The ink transfer mechanisms in the offset lithographic printing process is consisted by a complex inking roller train which a series of alternately rigid and deformable rollers, are used to precondition and deliver the printing fluid from the ink and fount reservoirs to the image carrier. The lithographic printing inks are complex formulated non-Newtonian fluids with high viscoelastic rheological profile and thixotropic behaviour. A set of ink dilutions was produced based on coldset lithographic printing ink diluted in concentration with Butyl-Diglycol. The rheological profile of the produced inks was examined by detailed rheological characterisation with particular interest on viscosity on tack, thixotropy, viscoelasticity, surface tension, extension and shear viscosity. Further examination established the relationships between shear viscosity and tack focusing on a printing nip between a rigid and elastic roller. A decrease in tack was found to be associated with a decrease in shear and the apparent extension viscosity. Developed imprinting and photographic techniques used to capture and characterise the fundamental phenomena of ribbing and misting associated with ink film splitting at the rollers nip in offset printing. Such techniques used to capture the dynamic profile of those mechanisms on a closed loop distribution system by using a tack meter. The detailed profile of those phenomena was characterised with particular interest on the relationship with the fluids rheological profile and the Capillary number. Extension rheometer was also used to analyse the mechanisms of ribbing and misting phenomena by experimental simulation of a printing nip. A factorial experiment was undertaken based on LI8 Orthogonal Array techniques. The parameters of rollers ratio, ink film thickness, temperature, distribution speed, distribution time and inks viscosity were found to have an influence on misting and ribbing phenomena. Results and analysis established responses and interactions between the process parameters but also between ribbing and misting as essential phenomena with the ink transfer mechanisms in lithographic printing process.

abstract: In this thesis, a novel silica nanosphere (SNS) lithography technique has been developed to offer a fast, cost-effective, and large area applicable nano-lithography approach. The SNS can be easily deposited with a simple spin-coating process after introducing a N,N-dimethyl-formamide (DMF) solvent which can produce a highly close packed SNS monolayer over large silicon (Si) surface area, since DMF offers greatly improved wetting, capillary and convective forces in addition to slow solvent evaporation rate. Since the period and dimension of the surface pattern can be conveniently changed and controlled by introducing a desired size of SNS, and additional SNS size reduction with dry etching process, using SNS for lithography provides a highly effective nano-lithography approach for periodically arrayed nano-/micro-scale surface patterns with a desired dimension and period. Various Si nanostructures (i.e., nanopillar, nanotip, inverted pyramid, nanohole) are successfully fabricated with the SNS nano-lithography technique by using different etching technique like anisotropic alkaline solution (i.e., KOH) etching, reactive-ion etching (RIE), and metal-assisted chemical etching (MaCE). In this research, computational optical modeling is also introduced to design the Si nanostructure, specifically nanopillars (NPs) with a desired period and dimension. The optical properties of Si NP are calculated with two different optical modeling techniques, which are the rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods. By using these two different optical modeling techniques, the optical properties of Si NPs with different periods and dimensions have been investigated to design ideal Si NP which can be potentially used for thin c-Si solar cell applications. From the results of the computational and experimental work, it was observed that low aspect ratio Si NPs fabricated in a periodic hexagonal array can provide highly enhanced light absorption for the target spectral range (600 ~ 1100nm), which is attributed to (1) the effective confinement of resonant scattering within the Si NP and (2) increased high order diffraction of transmitted light providing an extended absorption length. From the research, therefore, it is successfully demonstrated that the nano-fabrication process with SNS lithography can offer enhanced lithographical accuracy to fabricate desired Si nanostructures which can realize enhanced light absorption for thin Si solar cell. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

