint lithography. The gratings are compared in terms of the total and the specular reflectance, which determine their diffraction capabilities, i.e. the feature responsible for increasing the absorption. The pyramid grating showed the highest diffuse reflection of light compared to the half-sphere structure and the blazed grating. The diffraction efficiency measurements were in agreement with the numerical simulations. The validated model enables designing such metal/polymer back reflectors for other type of solar cells by refining the optimal dimensions of the gratings for different wavelength ranges.

A refined version of the IMPRINT software is applied for simultaneous calculation of the resist viscous flow in thermal nanoimprint lithography and the stamp/substrate deformation. This version applies a modified coarse-grain method as well as takes into account the composition and elastic properties of the imprint setup (the stamp/substrate + “pressure buffer layers”). The presented comparison of calculated and experimental results confirms the potential of the IMPRINT software as an efficient tool for the reduction of the stamp bending.

Grating-based X-ray phase-contrast interferometry has a high application impact in materials science and medicine for imaging of weakly absorbing (low Z) materials and soft tissues. For absorbing gratings, casting of highly X-ray absorbing metals, such as Au and Pb alloys, has proven to be a viable way to generate large area periodic high aspect ratio microstructures. In this paper, the authors review the grating fabrication strategy with a special focus on a novel approach of casting low temperature melting alloys (Au-Sn and Pb-based alloys) into Si grating templates using hot embossing. This process, similar to nanoimprint lithography, requires particular adjusting efforts of process parameters as a function of the metal alloy and the grating feature size. The transition between the solid and liquid state depends on the alloy phase diagram, the applied pressure can damage the high aspect ratio Si lamellas, and the microstructure of the solid metal can affect the grating structure....

We report the tuning of surface wetting through sacrificial nanoimprint lithography (SNIL). In this process, grown ZnO nanomaterials are transferred by imprint into a metallic glass (MG) and an elastomeric material, and then etched to impart controlled surface roughness. This process increases the hydrophilicity and hydrophobicity of both surfaces, the Pt57.5Cu14.7Ni5.3P22.5 MG and thermoplastic elastomer (TPE), respectively. The growth conditions of the ZnO change the characteristic length scale of the roughness, which in turn alters the properties of the patterned surface. The novelty of this approach includes reusability of templates and that it is able to create superhydrophilic and superhydrophobic surfaces in a manner compatible with the fabrication of macroscopic three-dimensional (3D) parts. Because the wettability is achieved by only modifying topography, without using any chemical surface modifiers, the prepared surfaces are relatively more durable.

We report on subwavelength reflective gratings for hyperspectral applications operating in the 340 nm-1040 nm spectral range. The blazed grating period is 30 μm and is composed of 2D subwavelength binary structures with sizes in-between 120 nm and 350 nm. We demonstrate the manufacturing of gratings on 3” wafers by two lithography technologies (e-beam or nanoimprint) followed by dry etching process. These subwavelength gratings enable broadband efficiency which is in average 15%-20% above the efficiency requirement for next generation of spectro-imagers for Earth observation missions and a wavefront error that is much smaller than the 100 nm requirement for space application.

Additive and lithographic manufacturing technologies using photopolymerisation provide a powerful tool for fabricating multiscale structures, which is especially interesting for biomimetic scaffolds and biointerfaces. However, most resins are tailored to one particular fabrication technology, showing drawbacks for versatile use. Hence, we used a resin based on thiol-ene chemistry, leveraging its numerous advantages such as low oxygen inhibition, minimal shrinkage and high monomer conversion. The resin is tailored to applications in additive and lithographic technologies for future biofabrication where fast curing kinetics in the presence of oxygen are required, namely 3D inkjet printing, digital light processing and nanoimprint lithography. These technologies enable us to fabricate scaffolds over a span of six orders of magnitude with a maximum of 10 mm and a minimum of 150 nm in height, including bioinspired porous structures with controlled architecture, holepatterned plates and micro/submicro patterned surfaces. Such versatile properties, combined with noncytotoxicity, degradability and the commercial availability of all the components render the resin as a prototyping material for tissue engineers.