Este trabalho teve como objetivo principal o estudo de técnicas de nanofabricação aplicadas a filmes semicondutores do grupo 111-V, crescidos pela técnica de epitaxia por feixe molecular. Padrões, visando o domínio da técnica e a produção de nano-estruturas foram criados em filmes de GaAs utilizando-se a técnica de litografia por feixe de elétrons e ataques químicos. Os padrões foram gerados a partir de um software especial de controle que, acoplado ao microscópio eletrônico de varredura, através de uma interface, permite o controle externo da varredura x-y do feixe de elétrons. Estudamos o comportamento da espessura do filme de elétron-resiste poli (metacrilato de metila) (PMMA) em função da temperatura, aplicando soluções com pesos moleculares variados sobre filmes semicondutores, dissolvidos em Xileno, Monoclorobenzeno e Acetona. Investigamos o uso do ultra-som nos processos de revelação do PMMA e no ataque químico de superfícies de GaAs. Através da análise do ataque químico empregando várias formulações a base de ácidos em GaAs (100) e (3 1 l)A e B, determinamos a velocidade de ataque em cada caso, classificando as propriedades obtidas para a superfície. Em GaAs (100) avaliamos a dependência entre a rugosidade da face atacada e o tempo de ataque para uma solução de NH4OH:H2O (pH=7). Os resultados por nós obtidos formam um conjunto de dados que servirão de apoio a trabalhos futuros, desenvolvidos em nano-fabricação aplicada a filmes de GaAs, crescido em planos diferentes do (100). / This work had as main objective the study of nanofabrication techniques applied to thin semiconductor 111-V films, grown by molecular beam epitaxy. Patterns were generated to verifying the domain of the technique in the production of nanostructures in GaAs films, by means of chemical attack and electro-lithography. The patterns were generated with special software that connects the electronic microscope(Leo 440), through an interface that allows the externa1 control of the x-y sweeping for the electron beam. We studied the behaviour of the thickness of the electron-resists films of poly-methyl-metacrilate in hnction of the Spinner rotation, applying solutions with varied molecular weights on semiconductor films, dissolved in Xilene, Monoclorobenzene and Acetone. We investigated the use of the ultra-sound in the processes of revelation of PMMA and in the chemical attack of surfaces of GaAs. Through the analysis of the chemical attack using severa1 formulations of acids in GaAs (100) and (311)A and B, we determined the attack rate in each case, classifying the properties obtained for the surface. In GaAs (100) we evaluated the dependence between the nano-rugosity of the attacked face with the time of attack for a solution of NH4OH:H2O2 (pH=7). The results obtained by us form a group of data that will support future works, to be developed in nanofabrication applied to GaAs thin films grown in plans different from the (100).

Halide perovskite-based photovoltaics are the fastest-growing solar technology in nowadays. Because of the low production costs, perovskite-based photovoltaics are competitive for commercial applications in the marketplace. Additionally, due to the remarkable optoelectronic properties, perovskites are also promising for other optoelectronics, including photodetector, light emitting diode and laser. However, for commercial applications in optoelectronics, there are still several crucial obstacles: (i) a robustness patterning technique is missing for nanofabrication of perovskite devices, (ii) hysteresis effect exits in perovskite devices, and (iii) the stability issue of perovskite. To address these problems, we have performed the fundamental study on perovskite from four aspects: orthogonal patterning, metal contact, carrier transport, and light emission stability. Due to the ionic nature, halide perovskite can be easily dissolved by most of the commonly used organic solvents, which means conventional lithography patternings are not applicable for perovskite, limiting the extensive applications of perovskite electronics. To adress this, we introduced chlorobenzene and hexane and proposed an orthogonal electron beam lithography method for fabrication of perovskite nanodevices without damaging their electrical and optical properties. By this orthogonal method, we fabricated a two-dimensional single crystalline (C6H5C2H4NH3)2PbI4 photodetector with device channel length of few hundred nanometers and outstanding photosensing capability. The hysteresis effect in perovskite is highly related to the interfacial recombination and ionic transport, which requires abundant fundamental understanding on perovskite contact and transport to help to solve this issue. In this study, we performed the lithography patterning method and the transfer length measurement on cm-sized single crystalline perovskite bulk single crystal for indicating the metal contact interface and charge transport, which are requared for efficienct device design and improving the device performance. For stable light emission, we fabricated perovskite nanowires in the nanopores of anodic aluminum oxide substrate using an inkjet printing technique. Lasing behaviors and color-tunable light emission of perovskite nanowires are demonstrated in this study, and the photostability is much better than reported all-inorganic perovskite quantum dots. We believe these fundamental studies provide solutions to some critical issues in current perovskite technology, thus paving the way for future optoelectronic applications.

Adhesion lithography has been used to pattern nanogaps between two electrodes of the same or different metals onto a substrate. Patterning Al and Ti/Pt bilayer electrodes have been shown to form nanogaps leaving behind relatively consistent nanogaps of less than 12 nm between the electrodes. These nanogaps are formed without the need for adhesion lithography due to the bilayer spontaneously delaminating from the aluminum electrodes, In this study, the stresses in the Ti/Pt bilayer are investigated to determine the amount of stress required for delamination and the properties causing it. The goal is to recreate this stress mechanism in other patterned metals such as Au and Al. Heat cycling is used to induce high stress in other metal electrode combinations in an attempt to induce spontaneous delamination in Al and Au but fails up to 310°C annealing temperature. Theoretical methods are used to determine the stress: searching for an appropriate mathematical model and using finite element analysis in ABAQUS software to create a simulation of the delaminating Ti/Pt bilayer. The stress is found to be caused by the residual stresses in platinum and the high energy e-beam deposition method. An experimental value for the stress and the ability to recreate it in other metals remains elusive.