This study investigated the impact of absorption layer thickness and back reflection layer incorporation on (CIGS/TiO2/ZTO/ZnO:Al) solar cell efficiency. Results demonstrated that cell efficiency increases with absorption layer thickness until stabilizing at an optimal balance with other layers. The addition of a back reflection layer enhanced the efficiency while allowing for reduced absorption layer thickness, potentially lowering production costs. MoSe 2 was identified as the optimal back reflection layer material, enabling a reduction in absorption layer thickness to 0.5 µm. Initial results yielded Voc = 0.6865 V, Jsc=40.32 mA/cm 2 , FF = 83.30 %, and η = 23.06 %. Further investigation revealed that back reflection layer thickness also influences cell performance, with efficiency increasing until stabilization. Optimizing this parameter resulted in improved final outcomes: Voc=0.6955 V, Jsc=42.98 mA/cm 2 , FF = 83.10 % and η = 24.84 %. These findings contribute to the ongoing efforts to enhance solar cell efficiency and reduce manufacturing costs. ☆ This article is part of a special issue entitled: 'Graphene Photonics' published in Results in Optics.

This study investigated the impact of absorption layer thickness and back reflection layer incorporation on (CIGS/TiO2/ZTO/ZnO:Al) solar cell efficiency. Results demonstrated that cell efficiency increases with absorption layer thickness until stabilizing at an optimal balance with other layers. The addition of a back reflection layer enhanced the efficiency while allowing for reduced absorption layer thickness, potentially lowering production costs. MoSe 2 was identified as the optimal back reflection layer material, enabling a reduction in absorption layer thickness to 0.5 µm. Initial results yielded Voc = 0.6865 V, Jsc=40.32 mA/cm 2 , FF = 83.30 %, and η = 23.06 %. Further investigation revealed that back reflection layer thickness also influences cell performance, with efficiency increasing until stabilization. Optimizing this parameter resulted in improved final outcomes: Voc=0.6955 V, Jsc=42.98 mA/cm 2 , FF = 83.10 % and η = 24.84 %. These findings contribute to the ongoing efforts to enhance solar cell efficiency and reduce manufacturing costs. ☆ This article is part of a special issue entitled: 'Graphene Photonics' published in Results in Optics.

A novel method to realizing printed active photonic devices was developed using nanoimprint lithography (NIL), combining a printable high-refractive index material and colloidal CdSe/CdS quantum dots (QDs) for applications in the visible region. Active media QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proofof-demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nanocavities were successfully fabricated following a simple reversenanoimprint process. We observed enhanced photoluminescence from the 2D photonic crystal and the 1D nanocavities. Outstandingly, the process presented in this study is fully compatible with large-scale manufacturing where the patterning areas are only limited by the size of the corresponding mold. This work shows that the integration of active media and functional materials is a promising approach to the realization of integrated photonics for visible light using high throughput technologies. We believe that this work represents a powerful and cost-effective route for the development of numerous nanophotonic structures and devices that will lead to the emergence of new applications.

A novel method to realizing printed active photonic devices was developed using nanoimprint lithography (NIL), combining a printable high-refractive index material and colloidal CdSe/CdS quantum dots (QDs) for applications in the visible region. Active media QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proof-of-demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nanocavities were successfully fabricated following a simple reverse-nanoimprint process. We observed enhanced photoluminescence from the 2D photonic crystal and the 1D nanocavities. Outstandingly, the process presented in this study is fully compatible with large-scale manufacturing where the patterning areas are only limited by the size of the corresponding mold. This work shows that t...

One of the major challenges to the widespread adoption of plasmonic and nano-optical devices in real-life applications is the difficulty to mass-fabricate nano-optical antennas in parallel and reproducible fashion, and the capability to precisely place nanoantennas into devices with nanometer-scale precision. In this study, we present a solution to this challenge using the state-of-the-art ultraviolet nanoimprint lithography (UV-NIL) to fabricate functional optical transformers onto the core of an optical fiber in a single step, mimicking the 'campanile' near-field probes. Imprinted probes were fabricated using a custom-built imprinter tool with co-axial alignment capability with sub <100 nm position accuracy, followed by a metallization step. Scanning electron micrographs confirm high imprint fidelity and precision with a thin residual layer to facilitate efficient optical coupling between the fiber and the imprinted optical transformer. The imprinted optical transformer...