The group of works that I am presenting as my Master of Fine Arts thesis exhibition is a selection of my best work from the past three years. It is made up of two different artistic forms: fairly small sculptures comprised of aluminum channel and plexiglas, on the one hand, and lithographs and watercolors, on the other.

The fabrication of new and novel materials contributes to qualitative enhancement of human life. Among the various branches of fabrication, nanolithography is an emerging neoteric fabrication technology. Even though nanofabrication procedures and the techniques can be precisely controlled through various error prevention techniques and algorithms, there is always a probability of human or instrumental error in a fabrication process. Minimization or rectification of errors during the fabrication process would increase the productivity and reduce cost per unit of the fabricated devices. Therefore there is a compelling need for an error rectification system. Compared to the number of techniques available for fabrication using nanolithography, the techniques available for error rectification are very limited. Successful implementation of more error rectification techniques may have a huge impact in device fabrication and manufacturing processes. The main focus our work is the development of a lithographic error rectification system that we named as Polymeric Submicron Editor (POSE). This system is made of submicron "pens" and "erasers" made from flexible polymers. The pens and erasers were made of polydiemethylsiloxane (PDMS) and agarose hydrogel respectively. They are fabricated by template synthesis from anisotropically track etched conical micropores in glass. The polymeric pens mounted to piezoelectric motors were used to deposit and remove submicron patterns driven by diffusion. This entire deposition system is housed on an inverted microscope to optically track and register the area of deposition so that if required it can be erased and rectified by agarose hydrogel erasers and PDMS pens. POSE can deposit, erase and rectify patterns with submicron resolution. Apart from the development of POSE, this process also led to the development of techniques for, (i) two dimensional gradient etching in tracked glass, (ii) mask less photolithography and with tracks etched glass and (iii) polymeric microfabrication which will also be covered in detail in this dissertation

Diblock copolymers like poly(styrene)-block-poly(2-vinylpyridine) pave the way for controllable self-assembled monolayers of nanoparticles. Using particular polymer weights and concentration, spherical micelles of PS-b-P2VP can be constructed with a non-polar PS corona and a polar P2VP core. Various precursor salts can be loaded into the core of the micelles due to interactions with the polar core which forms as the active site for nanoparticle growth. The PS corona protects the core from the atmosphere and non-polar solvents. The micelles can then act as nanobeakers for aqueous chemistry in two ways; spontaneous reactions between precursors result in nanoparticles or the trapping of precursor salts can be oxidized or reduced using polymer removal techniques like gas plasmas. In this way, reverse micelles are a facile method of growing metal, metal oxide or dielectric nanoparticles. Process parameters, such as concentration, molecular weights, nature of solvents and type of precursor salt, offer control over the periodicity and size of the monolayer of nanoparticles. Reverse micelle templating is a potentially useful nanofabrication method for tailor-made nanoparticles for use in electrical and optical devices which is not limited to form-factor of substrates. In this thesis, obstacles are identified that hinder the utility of PS-b-P2VP templated nanoparticles in device fabrication. The polymer is insulating which is detrimental to electrical applications. Additionally, the characterization of a monolayer of polymers, thus far, is limited to structural techniques such as SEM and AFM. This thesis sheds light on the mechanism of precursor loading in the micelle core, discusses the efficiency of different polymer removal techniques and uses vibrational spectroscopy for the characterization of monolayers of polymer, loaded polymer and nanoparticles. We have tested enhanced Raman methods using AFM probes to extend the resolution of normal Raman to view monolayers of empty polymers as well. Moreover, using FeCl3-loaded polymer micelles, the control offered by PS-b-P2VP templated growth on the crystal structure of nanoparticles is laid bare. The usefulness of the technique is further divulged by using ordered gamma-Fe2O3 nanoparticles in water-splitting photoanodes where they show an increased efficiency with the inclusion of nanoparticles and their periodicity. This is just an example of devices using reverse micelle templated nanoparticles, paving the way for future applications. The flexibility of this method is further revealed by constructing self-assembled Au/SnO2 nanojunctions within the PS-b-P2VP micelle cores. This was done by exploiting the spontaneous redox reaction between HAuCl4 and SnCl2 in an aqueous environment, and so can be replicated for other metals and metal oxides like Pt, Pd, Ag, TiO2 and ZnO2. The composite nanoparticles formed exhibit a tunable size and dispersion as typically seen with PS-b-P2VP micelles and so, can be used for various applications which require metal/metal oxide junctions. / Thesis / Doctor of Philosophy (PhD)