Nanoimprint lithography assisted by ultraviolet photopolymerization through a soft elastomer-based mold is applied to the fabrication of silicon-on-insulator slab photonic crystals for optical wavelengths. Variable angular reflectance is used to measure the dispersion of the photonic leaky modes. Experimental results are in good agreement with both theoretical calculations and previous results obtained by standard nanoimprint lithography as well as conventional nanofabrication techniques such as electron-beam lithography.

We report on the progress towards developing a new method for fabricating more efficient, broadband antireflective (AR) moth-eye structures in As 2 Se 3 via a direct nanoimprinting technique. Thermal reflow is used during mold fabrication to reshape a conventional deep-ultraviolet lithography in order to promote a pattern transfer of "secant ogive"-like moth-eye structures. Once replicated, structures modified by reflow displayed greater AR efficiency compared to structures replicated by a conventional mold, achieving the highest spectrum-averaged transmittance improvement of 12.36% from 3.3 to 12 μm.

We have studied the geometry dependency of fishnet-like negative refractive index meta-materials (NIMs), and developed a process to fabricate such NIMs using nanoimprint lithography (NIL) in a controlled way for it to achieve negative refractive index in the desired frequency range. As an example, we fabricated a fishnet structure with a minimum negative refractive index of -1.7 at 1560 nm, which was only 10 nm off the targeted wavelength of 1550 nm.

Two types of optical metamaterials operating at near-IR and mid-IR frequencies, respectively, have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry. The structure for the near-IR range was a metal/dielectric/metal stack "fishnet" structure that demonstrated negative permittivity and permeability in the same frequency region and hence exhibited a negative refractive index at a wavelength near 1.7 µm. In the mid-IR range, the metamaterial was an ordered array of four-fold symmetric L-shaped resonators (LSRs) that showed both a dipole plasmon resonance resulting in negative permittivity and a magnetic resonance with negative permeability near wavelengths of 3.7 µm and 5.25 µm, respectively. The optical properties of both metamaterials are in agreement with theoretical predictions. This work demonstrates the feasibility of designing various optical negative-index metamaterials and fabricating them using the nanoimprint lithography as a lowcost, high-throughput fabrication approach.

We use spectroscopic ellipsometry to investigate the angular-dependent optical modes of fishnet metamaterials fabricated by nanoimprint lithography. Spectroscopic ellipsometry is demonstrated as a fast and efficient method for metamaterial characterization and the measured polarization ratios significantly simplify the calibration procedures compared to reflectance and transmittance measurements. We show that the modes can be well identified by a combination of comparing different substrates and considering the angular dependence of the Wood's anomalies. The lack of angular dispersion of the anti-symmetric gap-modes does not agree with the model and requires further theoretical investigation.

Contents 1 General introduction ………………………………………………… 1.1 Nanoimprint lithography …………………………………………… 1.2 Soft lithography …………………………………………………… 1.3 Substrate Conformal Imprint Lithography ………………………… 1.4 SCIL for nanophotonics …………………………………………… 1.5 Outline of this thesis …………………………………………… References ………………………………………………………………… 2 SCIL soft-nanoimprint of sol-gel materials ………………………… 2.1 Introduction into sol-gel soft-nanoimprint ………………………… 2.2 Silicon based sol-gel chemistry and synthesis ………………… 2.2.1 Basic silicon sol-gel chemistry ………………………… 2.2.2 Organically modified silicon precursors ………………… 2.2.3 Synthesis of TMOS-MTMS hydrolysis solution and sol-gel imprint resist ………………………………………… 2.2.4 Imprint results for varying TMOS:MTMS hydrolysis ratios… 2.2.5 Post cure shrinkage of imprinted sol-gel patterns ………… 2.3 High resolution poly-di-methyl-siloxane stamp materials ………… 2.3.1 Pattern instability in soft stamps ………………………… 2.3.2 Calculation of feature stability in PDMS stamps ………… 2.3.3 Mechanically stable nanoscale PDMS patterns ………… 2.3.4 PDMS with increased Young's modulus: X-PDMS ………… 2.3.5 Preparation of Q-siloxane modified PDMS ………………… 2.3.6 Young's modulus determination by indentation measurements ………………………………… 2.3.7 Sub-50 nm imprinted sol-gel patterns using X-PDMS stamps ………………………………… 2.4. Substrate Conformal Imprint Lithography method ………………… 2.4.1 SCIL composite stamp fabrication ………………………… 2.4.2 SCIL imprint method ………………………………………… 2.5 SCIL imprint performance ………………………………………… 2.5.1 Pattern deformation: ex-situ measurements ………………… 2.5.2 Design of overlay alignment markers ………………… II 2.5.3 The variation in magnification error between two stamps … 2.5.4 Design of Moiré interference alignment markers and in-situ pattern deformation characterization ………………… 2.6 SCIL overlay alignment method ………………………………… 2.6.1 SCIL imprint tool with incorporated substrate position control with nm resolution ………………………… 2.7 Overlay alignment results ………………………………………… 2.8 Sol-gel imprint resist optimization ………………………………… 2.8.1 Influence of the low vapor pressure solvents on the imprint time ………………………………………… 2.8.2 Influence of sol-gel synthesis on the imprint time ………… 2.8.3 The influence of water and alcohol on the sol-gel equilibrium state ………………………………… 2.8.4 Effect of water on sol-gel imprint performance ………… 2.8.5 Effect of the substrate on sol-gel imprint performance … 2.9 Conclusions ………………………………………………………… References ………………………………………………………………… III 5.2.2 Soft stamp fabrication ………………………………… 5.2.3 Wafer-scale grating replication ………………………… 5.2.4 VCSEL device processing ………………………………… 5.3 Opto-electronic device analysis ………………………………… 5.4 Summary and conclusions ………………………………………… References ………………………………………………………………… 6 Large area replication of high quality nanohole arrays in gold using soft-nanoimprint lithography ………………………………………… Chapter 2 SCIL soft-nanoimprint of sol-gel materials In this chapter we describe the SCIL soft-nanoimprint process using silica sol-gel resist. The solgel chemistry and resist is discussed and a systematic optimization of sol-gel parameters is described. The cause of feature collapse in soft stamps is investigated and a solution to this problem is given. We demonstrate a systematic study towards to a new high Young's modulus PDMS rubber of which the synthesis and characterization is described. The SCIL tooling and composite stamp fabrication is described. The SCIL method is characterized by measurements of the replication quality and induced pattern deformations. A procedure to obtain highly accurate overlay alignment is described and experiments are performed to determine the overlay accuracy of the SCIL process.

Roll-to-roll nanoimprint lithography (RTR-NIL) is a low-cost and continuous fabrication process for large-area functional films. However, the partial ultraviolet (UV) resin filling obstructs the ongoing production process. This study incorporates UV resin filling process into the nanopillars and nanopores by using RTR-NIL. A multiphase numerical model with a sliding mesh method is proposed in this study to show the actual phenomena of imprint mold rotation and feeding of UV resin on the polyethylene terephthalate (PET) substrate. The implementation of UV resin filling under environmental conditions was performed by utilizing the open-channel (OC) boundary conditions. The numerical model was solved by using the explicit volume of fluid (VOF) scheme to compute the filling on each node of the computational domain. The effects of different processing parameters were investigated through the proposed numerical model such as imprinting speed (IS), contact angles (CAs), viscosity, initial ...

We present an optimized process using very high resolution Electron Beam Lithography for the fabrication of high density nanostructures gratings, which can be used as molds for nanoimprint lithography. In our approach conventional PolyMethylMethAcrylate resist is exposed and, after lift-off and Reactive Ion Etching, pillars of 100 nm high are obtained on SIO2. Optimized conditions for the development of the resist after exposure are presented which enables the fabrication of high quality pillar gratings of 30nm pitch (-700Gbit/in2), and line gratings of 40nm pitch.

Grayscale structured surfaces with nanometer-scale features are used in a growing number of applications in optics and fluidics. Thermal scanning probe lithography achieves a lateral resolution below 10 nm and a vertical resolution below 1 nm, but its maximum depth in polymers is limited. Here, we present an innovative combination of nanowriting in thermal resist and plasma dry etching with substrate cooling, which achieves up to 10-fold amplification of polymer nanopatterns into SiO 2 without additional surface roughness. Sinusoidal nanopatterns in SiO 2 with 400 nm pitch and 150 nm depth are fabricated free of shape distortion after dry etching. To exemplify the possible applications of the proposed method, grayscale dielectric nanostructures are used for scalable manufacturing through nanoimprint lithography and for strain nanoengineering of 2D materials. Such method for high aspect ratio and smooth grayscale nanopatterning has the potential to find application in the fabrication of photonic and nanoelectronic devices.