PLE presents an alternative or complementary probe-based tool to DPN, PPL, and NFL. Unlike most scanning probe techniques, where patterning by deposition is usually employed, PLE is unique because it is capable of deposition and removal in one or multiple steps. Therefore, PLE allows rectification of patterning errors, and it can be employed for both additive and subtractive patterning through molecular deposition and chemical and electrochemical etching, respectively. PLE is a technique that exploits the intrinsic porosity of hydrogels like agarose and polyacrylamide. The probes are made by polymerizing a liquid mixture of agarose or acrylamide monomers in a conical or pyramidal master. The polymeric probe is hydrated in deionized water or ink of interest after polymerization. For deposition, PLE has shown promising results in the selective deposition of fluorescent inks on bare or functionalized glass substrates. Erasing via PLE has been done in two ways: the first method involves selectively erasing the fluorescent molecules using a probe loaded with deionized water by bringing the probe in contact with the area of interest. Thus, solvation and transportation of the molecules into the polymeric probes render selective removal of materials (fluorescent inks) from a substrate. On the other hand, erasing or removal of metals deposited on a substrate was demonstrated using redox reactions. Here, the probe is loaded with an etchant, which is selectively delivered onto the substrate by bringing the probe close to or in contact with the surface. Thus, the etchant molecules passively diffuse from the probe to the substrate through a meniscus formed at the probe-substrate interface. Removal of molecules occurs after the redox reaction between the ink, and the substrate is completed. Many in-length microscale complex patterns can be easily made by translocating the probe over the substrate while the probe’s tip is in contact with the surface. Since the probes used in PLE are made of polymers, the probe-substrate contacting area can be easily modulated, and damage to the substrate by the probe is minimum. Moreover, it has been shown that the probes can be used multiple times, a hurdle frequently faced by probes made of hard materials such as silicon-based probes. We explored the capabilities of a polymeric probe made of PAAM to selectively deliver and remove (erase) material deposited on a surface. PLE, pioneered by our group, takes advantage of the hydrophilic and porous nature of polyacrylamide. In addition, the conformability of PAAM hydrogels was exploited to make patterns of various sizes and to the pattern on non-planar surfaces. The main advantage of PLE is removing materials from various substrates. Additionally, selective delivery of material to planar and non-planar substrates was demonstrated. Whereas DPN and sister techniques require multiple steps for patterning through the etching process, PLE can perform etching in one step. Therefore, using PLE, microscale patterning on surfaces can save considerable time, labor, and cost. Further, chemical and supplies waste are minima in PLE. Notably, the deposition and etching at the microscale level can be simultaneously achieved in one single step, providing an extremely high throughput patterning rate (on the order of 1000 mm2/s). The PLE patterning rate is two to three orders larger than DPN-based patterning. However, PLE inherently deposits and removes materials with features much larger (microscale) than that can be achieved with DPN (sub-nanoscale). Therefore, PLE is an alternative to DPN, PPL, and related probe-based deposition and erasing techniques, and in some cases, PLE provides enhanced capabilities than its contemporary techniques. In this dissertation, I intend to demonstrate the potential of PLE for fabricating working devices at a lower cost as an alternative to contemporary fabrication. Chapter 2 involves the fabrication of micro-electrodes on rigid and flexible substrates by selectively removing copper and ITO from a glass and a PET substrate. As proof of concept, substrates coated with the PLE patterned surfaces were used to fabricate a photodetector, and LEDs were assembled on the electrodes made on ITO-PET substrates. Chapter 3 describes a series of experiments involving the evaluation of ink withholding capacity, large area patterning, and the effect of modification of substrate surface energy on PLE patterning. These experiments an increased understanding of processes involved in PLE editing and microscale patterning. A potential pitfall of PLE-based etching was also observed in these experiments, where a thin layer of material was left behind after subtractive editing with a PLE probe. EDS analysis indicated that the material was composed of iron, chlorine, and copper ─ components of the etchant solution and the copper film. The ring structure was attributed to the coffee-ring effect pinning the water meniscus to the substrate. By understanding the potential causes of the formation of the coffee-ring possible solutions to this problem were formulated. Chapter 4 describes the physical and mechanical properties of the hydrogel PAAM probes at the nanoscale. ESEM and AFM were employed to investigate the structural and mechanical properties of the probes after impregnation with metal etchants of various concentrations. The effect of local RH on PLE patterns was also investigated. More importantly, these experiments show critical structural differences of PAAM hydrogels composed of various monomer and crosslinker concentrations. ESEM showed the significant influence exerted by RH on meniscus size and its interaction with the substrate. The behavior of the water meniscus observed in ESEM shows that large RH promotes water spreading on the substrate generating larger patterning features. Chapter 5 describes the capability of PLE to selectively deliver metallic inks on a non-linear curved substrate to fabricate a microscale battery. PLE was used to deposit silver nitrate onto a non-planar flexible substrate which was used to grow a thin electrically conductive copper film via copper electroless deposition. Electrodeposition of zinc on the copper substrate was accomplished. By coupling a zinc electrode to a manganese oxide-graphite composite cathode, we demonstrated a working Zn-MnO2 aqueous microscale battery.

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