This paper explores applications of recently released MEMS (Micro Electro Mechanical System)based process densitometer for gas. The core of the sensor is a resonating silicon microtube which is flowed through by the process gas. Due to the very low density of silicon and the fact that the tube is resonating in a vacuum cavity very good density sensitivity is achieved even for low fluid densities. The sensor therefore perfectly suits gas density applications with a medium pressure between 5 and 20 bar. The microfluidic sensor has density and temperature measurement capabilities. Additionally pressure is monitored along the fluidic path. From these measured physical properties, real time quality information of the measured gas such as molar mass, reference density, specific gravity, gas composition and calorific value can be derived. Process applications are demonstrated with experimental and theoretical results.

The performance and the reliability of many devices are controlled by interfaces between thin films. In this study we investigated the use of patterned, nanoscale interfacial roughness as a way to increase the apparent interfacial toughness of brittle, thin-film material systems. The experimental portion of the study measured the interfacial toughness of a number of interfaces with nanoscale roughness. This included a silicon interface with a rectangular-toothed pattern of 60-nm wide by 90-nm deep channels fabricated using nanoimprint lithography techniques. Detailed finite element simulations were used to investigate the nature of interfacial crack growth when the interface is patterned. These simulations examined how geometric and material parameter choices affect the apparent toughness. Atomistic simulations were also performed with the aim of identifying possible modifications to the interfacial separation models currently used in nanoscale, finite element fracture analyses. The fundamental nature of atomistic tractionseparation for mixed mode loadings was investigated.

Nano‐scale patterns were produced with UV‐curable acrylated hyperbranched polymer nanocomposites using nanoimprint lithography with a glass master in a rapid, low‐pressure process. The pattern of the glass master was replicated with composites containing up to 25 vol% SiO2 with a shape fidelity better than 98%. Photo‐rheology, interferometry and atomic force microscopy were used to analyze the material behavior. Attention was paid to the relationship between composition, nanoparticle dispersion, kinetics of photo‐polymerisation, shrinkage, pressure and shape fidelity of nano‐gratings. It was shown that the gel‐point of the nanocomposite was an important factor that determined the stability as well as the dimensions of the imprinted structure. Dimensional accuracy also strongly depended on the level of internal stress, which in fact increased with the amount of silica. A resin rich layer on the surface of the composite accounted for the good surface quality of the nano‐pattern.

Superhydrophobic surfaces rely on a large number of surface micro/nano structures to increase the roughness of a material. Producing such structures is possible through a multitude of relatively slow methods; however, economic and large scale production of superhydrophobic surfaces require using a fast process on a cheap substrate. Here, we used femtosecond laser processing to fabricate micro and nanostructures on tungsten carbide that we use as a mold to thermally imprint polypropylene sheets. The fabricated tungsten carbide mold was used to imprint more than twenty superhydrophobic polypropylene sheets before mold contamination reduces the surface contact angle below 150°. Using Toluene solution, the mold is subsequently capable of being cleaned of contamination from polypropylene residue and reused for further imprinting. Ninety thermoplastic imprints were conducted using a single tungsten carbide mold with only minimal structural degradation apparent on the micro/nano structured surface.

This paper presents a novel process chain for fabrication of replication masters for serial manufacture. The proposed process chain is validated for serial fabrication of (large area) organic electronic devices on flexible substrates. The advantages and limitations of the component technologies in the proposed manufacturing route are discussed and their interdependencies in a process chain for producing both 2.5D and 3D nano-and micro-structures are analysed. The proposed master-making route relies on using different technologies for micro-structuring and sub-micron and nano patterning that are applied to the fabrication of Ni shims incorporating different length scale features. In particular, the capabilities of photolithography as a micro-structuring technology were combined with those of FIB machining to add submicron and nano-features on micro patterned fused silica templates. Then, by applying UV nanoimprint lithography such templates were validated and their nano and micro-structures were consistently replicated in one step. Finally, the feature transfer of such imprints onto Ni shims was also successfully accomplished with only minor deviations from the target dimensions.

A novel liquid photo-polymerization resist was prepared for nanoimprint lithography on transparent flexible plastic substrates. The resist is a mixture of polymethylmethacrylate (PMMA), methylmethacrylate (MMA), methacylic acid (MAA) and two photo-initiators, (2-isopropyl thioxanthone (ITX) and ethyl 4-(dimethylamino)benzoate (EDAB)). The resist can be imprinted at room temperature with a pressure of 0.25 kg/cm 2 , and then exposed from the transparent substrate side using a broad band UV lamp to obtain nano-and micro-scale patterns. Replications of high-density line and space patterns with resolution of 150 nm were obtained on a flexible indium tin oxide/poly(ethylene terephthalate) (ITO/PET) substrate. The liquid resist has low viscosity due to the liquid monomers, and low shrinkage due to the addition of PMMA as a binder.

In this work, we have developed low-cost, high modulus, flexible, and UV transparent polyimide plastic molds for nanoimprint lithography (NIL). Different structures of poly(amic acids) (PAA) and polyimides (PI) have been synthesized. By casting the PAA or PI solutions on a silicon master, flexible but still rigid plastic molds can be produced. The advantages of the PI molds are: (1) high glass-transition temperatures (Tg) up to 310 C, (2) high thermal stability over 500 C, (3) high tensile modulus, and (4) UV transparency for use in UV-NIL. Various micrometer and nanometer scale patterns could be obtained from the PI molds on a large area (4 inch wafer). The imprinting results showed that the PI molds could be faithfully used for both hot embossing NIL and UV-NIL.

It is a great pleasure to acknowledge many wonderful students, postdoctoral fellows, and colleagues who have contributed to the work described in this article. This review is dedicated to all of them. Special thanks to Dr. Peng-Fei Fu at Dow Corning Corporation (USA) for the recent collaborations on the development of new materials for nanoimprint technology.

We have characterised photonic-crystal and photonic-wire waveguides fabricated by thermal nanoimprint lithography. The structures, with feature sizes down below 20 nm, are benchmarked against similar structures defined by direct electron beam lithography.

We demonstrate a nanoimprint process for fabrication of photonic crystal devices. The nanoimprint process, defining stamp patterns in a thin e-beam resist, yields improved pattern replication compared to direct e-beam writing of the devices.

Dense wavelength division multiplexing lasers play a major role in today's long-haul broadband communication. Typical distributed feedback laser cavities consist of long half-pitch gratings in InGaAsP on InP substrates with grating periods of around 240 nm. The lasers include a quarter wavelength shift in the grating, and are single mode with high side-mode suppression. Typically, such lasers are patterned using e-beam lithography (EBL). We present a fabrication method based on patterning by thermal nanoimprint lithography, which is potentially less costly and faster than EBL. Thermal nanoimprint lithography of laser gratings raises two types of challenges: (1) The imprint process itself is delicate due to the mechanical fragility of indium phosphide substrates and the thermal mismatch between the substrate and the silicon stamp. (2) The subsequent processing puts requirements on the imprint resist thickness after patterning, and the alignment between the crystallographic direction of the substrate and the grating pattern. Working laser arrays were produced, with >40 mW optical power and side mode suppression ratios of more than 50 dB in all 12 channels.

In performing my research, I received support, help and guidance from many respected individuals, who deserve my greatest gratitude. First of all, I am indebted to my research adviser, Prof. Mark T. Tuominen for countless advises, encouragements and patiently guiding me and investing in my research education for the last five years. Also, I would like to thank Prof. Adrian Parsegian, Prof. Narayanan Menon and Prof. Dhandapani Venkataraman for serving on my thesis committee and giving insightful advises. Further, I pay my gratitude to Prof. Katherine Aidala at Mt Holyoke Collage for her helpful guidance in conducting my research. I'm specially grateful to former group members Dr. Nihar Pradhan, Dr. Nikhil Malvankar, Dr. Stefan Dickert, Dr. Tianyu Yang, Dr. Huajie Ke as I received most of my training from them. I would also thank Dr. Craig Versek for his help and guidance in micromagnetic work and Mr. Michel Thorn for his useful advises. I further acknowledge Ms. Dan Wang, Mr. Ramesh Adhikari and Mr. Asanka Weerasinghe for helping me with some of my sample preparation and measurements, and all current group members for helping me to maintain and repair lab equipment. In addition, I'm very grateful to my collaborators from other departments and other universities: Dr. Jacob John and Prof Ken Carter at the department of Polymer Science and Engineering for providing me nanoimprinted gratings and teaching me nanoimprint v lithography, Dr. Saikat Gosh from Food Science department for helping me in analyzing nanoparticle properties, Mr. Viraj Thanthirige, Prof. Guda Ramakrishna and Prof. Ekkehard Sinn at department of Chemistry, Western Michigan University for supplying me Au25(SC6H13)18 nanoclusters and sharing valuable information about recent developments in diamagnetic nanoclusters and their optical absorption properties, Dr. Deepak Singh from NIST for fruitful discussions and inspiring me with novel fabrication ideas. I would also like to pay my special gratitude to Mr. John Nicholson for all his help with cleanroom instruments and sharing information about new sample fabrication techniques and capabilities. Further, I acknowledge Mr. Jacob Hirsch and Mr. Pete Dawson for their help in XPS and XRD measurements. Also, I'm grateful to Mrs. Jane Knapp, Mrs.

This dissertation examines two salient issues that arise in the strategic planning of disaster management operations for providing relief to populations that are impacted by a disaster, such as an earthquake. The first issue is the alleviation of destitution faced by affected populations in the immediate aftermath of a disaster. The second is the establishment of an infrastructure for provision of relief, for a much longer period of time, until normalcy is restored. Central to the alleviation of destitution is the avoidance of critical shortages in meeting the demand for relief supplies. The literature on pro-active and strategic planning of relief operations primarily focuses on the minimization of unmet demand to address shortfalls in meeting required levels of relief. However, compromised handling capacity, which can be attributed to insufficient manpower, can deteriorate provision of supplies. The same is true for transport capacity of which there can be limited capability in th...

A Photonic Crystal surface fabricated upon a quartz substrate using nanoimprint lithography has been demonstrated with a signal enhancement factor as high as 7500× for the detection of LD-700 dye spin-coated upon the PC. The detection of spotted Alexa-647 labeled polypeptide on the PC exhibits a 330× SNR improvement. Using dose-response characterization of deposited fluorophore-tagged protein spots, the PCEF surface demonstrated a 140× lower limit of detection compared to a conventional glass substrate.

A Photonic Crystal (PC) surface fabricated upon a quartz substrate using nanoimprint lithography has been demonstrated to enhance light emission from fluorescent molecules in close proximity to the PC surface. Quartz was selected for its low autofluorescence characteristics compared to polymer-based PCs, improving the detection sensitivity and signal-to-noise ratio (SNR) of PC Enhanced Fluorescence (PCEF). Nanoimprint lithography enables economical fabrication of the subwavelength PCEF surface structure over entire 1x3 in 2 quartz slides. The demonstrated PCEF surface supports a transverse magnetic (TM) resonant mode at a wavelength of λ = 632.8 nm and an incident angle of θ = 11°, which amplifies the electric field magnitude experienced by surface-bound fluorophores. Meanwhile, another TM mode at a wavelength of λ = 690 nm and incident angle of θ = 0° efficiently directs the fluorescent emission toward the detection optics. An enhancement factor as high as 7500 × was achieved for the detection of LD-700 dye spin-coated upon the PC, compared to detecting the same material on an unpatterned glass surface. The detection of spotted Alexa-647 labeled polypeptide on the PC exhibits a 330 × SNR improvement. Using dose-response characterization of deposited fluorophore-tagged protein spots, the PCEF surface demonstrated a 140 × lower limit of detection compared to a conventional glass substrate.

Emerging nanoscale applications in energy, electronics, optics, and medicine can exhibit enhanced performance by incorporating nanoshaped structures (nanoshape structures here are defined as shapes enabled by sharp corners with radius of curvature < 5 nm). Nanoshaped fabrication at high-throughput is well beyond the capabilities of advanced optical lithography. Although the highest-resolution e-beams and large-area e-beams have a resolution limit of 5 and 18 nm half-pitch lines or 20 nm half-pitch holes, respectively, their low throughput necessitates finding other fabrication techniques. By using nanoimprint lithography followed by metal-assisted chemical etching, diamond-like nanoshapes with ~3 nm radius corners and 100 nm half-pitch over large areas have been previously demonstrated to improve the nanowire capacitor performance (by ~90%). In future dynamic random-access memory (DRAM) nodes (with DRAM being an exemplar CMOS application), the implementation of nanowire capacitor...